path: root/Build/source/texk/web2c/luatexdir/luatex.web

% Copyright (c) 2007 Hartmut Henkel, Taco Hoekwater

% This file is part of luaTeX.

% luaTeX is free software; you can redistribute it and/or modify it under the
% terms of the GNU General Public License as published by the Free Software
% Foundation; either version 2 of the License, or (at your option) any later
% version.

% luaTeX is distributed in the hope that it will be useful, but WITHOUT ANY
% WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
% A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

% You should have received a copy of the GNU General Public License
% along with luaTeX; if not, write to the Free Software Foundation, Inc.,
% 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA

% pdfTeX is copyright (C) 1996-2006 Han The Thanh, <thanh@@pdftex.org>.
% e-TeX is copyright (C) 1994,98 by Peter Breitenlohner.

% This program is directly derived from Donald E. Knuth's TeX;
% the change history which follows and the reward offered for finders of
% bugs refer specifically to TeX; they should not be taken as referring
% to e-TeX, although the change history is relevant in that it
% demonstrates the evolutionary path followed.  This program is not TeX;
% that name is reserved strictly for the program which is the creation
% and sole responsibility of Professor Knuth.

% Version 0 was released in September 1982 after it passed a variety of tests.
% Version 1 was released in November 1983 after thorough testing.
% Version 1.1 fixed ``disappearing font identifiers'' et alia (July 1984).
% Version 1.2 allowed `0' in response to an error, et alia (October 1984).
% Version 1.3 made memory allocation more flexible and local (November 1984).
% Version 1.4 fixed accents right after line breaks, et alia (April 1985).
% Version 1.5 fixed \the\toks after other expansion in \edefs (August 1985).
% Version 2.0 (almost identical to 1.5) corresponds to "Volume B" (April 1986).
% Version 2.1 corrected anomalies in discretionary breaks (January 1987).
% Version 2.2 corrected "(Please type...)" with null \endlinechar (April 1987).
% Version 2.3 avoided incomplete page in premature termination (August 1987).
% Version 2.4 fixed \noaligned rules in indented displays (August 1987).
% Version 2.5 saved cur_order when expanding tokens (September 1987).
% Version 2.6 added 10sp slop when shipping leaders (November 1987).
% Version 2.7 improved rounding of negative-width characters (November 1987).
% Version 2.8 fixed weird bug if no \patterns are used (December 1987).
% Version 2.9 made \csname\endcsname's "relax" local (December 1987).
% Version 2.91 fixed \outer\def\a0{}\a\a bug (April 1988).
% Version 2.92 fixed \patterns, also file names with complex macros (May 1988).
% Version 2.93 fixed negative halving in allocator when mem_min<0 (June 1988).
% Version 2.94 kept open_log_file from calling fatal_error (November 1988).
% Version 2.95 solved that problem a better way (December 1988).
% Version 2.96 corrected bug in "Infinite shrinkage" recovery (January 1989).
% Version 2.97 corrected blunder in creating 2.95 (February 1989).
% Version 2.98 omitted save_for_after at outer level (March 1989).
% Version 2.99 caught $$\begingroup\halign..$$ (June 1989).
% Version 2.991 caught .5\ifdim.6... (June 1989).
% Version 2.992 introduced major changes for 8-bit extensions (September 1989).
% Version 2.993 fixed a save_stack synchronization bug et alia (December 1989).
% Version 3.0 fixed unusual displays; was more \output robust (March 1990).
% Version 3.1 fixed nullfont, disabled \write{\the\prevgraf} (September 1990).
% Version 3.14 fixed unprintable font names and corrected typos (March 1991).
% Version 3.141 more of same; reconstituted ligatures better (March 1992).
% Version 3.1415 preserved nonexplicit kerns, tidied up (February 1993).
% Version 3.14159 allowed fontmemsize to change; bulletproofing (March 1995).
% Version 3.141592 fixed \xleaders, glueset, weird alignments (December 2002).


% Although considerable effort has been expended to make the luaTeX program
% correct and reliable, no warranty is implied; the authors disclaim any
% obligation or liability for damages, including but not limited to
% special, indirect, or consequential damages arising out of or in
% connection with the use or performance of this software. This work has
% been a ``labor of love'' and the authors hope that users enjoy it.

% Here is TeX material that gets inserted after \input webmac
\def\hang{\hangindent 3em\noindent\ignorespaces}
\def\hangg#1 {\hang\hbox{#1 }}
\def\textindent#1{\hangindent2.5em\noindent\hbox to2.5em{\hss#1 }\ignorespaces}
\font\ninerm=cmr9
\let\mc=\ninerm % medium caps for names like SAIL
\def\PASCAL{Pascal}
\def\pdfTeX{pdf\TeX}
\def\pdfeTeX{pdf\eTeX}
\def\PDF{PDF}
\def\Aleph{Aleph}
\def\eTeX{e\TeX}
\def\LuaTeX{Lua\TeX}
\def\THANH{H\`an Th\^e\llap{\raise 0.5ex\hbox{\'{}}} Th\`anh}
\def\ph{\hbox{Pascal-H}}
\def\pct!{{\char`\%}} % percent sign in ordinary text
\def\grp{\.{\char'173...\char'175}}
\font\logo=logo10 % font used for the METAFONT logo
\def\MF{{\logo META}\-{\logo FONT}}
\def\<#1>{$\langle#1\rangle$}
\def\section{\mathhexbox278}

\def\(#1){} % this is used to make section names sort themselves better
\def\9#1{} % this is used for sort keys in the index via @@:sort key}{entry@@>

\outer\def\N#1. \[#2]#3.{\MN#1.\vfil\eject % begin starred section
  \def\rhead{PART #2:\uppercase{#3}} % define running headline
  \message{*\modno} % progress report
  \edef\next{\write\cont{\Z{\?#2]#3}{\modno}{\the\pageno}}}\next
  \ifon\startsection{\bf\ignorespaces#3.\quad}\ignorespaces}
\let\?=\relax % we want to be able to \write a \?

\def\title{LuaTeX}
\let\maybe=\iffalse % print only changed modules
\def\topofcontents{\hsize 5.5in
  \vglue 0pt plus 1fil minus 1.5in
  \def\?##1]{\hbox to 1in{\hfil##1.\ }}
  }
\def\botofcontents{\vskip 0pt plus 1fil minus 1.5in}
\pageno=3
\def\glob{13} % this should be the section number of "<Global...>"
\def\gglob{20, 26} % this should be the next two sections of "<Global...>"

@* \[1] Introduction.

This is LuaTeX, a continuation of $\pdfTeX$ and $\Aleph$.  LuaTeX is a
document compiler intended to simplify high-quality typesetting for
many of the world's languages.  It is an extension of D. E. Knuth's
\TeX, which was designed essentially for the typesetting of languages
using the Latin alphabet.

The $\Aleph$ subsystem loosens many of the restrictions imposed by~\TeX:
register numbers are no longer limited to 8~bits;  fonts may have more
than 256~characters;  more than 256~fonts may be used;  etc.

The \PASCAL\ program that follows is the definition of \TeX82, a standard
@:PASCAL}{\PASCAL@>
@!@:TeX82}{\TeX82@>
version of \TeX\ that is designed to be highly portable so that
identical output will be obtainable on a great variety of computers.

The main purpose of the following program is to explain the algorithms of \TeX\
as clearly as possible. As a result, the program will not necessarily be very
efficient when a particular \PASCAL\ compiler has translated it into a
particular machine language. However, the program has been written so that it
can be tuned to run efficiently in a wide variety of operating environments
by making comparatively few changes. Such flexibility is possible because
the documentation that follows is written in the \.{WEB} language, which is
at a higher level than \PASCAL; the preprocessing step that converts \.{WEB}
to \PASCAL\ is able to introduce most of the necessary refinements.
Semi-automatic translation to other languages is also feasible, because the
program below does not make extensive use of features that are peculiar to
\PASCAL.

A large piece of software like \TeX\ has inherent complexity that cannot
be reduced below a certain level of difficulty, although each individual
part is fairly simple by itself. The \.{WEB} language is intended to make
the algorithms as readable as possible, by reflecting the way the
individual program pieces fit together and by providing the
cross-references that connect different parts. Detailed comments about
what is going on, and about why things were done in certain ways, have
been liberally sprinkled throughout the program.  These comments explain
features of the implementation, but they rarely attempt to explain the
\TeX\ language itself, since the reader is supposed to be familiar with
{\sl The \TeX book}.
@.WEB@>
@:TeXbook}{\sl The \TeX book@>

@ The present implementation has a long ancestry, beginning in the summer
of~1977, when Michael~F. Plass and Frank~M. Liang designed and coded
a prototype
@^Plass, Michael Frederick@>
@^Liang, Franklin Mark@>
@^Knuth, Donald Ervin@>
based on some specifications that the author had made in May of that year.
This original proto\TeX\ included macro definitions and elementary
manipulations on boxes and glue, but it did not have line-breaking,
page-breaking, mathematical formulas, alignment routines, error recovery,
or the present semantic nest; furthermore,
it used character lists instead of token lists, so that a control sequence
like \.{\\halign} was represented by a list of seven characters. A
complete version of \TeX\ was designed and coded by the author in late
1977 and early 1978; that program, like its prototype, was written in the
{\mc SAIL} language, for which an excellent debugging system was
available. Preliminary plans to convert the {\mc SAIL} code into a form
somewhat like the present ``web'' were developed by Luis Trabb~Pardo and
the author at the beginning of 1979, and a complete implementation was
created by Ignacio~A. Zabala in 1979 and 1980. The \TeX82 program, which
@^Zabala Salelles, Ignacio Andr\'es@>
was written by the author during the latter part of 1981 and the early
part of 1982, also incorporates ideas from the 1979 implementation of
@^Guibas, Leonidas Ioannis@>
@^Sedgewick, Robert@>
@^Wyatt, Douglas Kirk@>
\TeX\ in {\mc MESA} that was written by Leonidas Guibas, Robert Sedgewick,
and Douglas Wyatt at the Xerox Palo Alto Research Center.  Several hundred
refinements were introduced into \TeX82 based on the experiences gained with
the original implementations, so that essentially every part of the system
has been substantially improved. After the appearance of ``Version 0'' in
September 1982, this program benefited greatly from the comments of
many other people, notably David~R. Fuchs and Howard~W. Trickey.
A final revision in September 1989 extended the input character set to
eight-bit codes and introduced the ability to hyphenate words from
different languages, based on some ideas of Michael~J. Ferguson.
@^Fuchs, David Raymond@>
@^Trickey, Howard Wellington@>
@^Ferguson, Michael John@>

No doubt there still is plenty of room for improvement, but the author
is firmly committed to keeping \TeX82 ``frozen'' from now on; stability
and reliability are to be its main virtues.

On the other hand, the \.{WEB} description can be extended without changing
the core of \TeX82 itself, and the program has been designed so that such
extensions are not extremely difficult to make.
The |banner| string defined here should be changed whenever \TeX\
undergoes any modifications, so that it will be clear which version of
\TeX\ might be the guilty party when a problem arises.
@^extensions to \TeX@>
@^system dependencies@>

This program contains code for various features extending \TeX,
therefore this program is called `\eTeX' and not
`\TeX'; the official name `\TeX' by itself is reserved
for software systems that are fully compatible with each other.
A special test suite called the ``\.{TRIP} test'' is available for
helping to determine whether a particular implementation deserves to be
known as `\TeX' [cf.~Stanford Computer Science report CS1027,
November 1984].

A similar test suite called the ``\.{e-TRIP} test'' is available for
helping to determine whether a particular implementation deserves to be
known as `\eTeX'.

@d eTeX_version_string=="2.2" {current \eTeX\ version}
@d Omega_version_string=="1.15" { \.{\\OmegaVersion} }
@d Aleph_version_string=="0.0" { \.{\\AlephVersion} }
@d eTeX_version=2 { \.{\\eTeXversion} }
@d Omega_version=1 { \.{\\Omegaversion} }
@d Aleph_version=0 { \.{\\Alephversion} }
@d eTeX_minor_version=1 { \.{\\eTeXminorversion} }
@d Omega_minor_version=15 { \.{\\Omegaminorversion} }
@d Aleph_minor_version=0 { \.{\\Alephminorversion} }
@d eTeX_revision==".2" { \.{\\eTeXrevision} }
@d Omega_revision==".15" { \.{\\Omegarevision} }
@d Aleph_revision==".0" { \.{\\Alephrevision} }
@#
@d pdftex_version==200 { \.{\\pdftexversion} }
@d pdftex_revision=="0" { \.{\\pdftexrevision} }
@d pdftex_version_string=='-2.00.0' {current \pdfTeX\ version}
@#
@d luatex_version==25 { \.{\\luatexversion} }
@d luatex_revision=="3" { \.{\\luatexrevision} }
@d luatex_version_string=='snapshot-0.25.3' {current \LuaTeX\ version}
@d luatex_date_info==-extra_version_info { the compile date is negated }
@#
@d luaTeX_banner=='This is LuaTeX, Version ',luatex_version_string,extra_version_info
   {printed when \LuaTeX\ starts}
@#
@d banner==luaTeX_banner
@#
@d TEX==ETEX {change program name into |ETEX|}

@ Different \PASCAL s have slightly different conventions, and the present
@!@:PASCAL H}{\ph@>
program expresses \TeX\ in terms of the \PASCAL\ that was
available to the author in 1982. Constructions that apply to
this particular compiler, which we shall call \ph, should help the
reader see how to make an appropriate interface for other systems
if necessary. (\ph\ is Charles Hedrick's modification of a compiler
@^Hedrick, Charles Locke@>
for the DECsystem-10 that was originally developed at the University of
Hamburg; cf.\ {\sl SOFTWARE---Practice \AM\ Experience \bf6} (1976),
29--42. The \TeX\ program below is intended to be adaptable, without
extensive changes, to most other versions of \PASCAL, so it does not fully
use the admirable features of \ph. Indeed, a conscious effort has been
made here to avoid using several idiosyncratic features of standard
\PASCAL\ itself, so that most of the code can be translated mechanically
into other high-level languages. For example, the `\&{with}' and `\\{new}'
features are not used, nor are pointer types, set types, or enumerated
scalar types; there are no `\&{var}' parameters, except in the case of files
--- \eTeX, however, does use `\&{var}' parameters for the |reverse| function;
there are no tag fields on variant records; there are no assignments
|real:=integer|; no procedures are declared local to other procedures.)

The portions of this program that involve system-dependent code, where
changes might be necessary because of differences between \PASCAL\ compilers
and/or differences between
operating systems, can be identified by looking at the sections whose
numbers are listed under `system dependencies' in the index. Furthermore,
the index entries for `dirty \PASCAL' list all places where the restrictions
of \PASCAL\ have not been followed perfectly, for one reason or another.
@!@^system dependencies@>
@!@^dirty \PASCAL@>

Incidentally, \PASCAL's standard |round| function can be problematical,
because it disagrees with the IEEE floating-point standard.
Many implementors have
therefore chosen to substitute their own home-grown rounding procedure.

@ The program begins with a normal \PASCAL\ program heading, whose
components will be filled in later, using the conventions of \.{WEB}.
@.WEB@>
For example, the portion of the program called `\X\glob:Global
variables\X' below will be replaced by a sequence of variable declarations
that starts in $\section\glob$ of this documentation. In this way, we are able
to define each individual global variable when we are prepared to
understand what it means; we do not have to define all of the globals at
once.  Cross references in $\section\glob$, where it says ``See also
sections \gglob, \dots,'' also make it possible to look at the set of
all global variables, if desired.  Similar remarks apply to the other
portions of the program heading.

Actually the heading shown here is not quite normal: The |program| line
does not mention any |output| file, because \ph\ would ask the \TeX\ user
to specify a file name if |output| were specified here.
@^system dependencies@>

@d mtype==t@&y@&p@&e {this is a \.{WEB} coding trick:}
@f mtype==type {`\&{mtype}' will be equivalent to `\&{type}'}
@f type==true {but `|type|' will not be treated as a reserved word}

@p @t\4@>@<Compiler directives@>@/
program TEX; {all file names are defined dynamically}
label @<Labels in the outer block@>@/
const @<Constants in the outer block@>@/
mtype @<Types in the outer block@>@/
var @<Global variables@>@/
@#
procedure initialize; {this procedure gets things started properly}
  var @<Local variables for initialization@>@/
  begin @<Initialize whatever \TeX\ might access@>@;
  end;@#
@t\4@>@<Basic printing procedures@>@/
@t\4@>@<Error handling procedures@>@/

@ The overall \TeX\ program begins with the heading just shown, after which
comes a bunch of procedure declarations and function declarations.
Finally we will get to the main program, which begins with the
comment `|start_here|'. If you want to skip down to the
main program now, you can look up `|start_here|' in the index.
But the author suggests that the best way to understand this program
is to follow pretty much the order of \TeX's components as they appear in the
\.{WEB} description you are now reading, since the present ordering is
intended to combine the advantages of the ``bottom up'' and ``top down''
approaches to the problem of understanding a somewhat complicated system.

@ Three labels must be declared in the main program, so we give them
symbolic names.

@d start_of_TEX=1 {go here when \TeX's variables are initialized}
@d end_of_TEX=9998 {go here to close files and terminate gracefully}
@d final_end=9999 {this label marks the ending of the program}

@<Labels in the out...@>=
start_of_TEX@t\hskip-2pt@>, end_of_TEX@t\hskip-2pt@>,@,final_end;
  {key control points}

@ Some of the code below is intended to be used only when diagnosing the
strange behavior that sometimes occurs when \TeX\ is being installed or
when system wizards are fooling around with \TeX\ without quite knowing
what they are doing. Such code will not normally be compiled; it is
delimited by the codewords `$|debug|\ldots|gubed|$', with apologies
to people who wish to preserve the purity of English.

Similarly, there is some conditional code delimited by
`$|stat|\ldots|tats|$' that is intended for use when statistics are to be
kept about \TeX's memory usage.  The |stat| $\ldots$ |tats| code also
implements diagnostic information for \.{\\tracingparagraphs} and
\.{\\tracingpages}.
@^debugging@>

@d debug==@{ {change this to `$\\{debug}\equiv\null$' when debugging}
@d gubed==@t@>@} {change this to `$\\{gubed}\equiv\null$' when debugging}
@f debug==begin
@f gubed==end
@#
@d stat==@{ {change this to `$\\{stat}\equiv\null$' when gathering
  usage statistics}
@d tats==@t@>@} {change this to `$\\{tats}\equiv\null$' when gathering
  usage statistics}
@f stat==begin
@f tats==end

@ This program has two important variations: (1) There is a long and slow
version called \.{INITEX}, which does the extra calculations needed to
@.INITEX@>
initialize \TeX's internal tables; and (2)~there is a shorter and faster
production version, which cuts the initialization to a bare minimum.
Parts of the program that are needed in (1) but not in (2) are delimited by
the codewords `$|init|\ldots|tini|$'.

@d init== {change this to `$\\{init}\equiv\.{@@\{}$' in the production version}
@d tini== {change this to `$\\{tini}\equiv\.{@@\}}$' in the production version}
@f init==begin
@f tini==end

@<Initialize whatever...@>=
@<Set initial values of key variables@>@/
@!init @<Initialize table entries (done by \.{INITEX} only)@>@;@+tini

@ If the first character of a \PASCAL\ comment is a dollar sign,
\ph\ treats the comment as a list of ``compiler directives'' that will
affect the translation of this program into machine language.  The
directives shown below specify full checking and inclusion of the \PASCAL\
debugger when \TeX\ is being debugged, but they cause range checking and other
redundant code to be eliminated when the production system is being generated.
Arithmetic overflow will be detected in all cases.
@^system dependencies@>
@^Overflow in arithmetic@>

@<Compiler directives@>=
@{@&$C-,A+,D-@} {no range check, catch arithmetic overflow, no debug overhead}
@!debug @{@&$C+,D+@}@+ gubed {but turn everything on when debugging}

@ This \TeX\ implementation conforms to the rules of the {\sl Pascal User
@:PASCAL}{\PASCAL@>
@^system dependencies@>
Manual} published by Jensen and Wirth in 1975, except where system-dependent
@^Wirth, Niklaus@>
@^Jensen, Kathleen@>
code is necessary to make a useful system program, and except in another
respect where such conformity would unnecessarily obscure the meaning
and clutter up the code: We assume that |case| statements may include a
default case that applies if no matching label is found. Thus, we shall use
constructions like
$$\vbox{\halign{\ignorespaces#\hfil\cr
|case x of|\cr
1: $\langle\,$code for $x=1\,\rangle$;\cr
3: $\langle\,$code for $x=3\,\rangle$;\cr
|othercases| $\langle\,$code for |x<>1| and |x<>3|$\,\rangle$\cr
|endcases|\cr}}$$
since most \PASCAL\ compilers have plugged this hole in the language by
incorporating some sort of default mechanism. For example, the \ph\
compiler allows `|others|:' as a default label, and other \PASCAL s allow
syntaxes like `\&{else}' or `\&{otherwise}' or `\\{otherwise}:', etc. The
definitions of |othercases| and |endcases| should be changed to agree with
local conventions.  Note that no semicolon appears before |endcases| in
this program, so the definition of |endcases| should include a semicolon
if the compiler wants one. (Of course, if no default mechanism is
available, the |case| statements of \TeX\ will have to be laboriously
extended by listing all remaining cases. People who are stuck with such
\PASCAL s have, in fact, done this, successfully but not happily!)

@d othercases == others: {default for cases not listed explicitly}
@d endcases == @+end {follows the default case in an extended |case| statement}
@f othercases == else
@f endcases == end

@ The following parameters can be changed at compile time to extend or
reduce \TeX's capacity. They may have different values in \.{INITEX} and
in production versions of \TeX.
@.INITEX@>
@^system dependencies@>

@<Constants...@>=
@!buf_size=500; {maximum number of characters simultaneously present in
  current lines of open files and in control sequences between
  \.{\\csname} and \.{\\endcsname}; must not exceed |max_halfword|}
@!error_line=72; {width of context lines on terminal error messages}
@!half_error_line=42; {width of first lines of contexts in terminal
  error messages; should be between 30 and |error_line-15|}
@!max_print_line=79; {width of longest text lines output; should be at least 60}
@!stack_size=200; {maximum number of simultaneous input sources}
@!max_in_open=6; {maximum number of input files and error insertions that
  can be going on simultaneously}
@!param_size=60; {maximum number of simultaneous macro parameters}
@!nest_size=40; {maximum number of semantic levels simultaneously active}
@!max_strings=3000; {maximum number of strings; must not exceed |max_halfword|}
@!string_vacancies=8000; {the minimum number of characters that should be
  available for the user's control sequences and font names,
  after \TeX's own error messages are stored}
@!pool_size=32000; {maximum number of characters in strings, including all
  error messages and help texts, and the names of all fonts and
  control sequences; must exceed |string_vacancies| by the total
  length of \TeX's own strings, which is currently about 23000}
@!save_size=600; {space for saving values outside of current group; must be
  at most |max_halfword|}
@!dvi_buf_size=800; {size of the output buffer; must be a multiple of 8}
@!expand_depth=10000; {limits recursive calls of the |expand| procedure}
@!file_name_size=40; {file names shouldn't be longer than this}
@!pool_name='TeXformats:TEX.POOL                     ';
  {string of length |file_name_size|; tells where the string pool appears}
@.TeXformats@>
@!active_mem_size=50000; {number of words of |active_info| for active ocps}
@!ocp_maxint=@"10000000;


@ Like the preceding parameters, the following quantities can be changed
at compile time to extend or reduce \TeX's capacity. But if they are changed,
it is necessary to rerun the initialization program \.{INITEX}
@.INITEX@>
to generate new tables for the production \TeX\ program.
One can't simply make helter-skelter changes to the following constants,
since certain rather complex initialization
numbers are computed from them. They are defined here using
\.{WEB} macros, instead of being put into \PASCAL's |const| list, in order to
emphasize this distinction.

@d font_base=0 {smallest internal font number; must not be less
  than |min_quarterword|}
@d hash_size=2100 {maximum number of control sequences; it should be at most
  about |(fix_mem_max-fix_mem_min)/10|}
@d hash_prime=1777 {a prime number equal to about 85\pct! of |hash_size|}
@d ocp_base=0 {smallest internal ocp number; must not be less
  than |min_quarterword|}
@d ocp_biggest=32767 {the real biggest ocp}
@d number_ocps=ocp_biggest-ocp_base+1
@d ocp_list_base=0 {smallest internal ocp list number; must not be less
  than |min_quarterword|}
@d ocp_list_biggest=32727 {the real biggest ocp list}
@d number_ocp_lists=ocp_list_biggest-ocp_list_base+1
@d max_active_ocp_lists=32768
@d biggest_reg=65535 {the largest allowed register number; must be |<=max_quarterword|}
@d number_regs=65536 {|biggest_reg+1|}
@d number_attrs=65536 {total numbeer of attributes}
@d biggest_mark=65535 {the largest allowed marks class; must be |<=max_quarterword|}
@d number_marks=65536 {|biggest_mark+1|}
{using |2^20+2^16| characters instead of |2^21| saves 286MB on the virtual memory size
 of the running executable}
@d biggest_char=1114111 {2097151} {the largest allowed character number; must be |<=max_halfword|}
@d too_big_char=1114112 {2097152} {|biggest_char+1|}
@d special_char=1114113 {2097153} {|biggest_char+2|}
@d number_chars=1114112 {2097152} {|biggest_char+1|}
@d number_active_chars=65536+65536 {to reduce the memory req. only two planes }
@d string_offset=2097152
@d font_biggest=5535 {the real biggest font}
@d number_fonts=font_biggest-font_base+1
@d number_math_fonts=768
@d math_font_biggest=767
@d biggest_lang=32767
@d too_big_lang=32768
@d text_size=0 {size code for the largest size in a family}
@d script_size=256 {size code for the medium size in a family}
@d script_script_size=512 {size code for the smallest size in a family}


@ In case somebody has inadvertently made bad settings of the ``constants,''
\TeX\ checks them using a global variable called |bad|.

This is the first of many sections of \TeX\ where global variables are
defined.

@<Glob...@>=
@!bad:integer; {is some ``constant'' wrong?}
@!luainit:boolean; {are we using lua for initializations }
@!tracefilenames:boolean; { print file open-close  info? }

@ Later on we will say `\ignorespaces|if X>=max_halfword then bad:=14|',
or something similar. (We can't do that until |max_halfword| has been defined.)

@<Check the ``constant'' values for consistency@>=
bad:=0;
if not luainit then  tracefilenames:=true;
if (half_error_line<30)or(half_error_line>error_line-15) then bad:=1;
if max_print_line<60 then bad:=2;
if dvi_buf_size mod 8<>0 then bad:=3;
if hash_prime>hash_size then bad:=5;
if max_in_open>=128 then bad:=6;
{ |if null_list<256 then bad:=7;| } {we will want |null_list>255|}

@ Labels are given symbolic names by the following definitions, so that
occasional |goto| statements will be meaningful. We insert the label
`|exit|' just before the `\ignorespaces|end|\unskip' of a procedure in
which we have used the `|return|' statement defined below; the label
`|restart|' is occasionally used at the very beginning of a procedure; and
the label `|reswitch|' is occasionally used just prior to a |case|
statement in which some cases change the conditions and we wish to branch
to the newly applicable case.  Loops that are set up with the |loop|
construction defined below are commonly exited by going to `|done|' or to
`|found|' or to `|not_found|', and they are sometimes repeated by going to
`|continue|'.  If two or more parts of a subroutine start differently but
end up the same, the shared code may be gathered together at
`|common_ending|'.

Incidentally, this program never declares a label that isn't actually used,
because some fussy \PASCAL\ compilers will complain about redundant labels.

@d exit=10 {go here to leave a procedure}
@d restart=20 {go here to start a procedure again}
@d reswitch=21 {go here to start a case statement again}
@d continue=22 {go here to resume a loop}
@d done=30 {go here to exit a loop}
@d done1=31 {like |done|, when there is more than one loop}
@d done2=32 {for exiting the second loop in a long block}
@d done3=33 {for exiting the third loop in a very long block}
@d done4=34 {for exiting the fourth loop in an extremely long block}
@d done5=35 {for exiting the fifth loop in an immense block}
@d done6=36 {for exiting the sixth loop in a block}
@d found=40 {go here when you've found it}
@d found1=41 {like |found|, when there's more than one per routine}
@d found2=42 {like |found|, when there's more than two per routine}
@d not_found=45 {go here when you've found nothing}
@d not_found1=46 {like |not_found|, when there's more than one}
@d not_found2=47 {like |not_found|, when there's more than two}
@d not_found3=48 {like |not_found|, when there's more than three}
@d not_found4=49 {like |not_found|, when there's more than four}
@d common_ending=50 {go here when you want to merge with another branch}

@ Here are some macros for common programming idioms.

@d incr(#) == #:=#+1 {increase a variable by unity}
@d decr(#) == #:=#-1 {decrease a variable by unity}
@d negate(#) == #:=-# {change the sign of a variable}
@d loop == @+ while true do@+ {repeat over and over until a |goto| happens}
@f loop == xclause
  {\.{WEB}'s |xclause| acts like `\ignorespaces|while true do|\unskip'}
@d do_nothing == pdfassert(1) {empty statement}
@d return == goto exit {terminate a procedure call}
@f return == nil
@d empty=0 {symbolic name for a null constant}

@* \[2] The character set.
In order to make \TeX\ readily portable to a wide variety of
computers, all of its input text is converted to an internal
twenty-one-bit code that covers all of unicode, including ASCII, the
``American Standard Code for Information Interchange.''  This
conversion is done immediately when each character is read
in. Conversely, characters are converted from ASCII to the user's
external representation just before they are output to a text file.

Such an internal code is relevant to users of \TeX\ primarily because it
governs the positions of characters in the fonts. For example, the
character `\.A' has ASCII code $65=@'101$, and when \TeX\ typesets
this letter it specifies character number 65 in the current font.
If that font actually has `\.A' in a different position, \TeX\ doesn't
know what the real position is; the program that does the actual printing from
\TeX's device-independent files is responsible for converting from ASCII to
a particular font encoding.
@^ASCII code@>

\TeX's internal code also defines the value of constants
that begin with a reverse apostrophe; and it provides an index to the
\.{\\catcode}, \.{\\mathcode}, \.{\\uccode}, \.{\\lccode}, and \.{\\delcode}
tables.

@ Characters of text that have been converted to \TeX's internal form
are said to be of type |ASCII_code|, which is a subrange of the integers.

@<Types...@>=
@!ASCII_code=0..biggest_char; {eight-bit numbers}
@!BMP_code=0..65535; {sixteen-bit numbers}

@ The original \PASCAL\ compiler was designed in the late 60s, when six-bit
character sets were common, so it did not make provision for lowercase
letters. Nowadays, of course, we need to deal with both capital and small
letters in a convenient way, especially in a program for typesetting;
so the present specification of \TeX\ has been written under the assumption
that the \PASCAL\ compiler and run-time system permit the use of text files
with more than 64 distinguishable characters. More precisely, we assume that
the character set contains at least the letters and symbols associated
with ASCII codes @'40 through @'176; all of these characters are now
available on most computer terminals.

Since we are dealing with more characters than were present in the first
\PASCAL\ compilers, we have to decide what to call the associated data
type. Some \PASCAL s use the original name |char| for the
characters in text files, even though there now are more than 64 such
characters, while other \PASCAL s consider |char| to be a 64-element
subrange of a larger data type that has some other name.

In order to accommodate this difference, we shall use the name |text_char|
to stand for the data type of the characters that are converted to and
from |ASCII_code| when they are input and output. We shall also assume
that |text_char| consists of the elements |chr(first_text_char)| through
|chr(last_text_char)|, inclusive. The following definitions should be
adjusted if necessary.
@^system dependencies@>

@d text_char == char {the data type of characters in text files}
@d first_text_char=0 {ordinal number of the smallest element of |text_char|}
@d last_text_char=255 {ordinal number of the largest element of |text_char|}

@<Local variables for init...@>=
@!i:integer;

@ The \TeX\ processor converts between ASCII code and
the user's external character set by means of arrays |xord| and |xchr|
that are analogous to \PASCAL's |ord| and |chr| functions.

@<Glob...@>=
@!xchr: array [ASCII_code] of text_char;
  {specifies conversion of output characters}

@ Since we are assuming that our \PASCAL\ system is able to read and
write the visible characters of standard ASCII (although not
necessarily using the ASCII codes to represent them), the following
assignment statements initialize the standard part of the |xchr| array
properly, without needing any system-dependent changes. On the other
hand, it is possible to implement \TeX\ with less complete character
sets, and in such cases it will be necessary to change something here.
@^system dependencies@>

@<Set init...@>=
xchr[@'40]:=' ';
xchr[@'41]:='!';
xchr[@'42]:='"';
xchr[@'43]:='#';
xchr[@'44]:='$';
xchr[@'45]:='%';
xchr[@'46]:='&';
xchr[@'47]:='''';@/
xchr[@'50]:='(';
xchr[@'51]:=')';
xchr[@'52]:='*';
xchr[@'53]:='+';
xchr[@'54]:=',';
xchr[@'55]:='-';
xchr[@'56]:='.';
xchr[@'57]:='/';@/
xchr[@'60]:='0';
xchr[@'61]:='1';
xchr[@'62]:='2';
xchr[@'63]:='3';
xchr[@'64]:='4';
xchr[@'65]:='5';
xchr[@'66]:='6';
xchr[@'67]:='7';@/
xchr[@'70]:='8';
xchr[@'71]:='9';
xchr[@'72]:=':';
xchr[@'73]:=';';
xchr[@'74]:='<';
xchr[@'75]:='=';
xchr[@'76]:='>';
xchr[@'77]:='?';@/
xchr[@'100]:='@@';
xchr[@'101]:='A';
xchr[@'102]:='B';
xchr[@'103]:='C';
xchr[@'104]:='D';
xchr[@'105]:='E';
xchr[@'106]:='F';
xchr[@'107]:='G';@/
xchr[@'110]:='H';
xchr[@'111]:='I';
xchr[@'112]:='J';
xchr[@'113]:='K';
xchr[@'114]:='L';
xchr[@'115]:='M';
xchr[@'116]:='N';
xchr[@'117]:='O';@/
xchr[@'120]:='P';
xchr[@'121]:='Q';
xchr[@'122]:='R';
xchr[@'123]:='S';
xchr[@'124]:='T';
xchr[@'125]:='U';
xchr[@'126]:='V';
xchr[@'127]:='W';@/
xchr[@'130]:='X';
xchr[@'131]:='Y';
xchr[@'132]:='Z';
xchr[@'133]:='[';
xchr[@'134]:='\';
xchr[@'135]:=']';
xchr[@'136]:='^';
xchr[@'137]:='_';@/
xchr[@'140]:='`';
xchr[@'141]:='a';
xchr[@'142]:='b';
xchr[@'143]:='c';
xchr[@'144]:='d';
xchr[@'145]:='e';
xchr[@'146]:='f';
xchr[@'147]:='g';@/
xchr[@'150]:='h';
xchr[@'151]:='i';
xchr[@'152]:='j';
xchr[@'153]:='k';
xchr[@'154]:='l';
xchr[@'155]:='m';
xchr[@'156]:='n';
xchr[@'157]:='o';@/
xchr[@'160]:='p';
xchr[@'161]:='q';
xchr[@'162]:='r';
xchr[@'163]:='s';
xchr[@'164]:='t';
xchr[@'165]:='u';
xchr[@'166]:='v';
xchr[@'167]:='w';@/
xchr[@'170]:='x';
xchr[@'171]:='y';
xchr[@'172]:='z';
xchr[@'173]:='{';
xchr[@'174]:='|';
xchr[@'175]:='}';
xchr[@'176]:='~';@/

@ Some of the ASCII codes without visible characters have been given symbolic
names in this program because they are used with a special meaning.

@d null_code=@'0 {ASCII code that might disappear}
@d carriage_return=@'15 {ASCII code used at end of line}
@d invalid_code=@'177 {ASCII code that many systems prohibit in text files}

@ The ASCII code is ``standard'' only to a certain extent, since many
computer installations have found it advantageous to have ready access
to more than 94 printing characters. Appendix~C of {\sl The \TeX book\/}
gives a complete specification of the intended correspondence between
characters and \TeX's internal representation.
@:TeXbook}{\sl The \TeX book@>

If \TeX\ is being used
on a garden-variety \PASCAL\ for which only standard ASCII
codes will appear in the input and output files, it doesn't really matter
what codes are specified in |xchr[0..@'37]|, but the safest policy is to
blank everything out by using the code shown below.

However, other settings of |xchr| will make \TeX\ more friendly on
computers that have an extended character set, so that users can type things
like `\.^^Z' instead of `\.{\\ne}'. People with extended character sets can
assign codes arbitrarily, giving an |xchr| equivalent to whatever
characters the users of \TeX\ are allowed to have in their input files.
It is best to make the codes correspond to the intended interpretations as
shown in Appendix~C whenever possible; but this is not necessary. For
example, in countries with an alphabet of more than 26 letters, it is
usually best to map the additional letters into codes less than~@'40.
To get the most ``permissive'' character set, change |' '| on the
right of these assignment statements to |chr(i)|.
@^character set dependencies@>
@^system dependencies@>

@<Set init...@>=
for i:=0 to biggest_char do xchr[i]:=i;

@ The following system-independent code makes the |xord| array contain a
suitable inverse to the information in |xchr|. Note that if |xchr[i]=xchr[j]|
where |i<j<@'177|, the value of |xord[xchr[i]]| will turn out to be
|j| or more; hence, standard ASCII code numbers will be used instead of
codes below @'40 in case there is a coincidence.

@<Set init...@>=

@* \[3] Input and output.
The bane of portability is the fact that different operating systems treat
input and output quite differently, perhaps because computer scientists
have not given sufficient attention to this problem. People have felt somehow
that input and output are not part of ``real'' programming. Well, it is true
that some kinds of programming are more fun than others. With existing
input/output conventions being so diverse and so messy, the only sources of
joy in such parts of the code are the rare occasions when one can find a
way to make the program a little less bad than it might have been. We have
two choices, either to attack I/O now and get it over with, or to postpone
I/O until near the end. Neither prospect is very attractive, so let's
get it over with.

The basic operations we need to do are (1)~inputting and outputting of
text, to or from a file or the user's terminal; (2)~inputting and
outputting of eight-bit bytes, to or from a file; (3)~instructing the
operating system to initiate (``open'') or to terminate (``close'') input or
output from a specified file; (4)~testing whether the end of an input
file has been reached.

\TeX\ needs to deal with two kinds of files.
We shall use the term |alpha_file| for a file that contains textual data,
and the term |byte_file| for a file that contains eight-bit binary information.
These two types turn out to be the same on many computers, but
sometimes there is a significant distinction, so we shall be careful to
distinguish between them. Standard protocols for transferring
such files from computer to computer, via high-speed networks, are
now becoming available to more and more communities of users.

The program actually makes use also of a third kind of file, called a
|word_file|, when dumping and reloading base information for its own
initialization.  We shall define a word file later; but it will be possible
for us to specify simple operations on word files before they are defined.

@<Types...@>=
@!eight_bits=0..65535; {unsigned one-byte quantity}
@!real_eight_bits=0..255; {unsigned one-byte quantity}
@!alpha_file=packed file of text_char; {files that contain textual data}
@!byte_file=packed file of real_eight_bits; {files that contain binary data}

@ Most of what we need to do with respect to input and output can be handled
by the I/O facilities that are standard in \PASCAL, i.e., the routines
called |get|, |put|, |eof|, and so on. But
standard \PASCAL\ does not allow file variables to be associated with file
names that are determined at run time, so it cannot be used to implement
\TeX; some sort of extension to \PASCAL's ordinary |reset| and |rewrite|
is crucial for our purposes. We shall assume that |nameoffile| is a variable
of an appropriate type such that the \PASCAL\ run-time system being used to
implement \TeX\ can open a file whose external name is specified by
|nameoffile|.
@^system dependencies@>

@<Glob...@>=
@!nameoffile:packed array[1..file_name_size] of char;@;@/
  {on some systems this may be a \&{record} variable}
@!namelength:0..file_name_size;@/{this many characters are actually
  relevant in |nameoffile| (the rest are blank)}
@!name_file_pointer:alpha_file;

@ The \ph\ compiler with which the present version of \TeX\ was prepared has
extended the rules of \PASCAL\ in a very convenient way. To open file~|f|,
we can write
$$\vbox{\halign{#\hfil\qquad&#\hfil\cr
|reset(f,@t\\{name}@>,'/O')|&for input;\cr
|rewrite(f,@t\\{name}@>,'/O')|&for output.\cr}}$$
The `\\{name}' parameter, which is of type `{\bf packed array
$[\langle\\{any}\rangle]$ of \\{char}}', stands for the name of
the external file that is being opened for input or output.
Blank spaces that might appear in \\{name} are ignored.

The `\.{/O}' parameter tells the operating system not to issue its own
error messages if something goes wrong. If a file of the specified name
cannot be found, or if such a file cannot be opened for some other reason
(e.g., someone may already be trying to write the same file), we will have
|@!erstat(f)<>0| after an unsuccessful |reset| or |rewrite|.  This allows
\TeX\ to undertake appropriate corrective action.
@:PASCAL H}{\ph@>
@^system dependencies@>

\TeX's file-opening procedures return |false| if no file identified by
|nameoffile| could be opened.

@d reset_OK(#)==erstat(#)=0
@d rewrite_OK(#)==erstat(#)=0

@p function a_open_in(var f:alpha_file):boolean;
  {open a text file for input}
begin reset(f,nameoffile,'/O'); a_open_in:=reset_OK(f);
end;
@#
function a_open_out(var f:alpha_file):boolean;
  {open a text file for output}
begin rewrite(f,nameoffile,'/O'); a_open_out:=rewrite_OK(f);
end;
@#
function b_open_in(var f:byte_file):boolean;
  {open a binary file for input}
begin reset(f,nameoffile,'/O'); b_open_in:=reset_OK(f);
end;
@#
function b_open_out(var f:byte_file):boolean;
  {open a binary file for output}
begin rewrite(f,nameoffile,'/O'); b_open_out:=rewrite_OK(f);
end;
@#
function w_open_in(var f:word_file):boolean;
  {open a word file for input}
begin reset(f,nameoffile,'/O'); w_open_in:=reset_OK(f);
end;
@#
function w_open_out(var f:word_file):boolean;
  {open a word file for output}
begin rewrite(f,nameoffile,'/O'); w_open_out:=rewrite_OK(f);
end;

@ When input files are opened via a callback, they will also be read using
callbacks. for that purpose, the |open_read_file_callback| returns an
integer to uniquely identify a callback table. This id replaces the file
point |f| in this case, because the input does not have to be a file
in the traditional sense.

Signalling this fact is achieved by having two arrays of integers.

@<Glob...@>=
@!input_file_callback_id : ^integer;
@!read_file_callback_id : array[0..16] of integer;

@ 
@p function lua_a_open_in(var f:alpha_file; n:quarterword):boolean;
var k:integer; { a temporary value }
  fnam:str_number; { string returned by find callback }
  callback_id:integer;
  file_ok:boolean; { the status so far }
begin 
  file_ok:=true;
  if n=0 then begin
    texinputtype := 1; {Tell |open_input| we are \.{\\input}.}
    input_file_callback_id[index] := 0;
    end
  else begin
    texinputtype:=0; 
    read_file_callback_id[n] := 0;
    end;
  callback_id:=callback_defined(find_read_file_callback);
  if callback_id>0 then begin
    fnam:=0;
    file_ok:=run_callback(callback_id,'dS->s',n,stringcast(nameoffile+1),addressof(fnam));
    if (file_ok)and(fnam<>0)and(length(fnam)>0) then begin
      @<Fixup |nameoffile| after callback@>;
      end 
    else 
      file_ok:=false; {file not found}
    end;
  if file_ok then begin
    callback_id:=callback_defined(open_read_file_callback);
    if callback_id>0 then begin
      k := run_and_save_callback(callback_id,'S->',stringcast(nameoffile+1));
      if k>0 then begin
        lua_a_open_in := true;
        if n=0 then
          input_file_callback_id[index] := k
        else 
          read_file_callback_id[n] := k;
        end
      else 
        file_ok:=false; {read failed}
      end
    else begin {no read callback}
      if openinnameok(stringcast(nameoffile+1)) then begin
        lua_a_open_in := a_open_in(f,kpsetexformat);
        name_file_pointer := f;
        end
      else 
        file_ok:=false; {open failed}
      end;
    end;
  if not file_ok then begin
    lua_a_open_in := false;
    name_file_pointer := 0;
    end;
end;
@#
function lua_a_open_out(var f:alpha_file; n:quarterword):boolean;
var test:boolean;
  k:integer;
  fnam:str_number;
  callback_id:integer;
begin
  name_file_pointer := 0;
  callback_id:=callback_defined(find_write_file_callback);
  if callback_id>0 then begin
    fnam:=0;
    test:=run_callback(callback_id,'dS->s',n,stringcast(nameoffile+1),addressof(fnam));
    if (test)and(fnam<>0)and(length(fnam)>0) then begin
      @<Fixup |nameoffile| after callback@>;
      lua_a_open_out := do_a_open_out(f);
	  name_file_pointer := f;
      end
    else 
      lua_a_open_out := false;
    end 
  else begin
	if openoutnameok(stringcast(nameoffile+1)) then begin
      lua_a_open_out := a_open_out(f);
      name_file_pointer := f;
      end
    else
      lua_a_open_out := false;
   end;
end;
function lua_b_open_out(var f:alpha_file):boolean;
var test:boolean;
  k:integer;
  fnam:str_number;
  callback_id:integer;
begin
  name_file_pointer := 0;
  callback_id:=callback_defined(find_output_file_callback);
  if callback_id>0 then begin
    fnam:=0;
    test:=run_callback(callback_id,'S->s',stringcast(nameoffile+1),addressof(fnam));
    if (test)and(fnam<>0)and(length(fnam)>0) then begin
      @<Fixup |nameoffile| after callback@>;
      lua_b_open_out := do_b_open_out(f);
	  name_file_pointer := f;
      end
    else 
      lua_b_open_out := false;
    end 
  else begin
	if openoutnameok(stringcast(nameoffile+1)) then begin
      lua_b_open_out := b_open_out(f);
      name_file_pointer := f;
      end
    else
      lua_b_open_out := false;
   end;
end;

@ 
@<Fixup |nameoffile| after callback@>=
libcfree (nameoffile);
nameoffile := xmallocarray (packed_ASCII_code, length(fnam)+2);
for k:=str_start_macro(fnam) to str_start_macro(fnam+1)-1 do
  nameoffile[k-str_start_macro(fnam)+1] := str_pool[k];
nameoffile[length(fnam)+1]:=0;
namelength := length(fnam);
flush_string

@ Files can be closed with the \ph\ routine `|close(f)|', which
@^system dependencies@>
should be used when all input or output with respect to |f| has been completed.
This makes |f| available to be opened again, if desired; and if |f| was used for
output, the |close| operation makes the corresponding external file appear
on the user's area, ready to be read.

These procedures should not generate error messages if a file is
being closed before it has been successfully opened.

@p procedure a_close(var f:alpha_file); {close a text file}
begin close(f);
end;
@#
procedure b_close(var f:byte_file); {close a binary file}
begin close(f);
end;
@#
procedure w_close(var f:word_file); {close a word file}
begin close(f);
end;


@
 
@p procedure lua_a_close_in(var f:alpha_file; n:quarterword); {close a text file}
var ret:boolean;
    callback_id:integer;
begin
if n=0 then
  callback_id:=input_file_callback_id[index]
else
  callback_id:=read_file_callback_id[n];
if callback_id>0 then begin
  ret:=run_saved_callback(callback_id,'close','->');
  destroy_saved_callback(callback_id);
  if n=0 then
    input_file_callback_id[index] := 0
  else
    read_file_callback_id[n] := 0;
  end
else
  a_close(f);
end;
@#
procedure lua_a_close_out(var f:alpha_file); {close a text file}
begin
  a_close(f);
end;


@ Binary input and output are done with \PASCAL's ordinary |get| and |put|
procedures, so we don't have to make any other special arrangements for
binary~I/O. Text output is also easy to do with standard \PASCAL\ routines.
The treatment of text input is more difficult, however, because
of the necessary translation to |ASCII_code| values.
\TeX's conventions should be efficient, and they should
blend nicely with the user's operating environment.

@ Input from text files is read one line at a time, using a routine called
|lua_input_ln|. This function is defined in terms of global variables called
|buffer|, |first|, and |last| that will be described in detail later; for
now, it suffices for us to know that |buffer| is an array of |ASCII_code|
values, and that |first| and |last| are indices into this array
representing the beginning and ending of a line of text.

@<Glob...@>=
@!buffer:array[0..buf_size] of packed_ASCII_code; {lines of characters being read}
@!first:0..buf_size; {the first unused position in |buffer|}
@!last:0..buf_size; {end of the line just input to |buffer|}
@!max_buf_stack:0..buf_size; {largest index used in |buffer|}

@ The |lua_input_ln| function brings the next line of input from the specified
file into available positions of the buffer array and returns the value
|true|, unless the file has already been entirely read, in which case it
returns |false| and sets |last:=first|.  In general, the |ASCII_code|
numbers that represent the next line of the file are input into
|buffer[first]|, |buffer[first+1]|, \dots, |buffer[last-1]|; and the
global variable |last| is set equal to |first| plus the length of the
line. Trailing blanks are removed from the line; thus, either |last=first|
(in which case the line was entirely blank) or |buffer[last-1]<>" "|.

An overflow error is given, however, if the normal actions of |lua_input_ln|
would make |last>=buf_size|; this is done so that other parts of \TeX\
can safely look at the contents of |buffer[last+1]| without overstepping
the bounds of the |buffer| array. Upon entry to |lua_input_ln|, the condition
|first<buf_size| will always hold, so that there is always room for an
``empty'' line.

The variable |max_buf_stack|, which is used to keep track of how large
the |buf_size| parameter must be to accommodate the present job, is
also kept up to date by |lua_input_ln|.

If the |bypass_eoln| parameter is |true|, |lua_input_ln| will do a |get|
before looking at the first character of the line; this skips over
an |eoln| that was in |f^|. The procedure does not do a |get| when it
reaches the end of the line; therefore it can be used to acquire input
from the user's terminal as well as from ordinary text files.

Standard \PASCAL\ says that a file should have |eoln| immediately
before |eof|, but \TeX\ needs only a weaker restriction: If |eof|
occurs in the middle of a line, the system function |eoln| should return
a |true| result (even though |f^| will be undefined).

Since the inner loop of |lua_input_ln| is part of \TeX's ``inner loop''---each
character of input comes in at this place---it is wise to reduce system
overhead by making use of special routines that read in an entire array
of characters at once, if such routines are available. The following
code uses standard \PASCAL\ to illustrate what needs to be done, but
finer tuning is often possible at well-developed \PASCAL\ sites.
@^inner loop@>

@p function input_ln(var f:alpha_file;@!bypass_eoln:boolean):boolean;
  {inputs the next line or returns |false|}
var last_nonblank:0..buf_size; {|last| with trailing blanks removed}
begin if bypass_eoln then if not eof(f) then get(f);
  {input the first character of the line into |f^|}
last:=first; {cf.\ Matthew 19\thinspace:\thinspace30}
if eof(f) then input_ln:=false
else  begin last_nonblank:=first;
  while not eoln(f) do
    begin if last>=max_buf_stack then
      begin max_buf_stack:=last+1;
      if max_buf_stack=buf_size then
        @<Report overflow of the input buffer, and abort@>;
      end;
    buffer[last]:=f^; get(f); incr(last);
    if buffer[last-1]<>" " then last_nonblank:=last;
    end;
  last:=last_nonblank; input_ln:=true;
  end;
end;

function lua_input_ln(var f:alpha_file;n:quarterword;@!bypass_eoln:boolean):boolean;
var lua_result:boolean;
	last_ptr:integer;
    callback_id:integer;
	bypass_p:boolean;
begin
if n=0 then
  callback_id:=input_file_callback_id[index]
else 
  callback_id:=read_file_callback_id[n];
if callback_id>0 then begin
    last:=first;
	last_ptr := first;
    lua_result := run_saved_callback(callback_id,'reader','->l', addressof(last_ptr));
	if (lua_result=true)and(last_ptr<>0) then begin
	  last := last_ptr;
	  if last>max_buf_stack then max_buf_stack:=last; 
	  lua_input_ln := true;
      @<Fix up the input buffer using callbacks@>; 
      end
    else 
      lua_input_ln := false;
    end
  else begin
    bypass_p := bypass_eoln; {this is for -Wextra}
    lua_result := input_ln(f,bypass_p);
	if lua_result=true then begin
      lua_input_ln := true;
      @<Fix up the input buffer using callbacks@>; 
      end
    else
      lua_input_ln := false;
    end
end;

@ 
@<Fix up the input buffer using callbacks@>=
if last>=first then begin
  callback_id := callback_defined(process_input_buffer_callback);
  if callback_id>0 then begin
    last_ptr := first;
    lua_result := run_callback(callback_id, 'l->l', (last-first), addressof(last_ptr)); 
    if (lua_result=true)and(last_ptr<>0) then begin
	  last := last_ptr;
	  if last>max_buf_stack then max_buf_stack:=last; 
      end;
    end;
  end



@ The user's terminal acts essentially like other files of text, except
that it is used both for input and for output. When the terminal is
considered an input file, the file variable is called |term_in|, and when it
is considered an output file the file variable is |term_out|.
@^system dependencies@>

@<Glob...@>=
@!term_in:alpha_file; {the terminal as an input file}
@!term_out:alpha_file; {the terminal as an output file}

@ Here is how to open the terminal files
in \ph. The `\.{/I}' switch suppresses the first |get|.
@^system dependencies@>

@d t_open_in==reset(term_in,'TTY:','/O/I') {open the terminal for text input}
@d t_open_out==rewrite(term_out,'TTY:','/O') {open the terminal for text output}

@ Sometimes it is necessary to synchronize the input/output mixture that
happens on the user's terminal, and three system-dependent
procedures are used for this
purpose. The first of these, |update_terminal|, is called when we want
to make sure that everything we have output to the terminal so far has
actually left the computer's internal buffers and been sent.
The second, |clear_terminal|, is called when we wish to cancel any
input that the user may have typed ahead (since we are about to
issue an unexpected error message). The third, |wake_up_terminal|,
is supposed to revive the terminal if the user has disabled it by
some instruction to the operating system.  The following macros show how
these operations can be specified in \ph:
@^system dependencies@>

@d update_terminal == break(term_out) {empty the terminal output buffer}
@d clear_terminal == break_in(term_in,true) {clear the terminal input buffer}
@d wake_up_terminal == do_nothing {cancel the user's cancellation of output}

@ We need a special routine to read the first line of \TeX\ input from
the user's terminal. This line is different because it is read before we
have opened the transcript file; there is sort of a ``chicken and
egg'' problem here. If the user types `\.{\\input paper}' on the first
line, or if some macro invoked by that line does such an \.{\\input},
the transcript file will be named `\.{paper.log}'; but if no \.{\\input}
commands are performed during the first line of terminal input, the transcript
file will acquire its default name `\.{texput.log}'. (The transcript file
will not contain error messages generated by the first line before the
first \.{\\input} command.)
@.texput@>

The first line is even more special if we are lucky enough to have an operating
system that treats \TeX\ differently from a run-of-the-mill \PASCAL\ object
program. It's nice to let the user start running a \TeX\ job by typing
a command line like `\.{tex paper}'; in such a case, \TeX\ will operate
as if the first line of input were `\.{paper}', i.e., the first line will
consist of the remainder of the command line, after the part that invoked
\TeX.

The first line is special also because it may be read before \TeX\ has
input a format file. In such cases, normal error messages cannot yet
be given. The following code uses concepts that will be explained later.
(If the \PASCAL\ compiler does not support non-local |@!goto|\unskip, the
@^system dependencies@>
statement `|goto final_end|' should be replaced by something that
quietly terminates the program.)

@<Report overflow of the input buffer, and abort@>=
if format_ident=0 then
  begin writeln(term_out,'Buffer size exceeded!'); goto final_end;
@.Buffer size exceeded@>
  end
else 
  check_buffer_overflow(buf_size+10) { need  a little bit more}

@ Different systems have different ways to get started. But regardless of
what conventions are adopted, the routine that initializes the terminal
should satisfy the following specifications:

\yskip\textindent{1)}It should open file |term_in| for input from the
  terminal. (The file |term_out| will already be open for output to the
  terminal.)

\textindent{2)}If the user has given a command line, this line should be
  considered the first line of terminal input. Otherwise the
  user should be prompted with `\.{**}', and the first line of input
  should be whatever is typed in response.

\textindent{3)}The first line of input, which might or might not be a
  command line, should appear in locations |first| to |last-1| of the
  |buffer| array.

\textindent{4)}The global variable |loc| should be set so that the
  character to be read next by \TeX\ is in |buffer[loc]|. This
  character should not be blank, and we should have |loc<last|.

\yskip\noindent(It may be necessary to prompt the user several times
before a non-blank line comes in. The prompt is `\.{**}' instead of the
later `\.*' because the meaning is slightly different: `\.{\\input}' need
not be typed immediately after~`\.{**}'.)

@d loc==cur_input.loc_field {location of first unread character in |buffer|}

@ The following program does the required initialization
without retrieving a possible command line.
It should be clear how to modify this routine to deal with command lines,
if the system permits them.
@^system dependencies@>

@p function init_terminal:boolean; {gets the terminal input started}
label exit;
begin t_open_in;
loop@+begin wake_up_terminal; write(term_out,'**'); update_terminal;
@.**@>
  if not input_ln(term_in,true)
then {this shouldn't happen}
    begin writeln(term_out);
    write(term_out,'! End of file on the terminal... why?');
@.End of file on the terminal@>
    init_terminal:=false; return;
    end;
  loc:=first;
  while (loc<last)and(buffer[loc]=" ") do incr(loc);
  if loc<last then
    begin init_terminal:=true;
    return; {return unless the line was all blank}
    end;
  writeln(term_out,'Please type the name of your input file.');
  end;
exit:end;

@* \[4] String handling.
Control sequence names and diagnostic messages are variable-length strings
of eight-bit characters. Since \PASCAL\ does not have a well-developed string
mechanism, \TeX\ does all of its string processing by homegrown methods.

Elaborate facilities for dynamic strings are not needed, so all of the
necessary operations can be handled with a simple data structure.
The array |str_pool| contains all of the (eight-bit) ASCII codes in all
of the strings, and the array |str_start| contains indices of the starting
points of each string. Strings are referred to by integer numbers, so that
string number |s| comprises the characters |str_pool[j]| for
|str_start_macro(s)<=j<str_start_macro(s+1)|. Additional integer variables
|pool_ptr| and |str_ptr| indicate the number of entries used so far
in |str_pool| and |str_start|, respectively; locations
|str_pool[pool_ptr]| and |str_start_macro(str_ptr)| are
ready for the next string to be allocated.

String numbers 0 to |biggest_char| are reserved for strings that correspond to single
UNICODE characters. This is in accordance with the conventions of \.{WEB},
@.WEB@>
which converts single-character strings into the ASCII code number of the
single character involved, while it converts other strings into integers
and builds a string pool file. Thus, when the string constant \.{"."} appears
in the program below, \.{WEB} converts it into the integer 46, which is the
ASCII code for a period, while \.{WEB} will convert a string like \.{"hello"}
into some integer greater than~|biggest_char|. 

Some \PASCAL\ compilers won't pack integers into a single byte unless the
integers lie in the range |-128..127|. To accommodate such systems
we access the string pool only via macros that can easily be redefined.

@d si(#) == # {convert from |ASCII_code| to |packed_ASCII_code|}
@d so(#) == # {convert from |packed_ASCII_code| to |ASCII_code|}
@d str_start_macro(#) == str_start[(#) - string_offset]

@<Types...@>=
@!pool_pointer = integer; {for variables that point into |str_pool|}
@!str_number = integer; {for variables that point into |str_start|}
@!packed_ASCII_code = 0..255; {elements of |str_pool| array}

@ @<Glob...@>=
@!str_pool:packed array[pool_pointer] of packed_ASCII_code; {the characters}
@!str_start : array[str_number] of pool_pointer; {the starting pointers}
@!pool_ptr : pool_pointer; {first unused position in |str_pool|}
@!str_ptr : str_number; {number of the current string being created}
@!init_pool_ptr : pool_pointer; {the starting value of |pool_ptr|}
@!init_str_ptr : str_number; {the starting value of |str_ptr|}

@ Several of the elementary string operations are performed using \.{WEB}
macros instead of \PASCAL\ procedures, because many of the
operations are done quite frequently and we want to avoid the
overhead of procedure calls. For example, here is
a simple macro that computes the length of a string.
@.WEB@>

@d length(#)==(str_start_macro(#+1)-str_start_macro(#)) {the number of characters
  in string number \#}

@ The length of the current string is called |cur_length|:

@d cur_length == (pool_ptr - str_start_macro(str_ptr))

@ Strings are created by appending character codes to |str_pool|.
The |append_char| macro, defined here, does not check to see if the
value of |pool_ptr| has gotten too high; this test is supposed to be
made before |append_char| is used. There is also a |flush_char|
macro, which erases the last character appended.

To test if there is room to append |l| more characters to |str_pool|,
we shall write |str_room(l)|, which aborts \TeX\ and gives an
apologetic error message if there isn't enough room.

@d append_char(#) == {put |ASCII_code| \# at the end of |str_pool|}
begin str_pool[pool_ptr]:=si(#); incr(pool_ptr);
end
@d flush_char == decr(pool_ptr) {forget the last character in the pool}
@d str_room(#) == check_pool_overflow((pool_ptr+#)) {test or grow the pool}

@p procedure string_room(t:integer);
begin
	str_room(t);
end;
@#
procedure append_pool_char(c:ASCII_code);
begin
	append_char(c);
end;


@ Once a sequence of characters has been appended to |str_pool|, it
officially becomes a string when the function |make_string| is called.
This function returns the identification number of the new string as its
value.

@p function make_string : str_number; {current string enters the pool}
begin if str_ptr=(max_strings+string_offset) then
  overflow("number of strings",max_strings-init_str_ptr);
@:TeX capacity exceeded number of strings}{\quad number of strings@>
incr(str_ptr); str_start_macro(str_ptr):=pool_ptr;
make_string:=str_ptr-1;
end;

@ To destroy the most recently made string, we say |flush_string|.

The helper routines reads one utf sequence from the pool resp. the
buffer, and returns its character value. 

@d flush_string==begin decr(str_ptr); pool_ptr:=str_start_macro(str_ptr);
  end
@d test_sequence_byte(#)==if (#<@"80) or (#>=@"C0) then begin
  print_err("Text line contains an invalid utf-8 sequence");
@.Text line contains...@>
  help2("A funny symbol that I can't read has just been input.")@/
    ("Just continue, I'll change it to 0xFFFD.");@/
  deletions_allowed:=false; error; deletions_allowed:=true;
{the assigment before return is needed because web2c generates incorrect code}
  a:=@"FFFD; buffer_to_unichar:=a; return; end


@p function buffer_to_unichar(@!k:integer):integer;
label exit;
var a:@!integer; {a utf char}
b:@!integer; { a utf nibble}
begin
    b := buffer[k];
    if b<@"80 then
      a := b
    else if b>=@"F0 then begin
	  a := (b-@"F0) * 64;
	  b := buffer[k+1];
	  test_sequence_byte(b);
	  a := (a + (b-128)) * 64;
	  b := buffer[k+2];
	  test_sequence_byte(b);
	  a := (a + (b-128)) * 64;
	  b := buffer[k+3];
	  test_sequence_byte(b);
	  a := a + (b-128);
      end 
    else if b>=@"E0 then begin
	  a := (b-@"E0) * 64;
	  b := buffer[k+1];
	  test_sequence_byte(b);
	  a := (a + (b-128)) * 64;
	  b := buffer[k+2];
	  test_sequence_byte(b);
	  a := a + (b-128);
      end 
    else if b>=@"C0 then begin
	  a := (b-@"C0) * 64;
	  b := buffer[k+1];
	  test_sequence_byte(b);
	  a := a + (b-128);
      end
    else begin { NI: this is an encoding error }
	  print_err("Buffer contains an invalid utf-8 sequence");
@.Text line contains...@>
	  help2("A funny symbol somehow ended up in the input buffer.")@/
    	   ("Just continue, I'll change it to 0xFFFD.");@/
      deletions_allowed:=false; error; deletions_allowed:=true;
      a:=@"FFFD;
      end;
exit: 
  buffer_to_unichar := a;
end ;



@ The following subroutine compares string |s| with another string of the
same length that appears in |buffer| starting at position |k|;
the result is |true| if and only if the strings are equal.
Empirical tests indicate that |str_eq_buf| is used in such a way that
it tends to return |true| about 80 percent of the time.

@p function str_eq_buf(@!s:str_number;@!k:integer):boolean;
  {test equality of strings}
label not_found; {loop exit}
var j: pool_pointer; {running index}
a: ASCII_code; {a unicode character }
@!result: boolean; {result of comparison}
begin result:=false; 
if s<string_offset then begin
  a := buffer_to_unichar(k); 
  if a<>s then goto not_found;
  end
else begin
j:=str_start_macro(s);
while j<str_start_macro(s+1) do
  begin if so(str_pool[j])<>buffer[k] then
    begin goto not_found;
    end;
  incr(j); incr(k);
  end;
end;
result:=true;
not_found: str_eq_buf:=result;
end;

@ Here is a similar routine, but it compares two strings in the string pool,
and it does not assume that they have the same length.

@p function str_eq_str(@!s,@!t:str_number):boolean;
  {test equality of strings}
label found,not_found; {loop exit}
var j,@!k: pool_pointer; {running indices}
a: ASCII_code; {a utf char}
@!result: boolean; {result of comparison}
begin result:=false;
a:= 0;
if s<string_offset then begin
  if t>=string_offset then begin
    if s<=@"7F then
     if length(t)=1 then
       if str_pool[str_start_macro(t)]=s then
          goto found;
	a := pool_to_unichar(str_start_macro(t));
    if a<>s then goto not_found;
    end 
  else
    if t<>s then goto not_found;
  end
else if t<string_offset then begin
 if t<=@"7F then
   if length(s)=1 then
     if str_pool[str_start_macro(s)]=t then
       goto found;
  a := pool_to_unichar(str_start_macro(s));
  if a<>t then goto not_found;
  end 
else begin 
  if length(s)<>length(t) then goto not_found;
  j:=str_start_macro(s); k:=str_start_macro(t);
  while j<str_start_macro(s+1) do
    begin if str_pool[j]<>str_pool[k] then goto not_found;
    incr(j); incr(k);
    end;
  end;
found: result:=true;
not_found: str_eq_str:=result;
end;

@ The initial values of |str_pool|, |str_start|, |pool_ptr|,
and |str_ptr| are computed by the \.{INITEX} program, based in part
on the information that \.{WEB} has output while processing \TeX.
@.INITEX@>
@^string pool@>

The first |string_offset| strings are single-characters strings matching
Unicode. There is no point in generating all of these. But |str_ptr| has
initialized properly, otherwise |print_char| cannot see the difference
between characters and strings.

@p @!init function get_strings_started:boolean; {initializes the string pool,
  but returns |false| if something goes wrong}
label done,exit;
var @!g:str_number; {garbage}
begin pool_ptr:=0; str_ptr:=string_offset; str_start[0]:=0;
@<Read the other strings from the \.{TEX.POOL} file and return |true|,
  or give an error message and return |false|@>;
exit:end;
tini

@ @d app_lc_hex(#)==l:=#;
  if l<10 then append_char(l+"0")@+else append_char(l-10+"a")

@ The first 128 strings will contain 95 standard ASCII characters, and the
other 33 characters will be printed in three-symbol form like `\.{\^\^A}'
unless a system-dependent change is made here. Installations that have
an extended character set, where for example |xchr[@'32]=@t\.{\'^^Z\'}@>|,
would like string @'32 to be the single character @'32 instead of the
three characters @'136, @'136, @'132 (\.{\^\^Z}). On the other hand,
even people with an extended character set will want to represent string
@'15 by \.{\^\^M}, since @'15 is |carriage_return|; the idea is to
produce visible strings instead of tabs or line-feeds or carriage-returns
or bell-rings or characters that are treated anomalously in text files.

Unprintable characters of codes 128--255 are, similarly, rendered
\.{\^\^80}--\.{\^\^ff}.

Unprintable characters of codes 256--|65535| are, similarly, rendered
\.{\^\^\^\^0100}--\.{\^\^\^\^ffff}.

The boolean expression defined here should be |true| unless \TeX\
internal code number~|k| corresponds to a non-troublesome visible
symbol in the local character set.  An appropriate formula for the
extended character set recommended in {\sl The \TeX book\/} would, for
example, be `|k in [0,@'10..@'12,@'14,@'15,@'33,@'177..@'377]|'.
If character |k| cannot be printed, and |k<@'200|, then character |k+@'100| or
|k-@'100| must be printable; moreover, ASCII codes |[@'41..@'46,
@'60..@'71, @'141..@'146, @'160..@'171]| must be printable.
Thus, at least 80 printable characters are needed.
@:TeXbook}{\sl The \TeX book@>
@^character set dependencies@>
@^system dependencies@>

@ @<Read the other strings...@>=
  g := loadpoolstrings((pool_size-string_vacancies));
  if g=0 then begin
     wake_up_terminal; writeln(term_out,'! You have to increase POOLSIZE.');
     get_strings_started:=false;
     return;
  end;
  get_strings_started:=true;

@* \[5] On-line and off-line printing.
Messages that are sent to a user's terminal and to the transcript-log file
are produced by several `|print|' procedures. These procedures will
direct their output to a variety of places, based on the setting of
the global variable |selector|, which has the following possible
values:

\yskip
\hang |term_and_log|, the normal setting, prints on the terminal and on the
  transcript file.

\hang |log_only|, prints only on the transcript file.

\hang |term_only|, prints only on the terminal.

\hang |no_print|, doesn't print at all. This is used only in rare cases
  before the transcript file is open.

\hang |pseudo|, puts output into a cyclic buffer that is used
  by the |show_context| routine; when we get to that routine we shall discuss
  the reasoning behind this curious mode.

\hang |new_string|, appends the output to the current string in the
  string pool.

\hang 0 to 15, prints on one of the sixteen files for \.{\\write} output.

\yskip
\noindent The symbolic names `|term_and_log|', etc., have been assigned
numeric codes that satisfy the convenient relations |no_print+1=term_only|,
|no_print+2=log_only|, |term_only+2=log_only+1=term_and_log|.

Three additional global variables, |tally| and |term_offset| and
|file_offset|, record the number of characters that have been printed
since they were most recently cleared to zero. We use |tally| to record
the length of (possibly very long) stretches of printing; |term_offset|
and |file_offset|, on the other hand, keep track of how many characters
have appeared so far on the current line that has been output to the
terminal or to the transcript file, respectively.

@d no_print=16 {|selector| setting that makes data disappear}
@d term_only=17 {printing is destined for the terminal only}
@d log_only=18 {printing is destined for the transcript file only}
@d term_and_log=19 {normal |selector| setting}
@d pseudo=20 {special |selector| setting for |show_context|}
@d new_string=21 {printing is deflected to the string pool}
@d max_selector=21 {highest selector setting}

@<Glob...@>=
@!log_file : alpha_file; {transcript of \TeX\ session}
@!term_out_mode:halfword;
@!term_out_translation:halfword;
@!selector : 0..max_selector; {where to print a message}
@!dig : array[0..22] of 0..15; {digits in a number being output}
@!tally : integer; {the number of characters recently printed}
@!term_offset : 0..max_print_line;
  {the number of characters on the current terminal line}
@!file_offset : 0..max_print_line;
  {the number of characters on the current file line}
@!trick_buf:array[0..error_line] of packed_ASCII_code; {circular buffer for
  pseudoprinting}
@!trick_count: integer; {threshold for pseudoprinting, explained later}
@!first_count: integer; {another variable for pseudoprinting}
@!inhibit_par_tokens:boolean; { for minor adjustments to |show_token_list| }

@ @<Initialize the output routines@>=
selector:=term_only; tally:=0; term_offset:=0; file_offset:=0;
inhibit_par_tokens:=false;

@ Macro abbreviations for output to the terminal and to the log file are
defined here for convenience. Some systems need special conventions
for terminal output, and it is possible to adhere to those conventions
by changing |wterm|, |wterm_ln|, and |wterm_cr| in this section.
@^system dependencies@>

@d wterm(#)==write(term_out,#)
@d wterm_ln(#)==writeln(term_out,#)
@d wterm_cr==writeln(term_out)
@d wlog(#)==write(log_file,#)
@d wlog_ln(#)==writeln(log_file,#)
@d wlog_cr==writeln(log_file)

@ To end a line of text output, we call |print_ln|.

@<Basic print...@>=
procedure print_ln; {prints an end-of-line}
begin case selector of
term_and_log: begin wterm_cr; wlog_cr;
  term_offset:=0; file_offset:=0;
  end;
log_only: begin wlog_cr; file_offset:=0;
  end;
term_only: begin wterm_cr; term_offset:=0;
  end;
no_print,pseudo,new_string: do_nothing;
othercases writeln(write_file[selector])
endcases;@/
end; {|tally| is not affected}

@ The |print_char| procedure sends one character to the desired destination,
using the |xchr| array to map it into an external character compatible with
|lua_input_ln|. All printing comes through |print_ln| or |print_char|.

@d wterm_char(#)==begin if (#>=@"20)or(#=@"0A)or(#=@"0D)or(#=@"09) then wterm(xchr[#])
                  else begin if term_offset+2>=max_print_line then begin
                     wterm_cr; term_offset:=0;
                     end;
                     incr(term_offset); wterm('^'); incr(term_offset); wterm('^'); 
                     wterm(xchr[#+64]);  
                 end; end
@d fix_term_offset(#)==
      if ((#>=@"C0) and (#<=@"DF) and (term_offset+2>=max_print_line)) or
         ((#>=@"E0) and (#<=@"EF) and (term_offset+3>=max_print_line)) or
         ((#>=@"F0) and (term_offset+4>=max_print_line)) then begin
        wterm_cr; term_offset:=0;
       end
@d fix_log_offset(#)==
      if ((#>=@"C0) and (#<=@"DF) and (file_offset+2>=max_print_line)) or
         ((#>=@"E0) and (#<=@"EF) and (file_offset+3>=max_print_line)) or
         ((#>=@"F0) and (file_offset+4>=max_print_line)) then begin
        wlog_cr; file_offset:=0;
       end

@<Basic print...@>=
procedure print_char(@!s:ASCII_code); {prints a single character}
label exit;
begin if @<Character |s| is the current new-line character@> then
 if selector<pseudo then
  begin print_ln; return;
  end;
case selector of
term_and_log: begin 
  fix_term_offset(s); fix_log_offset(s);
  wterm_char(s); wlog(xchr[s]);
  incr(term_offset); incr(file_offset);
  if term_offset=max_print_line then
    begin wterm_cr; term_offset:=0;
    end;
  if file_offset=max_print_line then
    begin wlog_cr; file_offset:=0;
    end;
  end;
log_only: begin 
  fix_log_offset(s);
  wlog(xchr[s]); incr(file_offset);
  if file_offset=max_print_line then print_ln;
  end;
term_only: begin 
  fix_term_offset(s); 
  wterm_char(s); incr(term_offset);
  if term_offset=max_print_line then print_ln;
  end;
no_print: do_nothing;
pseudo: if tally<trick_count then trick_buf[tally mod error_line]:=s;
new_string: begin if pool_ptr<pool_size then append_char(s);
  end; {we drop characters if the string space is full}
othercases write(write_file[selector],xchr[s])
endcases;@/
incr(tally);
exit:end;

@ An entire string is output by calling |print|. Note that if we are outputting
the single standard ASCII character \.c, we could call |print("c")|, since
|"c"=99| is the number of a single-character string, as explained above. But
|print_char("c")| is quicker, so \TeX\ goes directly to the |print_char|
routine when it knows that this is safe. (The present implementation
assumes that it is always safe to print a visible ASCII character.)
@^system dependencies@>

The first 256 entries above the 17th unicode plane are used for a
special trick: when \TeX\ has to print items in that range, it will
instead print the character that results from substracting @"110000
from that value. This allows byte-oriented output to things like
\.{\\specials} and \.{\\pdfliterals}. Todo: Perhaps it would be useful 
to do the same substraction while typesetting.
 
@d print_lc_hex(#)==l:=#;
   if l<10 then print_char(l+"0") else print_char(l-10+"a");

@<Basic print...@>=
function pool_to_unichar(@!t:pool_pointer):ASCII_code;
var a,result:@!ASCII_code; {a utf char}
b:@!quarterword; { a utf nibble}
begin
    b := str_pool[t];
    if b<=@"7F then
      a := b
    else if b>=@"F0 then begin
	  a := (b-@"F0) * 64;
	  b := str_pool[t+1];
	  a := (a + (b-128)) * 64;
	  b := str_pool[t+2];
	  a := (a + (b-128)) * 64;
	  b := str_pool[t+3];
	  a := a + (b-128);
      end
    else if b>=@"E0 then begin
	  a := (b-@"E0) * 64;
	  b := str_pool[t+1];
	  a := (a + (b-128)) * 64;
	  b := str_pool[t+2];
	  a := a + (b-128);
      end 
    else if b>=@"C0 then begin
	  a := (b-@"C0) * 64;
	  b := str_pool[t+1];
	  a := a + (b-128);
      end
    else begin  { NI: this is an encoding error }
	  wlog_ln('! Pool contains an invalid utf-8 sequence');
	  wterm_ln('! Pool contains an invalid utf-8 sequence');
@.Text line contains...@>
	  help2("A funny symbol somehow ended up in the string pool.")@/
    	   ("Just continue, I'll change it to 0xFFFD.");@/
      deletions_allowed:=false; error; deletions_allowed:=true;
      a:=@"FFFD;
      end;
result := a;
pool_to_unichar := result;
end ;

procedure print(@!s:integer); {prints string |s|}
label exit;
var j:pool_pointer; {current character code position}
@!v:integer; { a unicode char }
begin if s>=str_ptr then s:="???" {this can't happen}
@.???@>
else if s<string_offset then
  if s<0 then s:="???" {can't happen}
  else begin 
    {TH not sure about this, disabled for now!}
    if (false)and(selector>pseudo) then
      begin print_char(s); return; {internal strings are not expanded}
      end;
    if (@<Character |s| is the current new-line character@>) then
      if selector<pseudo then
        begin print_ln; return;
        end;
    if s<=@"7F then
      print_char(s)
    else if s<=@"7FF then begin
      print_char(@"C0 + (s div @"40));
      print_char(@"80 + (s mod @"40));
      end
    else if s<=@"FFFF then begin
      print_char(@"E0 + (s div @"1000));
      print_char(@"80 + ((s mod @"1000) div @"40));
      print_char(@"80 + ((s mod @"1000) mod @"40));
      end 
    else begin 
      if s>=@"110000 then 
	    print_char(s-@"110000)
      else begin
        print_char(@"F0 + (s div @"40000));
        print_char(@"80 + ((s mod @"40000) div @"1000));
        print_char(@"80 + (((s mod @"40000) mod @"1000) div @"40));
        print_char(@"80 + (((s mod @"40000) mod @"1000) mod @"40));
        end;
      end;
    return;
    end;
j:=str_start_macro(s);
while j<str_start_macro(s+1) do
  begin { 0x110000 in utf=8: 0xF4 0x90 0x80 0x80 }
    if (str_pool[j]=@"F4)and(j<str_start_macro(s+4))and(str_pool[j+1]=@"90) then begin
	  v := (((7*64+63)*64)+ (str_pool[j+2]-128))*64 +(str_pool[j+3]-128);
	  print_char(v-@"110000); j := j+4;
      end
    else begin
      print_char(str_pool[j]); incr(j);
    end;
  end;
exit:end;

procedure print_nl(@!s:str_number); {prints string |s| at beginning of line}
begin if ((term_offset>0)and(odd(selector)))or@|
  ((file_offset>0)and(selector>=log_only)) then print_ln;
print(s);
end;

procedure print_nlp; {move to beginning of a line}
begin if ((term_offset>0)and(odd(selector)))or@|
  ((file_offset>0)and(selector>=log_only)) then print_ln;
end;

@ Control sequence names, file names, and strings constructed with
\.{\\string} might contain |ASCII_code| values that can't
be printed using |print_char|. Therefore we use |slow_print| for them:

@<Basic print...@>=
procedure slow_print(@!s:integer); {prints string |s|}
var j:pool_pointer; {current character code position}
begin if (s>=str_ptr) or (s<string_offset) then print(s)
else begin j:=str_start_macro(s);
  while j<str_start_macro(s+1) do
    begin print(so(str_pool[j])); incr(j);
    end;
  end;
end;

@ Here is the very first thing that \TeX\ prints: a headline that identifies
the version number and format package. The |term_offset| variable is temporarily
incorrect, but the discrepancy is not serious since we assume that the banner
and format identifier together will occupy at most |max_print_line|
character positions.

@<Initialize the output...@>=
print_banner;

@ The procedure |print_nl| is like |print|, but it makes sure that the
string appears at the beginning of a new line. (moved)

@<Basic print...@>=

@ The procedure |print_esc| prints a string that is preceded by
the user's escape character (which is usually a backslash).

@<Basic print...@>=
procedure print_esc(@!s:str_number); {prints escape character, then |s|}
var c:integer; {the escape character code}
begin  @<Set variable |c| to the current escape character@>;
if c>=0 then if c<string_offset then print(c);
slow_print(s);
end;

@ An array of digits in the range |0..15| is printed by |print_the_digs|.

@<Basic print...@>=
procedure print_the_digs(@!k:eight_bits);
  {prints |dig[k-1]|$\,\ldots\,$|dig[0]|}
begin while k>0 do
  begin decr(k);
  if dig[k]<10 then print_char("0"+dig[k])
  else print_char("A"-10+dig[k]);
  end;
end;

@ The following procedure, which prints out the decimal representation of a
given integer |n|, has been written carefully so that it works properly
if |n=0| or if |(-n)| would cause overflow. It does not apply |mod| or |div|
to negative arguments, since such operations are not implemented consistently
by all \PASCAL\ compilers.

@<Basic print...@>=
procedure print_int(@!n:integer); {prints an integer in decimal form}
var k:0..23; {index to current digit; we assume that $|n|<10^{23}$}
@!m:integer; {used to negate |n| in possibly dangerous cases}
begin k:=0;
if n<0 then
  begin print_char("-");
  if n>-100000000 then negate(n)
  else  begin m:=-1-n; n:=m div 10; m:=(m mod 10)+1; k:=1;
    if m<10 then dig[0]:=m
    else  begin dig[0]:=0; incr(n);
      end;
    end;
  end;
repeat dig[k]:=n mod 10; n:=n div 10; incr(k);
until n=0;
print_the_digs(k);
end;

@ Here is a trivial procedure to print two digits; it is usually called with
a parameter in the range |0<=n<=99|.

@p procedure print_two(@!n:integer); {prints two least significant digits}
begin n:=abs(n) mod 100; print_char("0"+(n div 10));
print_char("0"+(n mod 10));
end;

@ Hexadecimal printing of nonnegative integers is accomplished by |print_hex|.

@p procedure print_hex(@!n:integer);
  {prints a positive integer in hexadecimal form}
var k:0..22; {index to current digit; we assume that $0\L n<16^{22}$}
begin k:=0; print_char("""");
repeat dig[k]:=n mod 16; n:=n div 16; incr(k);
until n=0;
print_the_digs(k);
end;

@ Old versions of \TeX\ needed a procedure called |print_ASCII| whose function
is now subsumed by |print|. We retain the old name here as a possible aid to
future software arch\ae ologists.

@d print_ASCII == print
@d print_font_name(#)==begin print(tex_font_name(#)); flush_string; end
 
@ Roman numerals are produced by the |print_roman_int| routine.  Readers
who like puzzles might enjoy trying to figure out how this tricky code
works; therefore no explanation will be given. Notice that 1990 yields
\.{mcmxc}, not \.{mxm}.

@p procedure print_roman_int(@!n:integer);
label exit;
var j,@!k: pool_pointer; {mysterious indices into |str_pool|}
@!u,@!v: nonnegative_integer; {mysterious numbers}
begin j:=str_start_macro("m2d5c2l5x2v5i"); v:=1000;
loop@+  begin while n>=v do
    begin print_char(so(str_pool[j])); n:=n-v;
    end;
  if n<=0 then return; {nonpositive input produces no output}
  k:=j+2; u:=v div (so(str_pool[k-1])-"0");
  if str_pool[k-1]=si("2") then
    begin k:=k+2; u:=u div (so(str_pool[k-1])-"0");
    end;
  if n+u>=v then
    begin print_char(so(str_pool[k])); n:=n+u;
    end
  else  begin j:=j+2; v:=v div (so(str_pool[j-1])-"0");
    end;
  end;
exit:end;

@ The |print| subroutine will not print a string that is still being
created. The following procedure will.

@p procedure print_current_string; {prints a yet-unmade string}
var j:pool_pointer; {points to current character code}
begin j:=str_start_macro(str_ptr);
while j<pool_ptr do
  begin print_char(so(str_pool[j])); incr(j);
  end;
end;

@ Here is a procedure that asks the user to type a line of input,
assuming that the |selector| setting is either |term_only| or |term_and_log|.
The input is placed into locations |first| through |last-1| of the
|buffer| array, and echoed on the transcript file if appropriate.

This procedure is never called when |interaction<scroll_mode|.

@<Basic print...@>=
procedure prompt_input(s:str_number); 
begin wake_up_terminal; print(s); term_input;
end;

@ 
@p procedure term_input; {gets a line from the terminal}
var k:0..buf_size; {index into |buffer|}
begin update_terminal; {now the user sees the prompt for sure}
if not input_ln(term_in,true)
then fatal_error("End of file on the terminal!");
@.End of file on the terminal@>
term_offset:=0; {the user's line ended with \<\rm return>}
decr(selector); {prepare to echo the input}
if last<>first then for k:=first to last-1 do print(buffer[k]);
print_ln; incr(selector); {restore previous status}
end;

@* \[6] Reporting errors.
When something anomalous is detected, \TeX\ typically does something like this:
$$\vbox{\halign{#\hfil\cr
|print_err("Something anomalous has been detected");|\cr
|help3("This is the first line of my offer to help.")|\cr
|("This is the second line. I'm trying to")|\cr
|("explain the best way for you to proceed.");|\cr
|error;|\cr}}$$
A two-line help message would be given using |help2|, etc.; these informal
helps should use simple vocabulary that complements the words used in the
official error message that was printed. (Outside the U.S.A., the help
messages should preferably be translated into the local vernacular. Each
line of help is at most 60 characters long, in the present implementation,
so that |max_print_line| will not be exceeded.)

The |print_err| procedure supplies a `\.!' before the official message,
and makes sure that the terminal is awake if a stop is going to occur.
The |error| procedure supplies a `\..' after the official message, then it
shows the location of the error; and if |interaction=error_stop_mode|,
it also enters into a dialog with the user, during which time the help
message may be printed.
@^system dependencies@>

@ The global variable |interaction| has four settings, representing increasing
amounts of user interaction:

@d batch_mode=0 {omits all stops and omits terminal output}
@d nonstop_mode=1 {omits all stops}
@d scroll_mode=2 {omits error stops}
@d error_stop_mode=3 {stops at every opportunity to interact}
@d print_err(#)==begin if interaction=error_stop_mode then wake_up_terminal;
  print_nl("! "); print(#);
  last_error:=#; end
@d print_warn(#)==begin if interaction=error_stop_mode then wake_up_terminal;
  if prepend_nl then begin print_nl(""); print_ln end;
  print_nl(#);
  end

@<Glob...@>=
@!interaction:batch_mode..error_stop_mode; {current level of interaction}
@!last_error:str_number;

@ @<Set init...@>=interaction:=error_stop_mode;

@ \TeX\ is careful not to call |error| when the print |selector| setting
might be unusual. The only possible values of |selector| at the time of
error messages are

\yskip\hang|no_print| (when |interaction=batch_mode|
  and |log_file| not yet open);

\hang|term_only| (when |interaction>batch_mode| and |log_file| not yet open);

\hang|log_only| (when |interaction=batch_mode| and |log_file| is open);

\hang|term_and_log| (when |interaction>batch_mode| and |log_file| is open).

@<Initialize the print |selector| based on |interaction|@>=
if interaction=batch_mode then selector:=no_print@+else selector:=term_only

@ A global variable |deletions_allowed| is set |false| if the |get_next|
routine is active when |error| is called; this ensures that |get_next|
and related routines like |get_token| will never be called recursively.
A similar interlock is provided by |set_box_allowed|.
@^recursion@>

The global variable |history| records the worst level of error that
has been detected. It has four possible values: |spotless|, |warning_issued|,
|error_message_issued|, and |fatal_error_stop|.

Another global variable, |error_count|, is increased by one when an
|error| occurs without an interactive dialog, and it is reset to zero at
the end of every paragraph.  If |error_count| reaches 100, \TeX\ decides
that there is no point in continuing further.

@d spotless=0 {|history| value when nothing has been amiss yet}
@d warning_issued=1 {|history| value when |begin_diagnostic| has been called}
@d error_message_issued=2 {|history| value when |error| has been called}
@d fatal_error_stop=3 {|history| value when termination was premature}

@<Glob...@>=
@!deletions_allowed:boolean; {is it safe for |error| to call |get_token|?}
@!set_box_allowed:boolean; {is it safe to do a \.{\\setbox} assignment?}
@!history:spotless..fatal_error_stop; {has the source input been clean so far?}
@!error_count:-1..100; {the number of scrolled errors since the
  last paragraph ended}

@ The value of |history| is initially |fatal_error_stop|, but it will
be changed to |spotless| if \TeX\ survives the initialization process.

@<Set init...@>=
deletions_allowed:=true; set_box_allowed:=true;
error_count:=0; {|history| is initialized elsewhere}

@ Since errors can be detected almost anywhere in \TeX, we want to declare the
error procedures near the beginning of the program. But the error procedures
in turn use some other procedures, which need to be declared |forward|
before we get to |error| itself.

It is possible for |error| to be called recursively if some error arises
when |get_token| is being used to delete a token, and/or if some fatal error
occurs while \TeX\ is trying to fix a non-fatal one. But such recursion
@^recursion@>
is never more than two levels deep.

@<Error handling...@>=
procedure@?normalize_selector; forward;@t\2@>@/
procedure@?get_token; forward;@t\2@>@/
procedure@?term_input; forward;@t\2@>@/
procedure@?show_context; forward;@t\2@>@/
procedure@?begin_file_reading; forward;@t\2@>@/
procedure@?open_log_file; forward;@t\2@>@/
procedure@?close_files_and_terminate; forward;@t\2@>@/
procedure@?clear_for_error_prompt; forward;@t\2@>@/
procedure@?give_err_help; forward;@t\2@>@/
@t\4\hskip-\fontdimen2\font@>@;@+@!debug@+procedure@?debug_help;
  forward;@;@+gubed

@ Individual lines of help are recorded in the array |help_line|, which
contains entries in positions |0..(help_ptr-1)|. They should be printed
in reverse order, i.e., with |help_line[0]| appearing last.

@d hlp1(#)==help_line[0]:=#;@+end
@d hlp2(#)==help_line[1]:=#; hlp1
@d hlp3(#)==help_line[2]:=#; hlp2
@d hlp4(#)==help_line[3]:=#; hlp3
@d hlp5(#)==help_line[4]:=#; hlp4
@d hlp6(#)==help_line[5]:=#; hlp5
@d help0==help_ptr:=0 {sometimes there might be no help}
@d help1==@+begin help_ptr:=1; hlp1 {use this with one help line}
@d help2==@+begin help_ptr:=2; hlp2 {use this with two help lines}
@d help3==@+begin help_ptr:=3; hlp3 {use this with three help lines}
@d help4==@+begin help_ptr:=4; hlp4 {use this with four help lines}
@d help5==@+begin help_ptr:=5; hlp5 {use this with five help lines}
@d help6==@+begin help_ptr:=6; hlp6 {use this with six help lines}

@p 
procedure dohelp5 (@!a,b,c,d,e:str_number);
begin
  help5(a)(b)(c)(d)(e);
end;
@#
procedure dohelp4 (@!a,b,c,d:str_number);
begin
  help4(a)(b)(c)(d);
end;
@#
procedure dohelp3 (@!a,b,c:str_number);
begin
  help3(a)(b)(c);
end;
@#
procedure dohelp2 (@!a,b:str_number);
begin
  help2(a)(b);
end;
@#
procedure dohelp1 (@!a:str_number);
begin
  help1(a);
end;
@#
procedure do_print_err (s:str_number);
begin
  print_err(s);
end;

@ @<Glob...@>=
@!help_line:array[0..5] of str_number; {helps for the next |error|}
@!help_ptr:0..6; {the number of help lines present}
@!use_err_help:boolean; {should the |err_help| list be shown?}

@ @<Set init...@>=
help_ptr:=0; use_err_help:=false;

@ The |jump_out| procedure just cuts across all active procedure levels and
goes to |end_of_TEX|. This is the only nontrivial |@!goto| statement in the
whole program. It is used when there is no recovery from a particular error.

Some \PASCAL\ compilers do not implement non-local |goto| statements.
@^system dependencies@>
In such cases the body of |jump_out| should simply be
`|close_files_and_terminate|;\thinspace' followed by a call on some system
procedure that quietly terminates the program.

@<Error hand...@>=
procedure jump_out;
begin goto end_of_TEX;
end;

@ Here now is the general |error| routine.

@<Error hand...@>=
procedure error; {completes the job of error reporting}
label continue,exit;
var c:ASCII_code; {what the user types}
callback_id:integer;
@!s1,@!s2,@!s3,@!s4:integer;
  {used to save global variables when deleting tokens}
@!t:boolean;
begin if history<error_message_issued then history:=error_message_issued;
print_char("."); 
callback_id := callback_defined(show_error_hook_callback) ;
if callback_id>0 then t := run_callback(callback_id,'->');
show_context;
if interaction=error_stop_mode then @<Get user's advice and |return|@>;
incr(error_count);
if error_count=100 then
  begin print_nl("(That makes 100 errors; please try again.)");
@.That makes 100 errors...@>
  history:=fatal_error_stop; jump_out;
  end;
@<Put help message on the transcript file@>;
exit:end;

@ @<Get user's advice...@>=
loop@+begin continue: clear_for_error_prompt; prompt_input("? ");
@.?\relax@>
  if last=first then return;
  c:=buffer[first];
  if c>="a" then c:=c+"A"-"a"; {convert to uppercase}
  @<Interpret code |c| and |return| if done@>;
  end

@ It is desirable to provide an `\.E' option here that gives the user
an easy way to return from \TeX\ to the system editor, with the offending
line ready to be edited. But such an extension requires some system
wizardry, so the present implementation simply types out the name of the
file that should be
edited and the relevant line number.
@^system dependencies@>

There is a secret `\.D' option available when the debugging routines haven't
been commented~out.
@^debugging@>

@<Interpret code |c| and |return| if done@>=
case c of
"0","1","2","3","4","5","6","7","8","9": if deletions_allowed then
  @<Delete \(c)|c-"0"| tokens and |goto continue|@>;
@t\4\4@>@;@+@!debug "D": begin debug_help; goto continue;@+end;@+gubed@/
"E": if base_ptr>0 then
  begin print_nl("You want to edit file ");
@.You want to edit file x@>
  slow_print(input_stack[base_ptr].name_field);
  print(" at line "); print_int(line);
  interaction:=scroll_mode; jump_out;
  end;
"H": @<Print the help information and |goto continue|@>;
"I":@<Introduce new material from the terminal and |return|@>;
"Q","R","S":@<Change the interaction level and |return|@>;
"X":begin interaction:=scroll_mode; jump_out;
  end;
othercases do_nothing
endcases;@/
@<Print the menu of available options@>

@ @<Print the menu...@>=
begin print("Type <return> to proceed, S to scroll future error messages,");@/
@.Type <return> to proceed...@>
print_nl("R to run without stopping, Q to run quietly,");@/
print_nl("I to insert something, ");
if base_ptr>0 then print("E to edit your file,");
if deletions_allowed then
  print_nl("1 or ... or 9 to ignore the next 1 to 9 tokens of input,");
print_nl("H for help, X to quit.");
end

@ Here the author of \TeX\ apologizes for making use of the numerical
relation between |"Q"|, |"R"|, |"S"|, and the desired interaction settings
|batch_mode|, |nonstop_mode|, |scroll_mode|.
@^Knuth, Donald Ervin@>

@<Change the interaction...@>=
begin error_count:=0; interaction:=batch_mode+c-"Q";
print("OK, entering ");
case c of
"Q":begin print_esc("batchmode"); decr(selector);
  end;
"R":print_esc("nonstopmode");
"S":print_esc("scrollmode");
end; {there are no other cases}
print("..."); print_ln; update_terminal; return;
end

@ When the following code is executed, |buffer[(first+1)..(last-1)]| may
contain the material inserted by the user; otherwise another prompt will
be given. In order to understand this part of the program fully, you need
to be familiar with \TeX's input stacks.

@<Introduce new material...@>=
begin begin_file_reading; {enter a new syntactic level for terminal input}
{now |state=mid_line|, so an initial blank space will count as a blank}
if last>first+1 then
  begin loc:=first+1; buffer[first]:=" ";
  end
else  begin prompt_input("insert>"); loc:=first;
@.insert>@>
  end;
first:=last;
cur_input.limit_field:=last-1; {no |end_line_char| ends this line}
return;
end

@ We allow deletion of up to 99 tokens at a time.

@<Delete \(c)|c-"0"| tokens...@>=
begin s1:=cur_tok; s2:=cur_cmd; s3:=cur_chr; s4:=align_state;
align_state:=1000000; OK_to_interrupt:=false;
if (last>first+1) and (buffer[first+1]>="0")and(buffer[first+1]<="9") then
  c:=c*10+buffer[first+1]-"0"*11
else c:=c-"0";
while c>0 do
  begin get_token; {one-level recursive call of |error| is possible}
  decr(c);
  end;
cur_tok:=s1; cur_cmd:=s2; cur_chr:=s3; align_state:=s4; OK_to_interrupt:=true;
help2("I have just deleted some text, as you asked.")@/
("You can now delete more, or insert, or whatever.");
show_context; goto continue;
end

@ @<Print the help info...@>=
begin if use_err_help then
  begin give_err_help; use_err_help:=false;
  end
else  begin if help_ptr=0 then
    help2("Sorry, I don't know how to help in this situation.")@/
    @t\kern1em@>("Maybe you should try asking a human?");
  repeat decr(help_ptr); print(help_line[help_ptr]); print_ln;
  until help_ptr=0;
  end;
help4("Sorry, I already gave what help I could...")@/
  ("Maybe you should try asking a human?")@/
  ("An error might have occurred before I noticed any problems.")@/
  ("``If all else fails, read the instructions.''");@/
goto continue;
end

@ @<Put help message on the transcript file@>=
if interaction>batch_mode then decr(selector); {avoid terminal output}
if use_err_help then
  begin print_ln; give_err_help;
  end
else while help_ptr>0 do
  begin decr(help_ptr); print_nl(help_line[help_ptr]);
  end;
print_ln;
if interaction>batch_mode then incr(selector); {re-enable terminal output}
print_ln

@ A dozen or so error messages end with a parenthesized integer, so we
save a teeny bit of program space by declaring the following procedure:

@p procedure int_error(@!n:integer);
begin print(" ("); print_int(n); print_char(")"); error;
end;

@ In anomalous cases, the print selector might be in an unknown state;
the following subroutine is called to fix things just enough to keep
running a bit longer.

@p procedure normalize_selector;
begin if log_opened then selector:=term_and_log
else selector:=term_only;
if job_name=0 then open_log_file;
if interaction=batch_mode then decr(selector);
end;

@ The following procedure prints \TeX's last words before dying.

@d succumb==begin if interaction=error_stop_mode then
    interaction:=scroll_mode; {no more interaction}
  if log_opened then error;
  @!debug if interaction>batch_mode then debug_help;@+gubed@;@/
  history:=fatal_error_stop; jump_out; {irrecoverable error}
  end

@<Error hand...@>=
procedure fatal_error(@!s:str_number); {prints |s|, and that's it}
begin normalize_selector;@/
print_err("Emergency stop"); help1(s); succumb;
@.Emergency stop@>
end;

@ Here is the most dreaded error message.

@<Error hand...@>=
procedure lua_norm_error(@!s:str_number); {lua found a problem}
begin
print_err("LuaTeX error "); print(s);
help2("The lua interpreter ran into a problem, so the")@/
  ("remainder of this lua chunk will be ignored.");
error;
end;

procedure lua_fatal_error(@!s:str_number); {lua found a problem}
begin normalize_selector;
print_err("LuaTeX fatal error "); print(s);
succumb;
end;

procedure overflow(@!s:str_number;@!n:integer); {stop due to finiteness}
begin normalize_selector;
print_err("TeX capacity exceeded, sorry [");
@.TeX capacity exceeded ...@>
print(s); print_char("="); print_int(n); print_char("]");
help2("If you really absolutely need more capacity,")@/
  ("you can ask a wizard to enlarge me.");
succumb;
end;

procedure overflow_ocp_buf_size;
begin
overflow("ocp_buf_size",ocp_buf_size);
end;

procedure overflow_ocp_stack_size;
begin
overflow("ocp_stack_size",ocp_stack_size);
end;


@ The program might sometime run completely amok, at which point there is
no choice but to stop. If no previous error has been detected, that's bad
news; a message is printed that is really intended for the \TeX\
maintenance person instead of the user (unless the user has been
particularly diabolical).  The index entries for `this can't happen' may
help to pinpoint the problem.
@^dry rot@>

@<Error hand...@>=
procedure confusion(@!s:str_number);
  {consistency check violated; |s| tells where}
begin normalize_selector;
if history<error_message_issued then
  begin print_err("This can't happen ("); print(s); print_char(")");
@.This can't happen@>
  help1("I'm broken. Please show this to someone who can fix can fix");
  end
else  begin print_err("I can't go on meeting you like this");
@.I can't go on...@>
  help2("One of your faux pas seems to have wounded me deeply...")@/
    ("in fact, I'm barely conscious. Please fix it and try again.");
  end;
succumb;
end;

@ Users occasionally want to interrupt \TeX\ while it's running.
If the \PASCAL\ runtime system allows this, one can implement
a routine that sets the global variable |interrupt| to some nonzero value
when such an interrupt is signalled. Otherwise there is probably at least
a way to make |interrupt| nonzero using the \PASCAL\ debugger.
@^system dependencies@>
@^debugging@>

@<Global...@>=
@!interrupt:integer; {should \TeX\ pause for instructions?}
@!OK_to_interrupt:boolean; {should interrupts be observed?}
@!detokenized_line:boolean; {indicates this is a 'detokenized' input line }
@!line_catcode_table:integer; {the used catcode table for input lines}
@!local_catcode_table:boolean; {the used catcode table for input lines}
@!static_int_base:integer; {C version of |int_base|}

@ @p procedure check_interrupt;
begin 
if interrupt<>0 then pause_for_instructions;
end;


@ @<Set init...@>=
interrupt:=0; OK_to_interrupt:=true; detokenized_line:=false;
line_catcode_table:=0; local_catcode_table:=false;

@ When an interrupt has been detected, the program goes into its
highest interaction level and lets the user have nearly the full flexibility of
the |error| routine.  \TeX\ checks for interrupts only at times when it is
safe to do this.

@p procedure pause_for_instructions;
begin if OK_to_interrupt then
  begin interaction:=error_stop_mode;
  if (selector=log_only)or(selector=no_print) then
    incr(selector);
  print_err("Interruption");
@.Interruption@>
  help3("You rang?")@/
  ("Try to insert some instructions for me (e.g.,`I\showlists'),")@/
  ("unless you just want to quit by typing `X'.");
  deletions_allowed:=false; error; deletions_allowed:=true;
  interrupt:=0;
  end;
end;

@* \[7] Arithmetic with scaled dimensions.
The principal computations performed by \TeX\ are done entirely in terms of
integers less than $2^{31}$ in magnitude; and divisions are done only when both
dividend and divisor are nonnegative. Thus, the arithmetic specified in this
program can be carried out in exactly the same way on a wide variety of
computers, including some small ones. Why? Because the arithmetic
calculations need to be spelled out precisely in order to guarantee that
\TeX\ will produce identical output on different machines. If some
quantities were rounded differently in different implementations, we would
find that line breaks and even page breaks might occur in different places.
Hence the arithmetic of \TeX\ has been designed with care, and systems that
claim to be implementations of \TeX82 should follow precisely the
@:TeX82}{\TeX82@>
calculations as they appear in the present program.

(Actually there are three places where \TeX\ uses |div| with a possibly negative
numerator. These are harmless; see |div| in the index. Also if the user
sets the \.{\\time} or the \.{\\year} to a negative value, some diagnostic
information will involve negative-numerator division. The same remarks
apply for |mod| as well as for |div|.)

@ Here is a routine that calculates half of an integer, using an
unambiguous convention with respect to signed odd numbers.

@p function half(@!x:integer):integer;
begin if odd(x) then half:=(x+1) div 2
else half:=x @!div 2;
end;

@ Fixed-point arithmetic is done on {\sl scaled integers\/} that are multiples
of $2^{-16}$. In other words, a binary point is assumed to be sixteen bit
positions from the right end of a binary computer word.

@d unity == @'200000 {$2^{16}$, represents 1.00000}
@d two == @'400000 {$2^{17}$, represents 2.00000}

@<Types...@>=
@!scaled = integer; {this type is used for scaled integers}
@!nonnegative_integer=0..@'17777777777; {$0\L x<2^{31}$}
@!small_number=0..63; {this type is self-explanatory}

@ The following function is used to create a scaled integer from a given decimal
fraction $(.d_0d_1\ldots d_{k-1})$, where |0<=k<=17|. The digit $d_i$ is
given in |dig[i]|, and the calculation produces a correctly rounded result.

@p function round_decimals(@!k:small_number) : scaled;
  {converts a decimal fraction}
var a:integer; {the accumulator}
begin a:=0;
while k>0 do
  begin decr(k); a:=(a+dig[k]*two) div 10;
  end;
round_decimals:=(a+1) div 2;
end;

@ Conversely, here is a procedure analogous to |print_int|. If the output
of this procedure is subsequently read by \TeX\ and converted by the
|round_decimals| routine above, it turns out that the original value will
be reproduced exactly; the ``simplest'' such decimal number is output,
but there is always at least one digit following the decimal point.

The invariant relation in the \&{repeat} loop is that a sequence of
decimal digits yet to be printed will yield the original number if and only if
they form a fraction~$f$ in the range $s-\delta\L10\cdot2^{16}f<s$.
We can stop if and only if $f=0$ satisfies this condition; the loop will
terminate before $s$ can possibly become zero.

@p procedure print_scaled(@!s:scaled); {prints scaled real, rounded to five
  digits}
var delta:scaled; {amount of allowable inaccuracy}
begin if s<0 then
  begin print_char("-"); negate(s); {print the sign, if negative}
  end;
print_int(s div unity); {print the integer part}
print_char(".");
s:=10*(s mod unity)+5; delta:=10;
repeat if delta>unity then s:=s+@'100000-50000; {round the last digit}
print_char("0"+(s div unity)); s:=10*(s mod unity); delta:=delta*10;
until s<=delta;
end;

@ Physical sizes that a \TeX\ user specifies for portions of documents are
represented internally as scaled points. Thus, if we define an `sp' (scaled
@^sp@>
point) as a unit equal to $2^{-16}$ printer's points, every dimension
inside of \TeX\ is an integer number of sp. There are exactly
4,736,286.72 sp per inch.  Users are not allowed to specify dimensions
larger than $2^{30}-1$ sp, which is a distance of about 18.892 feet (5.7583
meters); two such quantities can be added without overflow on a 32-bit
computer.

The present implementation of \TeX\ does not check for overflow when
@^Overflow in arithmetic@>
dimensions are added or subtracted. This could be done by inserting a
few dozen tests of the form `\ignorespaces|if x>=@'10000000000 then
@t\\{report\_overflow}@>|', but the chance of overflow is so remote that
such tests do not seem worthwhile.

\TeX\ needs to do only a few arithmetic operations on scaled quantities,
other than addition and subtraction, and the following subroutines do most of
the work. A single computation might use several subroutine calls, and it is
desirable to avoid producing multiple error messages in case of arithmetic
overflow; so the routines set the global variable |arith_error| to |true|
instead of reporting errors directly to the user. Another global variable,
|remainder|, holds the remainder after a division.

@<Glob...@>=
@!arith_error:boolean; {has arithmetic overflow occurred recently?}
@!remainder:scaled; {amount subtracted to get an exact division}

@ The first arithmetical subroutine we need computes $nx+y$, where |x|
and~|y| are |scaled| and |n| is an integer. We will also use it to
multiply integers.

@d nx_plus_y(#)==mult_and_add(#,@'7777777777)
@d mult_integers(#)==mult_and_add(#,0,@'17777777777)

@p function mult_and_add(@!n:integer;@!x,@!y,@!max_answer:scaled):scaled;
begin if n<0 then
  begin negate(x); negate(n);
  end;
if n=0 then mult_and_add:=y
else if ((x<=(max_answer-y) div n)and(-x<=(max_answer+y) div n)) then
  mult_and_add:=n*x+y
else  begin arith_error:=true; mult_and_add:=0;
  end;
end;

@ We also need to divide scaled dimensions by integers.

@p function x_over_n(@!x:scaled;@!n:integer):scaled;
var negative:boolean; {should |remainder| be negated?}
begin negative:=false;
if n=0 then
  begin arith_error:=true; x_over_n:=0; remainder:=x;
  end
else  begin if n<0 then
    begin negate(x); negate(n); negative:=true;
    end;
  if x>=0 then
    begin x_over_n:=x div n; remainder:=x mod n;
    end
  else  begin x_over_n:=-((-x) div n); remainder:=-((-x) mod n);
    end;
  end;
if negative then negate(remainder);
end;

@ Then comes the multiplication of a scaled number by a fraction |n/d|,
where |n| and |d| are nonnegative integers |<=@t$2^{16}$@>| and |d| is
positive. It would be too dangerous to multiply by~|n| and then divide
by~|d|, in separate operations, since overflow might well occur; and it
would be too inaccurate to divide by |d| and then multiply by |n|. Hence
this subroutine simulates 1.5-precision arithmetic.

@p function xn_over_d(@!x:scaled; @!n,@!d:integer):scaled;
var positive:boolean; {was |x>=0|?}
@!t,@!u,@!v:nonnegative_integer; {intermediate quantities}
begin if x>=0 then positive:=true
else  begin negate(x); positive:=false;
  end;
t:=(x mod @'100000)*n;
u:=(x div @'100000)*n+(t div @'100000);
v:=(u mod d)*@'100000 + (t mod @'100000);
if u div d>=@'100000 then arith_error:=true
else u:=@'100000*(u div d) + (v div d);
if positive then
  begin xn_over_d:=u; remainder:=v mod d;
  end
else  begin xn_over_d:=-u; remainder:=-(v mod d);
  end;
end;

@ The next subroutine is used to compute the ``badness'' of glue, when a
total~|t| is supposed to be made from amounts that sum to~|s|.  According
to {\sl The \TeX book}, the badness of this situation is $100(t/s)^3$;
however, badness is simply a heuristic, so we need not squeeze out the
last drop of accuracy when computing it. All we really want is an
approximation that has similar properties.
@:TeXbook}{\sl The \TeX book@>

The actual method used to compute the badness is easier to read from the
program than to describe in words. It produces an integer value that is a
reasonably close approximation to $100(t/s)^3$, and all implementations
of \TeX\ should use precisely this method. Any badness of $2^{13}$ or more is
treated as infinitely bad, and represented by 10000.

It is not difficult to prove that $$\hbox{|badness(t+1,s)>=badness(t,s)
>=badness(t,s+1)|}.$$ The badness function defined here is capable of
computing at most 1095 distinct values, but that is plenty.

@d inf_bad = 10000 {infinitely bad value}

@p function badness(@!t,@!s:scaled):halfword; {compute badness, given |t>=0|}
var r:integer; {approximation to $\alpha t/s$, where $\alpha^3\approx
  100\cdot2^{18}$}
begin if t=0 then badness:=0
else if s<=0 then badness:=inf_bad
else  begin if t<=7230584 then  r:=(t*297) div s {$297^3=99.94\times2^{18}$}
  else if s>=1663497 then r:=t div (s div 297)
  else r:=t;
  if r>1290 then badness:=inf_bad {$1290^3<2^{31}<1291^3$}
  else badness:=(r*r*r+@'400000) div @'1000000;
  end; {that was $r^3/2^{18}$, rounded to the nearest integer}
end;

@ When \TeX\ ``packages'' a list into a box, it needs to calculate the
proportionality ratio by which the glue inside the box should stretch
or shrink. This calculation does not affect \TeX's decision making,
so the precise details of rounding, etc., in the glue calculation are not
of critical importance for the consistency of results on different computers.

We shall use the type |glue_ratio| for such proportionality ratios.
A glue ratio should take the same amount of memory as an
|integer| (usually 32 bits) if it is to blend smoothly with \TeX's
other data structures. Thus |glue_ratio| should be equivalent to
|short_real| in some implementations of \PASCAL. Alternatively,
it is possible to deal with glue ratios using nothing but fixed-point
arithmetic; see {\sl TUGboat \bf3},1 (March 1982), 10--27. (But the
routines cited there must be modified to allow negative glue ratios.)
@^system dependencies@>

@d set_glue_ratio_zero(#) == #:=0.0 {store the representation of zero ratio}
@d set_glue_ratio_one(#) == #:=1.0 {store the representation of unit ratio}
@d float(#) == # {convert from |glue_ratio| to type |real|}
@d unfloat(#) == # {convert from |real| to type |glue_ratio|}
@d float_constant(#) == #.0 {convert |integer| constant to |real|}

@<Types...@>=
@!glue_ratio=real; {one-word representation of a glue expansion factor}

@* \[7b] Random numbers.

\font\tenlogo=logo10 % font used for the METAFONT logo
\def\MP{{\tenlogo META}\-{\tenlogo POST}}

This section is (almost) straight from MetaPost. I had to change
the types (use |integer| instead of |fraction|), but that should
not have any influence on the actual calculations (the original
comments refer to quantities like |fraction_four| ($2^{30}$), and
that is the same as the numeric representation of |maxdimen|).

I've copied the low-level variables and routines that are needed, but
only those (e.g. |m_log|), not the accompanying ones like |m_exp|. Most
of the following low-level numeric routines are only needed within the
calculation of |norm_rand|. I've been forced to rename |make_fraction|
to |make_frac| because TeX already has a routine by that name with
a wholly different function (it creates a |fraction_noad| for math
typesetting) -- Taco

And now let's complete our collection of numeric utility routines
by considering random number generation.
\MP\ generates pseudo-random numbers with the additive scheme recommended
in Section 3.6 of {\sl The Art of Computer Programming}; however, the
results are random fractions between 0 and |fraction_one-1|, inclusive.

There's an auxiliary array |randoms| that contains 55 pseudo-random
fractions. Using the recurrence $x_n=(x_{n-55}-x_{n-31})\bmod 2^{28}$,
we generate batches of 55 new $x_n$'s at a time by calling |new_randoms|.
The global variable |j_random| tells which element has most recently
been consumed.

@<Glob...@>=
@!randoms:array[0..54] of integer; {the last 55 random values generated}
@!j_random:0..54; {the number of unused |randoms|}
@!random_seed:scaled; {the default random seed}

@ A small bit of metafont is needed.

@d fraction_half==@'1000000000 {$2^{27}$, represents 0.50000000}
@d fraction_one==@'2000000000 {$2^{28}$, represents 1.00000000}
@d fraction_four==@'10000000000 {$2^{30}$, represents 4.00000000}
@d el_gordo == @'17777777777 {$2^{31}-1$, the largest value that \MP\ likes}
@d halfp(#)==(#) div 2
@d double(#) == #:=#+# {multiply a variable by two}

@ The |make_frac| routine produces the |fraction| equivalent of
|p/q|, given integers |p| and~|q|; it computes the integer
$f=\lfloor2^{28}p/q+{1\over2}\rfloor$, when $p$ and $q$ are
positive. If |p| and |q| are both of the same scaled type |t|,
the ``type relation'' |make_frac(t,t)=fraction| is valid;
and it's also possible to use the subroutine ``backwards,'' using
the relation |make_frac(t,fraction)=t| between scaled types.

If the result would have magnitude $2^{31}$ or more, |make_frac|
sets |arith_error:=true|. Most of \MP's internal computations have
been designed to avoid this sort of error.

If this subroutine were programmed in assembly language on a typical
machine, we could simply compute |(@t$2^{28}$@>*p)div q|, since a
double-precision product can often be input to a fixed-point division
instruction. But when we are restricted to \PASCAL\ arithmetic it
is necessary either to resort to multiple-precision maneuvering
or to use a simple but slow iteration. The multiple-precision technique
would be about three times faster than the code adopted here, but it
would be comparatively long and tricky, involving about sixteen
additional multiplications and divisions.

This operation is part of \MP's ``inner loop''; indeed, it will
consume nearly 10\pct! of the running time (exclusive of input and output)
if the code below is left unchanged. A machine-dependent recoding
will therefore make \MP\ run faster. The present implementation
is highly portable, but slow; it avoids multiplication and division
except in the initial stage. System wizards should be careful to
replace it with a routine that is guaranteed to produce identical
results in all cases.
@^system dependencies@>

As noted below, a few more routines should also be replaced by machine-dependent
code, for efficiency. But when a procedure is not part of the ``inner loop,''
such changes aren't advisable; simplicity and robustness are
preferable to trickery, unless the cost is too high.
@^inner loop@>

@p function make_frac(@!p,@!q:integer):integer;
var @!f:integer; {the fraction bits, with a leading 1 bit}
@!n:integer; {the integer part of $\vert p/q\vert$}
@!negative:boolean; {should the result be negated?}
@!be_careful:integer; {disables certain compiler optimizations}
begin if p>=0 then negative:=false
else  begin negate(p); negative:=true;
  end;
if q<=0 then
  begin debug if q=0 then confusion("/");@;@+gubed@;@/
@:this can't happen /}{\quad \./@>
  negate(q); negative:=not negative;
  end;
n:=p div q; p:=p mod q;
if n>=8 then
  begin arith_error:=true;
  if negative then make_frac:=-el_gordo@+else make_frac:=el_gordo;
  end
else  begin n:=(n-1)*fraction_one;
  @<Compute $f=\lfloor 2^{28}(1+p/q)+{1\over2}\rfloor$@>;
  if negative then make_frac:=-(f+n)@+else make_frac:=f+n;
  end;
end;

@ The |repeat| loop here preserves the following invariant relations
between |f|, |p|, and~|q|:
(i)~|0<=p<q|; (ii)~$fq+p=2^k(q+p_0)$, where $k$ is an integer and
$p_0$ is the original value of~$p$.

Notice that the computation specifies
|(p-q)+p| instead of |(p+p)-q|, because the latter could overflow.
Let us hope that optimizing compilers do not miss this point; a
special variable |be_careful| is used to emphasize the necessary
order of computation. Optimizing compilers should keep |be_careful|
in a register, not store it in memory.
@^inner loop@>

@<Compute $f=\lfloor 2^{28}(1+p/q)+{1\over2}\rfloor$@>=
f:=1;
repeat be_careful:=p-q; p:=be_careful+p;
if p>=0 then f:=f+f+1
else  begin double(f); p:=p+q;
  end;
until f>=fraction_one;
be_careful:=p-q;
if be_careful+p>=0 then incr(f)

@

@p function take_frac(@!q:integer;@!f:integer):integer;
var @!p:integer; {the fraction so far}
@!negative:boolean; {should the result be negated?}
@!n:integer; {additional multiple of $q$}
@!be_careful:integer; {disables certain compiler optimizations}
begin @<Reduce to the case that |f>=0| and |q>0|@>;
if f<fraction_one then n:=0
else  begin n:=f div fraction_one; f:=f mod fraction_one;
  if q<=el_gordo div n then n:=n*q
  else  begin arith_error:=true; n:=el_gordo;
    end;
  end;
f:=f+fraction_one;
@<Compute $p=\lfloor qf/2^{28}+{1\over2}\rfloor-q$@>;
be_careful:=n-el_gordo;
if be_careful+p>0 then
  begin arith_error:=true; n:=el_gordo-p;
  end;
if negative then take_frac:=-(n+p)
else take_frac:=n+p;
end;

@ @<Reduce to the case that |f>=0| and |q>0|@>=
if f>=0 then negative:=false
else  begin negate(f); negative:=true;
  end;
if q<0 then
  begin negate(q); negative:=not negative;
  end;

@ The invariant relations in this case are (i)~$\lfloor(qf+p)/2^k\rfloor
=\lfloor qf_0/2^{28}+{1\over2}\rfloor$, where $k$ is an integer and
$f_0$ is the original value of~$f$; (ii)~$2^k\L f<2^{k+1}$.
@^inner loop@>

@<Compute $p=\lfloor qf/2^{28}+{1\over2}\rfloor-q$@>=
p:=fraction_half; {that's $2^{27}$; the invariants hold now with $k=28$}
if q<fraction_four then
  repeat if odd(f) then p:=halfp(p+q)@+else p:=halfp(p);
  f:=halfp(f);
  until f=1
else  repeat if odd(f) then p:=p+halfp(q-p)@+else p:=halfp(p);
  f:=halfp(f);
  until f=1

@ The subroutines for logarithm and exponential involve two tables.
The first is simple: |two_to_the[k]| equals $2^k$. The second involves
a bit more calculation, which the author claims to have done correctly:
|spec_log[k]| is $2^{27}$ times $\ln\bigl(1/(1-2^{-k})\bigr)=
2^{-k}+{1\over2}2^{-2k}+{1\over3}2^{-3k}+\cdots\,$, rounded to the
nearest integer.

@<Glob...@>=
@!two_to_the:array[0..30] of integer; {powers of two}
@!spec_log:array[1..28] of integer; {special logarithms}


@ @<Set init...@>=
two_to_the[0]:=1;
for k:=1 to 30 do two_to_the[k]:=2*two_to_the[k-1];
spec_log[1]:=93032640;
spec_log[2]:=38612034;
spec_log[3]:=17922280;
spec_log[4]:=8662214;
spec_log[5]:=4261238;
spec_log[6]:=2113709;
spec_log[7]:=1052693;
spec_log[8]:=525315;
spec_log[9]:=262400;
spec_log[10]:=131136;
spec_log[11]:=65552;
spec_log[12]:=32772;
spec_log[13]:=16385;
for k:=14 to 27 do spec_log[k]:=two_to_the[27-k];
spec_log[28]:=1;

@

@p function m_log(@!x:integer):integer;
var @!y,@!z:integer; {auxiliary registers}
@!k:integer; {iteration counter}
begin if x<=0 then @<Handle non-positive logarithm@>
else  begin y:=1302456956+4-100; {$14\times2^{27}\ln2\approx1302456956.421063$}
  z:=27595+6553600; {and $2^{16}\times .421063\approx 27595$}
  while x<fraction_four do
    begin double(x); y:=y-93032639; z:=z-48782;
    end; {$2^{27}\ln2\approx 93032639.74436163$
      and $2^{16}\times.74436163\approx 48782$}
  y:=y+(z div unity); k:=2;
  while x>fraction_four+4 do
    @<Increase |k| until |x| can be multiplied by a
      factor of $2^{-k}$, and adjust $y$ accordingly@>;
  m_log:=y div 8;
  end;
end;

@ @<Increase |k| until |x| can...@>=
begin z:=((x-1) div two_to_the[k])+1; {$z=\lceil x/2^k\rceil$}
while x<fraction_four+z do
  begin z:=halfp(z+1); k:=k+1;
  end;
y:=y+spec_log[k]; x:=x-z;
end

@ @<Handle non-positive logarithm@>=
begin print_err("Logarithm of ");
@.Logarithm...replaced by 0@>
print_scaled(x); print(" has been replaced by 0");
help2("Since I don't take logs of non-positive numbers,")@/
  ("I'm zeroing this one. Proceed, with fingers crossed.");
error; m_log:=0;
end

@ The following somewhat different subroutine tests rigorously if $ab$ is
greater than, equal to, or less than~$cd$,
given integers $(a,b,c,d)$. In most cases a quick decision is reached.
The result is $+1$, 0, or~$-1$ in the three respective cases.

@d return_sign(#)==begin ab_vs_cd:=#; return;
  end

@p function ab_vs_cd(@!a,b,c,d:integer):integer;
label exit;
var @!q,@!r:integer; {temporary registers}
begin @<Reduce to the case that |a,c>=0|, |b,d>0|@>;
loop@+  begin q := a div d; r := c div b;
  if q<>r then
    if q>r then return_sign(1)@+else return_sign(-1);
  q := a mod d; r := c mod b;
  if r=0 then
    if q=0 then return_sign(0)@+else return_sign(1);
  if q=0 then return_sign(-1);
  a:=b; b:=q; c:=d; d:=r;
  end; {now |a>d>0| and |c>b>0|}
exit:end;

@ @<Reduce to the case that |a...@>=
if a<0 then
  begin negate(a); negate(b);
  end;
if c<0 then
  begin negate(c); negate(d);
  end;
if d<=0 then
  begin if b>=0 then
    if ((a=0)or(b=0))and((c=0)or(d=0)) then return_sign(0)
    else return_sign(1);
  if d=0 then
    if a=0 then return_sign(0)@+else return_sign(-1);
  q:=a; a:=c; c:=q; q:=-b; b:=-d; d:=q;
  end
else if b<=0 then
  begin if b<0 then if a>0 then return_sign(-1);
  if c=0 then return_sign(0) else return_sign(-1);
  end

@ To consume a random integer, the program below will say `|next_random|'
and then it will fetch |randoms[j_random]|.

@d next_random==if j_random=0 then new_randoms
  else decr(j_random)

@p procedure new_randoms;
var @!k:0..54; {index into |randoms|}
@!x:integer; {accumulator}
begin for k:=0 to 23 do
  begin x:=randoms[k]-randoms[k+31];
  if x<0 then x:=x+fraction_one;
  randoms[k]:=x;
  end;
for k:=24 to 54 do
  begin x:=randoms[k]-randoms[k-24];
  if x<0 then x:=x+fraction_one;
  randoms[k]:=x;
  end;
j_random:=54;
end;

@ To initialize the |randoms| table, we call the following routine.

@p procedure init_randoms(@!seed:integer);
var @!j,@!jj,@!k:integer; {more or less random integers}
@!i:0..54; {index into |randoms|}
begin j:=abs(seed);
while j>=fraction_one do j:=halfp(j);
k:=1;
for i:=0 to 54 do
  begin jj:=k; k:=j-k; j:=jj;
  if k<0 then k:=k+fraction_one;
  randoms[(i*21)mod 55]:=j;
  end;
new_randoms; new_randoms; new_randoms; {``warm up'' the array}
end;

@ To produce a uniform random number in the range |0<=u<x| or |0>=u>x|
or |0=u=x|, given a |scaled| value~|x|, we proceed as shown here.

Note that the call of |take_frac| will produce the values 0 and~|x|
with about half the probability that it will produce any other particular
values between 0 and~|x|, because it rounds its answers.

@p function unif_rand(@!x:integer):integer;
var @!y:integer; {trial value}
begin next_random; y:=take_frac(abs(x),randoms[j_random]);
if y=abs(x) then unif_rand:=0
else if x>0 then unif_rand:=y
else unif_rand:=-y;
end;

@ Finally, a normal deviate with mean zero and unit standard deviation
can readily be obtained with the ratio method (Algorithm 3.4.1R in
{\sl The Art of Computer Programming\/}).

@p function norm_rand:integer;
var @!x,@!u,@!l:integer; {what the book would call $2^{16}X$, $2^{28}U$,
  and $-2^{24}\ln U$}
begin repeat
  repeat next_random;
  x:=take_frac(112429,randoms[j_random]-fraction_half);
    {$2^{16}\sqrt{8/e}\approx 112428.82793$}
  next_random; u:=randoms[j_random];
  until abs(x)<u;
x:=make_frac(x,u);
l:=139548960-m_log(u); {$2^{24}\cdot12\ln2\approx139548959.6165$}
until ab_vs_cd(1024,l,x,x)>=0;
norm_rand:=x;
end;

@* \[8] Packed data.
In order to make efficient use of storage space, \TeX\ bases its major data
structures on a |memory_word|, which contains either a (signed) integer,
possibly scaled, or a (signed) |glue_ratio|, or a small number of
fields that are one half or one quarter of the size used for storing
integers.

If |x| is a variable of type |memory_word|, it contains up to four
fields that can be referred to as follows:
$$\vbox{\halign{\hfil#&#\hfil&#\hfil\cr
|x|&.|int|&(an |integer|)\cr
|x|&.|sc|\qquad&(a |scaled| integer)\cr
|x|&.|gr|&(a |glue_ratio|)\cr
|x.hh.lh|, |x.hh|&.|rh|&(two halfword fields)\cr
|x.hh.b0|, |x.hh.b1|, |x.hh|&.|rh|&(two quarterword fields, one halfword
  field)\cr
|x.qqqq.b0|, |x.qqqq.b1|, |x.qqqq|&.|b2|, |x.qqqq.b3|\hskip-100pt
  &\qquad\qquad\qquad(four quarterword fields)\cr}}$$
This is somewhat cumbersome to write, and not very readable either, but
macros will be used to make the notation shorter and more transparent.
The \PASCAL\ code below gives a formal definition of |memory_word| and
its subsidiary types, using packed variant records. \TeX\ makes no
assumptions about the relative positions of the fields within a word.

We are assuming 32-bit integers, a halfword must contain at least
32 bits, and a quarterword must contain at least 16 bits.
@^system dependencies@>

N.B.: Valuable memory space will be dreadfully wasted unless \TeX\ is compiled
by a \PASCAL\ that packs all of the |memory_word| variants into
the space of a single integer. This means, for example, that |glue_ratio|
words should be |short_real| instead of |real| on some computers. Some
\PASCAL\ compilers will pack an integer whose subrange is `|0..255|' into
an eight-bit field, but others insist on allocating space for an additional
sign bit; on such systems you can get 256 values into a quarterword only
if the subrange is `|-128..127|'.

The present implementation tries to accommodate as many variations as possible,
so it makes few assumptions. If integers having the subrange
`|min_quarterword..max_quarterword|' can be packed into a quarterword,
and if integers having the subrange `|min_halfword..max_halfword|'
can be packed into a halfword, everything should work satisfactorily.

It is usually most efficient to have |min_quarterword=min_halfword=0|,
so one should try to achieve this unless it causes a severe problem.
The values defined here are recommended for most 32-bit computers.

We cannot use the full range of 32 bits in a halfword, because we have
to allow negative values for potential backend tricks like web2c's
dynamic allocation, and parshapes pointers have to be able to store at
least twice the value |max_halfword| (see below). Therefore,
|max_halfword| is $2^{30}-1$

@d min_quarterword=0 {smallest allowable value in a |quarterword|}
@d max_quarterword=65535 {largest allowable value in a |quarterword|}
@d min_halfword==-@"3FFFFFFF {smallest allowable value in a |halfword|}
@d max_halfword==@"3FFFFFFF {largest allowable value in a |halfword|}

@ Here are the inequalities that the quarterword and halfword values
must satisfy (or rather, the inequalities that they mustn't satisfy):

@<Check the ``constant''...@>=
if (min_quarterword>0)or(max_quarterword<@"7FFF) then bad:=11;
if (min_halfword>0)or(max_halfword<@"3FFFFFFF) then bad:=12;
if (min_quarterword<min_halfword)or@|
  (max_quarterword>max_halfword) then bad:=13;
if font_base<min_quarterword then bad:=15;
if (save_size>max_halfword)or(max_strings>max_halfword) then bad:=17;
if buf_size>max_halfword then bad:=18;
if max_quarterword-min_quarterword<@"FFFF then bad:=19;

@ The operation of adding or subtracting |min_quarterword| occurs quite
frequently in \TeX, so it is convenient to abbreviate this operation
by using the macros |qi| and |qo| for input and output to and from
quarterword format.

The inner loop of \TeX\ will run faster with respect to compilers
that don't optimize expressions like `|x+0|' and `|x-0|', if these
macros are simplified in the obvious way when |min_quarterword=0|.
@^inner loop@>@^system dependencies@>

@d qi(#)==#+min_quarterword
  {to put an |eight_bits| item into a quarterword}
@d qo(#)==#-min_quarterword
  {to take an |eight_bits| item out of a quarterword}
@d hi(#)==#+min_halfword
  {to put a sixteen-bit item into a halfword}
@d ho(#)==#-min_halfword
  {to take a sixteen-bit item from a halfword}

@ The reader should study the following definitions closely:
@^system dependencies@>

@d sc==int {|scaled| data is equivalent to |integer|}

@<Types...@>=
@!quarterword = min_quarterword..max_quarterword; {1/4 of a word}
@!halfword=min_halfword..max_halfword; {1/2 of a word}
@!two_choices = 1..2; {used when there are two variants in a record}
@!four_choices = 1..4; {used when there are four variants in a record}
@!two_halves = packed record@;@/
  @!rh:halfword;
  case two_choices of
  1: (@!lh:halfword);
  2: (@!b0:quarterword; @!b1:quarterword);
  end;
@!four_quarters = packed record@;@/
  @!b0:quarterword;
  @!b1:quarterword;
  @!b2:quarterword;
  @!b3:quarterword;
  end;
@!memory_word = record@;@/
  case four_choices of
  1: (@!int:integer);
  2: (@!gr:glue_ratio);
  3: (@!hh:two_halves);
  4: (@!qqqq:four_quarters);
  end;
@!word_file = file of memory_word;

@ When debugging, we may want to print a |memory_word| without knowing
what type it is; so we print it in all modes.
@^dirty \PASCAL@>@^debugging@>

@p @!debug procedure print_word(@!w:memory_word);
  {prints |w| in all ways}
begin print_int(w.int); print_char(" ");@/
print_scaled(w.sc); print_char(" ");@/
print_scaled(round(unity*float(w.gr))); print_ln;@/
@^real multiplication@>
print_int(w.hh.lh); print_char("="); print_int(w.hh.b0); print_char(":");
print_int(w.hh.b1); print_char(";"); print_int(w.hh.rh); print_char(" ");@/
print_int(w.qqqq.b0); print_char(":"); print_int(w.qqqq.b1); print_char(":");
print_int(w.qqqq.b2); print_char(":"); print_int(w.qqqq.b3);
end;
gubed

@* \[9] Dynamic memory allocation.
The \TeX\ system does nearly all of its own memory allocation, so that it
can readily be transported into environments that do not have automatic
facilities for strings, garbage collection, etc., and so that it can be in
control of what error messages the user receives. The dynamic storage
requirements of \TeX\ are handled by providing two large arrays called
|fixmem| and |varmem| in which consecutive blocks of words are used as 
nodes by the \TeX\ routines.

Pointer variables are indices into this array, or into another array
called |eqtb| that will be explained later. A pointer variable might
also be a special flag that lies outside the bounds of |mem|, so we
allow pointers to assume any |halfword| value. The minimum halfword
value represents a null pointer. \TeX\ does not assume that |mem[null]| exists.

@d pointer==halfword {a flag or a location in |mem| or |eqtb|}
@d null==0 {the null pointer}

@<Glob...@>=
@!temp_ptr:pointer; {a pointer variable for occasional emergency use}

@ @<Types...@>=
@!smemory_word = packed record@;@/
  @!hhrh:halfword;
  @!hhlh:halfword;
  end;


@ The |mem| array is divided into two items that are allocated separately; 
they grow until finding their ``natural'' size in a particular job.
Locations in |varmem| are used for storing variable-length records
consisting of two or more words each. This region
is maintained using an algorithm similar to the one described in exercise
2.5--19 of {\sl The Art of Computer Programming}. However, no size field
appears in the allocated nodes; the program is responsible for knowing the
relevant size when a node is freed. Locations in |fixmem| are used for storing 
one-word records; a conventional \.{AVAIL} stack is used for allocation 
in this array.

Empirical tests show that the present implementation of \TeX\ tends to
spend about 9\pct! of its running time allocating nodes, and about 6\pct!
deallocating them after their use.

@d fix_mem_init==10000

@<Glob...@>=
@!fixmem : ^smemory_word; {the big dynamic storage area}
@!fix_mem_min : pointer; {the smallest location of one-word memory in use}
@!fix_mem_max : pointer; {the largest location of one-word memory in use}

@ In order to study the memory requirements of particular applications, it
is possible to prepare a version of \TeX\ that keeps track of current and
maximum memory usage. When code between the delimiters |@!stat| $\ldots$
|tats| is not ``commented out,'' \TeX\ will run a bit slower but it will
report these statistics when |tracing_stats| is sufficiently large.

@<Glob...@>=
@!var_used, @!dyn_used : integer; {how much memory is in use}

@ Let's consider the one-word memory region first, since it's the
simplest. The pointer variable |fix_mem_end| holds the highest-numbered location
of |mem| that has ever been used. The free locations of |mem| that
occur between |hi_mem_min| and |fix_mem_end|, inclusive, are of type
|two_halves|, and we write |info(p)| and |link(p)| for the |lh|
and |rh| fields of |mem[p]| when it is of this type. The single-word
free locations form a linked list
$$|avail|,\;\hbox{|link(avail)|},\;\hbox{|link(link(avail))|},\;\ldots$$
terminated by |null|.

@d mem(#) == fixmem[#]
@d link(#) == mem(#).hhrh {the |link| field of a memory word}
@d info(#) == mem(#).hhlh {the |info| field of a memory word}

@<Glob...@>=
@!avail : pointer; {head of the list of available one-word nodes}
@!fix_mem_end : pointer; {the last one-word node used in |mem|}

@ If memory is exhausted, it might mean that the user has forgotten
a right brace. We will define some procedures later that try to help
pinpoint the trouble.

@p @<Declare the procedure called |show_token_list|@>@/
@<Declare the procedure called |runaway|@>

@ The function |get_avail| returns a pointer to a new one-word node whose
|link| field is null. However, \TeX\ will halt if there is no more room left.
@^inner loop@>

If the available-space list is empty, i.e., if |avail=null|,
we try first to increase |fix_mem_end|. If that cannot be done, i.e., if
|fix_mem_end=fix_mem_max|, we try to reallocate array |fixmem|. 
If, that doesn't work, we have to quit.

@p function get_avail : pointer; {single-word node allocation}
var p:pointer; {the new node being got}
t:integer;
begin p:=avail; {get top location in the |avail| stack}
if p<>null then avail:=link(avail) {and pop it off}
else if fix_mem_end<fix_mem_max then {or go into virgin territory}
  begin incr(fix_mem_end); p:=fix_mem_end;
  end
else  begin
  t:=(fix_mem_max/5);
  fixmem := fixmemcast(realloc(fixmem,sizeof(smemory_word)*(fix_mem_max+t+1)));
  if fixmem=NULL then
    begin runaway; {if memory is exhausted, display possible runaway text}
    overflow("token memory size",fix_mem_max);
      {quit; all one-word nodes are busy}
@:TeX capacity exceeded main memory size}{\quad main memory size@>
    end;
  memset (voidcast(fixmem+fix_mem_max+1),0,t*sizeof(smemory_word));
  fix_mem_max:=fix_mem_max+t; incr(fix_mem_end); p:=fix_mem_end;
  end;
link(p):=null; {provide an oft-desired initialization of the new node}
@!stat incr(dyn_used);@+tats@;{maintain statistics}
get_avail:=p;
end;

@ Conversely, a one-word node is recycled by calling |free_avail|.
This routine is part of \TeX's ``inner loop,'' so we want it to be fast.
@^inner loop@>

@d free_avail(#)== {single-word node liberation}
  begin link(#):=avail; avail:=#;
  @!stat decr(dyn_used);@+tats@/
  end

@ There's also a |fast_get_avail| routine, which saves the procedure-call
overhead at the expense of extra programming. This routine is used in
the places that would otherwise account for the most calls of |get_avail|.
@^inner loop@>

@d fast_get_avail(#)==@t@>@;@/
  begin #:=avail; {avoid |get_avail| if possible, to save time}
  if #=null then #:=get_avail
  else  begin avail:=link(#); link(#):=null;
    @!stat incr(dyn_used);@+tats@/
    end;
  end

@ The procedure |flush_list(p)| frees an entire linked list of
one-word nodes that starts at position |p|.
@^inner loop@>

@p procedure flush_list(@!p:pointer); {makes list of single-word nodes available}
var @!q,@!r:pointer; {list traversers}
begin if p<>null then
  begin r:=p;
  repeat q:=r; r:=link(r); @!stat decr(dyn_used);@+tats@/
  until r=null; {now |q| is the last node on the list}
  link(q):=avail; avail:=p;
  end;
end;

@ The available-space list that keeps track of the variable-size portion
of |mem| is a nonempty, doubly-linked circular list of empty nodes,
pointed to by the roving pointer |rover|.

@d temp_node==46
@d temp_node_size==2
@d vmem(#) == varmem[#]
@d vlink(#) == vmem(#).hh.rh {the |link| field of a memory word}
@d vinfo(#) == vmem(#).hh.lh {the |info| field of a memory word}
@d alink(#) == vlink(#+1) {backlink in doubly-linked list of empty nodes}

@* \[10] Data structures for boxes and their friends.
From the computer's standpoint, \TeX's chief mission is to create
horizontal and vertical lists. We shall now investigate how the elements
of these lists are represented internally as nodes in the dynamic memory.

A horizontal or vertical list is linked together by |link| fields in
the first word of each node. Individual nodes represent boxes, glue,
penalties, or special things like discretionary hyphens; because of this
variety, some nodes are longer than others, and we must distinguish different
kinds of nodes. We do this by putting a `|type|' field in the first word,
together with the link and an optional `|subtype|'.

@d type(#)    == vmem(#).hh.b0  {identifies what kind of node this is}
@d subtype(#) == vmem(#).hh.b1 {secondary identification in some cases}

@ TH: This module section is superceded.

A |@!char_node|, which represents a single character, is the most important
kind of node because it accounts for the vast majority of all boxes.
Special precautions are therefore taken to ensure that a |char_node| does
not take up much memory space. Every such node is one word long, and in fact
it is identifiable by this property, since other kinds of nodes have at least
two words, and they appear in |mem| locations less than |hi_mem_min|.
This makes it possible to omit the |type| field in a |char_node|, leaving
us room for two bytes that identify a |font| and a |character| within
that font.

Note that the format of a |char_node| allows for up to 256 different
fonts and up to 256 characters per font; but most implementations will
probably limit the total number of fonts to fewer than 75 per job,
and most fonts will stick to characters whose codes are
less than 128 (since higher codes
are more difficult to access on most keyboards).

Extensions of \TeX\ intended for oriental languages will need even more
than $256\times256$ possible characters, when we consider different sizes
@^oriental characters@>@^Chinese characters@>@^Japanese characters@>
and styles of type.  It is suggested that Chinese and Japanese fonts be
handled by representing such characters in two consecutive |char_node|
entries: The first of these has |font=font_base|, and its |link| points
to the second;
the second identifies the font and the character dimensions.
The saving feature about oriental characters is that most of them have
the same box dimensions. The |character| field of the first |char_node|
is a ``\\{charext}'' that distinguishes between graphic symbols whose
dimensions are identical for typesetting purposes. (See the \MF\ manual.)
Such an extension of \TeX\ would not be difficult; further details are
left to the reader.

In order to make sure that the |character| code fits in a quarterword,
\TeX\ adds the quantity |min_quarterword| to the actual code.

Character nodes appear only in horizontal lists, never in vertical lists.

@ Attribute lists need two extra globals to increase processing efficiency.
|max_used_attr| limits the test loop that checks for set attributes, and
|attr_list_cache| contains a pointer to an already created attribute list.  It is
set to the special value |cache_disabled| when the current value can no longer be
trusted: after an assignment to an attribute register, and after a group has
ended.

@d cache_disabled==max_halfword
 
@<Glob...@>=
max_used_attr:integer; { maximum assigned attribute id }
attr_list_cache:pointer;

@ @<Set init...@>=
max_used_attr:=-1; attr_list_cache:=cache_disabled;

@ Attribute lists are maintained in C, but they need access to the current
attributes in eqtb. 

@p function get_attribute(i:halfword):halfword;
begin
  get_attribute := attribute(i);
end;


@ An |hlist_node| stands for a box that was made from a horizontal list.
Each |hlist_node| is seven words long, and contains the following fields
(in addition to the mandatory |type| and |link|, which we shall not
mention explicitly when discussing the other node types): The |height| and
|width| and |depth| are scaled integers denoting the dimensions of the
box.  There is also a |shift_amount| field, a scaled integer indicating
how much this box should be lowered (if it appears in a horizontal list),
or how much it should be moved to the right (if it appears in a vertical
list). There is a |list_ptr| field, which points to the beginning of the
list from which this box was fabricated; if |list_ptr| is |null|, the box
is empty. Finally, there are three fields that represent the setting of
the glue:  |glue_set(p)| is a word of type |glue_ratio| that represents
the proportionality constant for glue setting; |glue_sign(p)| is
|stretching| or |shrinking| or |normal| depending on whether or not the
glue should stretch or shrink or remain rigid; and |glue_order(p)|
specifies the order of infinity to which glue setting applies (|normal|,
|sfi|, |fil|, |fill|, or |filll|). The |subtype| field is not used.

@d hlist_node=0 {|type| of hlist nodes}
@d box_node_size=8 {number of words to allocate for a box node}
@d width_offset=2 {position of |width| field in a box node}
@d depth_offset=3 {position of |depth| field in a box node}
@d height_offset=4 {position of |height| field in a box node}
@d width(#) == vmem(#+width_offset).sc {width of the box, in sp}
@d depth(#) == vmem(#+depth_offset).sc {depth of the box, in sp}
@d height(#) == vmem(#+height_offset).sc {height of the box, in sp}
@d shift_amount(#) == vlink(#+5) {repositioning distance, in sp}
@d box_dir(#) == vinfo(#+5) {position of |box_dir| in a box node}
@d list_offset=6 {position of |list_ptr| field in a box node}
@d list_ptr(#) == vlink(#+list_offset) {beginning of the list inside the box}
@d glue_order(#) == subtype(#+list_offset) {applicable order of infinity}
@d glue_sign(#) == type(#+list_offset) {stretching or shrinking}
@d normal=0 {the most common case when several cases are named}
@d stretching = 1 {glue setting applies to the stretch components}
@d shrinking = 2 {glue setting applies to the shrink components}
@d glue_offset = 7 {position of |glue_set| in a box node}
@d glue_set(#) == vmem(#+glue_offset).gr
  {a word of type |glue_ratio| for glue setting}

@ The |new_null_box| function returns a pointer to an |hlist_node| in
which all subfields have the values corresponding to `\.{\\hbox\{\}}'.
The |subtype| field is set to |min_quarterword|, since that's the desired
|span_count| value if this |hlist_node| is changed to an |unset_node|.

@p function new_null_box:pointer; {creates a new box node}
var p:pointer; {the new node}
begin p:=new_node(hlist_node,min_quarterword);
box_dir(p):=text_direction; 
new_null_box:=p;
end;

@ A |vlist_node| is like an |hlist_node| in all respects except that it
contains a vertical list.

@d vlist_node=1 {|type| of vlist nodes}

@ A |rule_node| stands for a solid black rectangle; it has |width|,
|depth|, and |height| fields just as in an |hlist_node|. However, if
any of these dimensions is $-2^{30}$, the actual value will be determined
by running the rule up to the boundary of the innermost enclosing box.
This is called a ``running dimension.'' The |width| is never running in
an hlist; the |height| and |depth| are never running in a~vlist.

@d rule_node=2 {|type| of rule nodes}
@d rule_node_size=6 {number of words to allocate for a rule node}
@d null_flag==-@'10000000000 {$-2^{30}$, signifies a missing item}
@d is_running(#) == (#=null_flag) {tests for a running dimension}
@d rule_dir(#)==vlink(#+5)

@ A new rule node is delivered by the |new_rule| function. It
makes all the dimensions ``running,'' so you have to change the
ones that are not allowed to run.

@p 
function new_rule:pointer;
var p:pointer; {the new node}
begin p:=new_node(rule_node,0); {the |subtype| is not used}
new_rule:=p;
end;


@ Insertions are represented by |ins_node| records, where the |subtype|
indicates the corresponding box number. For example, `\.{\\insert 250}'
leads to an |ins_node| whose |subtype| is |250+min_quarterword|.
The |height| field of an |ins_node| is slightly misnamed; it actually holds
the natural height plus depth of the vertical list being inserted.
The |depth| field holds the |split_max_depth| to be used in case this
insertion is split, and the |split_top_ptr| points to the corresponding
|split_top_skip|. The |float_cost| field holds the |floating_penalty| that
will be used if this insertion floats to a subsequent page after a
split insertion of the same class.  There is one more field, the
|ins_ptr|, which points to the beginning of the vlist for the insertion.

@d ins_node=3 {|type| of insertion nodes}
@d ins_node_size=6 {number of words to allocate for an insertion}
@d float_cost(#)==vmem(#+2).int {the |floating_penalty| to be used}
@d ins_ptr(#)==vinfo(#+5) {the vertical list to be inserted}
@d split_top_ptr(#)==vlink(#+5) {the |split_top_skip| to be used}

@ A |mark_node| has a |mark_ptr| field that points to the reference count
of a token list that contains the user's \.{\\mark} text.
In addition there is a |mark_class| field that contains the mark class.

@d mark_node=4 {|type| of a mark node}
@d mark_node_size=3 {number of words to allocate for a mark node}
@d mark_ptr(#)==vlink(#+2) {head of the token list for a mark}
@d mark_class(#)==vinfo(#+2) {the mark class}

@ An |adjust_node|, which occurs only in horizontal lists,
specifies material that will be moved out into the surrounding
vertical list; i.e., it is used to implement \TeX's `\.{\\vadjust}'
operation.  The |adjust_ptr| field points to the vlist containing this
material.

@d adjust_node=5 {|type| of an adjust node}
@d adjust_node_size=3
@d adjust_pre == subtype  {pre-adjustment?}
@d adjust_ptr(#)==vlink(#+2) {vertical list to be moved out of horizontal list}
@#{|append_list| is used to append a list to |tail|}
@d append_list(#) == begin vlink(tail) := vlink(#); append_list_end
@d append_list_end(#) == tail := #; end

@ A |glyph_node|, which occurs only in horizontal lists, specifies a
glyph in a particular font, along with its attribute list. Older
versions of \TeX\ could use token memory for characters, because the
font,char combination would fit in a single word (both values were
required to be strictly less than $2^{16}$). In \LuaTeX, room is
needed for characters that are larger than that, as well as a pointer
to a potential attribute list, and the two displacement values.  

In turn, that made the node so large that it made sense to merge
ligature glyphs as well, as that requires only one extra pointer.  A
few extra classes of glyph nodes will be introduced later.  The
unification of all those types makes it easier to manipulate lists of
glyphs. The subtype differentiates various glyph kinds.

First, here is a function that returns a pointer to a glyph node for a given
glyph in a given font. If that glyph doesn't exist, |null| is returned
instead.  Nodes of this subtype are directly created only for accents
and their base (through |make_accent|), and math nucleus items (in the
conversion from |mlist| to |hlist|).


@d glyph_node_size=5
@d glyph_node=33 {|type| of a glyph node}
@d is_char_node(#) == ((#<>null)and(type(#)=glyph_node))
@d font(#)==vlink(#+2) {the font code in a |glyph_node|}
@d character(#)==vinfo(#+2) {the character code in a |glyph_node|}
@d lig_ptr(#)==vlink(#+3) {the list of characters for ligature replacements }
@d lang_data(#)==vinfo(#+3) {language information }
@d x_displace(#)==vinfo(#+4) { horizontal displacement }
@d y_displace(#)==vlink(#+4) { vertical displacement  }

@p function new_glyph(@!f,@!c:integer):pointer;
var p:pointer; {the new node}
begin p:=null;
if (f=0) or (char_exists(f,c)) then begin
  p:=new_glyph_node;
  set_to_glyph(p); font(p):=f;  character(p):=c; 
  end;
new_glyph:=p;
end;


@ A subset of the glyphs nodes represent ligatures: characters
fabricated from the interaction of two or more actual characters.  The
characters that generated the ligature have not been forgotten, since
they are needed for diagnostic messages; the |lig_ptr| field points to
a linked list of character nodes for all original characters that have
been deleted. (This list might be empty if the characters that
generated the ligature were retained in other nodes.)

The |subtype| field of these |glyph_node|s is 1, plus 2 and/or 1 if
the original source of the ligature included implicit left and/or
right boundaries. These nodes are created by the C function |new_ligkern|.

@ A third general type of glyphs could be called a character, as it
only appears in lists that are not yet processed by the ligaturing and
kerning steps of the program.

|main_control| inserts these, and they are later converted to
|subtype_normal| by |new_ligkern|.

@p function norm_min(@!h:integer):quarterword;
begin if h<=0 then norm_min:=1@+else if h>=255 then norm_min:=255@+
else norm_min:=h;
end;
@#
function new_char(@!f,@!c:integer):pointer;
var p:pointer; {the new node}
begin p:=new_glyph_node;
set_to_character(p); font(p):=f;  character(p):=c;
lang_data(p):=make_lang_data(uc_hyph,cur_lang,left_hyphen_min,right_hyphen_min);
new_char:=p;
end;

@ Left and right ghost glyph nodes are the result of \.{\\leftghost}
and \.{\\rightghost}, respectively. They are going to be removed by
|new_ligkern|, at the end of which they are no longer needed.

@ Here are a few handy helpers used by the list output routines.

@p
function glyph_width(@!p:halfword):pointer;
var w:integer;
begin
  w := char_width(font(p),character(p)); { |+ x_displace(p);| }
  glyph_width := w;
end;
@#
function glyph_height(@!p:halfword):pointer;
var w:integer;
begin
  w := char_height(font(p),character(p)) + y_displace(p);
  if w<0 then w:=0;
  glyph_height := w;
end;
@#
function glyph_depth(@!p:halfword):pointer;
var w:integer;
begin
  w := char_depth(font(p),character(p));
  if y_displace(p)>0 then w := w - y_displace(p);
  if w<0 then w:=0;
  glyph_depth := w;
end;


@ A |disc_node|, which occurs only in horizontal lists, specifies a
``dis\-cretion\-ary'' line break. If such a break occurs at node |p|, the text
that starts at |pre_break(p)| will precede the break, the text that starts at
|post_break(p)| will follow the break, and text that appears in 
|no_break(p)| nodes will be ignored. For example, an ordinary
discretionary hyphen, indicated by `\.{\\-}', yields a |disc_node| with
|pre_break| pointing to a |char_node| containing a hyphen, |post_break=null|,
and |no_break=null|. 

{TODO: Knuth said: All three of the discretionary texts must be lists
that consist entirely of character, kern, box and rule nodes.}

If |subtype(p)=automatic_disc|, the |ex_hyphen_penalty| will be charged for this
break.  Otherwise the |hyphen_penalty| will be charged.  The texts will
actually be substituted into the list by the line-breaking algorithm if it
decides to make the break, and the discretionary node will disappear at
that time; thus, the output routine sees only discretionaries that were
not chosen.

@d disc_node=7 {|type| of a discretionary node}
@d disc_node_size=10
@d automatic_disc=2
@d syllable_disc=3
@d disc_type==subtype {the kind of discretionary}
@d pre_break(#)==vinfo(#+2) {text that precedes a discretionary break}
@d post_break(#)==vlink(#+2) {text that follows a discretionary break}
@d no_break(#)==vlink(#+3) {text this discretionary break replaces}
@d pre_break_head(#)==(#+4)
@d post_break_head(#)==(#+6)
@d no_break_head(#)==(#+8)
@d tlink(#)==vinfo(#+1)

@p function new_disc:pointer; {creates an empty |disc_node|}
var p:pointer; {the new node}
begin p:=new_node(disc_node,0);
new_disc:=p;
end;

@ A |whatsit_node| is a wild card reserved for extensions to \TeX. The
|subtype| field in its first word says what `\\{whatsit}' it is, and
implicitly determines the node size (which must be 2 or more) and the
format of the remaining words. When a |whatsit_node| is encountered
in a list, special actions are invoked; knowledgeable people who are
careful not to mess up the rest of \TeX\ are able to make \TeX\ do new
things by adding code at the end of the program. For example, there
might be a `\TeX nicolor' extension to specify different colors of ink,
@^extensions to \TeX@>
and the whatsit node might contain the desired parameters.

The present implementation of \TeX\ treats the features associated with
`\.{\\write}' and `\.{\\special}' as if they were extensions, in order to
illustrate how such routines might be coded. We shall defer further
discussion of extensions until the end of this program.

@d whatsit_node=8 {|type| of special extension nodes}

@ A |math_node|, which occurs only in horizontal lists, appears before and
after mathematical formulas. The |subtype| field is |before| before the
formula and |after| after it. There is a |surround| field, which represents
the amount of surrounding space inserted by \.{\\mathsurround}.

@d math_node=9 {|type| of a math node}
@d math_node_size=3
@d surround(#)==vlink(#+2)
@d before=0 {|subtype| for math node that introduces a formula}
@d after=1 {|subtype| for math node that winds up a formula}

@p function new_math(@!w:scaled;@!s:small_number):pointer;
var p:pointer; {the new node}
begin p:=new_node(math_node,s);
surround(p):=w; new_math:=p;
end;

@ \TeX\ makes use of the fact that |hlist_node|, |vlist_node|,
|rule_node|, |ins_node|, |mark_node|, |adjust_node|, 
|disc_node|, |whatsit_node|, and |math_node| are at the low end of the
type codes, by permitting a break at glue in a list if and only if the
|type| of the previous node is less than |math_node|. Furthermore, a
node is discarded after a break if its type is |math_node| or~more.

@d precedes_break(#)==(type(#)<math_node)
@d non_discardable(#)==(type(#)<math_node)

@ A |glue_node| represents glue in a list. However, it is really only
a pointer to a separate glue specification, since \TeX\ makes use of the
fact that many essentially identical nodes of glue are usually present.
If |p| points to a |glue_node|, |glue_ptr(p)| points to
another packet of words that specify the stretch and shrink components, etc.

Glue nodes also serve to represent leaders; the |subtype| is used to
distinguish between ordinary glue (which is called |normal|) and the three
kinds of leaders (which are called |a_leaders|, |c_leaders|, and |x_leaders|).
The |leader_ptr| field points to a rule node or to a box node containing the
leaders; it is set to |null| in ordinary glue nodes.

Many kinds of glue are computed from \TeX's ``skip'' parameters, and
it is helpful to know which parameter has led to a particular glue node.
Therefore the |subtype| is set to indicate the source of glue, whenever
it originated as a parameter. We will be defining symbolic names for the
parameter numbers later (e.g., |line_skip_code=0|, |baseline_skip_code=1|,
etc.); it suffices for now to say that the |subtype| of parametric glue
will be the same as the parameter number, plus~one.

In math formulas there are two more possibilities for the |subtype| in a
glue node: |mu_glue| denotes an \.{\\mskip} (where the units are scaled \.{mu}
instead of scaled \.{pt}); and |cond_math_glue| denotes the `\.{\\nonscript}'
feature that cancels the glue node immediately following if it appears
in a subscript.

@d glue_node=10 {|type| of node that points to a glue specification}
@d glue_node_size=3
@d cond_math_glue=98 {special |subtype| to suppress glue in the next node}
@d mu_glue=99 {|subtype| for math glue}
@d a_leaders=100 {|subtype| for aligned leaders}
@d c_leaders=101 {|subtype| for centered leaders}
@d x_leaders=102 {|subtype| for expanded leaders}
@d glue_ptr(#)==vinfo(#+2) {pointer to a glue specification}
@d leader_ptr(#)==vlink(#+2) {pointer to box or rule node for leaders}

@ A glue specification has a halfword reference count in its first word,
@^reference counts@>
representing |null| plus the number of glue nodes that point to it (less one).
Note that the reference count appears in the same position as
the |link| field in list nodes; this is the field that is initialized
to |null| when a node is allocated, and it is also the field that is flagged
by |empty_flag| in empty nodes.

Glue specifications also contain three |scaled| fields, for the |width|,
|stretch|, and |shrink| dimensions. Finally, there are two one-byte
fields called |stretch_order| and |shrink_order|; these contain the
orders of infinity (|normal|, |sfi|, |fil|, |fill|, or |filll|)
corresponding to the stretch and shrink values.

@d glue_spec_size=4 {number of words to allocate for a glue specification}
@d glue_spec_node=43
@d glue_ref_count(#) == vlink(#+3) {reference count of a glue specification}
@d stretch(#) == vlink(#+1) {the stretchability of this glob of glue}
@d shrink(#) == vinfo(#+1) {the shrinkability of this glob of glue}
@d stretch_order(#) == type(#+3) {order of infinity for stretching}
@d shrink_order(#) == subtype(#+3) {order of infinity for shrinking}
@d sfi=1 {first-order infinity}
@d fil=2 {second-order infinity}
@d fill=3 {third-order infinity}
@d filll=4 {fourth-order infinity}

@<Types...@>=
@!glue_ord=normal..filll; {infinity to the 0, 1, 2, 3, or 4 power}

@ Here is a function that returns a pointer to a copy of a glue spec.
The reference count in the copy is |null|, because there is assumed
to be exactly one reference to the new specification.

@p function new_spec(@!p:pointer):pointer; {duplicates a glue specification}
var q:pointer; {the new spec}
begin q:=copy_node(p); 
glue_ref_count(q):=null;
new_spec:=q;
end;

@ And here's a function that creates a glue node for a given parameter
identified by its code number; for example,
|new_param_glue(line_skip_code)| returns a pointer to a glue node for the
current \.{\\lineskip}.

@p function new_param_glue(@!n:small_number):pointer;
var p:pointer; {the new node}
@!q:pointer; {the glue specification}
begin p:=new_node(glue_node,n+1);
q:=@<Current |mem| equivalent of glue parameter number |n|@>@t@>;
glue_ptr(p):=q; incr(glue_ref_count(q));
new_param_glue:=p;
end;

@ Glue nodes that are more or less anonymous are created by |new_glue|,
whose argument points to a glue specification.

@p function new_glue(@!q:pointer):pointer;
var p:pointer; {the new node}
begin p:=new_node(glue_node,normal);
glue_ptr(p):=q; incr(glue_ref_count(q));
new_glue:=p;
end;

@ Still another subroutine is needed: this one is sort of a combination
of |new_param_glue| and |new_glue|. It creates a glue node for one of
the current glue parameters, but it makes a fresh copy of the glue
specification, since that specification will probably be subject to change,
while the parameter will stay put. The global variable |temp_ptr| is
set to the address of the new spec.

@p function new_skip_param(@!n:small_number):pointer;
var p:pointer; {the new node}
begin temp_ptr:=new_spec(@<Current |mem| equivalent of glue parameter...@>);
p:=new_glue(temp_ptr); glue_ref_count(temp_ptr):=null; subtype(p):=n+1;
new_skip_param:=p;
end;

@ A |kern_node| has a |width| field to specify a (normally negative)
amount of spacing. This spacing correction appears in horizontal lists
between letters like A and V when the font designer said that it looks
better to move them closer together or further apart. A kern node can
also appear in a vertical list, when its `|width|' denotes additional
spacing in the vertical direction. The |subtype| is either |normal| (for
kerns inserted from font information or math mode calculations) or |explicit|
(for kerns inserted from \.{\\kern} and \.{\\/} commands) or |acc_kern|
(for kerns inserted from non-math accents) or |mu_glue| (for kerns
inserted from \.{\\mkern} specifications in math formulas).

@d kern_node=11 {|type| of a kern node}
@d kern_node_size=3
@d explicit=1 {|subtype| of kern nodes from \.{\\kern} and \.{\\/}}
@d acc_kern=2 {|subtype| of kern nodes from accents}

@# {memory structure for marginal kerns}
@d margin_kern_node = 32
@d margin_kern_node_size = 4
@d margin_char(#) == vlink(#+3)

@# {|subtype| of marginal kerns}
@d left_side == 0
@d right_side == 1

@# {base for lp/rp/ef codes starts from 2:
    0 for |hyphen_char|,
    1 for |skew_char|}
@d lp_code_base == 2
@d rp_code_base == 3
@d ef_code_base == 4
@d tag_code == 5

@d auto_kern == explicit
@d no_lig_code == 6

@ The |new_kern| function creates a kern node having a given width.

@p function new_kern(@!w:scaled):pointer;
var p:pointer; {the new node}
begin p:=new_node(kern_node,normal);
width(p):=w;
new_kern:=p;
end;

@ A |penalty_node| specifies the penalty associated with line or page
breaking, in its |penalty| field. This field is a fullword integer, but
the full range of integer values is not used: Any penalty |>=10000| is
treated as infinity, and no break will be allowed for such high values.
Similarly, any penalty |<=-10000| is treated as negative infinity, and a
break will be forced.

@d penalty_node=12 {|type| of a penalty node}
@d penalty_node_size=3 {has to be the same as |glue_node_size|}
@d inf_penalty=inf_bad {``infinite'' penalty value}
@d eject_penalty=-inf_penalty {``negatively infinite'' penalty value}
@d penalty(#) == vlink(#+2) {the added cost of breaking a list here}

@ Anyone who has been reading the last few sections of the program will
be able to guess what comes next.

@p function new_penalty(@!m:integer):pointer;
var p:pointer; {the new node}
begin p:=new_node(penalty_node,0); {the |subtype| is not used}
penalty(p):=m; new_penalty:=p;
end;

@ You might think that we have introduced enough node types by now. Well,
almost, but there is one more: An |unset_node| has nearly the same format
as an |hlist_node| or |vlist_node|; it is used for entries in \.{\\halign}
or \.{\\valign} that are not yet in their final form, since the box
dimensions are their ``natural'' sizes before any glue adjustment has been
made. The |glue_set| word is not present; instead, we have a |glue_stretch|
field, which contains the total stretch of order |glue_order| that is
present in the hlist or vlist being boxed.
Similarly, the |shift_amount| field is replaced by a |glue_shrink| field,
containing the total shrink of order |glue_sign| that is present.
The |subtype| field is called |span_count|; an unset box typically
contains the data for |qo(span_count)+1| columns.
Unset nodes will be changed to box nodes when alignment is completed.

@d unset_node=13 {|type| for an unset node}
@d glue_stretch(#)==vmem(#+glue_offset).sc {total stretch in an unset node}
@d glue_shrink==shift_amount {total shrink in an unset node}
@d span_count==subtype {indicates the number of spanned columns}

@ In fact, there are still more types coming. When we get to math formula
processing we will see that a |style_node| has |type=14|; and a number
of larger type codes will also be defined, for use in math mode only.

@ Warning: If any changes are made to these data structure layouts, such as
changing any of the node sizes or even reordering the words of nodes,
the |copy_node_list| procedure and the memory initialization code
below may have to be changed. Such potentially dangerous parts of the
program are listed in the index under `data structure assumptions'.
@!@^data structure assumptions@>
However, other references to the nodes are made symbolically in terms of
the \.{WEB} macro definitions above, so that format changes will leave
\TeX's other algorithms intact.
@^system dependencies@>

@* \[11] Memory layout.
Some areas of |mem| are dedicated to fixed usage, since static allocation is
more efficient than dynamic allocation when we can get away with it. For
example, |zero_glue| used for glue that is `\.{0pt plus 0pt minus 0pt}'. The
following macro definitions accomplish the static allocation by giving
symbolic names to the fixed positions. 

@d zero_glue==0 {specification for \.{0pt plus 0pt minus 0pt}}
@d sfi_glue==zero_glue+glue_spec_size {\.{0pt plus 1fi minus 0pt}}
@d fil_glue==sfi_glue+glue_spec_size {\.{0pt plus 1fil minus 0pt}}
@d fill_glue==fil_glue+glue_spec_size {\.{0pt plus 1fill minus 0pt}}
@d ss_glue==fill_glue+glue_spec_size {\.{0pt plus 1fil minus 1fil}}
@d fil_neg_glue==ss_glue+glue_spec_size {\.{0pt plus -1fil minus 0pt}}
@d page_ins_head==fil_neg_glue+glue_spec_size {list of insertion data for current page}
@d contrib_head==page_ins_head+temp_node_size {list of items not yet on current page}
@d page_head==contrib_head+temp_node_size {list for current page}
@d temp_head==page_head+temp_node_size {head of a temporary list of some kind}
@d hold_head==temp_head+temp_node_size {head of a temporary list of another kind}
@d adjust_head==hold_head+temp_node_size {head of adjustment list returned by |hpack|}
@d pre_adjust_head==adjust_head+temp_node_size {head of pre-adjustment list returned by |hpack|}
@d active==pre_adjust_head+temp_node_size {head of active list in |line_break|}
@d align_head==active+active_node_size {head of preamble list for alignments}
@d end_span==align_head+temp_node_size {tail of spanned-width lists}
@d begin_point==end_span+span_node_size {left-side dot for words in hyphenation}
@d end_point==begin_point+glyph_node_size {right-side dot for words in hyphenation}
@d var_mem_stat_max==(end_point+glyph_node_size-1) {largest statically allocated word in the variable-size |mem|}

@<Glob...@>=
garbage:pointer;         {head of a junk list, write only}
temp_token_head:pointer; {head of a temporary list of some kind}
hold_token_head:pointer; {head of a temporary list of another kind}
omit_template:pointer;   {a constant token list}
null_list:pointer;       {permanently empty list}
backup_head:pointer;     {head of token list built by |scan_keyword|}

@ The following code gets |mem| off to a good start, when \TeX\ is
initializing itself the slow~way.

@<Local variables for init...@>=
@!k:integer; {index into |mem|, |eqtb|, etc.}

@ @<Initialize table entries...@>=
procedure init_link_heads;forward;
init_node_mem(var_mem_stat_max,500); 
glue_ref_count(zero_glue):=null+1; width(zero_glue):=0; 
type(zero_glue):=glue_spec_node; vlink(zero_glue):=null;
stretch(zero_glue):=0; stretch_order(zero_glue):=normal;@/
shrink(zero_glue):=0; shrink_order(zero_glue):=normal;@/
glue_ref_count(sfi_glue):=null+1; width(sfi_glue):=0; 
type(sfi_glue):=glue_spec_node;  vlink(sfi_glue):=null;
stretch(sfi_glue):=0; stretch_order(sfi_glue):=sfi;@/
shrink(sfi_glue):=0; shrink_order(sfi_glue):=normal;@/
glue_ref_count(fil_glue):=null+1; width(fil_glue):=0; 
type(fil_glue):=glue_spec_node;  vlink(fil_glue):=null;
stretch(fil_glue):=unity; stretch_order(fil_glue):=fil;@/
shrink(fil_glue):=0; shrink_order(fil_glue):=normal;@/
glue_ref_count(fill_glue):=null+1; width(fill_glue):=0; 
type(fill_glue):=glue_spec_node;  vlink(fill_glue):=null;
stretch(fill_glue):=unity; stretch_order(fill_glue):=fill;@/
shrink(fill_glue):=0; shrink_order(fill_glue):=normal;@/
glue_ref_count(ss_glue):=null+1; width(ss_glue):=0; 
type(ss_glue):=glue_spec_node;  vlink(ss_glue):=null;
stretch(ss_glue):=unity; stretch_order(ss_glue):=fil;@/
shrink(ss_glue):=unity; shrink_order(ss_glue):=fil;@/
glue_ref_count(fil_neg_glue):=null+1; width(fil_neg_glue):=0; 
type(fil_neg_glue):=glue_spec_node;  vlink(fil_neg_glue):=null;
stretch(fil_neg_glue):=-unity; stretch_order(fil_neg_glue):=fil;@/
shrink(fil_neg_glue):=0; shrink_order(fil_neg_glue):=normal;@/
{initialize node list heads}
vinfo(page_ins_head):=0; vlink(page_ins_head):=null; alink(page_ins_head):=null;
vinfo(contrib_head):=0; vlink(contrib_head):=null; alink(contrib_head):=null;
vinfo(page_head):=0; vlink(page_head):=null; alink(page_head):=null;
vinfo(temp_head):=0; vlink(temp_head):=null; alink(temp_head):=null;
vinfo(hold_head):=0; vlink(hold_head):=null; alink(hold_head):=null;
vinfo(adjust_head):=0; vlink(adjust_head):=null; alink(adjust_head):=null;
vinfo(pre_adjust_head):=0; vlink(pre_adjust_head):=null; alink(pre_adjust_head):=null;
vinfo(active):=0; vlink(active):=null; alink(active):=null;
vinfo(align_head):=0; vlink(align_head):=null; alink(align_head):=null;
vinfo(end_span):=0; vlink(end_span):=null; alink(end_span):=null;
type(begin_point):=glyph_node; subtype(begin_point):=0; vlink(begin_point):=null; 
vinfo(begin_point+1):=null; alink(begin_point):=null; 
font(begin_point):=0; character(begin_point):='.';
vinfo(begin_point+3):=0; vlink(begin_point+3):=0; 
vinfo(begin_point+4):=0; vlink(begin_point+4):=0; 
type(end_point):=glyph_node; subtype(end_point):=0; vlink(end_point):=null; 
vinfo(end_point+1):=null; alink(end_point):=null; 
font(end_point):=0; character(end_point):='.';
vinfo(end_point+3):=0; vlink(end_point+3):=0; 
vinfo(end_point+4):=0; vlink(end_point+4):=0; 
avail:=null; fix_mem_end:=0;
init_list_heads;
@<Initialize the special list heads and constant nodes@>;
initialize_active;
dyn_used:=0; {initialize statistics}

@ @p procedure init_list_heads; {initialize token list heads}
var p:halfword;
begin
p:=get_avail; temp_token_head:=p; info(temp_token_head):=0;
p:=get_avail; hold_token_head:=p; info(hold_token_head):=0;
p:=get_avail; omit_template:=p;   info(omit_template):=0; 
p:=get_avail; null_list:=p;       info(null_list):=0; 
p:=get_avail; backup_head:=p;     info(backup_head):=0;
p:=get_avail; garbage:=p;         info(garbage):=0;
end;

@ @p
@<Declare procedures that need to be declared forward for \pdfTeX@>

@* \[12] Displaying boxes.
We can reinforce our knowledge of the data structures just introduced
by considering two procedures that display a list in symbolic form.
The first of these, called |short_display|, is used in ``overfull box''
messages to give the top-level description of a list. The other one,
called |show_node_list|, prints a detailed description of exactly what
is in the data structure.

The philosophy of |short_display| is to ignore the fine points about exactly
what is inside boxes, except that ligatures and discretionary breaks are
expanded. As a result, |short_display| is a recursive procedure, but the
recursion is never more than one level deep.
@^recursion@>

A global variable |font_in_short_display| keeps track of the font code that
is assumed to be present when |short_display| begins; deviations from this
font will be printed.

@<Glob...@>=
@!font_in_short_display:integer; {an internal font number}

@ Boxes, rules, inserts, whatsits, marks, and things in general that are
sort of ``complicated'' are indicated only by printing `\.{[]}'.

@p
procedure print_font_identifier(f: internal_font_number);
begin
    if pdf_font_blink(f) = null_font then
        print_esc(font_id_text(f))
    else
        print_esc(font_id_text(pdf_font_blink(f)));
    if pdf_tracing_fonts > 0 then begin
        print(" (");
        print_font_name(f);
        if font_size(f) <> font_dsize(f) then begin
            print("@@");
            print_scaled(font_size(f));
            print("pt");
        end;
        print(")");
    end else
        if pdf_font_expand_ratio(f) <> 0 then begin
            print(" (");
            if pdf_font_expand_ratio(f) > 0 then
                print("+");
            print_int(pdf_font_expand_ratio(f));
            print(")");
        end;
end;

procedure short_display(@!p:integer); {prints highlights of list |p|}
begin while p<>null do
  begin if is_char_node(p) then
      begin if lig_ptr(p)<>null then 
           short_display(lig_ptr(p))
        else begin
          if font(p)<>font_in_short_display then
          begin if not is_valid_font(font(p)) then
            print_char("*")
@.*\relax@>
          else print_font_identifier(font(p));
          print_char(" "); font_in_short_display:=font(p);
          end;
        print(qo(character(p)));
      end;
    end
  else @<Print a short indication of the contents of node |p|@>;
  p:=vlink(p);
  end;
end;

@ @<Print a short indication of the contents of node |p|@>=
case type(p) of
hlist_node,vlist_node,ins_node,whatsit_node,mark_node,adjust_node,
  unset_node: print("[]");
rule_node: print_char("|");
glue_node: if glue_ptr(p)<>zero_glue then print_char(" ");
math_node: print_char("$");
disc_node: begin short_display(vlink(pre_break(p)));
  short_display(vlink(post_break(p)));@/
  end;
othercases do_nothing
endcases

@ The |show_node_list| routine requires some auxiliary subroutines: one to
print a font-and-character combination, one to print a token list without
its reference count, and one to print a rule dimension.

@p procedure print_font_and_char(@!p:integer); {prints |char_node| data}
begin if not is_valid_font(font(p)) then print_char("*")
@.*\relax@>
  else print_font_identifier(font(p));
  print_char(" "); print(character(p));
end;
@#
procedure print_mark(@!p:integer); {prints token list data in braces}
begin print_char("{");
if (p<fix_mem_min)or(p>fix_mem_end) then print_esc("CLOBBERED.")
else show_token_list(link(p),null,max_print_line-10);
print_char("}");
end;
@#
procedure print_rule_dimen(@!d:scaled); {prints dimension in rule node}
begin if is_running(d) then print_char("*") else print_scaled(d);
@.*\relax@>
end;
@#
procedure print_dir(d:integer);
begin
print(dir_names[dir_primary[d]]);
print(dir_names[dir_secondary[d]]);
print(dir_names[dir_tertiary[d]]);
end;


@ Then there is a subroutine that prints glue stretch and shrink, possibly
followed by the name of finite units:

@p procedure print_glue(@!d:scaled;@!order:integer;@!s:str_number);
  {prints a glue component}
begin print_scaled(d);
if (order<normal)or(order>filll) then print("foul")
else if order>normal then
  begin print("fi");
  while order>sfi do
    begin print_char("l"); decr(order);
    end;
  end
else if s<>0 then print(s);
end;

@ The next subroutine prints a whole glue specification.

@p procedure print_spec(@!p:integer;@!s:str_number);
  {prints a glue specification}
begin if p<0 then print_char("*")
@.*\relax@>
else  begin print_scaled(width(p));
  if s<>0 then print(s);
  if stretch(p)<>0 then
    begin print(" plus "); print_glue(stretch(p),stretch_order(p),s);
    end;
  if shrink(p)<>0 then
    begin print(" minus "); print_glue(shrink(p),shrink_order(p),s);
    end;
  end;
end;

@ We also need to declare some procedures that appear later in this
documentation.

@p @<Declare procedures needed for displaying the elements of mlists@>@;
@<Declare the procedure called |print_skip_param|@>

@ Since boxes can be inside of boxes, |show_node_list| is inherently recursive,
@^recursion@>
up to a given maximum number of levels.  The history of nesting is indicated
by the current string, which will be printed at the beginning of each line;
the length of this string, namely |cur_length|, is the depth of nesting.

Recursive calls on |show_node_list| therefore use the following pattern:

@d node_list_display(#)==
  begin append_char("."); show_node_list(#); flush_char;
  end {|str_room| need not be checked; see |show_box| below}

@ A global variable called |depth_threshold| is used to record the maximum
depth of nesting for which |show_node_list| will show information.  If we
have |depth_threshold=0|, for example, only the top level information will
be given and no sublists will be traversed. Another global variable, called
|breadth_max|, tells the maximum number of items to show at each level;
|breadth_max| had better be positive, or you won't see anything.

@<Glob...@>=
@!depth_threshold : integer; {maximum nesting depth in box displays}
@!breadth_max : integer; {maximum number of items shown at the same list level}

@ Now we are ready for |show_node_list| itself. This procedure has been
written to be ``extra robust'' in the sense that it should not crash or get
into a loop even if the data structures have been messed up by bugs in
the rest of the program. You can safely call its parent routine
|show_box(p)| for arbitrary values of |p| when you are debugging \TeX.
However, in the presence of bad data, the procedure may
@^dirty \PASCAL@>@^debugging@>
fetch a |memory_word| whose variant is different from the way it was stored;
for example, it might try to read |mem[p].hh| when |mem[p]|
contains a scaled integer, if |p| is a pointer that has been
clobbered or chosen at random.

@p procedure show_node_list(@!p:integer); {prints a node list symbolically}
label exit;
var n:integer; {the number of items already printed at this level}
@!g:real; {a glue ratio, as a floating point number}
begin if cur_length>depth_threshold then
  begin if p>null then print(" []");
    {indicate that there's been some truncation}
  return;
  end;
n:=0;
while p<>null do
  begin print_ln; print_current_string; {display the nesting history}
  if tracing_online<-2 then print_int(p); 
    incr(n); if n>breadth_max then {time to stop}
    begin print("etc."); return;
@.etc@>
    end;
  @<Display node |p|@>;
  p:=vlink(p);
  end;
exit:
end;

@ @<Display node |p|@>=
if is_char_node(p) then begin 
 print_font_and_char(p);
 if is_ligature(p) then @<Display ligature |p|@>;
 end
else case type(p) of
  hlist_node,vlist_node,unset_node: @<Display box |p|@>;
  rule_node: @<Display rule |p|@>;
  ins_node: @<Display insertion |p|@>;
  whatsit_node: @<Display the whatsit node |p|@>;
  glue_node: @<Display glue |p|@>;
  margin_kern_node: begin
    print_esc("kern");
    print_scaled(width(p));
    if subtype(p) = left_side then
        print(" (left margin)")
    else
        print(" (right margin)");
    end;
  kern_node: @<Display kern |p|@>;
  math_node: @<Display math node |p|@>;
  penalty_node: @<Display penalty |p|@>;
  disc_node: @<Display discretionary |p|@>;
  mark_node: @<Display mark |p|@>;
  adjust_node: @<Display adjustment |p|@>;
  @t\4@>@<Cases of |show_node_list| that arise in mlists only@>@;
  othercases print("Unknown node type!")
  endcases

@ @<Display box |p|@>=
begin if type(p)=hlist_node then print_esc("h")
else if type(p)=vlist_node then print_esc("v")
else print_esc("unset");
print("box("); print_scaled(height(p)); print_char("+");
print_scaled(depth(p)); print(")x"); print_scaled(width(p));
if type(p)=unset_node then
  @<Display special fields of the unset node |p|@>
else  begin @<Display the value of |glue_set(p)|@>;
  if shift_amount(p)<>0 then
    begin print(", shifted "); print_scaled(shift_amount(p));
    end;
  print(", direction "); print_dir(box_dir(p));
  end;
{|pdfassert(list_ptr(p)<>0);|}
node_list_display(list_ptr(p)); {recursive call}
end

@ @<Display special fields of the unset node |p|@>=
begin if span_count(p)<>min_quarterword then
  begin print(" ("); print_int(qo(span_count(p))+1);
  print(" columns)");
  end;
if glue_stretch(p)<>0 then
  begin print(", stretch "); print_glue(glue_stretch(p),glue_order(p),0);
  end;
if glue_shrink(p)<>0 then
  begin print(", shrink "); print_glue(glue_shrink(p),glue_sign(p),0);
  end;
end

@ The code will have to change in this place if |glue_ratio| is
a structured type instead of an ordinary |real|. Note that this routine
should avoid arithmetic errors even if the |glue_set| field holds an
arbitrary random value. The following code assumes that a properly
formed nonzero |real| number has absolute value $2^{20}$ or more when
it is regarded as an integer; this precaution was adequate to prevent
floating point underflow on the author's computer.
@^system dependencies@>
@^dirty \PASCAL@>

@<Display the value of |glue_set(p)|@>=
g:=float(glue_set(p));
if (g<>float_constant(0))and(glue_sign(p)<>normal) then
  begin print(", glue set ");
  if glue_sign(p)=shrinking then print("- ");
  if abs(vmem(p+glue_offset).int)<@'4000000 then print("?.?")
  else if abs(g)>float_constant(20000) then
    begin if g>float_constant(0) then print_char(">")
    else print("< -");
    print_glue(20000*unity,glue_order(p),0);
    end
  else print_glue(round(unity*g),glue_order(p),0);
@^real multiplication@>
  end

@ @<Display rule |p|@>=
begin print_esc("rule("); print_rule_dimen(height(p)); print_char("+");
print_rule_dimen(depth(p)); print(")x"); print_rule_dimen(width(p));
end

@ @<Display insertion |p|@>=
begin print_esc("insert"); print_int(qo(subtype(p)));
print(", natural size "); print_scaled(height(p));
print("; split("); print_spec(split_top_ptr(p),0);
print_char(","); print_scaled(depth(p));
print("); float cost "); print_int(float_cost(p));
node_list_display(ins_ptr(p)); {recursive call}
end

@ @<Display glue |p|@>=
if subtype(p)>=a_leaders then @<Display leaders |p|@>
else  begin print_esc("glue");
  if subtype(p)<>normal then
    begin print_char("(");
    if subtype(p)<cond_math_glue then
      print_skip_param(subtype(p)-1)
    else if subtype(p)=cond_math_glue then print_esc("nonscript")
    else print_esc("mskip");
    print_char(")");
    end;
  if subtype(p)<>cond_math_glue then
    begin print_char(" ");
    if subtype(p)<cond_math_glue then print_spec(glue_ptr(p),0)
    else print_spec(glue_ptr(p),"mu");
    end;
  end

@ @<Display leaders |p|@>=
begin print_esc("");
if subtype(p)=c_leaders then print_char("c")
else if subtype(p)=x_leaders then print_char("x");
print("leaders "); print_spec(glue_ptr(p),0);
node_list_display(leader_ptr(p)); {recursive call}
end

@ An ``explicit'' kern value is indicated implicitly by an explicit space.

@<Display kern |p|@>=
if subtype(p)<>mu_glue then
  begin print_esc("kern");
  if subtype(p)<>normal then print_char(" ");
  print_scaled(width(p));
  if subtype(p)=acc_kern then print(" (for accent)");
@.for accent@>
  end
else  begin print_esc("mkern"); print_scaled(width(p)); print("mu");
  end

@ @<Display math node |p|@>=
begin print_esc("math");
if subtype(p)=before then print("on")
else print("off");
if width(p)<>0 then
  begin print(", surrounded "); print_scaled(width(p));
  end;
end

@ @<Display ligature |p|@>=
begin print(" (ligature ");
if is_leftboundary(p) then print_char("|");
font_in_short_display:=font(p); short_display(lig_ptr(p));
if is_rightboundary(p) then print_char("|");
print_char(")");
end

@ @<Display penalty |p|@>=
begin print_esc("penalty "); print_int(penalty(p));
end

@ The |post_break| list of a discretionary node is indicated by a prefixed
`\.{\char'174}' instead of the `\..' before the |pre_break| list.

@<Display discretionary |p|@>=
begin print_esc("discretionary");
if vlink(no_break(p))<>null then
  begin print(" replacing "); node_list_display(vlink(no_break(p)));
  end;
node_list_display(vlink(pre_break(p))); {recursive call}
append_char("|"); show_node_list(vlink(post_break(p))); flush_char; {recursive call}
end

@ @<Display mark |p|@>=
begin print_esc("mark");
if mark_class(p)<>0 then
  begin print_char("s"); print_int(mark_class(p));
  end;
print_mark(mark_ptr(p));
end

@ @<Display adjustment |p|@>=
begin print_esc("vadjust"); if adjust_pre(p) <> 0 then print(" pre ");
node_list_display(adjust_ptr(p)); {recursive call}
end

@ The recursive machinery is started by calling |show_box|.
@^recursion@>

@p procedure show_box(@!p:pointer);
begin @<Assign the values |depth_threshold:=show_box_depth| and
  |breadth_max:=show_box_breadth|@>;
if breadth_max<=0 then breadth_max:=5;
if pool_ptr+depth_threshold>=pool_size then
  depth_threshold:=pool_size-pool_ptr-1;
  {now there's enough room for prefix string}
show_node_list(p); {the show starts at |p|}
print_ln;
end;

@* \[13] Destroying boxes.
When we are done with a node list, we are obliged to return it to free
storage, including all of its sublists. The recursive procedure
|flush_node_list| does this for us.

@ First, however, we shall consider two non-recursive procedures that do
simpler tasks. The first of these, |delete_token_ref|, is called when
a pointer to a token list's reference count is being removed. This means
that the token list should disappear if the reference count was |null|,
otherwise the count should be decreased by one.
@^reference counts@>

@d token_ref_count(#) == info(#) {reference count preceding a token list}

@p procedure delete_token_ref(@!p:pointer); {|p| points to the reference count
  of a token list that is losing one reference}
begin pdfassert(token_ref_count(p)>=0);
if token_ref_count(p)=0 then flush_list(p)
else decr(token_ref_count(p));
end;

@ Similarly, |delete_glue_ref| is called when a pointer to a glue
specification is being withdrawn.
@^reference counts@>
@d fast_delete_glue_ref(#)==@t@>@;@/
  begin if glue_ref_count(#)=null then begin 
    flush_node(#);
    end
  else decr(glue_ref_count(#));
  end

@p procedure delete_glue_ref(@!p:pointer); {|p| points to a glue specification}
begin
  pdfassert(type(p)=glue_spec_node);
  fast_delete_glue_ref(p);
end;

@ Now we are ready to delete any node list, recursively.
In practice, the nodes deleted are usually charnodes (about 2/3 of the time),
and they are glue nodes in about half of the remaining cases.
@^recursion@>


@* \[14] Copying boxes.
Another recursive operation that acts on boxes is sometimes needed: The
procedure |copy_node_list| returns a pointer to another node list that has
the same structure and meaning as the original. Note that since glue
specifications and token lists have reference counts, we need not make
copies of them. Reference counts can never get too large to fit in a
halfword, since each pointer to a node is in a different memory address,
and the total number of memory addresses fits in a halfword.
@^recursion@>
@^reference counts@>

(Well, there actually are also references from outside |mem|; if the
|save_stack| is made arbitrarily large, it would theoretically be possible
to break \TeX\ by overflowing a reference count. But who would want to do that?)

@d add_token_ref(#)==incr(token_ref_count(#)) {new reference to a token list}
@d add_glue_ref(#)==incr(glue_ref_count(#)) {new reference to a glue spec}

@p function tail_of_list (@!p:pointer):pointer;
var q:pointer;
begin
  q:=p;
  while vlink(q)<>null do q:=vlink(q);
  tail_of_list:=q;
end;

@* \[15] The command codes.
Before we can go any further, we need to define symbolic names for the internal
code numbers that represent the various commands obeyed by \TeX. These codes
are somewhat arbitrary, but not completely so. For example, the command
codes for character types are fixed by the language, since a user says,
e.g., `\.{\\catcode \`\\\${} = 3}' to make \.{\char'44} a math delimiter,
and the command code |math_shift| is equal to~3. Some other codes have
been made adjacent so that |case| statements in the program need not consider
cases that are widely spaced, or so that |case| statements can be replaced
by |if| statements.

At any rate, here is the list, for future reference. First come the
``catcode'' commands, several of which share their numeric codes with
ordinary commands when the catcode cannot emerge from \TeX's scanning routine.

@d escape=0 {escape delimiter (called \.\\ in {\sl The \TeX book\/})}
@:TeXbook}{\sl The \TeX book@>
@d relax=0 {do nothing ( \.{\\relax} )}
@d left_brace=1 {beginning of a group ( \.\{ )}
@d right_brace=2 {ending of a group ( \.\} )}
@d math_shift=3 {mathematics shift character ( \.\$ )}
@d tab_mark=4 {alignment delimiter ( \.\&, \.{\\span} )}
@d car_ret=5 {end of line ( |carriage_return|, \.{\\cr}, \.{\\crcr} )}
@d out_param=5 {output a macro parameter}
@d mac_param=6 {macro parameter symbol ( \.\# )}
@d sup_mark=7 {superscript ( \.{\char'136} )}
@d sub_mark=8 {subscript ( \.{\char'137} )}
@d ignore=9 {characters to ignore ( \.{\^\^@@} )}
@d endv=9 {end of \<v_j> list in alignment template}
@d spacer=10 {characters equivalent to blank space ( \.{\ } )}
@d letter=11 {characters regarded as letters ( \.{A..Z}, \.{a..z} )}
@d other_char=12 {none of the special character types}
@d active_char=13 {characters that invoke macros ( \.{\char`\~} )}
@d par_end=13 {end of paragraph ( \.{\\par} )}
@d match=13 {match a macro parameter}
@d comment=14 {characters that introduce comments ( \.\% )}
@d end_match=14 {end of parameters to macro}
@d stop=14 {end of job ( \.{\\end}, \.{\\dump} )}
@d invalid_char=15 {characters that shouldn't appear ( \.{\^\^?} )}
@d delim_num=15 {specify delimiter numerically ( \.{\\delimiter} )}
@d max_char_code=15 {largest catcode for individual characters}

@ Next are the ordinary run-of-the-mill command codes.  Codes that are
|min_internal| or more represent internal quantities that might be
expanded by `\.{\\the}'.

@d char_num=16 {character specified numerically ( \.{\\char} )}
@d math_char_num=17 {explicit math code ( \.{\\mathchar} )}
@d mark=18 {mark definition ( \.{\\mark} )}
@d xray=19 {peek inside of \TeX\ ( \.{\\show}, \.{\\showbox}, etc.~)}
@d make_box=20 {make a box ( \.{\\box}, \.{\\copy}, \.{\\hbox}, etc.~)}
@d hmove=21 {horizontal motion ( \.{\\moveleft}, \.{\\moveright} )}
@d vmove=22 {vertical motion ( \.{\\raise}, \.{\\lower} )}
@d un_hbox=23 {unglue a box ( \.{\\unhbox}, \.{\\unhcopy} )}
@d un_vbox=24 {unglue a box ( \.{\\unvbox}, \.{\\unvcopy} )}
  {( or \.{\\pagediscards}, \.{\\splitdiscards} )}
@d remove_item=25 {nullify last item ( \.{\\unpenalty},
  \.{\\unkern}, \.{\\unskip} )}
@d hskip=26 {horizontal glue ( \.{\\hskip}, \.{\\hfil}, etc.~)}
@d vskip=27 {vertical glue ( \.{\\vskip}, \.{\\vfil}, etc.~)}
@d mskip=28 {math glue ( \.{\\mskip} )}
@d kern=29 {fixed space ( \.{\\kern})}
@d mkern=30 {math kern ( \.{\\mkern} )}
@d leader_ship=31 {use a box ( \.{\\shipout}, \.{\\leaders}, etc.~)}
@d halign=32 {horizontal table alignment ( \.{\\halign} )}
@d valign=33 {vertical table alignment ( \.{\\valign} )}
@d no_align=34 {temporary escape from alignment ( \.{\\noalign} )}
@d vrule=35 {vertical rule ( \.{\\vrule} )}
@d hrule=36 {horizontal rule ( \.{\\hrule} )}
@d insert=37 {vlist inserted in box ( \.{\\insert} )}
@d vadjust=38 {vlist inserted in enclosing paragraph ( \.{\\vadjust} )}
@d ignore_spaces=39 {gobble |spacer| tokens ( \.{\\ignorespaces} )}
@d after_assignment=40 {save till assignment is done ( \.{\\afterassignment} )}
@d after_group=41 {save till group is done ( \.{\\aftergroup} )}
@d break_penalty=42 {additional badness ( \.{\\penalty} )}
@d start_par=43 {begin paragraph ( \.{\\indent}, \.{\\noindent} )}
@d ital_corr=44 {italic correction ( \.{\\/} )}
@d accent=45 {attach accent in text ( \.{\\accent} )}
@d math_accent=46 {attach accent in math ( \.{\\mathaccent} )}
@d discretionary=47 {discretionary texts ( \.{\\-}, \.{\\discretionary} )}
@d eq_no=48 {equation number ( \.{\\eqno}, \.{\\leqno} )}
@d left_right=49 {variable delimiter ( \.{\\left}, \.{\\right} )}
  {( or \.{\\middle} )}
@d math_comp=50 {component of formula ( \.{\\mathbin}, etc.~)}
@d limit_switch=51 {diddle limit conventions ( \.{\\displaylimits}, etc.~)}
@d above=52 {generalized fraction ( \.{\\above}, \.{\\atop}, etc.~)}
@d math_style=53 {style specification ( \.{\\displaystyle}, etc.~)}
@d math_choice=54 {choice specification ( \.{\\mathchoice} )}
@d non_script=55 {conditional math glue ( \.{\\nonscript} )}
@d vcenter=56 {vertically center a vbox ( \.{\\vcenter} )}
@d case_shift=57 {force specific case ( \.{\\lowercase}, \.{\\uppercase}~)}
@d message=58 {send to user ( \.{\\message}, \.{\\errmessage} )}
@d extension=59 {extensions to \TeX\ ( \.{\\write}, \.{\\special}, etc.~)}
@d in_stream=60 {files for reading ( \.{\\openin}, \.{\\closein} )}
@d begin_group=61 {begin local grouping ( \.{\\begingroup} )}
@d end_group=62 {end local grouping ( \.{\\endgroup} )}
@d omit=63 {omit alignment template ( \.{\\omit} )}
@d ex_space=64 {explicit space ( \.{\\\ } )}
@d no_boundary=65 {suppress boundary ligatures ( \.{\\noboundary} )}
@d radical=66 {square root and similar signs ( \.{\\radical} )}
@d end_cs_name=67 {end control sequence ( \.{\\endcsname} )}
@d char_ghost=end_cs_name+1
   {\.{\\ghostleft}, \.{\\ghostright} character for kerning}
@d assign_local_box=char_ghost+1
   {box for guillemets \.{\\localleftbox} or \.{\\localrightbox}}
@d min_internal=assign_local_box+1 {the smallest code that can follow \.{\\the}}
@d char_given=min_internal {character code defined by \.{\\chardef}}
@d math_given=char_given+1 {math code defined by \.{\\mathchardef}}
@d omath_given=math_given+1 {math code defined by \.{\\omathchardef}}
@d last_item=omath_given+1 {most recent item ( \.{\\lastpenalty},
  \.{\\lastkern}, \.{\\lastskip} )}
@d max_non_prefixed_command=last_item
   {largest command code that can't be \.{\\global}}

@ The next codes are special; they all relate to mode-independent
assignment of values to \TeX's internal registers or tables.
Codes that are |max_internal| or less represent internal quantities
that might be expanded by `\.{\\the}'.

There is no matching primitive to go with |assign_attr|, but even if
there was no \.{\\attributedef}, a reserved number would still be
needed because there is an implied correspondence between the
|assign_xxx| commands and |xxx_val| expression values. That would 
break down otherwise.

@d toks_register=max_non_prefixed_command+1
   {token list register ( \.{\\toks} )}
@d assign_toks=toks_register+1
   {special token list ( \.{\\output}, \.{\\everypar}, etc.~)}
@d assign_int=assign_toks+1
   {user-defined integer ( \.{\\tolerance}, \.{\\day}, etc.~)}
@d assign_attr=assign_int+1 { user-defined attributes }
@d assign_dimen=assign_attr+1
   {user-defined length ( \.{\\hsize}, etc.~)}
@d assign_glue=assign_dimen+1
   {user-defined glue ( \.{\\baselineskip}, etc.~)}
@d assign_mu_glue=assign_glue+1
   {user-defined muglue ( \.{\\thinmuskip}, etc.~)}
@d assign_font_dimen=assign_mu_glue+1
   {user-defined font dimension ( \.{\\fontdimen} )}
@d assign_font_int=assign_font_dimen+1
   {user-defined font integer ( \.{\\hyphenchar}, \.{\\skewchar} )}
@d set_aux=assign_font_int+1
   {specify state info ( \.{\\spacefactor}, \.{\\prevdepth} )}
@d set_prev_graf=set_aux+1
   {specify state info ( \.{\\prevgraf} )}
@d set_page_dimen=set_prev_graf+1
   {specify state info ( \.{\\pagegoal}, etc.~)}
@d set_page_int=set_page_dimen+1
   {specify state info ( \.{\\deadcycles},
  \.{\\insertpenalties} )}
@d set_box_dimen=set_page_int+1
   {change dimension of box ( \.{\\wd}, \.{\\ht}, \.{\\dp} )}
@d set_shape=set_box_dimen+1
   {specify fancy paragraph shape ( \.{\\parshape} )}
@d def_code=set_shape+1
   {define a character code ( \.{\\catcode}, etc.~)}
@d extdef_code=def_code+1
   {define an extended character code ( \.{\\omathcode}, etc.~)}
@d def_family=extdef_code+1
   {declare math fonts ( \.{\\textfont}, etc.~)}
@d set_font=def_family+1
   {set current font ( font identifiers )}
@d def_font=set_font+1
   {define a font file ( \.{\\font} )}
@d register=def_font+1
   {internal register ( \.{\\count}, \.{\\dimen}, etc.~)}
@d assign_box_dir=register+1 {(\.{\\boxdir})}
@d assign_dir=register+2 {(\.{\\pagedir}, \.{\\textdir})}
@d max_internal=assign_dir
   {the largest code that can follow \.{\\the}}
@d advance=max_internal+1
   {advance a register or parameter ( \.{\\advance} )}
@d multiply=advance+1
   {multiply a register or parameter ( \.{\\multiply} )}
@d divide=multiply+1
   {divide a register or parameter ( \.{\\divide} )}
@d prefix=divide+1
   {qualify a definition ( \.{\\global}, \.{\\long}, \.{\\outer} )}
@d let=prefix+1
   {assign a command code ( \.{\\let}, \.{\\futurelet} )}
@d shorthand_def=let+1
   {code definition ( \.{\\chardef}, \.{\\countdef}, etc.~)}
@d read_to_cs=shorthand_def+1
   {read into a control sequence ( \.{\\read} )}
@d def=read_to_cs+1
   {macro definition ( \.{\\def}, \.{\\gdef}, \.{\\xdef}, \.{\\edef} )}
@d set_box=def+1
   {set a box ( \.{\\setbox} )}
@d hyph_data=set_box+1
   {hyphenation data ( \.{\\hyphenation}, \.{\\patterns} )}
@d set_interaction=hyph_data+1
   {define level of interaction ( \.{\\batchmode}, etc.~)}
@d letterspace_font=set_interaction+1
   {letterspace a font ( \.{\\letterspacefont} )}
@d set_ocp=letterspace_font+1
   {Place a translation process in the stream}
@d def_ocp=set_ocp+1
   {Define and load a translation process}
@d set_ocp_list=def_ocp+1
   {Place a list of OCPs in the stream}
@d def_ocp_list=set_ocp_list+1
   {Define a list of OCPs}
@d clear_ocp_lists=def_ocp_list+1
   {Remove all active OCP lists}
@d push_ocp_list=clear_ocp_lists+1
   {Add to the sequence of active OCP lists}
@d pop_ocp_list=push_ocp_list+1
   {Remove from the sequence of active OCP lists}
@d ocp_list_op=pop_ocp_list+1
   {Operations for building a list of OCPs}
@d ocp_trace_level=ocp_list_op+1
   {Tracing of active OCPs, either 0 or 1}
@d max_command=ocp_trace_level 
  {the largest command code seen at |big_switch|}

@ The remaining command codes are extra special, since they cannot get through
\TeX's scanner to the main control routine. They have been given values higher
than |max_command| so that their special nature is easily discernible.
The ``expandable'' commands come first.

@d undefined_cs=max_command+1 {initial state of most |eq_type| fields}
@d expand_after=max_command+2 {special expansion ( \.{\\expandafter} )}
@d no_expand=max_command+3 {special nonexpansion ( \.{\\noexpand} )}
@d input=max_command+4 {input a source file ( \.{\\input}, \.{\\endinput} )}
  {( or \.{\\scantokens} or \.{\\scantextokens} )}
@d if_test=max_command+5 {conditional text ( \.{\\if}, \.{\\ifcase}, etc.~)}
@d fi_or_else=max_command+6 {delimiters for conditionals ( \.{\\else}, etc.~)}
@d cs_name=max_command+7 {make a control sequence from tokens ( \.{\\csname} )}
@d convert=max_command+8 {convert to text ( \.{\\number}, \.{\\string}, etc.~)}
@d the=max_command+9 {expand an internal quantity ( \.{\\the} )}
  {( or \.{\\unexpanded}, \.{\\detokenize} )}
@d top_bot_mark=max_command+10 {inserted mark ( \.{\\topmark}, etc.~)}
@d call=max_command+11 {non-long, non-outer control sequence}
@d long_call=max_command+12 {long, non-outer control sequence}
@d outer_call=max_command+13 {non-long, outer control sequence}
@d long_outer_call=max_command+14 {long, outer control sequence}
@d end_template=max_command+15 {end of an alignment template}
@d dont_expand=max_command+16 {the following token was marked by \.{\\noexpand}}
@d glue_ref=max_command+17 {the equivalent points to a glue specification}
@d shape_ref=max_command+18 {the equivalent points to a parshape specification}
@d box_ref=max_command+19 {the equivalent points to a box node, or is |null|}
@d data=max_command+20 {the equivalent is simply a halfword number}

@* \[16] The semantic nest.
\TeX\ is typically in the midst of building many lists at once. For example,
when a math formula is being processed, \TeX\ is in math mode and
working on an mlist; this formula has temporarily interrupted \TeX\ from
being in horizontal mode and building the hlist of a paragraph; and this
paragraph has temporarily interrupted \TeX\ from being in vertical mode
and building the vlist for the next page of a document. Similarly, when a
\.{\\vbox} occurs inside of an \.{\\hbox}, \TeX\ is temporarily
interrupted from working in restricted horizontal mode, and it enters
internal vertical mode.  The ``semantic nest'' is a stack that
keeps track of what lists and modes are currently suspended.

At each level of processing we are in one of six modes:

\yskip\hang|vmode| stands for vertical mode (the page builder);

\hang|hmode| stands for horizontal mode (the paragraph builder);

\hang|mmode| stands for displayed formula mode;

\hang|-vmode| stands for internal vertical mode (e.g., in a \.{\\vbox});

\hang|-hmode| stands for restricted horizontal mode (e.g., in an \.{\\hbox});

\hang|-mmode| stands for math formula mode (not displayed).

\yskip\noindent The mode is temporarily set to zero while processing \.{\\write}
texts in the |ship_out| routine.

Numeric values are assigned to |vmode|, |hmode|, and |mmode| so that
\TeX's ``big semantic switch'' can select the appropriate thing to
do by computing the value |abs(mode)+cur_cmd|, where |mode| is the current
mode and |cur_cmd| is the current command code.

@d vmode=1 {vertical mode}
@d hmode=vmode+max_command+1 {horizontal mode}
@d mmode=hmode+max_command+1 {math mode}

@p procedure print_mode(@!m:integer); {prints the mode represented by |m|}
begin if m>0 then
  case m div (max_command+1) of
  0:print("vertical");
  1:print("horizontal");
  2:print("display math");
  end
else if m=0 then print("no")
else  case (-m) div (max_command+1) of
  0:print("internal vertical");
  1:print("restricted horizontal");
  2:print("math");
  end;
print(" mode");
end;
function get_mode_id:integer; {returns the mode represented by |m|}
var m:integer ;
begin 
  m := mode;
  if m>0 then
  case m div (max_command+1) of
  0:get_mode_id := "v";
  1:get_mode_id := "h";
  2:get_mode_id := "m"; 
  othercases get_mode_id := "";
  end
else if m=0 then get_mode_id := "n"
else  case (-m) div (max_command+1) of
  0:get_mode_id := "V";
  1:get_mode_id := "H";
  2:get_mode_id := "M";
  othercases get_mode_id := "";
  end;
end;

@ The state of affairs at any semantic level can be represented by
five values:

\yskip\hang|mode| is the number representing the semantic mode, as
just explained.

\yskip\hang|head| is a |pointer| to a list head for the list being built;
|link(head)| therefore points to the first element of the list, or
to |null| if the list is empty.

\yskip\hang|tail| is a |pointer| to the final node of the list being
built; thus, |tail=head| if and only if the list is empty.

\yskip\hang|prev_graf| is the number of lines of the current paragraph that
have already been put into the present vertical list.

\yskip\hang|aux| is an auxiliary |memory_word| that gives further information
that is needed to characterize the situation.

\yskip\noindent
In vertical mode, |aux| is also known as |prev_depth|; it is the scaled
value representing the depth of the previous box, for use in baseline
calculations, or it is |<=-1000|pt if the next box on the vertical list is to
be exempt from baseline calculations.  In horizontal mode, |aux| is also
known as |space_factor|; it holds the current space factor used in
spacing calculations. In math mode, |aux| is also known as |incompleat_noad|; 
if not |null|, it points to a record that represents the numerator of a
generalized fraction for which the denominator is currently being formed
in the current list.

There is also a sixth quantity, |mode_line|, which correlates
the semantic nest with the user's input; |mode_line| contains the source
line number at which the current level of nesting was entered. The negative
of this line number is the |mode_line| at the level of the
user's output routine.

A seventh quantity, |eTeX_aux|, is used by the extended features \eTeX.
In math mode it is known as |delim_ptr| and points to the most
recent |left_noad| or |middle_noad| of a |math_left_group|.

In horizontal mode, the |prev_graf| field is used for initial language data.

The semantic nest is an array called |nest| that holds the |mode|, |head|,
|tail|, |prev_graf|, |aux|, and |mode_line| values for all semantic levels
below the currently active one. Information about the currently active
level is kept in the global quantities |mode|, |head|, |tail|, |prev_graf|,
|aux|, and |mode_line|, which live in a \PASCAL\ record that is ready to
be pushed onto |nest| if necessary.

@d ignore_depth==-65536000 {|prev_depth| value that is ignored}

@<Types...@>=
@!list_state_record=record@!mode_field:-mmode..mmode;@+
  @!head_field,@!tail_field: pointer;
  @!eTeX_aux_field: pointer;
  @!pg_field,@!ml_field: integer;@+
  @!aux_field: memory_word;
  @!dirs_field: halfword;
  @!math_field: integer;
  @!local_par_field: pointer;
  @!local_par_bool_field: boolean;
  end;

@ @d mode==cur_list.mode_field {current mode}
@d head==cur_list.head_field {header node of current list}
@d tail==cur_list.tail_field {final node on current list}
@d eTeX_aux==cur_list.eTeX_aux_field {auxiliary data for \eTeX}
@d delim_ptr==eTeX_aux {most recent left or right noad of a math left group}
@d prev_graf==cur_list.pg_field {number of paragraph lines accumulated}
@d aux==cur_list.aux_field {auxiliary data about the current list}
@d prev_depth==aux.sc {the name of |aux| in vertical mode}
@d space_factor==aux.hh.lh {part of |aux| in horizontal mode}
@d incompleat_noad==aux.int {the name of |aux| in math mode}
@d mode_line==cur_list.ml_field {source file line number at beginning of list}
@d dir_save==cur_list.dirs_field {dir stack when a paragraph is interrupted}
@d dir_math_save==cur_list.math_field
   {should begin/end dir nodes be placed around mathematics?}
@d local_par==cur_list.local_par_field
   {pointer to whatsit for local stuff}
@d local_par_bool==cur_list.local_par_bool_field
   {has local stuff been changed in this group?}

@<Glob...@>=
@!nest:array[0..nest_size] of list_state_record;
@!nest_ptr:0..nest_size; {first unused location of |nest|}
@!max_nest_stack:0..nest_size; {maximum of |nest_ptr| when pushing}
@!cur_list:list_state_record; {the ``top'' semantic state}
@!shown_mode:-mmode..mmode; {most recent mode shown by \.{\\tracingcommands}}
@!save_tail: pointer; {save |tail| so we can examine whether we have an auto
                       kern before a glue}

@ Here is a common way to make the current list grow:

@p 
procedure tail_append(p:pointer);
begin 
vlink(tail):=p; tail:=vlink(tail);
end;
@#
procedure new_tail_append(p:pointer);
begin 
couple_nodes(tail,p); tail:=vlink(tail);
end;
@#
function pop_tail:pointer;
label exit;
var n,r:pointer;
begin 
  if tail<>head then begin
    r:=tail;
    if vlink(alink(tail))=tail then 
      n:=alink(tail)
    else begin
      n:=head;
      while vlink(n)<>tail do n:=vlink(n);
      end;
    flush_node(tail);
    tail:=n;
    vlink(n):=null;
    pop_tail:=r;
    end
  else 
    pop_tail:=null;
exit:end;


@ We will see later that the vertical list at the bottom semantic level is split
into two parts; the ``current page'' runs from |page_head| to |page_tail|,
and the ``contribution list'' runs from |contrib_head| to |tail| of
semantic level zero. The idea is that contributions are first formed in
vertical mode, then ``contributed'' to the current page (during which time
the page-breaking decisions are made). For now, we don't need to know
any more details about the page-building process.

@<Set init...@>=
nest_ptr:=0; max_nest_stack:=0;
mode:=vmode; head:=contrib_head; tail:=contrib_head;
eTeX_aux:=null;
prev_depth:=ignore_depth; mode_line:=0;
prev_graf:=0; shown_mode:=0;
dir_save:=null; dir_math_save:=false;
local_par:=null; local_par_bool:=false;
@<Start a new current page@>;

@ @p @<LOCAL: Declare |make_local_par_node|@>;

@ @p @<DIR: Declare |new_dir|@>;

@ When \TeX's work on one level is interrupted, the state is saved by
calling |push_nest|. This routine changes |head| and |tail| so that
a new (empty) list is begun; it does not change |mode| or |aux|.

@p procedure push_nest; {enter a new semantic level, save the old}
begin if nest_ptr>max_nest_stack then
  begin max_nest_stack:=nest_ptr;
  if nest_ptr=nest_size then overflow("semantic nest size",nest_size);
@:TeX capacity exceeded semantic nest size}{\quad semantic nest size@>
  end;
nest[nest_ptr]:=cur_list; {stack the record}
incr(nest_ptr); head:=new_node(temp_node,0); tail:=head; prev_graf:=0; mode_line:=line;
dir_save:=null; dir_math_save:=false;
local_par:=make_local_par_node; local_par_bool:=false;
eTeX_aux:=null;
end;

@ Conversely, when \TeX\ is finished on the current level, the former
state is restored by calling |pop_nest|. This routine will never be
called at the lowest semantic level, nor will it be called unless |head|
is a node that should be returned to free memory.

@p procedure pop_nest; {leave a semantic level, re-enter the old}
begin
if local_par<>null then begin
  if local_par_bool then begin end {|tail_append(local_par)|}
  else flush_node(local_par);
  end;
flush_node(head); decr(nest_ptr); cur_list:=nest[nest_ptr];
end;

@ Here is a procedure that displays what \TeX\ is working on, at all levels.

@p procedure@?print_totals; forward;@t\2@>
procedure show_activities;
var p:0..nest_size; {index into |nest|}
@!m:-mmode..mmode; {mode}
@!a:memory_word; {auxiliary}
@!q,@!r:pointer; {for showing the current page}
@!t:integer; {ditto}
begin nest[nest_ptr]:=cur_list; {put the top level into the array}
print_nl(""); print_ln;
for p:=nest_ptr downto 0 do
  begin m:=nest[p].mode_field; a:=nest[p].aux_field;
  print_nl("### "); print_mode(m);
  print(" entered at line "); print_int(abs(nest[p].ml_field));
  if m=hmode then if nest[p].pg_field <> @'40600000 then
    begin print(" (language"); print_int(nest[p].pg_field mod @'200000);
    print(":hyphenmin"); print_int(nest[p].pg_field div @'20000000);
    print_char(","); print_int((nest[p].pg_field div @'200000) mod @'100);
    print_char(")");
    end;
  if nest[p].ml_field<0 then print(" (\output routine)");
  if p=0 then
    begin @<Show the status of the current page@>;
    if vlink(contrib_head)<>null then
      print_nl("### recent contributions:");
    end;
  show_box(vlink(nest[p].head_field));
  @<Show the auxiliary field, |a|@>;
  end;
end;

@ @<Show the auxiliary...@>=
case abs(m) div (max_command+1) of
0: begin print_nl("prevdepth ");
  if a.sc<=ignore_depth then print("ignored")
  else print_scaled(a.sc);
  if nest[p].pg_field<>0 then
    begin print(", prevgraf ");
    print_int(nest[p].pg_field); print(" line");
    if nest[p].pg_field<>1 then print_char("s");
    end;
  end;
1: begin print_nl("spacefactor "); print_int(a.hh.lh);
  if m>0 then@+ if a.hh.rh>0 then
    begin print(", current language "); print_int(a.hh.rh);@+
    end;
  end;
2: if a.int<>null then
  begin print("this will be denominator of:"); show_box(a.int);@+
  end;
end {there are no other cases}

@* \[17] The table of equivalents.
Now that we have studied the data structures for \TeX's semantic routines,
we ought to consider the data structures used by its syntactic routines. In
other words, our next concern will be
the tables that \TeX\ looks at when it is scanning
what the user has written.

The biggest and most important such table is called |eqtb|. It holds the
current ``equivalents'' of things; i.e., it explains what things mean
or what their current values are, for all quantities that are subject to
the nesting structure provided by \TeX's grouping mechanism. There are six
parts to |eqtb|:

\yskip\hangg 1) |eqtb[active_base..(hash_base-1)]| holds the current
equivalents of single-character control sequences.

\yskip\hangg 2) |eqtb[hash_base..(glue_base-1)]| holds the current
equivalents of multiletter control sequences.

\yskip\hangg 3) |eqtb[glue_base..(local_base-1)]| holds the current
equivalents of glue parameters like the current baselineskip.

\yskip\hangg 4) |eqtb[local_base..(int_base-1)]| holds the current
equivalents of local halfword quantities like the current box registers,
the current ``catcodes,'' the current font, and a pointer to the current
paragraph shape.

\yskip\hangg 5) |eqtb[int_base..(dimen_base-1)]| holds the current
equivalents of fullword integer parameters like the current hyphenation
penalty.

\yskip\hangg 6) |eqtb[dimen_base..eqtb_size]| holds the current equivalents
of fullword dimension parameters like the current hsize or amount of
hanging indentation.

\yskip\noindent Note that, for example, the current amount of
baselineskip glue is determined by the setting of a particular location
in region~3 of |eqtb|, while the current meaning of the control sequence
`\.{\\baselineskip}' (which might have been changed by \.{\\def} or
\.{\\let}) appears in region~2.

@ Each entry in |eqtb| is a |memory_word|. Most of these words are of type
|two_halves|, and subdivided into three fields:

\yskip\hangg 1) The |eq_level| (a quarterword) is the level of grouping at
which this equivalent was defined. If the level is |level_zero|, the
equivalent has never been defined; |level_one| refers to the outer level
(outside of all groups), and this level is also used for global
definitions that never go away. Higher levels are for equivalents that
will disappear at the end of their group.  @^global definitions@>

\yskip\hangg 2) The |eq_type| (another quarterword) specifies what kind of
entry this is. There are many types, since each \TeX\ primitive like
\.{\\hbox}, \.{\\def}, etc., has its own special code. The list of
command codes above includes all possible settings of the |eq_type| field.

\yskip\hangg 3) The |equiv| (a halfword) is the current equivalent value.
This may be a font number, a pointer into |mem|, or a variety of other
things.

@d eq_level_field(#)==#.hh.b1
@d eq_type_field(#)==#.hh.b0
@d equiv_field(#)==#.hh.rh
@d eq_level(#)==eq_level_field(eqtb[#]) {level of definition}
@d eq_type(#)==eq_type_field(eqtb[#]) {command code for equivalent}
@d equiv(#)==equiv_field(eqtb[#]) {equivalent value}
@d level_zero=min_quarterword {level for undefined quantities}
@d level_one=level_zero+1 {outermost level for defined quantities}

@ Many locations in |eqtb| have symbolic names. The purpose of the next
paragraphs is to define these names, and to set up the initial values of the
equivalents.

In the first region we have |number_active_chars| equivalents for ``active
characters'' that act as control sequences.

Then comes region~2, which corresponds to the hash table that we will
define later.  The maximum address in this region is used for a dummy
control sequence that is perpetually undefined. There also are several
locations for control sequences that are perpetually defined
(since they are used in error recovery).

@d active_base=1 {beginning of region 1, for active character equivalents}
@d null_cs=active_base+number_active_chars {equivalent of \.{\\csname\\endcsname}}
@d hash_base=null_cs+1 {beginning of region 2, for the hash table}
@d frozen_control_sequence=hash_base+hash_size {for error recovery}
@d frozen_protection=frozen_control_sequence {inaccessible but definable}
@d frozen_cr=frozen_control_sequence+1 {permanent `\.{\\cr}'}
@d frozen_end_group=frozen_control_sequence+2 {permanent `\.{\\endgroup}'}
@d frozen_right=frozen_control_sequence+3 {permanent `\.{\\right}'}
@d frozen_fi=frozen_control_sequence+4 {permanent `\.{\\fi}'}
@d frozen_end_template=frozen_control_sequence+5 {permanent `\.{\\endtemplate}'}
@d frozen_endv=frozen_control_sequence+6 {second permanent `\.{\\endtemplate}'}
@d frozen_relax=frozen_control_sequence+7 {permanent `\.{\\relax}'}
@d end_write=frozen_control_sequence+8 {permanent `\.{\\endwrite}'}
@d frozen_dont_expand=frozen_control_sequence+9
  {permanent `\.{\\notexpanded:}'}
@d frozen_primitive=frozen_control_sequence+11
  {permanent `\.{\\pdfprimitive}'}
@d frozen_null_font=frozen_control_sequence+12
  {permanent `\.{\\nullfont}'}
@d font_id_base=frozen_null_font-font_base
  {begins table of |number_fonts| permanent font identifiers}
@d frozen_null_ocp=frozen_null_font+number_fonts
  {permanent `\.{\\nullocp}'}
@d ocp_id_base=frozen_null_ocp-ocp_base
  {begins table of |number_ocps| permanent ocp identifiers}
@d frozen_null_ocp_list=frozen_null_ocp+number_ocps
  {permanent `\.{\\nullocplist}'}
@d ocp_list_id_base=frozen_null_ocp_list-ocp_list_base
  {begins table of |number_ocp_lists| permanent ocp list identifiers}
@d undefined_control_sequence=frozen_null_ocp_list+number_ocp_lists 
@d glue_base=undefined_control_sequence+1 {beginning of region 3}

@<Initialize table entries...@>=
eq_type(undefined_control_sequence):=undefined_cs;
equiv(undefined_control_sequence):=null;
eq_level(undefined_control_sequence):=level_zero;
for k:=active_base to undefined_control_sequence-1 do
  eqtb[k]:=eqtb[undefined_control_sequence];

@ Here is a routine that displays the current meaning of an |eqtb| entry
in region 1 or~2. (Similar routines for the other regions will appear
below.)

@<Show equivalent |n|, in region 1 or 2@>=
begin sprint_cs(n); print_char("="); print_cmd_chr(eq_type(n),equiv(n));
if eq_type(n)>=call then
  begin print_char(":"); show_token_list(link(equiv(n)),null,32);
  end;
end

@ Region 3 of |eqtb| contains the |number_regs| \.{\\skip} registers, as well as the
glue parameters defined here. It is important that the ``muskip''
parameters have larger numbers than the others.

@d line_skip_code=0 {interline glue if |baseline_skip| is infeasible}
@d baseline_skip_code=1 {desired glue between baselines}
@d par_skip_code=2 {extra glue just above a paragraph}
@d above_display_skip_code=3 {extra glue just above displayed math}
@d below_display_skip_code=4 {extra glue just below displayed math}
@d above_display_short_skip_code=5
  {glue above displayed math following short lines}
@d below_display_short_skip_code=6
  {glue below displayed math following short lines}
@d left_skip_code=7 {glue at left of justified lines}
@d right_skip_code=8 {glue at right of justified lines}
@d top_skip_code=9 {glue at top of main pages}
@d split_top_skip_code=10 {glue at top of split pages}
@d tab_skip_code=11 {glue between aligned entries}
@d space_skip_code=12 {glue between words (if not |zero_glue|)}
@d xspace_skip_code=13 {glue after sentences (if not |zero_glue|)}
@d par_fill_skip_code=14 {glue on last line of paragraph}
@d thin_mu_skip_code=15 {thin space in math formula}
@d med_mu_skip_code=16 {medium space in math formula}
@d thick_mu_skip_code=17 {thick space in math formula}
@d glue_pars=18 {total number of glue parameters}
@d skip_base=glue_base+glue_pars {table of |number_regs| ``skip'' registers}
@d mu_skip_base=skip_base+number_regs {table of |number_regs| ``muskip'' registers}
@d local_base=mu_skip_base+number_regs {beginning of region 4}
@#
@d skip(#)==equiv(skip_base+#) {|mem| location of glue specification}
@d mu_skip(#)==equiv(mu_skip_base+#) {|mem| location of math glue spec}
@d glue_par(#)==equiv(glue_base+#) {|mem| location of glue specification}
@d line_skip==glue_par(line_skip_code)
@d baseline_skip==glue_par(baseline_skip_code)
@d par_skip==glue_par(par_skip_code)
@d above_display_skip==glue_par(above_display_skip_code)
@d below_display_skip==glue_par(below_display_skip_code)
@d above_display_short_skip==glue_par(above_display_short_skip_code)
@d below_display_short_skip==glue_par(below_display_short_skip_code)
@d left_skip==glue_par(left_skip_code)
@d right_skip==glue_par(right_skip_code)
@d top_skip==glue_par(top_skip_code)
@d split_top_skip==glue_par(split_top_skip_code)
@d tab_skip==glue_par(tab_skip_code)
@d space_skip==glue_par(space_skip_code)
@d xspace_skip==glue_par(xspace_skip_code)
@d par_fill_skip==glue_par(par_fill_skip_code)
@d thin_mu_skip==glue_par(thin_mu_skip_code)
@d med_mu_skip==glue_par(med_mu_skip_code)
@d thick_mu_skip==glue_par(thick_mu_skip_code)

@<Current |mem| equivalent of glue parameter number |n|@>=glue_par(n)

@ Sometimes we need to convert \TeX's internal code numbers into symbolic
form. The |print_skip_param| routine gives the symbolic name of a glue
parameter.

@<Declare the procedure called |print_skip_param|@>=
procedure print_skip_param(@!n:integer);
begin case n of
line_skip_code: print_esc("lineskip");
baseline_skip_code: print_esc("baselineskip");
par_skip_code: print_esc("parskip");
above_display_skip_code: print_esc("abovedisplayskip");
below_display_skip_code: print_esc("belowdisplayskip");
above_display_short_skip_code: print_esc("abovedisplayshortskip");
below_display_short_skip_code: print_esc("belowdisplayshortskip");
left_skip_code: print_esc("leftskip");
right_skip_code: print_esc("rightskip");
top_skip_code: print_esc("topskip");
split_top_skip_code: print_esc("splittopskip");
tab_skip_code: print_esc("tabskip");
space_skip_code: print_esc("spaceskip");
xspace_skip_code: print_esc("xspaceskip");
par_fill_skip_code: print_esc("parfillskip");
thin_mu_skip_code: print_esc("thinmuskip");
med_mu_skip_code: print_esc("medmuskip");
thick_mu_skip_code: print_esc("thickmuskip");
othercases print("[unknown glue parameter!]")
endcases;
end;

@ The symbolic names for glue parameters are put into \TeX's hash table
by using the routine called |primitive|, defined below. Let us enter them
now, so that we don't have to list all those parameter names anywhere else.

@<Put each of \TeX's primitives into the hash table@>=
primitive("lineskip",assign_glue,glue_base+line_skip_code);@/
@!@:line_skip_}{\.{\\lineskip} primitive@>
primitive("baselineskip",assign_glue,glue_base+baseline_skip_code);@/
@!@:baseline_skip_}{\.{\\baselineskip} primitive@>
primitive("parskip",assign_glue,glue_base+par_skip_code);@/
@!@:par_skip_}{\.{\\parskip} primitive@>
primitive("abovedisplayskip",assign_glue,glue_base+above_display_skip_code);@/
@!@:above_display_skip_}{\.{\\abovedisplayskip} primitive@>
primitive("belowdisplayskip",assign_glue,glue_base+below_display_skip_code);@/
@!@:below_display_skip_}{\.{\\belowdisplayskip} primitive@>
primitive("abovedisplayshortskip",
  assign_glue,glue_base+above_display_short_skip_code);@/
@!@:above_display_short_skip_}{\.{\\abovedisplayshortskip} primitive@>
primitive("belowdisplayshortskip",
  assign_glue,glue_base+below_display_short_skip_code);@/
@!@:below_display_short_skip_}{\.{\\belowdisplayshortskip} primitive@>
primitive("leftskip",assign_glue,glue_base+left_skip_code);@/
@!@:left_skip_}{\.{\\leftskip} primitive@>
primitive("rightskip",assign_glue,glue_base+right_skip_code);@/
@!@:right_skip_}{\.{\\rightskip} primitive@>
primitive("topskip",assign_glue,glue_base+top_skip_code);@/
@!@:top_skip_}{\.{\\topskip} primitive@>
primitive("splittopskip",assign_glue,glue_base+split_top_skip_code);@/
@!@:split_top_skip_}{\.{\\splittopskip} primitive@>
primitive("tabskip",assign_glue,glue_base+tab_skip_code);@/
@!@:tab_skip_}{\.{\\tabskip} primitive@>
primitive("spaceskip",assign_glue,glue_base+space_skip_code);@/
@!@:space_skip_}{\.{\\spaceskip} primitive@>
primitive("xspaceskip",assign_glue,glue_base+xspace_skip_code);@/
@!@:xspace_skip_}{\.{\\xspaceskip} primitive@>
primitive("parfillskip",assign_glue,glue_base+par_fill_skip_code);@/
@!@:par_fill_skip_}{\.{\\parfillskip} primitive@>
primitive("thinmuskip",assign_mu_glue,glue_base+thin_mu_skip_code);@/
@!@:thin_mu_skip_}{\.{\\thinmuskip} primitive@>
primitive("medmuskip",assign_mu_glue,glue_base+med_mu_skip_code);@/
@!@:med_mu_skip_}{\.{\\medmuskip} primitive@>
primitive("thickmuskip",assign_mu_glue,glue_base+thick_mu_skip_code);@/
@!@:thick_mu_skip_}{\.{\\thickmuskip} primitive@>

@ @<Cases of |print_cmd_chr| for symbolic printing of primitives@>=
assign_glue,assign_mu_glue: if chr_code<skip_base then
    print_skip_param(chr_code-glue_base)
  else if chr_code<mu_skip_base then
    begin print_esc("skip"); print_int(chr_code-skip_base);
    end
  else  begin print_esc("muskip"); print_int(chr_code-mu_skip_base);
    end;

@ All glue parameters and registers are initially `\.{0pt plus0pt minus0pt}'.

@<Initialize table entries...@>=
equiv(glue_base):=zero_glue; eq_level(glue_base):=level_one;
eq_type(glue_base):=glue_ref;
for k:=glue_base+1 to local_base-1 do eqtb[k]:=eqtb[glue_base];
glue_ref_count(zero_glue):=glue_ref_count(zero_glue)+local_base-glue_base;

@ @<Show equivalent |n|, in region 3@>=
if n<skip_base then
  begin print_skip_param(n-glue_base); print_char("=");
  if n<glue_base+thin_mu_skip_code then print_spec(equiv(n),"pt")
  else print_spec(equiv(n),"mu");
  end
else if n<mu_skip_base then
  begin print_esc("skip"); print_int(n-skip_base); print_char("=");
  print_spec(equiv(n),"pt");
  end
else  begin print_esc("muskip"); print_int(n-mu_skip_base); print_char("=");
  print_spec(equiv(n),"mu");
  end

@ Region 4 of |eqtb| contains the local quantities defined here. The
bulk of this region is taken up by five tables that are indexed by eight-bit
characters; these tables are important to both the syntactic and semantic
portions of \TeX. There are also a bunch of special things like font and
token parameters, as well as the tables of \.{\\toks} and \.{\\box}
registers.

@d par_shape_loc=local_base {specifies paragraph shape}
@d output_routine_loc=local_base+1 {points to token list for \.{\\output}}
@d every_par_loc=local_base+2 {points to token list for \.{\\everypar}}
@d every_math_loc=local_base+3 {points to token list for \.{\\everymath}}
@d every_display_loc=local_base+4 {points to token list for \.{\\everydisplay}}
@d every_hbox_loc=local_base+5 {points to token list for \.{\\everyhbox}}
@d every_vbox_loc=local_base+6 {points to token list for \.{\\everyvbox}}
@d every_job_loc=local_base+7 {points to token list for \.{\\everyjob}}
@d every_cr_loc=local_base+8 {points to token list for \.{\\everycr}}
@d err_help_loc=local_base+9 {points to token list for \.{\\errhelp}}
@d tex_toks=local_base+10 {end of \TeX's token list parameters}
@#
@d pdftex_first_loc       = tex_toks {base for \pdfTeX's token list parameters}
@d pdf_pages_attr_loc     = pdftex_first_loc + 0 {points to token list for \.{\\pdfpagesattr}}
@d pdf_page_attr_loc      = pdftex_first_loc + 1 {points to token list for \.{\\pdfpageattr}}
@d pdf_page_resources_loc = pdftex_first_loc + 2 {points to token list for \.{\\pdfpageresources}}
@d pdf_pk_mode_loc        = pdftex_first_loc + 3 {points to token list for \.{\\pdfpkmode}}
@d pdf_toks=pdftex_first_loc+4 {end of \pdfTeX's token list parameters}
@#
@d etex_toks_base=pdf_toks {base for \eTeX's token list parameters}
@d every_eof_loc=etex_toks_base {points to token list for \.{\\everyeof}}
@d etex_toks=etex_toks_base+1 {end of \eTeX's token list parameters}
@#
@d ocp_trace_level_base=etex_toks
@d ocp_active_number_base=ocp_trace_level_base+1
@d ocp_active_min_ptr_base = ocp_active_number_base+1
@d ocp_active_max_ptr_base = ocp_active_min_ptr_base+1
@d ocp_active_base = ocp_active_max_ptr_base+1
@d toks_base       = ocp_active_base+max_active_ocp_lists
   {table of |number_regs| token list registers}
@#
@d etex_pen_base=toks_base+number_regs {start of table of \eTeX's penalties}
@d inter_line_penalties_loc=etex_pen_base {additional penalties between lines}
@d club_penalties_loc=etex_pen_base+1 {penalties for creating club lines}
@d widow_penalties_loc=etex_pen_base+2 {penalties for creating widow lines}
@d display_widow_penalties_loc=etex_pen_base+3 {ditto, just before a display}
@d etex_pens=etex_pen_base+4 {end of table of \eTeX's penalties}
@#
@d local_left_box_base=etex_pens
@d local_right_box_base=local_left_box_base+1
@d box_base=local_right_box_base+1 {table of |number_regs| box registers}
@d cur_font_loc=box_base+number_regs {internal font number outside math mode}
@d math_font_base=cur_font_loc+1 
   {table of |number_math_fonts| math font numbers}
@d cat_code_base=math_font_base+number_math_fonts 
   {table of |number_chars| command codes (the ``catcodes'')}
@d lc_code_base=cat_code_base+1 {table of |number_chars| lowercase mappings}
@d uc_code_base=lc_code_base+1 {table of |number_chars| uppercase mappings}
@d sf_code_base=uc_code_base+1 {table of |number_chars| spacefactor mappings}
@d math_code_base=sf_code_base+1 {table of |number_chars| math mode mappings}
@d int_base=math_code_base+1 {beginning of region 5}
@#
@d par_shape_ptr==equiv(par_shape_loc)
@d output_routine==equiv(output_routine_loc)
@d every_par==equiv(every_par_loc)
@d every_math==equiv(every_math_loc)
@d every_display==equiv(every_display_loc)
@d every_hbox==equiv(every_hbox_loc)
@d every_vbox==equiv(every_vbox_loc)
@d every_job==equiv(every_job_loc)
@d every_cr==equiv(every_cr_loc)
@d err_help==equiv(err_help_loc)
@d pdf_pages_attr==equiv(pdf_pages_attr_loc)
@d pdf_page_attr==equiv(pdf_page_attr_loc)
@d pdf_page_resources==equiv(pdf_page_resources_loc)
@d pdf_pk_mode==equiv(pdf_pk_mode_loc)
@d toks(#)==equiv(toks_base+#)
@d local_left_box==equiv(local_left_box_base)
@d local_right_box==equiv(local_right_box_base)
@d box(#)==equiv(box_base+#)
@d cur_font==equiv(cur_font_loc)
@d fam_fnt(#)==equiv(math_font_base+#)

@<Put each...@>=
primitive("output",assign_toks,output_routine_loc);
@!@:output_}{\.{\\output} primitive@>
primitive("everypar",assign_toks,every_par_loc);
@!@:every_par_}{\.{\\everypar} primitive@>
primitive("everymath",assign_toks,every_math_loc);
@!@:every_math_}{\.{\\everymath} primitive@>
primitive("everydisplay",assign_toks,every_display_loc);
@!@:every_display_}{\.{\\everydisplay} primitive@>
primitive("everyhbox",assign_toks,every_hbox_loc);
@!@:every_hbox_}{\.{\\everyhbox} primitive@>
primitive("everyvbox",assign_toks,every_vbox_loc);
@!@:every_vbox_}{\.{\\everyvbox} primitive@>
primitive("everyjob",assign_toks,every_job_loc);
@!@:every_job_}{\.{\\everyjob} primitive@>
primitive("everycr",assign_toks,every_cr_loc);
@!@:every_cr_}{\.{\\everycr} primitive@>
primitive("errhelp",assign_toks,err_help_loc);
@!@:err_help_}{\.{\\errhelp} primitive@>
primitive("pdfpagesattr",assign_toks,pdf_pages_attr_loc);
@!@:pdf_pages_attr_}{\.{\\pdfpagesattr} primitive@>
primitive("pdfpageattr",assign_toks,pdf_page_attr_loc);
@!@:pdf_page_attr_}{\.{\\pdfpageattr} primitive@>
primitive("pdfpageresources",assign_toks,pdf_page_resources_loc);
@!@:pdf_page_resources_}{\.{\\pdfpageresources} primitive@>
primitive("pdfpkmode",assign_toks,pdf_pk_mode_loc);
@!@:pdf_pk_mode_}{\.{\\pdfpkmode} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
assign_toks: if chr_code>=toks_base then
  begin print_esc("toks"); print_int(chr_code-toks_base);
  end
else  case chr_code of
  output_routine_loc: print_esc("output");
  every_par_loc: print_esc("everypar");
  every_math_loc: print_esc("everymath");
  every_display_loc: print_esc("everydisplay");
  every_hbox_loc: print_esc("everyhbox");
  every_vbox_loc: print_esc("everyvbox");
  every_job_loc: print_esc("everyjob");
  every_cr_loc: print_esc("everycr");
  @/@<Cases of |assign_toks| for |print_cmd_chr|@>@/
  pdf_pages_attr_loc: print_esc("pdfpagesattr");
  pdf_page_attr_loc: print_esc("pdfpageattr");
  pdf_page_resources_loc: print_esc("pdfpageresources");
  pdf_pk_mode_loc: print_esc("pdfpkmode");
  othercases print_esc("errhelp")
  endcases;

@ We initialize most things to null or undefined values. An undefined font
is represented by the internal code |font_base|.

However, the character code tables are given initial values based on the
conventional interpretation of ASCII code. These initial values should
not be changed when \TeX\ is adapted for use with non-English languages;
all changes to the initialization conventions should be made in format
packages, not in \TeX\ itself, so that global interchange of formats is
possible.

@d null_font==font_base
@d null_ocp==ocp_base
@d null_ocp_list==ocp_list_base
@d var_code==@"7000000 {math code meaning ``use the current family''}

@<Initialize table entries...@>=
par_shape_ptr:=null; eq_type(par_shape_loc):=shape_ref;
eq_level(par_shape_loc):=level_one;@/
for k:=etex_pen_base to etex_pens-1 do
  eqtb[k]:=eqtb[par_shape_loc];
for k:=output_routine_loc to toks_base+biggest_reg do
  eqtb[k]:=eqtb[undefined_control_sequence];
box(0):=null; eq_type(box_base):=box_ref; eq_level(box_base):=level_one;
for k:=box_base+1 to box_base+biggest_reg do eqtb[k]:=eqtb[box_base];
cur_font:=null_font; eq_type(cur_font_loc):=data;
eq_level(cur_font_loc):=level_one;@/
for k:=math_font_base to math_font_base+47 do eqtb[k]:=eqtb[cur_font_loc];
equiv(cat_code_base):=0; eq_type(cat_code_base):=data;
eq_level(cat_code_base):=level_one;@/
eqtb[lc_code_base] :=eqtb[cat_code_base];
eqtb[uc_code_base] :=eqtb[cat_code_base];
eqtb[sf_code_base] :=eqtb[cat_code_base];
eqtb[math_code_base]:=eqtb[cat_code_base];@/
cat_code_table:=0;
initex_cat_codes(0);
for k:="0" to "9" do set_math_code(k,(hi(k+var_code)),level_one);@/
for k:="A" to "Z" do begin 
  set_math_code(k,(hi(k+var_code+@"10000)),level_one);
  set_math_code(k+32,(hi(k+32+var_code+@"10000)),level_one);@/
  set_lc_code(k,k+32,level_one); set_lc_code(k+32,k+32,level_one);@/
  set_uc_code(k,k,level_one);    set_uc_code(k+32,k,level_one);@/
  set_sf_code(k,999,level_one);
  end;

@ @<Set init...@>=
static_int_base:=int_base;
initialize_math_codes;
initialize_text_codes;

@ @<Show equivalent |n|, in region 4@>=
if (n=par_shape_loc) or ((n>=etex_pen_base) and (n<etex_pens)) then
  begin print_cmd_chr(set_shape,n); print_char("=");
  if equiv(n)=null then print_char("0")
  else if n>par_shape_loc then
    begin print_int(penalty(equiv(n))); print_char(" ");
    print_int(penalty(equiv(n)+1));
    if penalty(equiv(n))>1 then print_esc("ETC.");
    end
  else print_int(vinfo(par_shape_ptr));
  end
else if n<toks_base then
  {TH TODO make extra cases for ocps here! }
  begin print_cmd_chr(assign_toks,n); print_char("=");
  if equiv(n)<>null then show_token_list(link(equiv(n)),null,32);
  end
else if n<box_base then
  begin print_esc("toks"); print_int(n-toks_base); print_char("=");
  if equiv(n)<>null then show_token_list(link(equiv(n)),null,32);
  end
else if n<cur_font_loc then
  begin print_esc("box"); print_int(n-box_base); print_char("=");
  if equiv(n)=null then print("void")
  else  begin depth_threshold:=0; breadth_max:=1; show_node_list(equiv(n));
    end;
  end
else if n<cat_code_base then @<Show the font identifier in |eqtb[n]|@>
else @<Show the halfword code in |eqtb[n]|@>

@ @<Show the font identifier in |eqtb[n]|@>=
begin if n=cur_font_loc then print("current font")
else if n<math_font_base+script_size then
  begin print_esc("textfont"); print_int(n-math_font_base);
  end
else if n<math_font_base+script_script_size then
  begin print_esc("scriptfont"); print_int(n-math_font_base-script_size);
  end
else  begin print_esc("scriptscriptfont"); print_int(n-math_font_base-script_script_size);
  end;
print_char("=");@/
print_esc(hash[font_id_base+equiv(n)].rh);
  {that's |font_id_text(equiv(n))|}
end

@ 
@d is_omath(#)==  ((((#) mod @"1000000) div @"10000)>15) or
     (((#) mod @"10000)>255)

@<Show the halfword code in |eqtb[n]|@>=
if n<math_code_base then
  begin if n<lc_code_base then
    begin print_esc("catcode"); print_int(n-cat_code_base);
    end
  else if n<uc_code_base then
    begin print_esc("lccode"); print_int(n-lc_code_base);
    end
  else if n<sf_code_base then
    begin print_esc("uccode"); print_int(n-uc_code_base);
    end
  else  begin print_esc("sfcode"); print_int(n-sf_code_base);
    end;
  print_char("="); print_int(equiv(n));
  end
else begin 
  if is_omath(get_math_code(n-math_code_base)) then
    print_esc("omathcode")
  else    
    print_esc("mathcode"); 
  print_int(n-math_code_base);
  print_char("="); print_int(get_math_code(n-math_code_base));
  end

@ Region 5 of |eqtb| contains the integer parameters and registers defined
here, as well as the |del_code| table. The latter table differs from the
|cat_code..math_code| tables that precede it, since delimiter codes are
fullword integers while the other kinds of codes occupy at most a
halfword. This is what makes region~5 different from region~4. We will
store the |eq_level| information in an auxiliary array of quarterwords
that will be defined later.

@d pretolerance_code=0 {badness tolerance before hyphenation}
@d tolerance_code=1 {badness tolerance after hyphenation}
@d line_penalty_code=2 {added to the badness of every line}
@d hyphen_penalty_code=3 {penalty for break after discretionary hyphen}
@d ex_hyphen_penalty_code=4 {penalty for break after explicit hyphen}
@d club_penalty_code=5 {penalty for creating a club line}
@d widow_penalty_code=6 {penalty for creating a widow line}
@d display_widow_penalty_code=7 {ditto, just before a display}
@d broken_penalty_code=8 {penalty for breaking a page at a broken line}
@d bin_op_penalty_code=9 {penalty for breaking after a binary operation}
@d rel_penalty_code=10 {penalty for breaking after a relation}
@d pre_display_penalty_code=11
  {penalty for breaking just before a displayed formula}
@d post_display_penalty_code=12
  {penalty for breaking just after a displayed formula}
@d inter_line_penalty_code=13 {additional penalty between lines}
@d double_hyphen_demerits_code=14 {demerits for double hyphen break}
@d final_hyphen_demerits_code=15 {demerits for final hyphen break}
@d adj_demerits_code=16 {demerits for adjacent incompatible lines}
@d mag_code=17 {magnification ratio}
@d delimiter_factor_code=18 {ratio for variable-size delimiters}
@d looseness_code=19 {change in number of lines for a paragraph}
@d time_code=20 {current time of day}
@d day_code=21 {current day of the month}
@d month_code=22 {current month of the year}
@d year_code=23 {current year of our Lord}
@d show_box_breadth_code=24 {nodes per level in |show_box|}
@d show_box_depth_code=25 {maximum level in |show_box|}
@d hbadness_code=26 {hboxes exceeding this badness will be shown by |hpack|}
@d vbadness_code=27 {vboxes exceeding this badness will be shown by |vpack|}
@d pausing_code=28 {pause after each line is read from a file}
@d tracing_online_code=29 {show diagnostic output on terminal}
@d tracing_macros_code=30 {show macros as they are being expanded}
@d tracing_stats_code=31 {show memory usage if \TeX\ knows it}
@d tracing_paragraphs_code=32 {show line-break calculations}
@d tracing_pages_code=33 {show page-break calculations}
@d tracing_output_code=34 {show boxes when they are shipped out}
@d tracing_lost_chars_code=35 {show characters that aren't in the font}
@d tracing_commands_code=36 {show command codes at |big_switch|}
@d tracing_restores_code=37 {show equivalents when they are restored}
@d uc_hyph_code=38 {hyphenate words beginning with a capital letter}
@d output_penalty_code=39 {penalty found at current page break}
@d max_dead_cycles_code=40 {bound on consecutive dead cycles of output}
@d hang_after_code=41 {hanging indentation changes after this many lines}
@d floating_penalty_code=42 {penalty for insertions heldover after a split}
@d global_defs_code=43 {override \.{\\global} specifications}
@d cur_fam_code=44 {current family}
@d escape_char_code=45 {escape character for token output}
@d default_hyphen_char_code=46 {value of \.{\\hyphenchar} when a font is loaded}
@d default_skew_char_code=47 {value of \.{\\skewchar} when a font is loaded}
@d end_line_char_code=48 {character placed at the right end of the buffer}
@d new_line_char_code=49 {character that prints as |print_ln|}
@d language_code=50 {current hyphenation table}
@d left_hyphen_min_code=51 {minimum left hyphenation fragment size}
@d right_hyphen_min_code=52 {minimum right hyphenation fragment size}
@d holding_inserts_code=53 {do not remove insertion nodes from \.{\\box255}}
@d error_context_lines_code=54 {maximum intermediate line pairs shown}
@d local_inter_line_penalty_code=55 {local \.{\\interlinepenalty}}
@d local_broken_penalty_code=56 {local \.{\\brokenpenalty}}
@d no_local_whatsits_code=57 {counts local whatsits}
@d no_local_dirs_code=58
@d level_local_dir_code=59
@d luastartup_id_code=60
@d disable_lig_code=61
@d disable_kern_code=62
@d cat_code_table_code=63
@d cur_lang_code=64 {current language id}
@d ex_hyphen_char_code=65
@d tex_int_pars=66 {total number of \.{\\TeX} + Aleph integer parameters}
@#
@d dir_base=int_base+tex_int_pars
@d page_direction_code=0
@d body_direction_code=1
@d par_direction_code=2
@d text_direction_code=3
@d math_direction_code=4
@d dir_pars=5
@#
@d pdftex_first_integer_code = dir_base+dir_pars {base for \pdfTeX's integer parameters}
@d pdf_output_code           = pdftex_first_integer_code + 0 {switch on PDF output if positive}
@d pdf_compress_level_code   = pdftex_first_integer_code + 1 {compress level of streams}
@d pdf_decimal_digits_code   = pdftex_first_integer_code + 2 {digits after the decimal point of numbers}
@d pdf_move_chars_code       = pdftex_first_integer_code + 3 {move chars 0..31 to higher area if possible}
@d pdf_image_resolution_code = pdftex_first_integer_code + 4 {default image resolution}
@d pdf_pk_resolution_code    = pdftex_first_integer_code + 5 {default resolution of PK font}
@d pdf_unique_resname_code   = pdftex_first_integer_code + 6 {generate unique names for resouces}
@d pdf_option_always_use_pdfpagebox_code = pdftex_first_integer_code + 7 {if the PDF inclusion should always use a specific PDF page box}
@d pdf_option_pdf_inclusion_errorlevel_code = pdftex_first_integer_code + 8 {if the PDF inclusion should treat pdfs newer than |pdf_minor_version| as an error}
@d pdf_minor_version_code = pdftex_first_integer_code + 9 {fractional part of the PDF version produced}
@d pdf_force_pagebox_code = pdftex_first_integer_code + 10 {if the PDF inclusion should always use a specific PDF page box}
@d pdf_pagebox_code = pdftex_first_integer_code + 11 {default pagebox to use for PDF inclusion}
@d pdf_inclusion_errorlevel_code = pdftex_first_integer_code + 12 {if the PDF inclusion should treat pdfs newer than |pdf_minor_version| as an error}
@d pdf_gamma_code            = pdftex_first_integer_code + 13
@d pdf_image_gamma_code      = pdftex_first_integer_code + 14
@d pdf_image_hicolor_code    = pdftex_first_integer_code + 15
@d pdf_image_apply_gamma_code = pdftex_first_integer_code + 16
@d pdf_adjust_spacing_code   = pdftex_first_integer_code + 17 {level of spacing adjusting}
@d pdf_protrude_chars_code   = pdftex_first_integer_code + 18 {protrude chars at left/right edge of paragraphs}
@d pdf_tracing_fonts_code    = pdftex_first_integer_code + 19 {level of font detail in log}
@d pdf_objcompresslevel_code = pdftex_first_integer_code + 20 {activate object streams}
@d pdf_gen_tounicode_code    = pdftex_first_integer_code + 24 {generate ToUnicode for fonts?}
@d pdf_draftmode_code        = pdftex_first_integer_code + 25 {switch on draftmode if positive}
@d pdf_replace_font_code     = pdftex_first_integer_code + 26 {generate ToUnicode for fonts?}
@d pdf_int_pars=pdftex_first_integer_code + 27 {total number of \pdfTeX's integer parameters}
@#
@d etex_int_base=pdf_int_pars {base for \eTeX's integer parameters}
@d tracing_assigns_code=etex_int_base {show assignments}
@d tracing_groups_code=etex_int_base+1 {show save/restore groups}
@d tracing_ifs_code=etex_int_base+2 {show conditionals}
@d tracing_scan_tokens_code=etex_int_base+3 {show pseudo file open and close}
@d tracing_nesting_code=etex_int_base+4 {show incomplete groups and ifs within files}
@d pre_display_direction_code=etex_int_base+5 {text direction preceding a display}
@d last_line_fit_code=etex_int_base+6 {adjustment for last line of paragraph}
@d saving_vdiscards_code=etex_int_base+7 {save items discarded from vlists}
@d saving_hyph_codes_code=etex_int_base+8 {save hyphenation codes for languages}
@d suppress_fontnotfound_error_code=etex_int_base+9 {surpress errors for missing fonts}
@d etex_int_pars=etex_int_base+10 {total number of \eTeX's integer parameters}
@#
@d int_pars=etex_int_pars {total number of integer parameters}
@d count_base=int_base+int_pars {|number_regs| user \.{\\count} registers}
@d attribute_base=count_base+number_regs {|number_attrs| user \.{\\attribute} registers}
@d del_code_base=attribute_base+number_attrs {|number_chars| delimiter code mappings}
@d dimen_base=del_code_base+1 {beginning of region 6}
@#
@d count(#)==eqtb[count_base+#].int
@d attribute(#)==eqtb[attribute_base+#].int
@d int_par(#)==eqtb[int_base+#].int {an integer parameter}
@d pretolerance==int_par(pretolerance_code)
@d tolerance==int_par(tolerance_code)
@d line_penalty==int_par(line_penalty_code)
@d hyphen_penalty==int_par(hyphen_penalty_code)
@d ex_hyphen_penalty==int_par(ex_hyphen_penalty_code)
@d club_penalty==int_par(club_penalty_code)
@d widow_penalty==int_par(widow_penalty_code)
@d display_widow_penalty==int_par(display_widow_penalty_code)
@d broken_penalty==int_par(broken_penalty_code)
@d bin_op_penalty==int_par(bin_op_penalty_code)
@d rel_penalty==int_par(rel_penalty_code)
@d pre_display_penalty==int_par(pre_display_penalty_code)
@d post_display_penalty==int_par(post_display_penalty_code)
@d inter_line_penalty==int_par(inter_line_penalty_code)
@d double_hyphen_demerits==int_par(double_hyphen_demerits_code)
@d final_hyphen_demerits==int_par(final_hyphen_demerits_code)
@d adj_demerits==int_par(adj_demerits_code)
@d mag==int_par(mag_code)
@d delimiter_factor==int_par(delimiter_factor_code)
@d looseness==int_par(looseness_code)
@d time==int_par(time_code)
@d day==int_par(day_code)
@d month==int_par(month_code)
@d year==int_par(year_code)
@d show_box_breadth==int_par(show_box_breadth_code)
@d show_box_depth==int_par(show_box_depth_code)
@d hbadness==int_par(hbadness_code)
@d vbadness==int_par(vbadness_code)
@d pausing==int_par(pausing_code)
@d tracing_online==int_par(tracing_online_code)
@d tracing_macros==int_par(tracing_macros_code)
@d tracing_stats==int_par(tracing_stats_code)
@d tracing_paragraphs==int_par(tracing_paragraphs_code)
@d tracing_pages==int_par(tracing_pages_code)
@d tracing_output==int_par(tracing_output_code)
@d tracing_lost_chars==int_par(tracing_lost_chars_code)
@d tracing_commands==int_par(tracing_commands_code)
@d tracing_restores==int_par(tracing_restores_code)
@d uc_hyph==int_par(uc_hyph_code)
@d output_penalty==int_par(output_penalty_code)
@d max_dead_cycles==int_par(max_dead_cycles_code)
@d hang_after==int_par(hang_after_code)
@d floating_penalty==int_par(floating_penalty_code)
@d global_defs==int_par(global_defs_code)
@d cur_fam==int_par(cur_fam_code)
@d escape_char==int_par(escape_char_code)
@d default_hyphen_char==int_par(default_hyphen_char_code)
@d default_skew_char==int_par(default_skew_char_code)
@d end_line_char==int_par(end_line_char_code)
@d new_line_char==int_par(new_line_char_code)
@d local_inter_line_penalty==int_par(local_inter_line_penalty_code)
@d local_broken_penalty==int_par(local_broken_penalty_code)
@d no_local_whatsits==int_par(no_local_whatsits_code)
@d no_local_dirs==int_par(no_local_dirs_code)
@d level_local_dir==int_par(level_local_dir_code)
@d dir_par(#)==eqtb[dir_base+#].int {a direction parameter}
@d page_direction==dir_par(page_direction_code)
@d body_direction==dir_par(body_direction_code)
@d par_direction==dir_par(par_direction_code)
@d text_direction==dir_par(text_direction_code)
@d math_direction==dir_par(math_direction_code)
@d language==int_par(language_code)
@d cur_lang==int_par(cur_lang_code)
@d ex_hyphen_char==int_par(ex_hyphen_char_code)
@d left_hyphen_min==int_par(left_hyphen_min_code)
@d right_hyphen_min==int_par(right_hyphen_min_code)
@d holding_inserts==int_par(holding_inserts_code)
@d error_context_lines==int_par(error_context_lines_code)
@d luastartup_id==int_par(luastartup_id_code)
@d disable_lig==int_par(disable_lig_code)
@d disable_kern==int_par(disable_kern_code)
@d cat_code_table==int_par(cat_code_table_code)
@#
@d pdf_adjust_spacing   == int_par(pdf_adjust_spacing_code)
@d pdf_protrude_chars   == int_par(pdf_protrude_chars_code)
@d pdf_tracing_fonts    == int_par(pdf_tracing_fonts_code)
@d pdf_gen_tounicode    == int_par(pdf_gen_tounicode_code)
@d pdf_output           == int_par(pdf_output_code)
@d pdf_compress_level   == int_par(pdf_compress_level_code)
@d pdf_objcompresslevel == int_par(pdf_objcompresslevel_code)
@d pdf_decimal_digits   == int_par(pdf_decimal_digits_code)
@d pdf_move_chars       == int_par(pdf_move_chars_code)
@d pdf_image_resolution == int_par(pdf_image_resolution_code)
@d pdf_pk_resolution    == int_par(pdf_pk_resolution_code)
@d pdf_unique_resname   == int_par(pdf_unique_resname_code)
@d pdf_option_always_use_pdfpagebox == int_par(pdf_option_always_use_pdfpagebox_code)
@d pdf_option_pdf_inclusion_errorlevel == int_par(pdf_option_pdf_inclusion_errorlevel_code)
@d pdf_minor_version == int_par(pdf_minor_version_code)
@d pdf_force_pagebox == int_par(pdf_force_pagebox_code)
@d pdf_pagebox == int_par(pdf_pagebox_code)
@d pdf_inclusion_errorlevel == int_par(pdf_inclusion_errorlevel_code)
@d pdf_gamma            == int_par(pdf_gamma_code)
@d pdf_image_gamma      == int_par(pdf_image_gamma_code)
@d pdf_image_hicolor    == int_par(pdf_image_hicolor_code)
@d pdf_image_apply_gamma == int_par(pdf_image_apply_gamma_code)
@d pdf_draftmode        == int_par(pdf_draftmode_code)
@d pdf_replace_font == int_par(pdf_replace_font_code)
@#
@d tracing_assigns==int_par(tracing_assigns_code)
@d tracing_groups==int_par(tracing_groups_code)
@d tracing_ifs==int_par(tracing_ifs_code)
@d tracing_scan_tokens==int_par(tracing_scan_tokens_code)
@d tracing_nesting==int_par(tracing_nesting_code)
@d pre_display_direction==int_par(pre_display_direction_code)
@d last_line_fit==int_par(last_line_fit_code)
@d saving_vdiscards==int_par(saving_vdiscards_code)
@d saving_hyph_codes==int_par(saving_hyph_codes_code)
@d suppress_fontnotfound_error==int_par(suppress_fontnotfound_error_code)

@<Assign the values |depth_threshold:=show_box_depth|...@>=
depth_threshold:=show_box_depth;
breadth_max:=show_box_breadth

@ We can print the symbolic name of an integer parameter as follows.

@p procedure print_param(@!n:integer);
begin case n of
pretolerance_code:print_esc("pretolerance");
tolerance_code:print_esc("tolerance");
line_penalty_code:print_esc("linepenalty");
hyphen_penalty_code:print_esc("hyphenpenalty");
ex_hyphen_penalty_code:print_esc("exhyphenpenalty");
club_penalty_code:print_esc("clubpenalty");
widow_penalty_code:print_esc("widowpenalty");
display_widow_penalty_code:print_esc("displaywidowpenalty");
broken_penalty_code:print_esc("brokenpenalty");
bin_op_penalty_code:print_esc("binoppenalty");
rel_penalty_code:print_esc("relpenalty");
pre_display_penalty_code:print_esc("predisplaypenalty");
post_display_penalty_code:print_esc("postdisplaypenalty");
inter_line_penalty_code:print_esc("interlinepenalty");
double_hyphen_demerits_code:print_esc("doublehyphendemerits");
final_hyphen_demerits_code:print_esc("finalhyphendemerits");
adj_demerits_code:print_esc("adjdemerits");
mag_code:print_esc("mag");
delimiter_factor_code:print_esc("delimiterfactor");
looseness_code:print_esc("looseness");
time_code:print_esc("time");
day_code:print_esc("day");
month_code:print_esc("month");
year_code:print_esc("year");
show_box_breadth_code:print_esc("showboxbreadth");
show_box_depth_code:print_esc("showboxdepth");
hbadness_code:print_esc("hbadness");
vbadness_code:print_esc("vbadness");
pausing_code:print_esc("pausing");
tracing_online_code:print_esc("tracingonline");
tracing_macros_code:print_esc("tracingmacros");
tracing_stats_code:print_esc("tracingstats");
tracing_paragraphs_code:print_esc("tracingparagraphs");
tracing_pages_code:print_esc("tracingpages");
tracing_output_code:print_esc("tracingoutput");
tracing_lost_chars_code:print_esc("tracinglostchars");
tracing_commands_code:print_esc("tracingcommands");
tracing_restores_code:print_esc("tracingrestores");
uc_hyph_code:print_esc("uchyph");
output_penalty_code:print_esc("outputpenalty");
max_dead_cycles_code:print_esc("maxdeadcycles");
hang_after_code:print_esc("hangafter");
floating_penalty_code:print_esc("floatingpenalty");
global_defs_code:print_esc("globaldefs");
cur_fam_code:print_esc("fam");
escape_char_code:print_esc("escapechar");
default_hyphen_char_code:print_esc("defaulthyphenchar");
default_skew_char_code:print_esc("defaultskewchar");
end_line_char_code:print_esc("endlinechar");
new_line_char_code:print_esc("newlinechar");
language_code:print_esc("language");
cur_lang_code:print_esc("setlanguage");
ex_hyphen_char_code:print_esc("exhyphenchar");
left_hyphen_min_code:print_esc("lefthyphenmin");
right_hyphen_min_code:print_esc("righthyphenmin");
holding_inserts_code:print_esc("holdinginserts");
error_context_lines_code:print_esc("errorcontextlines");
luastartup_id_code:print_esc("luastartup");
disable_lig_code:print_esc("noligs");
disable_kern_code:print_esc("nokerns");
cat_code_table_code:print_esc("catcodetable");
@#
local_inter_line_penalty_code: print_esc("localinterlinepenalty");
local_broken_penalty_code: print_esc("localbrokenpenalty");
{the next three do not have a matching primitive}
no_local_whatsits_code: print("[no_local_whatsits]");
no_local_dirs_code: print("[no_local_dirs]");
level_local_dir_code: print("[level_local_dir]");
@#
pdf_output_code:           print_esc("pdfoutput");
pdf_compress_level_code:   print_esc("pdfcompresslevel");
pdf_objcompresslevel_code: print_esc("pdfobjcompresslevel");
pdf_decimal_digits_code:   print_esc("pdfdecimaldigits");
pdf_move_chars_code:       print_esc("pdfmovechars");
pdf_image_resolution_code: print_esc("pdfimageresolution");
pdf_pk_resolution_code:    print_esc("pdfpkresolution");
pdf_unique_resname_code:   print_esc("pdfuniqueresname");
pdf_option_always_use_pdfpagebox_code: print_esc("pdfoptionalwaysusepdfpagebox");
pdf_option_pdf_inclusion_errorlevel_code: print_esc("pdfoptionpdfinclusionerrorlevel");
pdf_minor_version_code: print_esc("pdfminorversion");
pdf_force_pagebox_code: print_esc("pdfforcepagebox");
pdf_pagebox_code: print_esc("pdfpagebox");
pdf_inclusion_errorlevel_code: print_esc("pdfinclusionerrorlevel");
pdf_gamma_code:            print_esc("pdfgamma");
pdf_image_gamma_code:      print_esc("pdfimagegamma");
pdf_image_hicolor_code:    print_esc("pdfimagehicolor");
pdf_image_apply_gamma_code: print_esc("pdfimageapplygamma");
pdf_adjust_spacing_code:   print_esc("pdfadjustspacing");
pdf_protrude_chars_code:   print_esc("pdfprotrudechars");
pdf_tracing_fonts_code:    print_esc("pdftracingfonts");
pdf_gen_tounicode_code:    print_esc("pdfgentounicode");
pdf_draftmode_code:        print_esc("pdfdraftmode");
pdf_replace_font_code:    print_esc("pdfreplacefont");
@/@<Cases for |print_param|@>@/
othercases begin print("[unknown integer parameter!]"); end
endcases;
end;

@ The integer parameter names must be entered into the hash table.

@<Put each...@>=
primitive("pretolerance",assign_int,int_base+pretolerance_code);@/
@!@:pretolerance_}{\.{\\pretolerance} primitive@>
primitive("tolerance",assign_int,int_base+tolerance_code);@/
@!@:tolerance_}{\.{\\tolerance} primitive@>
primitive("linepenalty",assign_int,int_base+line_penalty_code);@/
@!@:line_penalty_}{\.{\\linepenalty} primitive@>
primitive("hyphenpenalty",assign_int,int_base+hyphen_penalty_code);@/
@!@:hyphen_penalty_}{\.{\\hyphenpenalty} primitive@>
primitive("exhyphenpenalty",assign_int,int_base+ex_hyphen_penalty_code);@/
@!@:ex_hyphen_penalty_}{\.{\\exhyphenpenalty} primitive@>
primitive("clubpenalty",assign_int,int_base+club_penalty_code);@/
@!@:club_penalty_}{\.{\\clubpenalty} primitive@>
primitive("widowpenalty",assign_int,int_base+widow_penalty_code);@/
@!@:widow_penalty_}{\.{\\widowpenalty} primitive@>
primitive("displaywidowpenalty",
  assign_int,int_base+display_widow_penalty_code);@/
@!@:display_widow_penalty_}{\.{\\displaywidowpenalty} primitive@>
primitive("brokenpenalty",assign_int,int_base+broken_penalty_code);@/
@!@:broken_penalty_}{\.{\\brokenpenalty} primitive@>
primitive("binoppenalty",assign_int,int_base+bin_op_penalty_code);@/
@!@:bin_op_penalty_}{\.{\\binoppenalty} primitive@>
primitive("relpenalty",assign_int,int_base+rel_penalty_code);@/
@!@:rel_penalty_}{\.{\\relpenalty} primitive@>
primitive("predisplaypenalty",assign_int,int_base+pre_display_penalty_code);@/
@!@:pre_display_penalty_}{\.{\\predisplaypenalty} primitive@>
primitive("postdisplaypenalty",assign_int,int_base+post_display_penalty_code);@/
@!@:post_display_penalty_}{\.{\\postdisplaypenalty} primitive@>
primitive("interlinepenalty",assign_int,int_base+inter_line_penalty_code);@/
@!@:inter_line_penalty_}{\.{\\interlinepenalty} primitive@>
primitive("doublehyphendemerits",
  assign_int,int_base+double_hyphen_demerits_code);@/
@!@:double_hyphen_demerits_}{\.{\\doublehyphendemerits} primitive@>
primitive("finalhyphendemerits",
  assign_int,int_base+final_hyphen_demerits_code);@/
@!@:final_hyphen_demerits_}{\.{\\finalhyphendemerits} primitive@>
primitive("adjdemerits",assign_int,int_base+adj_demerits_code);@/
@!@:adj_demerits_}{\.{\\adjdemerits} primitive@>
primitive("mag",assign_int,int_base+mag_code);@/
@!@:mag_}{\.{\\mag} primitive@>
primitive("delimiterfactor",assign_int,int_base+delimiter_factor_code);@/
@!@:delimiter_factor_}{\.{\\delimiterfactor} primitive@>
primitive("looseness",assign_int,int_base+looseness_code);@/
@!@:looseness_}{\.{\\looseness} primitive@>
primitive("time",assign_int,int_base+time_code);@/
@!@:time_}{\.{\\time} primitive@>
primitive("day",assign_int,int_base+day_code);@/
@!@:day_}{\.{\\day} primitive@>
primitive("month",assign_int,int_base+month_code);@/
@!@:month_}{\.{\\month} primitive@>
primitive("year",assign_int,int_base+year_code);@/
@!@:year_}{\.{\\year} primitive@>
primitive("showboxbreadth",assign_int,int_base+show_box_breadth_code);@/
@!@:show_box_breadth_}{\.{\\showboxbreadth} primitive@>
primitive("showboxdepth",assign_int,int_base+show_box_depth_code);@/
@!@:show_box_depth_}{\.{\\showboxdepth} primitive@>
primitive("hbadness",assign_int,int_base+hbadness_code);@/
@!@:hbadness_}{\.{\\hbadness} primitive@>
primitive("vbadness",assign_int,int_base+vbadness_code);@/
@!@:vbadness_}{\.{\\vbadness} primitive@>
primitive("pausing",assign_int,int_base+pausing_code);@/
@!@:pausing_}{\.{\\pausing} primitive@>
primitive("tracingonline",assign_int,int_base+tracing_online_code);@/
@!@:tracing_online_}{\.{\\tracingonline} primitive@>
primitive("tracingmacros",assign_int,int_base+tracing_macros_code);@/
@!@:tracing_macros_}{\.{\\tracingmacros} primitive@>
primitive("tracingstats",assign_int,int_base+tracing_stats_code);@/
@!@:tracing_stats_}{\.{\\tracingstats} primitive@>
primitive("tracingparagraphs",assign_int,int_base+tracing_paragraphs_code);@/
@!@:tracing_paragraphs_}{\.{\\tracingparagraphs} primitive@>
primitive("tracingpages",assign_int,int_base+tracing_pages_code);@/
@!@:tracing_pages_}{\.{\\tracingpages} primitive@>
primitive("tracingoutput",assign_int,int_base+tracing_output_code);@/
@!@:tracing_output_}{\.{\\tracingoutput} primitive@>
primitive("tracinglostchars",assign_int,int_base+tracing_lost_chars_code);@/
@!@:tracing_lost_chars_}{\.{\\tracinglostchars} primitive@>
primitive("tracingcommands",assign_int,int_base+tracing_commands_code);@/
@!@:tracing_commands_}{\.{\\tracingcommands} primitive@>
primitive("tracingrestores",assign_int,int_base+tracing_restores_code);@/
@!@:tracing_restores_}{\.{\\tracingrestores} primitive@>
primitive("uchyph",assign_int,int_base+uc_hyph_code);@/
@!@:uc_hyph_}{\.{\\uchyph} primitive@>
primitive("outputpenalty",assign_int,int_base+output_penalty_code);@/
@!@:output_penalty_}{\.{\\outputpenalty} primitive@>
primitive("maxdeadcycles",assign_int,int_base+max_dead_cycles_code);@/
@!@:max_dead_cycles_}{\.{\\maxdeadcycles} primitive@>
primitive("hangafter",assign_int,int_base+hang_after_code);@/
@!@:hang_after_}{\.{\\hangafter} primitive@>
primitive("floatingpenalty",assign_int,int_base+floating_penalty_code);@/
@!@:floating_penalty_}{\.{\\floatingpenalty} primitive@>
primitive("globaldefs",assign_int,int_base+global_defs_code);@/
@!@:global_defs_}{\.{\\globaldefs} primitive@>
primitive("fam",assign_int,int_base+cur_fam_code);@/
@!@:fam_}{\.{\\fam} primitive@>
primitive("escapechar",assign_int,int_base+escape_char_code);@/
@!@:escape_char_}{\.{\\escapechar} primitive@>
primitive("defaulthyphenchar",assign_int,int_base+default_hyphen_char_code);@/
@!@:default_hyphen_char_}{\.{\\defaulthyphenchar} primitive@>
primitive("defaultskewchar",assign_int,int_base+default_skew_char_code);@/
@!@:default_skew_char_}{\.{\\defaultskewchar} primitive@>
primitive("endlinechar",assign_int,int_base+end_line_char_code);@/
@!@:end_line_char_}{\.{\\endlinechar} primitive@>
primitive("newlinechar",assign_int,int_base+new_line_char_code);@/
@!@:new_line_char_}{\.{\\newlinechar} primitive@>
primitive("language",assign_int,int_base+language_code);@/
@!@:language_}{\.{\\language} primitive@>
primitive("setlanguage",assign_int,int_base+cur_lang_code);@/
@!@:cur_lang_}{\.{\\setlanguage} primitive@>
primitive("exhyphenchar",assign_int,int_base+ex_hyphen_char_code);@/
@!@:ex_hyphen_char_}{\.{\\exhyphenchar} primitive@>
primitive("lefthyphenmin",assign_int,int_base+left_hyphen_min_code);@/
@!@:left_hyphen_min_}{\.{\\lefthyphenmin} primitive@>
primitive("righthyphenmin",assign_int,int_base+right_hyphen_min_code);@/
@!@:right_hyphen_min_}{\.{\\righthyphenmin} primitive@>
primitive("holdinginserts",assign_int,int_base+holding_inserts_code);@/
@!@:holding_inserts_}{\.{\\holdinginserts} primitive@>
primitive("errorcontextlines",assign_int,int_base+error_context_lines_code);@/
@!@:error_context_lines_}{\.{\\errorcontextlines} primitive@>
primitive("luastartup",assign_int,int_base+luastartup_id_code);@/
@!@:luastartup_id_}{\.{\\luastartup} primitive@>
primitive("nokerns",assign_int,int_base+disable_kern_code);@/
@!@:disable_kern_}{\.{\\noligkerns} primitive@>
primitive("noligs",assign_int,int_base+disable_lig_code);@/
@!@:disable_lig_}{\.{\\noligs} primitive@>
primitive("catcodetable",assign_int,int_base+cat_code_table_code);@/
@!@:cat_code_table_}{\.{\\catcodetable} primitive@>
primitive("pdfoutput",assign_int,int_base+pdf_output_code);@/
@!@:pdf_output_}{\.{\\pdfoutput} primitive@>
primitive("pdfcompresslevel",assign_int,int_base+pdf_compress_level_code);@/
@!@:pdf_compress_level_}{\.{\\pdfcompresslevel} primitive@>
primitive("pdfobjcompresslevel",assign_int,int_base+pdf_objcompresslevel_code);@/
@!@:pdf_objcompresslevel_}{\.{\\pdfobjcompresslevel} primitive@>
primitive("pdfdecimaldigits",assign_int,int_base+pdf_decimal_digits_code);@/
@!@:pdf_decimal_digits_}{\.{\\pdfdecimaldigits} primitive@>
primitive("pdfmovechars",assign_int,int_base+pdf_move_chars_code);@/
@!@:pdf_move_chars_}{\.{\\pdfmovechars} primitive@>
primitive("pdfimageresolution",assign_int,int_base+pdf_image_resolution_code);@/
@!@:pdf_image_resolution_}{\.{\\pdfimageresolution} primitive@>
primitive("pdfpkresolution",assign_int,int_base+pdf_pk_resolution_code);@/
@!@:pdf_pk_resolution_}{\.{\\pdfpkresolution} primitive@>
primitive("pdfuniqueresname",assign_int,int_base+pdf_unique_resname_code);@/
@!@:pdf_unique_resname_}{\.{\\pdfuniqueresname} primitive@>
primitive("pdfoptionpdfminorversion",assign_int,int_base+pdf_minor_version_code);@/
@!@:pdf_minor_version_}{\.{\\pdfoptionpdfminorversion} primitive@>
primitive("pdfoptionalwaysusepdfpagebox",assign_int,int_base+pdf_option_always_use_pdfpagebox_code);@/
@!@:pdf_option_always_use_pdfpagebox_}{\.{\\pdfoptionalwaysusepdfpagebox} primitive@>
primitive("pdfoptionpdfinclusionerrorlevel",assign_int,int_base+pdf_option_pdf_inclusion_errorlevel_code);@/
@!@:pdf_option_pdf_inclusion_errorlevel_}{\.{\\pdfoptionpdfinclusionerrorlevel} primitive@>
primitive("pdfminorversion",assign_int,int_base+pdf_minor_version_code);@/
@!@:pdf_minor_version_}{\.{\\pdfminorversion} primitive@>
primitive("pdfforcepagebox",assign_int,int_base+pdf_force_pagebox_code);@/
@!@:pdf_force_pagebox_}{\.{\\pdfforcepagebox} primitive@>
primitive("pdfpagebox",assign_int,int_base+pdf_pagebox_code);@/
@!@:pdf_pagebox_}{\.{\\pdfpagebox} primitive@>
primitive("pdfinclusionerrorlevel",assign_int,int_base+pdf_inclusion_errorlevel_code);@/
@!@:pdf_inclusion_errorlevel_}{\.{\\pdfinclusionerrorlevel} primitive@>
primitive("pdfgamma",assign_int,int_base+pdf_gamma_code);@/
@!@:pdf_gamma_}{\.{\\pdfgamma} primitive@>
primitive("pdfimagegamma",assign_int,int_base+pdf_image_gamma_code);@/
@!@:pdf_image_gamma_}{\.{\\pdfimagegamma} primitive@>
primitive("pdfimagehicolor",assign_int,int_base+pdf_image_hicolor_code);@/
@!@:pdf_image_hicolor_}{\.{\\pdfimagehicolor} primitive@>
primitive("pdfimageapplygamma",assign_int,int_base+pdf_image_apply_gamma_code);@/
@!@:pdf_image_apply_gamma_}{\.{\\pdfimageapplygamma} primitive@>
primitive("pdfadjustspacing",assign_int,int_base+pdf_adjust_spacing_code);@/
@!@:pdf_adjust_spacing_}{\.{\\pdfadjustspacing} primitive@>
primitive("pdfprotrudechars",assign_int,int_base+pdf_protrude_chars_code);@/
@!@:pdf_protrude_chars_}{\.{\\pdfprotrudechars} primitive@>
primitive("pdftracingfonts",assign_int,int_base+pdf_tracing_fonts_code);@/
@!@:pdf_tracing_fonts_}{\.{\\pdftracingfonts} primitive@>
primitive("pdfgentounicode",assign_int,int_base+pdf_gen_tounicode_code);@/
@!@:pdf_gen_tounicode_}{\.{\\pdfgentounicode} primitive@>
primitive("pdfdraftmode",assign_int,int_base+pdf_draftmode_code);@/
@!@:pdf_draftmode_}{\.{\\pdfdraftmode} primitive@>
primitive("pdfreplacefont",assign_int,int_base+pdf_replace_font_code);@/
@!@:pdf_replace_font_}{\.{\\pdfreplacefont} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
assign_int: if chr_code<count_base then print_param(chr_code-int_base)
  else  begin print_esc("count"); print_int(chr_code-count_base);
    end;
assign_attr: begin print_esc("attribute"); print_int(chr_code-attribute_base);
    end;

@ The integer parameters should really be initialized by a macro package;
the following initialization does the minimum to keep \TeX\ from
complete failure.
@^null delimiter@>

@<Initialize table entries...@>=
for k:=int_base to attribute_base-1 do eqtb[k].int:=0;
for k:=attribute_base to del_code_base-1 do eqtb[k].int:=-1;
mag:=1000; tolerance:=10000; hang_after:=1; max_dead_cycles:=25;
escape_char:="\"; end_line_char:=carriage_return;
eqtb[int_base+level_local_dir_code].int:=level_one;
set_del_code(".",0,0,level_one); {this null delimiter is used in error recovery}
ex_hyphen_char:="-";

@ The following procedure, which is called just before \TeX\ initializes its
input and output, establishes the initial values of the date and time.
@^system dependencies@>
Since standard \PASCAL\ cannot provide such information, something special
is needed. The program here simply specifies July 4, 1776, at noon; but
users probably want a better approximation to the truth.

@p procedure fix_date_and_time;
begin time:=12*60; {minutes since midnight}
day:=4; {fourth day of the month}
month:=7; {seventh month of the year}
year:=1776; {Anno Domini}
end;

@ @<Show equivalent |n|, in region 5@>=
begin if n<count_base then begin print_param(n-int_base);
    print_char("="); print_int(eqtb[n].int);
  end
else if n<attribute_base then
  begin print_esc("count"); print_int(n-count_base);
    print_char("="); print_int(eqtb[n].int);
  end
else if n<del_code_base then
  begin print_esc("attribute"); print_int(n-attribute_base);
    print_char("="); print_int(eqtb[n].int);
  end
else begin 
  {TH: todo, this stuff doesnt work}
  print_esc("delcode");
  end;
end

@ @<Set variable |c| to the current escape character@>=c:=escape_char

@ @<Character |s| is the current new-line character@>=s=new_line_char

@ \TeX\ is occasionally supposed to print diagnostic information that
goes only into the transcript file, unless |tracing_online| is positive.
Here are two routines that adjust the destination of print commands:

@p procedure begin_diagnostic; {prepare to do some tracing}
begin global_old_setting:=selector;
if (tracing_online<=0)and(selector=term_and_log) then
  begin decr(selector);
  if history=spotless then history:=warning_issued;
  end;
end;
@#
procedure end_diagnostic(@!blank_line:boolean);
  {restore proper conditions after tracing}
begin print_nl("");
if blank_line then print_ln;
selector:=global_old_setting;
end;

@ Of course we had better declare another global variable, if the previous
routines are going to work.

@<Glob...@>=
@!global_old_setting:0..max_selector;

@ The final region of |eqtb| contains the dimension parameters defined
here, and the |number_regs| \.{\\dimen} registers.

@d par_indent_code=0 {indentation of paragraphs}
@d math_surround_code=1 {space around math in text}
@d line_skip_limit_code=2 {threshold for |line_skip| instead of |baseline_skip|}
@d hsize_code=3 {line width in horizontal mode}
@d vsize_code=4 {page height in vertical mode}
@d max_depth_code=5 {maximum depth of boxes on main pages}
@d split_max_depth_code=6 {maximum depth of boxes on split pages}
@d box_max_depth_code=7 {maximum depth of explicit vboxes}
@d hfuzz_code=8 {tolerance for overfull hbox messages}
@d vfuzz_code=9 {tolerance for overfull vbox messages}
@d delimiter_shortfall_code=10 {maximum amount uncovered by variable delimiters}
@d null_delimiter_space_code=11 {blank space in null delimiters}
@d script_space_code=12 {extra space after subscript or superscript}
@d pre_display_size_code=13 {length of text preceding a display}
@d display_width_code=14 {length of line for displayed equation}
@d display_indent_code=15 {indentation of line for displayed equation}
@d overfull_rule_code=16 {width of rule that identifies overfull hboxes}
@d hang_indent_code=17 {amount of hanging indentation}
@d h_offset_code=18 {amount of horizontal offset when shipping pages out}
@d v_offset_code=19 {amount of vertical offset when shipping pages out}
@d emergency_stretch_code=20 {reduces badnesses on final pass of line-breaking}
@d page_right_offset_code=21
@d page_bottom_offset_code=22
@d pdftex_first_dimen_code = 23 {first number defined in this section}
@d pdf_h_origin_code       = pdftex_first_dimen_code + 0 {horigin of the PDF output}
@d pdf_v_origin_code       = pdftex_first_dimen_code + 1 {vorigin of the PDF output}
@d page_width_code         = pdftex_first_dimen_code + 2 {page width of the PDF output}
@d page_height_code        = pdftex_first_dimen_code + 3 {page height of the PDF output}
@d pdf_link_margin_code    = pdftex_first_dimen_code + 4 {link margin in the PDF output}
@d pdf_dest_margin_code    = pdftex_first_dimen_code + 5 {dest margin in the PDF output}
@d pdf_thread_margin_code  = pdftex_first_dimen_code + 6 {thread margin in the PDF output}
@d pdf_first_line_height_code = pdftex_first_dimen_code + 7
@d pdf_last_line_depth_code   = pdftex_first_dimen_code + 8
@d pdf_each_line_height_code  = pdftex_first_dimen_code + 9
@d pdf_each_line_depth_code   = pdftex_first_dimen_code + 10
@d pdf_px_dimen_code       = pdftex_first_dimen_code + 11
@d pdftex_last_dimen_code  = pdftex_first_dimen_code + 11 {last number defined in this section}
@d dimen_pars = pdftex_last_dimen_code + 1 {total number of dimension parameters}
@d scaled_base=dimen_base+dimen_pars
  {table of |number_regs| user-defined \.{\\dimen} registers}
@d eqtb_size=scaled_base+biggest_reg {largest subscript of |eqtb|}
@#
@d dimen(#)==eqtb[scaled_base+#].sc
@d dimen_par(#)==eqtb[dimen_base+#].sc {a scaled quantity}
@d par_indent==dimen_par(par_indent_code)
@d math_surround==dimen_par(math_surround_code)
@d line_skip_limit==dimen_par(line_skip_limit_code)
@d hsize==dimen_par(hsize_code)
@d vsize==dimen_par(vsize_code)
@d max_depth==dimen_par(max_depth_code)
@d split_max_depth==dimen_par(split_max_depth_code)
@d box_max_depth==dimen_par(box_max_depth_code)
@d hfuzz==dimen_par(hfuzz_code)
@d vfuzz==dimen_par(vfuzz_code)
@d delimiter_shortfall==dimen_par(delimiter_shortfall_code)
@d null_delimiter_space==dimen_par(null_delimiter_space_code)
@d script_space==dimen_par(script_space_code)
@d pre_display_size==dimen_par(pre_display_size_code)
@d display_width==dimen_par(display_width_code)
@d display_indent==dimen_par(display_indent_code)
@d overfull_rule==dimen_par(overfull_rule_code)
@d hang_indent==dimen_par(hang_indent_code)
@d h_offset==dimen_par(h_offset_code)
@d v_offset==dimen_par(v_offset_code)
@d emergency_stretch==dimen_par(emergency_stretch_code)
@d page_right_offset==dimen_par(page_right_offset_code)
@d page_bottom_offset==dimen_par(page_bottom_offset_code)
@d pdf_h_origin      == dimen_par(pdf_h_origin_code)
@d pdf_v_origin      == dimen_par(pdf_v_origin_code)
@d page_width    == dimen_par(page_width_code)
@d page_height   == dimen_par(page_height_code)
@d pdf_link_margin   == dimen_par(pdf_link_margin_code)
@d pdf_dest_margin   == dimen_par(pdf_dest_margin_code)
@d pdf_thread_margin == dimen_par(pdf_thread_margin_code)
@d pdf_first_line_height == dimen_par(pdf_first_line_height_code)
@d pdf_last_line_depth   == dimen_par(pdf_last_line_depth_code)
@d pdf_each_line_height  == dimen_par(pdf_each_line_height_code)
@d pdf_each_line_depth   == dimen_par(pdf_each_line_depth_code)
@d pdf_px_dimen      == dimen_par(pdf_px_dimen_code)

@p procedure print_length_param(@!n:integer);
begin case n of
par_indent_code:print_esc("parindent");
math_surround_code:print_esc("mathsurround");
line_skip_limit_code:print_esc("lineskiplimit");
hsize_code:print_esc("hsize");
vsize_code:print_esc("vsize");
max_depth_code:print_esc("maxdepth");
split_max_depth_code:print_esc("splitmaxdepth");
box_max_depth_code:print_esc("boxmaxdepth");
hfuzz_code:print_esc("hfuzz");
vfuzz_code:print_esc("vfuzz");
delimiter_shortfall_code:print_esc("delimitershortfall");
null_delimiter_space_code:print_esc("nulldelimiterspace");
script_space_code:print_esc("scriptspace");
pre_display_size_code:print_esc("predisplaysize");
display_width_code:print_esc("displaywidth");
display_indent_code:print_esc("displayindent");
overfull_rule_code:print_esc("overfullrule");
hang_indent_code:print_esc("hangindent");
h_offset_code:print_esc("hoffset");
v_offset_code:print_esc("voffset");
emergency_stretch_code:print_esc("emergencystretch");
page_right_offset_code:print_esc("pagerightoffset");
page_bottom_offset_code:print_esc("pagebottomoffset");
pdf_h_origin_code:      print_esc("pdfhorigin");
pdf_v_origin_code:      print_esc("pdfvorigin");
page_width_code:    print_esc("pagewidth");
page_height_code:   print_esc("pageheight");
pdf_link_margin_code:   print_esc("pdflinkmargin");
pdf_dest_margin_code:   print_esc("pdfdestmargin");
pdf_thread_margin_code: print_esc("pdfthreadmargin");
pdf_first_line_height_code: print_esc("pdffirstlineheight");
pdf_last_line_depth_code: print_esc("pdflastlinedepth");
pdf_each_line_height_code: print_esc("pdfeachlineheight");
pdf_each_line_depth_code: print_esc("pdfeachlinedepth");
pdf_px_dimen_code:      print_esc("pdfpxdimen");
othercases print("[unknown dimen parameter!]")
endcases;
end;

@ @<Put each...@>=
primitive("parindent",assign_dimen,dimen_base+par_indent_code);@/
@!@:par_indent_}{\.{\\parindent} primitive@>
primitive("mathsurround",assign_dimen,dimen_base+math_surround_code);@/
@!@:math_surround_}{\.{\\mathsurround} primitive@>
primitive("lineskiplimit",assign_dimen,dimen_base+line_skip_limit_code);@/
@!@:line_skip_limit_}{\.{\\lineskiplimit} primitive@>
primitive("hsize",assign_dimen,dimen_base+hsize_code);@/
@!@:hsize_}{\.{\\hsize} primitive@>
primitive("vsize",assign_dimen,dimen_base+vsize_code);@/
@!@:vsize_}{\.{\\vsize} primitive@>
primitive("maxdepth",assign_dimen,dimen_base+max_depth_code);@/
@!@:max_depth_}{\.{\\maxdepth} primitive@>
primitive("splitmaxdepth",assign_dimen,dimen_base+split_max_depth_code);@/
@!@:split_max_depth_}{\.{\\splitmaxdepth} primitive@>
primitive("boxmaxdepth",assign_dimen,dimen_base+box_max_depth_code);@/
@!@:box_max_depth_}{\.{\\boxmaxdepth} primitive@>
primitive("hfuzz",assign_dimen,dimen_base+hfuzz_code);@/
@!@:hfuzz_}{\.{\\hfuzz} primitive@>
primitive("vfuzz",assign_dimen,dimen_base+vfuzz_code);@/
@!@:vfuzz_}{\.{\\vfuzz} primitive@>
primitive("delimitershortfall",
  assign_dimen,dimen_base+delimiter_shortfall_code);@/
@!@:delimiter_shortfall_}{\.{\\delimitershortfall} primitive@>
primitive("nulldelimiterspace",
  assign_dimen,dimen_base+null_delimiter_space_code);@/
@!@:null_delimiter_space_}{\.{\\nulldelimiterspace} primitive@>
primitive("scriptspace",assign_dimen,dimen_base+script_space_code);@/
@!@:script_space_}{\.{\\scriptspace} primitive@>
primitive("predisplaysize",assign_dimen,dimen_base+pre_display_size_code);@/
@!@:pre_display_size_}{\.{\\predisplaysize} primitive@>
primitive("displaywidth",assign_dimen,dimen_base+display_width_code);@/
@!@:display_width_}{\.{\\displaywidth} primitive@>
primitive("displayindent",assign_dimen,dimen_base+display_indent_code);@/
@!@:display_indent_}{\.{\\displayindent} primitive@>
primitive("overfullrule",assign_dimen,dimen_base+overfull_rule_code);@/
@!@:overfull_rule_}{\.{\\overfullrule} primitive@>
primitive("hangindent",assign_dimen,dimen_base+hang_indent_code);@/
@!@:hang_indent_}{\.{\\hangindent} primitive@>
primitive("hoffset",assign_dimen,dimen_base+h_offset_code);@/
@!@:h_offset_}{\.{\\hoffset} primitive@>
primitive("voffset",assign_dimen,dimen_base+v_offset_code);@/
@!@:v_offset_}{\.{\\voffset} primitive@>
primitive("emergencystretch",assign_dimen,dimen_base+emergency_stretch_code);@/
@!@:emergency_stretch_}{\.{\\emergencystretch} primitive@>
primitive("pdfhorigin",assign_dimen,dimen_base+pdf_h_origin_code);@/
@!@:pdf_h_origin_}{\.{\\pdfhorigin} primitive@>
primitive("pdfvorigin",assign_dimen,dimen_base+pdf_v_origin_code);@/
@!@:pdf_v_origin_}{\.{\\pdfvorigin} primitive@>
@#
primitive("pagewidth",assign_dimen,dimen_base+page_width_code);@/
primitive("pdfpagewidth",assign_dimen,dimen_base+page_width_code);@/
@!@:page_width_}{\.{\\pdfpagewidth} primitive@>
primitive("pageheight",assign_dimen,dimen_base+page_height_code);@/
primitive("pdfpageheight",assign_dimen,dimen_base+page_height_code);@/
@!@:page_height_}{\.{\\pdfpageheight} primitive@>
@#
primitive("pdflinkmargin",assign_dimen,dimen_base+pdf_link_margin_code);@/
@!@:pdf_link_margin_}{\.{\\pdflinkmargin} primitive@>
primitive("pdfdestmargin",assign_dimen,dimen_base+pdf_dest_margin_code);@/
@!@:pdf_dest_margin_}{\.{\\pdfdestmargin} primitive@>
primitive("pdfthreadmargin",assign_dimen,dimen_base+pdf_thread_margin_code);@/
@!@:pdf_thread_margin_}{\.{\\pdfthreadmargin} primitive@>
primitive("pdffirstlineheight",assign_dimen,dimen_base+pdf_first_line_height_code);@/
@!@:pdf_first_line_height_}{\.{\\pdffirstlineheight} primitive@>
primitive("pdflastlinedepth",assign_dimen,dimen_base+pdf_last_line_depth_code);@/
@!@:pdf_last_line_depth_}{\.{\\pdflastlinedepth} primitive@>
primitive("pdfeachlineheight",assign_dimen,dimen_base+pdf_each_line_height_code);@/
@!@:pdf_each_line_height_}{\.{\\pdfeachlineheight} primitive@>
primitive("pdfeachlinedepth",assign_dimen,dimen_base+pdf_each_line_depth_code);@/
@!@:pdf_each_line_depth_}{\.{\\pdfeachlinedepth} primitive@>
primitive("pdfpxdimen",assign_dimen,dimen_base+pdf_px_dimen_code);@/
@!@:pdf_px_dimen_}{\.{\\pdfpxdimen} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
assign_dimen: if chr_code<scaled_base then
    print_length_param(chr_code-dimen_base)
  else  begin print_esc("dimen"); print_int(chr_code-scaled_base);
    end;

@ @<Initialize table entries...@>=
for k:=dimen_base to eqtb_size do eqtb[k].sc:=0;

@ @<Show equivalent |n|, in region 6@>=
begin if n<scaled_base then print_length_param(n-dimen_base)
else  begin print_esc("dimen"); print_int(n-scaled_base);
  end;
print_char("="); print_scaled(eqtb[n].sc); print("pt");
end

@ Here is a procedure that displays the contents of |eqtb[n]|
symbolically.

@p@t\4@>@<Declare the procedure called |print_cmd_chr|@>@;@/
@!stat procedure show_eqtb(@!n:pointer);
begin if n<active_base then print_char("?") {this can't happen}
else if n<glue_base then @<Show equivalent |n|, in region 1 or 2@>
else if n<local_base then @<Show equivalent |n|, in region 3@>
else if n<int_base then @<Show equivalent |n|, in region 4@>
else if n<dimen_base then @<Show equivalent |n|, in region 5@>
else if n<=eqtb_size then @<Show equivalent |n|, in region 6@>
else print_char("?"); {this can't happen either}
end;
tats

@ The last two regions of |eqtb| have fullword values instead of the
three fields |eq_level|, |eq_type|, and |equiv|. An |eq_type| is unnecessary,
but \TeX\ needs to store the |eq_level| information in another array
called |xeq_level|.

@<Glob...@>=
@!eqtb:array[active_base..eqtb_size] of memory_word;
@!xeq_level:array[int_base..eqtb_size] of quarterword;

@ @<Set init...@>=
for k:=int_base to eqtb_size do xeq_level[k]:=level_one;

@* \[18] The hash table.
Control sequences are stored and retrieved by means of a fairly standard hash
table algorithm called the method of ``coalescing lists'' (cf.\ Algorithm 6.4C
in {\sl The Art of Computer Programming\/}). Once a control sequence enters the
table, it is never removed, because there are complicated situations
involving \.{\\gdef} where the removal of a control sequence at the end of
a group would be a mistake preventable only by the introduction of a
complicated reference-count mechanism.

The actual sequence of letters forming a control sequence identifier is
stored in the |str_pool| array together with all the other strings. An
auxiliary array |hash| consists of items with two halfword fields per
word. The first of these, called |next(p)|, points to the next identifier
belonging to the same coalesced list as the identifier corresponding to~|p|;
and the other, called |text(p)|, points to the |str_start| entry for
|p|'s identifier. If position~|p| of the hash table is empty, we have
|text(p)=0|; if position |p| is either empty or the end of a coalesced
hash list, we have |next(p)=0|. An auxiliary pointer variable called
|hash_used| is maintained in such a way that all locations |p>=hash_used|
are nonempty. The global variable |cs_count| tells how many multiletter
control sequences have been defined, if statistics are being kept.

A global boolean variable called |no_new_control_sequence| is set to
|true| during the time that new hash table entries are forbidden.

@d next(#) == hash[#].lh {link for coalesced lists}
@d text(#) == hash[#].rh {string number for control sequence name}
@d hash_is_full == (hash_used=hash_base) {test if all positions are occupied}
@d font_id_text(#) == text(font_id_base+#) {a frozen font identifier's name}
@d ocp_id_text(#) == text(ocp_id_base+#) {a frozen ocp identifier's name}
@d ocp_list_id_text(#) == text(ocp_list_id_base+#) 
   {a frozen ocp list identifier's name}

@<Glob...@>=
@!hash: array[hash_base..undefined_control_sequence-1] of two_halves;
  {the hash table}
@!hash_used:pointer; {allocation pointer for |hash|}
@!no_new_control_sequence:boolean; {are new identifiers legal?}
@!cs_count:integer; {total number of known identifiers}

@ Primitive support needs a few extra variables and definitions

@d prim_size=2100 {maximum number of primitives }
@d prim_prime=1777 {about 85\pct! of |primitive_size|}
@d prim_base=1
@d prim_next(#) == prim[#].lh {link for coalesced lists}
@d prim_text(#) == prim[#].rh {string number for control sequence name}
@d prim_is_full == (prim_used=prim_base) {test if all positions are occupied}
@d prim_eq_level_field(#)==#.hh.b1
@d prim_eq_type_field(#)==#.hh.b0
@d prim_equiv_field(#)==#.hh.rh
@d prim_eq_level(#)==prim_eq_level_field(prim_eqtb[#]) {level of definition}
@d prim_eq_type(#)==prim_eq_type_field(prim_eqtb[#]) {command code for equivalent}
@d prim_equiv(#)==prim_equiv_field(prim_eqtb[#]) {equivalent value}
@d undefined_primitive=0

@<Glob...@>=
@!prim: array [0..prim_size] of two_halves;  {the primitives table}
@!prim_used:pointer; {allocation pointer for |prim|}
@!prim_eqtb:array[0..prim_size] of memory_word;

@ The extra set of functions make sure we can query the
primitive meanings of thing s from C code

@p 
function get_char_cat_code(c:integer):quarterword;
begin
  if local_catcode_table then 
     get_char_cat_code:=get_cat_code(line_catcode_table,c) 
  else 
     get_char_cat_code:=get_cat_code(cat_code_table,c)
end;
function get_prim_eq_level(p:integer):quarterword;
begin
  get_prim_eq_level := prim_eq_level(p);
end;
function get_prim_eq_type(p:integer):quarterword;
begin
  get_prim_eq_type := prim_eq_type(p);
end;
function get_prim_equiv(p:integer):halfword;
begin
  get_prim_equiv := prim_equiv(p);
end;
function get_eq_type(p:integer):quarterword;
begin
  get_eq_type := eq_type(p);
end;
function get_eq_level(p:integer):quarterword;
begin
  get_eq_level := eq_level(p);
end;
function is_undefined_cs(cs:integer):boolean;
begin
  is_undefined_cs := (cs=undefined_cs);
end;
function get_equiv(p:integer):halfword;
begin
  get_equiv := equiv(p);
end;
function get_cs_text(cs:integer):str_number;
begin if cs<hash_base then
    if cs<null_cs then get_cs_text := cs-active_base
      else  get_cs_text := "\csname\endcsname"
  else if (text(cs)<0)or(text(cs)>=str_ptr) then get_cs_text := ""
  else get_cs_text := text(cs);
end;
function get_max_command:integer;
begin
  get_max_command := max_command;
end;
function get_count_base:halfword;
begin
  get_count_base := count_base;
end;
function get_attribute_base:halfword;
begin
  get_attribute_base := attribute_base;
end;
function get_scaled_base:halfword;
begin
  get_scaled_base := scaled_base;
end;
function get_int_base:halfword;
begin
  get_int_base := int_base;
end;
function get_toks_base:halfword;
begin
  get_toks_base := toks_base;
end;
function get_every_eof:halfword;
begin
  get_every_eof := every_eof;
end;
function get_suppress_fontnotfound_error:boolean;
begin
  get_suppress_fontnotfound_error := suppress_fontnotfound_error;
end;
function get_pdf_image_resolution:integer;
begin
  get_pdf_image_resolution := pdf_image_resolution;
end;
function get_pdf_minor_version:integer;
begin
  get_pdf_minor_version := pdf_minor_version;
end;
function get_pdf_inclusion_errorlevel:integer;
begin
  get_pdf_inclusion_errorlevel := pdf_inclusion_errorlevel;
end;

@ @<Set init...@>=
no_new_control_sequence:=true; {new identifiers are usually forbidden}
prim_next(0):=0; prim_text(0):=0;
for k:=1 to prim_size do prim[k]:=prim[0];
prim_eq_level(0) := level_zero;
prim_eq_type(0) := undefined_cs;
prim_equiv(0) := null;
for k:=1 to prim_size do prim_eqtb[k]:=prim_eqtb[0];
next(hash_base):=0; text(hash_base):=0;
for k:=hash_base+1 to undefined_control_sequence-1 do hash[k]:=hash[hash_base];

@ @<Initialize table entries...@>=
prim_used:=prim_size; {nothing is used}
hash_used:=frozen_control_sequence; {nothing is used}
cs_count:=0;
eq_type(frozen_dont_expand):=dont_expand;
text(frozen_dont_expand):="notexpanded:";
@.notexpanded:@>

eq_type(frozen_primitive):=ignore_spaces;
equiv(frozen_primitive):=1;
eq_level(frozen_primitive):=level_one;
text(frozen_primitive):="primitive";

@ Here is the subroutine that searches the hash table for an identifier
that matches a given string of length |l>1| appearing in |buffer[j..
(j+l-1)]|. If the identifier is found, the corresponding hash table address
is returned. Otherwise, if the global variable |no_new_control_sequence|
is |true|, the dummy address |undefined_control_sequence| is returned.
Otherwise the identifier is inserted into the hash table and its location
is returned.

@p function id_lookup(@!j,@!l:integer):pointer; {search the hash table}
label found; {go here if you found it}
var h:integer; {hash code}
@!d:integer; {number of characters in incomplete current string}
@!p:pointer; {index in |hash| array}
@!k:pointer; {index in |buffer| array}
begin @<Compute the hash code |h|@>;
p:=h+hash_base; {we start searching here; note that |0<=h<hash_prime|}
loop@+begin if text(p)>0 then if length(text(p))=l then
  if str_eq_buf(text(p),j) then goto found;
  if next(p)=0 then
    begin if no_new_control_sequence then
      p:=undefined_control_sequence
    else @<Insert a new control sequence after |p|, then make
      |p| point to it@>;
    goto found;
    end;
  p:=next(p);
  end;
found: id_lookup:=p;
end;

@ @<Insert a new control...@>=
begin if text(p)>0 then
  begin repeat if hash_is_full then overflow("hash size",hash_size);
@:TeX capacity exceeded hash size}{\quad hash size@>
  decr(hash_used);
  until text(hash_used)=0; {search for an empty location in |hash|}
  next(p):=hash_used; p:=hash_used;
  end;
str_room(l); d:=cur_length;
while pool_ptr>str_start_macro(str_ptr) do
  begin decr(pool_ptr); str_pool[pool_ptr+l]:=str_pool[pool_ptr];
  end; {move current string up to make room for another}
for k:=j to j+l-1 do append_char(buffer[k]);
text(p):=make_string; pool_ptr:=pool_ptr+d; 
@!stat incr(cs_count);@+tats@;@/
end

@ The value of |hash_prime| should be roughly 85\pct! of |hash_size|, and it
should be a prime number.  The theory of hashing tells us to expect fewer
than two table probes, on the average, when the search is successful.
[See J.~S. Vitter, {\sl Journal of the ACM\/ \bf30} (1983), 231--258.]
@^Vitter, Jeffrey Scott@>

@<Compute the hash code |h|@>=
h:=buffer[j];
for k:=j+1 to j+l-1 do
  begin h:=h+h+buffer[k];
  while h>=hash_prime do h:=h-hash_prime;
  end

@ Here is the subroutine that searches the primitive table for an identifier

@p function prim_lookup(@!s:str_number):pointer; {search the primitives table}
label found; {go here if you found it}
var h:integer; {hash code}
@!p:pointer; {index in |hash| array}
@!k:pointer; {index in string pool}
@!the_hash_prime:halfword;
@!j,@!l:integer;
begin
the_hash_prime:= prim_prime;
if s<string_offset then begin
  p := s;
  if (p<0) or (get_prim_eq_level(p)<>level_one) then
    p := undefined_primitive;
end
else begin
  j:=str_start_macro(s);
  if s = str_ptr then l := cur_length else l := length(s);
  @<Compute the string hash code |h|@>;
  p:=h+prim_base; {we start searching here; note that |0<=h<hash_prime|}
  loop@+begin if prim_text(p)>0 then if length(prim_text(p))=l then
    if str_eq_str(prim_text(p),s) then goto found;
    if prim_next(p)=0 then
      begin if no_new_control_sequence then
        p:=undefined_primitive
      else @<Insert a new primitive after |p|, then make
        |p| point to it@>;
      goto found;
      end;
    p:=prim_next(p);
    end;
  end;
found: prim_lookup:=p;
end;

function string_lookup(@!s:str_number):pointer; {search the primitives table}
label found; {go here if you found it}
var h:integer; {hash code}
@!p:pointer; {index in |hash| array}
@!k:pointer; {index in string pool}
@!the_hash_prime: halfword;
@!j,@!l:integer;
begin
the_hash_prime := hash_prime;
if s<string_offset then begin
  p := s;
  if (p<0) or (eq_level(p)<>level_one) then
    p := undefined_cs;
end
else begin
  j:=str_start_macro(s);
  if s = str_ptr then l := cur_length else l := length(s);
  @<Compute the string hash code |h|@>;
  p:=h+hash_base; {we start searching here; note that |0<=h<hash_prime|}
  loop@+begin if text(p)>0 then if length(text(p))=l then
    if str_eq_str(text(p),s) then goto found;
    if next(p)=0 then
      begin 
     	p:=undefined_cs ;
        goto found;
      end;
    p:=next(p);
    end;
  end;
found: string_lookup:=p;
end;

function is_primitive(csname:str_number):boolean;
  var n,m:integer;
begin
  m := prim_lookup(csname);
  n := string_lookup(csname);
  is_primitive :=((n<>undefined_cs) and
       (m<>undefined_primitive) and
       (eq_type(n)=get_prim_eq_type(m)) and
       (equiv(n)=get_prim_equiv(m)));
end;

@ @<Insert a new primitive...@>=
begin if prim_text(p)>0 then
  begin repeat if prim_is_full then overflow("primitive size",prim_size);
@:TeX capacity exceeded primitive size}{\quad primitive size@>
  decr(prim_used);
  until prim_text(prim_used)=0; {search for an empty location in |prim|}
  prim_next(p):=prim_used; p:=prim_used;
  end;
prim_text(p):=s;
end

@ The value of |prim_prime| should be roughly 85\pct! of
|prim_size|, and it should be a prime number.

@<Compute the string hash code |h|@>=
h:=str_pool[j];
for k:=j+1 to j+l-1 do
  begin h:=h+h+str_pool[k];
  while h>=the_hash_prime do h:=h-the_hash_prime;
  end


@ The procedure |print_cs| prints the name of a control sequence, given
a pointer to its address in |eqtb|. A space is printed after the name
unless it is a single nonletter or an active character. This procedure
might be invoked with invalid data, so it is ``extra robust.'' The
individual characters must be printed one at a time using |print|, since
they may be unprintable.

@d single_letter(#)==(length(#)=1)or
   ((length(#)=4)and(str_pool[str_start_macro(#)]>=@"F0))or
   ((length(#)=3)and(str_pool[str_start_macro(#)]>=@"E0))or
   ((length(#)=2)and(str_pool[str_start_macro(#)]>=@"C0))

@<Basic printing...@>=
procedure print_cs(@!p:integer); {prints a purported control sequence}
begin if p<hash_base then {single character}
  if p=null_cs then
    begin print_esc("csname"); print_esc("endcsname");
    end
  else if p<active_base then print_esc("IMPOSSIBLE.")
@.IMPOSSIBLE@>
  else print(p-active_base)
else if p>=undefined_control_sequence then print_esc("IMPOSSIBLE.")
else if (text(p)<0)or(text(p)>=str_ptr) then print_esc("NONEXISTENT.")
@.NONEXISTENT@>
else  begin 
  print_esc(text(p));
  if single_letter(text(p)) then begin
   	if get_cat_code(cat_code_table,pool_to_unichar(str_start_macro(text(p))))=letter then
      print_char(" ")
    else
      do_nothing;
    end
  else
    print_char(" ");
  end;
end;

@ Here is a similar procedure; it avoids the error checks, and it never
prints a space after the control sequence.

@<Basic printing procedures@>=
procedure sprint_cs(@!p:pointer); {prints a control sequence}
begin if p<hash_base then
  if p<null_cs then print(p-active_base)
  else  begin print_esc("csname"); print_esc("endcsname");
    end
else print_esc(text(p));
end;

@ We need to put \TeX's ``primitive'' control sequences into the hash
table, together with their command code (which will be the |eq_type|)
and an operand (which will be the |equiv|). The |primitive| procedure
does this, in a way that no \TeX\ user can. The global value |cur_val|
contains the new |eqtb| pointer after |primitive| has acted.

@p @!init procedure primitive(@!ss:str_number;@!c:quarterword;@!o:halfword);
var k:pool_pointer; {index into |str_pool|}
@!s:str_number; {actual |str_number| used }
@!j:0..buf_size; {index into |buffer|}
@!l:small_number; {length of the string}
@!prim_val:integer; {needed to fill |prim_eqtb|}
begin if ss<number_chars then begin
  if ss>127 then confusion("prim"); { should be ASCII }
  append_char(ss); 
  s:=make_string;
  end
else
  s:=ss;
k:=str_start_macro(s); l:=str_start_macro(s+1)-k;
    {we will move |s| into the (possibly non-empty) |buffer|}
if first+l>buf_size+1 then
  check_buffer_overflow(first+l);
@:TeX capacity exceeded buffer size}{\quad buffer size@>
for j:=0 to l-1 do buffer[first+j]:=so(str_pool[k+j]);
cur_val:=id_lookup(first,l); {|no_new_control_sequence| is |false|}
flush_string; text(cur_val):=s; {we don't want to have the string twice}
prim_val:=prim_lookup(s);
eq_level(cur_val):=level_one; eq_type(cur_val):=c; equiv(cur_val):=o;
prim_eq_level(prim_val) := level_one;
prim_eq_type(prim_val) := c;
prim_equiv(prim_val) := o;
end;
tini

@ Many of \TeX's primitives need no |equiv|, since they are identifiable
by their |eq_type| alone. These primitives are loaded into the hash table
as follows:

@<Put each of \TeX's primitives into the hash table@>=
primitive(" ",ex_space,0);@/
@!@:Single-character primitives /}{\quad\.{\\\ }@>
primitive("/",ital_corr,0);@/
@!@:Single-character primitives /}{\quad\.{\\/}@>
primitive("accent",accent,0);@/
@!@:accent_}{\.{\\accent} primitive@>
primitive("advance",advance,0);@/
@!@:advance_}{\.{\\advance} primitive@>
primitive("afterassignment",after_assignment,0);@/
@!@:after_assignment_}{\.{\\afterassignment} primitive@>
primitive("aftergroup",after_group,0);@/
@!@:after_group_}{\.{\\aftergroup} primitive@>
primitive("begingroup",begin_group,0);@/
@!@:begin_group_}{\.{\\begingroup} primitive@>
primitive("char",char_num,0);@/
@!@:char_}{\.{\\char} primitive@>
primitive("csname",cs_name,0);@/
@!@:cs_name_}{\.{\\csname} primitive@>
primitive("delimiter",delim_num,0);@/
@!@:delimiter_}{\.{\\delimiter} primitive@>
primitive("odelimiter",delim_num,1);@/
@!@:odelimiter_}{\.{\\odelimiter} primitive@>
primitive("divide",divide,0);@/
@!@:divide_}{\.{\\divide} primitive@>
primitive("endcsname",end_cs_name,0);@/
@!@:end_cs_name_}{\.{\\endcsname} primitive@>
primitive("endgroup",end_group,0);
@!@:end_group_}{\.{\\endgroup} primitive@>
text(frozen_end_group):="endgroup"; eqtb[frozen_end_group]:=eqtb[cur_val];@/
primitive("expandafter",expand_after,0);@/
@!@:expand_after_}{\.{\\expandafter} primitive@>
primitive("font",def_font,0);@/
@!@:font_}{\.{\\font} primitive@>
primitive("letterspacefont",letterspace_font,0);@/
@!@:letterspace_font_}{\.{\\letterspacefont} primitive@>
primitive("fontdimen",assign_font_dimen,0);@/
@!@:font_dimen_}{\.{\\fontdimen} primitive@>
primitive("halign",halign,0);@/
@!@:halign_}{\.{\\halign} primitive@>
primitive("hrule",hrule,0);@/
@!@:hrule_}{\.{\\hrule} primitive@>
primitive("ignorespaces",ignore_spaces,0);@/
@!@:ignore_spaces_}{\.{\\ignorespaces} primitive@>
primitive("insert",insert,0);@/
@!@:insert_}{\.{\\insert} primitive@>
primitive("leftghost",char_ghost,0);@/
@!@:leftghost_}{\.{\\leftghost} primitive@>
primitive("mark",mark,0);@/
@!@:mark_}{\.{\\mark} primitive@>
primitive("mathaccent",math_accent,0);@/
@!@:math_accent_}{\.{\\mathaccent} primitive@>
primitive("mathchar",math_char_num,0);@/
@!@:math_char_}{\.{\\mathchar} primitive@>
primitive("omathaccent",math_accent,1);@/
@!@:math_accent_}{\.{\\omathaccent} primitive@>
primitive("omathchar",math_char_num,1);@/
@!@:math_char_}{\.{\\omathchar} primitive@>
primitive("mathchoice",math_choice,0);@/
@!@:math_choice_}{\.{\\mathchoice} primitive@>
primitive("multiply",multiply,0);@/
@!@:multiply_}{\.{\\multiply} primitive@>
primitive("noalign",no_align,0);@/
@!@:no_align_}{\.{\\noalign} primitive@>
primitive("noboundary",no_boundary,0);@/
@!@:no_boundary_}{\.{\\noboundary} primitive@>
primitive("noexpand",no_expand,0);@/
@!@:no_expand_}{\.{\\noexpand} primitive@>
primitive("primitive",no_expand,1);@/
@!@:primitive_}{\.{\\primitive} primitive@>
primitive("pdfprimitive",no_expand,1);@/
@!@:pdfprimitive_}{\.{\\pdfprimitive} primitive@>
primitive("nonscript",non_script,0);@/
@!@:non_script_}{\.{\\nonscript} primitive@>
primitive("omit",omit,0);@/
@!@:omit_}{\.{\\omit} primitive@>
primitive("parshape",set_shape,par_shape_loc);@/
@!@:par_shape_}{\.{\\parshape} primitive@>
primitive("penalty",break_penalty,0);@/
@!@:penalty_}{\.{\\penalty} primitive@>
primitive("prevgraf",set_prev_graf,0);@/
@!@:prev_graf_}{\.{\\prevgraf} primitive@>
primitive("radical",radical,0);@/
@!@:radical_}{\.{\\radical} primitive@>
primitive("oradical",radical,1);@/
@!@:radical_}{\.{\\oradical} primitive@>
primitive("read",read_to_cs,0);@/
@!@:read_}{\.{\\read} primitive@>
primitive("relax",relax,too_big_char);
@!@:relax_}{\.{\\relax} primitive@>
text(frozen_relax):="relax"; eqtb[frozen_relax]:=eqtb[cur_val];@/
primitive("rightghost",char_ghost,1);@/
@!@:rightghost_}{\.{\\rightghost} primitive@>
primitive("setbox",set_box,0);@/
@!@:set_box_}{\.{\\setbox} primitive@>
primitive("the",the,0);@/
@!@:the_}{\.{\\the} primitive@>
primitive("toks",toks_register,0);@/
@!@:toks_}{\.{\\toks} primitive@>
primitive("vadjust",vadjust,0);@/
@!@:vadjust_}{\.{\\vadjust} primitive@>
primitive("valign",valign,0);@/
@!@:valign_}{\.{\\valign} primitive@>
primitive("vcenter",vcenter,0);@/
@!@:vcenter_}{\.{\\vcenter} primitive@>
primitive("vrule",vrule,0);@/
@!@:vrule_}{\.{\\vrule} primitive@>

@ Each primitive has a corresponding inverse, so that it is possible to
display the cryptic numeric contents of |eqtb| in symbolic form.
Every call of |primitive| in this program is therefore accompanied by some
straightforward code that forms part of the |print_cmd_chr| routine
below.

@<Cases of |print_cmd_chr|...@>=
accent: print_esc("accent");
advance: print_esc("advance");
after_assignment: print_esc("afterassignment");
after_group: print_esc("aftergroup");
assign_font_dimen: print_esc("fontdimen");
begin_group: print_esc("begingroup");
break_penalty: print_esc("penalty");
char_num: print_esc("char");
char_ghost: if cur_chr=0 then print_esc("leftghost")
  else print_esc("rightghost");
cs_name: print_esc("csname");
def_font: print_esc("font");
letterspace_font: print_esc("letterspacefont");
delim_num: if chr_code=0 then print_esc("delimiter") else print_esc("odelimiter") ;
divide: print_esc("divide");
end_cs_name: print_esc("endcsname");
end_group: print_esc("endgroup");
ex_space: print_esc(" ");
expand_after: if chr_code=0 then print_esc("expandafter")
  @<Cases of |expandafter| for |print_cmd_chr|@>;
halign: print_esc("halign");
hrule: print_esc("hrule");
ignore_spaces: if chr_code=0 then print_esc("ignorespaces") else print_esc("primitive");
insert: print_esc("insert");
ital_corr: print_esc("/");
mark: begin
  if chr_code=0 then print_esc("mark")
  else if chr_code=1 then print_esc("clearmarks")
  else print_esc("marks");
  end;
math_accent: if chr_code=0 then print_esc("mathaccent") else print_esc("omathaccent");
math_char_num: if chr_code=0 then print_esc("mathchar") else print_esc("omathchar");
math_choice: print_esc("mathchoice");
multiply: print_esc("multiply");
no_align: print_esc("noalign");
no_boundary:print_esc("noboundary");
no_expand: if chr_code=0 then print_esc("noexpand")
   else print_esc("primitive");
non_script: print_esc("nonscript");
omit: print_esc("omit");
radical: if chr_code=0 then print_esc("radical") else print_esc("oradical");
read_to_cs: if chr_code=0 then print_esc("read")
  @<Cases of |read| for |print_cmd_chr|@>;
relax: print_esc("relax");
set_box: print_esc("setbox");
set_prev_graf: print_esc("prevgraf");
set_shape: case chr_code of
  par_shape_loc: print_esc("parshape");
  @<Cases of |set_shape| for |print_cmd_chr|@>@;@/
  end; {there are no other cases}
the: if chr_code=0 then print_esc("the")
  @<Cases of |the| for |print_cmd_chr|@>;
toks_register: print_esc("toks");
vadjust: print_esc("vadjust");
valign: print_esc("valign");
vcenter: print_esc("vcenter");
vrule: print_esc("vrule");

@ We will deal with the other primitives later, at some point in the program
where their |eq_type| and |equiv| values are more meaningful.  For example,
the primitives for math mode will be loaded when we consider the routines
that deal with formulas. It is easy to find where each particular
primitive was treated by looking in the index at the end; for example, the
section where |"radical"| entered |eqtb| is listed under `\.{\\radical}
primitive'. (Primitives consisting of a single nonalphabetic character,
@!like `\.{\\/}', are listed under `Single-character primitives'.)
@!@^Single-character primitives@>


@* \[19] Saving and restoring equivalents.
The nested structure provided by `$\.{\char'173}\ldots\.{\char'175}$' groups
in \TeX\ means that |eqtb| entries valid in outer groups should be saved
and restored later if they are overridden inside the braces. When a new |eqtb|
value is being assigned, the program therefore checks to see if the previous
entry belongs to an outer level. In such a case, the old value is placed
on the |save_stack| just before the new value enters |eqtb|. At the
end of a grouping level, i.e., when the right brace is sensed, the
|save_stack| is used to restore the outer values, and the inner ones are
destroyed.

Entries on the |save_stack| are of type |memory_word|. The top item on
this stack is |save_stack[p]|, where |p=save_ptr-1|; it contains three
fields called |save_type|, |save_level|, and |save_index|, and it is
interpreted in one of four ways:

\yskip\hangg 1) If |save_type(p)=restore_old_value|, then
|save_index(p)| is a location in |eqtb| whose current value should
be destroyed at the end of the current group and replaced by |save_stack[p-1]|.
Furthermore if |save_index(p)>=int_base|, then |save_level(p)|
should replace the corresponding entry in |xeq_level|.

\yskip\hangg 2) If |save_type(p)=restore_zero|, then |save_index(p)|
is a location in |eqtb| whose current value should be destroyed at the end
of the current group, when it should be
replaced by the current value of |eqtb[undefined_control_sequence]|.

\yskip\hangg 3) If |save_type(p)=insert_token|, then |save_index(p)|
is a token that should be inserted into \TeX's input when the current
group ends.

\yskip\hangg 4) If |save_type(p)=level_boundary|, then |save_level(p)|
is a code explaining what kind of group we were previously in, and
|save_index(p)| points to the level boundary word at the bottom of
the entries for that group.
Furthermore, in extended \eTeX\ mode, |save_stack[p-1]| contains the
source line number at which the current level of grouping was entered.

@d save_type(#)==save_stack[#].hh.b0 {classifies a |save_stack| entry}
@d save_level(#)==save_stack[#].hh.b1
  {saved level for regions 5 and 6, or group code}
@d save_index(#)==save_stack[#].hh.rh
  {|eqtb| location or |save_stack| location}
@d restore_old_value=0 {|save_type| when a value should be restored later}
@d restore_zero=1 {|save_type| when an undefined entry should be restored}
@d insert_token=2 {|save_type| when a token is being saved for later use}
@d level_boundary=3 {|save_type| corresponding to beginning of group}

@p@t\4@>@<Declare \eTeX\ procedures for tracing and input@>

@ Here are the group codes that are used to discriminate between different
kinds of groups. They allow \TeX\ to decide what special actions, if any,
should be performed when a group ends.
\def\grp{\.{\char'173...\char'175}}

Some groups are not supposed to be ended by right braces. For example,
the `\.\$' that begins a math formula causes a |math_shift_group| to
be started, and this should be terminated by a matching `\.\$'. Similarly,
a group that starts with \.{\\left} should end with \.{\\right}, and
one that starts with \.{\\begingroup} should end with \.{\\endgroup}.

@d bottom_level=0 {group code for the outside world}
@d simple_group=1 {group code for local structure only}
@d hbox_group=2 {code for `\.{\\hbox}\grp'}
@d adjusted_hbox_group=3 {code for `\.{\\hbox}\grp' in vertical mode}
@d vbox_group=4 {code for `\.{\\vbox}\grp'}
@d vtop_group=5 {code for `\.{\\vtop}\grp'}
@d align_group=6 {code for `\.{\\halign}\grp', `\.{\\valign}\grp'}
@d no_align_group=7 {code for `\.{\\noalign}\grp'}
@d output_group=8 {code for output routine}
@d math_group=9 {code for, e.g, `\.{\char'136}\grp'}
@d disc_group=10 {code for `\.{\\discretionary}\grp\grp\grp'}
@d insert_group=11 {code for `\.{\\insert}\grp', `\.{\\vadjust}\grp'}
@d vcenter_group=12 {code for `\.{\\vcenter}\grp'}
@d math_choice_group=13 {code for `\.{\\mathchoice}\grp\grp\grp\grp'}
@d semi_simple_group=14 {code for `\.{\\begingroup...\\endgroup}'}
@d math_shift_group=15 {code for `\.{\$...\$}'}
@d math_left_group=16 {code for `\.{\\left...\\right}'}
@d local_box_group=17 {code for `\.{\\localleftbox...\\localrightbox}'}
@d max_group_code=17
@d split_off_group=18 {box code for the top part of a \.{\\vsplit}}
@d split_keep_group=19 {box code for the bottom part of a \.{\\vsplit}}
@d preamble_group=20 {box code for the preamble processing  in an alignment}
@d align_set_group=21 {box code for the final item pass in an alignment}
@d fin_row_group=22 {box code for a provisory line in an alignment}

@<Types...@>=
@!group_code=0..max_group_code; {|save_level| for a level boundary}

@ The global variable |cur_group| keeps track of what sort of group we are
currently in. Another global variable, |cur_boundary|, points to the
topmost |level_boundary| word.  And |cur_level| is the current depth of
nesting. The routines are designed to preserve the condition that no entry
in the |save_stack| or in |eqtb| ever has a level greater than |cur_level|.

@ @<Glob...@>=
@!save_stack : array[0..save_size] of memory_word;
@!save_ptr : 0..save_size; {first unused entry on |save_stack|}
@!max_save_stack:0..save_size; {maximum usage of save stack}
@!cur_level: quarterword; {current nesting level for groups}
@!cur_group: group_code; {current group type}
@!cur_boundary: 0..save_size; {where the current level begins}

@ At this time it might be a good idea for the reader to review the introduction
to |eqtb| that was given above just before the long lists of parameter names.
Recall that the ``outer level'' of the program is |level_one|, since
undefined control sequences are assumed to be ``defined'' at |level_zero|.

@<Set init...@>=
save_ptr:=0; cur_level:=level_one; cur_group:=bottom_level; cur_boundary:=0;
max_save_stack:=0;

@ The following macro is used to test if there is room for up to eight more
entries on |save_stack|. By making a conservative test like this, we can
get by with testing for overflow in only a few places.

@d check_full_save_stack==if save_ptr>max_save_stack then
  begin max_save_stack:=save_ptr;
  if max_save_stack>save_size-8 then overflow("save size",save_size);
@:TeX capacity exceeded save size}{\quad save size@>
  end

@ Procedure |new_save_level| is called when a group begins. The
argument is a group identification code like `|hbox_group|'. After
calling this routine, it is safe to put six more entries on |save_stack|.

In some cases integer-valued items are placed onto the
|save_stack| just below a |level_boundary| word, because this is a
convenient place to keep information that is supposed to ``pop up'' just
when the group has finished.
For example, when `\.{\\hbox to 100pt}\grp' is being treated, the 100pt
dimension is stored on |save_stack| just before |new_save_level| is
called.

We use the notation |saved(k)| to stand for an integer item that
appears in location |save_ptr+k| of the save stack.

@d saved(#)==save_stack[save_ptr+#].int

@p procedure new_save_level(@!c:group_code); {begin a new level of grouping}
begin check_full_save_stack;
saved(0):=line; incr(save_ptr);
save_type(save_ptr):=level_boundary; save_level(save_ptr):=cur_group;
save_index(save_ptr):=cur_boundary;
if cur_level=max_quarterword then overflow("grouping levels",
@:TeX capacity exceeded grouping levels}{\quad grouping levels@>
  max_quarterword-min_quarterword);
  {quit if |(cur_level+1)| is too big to be stored in |eqtb|}
cur_boundary:=save_ptr; cur_group:=c;
@!stat if tracing_groups>0 then group_trace(false);@+tats@;@/
incr(cur_level); incr(save_ptr);
end;

@ Just before an entry of |eqtb| is changed, the following procedure should
be called to update the other data structures properly. It is important
to keep in mind that reference counts in |mem| include references from
within |save_stack|, so these counts must be handled carefully.
@^reference counts@>

@p procedure eq_destroy(@!w:memory_word); {gets ready to forget |w|}
var q:pointer; {|equiv| field of |w|}
begin case eq_type_field(w) of
call,long_call,outer_call,long_outer_call: delete_token_ref(equiv_field(w));
glue_ref: delete_glue_ref(equiv_field(w));
shape_ref: begin q:=equiv_field(w); {we need to free a \.{\\parshape} block}
  if q<>null then flush_node(q);
  end; {such a block is |2n+1| words long, where |n=vinfo(q)|}
box_ref: flush_node_list(equiv_field(w));
othercases do_nothing
endcases;
end;

@ To save a value of |eqtb[p]| that was established at level |l|, we
can use the following subroutine.

@p procedure eq_save(@!p:pointer;@!l:quarterword); {saves |eqtb[p]|}
begin check_full_save_stack;
if l=level_zero then save_type(save_ptr):=restore_zero
else  begin save_stack[save_ptr]:=eqtb[p]; incr(save_ptr);
  save_type(save_ptr):=restore_old_value;
  end;
save_level(save_ptr):=l; save_index(save_ptr):=p; incr(save_ptr);
end;

@ The procedure |eq_define| defines an |eqtb| entry having specified
|eq_type| and |equiv| fields, and saves the former value if appropriate.
This procedure is used only for entries in the first four regions of |eqtb|,
i.e., only for entries that have |eq_type| and |equiv| fields.
After calling this routine, it is safe to put four more entries on
|save_stack|, provided that there was room for four more entries before
the call, since |eq_save| makes the necessary test.

@d assign_trace(#)==@!stat if tracing_assigns>0 then restore_trace(#);
  tats

@p procedure eq_define(@!p:pointer;@!t:quarterword;@!e:halfword);
  {new data for |eqtb|}
label exit;
begin if (eq_type(p)=t)and(equiv(p)=e) then
  begin assign_trace(p,"reassigning")@;@/
  eq_destroy(eqtb[p]); return;
  end;
assign_trace(p,"changing")@;@/
if eq_level(p)=cur_level then eq_destroy(eqtb[p])
else if cur_level>level_one then eq_save(p,eq_level(p));
eq_level(p):=cur_level; eq_type(p):=t; equiv(p):=e;
assign_trace(p,"into")@;@/
exit:end;

@ The counterpart of |eq_define| for the remaining (fullword) positions in
|eqtb| is called |eq_word_define|. Since |xeq_level[p]>=level_one| for all
|p|, a `|restore_zero|' will never be used in this case.

@p procedure eq_word_define(@!p:pointer;@!w:integer);
label exit;
begin if eqtb[p].int=w then
  begin assign_trace(p,"reassigning")@;@/
  return;
  end;
assign_trace(p,"changing")@;@/
if xeq_level[p]<>cur_level then
  begin eq_save(p,xeq_level[p]); xeq_level[p]:=cur_level;
  end;
eqtb[p].int:=w;
assign_trace(p,"into")@;@/
exit:end;

@ The |eq_define| and |eq_word_define| routines take care of local definitions.
@^global definitions@>
Global definitions are done in almost the same way, but there is no need
to save old values, and the new value is associated with |level_one|.

@p procedure geq_define(@!p:pointer;@!t:quarterword;@!e:halfword);
  {global |eq_define|}
begin assign_trace(p,"globally changing")@;@/
begin eq_destroy(eqtb[p]);
eq_level(p):=level_one; eq_type(p):=t; equiv(p):=e;
end;
assign_trace(p,"into")@;@/
end;
@#
procedure geq_word_define(@!p:pointer;@!w:integer); {global |eq_word_define|}
begin assign_trace(p,"globally changing")@;@/
begin eqtb[p].int:=w; xeq_level[p]:=level_one;
end;
assign_trace(p,"into")@;@/
end;

@ Subroutine |save_for_after| puts a token on the stack for save-keeping.

@p procedure save_for_after(@!t:halfword);
begin if cur_level>level_one then
  begin check_full_save_stack;
  save_type(save_ptr):=insert_token; save_level(save_ptr):=level_zero;
  save_index(save_ptr):=t; incr(save_ptr);
  end;
end;

@ The |unsave| routine goes the other way, taking items off of |save_stack|.
This routine takes care of restoration when a level ends; everything
belonging to the topmost group is cleared off of the save stack.

@p
procedure@?back_input; forward; @t\2@>
procedure unsave; {pops the top level off the save stack}
label done;
var p:pointer; {position to be restored}
@!l:quarterword; {saved level, if in fullword regions of |eqtb|}
@!t:halfword; {saved value of |cur_tok|}
@!a:boolean; {have we already processed an \.{\\aftergroup} ?}
begin a:=false; l:=level_one; {just in case}
unsave_math_codes(cur_level);
unsave_cat_codes (cat_code_table,cur_level);
unsave_text_codes(cur_level);
if cur_level>level_one then
  begin decr(cur_level);
  @<Clear off top level from |save_stack|@>;
  end
else confusion("curlevel"); {|unsave| is not used when |cur_group=bottom_level|}
@:this can't happen curlevel}{\quad curlevel@>
attr_list_cache:=cache_disabled;
end;

@ @<Clear off...@>=
loop@+begin decr(save_ptr);
  if save_type(save_ptr)=level_boundary then goto done;
  p:=save_index(save_ptr);
  if save_type(save_ptr)=insert_token then
    @<Insert token |p| into \TeX's input@>
  else  begin if save_type(save_ptr)=restore_old_value then
      begin l:=save_level(save_ptr); decr(save_ptr);
      end
    else save_stack[save_ptr]:=eqtb[undefined_control_sequence];
    @<Store \(s)|save_stack[save_ptr]| in |eqtb[p]|, unless
      |eqtb[p]| holds a global value@>;
    end;
  end;
done: @!stat if tracing_groups>0 then group_trace(true);@+tats@;@/
if grp_stack[in_open]=cur_boundary then group_warning;
  {groups possibly not properly nested with files}
cur_group:=save_level(save_ptr); cur_boundary:=save_index(save_ptr);
decr(save_ptr)

@ A global definition, which sets the level to |level_one|,
@^global definitions@>
will not be undone by |unsave|. If at least one global definition of
|eqtb[p]| has been carried out within the group that just ended, the
last such definition will therefore survive.

@<Store \(s)|save...@>=
if p<int_base then
  if eq_level(p)=level_one then
    begin eq_destroy(save_stack[save_ptr]); {destroy the saved value}
    @!stat if tracing_restores>0 then restore_trace(p,"retaining");@+tats@;@/
    end
  else  begin eq_destroy(eqtb[p]); {destroy the current value}
    eqtb[p]:=save_stack[save_ptr]; {restore the saved value}
    @!stat if tracing_restores>0 then restore_trace(p,"restoring");@+tats@;@/
    end
else if xeq_level[p]<>level_one then
  begin eqtb[p]:=save_stack[save_ptr]; xeq_level[p]:=l;
  @!stat if tracing_restores>0 then restore_trace(p,"restoring");@+tats@;@/
  end
else  begin
  @!stat if tracing_restores>0 then restore_trace(p,"retaining");@+tats@;@/
  end

@ @<Declare \eTeX\ procedures for tr...@>=
@!stat procedure restore_trace(@!p:pointer;@!s:str_number);
  {|eqtb[p]| has just been restored or retained}
begin begin_diagnostic; print_char("{"); print(s); print_char(" ");
show_eqtb(p); print_char("}");
end_diagnostic(false);
end;
tats

@ Most of the parameters kept in |eqtb| can be changed freely, but there's
an exception:  The magnification should not be used with two different
values during any \TeX\ job, since a single magnification is applied to an
entire run. The global variable |mag_set| is set to the current magnification
whenever it becomes necessary to ``freeze'' it at a particular value.

@<Glob...@>=
@!mag_set:integer; {if nonzero, this magnification should be used henceforth}

@ @<Set init...@>=
mag_set:=0;

@ The |prepare_mag| subroutine is called whenever \TeX\ wants to use |mag|
for magnification.

@p procedure prepare_mag;
begin if (mag_set>0)and(mag<>mag_set) then
  begin print_err("Incompatible magnification ("); print_int(mag);
@.Incompatible magnification@>
  print(");"); print_nl(" the previous value will be retained");
  help2("I can handle only one magnification ratio per job. So I've")@/
  ("reverted to the magnification you used earlier on this run.");@/
  int_error(mag_set);
  geq_word_define(int_base+mag_code,mag_set); {|mag:=mag_set|}
  end;
if (mag<=0)or(mag>32768) then
  begin print_err("Illegal magnification has been changed to 1000");@/
@.Illegal magnification...@>
  help1("The magnification ratio must be between 1 and 32768.");
  int_error(mag); geq_word_define(int_base+mag_code,1000);
  end;
mag_set:=mag;
end;

@* \[20] Token lists.
A \TeX\ token is either a character or a control sequence, and it is
@^token@>
represented internally in one of two ways: (1)~A character whose ASCII
code number is |c| and whose command code is |m| is represented as the
number $2^{21}m+c$; the command code is in the range |1<=m<=14|. (2)~A control
sequence whose |eqtb| address is |p| is represented as the number
|cs_token_flag+p|. Here |cs_token_flag=@t$2^{25}-1$@>| is larger than
$2^{21}m+c$, yet it is small enough that |cs_token_flag+p< max_halfword|;
thus, a token fits comfortably in a halfword.

A token |t| represents a |left_brace| command if and only if
|t<left_brace_limit|; it represents a |right_brace| command if and only if
we have |left_brace_limit<=t<right_brace_limit|; and it represents a |match| or
|end_match| command if and only if |match_token<=t<=end_match_token|.
The following definitions take care of these token-oriented constants
and a few others.

@d cs_token_flag==@"1FFFFFFF {amount added to the |eqtb| location in a
  token that stands for a control sequence; is a multiple of~$2^{21}$, less~1}
@d left_brace_token=@"200000   {$2^{21}\cdot|left_brace|$}
@d left_brace_limit=@"400000   {$2^{21}\cdot(|left_brace|+1)$}
@d right_brace_token=@"400000  {$2^{21}\cdot|right_brace|$}
@d right_brace_limit=@"600000  {$2^{21}\cdot(|right_brace|+1)$}
@d math_shift_token= @"600000  {$2^{21}\cdot|math_shift|$}
@d tab_token=@"800000          {$2^{21}\cdot|tab_mark|$}
@d out_param_token=@"A00000    {$2^{21}\cdot|out_param|$}
@d space_token=@"1400020       {$2^{21}\cdot|spacer|+|" "|$}
@d letter_token=@"1600000      {$2^{21}\cdot|letter|$}
@d other_token=@"1800000       {$2^{21}\cdot|other_char|$}
@d match_token=@"1A00000       {$2^{21}\cdot|match|$}
@d end_match_token=@"1C00000   {$2^{21}\cdot|end_match|$}
@d protected_token=@"1C00001   {$2^{21}\cdot|end_match|+1$}

@ @<Check the ``constant''...@>=
if cs_token_flag+undefined_control_sequence>max_halfword then bad:=21;

@ A token list is a singly linked list of one-word nodes in |mem|, where
each word contains a token and a link. Macro definitions, output-routine
definitions, marks, \.{\\write} texts, and a few other things
are remembered by \TeX\ in the form
of token lists, usually preceded by a node with a reference count in its
|token_ref_count| field. The token stored in location |p| is called
|info(p)|.

Three special commands appear in the token lists of macro definitions.
When |m=match|, it means that \TeX\ should scan a parameter
for the current macro; when |m=end_match|, it means that parameter
matching should end and \TeX\ should start reading the macro text; and
when |m=out_param|, it means that \TeX\ should insert parameter
number |c| into the text at this point.

The enclosing \.{\char'173} and \.{\char'175} characters of a macro
definition are omitted, but the final right brace of an output routine
is included at the end of its token list.

Here is an example macro definition that illustrates these conventions.
After \TeX\ processes the text
$$\.{\\def\\mac a\#1\#2 \\b \{\#1\\-a \#\#1\#2 \#2\}}$$
the definition of \.{\\mac} is represented as a token list containing
$$\def\,{\hskip2pt}
\vbox{\halign{\hfil#\hfil\cr
(reference count), |letter|\,\.a, |match|\,\#, |match|\,\#, |spacer|\,\.\ ,
\.{\\b}, |end_match|,\cr
|out_param|\,1, \.{\\-}, |letter|\,\.a, |spacer|\,\.\ , |mac_param|\,\#,
|other_char|\,\.1,\cr
|out_param|\,2, |spacer|\,\.\ , |out_param|\,2.\cr}}$$
The procedure |scan_toks| builds such token lists, and |macro_call|
does the parameter matching.
@^reference counts@>

Examples such as
$$\.{\\def\\m\{\\def\\m\{a\}\ b\}}$$
explain why reference counts would be needed even if \TeX\ had no \.{\\let}
operation: When the token list for \.{\\m} is being read, the redefinition of
\.{\\m} changes the |eqtb| entry before the token list has been fully
consumed, so we dare not simply destroy a token list when its
control sequence is being redefined.

If the parameter-matching part of a definition ends with `\.{\#\{}',
the corresponding token list will have `\.\{' just before the `|end_match|'
and also at the very end. The first `\.\{' is used to delimit the parameter; the
second one keeps the first from disappearing.

@ The procedure |show_token_list|, which prints a symbolic form of
the token list that starts at a given node |p|, illustrates these
conventions. The token list being displayed should not begin with a reference
count. However, the procedure is intended to be robust, so that if the
memory links are awry or if |p| is not really a pointer to a token list,
nothing catastrophic will happen.

An additional parameter |q| is also given; this parameter is either null
or it points to a node in the token list where a certain magic computation
takes place that will be explained later. (Basically, |q| is non-null when
we are printing the two-line context information at the time of an error
message; |q| marks the place corresponding to where the second line
should begin.)

For example, if |p| points to the node containing the first \.a in the
token list above, then |show_token_list| will print the string
$$\hbox{`\.{a\#1\#2\ \\b\ ->\#1\\-a\ \#\#1\#2\ \#2}';}$$
and if |q| points to the node containing the second \.a,
the magic computation will be performed just before the second \.a is printed.

The generation will stop, and `\.{\\ETC.}' will be printed, if the length
of printing exceeds a given limit~|l|. Anomalous entries are printed in the
form of control sequences that are not followed by a blank space, e.g.,
`\.{\\BAD.}'; this cannot be confused with actual control sequences because
a real control sequence named \.{BAD} would come out `\.{\\BAD\ }'.

@<Declare the procedure called |show_token_list|@>=
procedure show_token_list(@!p,@!q:integer;@!l:integer);
label exit;
var m,@!c:integer; {pieces of a token}
@!match_chr:ASCII_code; {character used in a `|match|'}
@!n:ASCII_code; {the highest parameter number, as an ASCII digit}
begin match_chr:="#"; n:="0"; tally:=0;
while (p<>null) and (tally<l) do
  begin if p=q then @<Do magic computation@>;
  @<Display token |p|, and |return| if there are problems@>;
  p:=link(p);
  end;
if p<>null then print_esc("ETC.");
@.ETC@>
exit:
end;

@ @<Display token |p|...@>=
if (p<fix_mem_min) or (p>fix_mem_end) then
  begin print_esc("CLOBBERED."); return;
@.CLOBBERED@>
  end;
if info(p)>=cs_token_flag then begin
  if not ((inhibit_par_tokens) and (info(p)=par_token)) then
	  print_cs(info(p)-cs_token_flag);
  end
else  begin m:=info(p) div string_offset; c:=info(p) mod string_offset;
  if info(p)<0 then print_esc("BAD.")
@.BAD@>
  else @<Display the token $(|m|,|c|)$@>;
  end

@ The procedure usually ``learns'' the character code used for macro
parameters by seeing one in a |match| command before it runs into any
|out_param| commands.

@<Display the token ...@>=
case m of
left_brace,right_brace,math_shift,tab_mark,sup_mark,sub_mark,spacer,
  letter,other_char: print(c);
mac_param: begin print(c); print(c);
  end;
out_param: begin print(match_chr);
  if c<=9 then print_char(c+"0")
  else  begin print_char("!"); return;
    end;
  end;
match: begin match_chr:=c; print(c); incr(n); print_char(n);
  if n>"9" then return;
  end;
end_match: if c=0 then print("->");
@.->@>
othercases print_esc("BAD.")
@.BAD@>
endcases

@ Here's the way we sometimes want to display a token list, given a pointer
to its reference count; the pointer may be null.

@p procedure token_show(@!p:pointer);
begin if p<>null then show_token_list(link(p),null,10000000);
end;

@ The |print_meaning| subroutine displays |cur_cmd| and |cur_chr| in
symbolic form, including the expansion of a macro or mark.

@p procedure print_meaning;
begin print_cmd_chr(cur_cmd,cur_chr);
if cur_cmd>=call then
  begin print_char(":"); print_ln; token_show(cur_chr);
  end
else  @<Show the meaning of a mark node@>;
end;

@* \[21] Introduction to the syntactic routines.
Let's pause a moment now and try to look at the Big Picture.
The \TeX\ program consists of three main parts: syntactic routines,
semantic routines, and output routines. The chief purpose of the
syntactic routines is to deliver the user's input to the semantic routines,
one token at a time. The semantic routines act as an interpreter
responding to these tokens, which may be regarded as commands. And the
output routines are periodically called on to convert box-and-glue
lists into a compact set of instructions that will be sent
to a typesetter. We have discussed the basic data structures and utility
routines of \TeX, so we are good and ready to plunge into the real activity by
considering the syntactic routines.

Our current goal is to come to grips with the |get_next| procedure,
which is the keystone of \TeX's input mechanism. Each call of |get_next|
sets the value of three variables |cur_cmd|, |cur_chr|, and |cur_cs|,
representing the next input token.
$$\vbox{\halign{#\hfil\cr
  \hbox{|cur_cmd| denotes a command code from the long list of codes
   given above;}\cr
  \hbox{|cur_chr| denotes a character code or other modifier of the command
   code;}\cr
  \hbox{|cur_cs| is the |eqtb| location of the current control sequence,}\cr
  \hbox{\qquad if the current token was a control sequence,
   otherwise it's zero.}\cr}}$$
Underlying this external behavior of |get_next| is all the machinery
necessary to convert from character files to tokens. At a given time we
may be only partially finished with the reading of several files (for
which \.{\\input} was specified), and partially finished with the expansion
of some user-defined macros and/or some macro parameters, and partially
finished with the generation of some text in a template for \.{\\halign},
and so on. When reading a character file, special characters must be
classified as math delimiters, etc.; comments and extra blank spaces must
be removed, paragraphs must be recognized, and control sequences must be
found in the hash table. Furthermore there are occasions in which the
scanning routines have looked ahead for a word like `\.{plus}' but only
part of that word was found, hence a few characters must be put back
into the input and scanned again.

To handle these situations, which might all be present simultaneously,
\TeX\ uses various stacks that hold information about the incomplete
activities, and there is a finite state control for each level of the
input mechanism. These stacks record the current state of an implicitly
recursive process, but the |get_next| procedure is not recursive.
Therefore it will not be difficult to translate these algorithms into
low-level languages that do not support recursion.

@<Glob...@>=
@!cur_cmd: eight_bits; {current command set by |get_next|}
@!cur_chr: halfword; {operand of current command}
@!cur_cs: pointer; {control sequence found here, zero if none found}
@!cur_tok: halfword; {packed representative of |cur_cmd| and |cur_chr|}

@ The |print_cmd_chr| routine prints a symbolic interpretation of a
command code and its modifier. This is used in certain `\.{You can\'t}'
error messages, and in the implementation of diagnostic routines like
\.{\\show}.

The body of |print_cmd_chr| is a rather tedious listing of print
commands, and most of it is essentially an inverse to the |primitive|
routine that enters a \TeX\ primitive into |eqtb|. Therefore much of
this procedure appears elsewhere in the program,
together with the corresponding |primitive| calls.

@d chr_cmd(#)==begin print(#); print(chr_code);
  end

@<Declare the procedure called |print_cmd_chr|@>=
procedure print_cmd_chr(@!cmd:quarterword;@!chr_code:halfword);
var n:integer; {temp variable}
begin case cmd of
left_brace: chr_cmd("begin-group character ");
right_brace: chr_cmd("end-group character ");
math_shift: chr_cmd("math shift character ");
mac_param: chr_cmd("macro parameter character ");
sup_mark: chr_cmd("superscript character ");
sub_mark: chr_cmd("subscript character ");
endv: print("end of alignment template");
spacer: chr_cmd("blank space ");
letter: chr_cmd("the letter ");
other_char: chr_cmd("the character ");
@t\4@>@<Cases of |print_cmd_chr| for symbolic printing of primitives@>@/
othercases print("[unknown command code!]")
endcases;
end;

@ Here is a procedure that displays the current command.

@p procedure show_cur_cmd_chr;
var n:integer; {level of \.{\\if...\\fi} nesting}
@!l:integer; {line where \.{\\if} started}
@!p:pointer;
begin begin_diagnostic; print_nl("{");
if mode<>shown_mode then
  begin print_mode(mode); print(": "); shown_mode:=mode;
  end;
print_cmd_chr(cur_cmd,cur_chr);
if tracing_ifs>0 then
  if cur_cmd>=if_test then if cur_cmd<=fi_or_else then
    begin print(": ");
    if cur_cmd=fi_or_else then
      begin print_cmd_chr(if_test,cur_if); print_char(" ");
      n:=0; l:=if_line;
      end
    else  begin n:=1; l:=line;
      end;
    p:=cond_ptr;
    while p<>null do
      begin incr(n); p:=vlink(p);
      end;
    print("(level "); print_int(n); print_char(")"); print_if_line(l);
    end;
print_char("}");
end_diagnostic(false);
end;

@* \[22] Input stacks and states.
This implementation of
\TeX\ uses two different conventions for representing sequential stacks.
@^stack conventions@>@^conventions for representing stacks@>

\yskip\hangg 1) If there is frequent access to the top entry, and if the
stack is essentially never empty, then the top entry is kept in a global
variable (even better would be a machine register), and the other entries
appear in the array $\\{stack}[0\to(\\{ptr}-1)]$. For example, the
semantic stack described above is handled this way, and so is the input
stack that we are about to study.

\yskip\hangg 2) If there is infrequent top access, the entire stack contents
are in the array $\\{stack}[0\to(\\{ptr}-1)]$. For example, the |save_stack|
is treated this way, as we have seen.

\yskip\noindent
The state of \TeX's input mechanism appears in the input stack, whose
entries are records with six fields, called |state|, |index|, |start|, |loc|,
|limit|, and |name|. This stack is maintained with
convention~(1), so it is declared in the following way:

@<Types...@>=
@!in_state_record = record
  @!state_field, @!index_field: quarterword;
  @!start_field,@!loc_field, @!limit_field, @!name_field,
  @!ocp_lstack_field: halfword; {used for omega translation processes}
  @!ocp_no_field: halfword; {used for omega translation processes} 
  @!nofilter_field: boolean; {used by token filtering}
  end;

@ @<Glob...@>=
@!input_stack : array[0..stack_size] of in_state_record;
@!input_ptr : 0..stack_size; {first unused location of |input_stack|}
@!max_in_stack: 0..stack_size; {largest value of |input_ptr| when pushing}
@!cur_input : in_state_record;
  {the ``top'' input state, according to convention (1)}

@ We've already defined the special variable |loc==cur_input.loc_field|
in our discussion of basic input-output routines. The other components of
|cur_input| are defined in the same way:

@d state==cur_input.state_field {current scanner state}
@d index==cur_input.index_field {reference for buffer information}
@d start==cur_input.start_field {starting position in |buffer|}
@d limit==cur_input.limit_field {end of current line in |buffer|}
@d nofilter==cur_input.nofilter_field {is token filtering explicitly disallowed?}
@d name==cur_input.name_field {name of the current file}
@d current_ocp_lstack==cur_input.ocp_lstack_field {name of the current ocp}
@d current_ocp_no==cur_input.ocp_no_field {name of the current ocp}

@ Let's look more closely now at the control variables
(|state|,~|index|,~|start|,~|loc|,~|limit|,~|name|),
assuming that \TeX\ is reading a line of characters that have been input
from some file or from the user's terminal. There is an array called
|buffer| that acts as a stack of all lines of characters that are
currently being read from files, including all lines on subsidiary
levels of the input stack that are not yet completed. \TeX\ will return to
the other lines when it is finished with the present input file.

(Incidentally, on a machine with byte-oriented addressing, it might be
appropriate to combine |buffer| with the |str_pool| array,
letting the buffer entries grow downward from the top of the string pool
and checking that these two tables don't bump into each other.)

The line we are currently working on begins in position |start| of the
buffer; the next character we are about to read is |buffer[loc]|; and
|limit| is the location of the last character present.  If |loc>limit|,
the line has been completely read. Usually |buffer[limit]| is the
|end_line_char|, denoting the end of a line, but this is not
true if the current line is an insertion that was entered on the user's
terminal in response to an error message.

The |name| variable is a string number that designates the name of
the current file, if we are reading a text file. It is zero if we
are reading from the terminal; it is |n+1| if we are reading from
input stream |n|, where |0<=n<=16|. (Input stream 16 stands for
an invalid stream number; in such cases the input is actually from
the terminal, under control of the procedure |read_toks|.)
Finally |18<=name<=20| indicates that we are reading a pseudo file
created by the \.{\\scantokens} or \.{\\scantextokens} command.

The |state| variable has one of three values, when we are scanning such
files:
$$\baselineskip 15pt\vbox{\halign{#\hfil\cr
1) |state=mid_line| is the normal state.\cr
2) |state=skip_blanks| is like |mid_line|, but blanks are ignored.\cr
3) |state=new_line| is the state at the beginning of a line.\cr}}$$
These state values are assigned numeric codes so that if we add the state
code to the next character's command code, we get distinct values. For
example, `|mid_line+spacer|' stands for the case that a blank
space character occurs in the middle of a line when it is not being
ignored; after this case is processed, the next value of |state| will
be |skip_blanks|.

@d mid_line=1 {|state| code when scanning a line of characters}
@d skip_blanks=2+max_char_code {|state| code when ignoring blanks}
@d new_line=3+max_char_code+max_char_code {|state| code at start of line}

@ Additional information about the current line is available via the
|index| variable, which counts how many lines of characters are present
in the buffer below the current level. We have |index=0| when reading
from the terminal and prompting the user for each line; then if the user types,
e.g., `\.{\\input paper}', we will have |index=1| while reading
the file \.{paper.tex}. However, it does not follow that |index| is the
same as the input stack pointer, since many of the levels on the input
stack may come from token lists. For example, the instruction `\.{\\input
paper}' might occur in a token list.

The global variable |in_open| is equal to the |index|
value of the highest non-token-list level. Thus, the number of partially read
lines in the buffer is |in_open+1|, and we have |in_open=index|
when we are not reading a token list.

If we are not currently reading from the terminal, or from an input
stream, we are reading from the file variable |input_file[index]|. We use
the notation |terminal_input| as a convenient abbreviation for |name=0|,
and |cur_file| as an abbreviation for |input_file[index]|.

The global variable |line| contains the line number in the topmost
open file, for use in error messages. If we are not reading from
the terminal, |line_stack[index]| holds the line number for the
enclosing level, so that |line| can be restored when the current
file has been read. Line numbers should never be negative, since the
negative of the current line number is used to identify the user's output
routine in the |mode_line| field of the semantic nest entries.

If more information about the input state is needed, it can be
included in small arrays like those shown here. For example,
the current page or segment number in the input file might be
put into a variable |@!page|, maintained for enclosing levels in
`\ignorespaces|@!page_stack:array[1..max_in_open] of integer|\unskip'
by analogy with |line_stack|.
@^system dependencies@>

@d terminal_input==(name=0) {are we reading from the terminal?}
@d cur_file==input_file[index] {the current |alpha_file| variable}

@<Glob...@>=
@!in_open : 0..max_in_open; {the number of lines in the buffer, less one}
@!open_parens : 0..max_in_open; {the number of open text files}
@!input_file : array[1..max_in_open] of alpha_file;
@!line : integer; {current line number in the current source file}
@!line_stack : array[1..max_in_open] of integer;

@ Users of \TeX\ sometimes forget to balance left and right braces properly,
and one of the ways \TeX\ tries to spot such errors is by considering an
input file as broken into subfiles by control sequences that
are declared to be \.{\\outer}.

A variable called |scanner_status| tells \TeX\ whether or not to complain
when a subfile ends. This variable has six possible values:

\yskip\hang|normal|, means that a subfile can safely end here without incident.

\yskip\hang|skipping|, means that a subfile can safely end here, but not a file,
because we're reading past some conditional text that was not selected.

\yskip\hang|defining|, means that a subfile shouldn't end now because a
macro is being defined.

\yskip\hang|matching|, means that a subfile shouldn't end now because a
macro is being used and we are searching for the end of its arguments.

\yskip\hang|aligning|, means that a subfile shouldn't end now because we are
not finished with the preamble of an \.{\\halign} or \.{\\valign}.

\yskip\hang|absorbing|, means that a subfile shouldn't end now because we are
reading a balanced token list for \.{\\message}, \.{\\write}, etc.

\yskip\noindent
If the |scanner_status| is not |normal|, the variable |warning_index| points
to the |eqtb| location for the relevant control sequence name to print
in an error message.

@d skipping=1 {|scanner_status| when passing conditional text}
@d defining=2 {|scanner_status| when reading a macro definition}
@d matching=3 {|scanner_status| when reading macro arguments}
@d aligning=4 {|scanner_status| when reading an alignment preamble}
@d absorbing=5 {|scanner_status| when reading a balanced text}

@<Glob...@>=
@!scanner_status : normal..absorbing; {can a subfile end now?}
@!warning_index : pointer; {identifier relevant to non-|normal| scanner status}
@!def_ref : pointer; {reference count of token list being defined}

@ Here is a procedure that uses |scanner_status| to print a warning message
when a subfile has ended, and at certain other crucial times:

@<Declare the procedure called |runaway|@>=
procedure runaway;
var p:pointer; {head of runaway list}
begin p:=null;
  if scanner_status>skipping then
  begin print_nl("Runaway ");
@.Runaway...@>
  case scanner_status of
  defining: begin print("definition"); p:=def_ref;
    end;
  matching: begin print("argument"); p:=temp_token_head;
    end;
  aligning: begin print("preamble"); p:=hold_token_head;
    end;
  absorbing: begin print("text"); p:=def_ref;
    end;
  end; {there are no other cases}
  print_char("?");print_ln; show_token_list(link(p),null,error_line-10);
  end;
end;

@ However, all this discussion about input state really applies only to the
case that we are inputting from a file. There is another important case,
namely when we are currently getting input from a token list. In this case
|state=token_list|, and the conventions about the other state variables
are different:

\yskip\hang|loc| is a pointer to the current node in the token list, i.e.,
the node that will be read next. If |loc=null|, the token list has been
fully read.

\yskip\hang|start| points to the first node of the token list; this node
may or may not contain a reference count, depending on the type of token
list involved.

\yskip\hang|token_type|, which takes the place of |index| in the
discussion above, is a code number that explains what kind of token list
is being scanned.

\yskip\hang|name| points to the |eqtb| address of the control sequence
being expanded, if the current token list is a macro.

\yskip\hang|param_start|, which takes the place of |limit|, tells where
the parameters of the current macro begin in the |param_stack|, if the
current token list is a macro.

\yskip\noindent The |token_type| can take several values, depending on
where the current token list came from:

\yskip\hang|parameter|, if a parameter is being scanned;

\hang|u_template|, if the \<u_j> part of an alignment
template is being scanned;

\hang|v_template|, if the \<v_j> part of an alignment
template is being scanned;

\hang|backed_up|, if the token list being scanned has been inserted as
`to be read again'.

\hang|inserted|, if the token list being scanned has been inserted as
the text expansion of a \.{\\count} or similar variable;

\hang|macro|, if a user-defined control sequence is being scanned;

\hang|output_text|, if an \.{\\output} routine is being scanned;

\hang|every_par_text|, if the text of \.{\\everypar} is being scanned;

\hang|every_math_text|, if the text of \.{\\everymath} is being scanned;

\hang|every_display_text|, if the text of \.{\\everydisplay} is being scanned;

\hang|every_hbox_text|, if the text of \.{\\everyhbox} is being scanned;

\hang|every_vbox_text|, if the text of \.{\\everyvbox} is being scanned;

\hang|every_job_text|, if the text of \.{\\everyjob} is being scanned;

\hang|every_cr_text|, if the text of \.{\\everycr} is being scanned;

\hang|mark_text|, if the text of a \.{\\mark} is being scanned;

\hang|write_text|, if the text of a \.{\\write} is being scanned.

\yskip\noindent
The codes for |output_text|, |every_par_text|, etc., are equal to a constant
plus the corresponding codes for token list parameters |output_routine_loc|,
|every_par_loc|, etc.  The token list begins with a reference count if and
only if |token_type>=macro|.
@^reference counts@>

Since \eTeX's additional token list parameters precede |toks_base|, the
corresponding token types must precede |write_text|.

@d token_list=0 {|state| code when scanning a token list}
@d token_type==index {type of current token list}
@d param_start==limit {base of macro parameters in |param_stack|}
@d parameter=0 {|token_type| code for parameter}
@d u_template=1 {|token_type| code for \<u_j> template}
@d v_template=2 {|token_type| code for \<v_j> template}
@d backed_up=3 {|token_type| code for text to be reread}
@d inserted=4 {|token_type| code for inserted texts}
@d macro=5 {|token_type| code for defined control sequences}
@d output_text=6 {|token_type| code for output routines}
@d every_par_text=7 {|token_type| code for \.{\\everypar}}
@d every_math_text=8 {|token_type| code for \.{\\everymath}}
@d every_display_text=9 {|token_type| code for \.{\\everydisplay}}
@d every_hbox_text=10 {|token_type| code for \.{\\everyhbox}}
@d every_vbox_text=11 {|token_type| code for \.{\\everyvbox}}
@d every_job_text=12 {|token_type| code for \.{\\everyjob}}
@d every_cr_text=13 {|token_type| code for \.{\\everycr}}
@d mark_text=14 {|token_type| code for \.{\\topmark}, etc.}
@#
@d eTeX_text_offset=output_routine_loc-output_text
@d every_eof_text=every_eof_loc-eTeX_text_offset
  {|token_type| code for \.{\\everyeof}}
@#
@d write_text=etex_toks-eTeX_text_offset {|token_type| code for \.{\\write}}

@ The |param_stack| is an auxiliary array used to hold pointers to the token
lists for parameters at the current level and subsidiary levels of input.
This stack is maintained with convention (2), and it grows at a different
rate from the others.

@<Glob...@>=
@!param_stack:array [0..param_size] of pointer;
  {token list pointers for parameters}
@!param_ptr:0..param_size; {first unused entry in |param_stack|}
@!max_param_stack:integer;
  {largest value of |param_ptr|, will be |<=param_size+9|}

@ The input routines must also interact with the processing of
\.{\\halign} and \.{\\valign}, since the appearance of tab marks and
\.{\\cr} in certain places is supposed to trigger the beginning of special
\<v_j> template text in the scanner. This magic is accomplished by an
|align_state| variable that is increased by~1 when a `\.{\char'173}' is
scanned and decreased by~1 when a `\.{\char'175}' is scanned. The |align_state|
is nonzero during the \<u_j> template, after which it is set to zero; the
\<v_j> template begins when a tab mark or \.{\\cr} occurs at a time that
|align_state=0|.

@<Glob...@>=
@!align_state:integer; {group level with respect to current alignment}

@ Thus, the ``current input state'' can be very complicated indeed; there
can be many levels and each level can arise in a variety of ways. The
|show_context| procedure, which is used by \TeX's error-reporting routine to
print out the current input state on all levels down to the most recent
line of characters from an input file, illustrates most of these conventions.
The global variable |base_ptr| contains the lowest level that was
displayed by this procedure.

@<Glob...@>=
@!base_ptr:0..stack_size; {shallowest level shown by |show_context|}

@ The status at each level is indicated by printing two lines, where the first
line indicates what was read so far and the second line shows what remains
to be read. The context is cropped, if necessary, so that the first line
contains at most |half_error_line| characters, and the second contains
at most |error_line|. Non-current input levels whose |token_type| is
`|backed_up|' are shown only if they have not been fully read.

@p procedure show_context; {prints where the scanner is}
label done;
var old_setting:0..max_selector; {saved |selector| setting}
@!nn:integer; {number of contexts shown so far, less one}
@!bottom_line:boolean; {have we reached the final context to be shown?}
@<Local variables for formatting calculations@>@/
begin base_ptr:=input_ptr; input_stack[base_ptr]:=cur_input;
  {store current state}
nn:=-1; bottom_line:=false;
loop@+begin cur_input:=input_stack[base_ptr]; {enter into the context}
  if (state<>token_list) then
    if (name>21) or (base_ptr=0) then bottom_line:=true;
  if (base_ptr=input_ptr)or bottom_line or(nn<error_context_lines) then
    @<Display the current context@>
  else if nn=error_context_lines then
    begin print_nl("..."); incr(nn); {omitted if |error_context_lines<0|}
    end;
  if bottom_line then goto done;
  decr(base_ptr);
  end;
done: cur_input:=input_stack[input_ptr]; {restore original state}
end;

@ @<Display the current context@>=
begin if (base_ptr=input_ptr) or (state<>token_list) or
   (token_type<>backed_up) or (loc<>null) then
    {we omit backed-up token lists that have already been read}
  begin tally:=0; {get ready to count characters}
  old_setting:=selector;
  if current_ocp_lstack>0 then
  begin print_nl("OCP stack "); print_scaled(current_ocp_lstack); 
        print(" entry "); print_int(current_ocp_no); print(":");
    @<Pseudoprint the line@>;
  end
  else if state<>token_list then
    begin @<Print location of current line@>;
    @<Pseudoprint the line@>;
    end
  else  begin @<Print type of token list@>;
    @<Pseudoprint the token list@>;
    end;
  selector:=old_setting; {stop pseudoprinting}
  @<Print two lines using the tricky pseudoprinted information@>;
  incr(nn);
  end;
end

@ This routine should be changed, if necessary, to give the best possible
indication of where the current line resides in the input file.
For example, on some systems it is best to print both a page and line number.
@^system dependencies@>

@<Print location of current line@>=
if name<=17 then
  if terminal_input then
    if base_ptr=0 then print_nl("<*>") else print_nl("<insert> ")
  else  begin print_nl("<read ");
    if name=17 then print_char("*")@+else print_int(name-1);
@.*\relax@>
    print_char(">");
    end
else if index<>in_open then {input from a pseudo file}
  begin print_nl("l."); print_int(line_stack[index+1]);
  end
else  begin print_nl("l."); print_int(line);
  end;
print_char(" ")

@ @<Print type of token list@>=
case token_type of
parameter: print_nl("<argument> ");
u_template,v_template: print_nl("<template> ");
backed_up: if loc=null then print_nl("<recently read> ")
  else print_nl("<to be read again> ");
inserted: print_nl("<inserted text> ");
macro: begin print_ln; print_cs(name);
  end;
output_text: print_nl("<output> ");
every_par_text: print_nl("<everypar> ");
every_math_text: print_nl("<everymath> ");
every_display_text: print_nl("<everydisplay> ");
every_hbox_text: print_nl("<everyhbox> ");
every_vbox_text: print_nl("<everyvbox> ");
every_job_text: print_nl("<everyjob> ");
every_cr_text: print_nl("<everycr> ");
mark_text: print_nl("<mark> ");
every_eof_text: print_nl("<everyeof> ");
write_text: print_nl("<write> ");
othercases print_nl("?") {this should never happen}
endcases

@ Here it is necessary to explain a little trick. We don't want to store a long
string that corresponds to a token list, because that string might take up
lots of memory; and we are printing during a time when an error message is
being given, so we dare not do anything that might overflow one of \TeX's
tables. So `pseudoprinting' is the answer: We enter a mode of printing
that stores characters into a buffer of length |error_line|, where character
$k+1$ is placed into \hbox{|trick_buf[k mod error_line]|} if
|k<trick_count|, otherwise character |k| is dropped. Initially we set
|tally:=0| and |trick_count:=1000000|; then when we reach the
point where transition from line 1 to line 2 should occur, we
set |first_count:=tally| and |trick_count:=@tmax@>(error_line,
tally+1+error_line-half_error_line)|. At the end of the
pseudoprinting, the values of |first_count|, |tally|, and
|trick_count| give us all the information we need to print the two lines,
and all of the necessary text is in |trick_buf|.

Namely, let |l| be the length of the descriptive information that appears
on the first line. The length of the context information gathered for that
line is |k=first_count|, and the length of the context information
gathered for line~2 is $m=\min(|tally|, |trick_count|)-k$. If |l+k<=h|,
where |h=half_error_line|, we print |trick_buf[0..k-1]| after the
descriptive information on line~1, and set |n:=l+k|; here |n| is the
length of line~1. If $l+k>h$, some cropping is necessary, so we set |n:=h|
and print `\.{...}' followed by
$$\hbox{|trick_buf[(l+k-h+3)..k-1]|,}$$
where subscripts of |trick_buf| are circular modulo |error_line|. The
second line consists of |n|~spaces followed by |trick_buf[k..(k+m-1)]|,
unless |n+m>error_line|; in the latter case, further cropping is done.
This is easier to program than to explain.

@<Local variables for formatting...@>=
@!i:0..buf_size; {index into |buffer|}
@!j:0..buf_size; {end of current line in |buffer|}
@!l:0..half_error_line; {length of descriptive information on line 1}
@!m:integer; {context information gathered for line 2}
@!n:0..error_line; {length of line 1}
@!p: integer; {starting or ending place in |trick_buf|}
@!q: integer; {temporary index}

@ The following code sets up the print routines so that they will gather
the desired information.

@d begin_pseudoprint==
  begin l:=tally; tally:=0; selector:=pseudo;
  trick_count:=1000000;
  end
@d set_trick_count==
  begin first_count:=tally;
  trick_count:=tally+1+error_line-half_error_line;
  if trick_count<error_line then trick_count:=error_line;
  end

@ And the following code uses the information after it has been gathered.

@<Print two lines using the tricky pseudoprinted information@>=
if trick_count=1000000 then set_trick_count;
  {|set_trick_count| must be performed}
if tally<trick_count then m:=tally-first_count
else m:=trick_count-first_count; {context on line 2}
if l+first_count<=half_error_line then
  begin p:=0; n:=l+first_count;
  end
else  begin print("..."); p:=l+first_count-half_error_line+3;
  n:=half_error_line;
  end;
for q:=p to first_count-1 do print_char(trick_buf[q mod error_line]);
print_ln;
for q:=1 to n do print_char(" "); {print |n| spaces to begin line~2}
if m+n<=error_line then p:=first_count+m else p:=first_count+(error_line-n-3);
for q:=first_count to p-1 do print_char(trick_buf[q mod error_line]);
if m+n>error_line then print("...")

@ But the trick is distracting us from our current goal, which is to
understand the input state. So let's concentrate on the data structures that
are being pseudoprinted as we finish up the |show_context| procedure.

@<Pseudoprint the line@>=
begin_pseudoprint;
if buffer[limit]=end_line_char then j:=limit
else j:=limit+1; {determine the effective end of the line}
if j>0 then for i:=start to j-1 do
  begin if i=loc then set_trick_count;
  print_char(buffer[i]);
  end

@ @<Pseudoprint the token list@>=
begin_pseudoprint;
if token_type<macro then show_token_list(start,loc,100000)
else show_token_list(link(start),loc,100000) {avoid reference count}

@ Here is the missing piece of |show_token_list| that is activated when the
token beginning line~2 is about to be shown:

@<Do magic computation@>=set_trick_count

@* \[23] Maintaining the input stacks.
The following subroutines change the input status in commonly needed ways.

First comes |push_input|, which stores the current state and creates a
new level (having, initially, the same properties as the old).

@d push_input==@t@> {enter a new input level, save the old}
  begin if input_ptr>max_in_stack then
    begin max_in_stack:=input_ptr;
    if input_ptr=stack_size then overflow("input stack size",stack_size);
@:TeX capacity exceeded input stack size}{\quad input stack size@>
    end;
  input_stack[input_ptr]:=cur_input; {stack the record}
  nofilter:=false;
  incr(input_ptr);
  end

@ And of course what goes up must come down.

@d pop_input==@t@> {leave an input level, re-enter the old}
  begin decr(input_ptr); cur_input:=input_stack[input_ptr];
  end

@ Here is a procedure that starts a new level of token-list input, given
a token list |p| and its type |t|. If |t=macro|, the calling routine should
set |name| and |loc|.

@d back_list(#)==begin_token_list(#,backed_up) {backs up a simple token list}
@d ins_list(#)==begin_token_list(#,inserted) {inserts a simple token list}

@p procedure begin_token_list(@!p:pointer;@!t:quarterword);
begin push_input; state:=token_list; start:=p; token_type:=t;
if t>=macro then {the token list starts with a reference count}
  begin add_token_ref(p);
  if t=macro then param_start:=param_ptr
  else  begin loc:=link(p);
    if tracing_macros>1 then
      begin begin_diagnostic; print_nl("");
      case t of
      mark_text:print_esc("mark");
      write_text:print_esc("write");
      othercases print_cmd_chr(assign_toks,t-output_text+output_routine_loc)
      endcases;@/
      print("->"); token_show(p); end_diagnostic(false);
      end;
    end;
  end
else loc:=p;
end;

@ When a token list has been fully scanned, the following computations
should be done as we leave that level of input. The |token_type| tends
to be equal to either |backed_up| or |inserted| about 2/3 of the time.
@^inner loop@>

@p procedure end_token_list; {leave a token-list input level}
begin if token_type>=backed_up then {token list to be deleted}
  begin if token_type<=inserted then flush_list(start)
  else  begin delete_token_ref(start); {update reference count}
    if token_type=macro then {parameters must be flushed}
      while param_ptr>param_start do
        begin decr(param_ptr);
        flush_list(param_stack[param_ptr]);
        end;
    end;
  end
else if token_type=u_template then
  if align_state>500000 then align_state:=0
  else fatal_error("(interwoven alignment preambles are not allowed)");
@.interwoven alignment preambles...@>
pop_input;
check_interrupt;
end;

@ Sometimes \TeX\ has read too far and wants to ``unscan'' what it has
seen. The |back_input| procedure takes care of this by putting the token
just scanned back into the input stream, ready to be read again. This
procedure can be used only if |cur_tok| represents the token to be
replaced. Some applications of \TeX\ use this procedure a lot,
so it has been slightly optimized for speed.
@^inner loop@>

@p procedure back_input; {undoes one token of input}
var p:pointer; {a token list of length one}
begin while (state=token_list)and(loc=null)and(token_type<>v_template) do
  end_token_list; {conserve stack space}
p:=get_avail; info(p):=cur_tok;
if cur_tok<right_brace_limit then
  if cur_tok<left_brace_limit then decr(align_state)
  else incr(align_state);
push_input; state:=token_list; start:=p; token_type:=backed_up;
loc:=p; {that was |back_list(p)|, without procedure overhead}
end;

@ @<Insert token |p| into \TeX's input@>=
begin t:=cur_tok; cur_tok:=p;
if a then
  begin p:=get_avail; info(p):=cur_tok; link(p):=loc; loc:=p; start:=p;
  if cur_tok<right_brace_limit then
    if cur_tok<left_brace_limit then decr(align_state)
    else incr(align_state);
  end
else  begin back_input; a:=1; { etex is always on }
  end;
cur_tok:=t;
end

@ The |back_error| routine is used when we want to replace an offending token
just before issuing an error message. This routine, like |back_input|,
requires that |cur_tok| has been set. We disable interrupts during the
call of |back_input| so that the help message won't be lost.

@p procedure back_error; {back up one token and call |error|}
begin OK_to_interrupt:=false; back_input; OK_to_interrupt:=true; error;
end;
@#
procedure ins_error; {back up one inserted token and call |error|}
begin OK_to_interrupt:=false; back_input; token_type:=inserted;
OK_to_interrupt:=true; error;
end;

@ The |begin_file_reading| procedure starts a new level of input for lines
of characters to be read from a file, or as an insertion from the
terminal. It does not take care of opening the file, nor does it set |loc|
or |limit| or |line|.
@^system dependencies@>

@p procedure begin_file_reading;
begin if in_open=max_in_open then overflow("text input levels",max_in_open);
@:TeX capacity exceeded text input levels}{\quad text input levels@>
if first=buf_size then check_buffer_overflow(first);
@:TeX capacity exceeded buffer size}{\quad buffer size@>
incr(in_open); push_input; index:=in_open;
eof_seen[index]:=false;
grp_stack[index]:=cur_boundary; if_stack[index]:=cond_ptr;
line_stack[index]:=line; start:=first; state:=mid_line;
name:=0; {|terminal_input| is now |true|}
end;

@ Conversely, the variables must be downdated when such a level of input
is finished:

@p procedure end_file_reading;
begin first:=start; line:=line_stack[index];
if (name>=18)and(name<=20) then pseudo_close else
if name=21 then luacstring_close(index) else
if name>17 then lua_a_close_in(cur_file,0); {forget it}
pop_input; decr(in_open);
end;

@ In order to keep the stack from overflowing during a long sequence of
inserted `\.{\\show}' commands, the following routine removes completed
error-inserted lines from memory.

@p procedure clear_for_error_prompt;
begin while (state<>token_list)and terminal_input and@|
  (input_ptr>0)and(loc>limit) do end_file_reading;
print_ln; clear_terminal;
end;

@ To get \TeX's whole input mechanism going, we perform the following
actions.

@<Initialize the input routines@>=
begin input_ptr:=0; max_in_stack:=0;
in_open:=0; open_parens:=0; max_buf_stack:=0;
grp_stack[0]:=0; if_stack[0]:=null;
param_ptr:=0; max_param_stack:=0;
first:=buf_size; repeat buffer[first]:=0; decr(first); until first=0;
scanner_status:=normal; warning_index:=null; first:=1;
state:=new_line; start:=1; index:=0; line:=0; name:=0;
current_ocp_lstack:=0; current_ocp_no:=0; nofilter:=false;
force_eof:=false; luacstrings :=0;
align_state:=1000000;@/
if not init_terminal then goto final_end;
limit:=last; first:=last+1; {|init_terminal| has set |loc| and |last|}
end

@* \[24] Getting the next token.
The heart of \TeX's input mechanism is the |get_next| procedure, which
we shall develop in the next few sections of the program. Perhaps we
shouldn't actually call it the ``heart,'' however, because it really acts
as \TeX's eyes and mouth, reading the source files and gobbling them up.
And it also helps \TeX\ to regurgitate stored token lists that are to be
processed again.
@^eyes and mouth@>

The main duty of |get_next| is to input one token and to set |cur_cmd|
and |cur_chr| to that token's command code and modifier. Furthermore, if
the input token is a control sequence, the |eqtb| location of that control
sequence is stored in |cur_cs|; otherwise |cur_cs| is set to zero.

Underlying this simple description is a certain amount of complexity
because of all the cases that need to be handled.
However, the inner loop of |get_next| is reasonably short and fast.

When |get_next| is asked to get the next token of a \.{\\read} line,
it sets |cur_cmd=cur_chr=cur_cs=0| in the case that no more tokens
appear on that line. (There might not be any tokens at all, if the
|end_line_char| has |ignore| as its catcode.)

@ The value of |par_loc| is the |eqtb| address of `\.{\\par}'. This quantity
is needed because a blank line of input is supposed to be exactly equivalent
to the appearance of \.{\\par}; we must set |cur_cs:=par_loc|
when detecting a blank line.

@<Glob...@>=
@!par_loc:pointer; {location of `\.{\\par}' in |eqtb|}
@!par_token:halfword; {token representing `\.{\\par}'}

@ @<Put each...@>=
primitive("par",par_end,too_big_char); {cf. |scan_file_name|}
@!@:par_}{\.{\\par} primitive@>
par_loc:=cur_val; par_token:=cs_token_flag+par_loc;

@ @<Cases of |print_cmd_chr|...@>=
par_end:print_esc("par");

@ The function |get_next| is now defined in |textoken.c|. Parts of
this routine are executed more often than any other instructions of \TeX.
@^mastication@>@^inner loop@>

@ The global variable |force_eof| is normally |false|; it is set |true|
by an \.{\\endinput} command. |luacstrings| is the number of lua print 
statements waiting to be input, it is changed by |luatokencall|.
 
|no_expand_flag| is a special character value that is inserted by
|get_next| if it wants to suppress expansion.

@d no_expand_flag==special_char {this characterizes a special variant of |relax|}
@d end_line_char_inactive==(end_line_char<0)or(end_line_char>127)


@<Glob...@>=
@!force_eof:boolean; {should the next \.{\\input} be aborted early?}
@!luacstrings:integer;  {how many lua strings are waiting to be input?}

@ If the user has set the |pausing| parameter to some positive value,
and if nonstop mode has not been selected, each line of input is displayed
on the terminal and the transcript file, followed by `\.{=>}'.
\TeX\ waits for a response. If the response is simply |carriage_return|, the
line is accepted as it stands, otherwise the line typed is
used instead of the line in the file.

@p procedure firm_up_the_line;
var k:0..buf_size; {an index into |buffer|}
begin limit:=last;
if pausing>0 then if interaction>nonstop_mode then
  begin wake_up_terminal; print_ln;
  if start<limit then for k:=start to limit-1 do print(buffer[k]);
  first:=limit; prompt_input("=>"); {wait for user response}
@.=>@>
  if last>first then
    begin for k:=first to last-1 do {move line down in buffer}
      buffer[k+start-first]:=buffer[k];
    limit:=start+last-first;
    end;
  end;
end;

@ Since |get_next| is used so frequently in \TeX, it is convenient
to define three related procedures that do a little more:

\yskip\hang|get_token| not only sets |cur_cmd| and |cur_chr|, it
also sets |cur_tok|, a packed halfword version of the current token.

\yskip\hang|get_x_token|, meaning ``get an expanded token,'' is like
|get_token|, but if the current token turns out to be a user-defined
control sequence (i.e., a macro call), or a conditional,
or something like \.{\\topmark} or \.{\\expandafter} or \.{\\csname},
it is eliminated from the input by beginning the expansion of the macro
or the evaluation of the conditional.

\yskip\hang|x_token| is like |get_x_token| except that it assumes that
|get_next| has already been called.

\yskip\noindent
In fact, these three procedures account for {\sl all\/} uses of |get_next|,
except for two places in the ``inner loop'' when |cur_tok| need not be set,
and except when the arguments to \.{\\ifx} are being scanned.

@ No new control sequences will be defined except during a call of
|get_token|, or when \.{\\csname} compresses a token list, because
|no_new_control_sequence| is always |true| at other times.

@p procedure get_token; {sets |cur_cmd|, |cur_chr|, |cur_tok|}
begin no_new_control_sequence:=false; get_filtered_next; no_new_control_sequence:=true;
@^inner loop@>
if cur_cs=0 then cur_tok:=(cur_cmd*string_offset)+cur_chr
else cur_tok:=cs_token_flag+cur_cs;
end;

@* \[25] Expanding the next token.
Only a dozen or so command codes |>max_command| can possibly be returned by
|get_next|; in increasing order, they are |undefined_cs|, |expand_after|,
|no_expand|, |input|, |if_test|, |fi_or_else|, |cs_name|, |convert|, |the|,
|top_bot_mark|, |call|, |long_call|, |outer_call|, |long_outer_call|, and
|end_template|.{\emergencystretch=40pt\par}

@ Sometimes, recursive calls to the following |expand| routine may 
cause exhaustion of the run-time calling stack, resulting in
forced execution stops by the operating system. To diminish the chance
of this happening, a counter is used to keep track of the recursion
depth, in conjunction with a constant called |expand_depth|. 

Note that this does not catch all possible infinite recursion loops,
just the ones that exhaust the application calling stack. The
actual maximum value of |expand_depth| is outside of our control, but
the initial setting of |100| should be enough to prevent problems.
@^system dependencies@>

@<Global...@>=
expand_depth_count:integer;

@ @<Initialize whatever ...@>=
expand_depth_count:=0;

@ The |expand| subroutine is used when |cur_cmd>max_command|. It removes a
``call'' or a conditional or one of the other special operations just
listed.  It follows that |expand| might invoke itself recursively. In all
cases, |expand| destroys the current token, but it sets things up so that
the next |get_next| will deliver the appropriate next token. The value of
|cur_tok| need not be known when |expand| is called.

Since several of the basic scanning routines communicate via global variables,
their values are saved as local variables of |expand| so that
recursive calls don't invalidate them.
@^recursion@>

@p@t\4@>@<Declare the procedure called |macro_call|@>@;@/
@t\4@>@<Declare the procedure called |insert_relax|@>@;@/
@t\4@>@<Declare \eTeX\ procedures for expanding@>@;@/
procedure@?pass_text; forward;@t\2@>
procedure@?start_input; forward;@t\2@>
procedure@?conditional; forward;@t\2@>
procedure@?get_x_token; forward;@t\2@>
procedure@?conv_toks; forward;@t\2@>
procedure@?ins_the_toks; forward;@t\2@>
procedure expand;
label reswitch;
var t:halfword; {token that is being ``expanded after''}
@!p,@!q,@!r:pointer; {for list manipulation}
@!cur_ptr:pointer; { for a local token list pointer }
@!j:0..buf_size; {index into |buffer|}
@!s:ASCII_code; { a character }
@!cv_backup:integer; {to save the global quantity |cur_val|}
@!cvl_backup,@!radix_backup,@!co_backup:small_number;
  {to save |cur_val_level|, etc.}
@!backup_backup:pointer; {to save |link(backup_head)|}
@!save_scanner_status:small_number; {temporary storage of |scanner_status|}
begin 
incr(expand_depth_count);
if expand_depth_count>=expand_depth then overflow("expansion depth",expand_depth);
cv_backup:=cur_val; cvl_backup:=cur_val_level; radix_backup:=radix;
co_backup:=cur_order; backup_backup:=link(backup_head);
reswitch:
if cur_cmd<call then @<Expand a nonmacro@>
else if cur_cmd<end_template then macro_call
else @<Insert a token containing |frozen_endv|@>;
cur_val:=cv_backup; cur_val_level:=cvl_backup; radix:=radix_backup;
cur_order:=co_backup; link(backup_head):=backup_backup;
decr(expand_depth_count);
end;

@ @<Glob...@>=
@!is_in_csname: boolean;

@ @<Set init...@>=
is_in_csname := false;

@ @<Expand a nonmacro@>=
begin if tracing_commands>1 then show_cur_cmd_chr;
case cur_cmd of
top_bot_mark:@<Insert the \(a)appropriate mark text into the scanner@>;
expand_after:if cur_chr=0 then @<Expand the token after the next token@>
  else @<Negate a boolean conditional and |goto reswitch|@>;
no_expand: if cur_chr=0 then @<Suppress expansion of the next token@> 
  else @<Implement \.{\\primitive}@>;
cs_name:@<Manufacture a control sequence name@>;
convert:conv_toks; {this procedure is discussed in Part 27 below}
the:ins_the_toks; {this procedure is discussed in Part 27 below}
if_test:conditional; {this procedure is discussed in Part 28 below}
fi_or_else:@<Terminate the current conditional and skip to \.{\\fi}@>;
input:@<Initiate or terminate input from a file@>;
othercases @<Complain about an undefined macro@>
endcases;
end

@ It takes only a little shuffling to do what \TeX\ calls \.{\\expandafter}.

@<Expand the token after...@>=
begin get_token; t:=cur_tok; get_token;
if cur_cmd>max_command then expand@+else back_input;
cur_tok:=t; back_input;
end

@ The implementation of \.{\\noexpand} is a bit trickier, because it is
necessary to insert a special `|dont_expand|' marker into \TeX's reading
mechanism.  This special marker is processed by |get_next|, but it does
not slow down the inner loop.

Since \.{\\outer} macros might arise here, we must also
clear the |scanner_status| temporarily.

@<Suppress expansion...@>=
begin save_scanner_status:=scanner_status; scanner_status:=normal;
get_token; scanner_status:=save_scanner_status; t:=cur_tok;
back_input; {now |start| and |loc| point to the backed-up token |t|}
if t>=cs_token_flag then
  begin p:=get_avail; info(p):=cs_token_flag+frozen_dont_expand;
  link(p):=loc; start:=p; loc:=p;
  end;
end

@ The \.{\\primitive} handling. If the primitive meaning of the next 
token is an expandable command, it suffices to replace the current
token with the primitive one and restart |expand|. 

Otherwise, the token we just read has to be pushed back, as well
as a token matching the internal form of \.{\\primitive}, that is
sneaked in as an alternate form of |ignore_spaces|.
@!@:primitive_}{\.{\\primitive} primitive (internalized)@>

An implementation problem surfaces: There really is no |cur_cs|
attached to the inserted primitive command, so it is safer to set
|cur_cs| to zero.  |cur_tok| has a similar problem. And for the
non-expanded branch, simply pushing back a token that matches the
correct internal command does not work, because that approach would
not survive roundtripping to a temporary file or even a token list.

In a next version, it would be smart to create |frozen_| versions of
all the primitives.  Then, this problem would not happen, at the
expense of a few hundred extra control sequences.

@<Implement \.{\\primitive}@>=
begin save_scanner_status := scanner_status; scanner_status:=normal;
get_token; scanner_status:=save_scanner_status;
cur_cs := prim_lookup(text(cur_cs));
if cur_cs<>undefined_primitive then begin
  t:=get_prim_eq_type(cur_cs);
  if t>max_command then begin
    cur_cmd := t;
    cur_chr := get_prim_equiv(cur_cs);
    cur_tok := (cur_cmd*string_offset)+cur_chr;
    cur_cs  := 0;
    goto reswitch;
    end 
  else begin
    back_input; { now |loc| and |start| point to a one-item list }
    p:=get_avail; info(p):=cs_token_flag+frozen_primitive;
    link(p):=loc; loc:=p; start:=p; 
    end;
  end;
end

@ @<Complain about an undefined macro@>=
begin print_err("Undefined control sequence");
@.Undefined control sequence@>
help5("The control sequence at the end of the top line")@/
("of your error message was never \def'ed. If you have")@/
("misspelled it (e.g., `\hobx'), type `I' and the correct")@/
("spelling (e.g., `I\hbox'). Otherwise just continue,")@/
("and I'll forget about whatever was undefined.");
error;
end

@ The |expand| procedure and some other routines that construct token
lists find it convenient to use the following macros, which are valid only if
the variables |p| and |q| are reserved for token-list building.

@d store_new_token(#)==begin q:=get_avail; link(p):=q; info(q):=#;
  p:=q; {|link(p)| is |null|}
  end
@d fast_store_new_token(#)==begin fast_get_avail(q); link(p):=q; info(q):=#;
  p:=q; {|link(p)| is |null|}
  end

@ @<Manufacture a control...@>=
begin r:=get_avail; p:=r; {head of the list of characters}
is_in_csname := true;
repeat get_x_token;
if cur_cs=0 then store_new_token(cur_tok);
until cur_cs<>0;
if cur_cmd<>end_cs_name then @<Complain about missing \.{\\endcsname}@>;
is_in_csname := false;
@<Look up the characters of list |r| in the hash table, and set |cur_cs|@>;
flush_list(r);
if eq_type(cur_cs)=undefined_cs then
  begin eq_define(cur_cs,relax,too_big_char); {N.B.: The |save_stack| might change}
  end; {the control sequence will now match `\.{\\relax}'}
cur_tok:=cur_cs+cs_token_flag; back_input;
end

@ @<Complain about missing \.{\\endcsname}@>=
begin print_err("Missing "); print_esc("endcsname"); print(" inserted");
@.Missing \\endcsname...@>
help2("The control sequence marked <to be read again> should")@/
  ("not appear between \csname and \endcsname.");
back_error;
end

@ @<Look up the characters of list |r| in the hash table...@>=
j:=first; p:=link(r);
while p<>null do
  begin if j>=max_buf_stack then
    begin max_buf_stack:=j+4;
    if max_buf_stack=buf_size then
      check_buffer_overflow(max_buf_stack);
@:TeX capacity exceeded buffer size}{\quad buffer size@>
    end;
  s := info(p) mod string_offset;
  if s <= @"7F then begin
    buffer[j]:=s; incr(j);
    end
  else if s<=@"7FF then begin
    buffer[j]:=@"C0 + s div @"40; incr(j);
    buffer[j]:=@"80 + s mod @"40; incr(j);
    end
  else if s<=@"FFFF then begin
    buffer[j]:=@"E0 + s div @"1000; incr(j);
    buffer[j]:=@"80 + (s mod @"1000) div @"40; incr(j);
    buffer[j]:=@"80 + (s mod @"1000) mod @"40; incr(j);
    end 
  else begin
    buffer[j]:=@"F0 + s div @"40000;  incr(j);
    buffer[j]:=@"80 + (s mod @"40000) div @"1000;  incr(j);
    buffer[j]:=@"80 + ((s mod @"40000) mod @"1000) div @"40;  incr(j);
    buffer[j]:=@"80 + ((s mod @"40000) mod @"1000) mod @"40;  incr(j);
    end;
  p:=link(p); 
  end;
if j>first then
  begin no_new_control_sequence:=false; cur_cs:=id_lookup(first,j-first);
  no_new_control_sequence:=true;
  end
else if j=first then cur_cs:=null_cs {the list is empty}

@ An |end_template| command is effectively changed to an |endv| command
by the following code. (The reason for this is discussed below; the
|frozen_end_template| at the end of the template has passed the
|check_outer_validity| test, so its mission of error detection has been
accomplished.)

@<Insert a token containing |frozen_endv|@>=
begin cur_tok:=cs_token_flag+frozen_endv; back_input;
end

@ The processing of \.{\\input} involves the |start_input| subroutine,
which will be declared later; the processing of \.{\\endinput} is trivial.

@<Put each...@>=
primitive("input",input,0);@/
@!@:input_}{\.{\\input} primitive@>
primitive("endinput",input,1);@/
@!@:end_input_}{\.{\\endinput} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
input: if chr_code=0 then print_esc("input")
  @/@<Cases of |input| for |print_cmd_chr|@>@/
  else print_esc("endinput");

@ @<Initiate or terminate input...@>=
if cur_chr=1 then force_eof:=true
@/@<Cases for |input|@>@/
else if name_in_progress then insert_relax
else start_input

@ Sometimes the expansion looks too far ahead, so we want to insert
a harmless \.{\\relax} into the user's input.

@<Declare the procedure called |insert_relax|@>=
procedure insert_relax;
begin cur_tok:=cs_token_flag+cur_cs; back_input;
cur_tok:=cs_token_flag+frozen_relax; back_input; token_type:=inserted;
end;

@ Here is a recursive procedure that is \TeX's usual way to get the
next token of input. It has been slightly optimized to take account of
common cases.

@p procedure get_x_token; {sets |cur_cmd|, |cur_chr|, |cur_tok|,
  and expands macros}
label restart,done;
begin restart: get_filtered_next;
@^inner loop@>
if cur_cmd<=max_command then goto done;
if cur_cmd>=call then
  if cur_cmd<end_template then macro_call
  else  begin cur_cs:=frozen_endv; cur_cmd:=endv;
    goto done; {|cur_chr=null_list|}
    end
else expand;
goto restart;
done: if cur_cs=0 then cur_tok:=(cur_cmd*string_offset)+cur_chr
else cur_tok:=cs_token_flag+cur_cs;
end;

@ The |get_x_token| procedure is equivalent to two consecutive
procedure calls: |get_next; x_token|.

@p procedure x_token; {|get_x_token| without the initial |get_next|}
begin while cur_cmd>max_command do
  begin expand;
  get_filtered_next;
  end;
if cur_cs=0 then cur_tok:=(cur_cmd*string_offset)+cur_chr
else cur_tok:=cs_token_flag+cur_cs;
end;

@ The |get_filtered_next| procedure allows Lua code to mutate the 
output of |get_next| before \TeX\ looks at it. The implementation
is in the C file |luatoken.c|.

@d get_filtered_next==get_token_lua



@ A control sequence that has been \.{\\def}'ed by the user is expanded by
\TeX's |macro_call| procedure.

Before we get into the details of |macro_call|, however, let's consider the
treatment of primitives like \.{\\topmark}, since they are essentially
macros without parameters. The token lists for such marks are kept in five
global arrays of pointers; we refer to the individual entries of these
arrays by symbolic macros |top_mark|, etc. The value of |top_mark(x)|, etc.
is either |null| or a pointer to the reference count of a token list.

The variable |biggest_used_mark| is an aid to try and keep the code
somehwat efficient without too much extra work: it registers the
highest mark class ever instantiated by the user, so the loops
in |fire_up| and |vsplit| do not have to traverse the full range
|0..biggest_mark|.

@d top_mark_code=0 {the mark in effect at the previous page break}
@d first_mark_code=1 {the first mark between |top_mark| and |bot_mark|}
@d bot_mark_code=2 {the mark in effect at the current page break}
@d split_first_mark_code=3 {the first mark found by \.{\\vsplit}}
@d split_bot_mark_code=4 {the last mark found by \.{\\vsplit}}
@#
@d top_mark(#)==top_marks_array[#]
@d first_mark(#)==first_marks_array[#]
@d bot_mark(#)==bot_marks_array[#]
@d split_first_mark(#)==split_first_marks_array[#]
@d split_bot_mark(#)==split_bot_marks_array[#]
@#
@d delete_top_mark(#)==begin if top_mark(#)<>null then 
      delete_token_ref(top_mark(#)); top_mark(#):=null; end
@d delete_bot_mark(#)==begin if bot_mark(#)<>null then
      delete_token_ref(bot_mark(#)); bot_mark(#):=null; end
@d delete_first_mark(#)==begin if first_mark(#)<>null then
      delete_token_ref(first_mark(#)); first_mark(#):=null; end
@d delete_split_first_mark(#)==begin if split_first_mark(#)<>null then
      delete_token_ref(split_first_mark(#)); split_first_mark(#):=null; end
@d delete_split_bot_mark(#)==begin if split_bot_mark(#)<>null then
      delete_token_ref(split_bot_mark(#)); split_bot_mark(#):=null; end
@#
@d clear_marks_code=1
@d marks_code=5
@#

@<Glob...@>=
@!top_marks_array:array[0..biggest_mark] of pointer;
@!first_marks_array:array[0..biggest_mark] of pointer;
@!bot_marks_array:array[0..biggest_mark] of pointer;
@!split_first_marks_array:array[0..biggest_mark] of pointer;
@!split_bot_marks_array:array[0..biggest_mark] of pointer;
biggest_used_mark:halfword;

@ @<Set init...@>=
biggest_used_mark:=0;
for i:=0 to biggest_mark do begin
  top_mark(i):=null;
  first_mark(i):=null;
  bot_mark(i):=null;
  split_first_mark(i):=null;
  split_bot_mark(i):=null;
end;

@ @<Put each...@>=
primitive("topmark",top_bot_mark,top_mark_code);
@!@:top_mark_}{\.{\\topmark} primitive@>
primitive("firstmark",top_bot_mark,first_mark_code);
@!@:first_mark_}{\.{\\firstmark} primitive@>
primitive("botmark",top_bot_mark,bot_mark_code);
@!@:bot_mark_}{\.{\\botmark} primitive@>
primitive("splitfirstmark",top_bot_mark,split_first_mark_code);
@!@:split_first_mark_}{\.{\\splitfirstmark} primitive@>
primitive("splitbotmark",top_bot_mark,split_bot_mark_code);
@!@:split_bot_mark_}{\.{\\splitbotmark} primitive@>
primitive("clearmarks",mark,clear_marks_code);@/
@!@:clearmarks_}{\.{\\clearmarks} primitive@>
primitive("marks",mark,marks_code);
@!@:marks_}{\.{\\marks} primitive@>
primitive("topmarks",top_bot_mark,top_mark_code+marks_code);
@!@:top_marks_}{\.{\\topmarks} primitive@>
primitive("firstmarks",top_bot_mark,first_mark_code+marks_code);
@!@:first_marks_}{\.{\\firstmarks} primitive@>
primitive("botmarks",top_bot_mark,bot_mark_code+marks_code);
@!@:bot_marks_}{\.{\\botmarks} primitive@>
primitive("splitfirstmarks",top_bot_mark,split_first_mark_code+marks_code);
@!@:split_first_marks_}{\.{\\splitfirstmarks} primitive@>
primitive("splitbotmarks",top_bot_mark,split_bot_mark_code+marks_code);
@!@:split_bot_marks_}{\.{\\splitbotmarks} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
top_bot_mark: begin case (chr_code mod marks_code) of
  first_mark_code: print_esc("firstmark");
  bot_mark_code: print_esc("botmark");
  split_first_mark_code: print_esc("splitfirstmark");
  split_bot_mark_code: print_esc("splitbotmark");
  othercases print_esc("topmark")
  endcases;
  if chr_code>=marks_code then print_char("s");
  end;

@ The following code is activated when |cur_cmd=top_bot_mark| and
when |cur_chr| is a code like |top_mark_code|.

@<Insert the \(a)appropriate mark text into the scanner@>=
begin t:=cur_chr mod marks_code;
if cur_chr>=marks_code then scan_mark_num@+else cur_val:=0;
case t of
  first_mark_code:       cur_ptr:=first_mark(cur_val);
  bot_mark_code:         cur_ptr:=bot_mark(cur_val);
  split_first_mark_code: cur_ptr:=split_first_mark(cur_val);
  split_bot_mark_code:   cur_ptr:=split_bot_mark(cur_val);
  othercases             cur_ptr:=top_mark(cur_val)
endcases;
if cur_ptr<>null then begin_token_list(cur_ptr,mark_text);
end

@ Now let's consider |macro_call| itself, which is invoked when \TeX\ is
scanning a control sequence whose |cur_cmd| is either |call|, |long_call|,
|outer_call|, or |long_outer_call|.  The control sequence definition
appears in the token list whose reference count is in location |cur_chr|
of |mem|.

The global variable |long_state| will be set to |call| or to |long_call|,
depending on whether or not the control sequence disallows \.{\\par}
in its parameters. The |get_next| routine will set |long_state| to
|outer_call| and emit \.{\\par}, if a file ends or if an \.{\\outer}
control sequence occurs in the midst of an argument.

@<Glob...@>=
@!long_state:call..long_outer_call; {governs the acceptance of \.{\\par}}

@ The parameters, if any, must be scanned before the macro is expanded.
Parameters are token lists without reference counts. They are placed on
an auxiliary stack called |pstack| while they are being scanned, since
the |param_stack| may be losing entries during the matching process.
(Note that |param_stack| can't be gaining entries, since |macro_call| is
the only routine that puts anything onto |param_stack|, and it
is not recursive.)

@<Glob...@>=
@!pstack:array[0..8] of pointer; {arguments supplied to a macro}

@ After parameter scanning is complete, the parameters are moved to the
|param_stack|. Then the macro body is fed to the scanner; in other words,
|macro_call| places the defined text of the control sequence at the
top of\/ \TeX's input stack, so that |get_next| will proceed to read it
next.

The global variable |cur_cs| contains the |eqtb| address of the control sequence
being expanded, when |macro_call| begins. If this control sequence has not been
declared \.{\\long}, i.e., if its command code in the |eq_type| field is
not |long_call| or |long_outer_call|, its parameters are not allowed to contain
the control sequence \.{\\par}. If an illegal \.{\\par} appears, the macro
call is aborted, and the \.{\\par} will be rescanned.

@<Declare the procedure called |macro_call|@>=
procedure macro_call; {invokes a user-defined control sequence}
label exit, continue, done, done1, found;
var r:pointer; {current node in the macro's token list}
@!p:pointer; {current node in parameter token list being built}
@!q:pointer; {new node being put into the token list}
@!s:pointer; {backup pointer for parameter matching}
@!t:pointer; {cycle pointer for backup recovery}
@!u,@!v:pointer; {auxiliary pointers for backup recovery}
@!rbrace_ptr:pointer; {one step before the last |right_brace| token}
@!n:small_number; {the number of parameters scanned}
@!unbalance:halfword; {unmatched left braces in current parameter}
@!m:halfword; {the number of tokens or groups (usually)}
@!ref_count:pointer; {start of the token list}
@!save_scanner_status:small_number; {|scanner_status| upon entry}
@!save_warning_index:pointer; {|warning_index| upon entry}
@!match_chr:ASCII_code; {character used in parameter}
begin save_scanner_status:=scanner_status; save_warning_index:=warning_index;
warning_index:=cur_cs; ref_count:=cur_chr; r:=link(ref_count); n:=0;
p:=null; m:=0; rbrace_ptr:=null; match_chr:=0;
if tracing_macros>0 then @<Show the text of the macro being expanded@>;
if info(r)=protected_token then r:=link(r);
if info(r)<>end_match_token then
  @<Scan the parameters and make |link(r)| point to the macro body; but
    |return| if an illegal \.{\\par} is detected@>;
@<Feed the macro body and its parameters to the scanner@>;
exit:scanner_status:=save_scanner_status; warning_index:=save_warning_index;
end;

@ Before we put a new token list on the input stack, it is wise to clean off
all token lists that have recently been depleted. Then a user macro that ends
with a call to itself will not require unbounded stack space.

@<Feed the macro body and its parameters to the scanner@>=
while (state=token_list)and(loc=null)and(token_type<>v_template) do
  end_token_list; {conserve stack space}
begin_token_list(ref_count,macro); name:=warning_index; loc:=link(r);
if n>0 then
  begin if param_ptr+n>max_param_stack then
    begin max_param_stack:=param_ptr+n;
    if max_param_stack>param_size then
      overflow("parameter stack size",param_size);
@:TeX capacity exceeded parameter stack size}{\quad parameter stack size@>
    end;
  for m:=0 to n-1 do param_stack[param_ptr+m]:=pstack[m];
  param_ptr:=param_ptr+n;
  end

@ At this point, the reader will find it advisable to review the explanation
of token list format that was presented earlier, since many aspects of that
format are of importance chiefly in the |macro_call| routine.

The token list might begin with a string of compulsory tokens before the
first |match| or |end_match|. In that case the macro name is supposed to be
followed by those tokens; the following program will set |s=null| to
represent this restriction. Otherwise |s| will be set to the first token of
a string that will delimit the next parameter.

@<Scan the parameters and make |link(r)| point to the macro body...@>=
begin scanner_status:=matching; unbalance:=0;
long_state:=eq_type(cur_cs);
if long_state>=outer_call then long_state:=long_state-2;
repeat link(temp_token_head):=null;
if (info(r)>=end_match_token)or(info(r)<match_token) then s:=null
else  begin match_chr:=info(r)-match_token; s:=link(r); r:=s;
  p:=temp_token_head; m:=0;
  end;
@<Scan a parameter until its delimiter string has been found; or, if |s=null|,
  simply scan the delimiter string@>;@/
{now |info(r)| is a token whose command code is either |match| or |end_match|}
until info(r)=end_match_token;
end

@ If |info(r)| is a |match| or |end_match| command, it cannot be equal to
any token found by |get_token|. Therefore an undelimited parameter---i.e.,
a |match| that is immediately followed by |match| or |end_match|---will
always fail the test `|cur_tok=info(r)|' in the following algorithm.

@<Scan a parameter until its delimiter string has been found; or, ...@>=
continue: get_token; {set |cur_tok| to the next token of input}
if cur_tok=info(r) then
  @<Advance \(r)|r|; |goto found| if the parameter delimiter has been
    fully matched, otherwise |goto continue|@>;
@<Contribute the recently matched tokens to the current parameter, and
  |goto continue| if a partial match is still in effect;
  but abort if |s=null|@>;
if cur_tok=par_token then if long_state<>long_call then
  @<Report a runaway argument and abort@>;
if cur_tok<right_brace_limit then
  if cur_tok<left_brace_limit then
    @<Contribute an entire group to the current parameter@>
  else @<Report an extra right brace and |goto continue|@>
else @<Store the current token, but |goto continue| if it is
   a blank space that would become an undelimited parameter@>;
incr(m);
if info(r)>end_match_token then goto continue;
if info(r)<match_token then goto continue;
found: if s<>null then @<Tidy up the parameter just scanned, and tuck it away@>

@ @<Store the current token, but |goto continue| if it is...@>=
begin if cur_tok=space_token then
  if info(r)<=end_match_token then
    if info(r)>=match_token then goto continue;
store_new_token(cur_tok);
end

@ A slightly subtle point arises here: When the parameter delimiter ends
with `\.{\#\{}', the token list will have a left brace both before and
after the |end_match|\kern-.4pt. Only one of these should affect the
|align_state|, but both will be scanned, so we must make a correction.

@<Advance \(r)|r|; |goto found| if the parameter delimiter has been fully...@>=
begin r:=link(r);
if (info(r)>=match_token)and(info(r)<=end_match_token) then
  begin if cur_tok<left_brace_limit then decr(align_state);
  goto found;
  end
else goto continue;
end

@ @<Report an extra right brace and |goto continue|@>=
begin back_input; print_err("Argument of "); sprint_cs(warning_index);
@.Argument of \\x has...@>
print(" has an extra }");
help6("I've run across a `}' that doesn't seem to match anything.")@/
  ("For example, `\def\a#1{...}' and `\a}' would produce")@/
  ("this error. If you simply proceed now, the `\par' that")@/
  ("I've just inserted will cause me to report a runaway")@/
  ("argument that might be the root of the problem. But if")@/
  ("your `}' was spurious, just type `2' and it will go away.");
incr(align_state); long_state:=call; cur_tok:=par_token; ins_error;
end {a white lie; the \.{\\par} won't always trigger a runaway}

@ If |long_state=outer_call|, a runaway argument has already been reported.

@<Report a runaway argument and abort@>=
begin if long_state=call then
  begin runaway; print_err("Paragraph ended before ");
@.Paragraph ended before...@>
  sprint_cs(warning_index); print(" was complete");
  help3("I suspect you've forgotten a `}', causing me to apply this")@/
    ("control sequence to too much text. How can we recover?")@/
    ("My plan is to forget the whole thing and hope for the best.");
  back_error;
  end;
pstack[n]:=link(temp_token_head); align_state:=align_state-unbalance;
for m:=0 to n do flush_list(pstack[m]);
return;
end

@ When the following code becomes active, we have matched tokens from |s| to
the predecessor of |r|, and we have found that |cur_tok<>info(r)|. An
interesting situation now presents itself: If the parameter is to be
delimited by a string such as `\.{ab}', and if we have scanned `\.{aa}',
we want to contribute one `\.a' to the current parameter and resume
looking for a `\.b'. The program must account for such partial matches and
for others that can be quite complex.  But most of the time we have |s=r|
and nothing needs to be done.

Incidentally, it is possible for \.{\\par} tokens to sneak in to certain
parameters of non-\.{\\long} macros. For example, consider a case like
`\.{\\def\\a\#1\\par!\{...\}}' where the first \.{\\par} is not followed
by an exclamation point. In such situations it does not seem appropriate
to prohibit the \.{\\par}, so \TeX\ keeps quiet about this bending of
the rules.

@<Contribute the recently matched tokens to the current parameter...@>=
if s<>r then
  if s=null then @<Report an improper use of the macro and abort@>
  else  begin t:=s;
    repeat store_new_token(info(t)); incr(m); u:=link(t); v:=s;
    loop@+  begin if u=r then
        if cur_tok<>info(v) then goto done
        else  begin r:=link(v); goto continue;
          end;
      if info(u)<>info(v) then goto done;
      u:=link(u); v:=link(v);
      end;
    done: t:=link(t);
    until t=r;
    r:=s; {at this point, no tokens are recently matched}
    end

@ @<Report an improper use...@>=
begin print_err("Use of "); sprint_cs(warning_index);
@.Use of x doesn't match...@>
print(" doesn't match its definition");
help4("If you say, e.g., `\def\a1{...}', then you must always")@/
  ("put `1' after `\a', since control sequence names are")@/
  ("made up of letters only. The macro here has not been")@/
  ("followed by the required stuff, so I'm ignoring it.");
error; return;
end

@ @<Contribute an entire group to the current parameter@>=
begin unbalance:=1;
@^inner loop@>
loop@+  begin fast_store_new_token(cur_tok); get_token;
  if cur_tok=par_token then if long_state<>long_call then
    @<Report a runaway argument and abort@>;
  if cur_tok<right_brace_limit then
    if cur_tok<left_brace_limit then incr(unbalance)
    else  begin decr(unbalance);
      if unbalance=0 then goto done1;
      end;
  end;
done1: rbrace_ptr:=p; store_new_token(cur_tok);
end

@ If the parameter consists of a single group enclosed in braces, we must
strip off the enclosing braces. That's why |rbrace_ptr| was introduced.

@<Tidy up the parameter just scanned, and tuck it away@>=
begin if (m=1)and(info(p)<right_brace_limit)and(p<>temp_token_head) then
  begin link(rbrace_ptr):=null; free_avail(p);
  p:=link(temp_token_head); pstack[n]:=link(p); free_avail(p);
  end
else pstack[n]:=link(temp_token_head);
incr(n);
if tracing_macros>0 then
  begin begin_diagnostic; print_nl(match_chr); print_int(n);
  print("<-"); show_token_list(pstack[n-1],null,1000);
  end_diagnostic(false);
  end;
end

@ @<Show the text of the macro being expanded@>=
begin begin_diagnostic; print_ln; print_cs(warning_index);
token_show(ref_count); end_diagnostic(false);
end

@* \[26] Basic scanning subroutines.
Let's turn now to some procedures that \TeX\ calls upon frequently to digest
certain kinds of patterns in the input. Most of these are quite simple;
some are quite elaborate. Almost all of the routines call |get_x_token|,
which can cause them to be invoked recursively.
@^stomach@>
@^recursion@>

@ The |scan_left_brace| routine is called when a left brace is supposed to be
the next non-blank token. (The term ``left brace'' means, more precisely,
a character whose catcode is |left_brace|.) \TeX\ allows \.{\\relax} to
appear before the |left_brace|.

@p procedure scan_left_brace; {reads a mandatory |left_brace|}
begin @<Get the next non-blank non-relax non-call token@>;
if cur_cmd<>left_brace then
  begin print_err("Missing { inserted");
@.Missing \{ inserted@>
  help4("A left brace was mandatory here, so I've put one in.")@/
    ("You might want to delete and/or insert some corrections")@/
    ("so that I will find a matching right brace soon.")@/
    ("(If you're confused by all this, try typing `I}' now.)");
  back_error; cur_tok:=left_brace_token+"{"; cur_cmd:=left_brace;
  cur_chr:="{"; incr(align_state);
  end;
end;

@ The |scan_right_brace| routine is called when a right brace is supposed to be
the next non-blank token. (The term ``right brace'' means, more precisely,
a character whose catcode is |right_brace|.) \TeX\ allows \.{\\relax} to
appear before the |right_brace|.

@p procedure scan_right_brace; {reads a mandatory |right_brace|}
begin @<Get the next non-blank non-relax non-call token@>;
if cur_cmd<>right_brace then
  begin print_err("Missing { inserted");
@.Missing \{ inserted@>
  help4("A right brace was mandatory here, so I've put one in.")@/
    ("You might want to delete and/or insert some corrections")@/
    ("so that I will find a matching right brace soon.")@/
    ("(If you're confused by all this, try typing `I}' now.)");
  back_error; cur_tok:=right_brace_token+"}"; cur_cmd:=right_brace;
  cur_chr:="}"; incr(align_state);
  end;
end;

@ @<Get the next non-blank non-relax non-call token@>=
repeat get_x_token;
until (cur_cmd<>spacer)and(cur_cmd<>relax)

@ The |scan_optional_equals| routine looks for an optional `\.=' sign preceded
by optional spaces; `\.{\\relax}' is not ignored here.

@p procedure scan_optional_equals;
begin  @<Get the next non-blank non-call token@>;
if cur_tok<>other_token+"=" then back_input;
end;

@ @<Get the next non-blank non-call token@>=
repeat get_x_token;
until cur_cmd<>spacer

@ In case you are getting bored, here is a slightly less trivial routine:
Given a string of lowercase letters, like `\.{pt}' or `\.{plus}' or
`\.{width}', the |scan_keyword| routine checks to see whether the next
tokens of input match this string. The match must be exact, except that
uppercase letters will match their lowercase counterparts; uppercase
equivalents are determined by subtracting |"a"-"A"|, rather than using the
|uc_code| table, since \TeX\ uses this routine only for its own limited
set of keywords.

If a match is found, the characters are effectively removed from the input
and |true| is returned. Otherwise |false| is returned, and the input
is left essentially unchanged (except for the fact that some macros
may have been expanded, etc.).
@^inner loop@>

@p function scan_keyword(@!s:str_number):boolean; {look for a given string}
label exit;
var p:pointer; {tail of the backup list}
@!q:pointer; {new node being added to the token list via |store_new_token|}
@!k:pool_pointer; {index into |str_pool|}
begin 
if s<number_chars then begin 
	@<Get the next non-blank non-call token@>;
    if (cur_cs=0)and((cur_chr=s)or(cur_chr=s-"a"+"A")) then
      scan_keyword:=true
    else 
      begin back_input;
      scan_keyword:=false; return;
      end;
  end 
else begin
  p:=backup_head; link(p):=null; 
  k:=str_start_macro(s);
  while k<str_start_macro(s+1) do
    begin get_x_token; {recursion is possible here}
@^recursion@>
    if (cur_cs=0)and@|
     ((cur_chr=so(str_pool[k]))or(cur_chr=so(str_pool[k])-"a"+"A")) then
      begin store_new_token(cur_tok); incr(k);
      end
    else if (cur_cmd<>spacer)or(p<>backup_head) then
      begin 
      if p<>backup_head then begin
         q:=get_avail; info(q):=cur_tok; link(q):=null;
         link(p) := q;
         back_list(link(backup_head));
	     end
      else
         back_input;
      scan_keyword:=false; return;
      end;
    end;
  flush_list(link(backup_head)); scan_keyword:=true;
end;
exit:end;

@ Here is a procedure that sounds an alarm when mu and non-mu units
are being switched.

@p procedure mu_error;
begin print_err("Incompatible glue units");
@.Incompatible glue units@>
help1("I'm going to assume that 1mu=1pt when they're mixed.");
error;
end;

@ The next routine `|scan_something_internal|' is used to fetch internal
numeric quantities like `\.{\\hsize}', and also to handle the `\.{\\the}'
when expanding constructions like `\.{\\the\\toks0}' and
`\.{\\the\\baselineskip}'. Soon we will be considering the |scan_int|
procedure, which calls |scan_something_internal|; on the other hand,
|scan_something_internal| also calls |scan_int|, for constructions like
`\.{\\catcode\`\\\$}' or `\.{\\fontdimen} \.3 \.{\\ff}'. So we
have to declare |scan_int| as a |forward| procedure. A few other
procedures are also declared at this point.

@p procedure@?scan_int; forward; {scans an integer value}
@t\4\4@>@<Declare procedures that scan restricted classes of integers@>@;
@t\4\4@>@<Declare \eTeX\ procedures for scanning@>@;
@t\4\4@>@<Declare procedures that scan font-related stuff@>
@t\4\4@>@<Declare procedures that scan ocp-related stuff@>

@ \TeX\ doesn't know exactly what to expect when
|scan_something_internal| begins.  For example, an integer or
dimension or glue value could occur immediately after `\.{\\hskip}';
and one can even say \.{\\the} with respect to token lists in
constructions like `\.{\\xdef\\o\{\\the\\output\}}'.  On the other
hand, only integers are allowed after a construction like
`\.{\\count}'. To handle the various possibilities,
|scan_something_internal| has a |level| parameter, which tells the
``highest'' kind of quantity that |scan_something_internal| is allowed
to produce. Eight levels are distinguished, namely |int_val|,
|attr_val|, |dimen_val|, |glue_val|, |mu_val|, |dir_val|, |ident_val|,
and |tok_val|.

The output of |scan_something_internal| (and of the other routines
|scan_int|, |scan_dimen|, and |scan_glue| below) is put into the global
variable |cur_val|, and its level is put into |cur_val_level|. The highest
values of |cur_val_level| are special: |mu_val| is used only when
|cur_val| points to something in a ``muskip'' register, or to one of the
three parameters \.{\\thinmuskip}, \.{\\medmuskip}, \.{\\thickmuskip};
|ident_val| is used only when |cur_val| points to a font identifier;
|tok_val| is used only when |cur_val| points to |null| or to the reference
count of a token list. The last two cases are allowed only when
|scan_something_internal| is called with |level=tok_val|.

If the output is glue, |cur_val| will point to a glue specification, and
the reference count of that glue will have been updated to reflect this
reference; if the output is a nonempty token list, |cur_val| will point to
its reference count, but in this case the count will not have been updated.
Otherwise |cur_val| will contain the integer or scaled value in question.

@d int_val=0 {integer values}
@d attr_val=1 {integer values}
@d dimen_val=2 {dimension values}
@d glue_val=3 {glue specifications}
@d mu_val=4 {math glue specifications}
@d dir_val=5 {directions}
@d ident_val=6 {font identifier}
@d tok_val=7 {token lists}

@<Glob...@>=
@!cur_val:integer; {value returned by numeric scanners}
@!cur_val1:integer; {delcodes are now 51 digits}
@!cur_val_level:int_val..tok_val; {the ``level'' of this value}

@ The hash table is initialized with `\.{\\count}', `\.{\\attribute}',
`\.{\\dimen}', `\.{\\skip}', and `\.{\\muskip}' all having |register|
as their command code; they are distinguished by the |chr_code|, which
is either |int_val|, |attr_val|, |dimen_val|, |glue_val|, or |mu_val|.

@<Put each...@>=
primitive("count",register,int_val);
@!@:count_}{\.{\\count} primitive@>
primitive("attribute",register,attr_val);
@!@:count_}{\.{\\attribute} primitive@>
primitive("dimen",register,dimen_val);
@!@:dimen_}{\.{\\dimen} primitive@>
primitive("skip",register,glue_val);
@!@:skip_}{\.{\\skip} primitive@>
primitive("muskip",register,mu_val);

@ @<Cases of |print_cmd_chr|...@>=
register: if chr_code=int_val then print_esc("count")
  else if chr_code=attr_val then print_esc("attribute")
  else if chr_code=dimen_val then print_esc("dimen")
  else if chr_code=glue_val then print_esc("skip")
  else print_esc("muskip");

@ OK, we're ready for |scan_something_internal| itself. A second parameter,
|negative|, is set |true| if the value that is found should be negated.
It is assumed that |cur_cmd| and |cur_chr| represent the first token of
the internal quantity to be scanned; an error will be signalled if
|cur_cmd<min_internal| or |cur_cmd>max_internal|.

@d scanned_result_end(#)==cur_val_level:=#;@+end
@d scanned_result(#)==@+begin cur_val:=#;scanned_result_end

@p procedure scan_something_internal(@!level:small_number;@!negative:boolean);
  {fetch an internal parameter}
label exit;
var m:halfword; {|chr_code| part of the operand token}
    n, k: integer; {accumulators}
@!q:halfword; {general purpose index}
@!p:0..nest_size; {index into |nest|}
begin m:=cur_chr;
case cur_cmd of
def_code: @<Fetch a character code from some table@>;
extdef_code: @<Fetch an ext character code from some table@>;
toks_register,assign_toks,def_family,set_font,def_font,letterspace_font: @<Fetch a token list or
  font identifier, provided that |level=tok_val|@>;
assign_int: scanned_result(eqtb[m].int)(int_val);
assign_attr: scanned_result(eqtb[m].int)(int_val);
assign_box_dir: begin
  scan_register_num;
  m:=cur_val;
  if box(m)<>null then cur_val:=box_dir(box(m))
  else cur_val:=0;
  cur_val_level:=dir_val;
  end;
assign_dir: scanned_result(eqtb[m].int)(dir_val);
assign_dimen: scanned_result(eqtb[m].sc)(dimen_val);
assign_glue: scanned_result(equiv(m))(glue_val);
assign_mu_glue: scanned_result(equiv(m))(mu_val);
set_aux: @<Fetch the |space_factor| or the |prev_depth|@>;
set_prev_graf: @<Fetch the |prev_graf|@>;
set_page_int:@<Fetch the |dead_cycles| or the |insert_penalties|@>;
set_page_dimen: @<Fetch something on the |page_so_far|@>;
set_shape: @<Fetch the |par_shape| size@>;
set_box_dimen: @<Fetch a box dimension@>;
char_given,math_given,omath_given: scanned_result(cur_chr)(int_val);
assign_font_dimen: @<Fetch a font dimension@>;
assign_font_int: @<Fetch a font integer@>;
register: @<Fetch a register@>;
last_item: @<Fetch an item in the current node, if appropriate@>;
othercases @<Complain that \.{\\the} can't do this; give zero result@>
endcases;@/
while cur_val_level>level do @<Convert \(c)|cur_val| to a lower level@>;
@<Fix the reference count, if any, and negate |cur_val| if |negative|@>;
exit:end;

procedure scan_something_simple(@!cmd:halfword;@!subitem:halfword);
  {fetch an internal parameter}
label exit;
var m:halfword; {|chr_code| part of the operand token}
@!p:0..nest_size; {index into |nest|}
@!level:small_number; { allowed level}
begin m:=subitem; level:=tok_val;
case cmd of
assign_toks: scanned_result(equiv(m))(tok_val);
assign_int: scanned_result(eqtb[m].int)(int_val);
assign_attr: scanned_result(eqtb[m].int)(int_val);
assign_dir: scanned_result(eqtb[m].int)(dir_val);
assign_dimen: scanned_result(eqtb[m].sc)(dimen_val);
assign_glue: scanned_result(equiv(m))(glue_val);
assign_mu_glue: scanned_result(equiv(m))(mu_val);
set_aux: @<Fetch the |space_factor| or the |prev_depth|@>;
set_prev_graf: @<Fetch the |prev_graf|@>;
set_page_int:@<Fetch the |dead_cycles| or the |insert_penalties|@>;
set_page_dimen: @<Fetch something on the |page_so_far|@>;
set_shape: @<Fetch the |par_shape| size@>;
char_given,math_given,omath_given: scanned_result(m)(int_val); {TH: TODO, doesnt work}
othercases @<Complain that |texlib| can't do this; give zero result@>
endcases;@/
exit:end;

@ @<Fetch a character code from some table@>=
begin scan_char_num;
if m=math_code_base then begin
  cur_val1:=get_math_code(cur_val);
  if ((cur_val1 div @"1000000)>8) or
     (((cur_val1 mod @"1000000) div @"10000)>15) or
     ((cur_val1 mod @"10000)>255) then
    begin print_err("Extended mathchar used as mathchar");
@.Bad mathchar@>
    help2("A mathchar number must be between 0 and ""7FFF.")@/
      ("I changed this one to zero."); int_error(cur_val1); cur_val1:=0;
    end;
  cur_val1:=((cur_val1 div @"1000000)*@"1000) +
            (((cur_val1 mod @"1000000) div @"10000)*@"100) +
            (cur_val1 mod @"10000);
  scanned_result(cur_val1)(int_val);
  end
else if m=lc_code_base then begin
  cur_val1:=get_lc_code(cur_val);
  scanned_result(cur_val1)(int_val);
  end
else if m=uc_code_base then begin
  cur_val1:=get_uc_code(cur_val);
  scanned_result(cur_val1)(int_val);
  end
else if m=sf_code_base then begin
  cur_val1:=get_sf_code(cur_val);
  scanned_result(cur_val1)(int_val);
  end
else if m=cat_code_base then begin
  cur_val1:=get_cat_code(cat_code_table,cur_val);
  scanned_result(cur_val1)(int_val);
  end
else if m<math_code_base then scanned_result(equiv(m+cur_val))(int_val)
else scanned_result(eqtb[m+cur_val].int)(int_val);
end

@ @<Fetch an ext character code from some table@>=
begin scan_char_num;
if m=math_code_base then scanned_result(get_math_code(cur_val))(int_val)
{ TH: next two lines should not be possible }
else if m<math_code_base then scanned_result(equiv(m+cur_val))(int_val)
else scanned_result(eqtb[m+cur_val].int)(int_val);
end

@ @<Fetch a token list...@>=
if level<>tok_val then
  begin print_err("Missing number, treated as zero");
@.Missing number...@>
  help3("A number should have been here; I inserted `0'.")@/
    ("(If you can't figure out why I needed to see a number,")@/
    ("look up `weird error' in the index to The TeXbook.)");
@:TeXbook}{\sl The \TeX book@>
  back_error; scanned_result(0)(dimen_val);
  end
else if cur_cmd<=assign_toks then
  begin if cur_cmd<assign_toks then {|cur_cmd=toks_register|}
    begin scan_register_num; m:=toks_base+cur_val;
    end;
  scanned_result(equiv(m))(tok_val);
  end
else  begin back_input; scan_font_ident;
  scanned_result(font_id_base+cur_val)(ident_val);
  end

@ Users refer to `\.{\\the\\spacefactor}' only in horizontal
mode, and to `\.{\\the\\prevdepth}' only in vertical mode; so we put the
associated mode in the modifier part of the |set_aux| command.
The |set_page_int| command has modifier 0 or 1, for `\.{\\deadcycles}' and
`\.{\\insertpenalties}', respectively. The |set_box_dimen| command is
modified by either |width_offset|, |height_offset|, or |depth_offset|.
And the |last_item| command is modified by either |int_val|, |dimen_val|,
|glue_val|, |input_line_no_code|, or |badness_code|.
\pdfTeX\ adds the codes for its extensions: |pdftex_version_code|, \dots\ .
\eTeX\ inserts |last_node_type_code| after |glue_val| and adds
the codes for its extensions: |eTeX_version_code|, \dots\ .

@d last_node_type_code=glue_val+1 {code for \.{\\lastnodetype}}
@d input_line_no_code=glue_val+2 {code for \.{\\inputlineno}}
@d badness_code=input_line_no_code+1 {code for \.{\\badness}}
@#
@d pdftex_first_rint_code     = badness_code + 1 {base for \pdfTeX's command codes}
@d pdftex_version_code        = pdftex_first_rint_code + 0 {code for \.{\\pdftexversion}}
@d pdf_last_obj_code          = pdftex_first_rint_code + 1 {code for \.{\\pdflastobj}}
@d pdf_last_xform_code        = pdftex_first_rint_code + 2 {code for \.{\\pdflastxform}}
@d pdf_last_ximage_code       = pdftex_first_rint_code + 3 {code for \.{\\pdflastximage}}
@d pdf_last_ximage_pages_code = pdftex_first_rint_code + 4 {code for \.{\\pdflastximagepages}}
@d pdf_last_annot_code        = pdftex_first_rint_code + 5 {code for \.{\\pdflastannot}}
@d pdf_last_x_pos_code        = pdftex_first_rint_code + 6 {code for \.{\\pdflastxpos}}
@d pdf_last_y_pos_code        = pdftex_first_rint_code + 7 {code for \.{\\pdflastypos}}
@d pdf_retval_code            = pdftex_first_rint_code + 8 {global multi-purpose return value}
@d pdf_last_ximage_colordepth_code = pdftex_first_rint_code + 9 {code for \.{\\pdflastximagecolordepth}}
@d random_seed_code           = pdftex_first_rint_code + 10 {code for \.{\\pdfrandomseed}}
@d pdf_last_link_code         = pdftex_first_rint_code + 11 {code for \.{\\pdflastlink}}
@d luatex_version_code        = pdftex_first_rint_code + 12 {code for \.{\\luatexversion}}
@d pdftex_last_item_codes     = pdftex_first_rint_code + 12 {end of \pdfTeX's command codes}
@#
@d Aleph_int=pdftex_last_item_codes+1 {first of \Aleph\ codes for integers}
@d Aleph_int_num=5 {number of \Aleph\ integers}
@d eTeX_int=Aleph_int+Aleph_int_num {first of \eTeX\ codes for integers}
@d eTeX_dim=eTeX_int+8 {first of \eTeX\ codes for dimensions}
@d eTeX_glue=eTeX_dim+9 {first of \eTeX\ codes for glue}
@d eTeX_mu=eTeX_glue+1 {first of \eTeX\ codes for muglue}
@d eTeX_expr=eTeX_mu+1 {first of \eTeX\ codes for expressions}

@<Put each...@>=
primitive("spacefactor",set_aux,hmode);
@!@:space_factor_}{\.{\\spacefactor} primitive@>
primitive("prevdepth",set_aux,vmode);@/
@!@:prev_depth_}{\.{\\prevdepth} primitive@>
primitive("deadcycles",set_page_int,0);
@!@:dead_cycles_}{\.{\\deadcycles} primitive@>
primitive("insertpenalties",set_page_int,1);
@!@:insert_penalties_}{\.{\\insertpenalties} primitive@>
primitive("wd",set_box_dimen,width_offset);
@!@:wd_}{\.{\\wd} primitive@>
primitive("ht",set_box_dimen,height_offset);
@!@:ht_}{\.{\\ht} primitive@>
primitive("dp",set_box_dimen,depth_offset);
@!@:dp_}{\.{\\dp} primitive@>
primitive("lastpenalty",last_item,int_val);
@!@:last_penalty_}{\.{\\lastpenalty} primitive@>
primitive("lastkern",last_item,dimen_val);
@!@:last_kern_}{\.{\\lastkern} primitive@>
primitive("lastskip",last_item,glue_val);
@!@:last_skip_}{\.{\\lastskip} primitive@>
primitive("inputlineno",last_item,input_line_no_code);
@!@:input_line_no_}{\.{\\inputlineno} primitive@>
primitive("badness",last_item,badness_code);
@!@:badness_}{\.{\\badness} primitive@>
primitive("pdftexversion",last_item,pdftex_version_code);@/
@!@:pdftex_version_}{\.{\\pdftexversion} primitive@>
primitive("luatexversion",last_item,luatex_version_code);@/
@!@:luatex_version_}{\.{\\luatexversion} primitive@>
primitive("pdflastobj",last_item,pdf_last_obj_code);@/
@!@:pdf_last_obj_}{\.{\\pdflastobj} primitive@>
primitive("pdflastxform",last_item,pdf_last_xform_code);@/
@!@:pdf_last_xform_}{\.{\\pdflastxform} primitive@>
primitive("pdflastximage",last_item,pdf_last_ximage_code);@/
@!@:pdf_last_ximage_}{\.{\\pdflastximage} primitive@>
primitive("pdflastximagepages",last_item,pdf_last_ximage_pages_code);@/
@!@:pdf_last_ximage_pages_}{\.{\\pdflastximagepages} primitive@>
primitive("pdflastannot",last_item,pdf_last_annot_code);@/
@!@:pdf_last_annot_}{\.{\\pdflastannot} primitive@>
primitive("pdflastxpos",last_item,pdf_last_x_pos_code);@/
@!@:pdf_last_x_pos_}{\.{\\pdflastxpos} primitive@>
primitive("pdflastypos",last_item,pdf_last_y_pos_code);@/
@!@:pdf_last_y_pos_}{\.{\\pdflastypos} primitive@>
primitive("pdfretval",last_item,pdf_retval_code);@/
@!@:pdf_retval_}{\.{\\pdfretval} primitive@>
primitive("pdflastximagecolordepth",last_item,pdf_last_ximage_colordepth_code);@/
@!@:pdf_last_ximage_colordepth_}{\.{\\pdflastximagecolordepth} primitive@>
primitive("pdfrandomseed",last_item,random_seed_code);
@!@:random_seed_}{\.{\\pdfrandomseed} primitive@>
primitive("pdflastlink",last_item,pdf_last_link_code);@/
@!@:pdf_last_link_}{\.{\\pdflastlink} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
set_aux: if chr_code=vmode then print_esc("prevdepth")
@+else print_esc("spacefactor");
set_page_int: if chr_code=0 then print_esc("deadcycles")
@/@<Cases of |set_page_int| for |print_cmd_chr|@>@/
@+else print_esc("insertpenalties");
set_box_dimen: if chr_code=width_offset then print_esc("wd")
else if chr_code=height_offset then print_esc("ht")
else print_esc("dp");
last_item: case chr_code of
  int_val: print_esc("lastpenalty");
  dimen_val: print_esc("lastkern");
  glue_val: print_esc("lastskip");
  input_line_no_code: print_esc("inputlineno");
  @/@<Cases of |last_item| for |print_cmd_chr|@>@/
  pdftex_version_code:  print_esc("pdftexversion");
  luatex_version_code:  print_esc("luatexversion");
  pdf_last_obj_code:    print_esc("pdflastobj");
  pdf_last_xform_code:  print_esc("pdflastxform");
  pdf_last_ximage_code: print_esc("pdflastximage");
  pdf_last_ximage_pages_code: print_esc("pdflastximagepages");
  pdf_last_annot_code:  print_esc("pdflastannot");
  pdf_last_x_pos_code:  print_esc("pdflastxpos");
  pdf_last_y_pos_code:  print_esc("pdflastypos");
  pdf_retval_code:      print_esc("pdfretval");
  pdf_last_ximage_colordepth_code: print_esc("pdflastximagecolordepth");
  random_seed_code:     print_esc("pdfrandomseed");
  pdf_last_link_code:   print_esc("pdflastlink");
  othercases print_esc("badness")
  endcases;

@ @<Fetch the |space_factor| or the |prev_depth|@>=
if abs(mode)<>m then
  begin print_err("Improper "); print_cmd_chr(set_aux,m);
@.Improper \\spacefactor@>
@.Improper \\prevdepth@>
  help4("You can refer to \spacefactor only in horizontal mode;")@/
    ("you can refer to \prevdepth only in vertical mode; and")@/
    ("neither of these is meaningful inside \write. So")@/
    ("I'm forgetting what you said and using zero instead.");
  error;
  if level<>tok_val then scanned_result(0)(dimen_val)
  else scanned_result(0)(int_val);
  end
else if m=vmode then
  begin cur_val:=prev_depth; cur_val_level:=dimen_val;
  end
else begin cur_val:=space_factor; cur_val_level:=int_val;
  end

@ @<Fetch the |dead_cycles| or the |insert_penalties|@>=
begin if m=0 then cur_val:=dead_cycles
@/@<Cases for `Fetch the |dead_cycles| or the |insert_penalties|'@>@/
else cur_val:=insert_penalties;
cur_val_level:=int_val;
end

@ @<Fetch a box dimension@>=
begin scan_register_num;
if box(cur_val)=null then cur_val:=0 @+else cur_val:=vmem(box(cur_val)+m).sc;
cur_val_level:=dimen_val;
end

@ Inside an \.{\\output} routine, a user may wish to look at the page totals
that were present at the moment when output was triggered.

@d max_dimen==@'7777777777 {$2^{30}-1$}

@<Fetch something on the |page_so_far|@>=
begin if (page_contents=empty) and (not output_active) then
  if m=0 then cur_val:=max_dimen@+else cur_val:=0
else cur_val:=page_so_far[m];
cur_val_level:=dimen_val;
end

@ @<Fetch the |prev_graf|@>=
if mode=0 then scanned_result(0)(int_val) {|prev_graf=0| within \.{\\write}}
else begin nest[nest_ptr]:=cur_list; p:=nest_ptr;
  while abs(nest[p].mode_field)<>vmode do decr(p);
  scanned_result(nest[p].pg_field)(int_val);
  end

@ @<Fetch the |par_shape| size@>=
begin if m>par_shape_loc then @<Fetch a penalties array element@>
else if par_shape_ptr=null then cur_val:=0
else cur_val:=vinfo(par_shape_ptr);
cur_val_level:=int_val;
end

@ Here is where \.{\\lastpenalty}, \.{\\lastkern}, and \.{\\lastskip} are
implemented. The reference count for \.{\\lastskip} will be updated later.

We also handle \.{\\inputlineno} and \.{\\badness} here, because they are
legal in similar contexts.

@<Fetch an item in the current node...@>=
if m>=input_line_no_code then
 if m>=eTeX_glue then @<Process an expression and |return|@>@;
 else if m>=eTeX_dim then
  begin case m of
  @/@<Cases for fetching a dimension value@>@/
  end; {there are no other cases}
  cur_val_level:=dimen_val;
  end
 else begin case m of
  input_line_no_code: cur_val:=line;
  badness_code: cur_val:=last_badness;
  pdftex_version_code:  cur_val := pdftex_version;
  luatex_version_code:  cur_val := luatex_version;
  pdf_last_obj_code:    cur_val := pdf_last_obj;
  pdf_last_xform_code:  cur_val := pdf_last_xform;
  pdf_last_ximage_code: cur_val := pdf_last_ximage;
  pdf_last_ximage_pages_code: cur_val := pdf_last_ximage_pages;
  pdf_last_annot_code:  cur_val := pdf_last_annot;
  pdf_last_x_pos_code:  cur_val := pdf_last_x_pos;
  pdf_last_y_pos_code:  cur_val := pdf_last_y_pos;
  pdf_retval_code:      cur_val := pdf_retval;
  pdf_last_ximage_colordepth_code: cur_val := pdf_last_ximage_colordepth;
  random_seed_code:  cur_val := random_seed;
  pdf_last_link_code:   cur_val := pdf_last_link;
  @/@<Cases for fetching an integer value@>@/
  end; {there are no other cases}
  cur_val_level:=int_val;
  end
else begin if cur_chr=glue_val then cur_val:=zero_glue@+else cur_val:=0;
  if cur_chr=last_node_type_code then
    begin cur_val_level:=int_val;
    if (tail=head)or(mode=0) then cur_val:=-1;
    end
  else cur_val_level:=cur_chr;
  {TODO: check this thoroughly! The structural change to the 
   |is_char_node| macro was wreaking havoc here, and possibly elsewhere.}
  if tail<>contrib_head and not is_char_node(tail)and(mode<>0) then
    case cur_chr of
    int_val: if type(tail)=penalty_node then cur_val:=penalty(tail);
    dimen_val: if type(tail)=kern_node then cur_val:=width(tail);
    glue_val: if type(tail)=glue_node then
      begin cur_val:=glue_ptr(tail);
      if subtype(tail)=mu_glue then cur_val_level:=mu_val;
      end;
    last_node_type_code:
      cur_val := visible_last_node_type(tail);
    end {there are no other cases}
  else if (mode=vmode)and(tail=head) then
    case cur_chr of
    int_val: cur_val:=last_penalty;
    dimen_val: cur_val:=last_kern;
    glue_val: if last_glue<>max_halfword then cur_val:=last_glue;
    last_node_type_code: cur_val:=last_node_type;
    end; {there are no other cases}
  end

@ @<Fetch a font dimension@>=
get_font_dimen

@ @<Fetch a font integer@>=
begin scan_font_ident;
if m=0 then scanned_result(hyphen_char(cur_val))(int_val)
else if m=1 then scanned_result(skew_char(cur_val))(int_val)
else if m=no_lig_code then scanned_result(test_no_ligatures(cur_val))(int_val)
else begin
    n := cur_val;
    scan_char_num;
    k := cur_val;
    case m of
    lp_code_base: scanned_result(get_lp_code(n, k))(int_val);
    rp_code_base: scanned_result(get_rp_code(n, k))(int_val);
    ef_code_base: scanned_result(get_ef_code(n, k))(int_val);
    tag_code: scanned_result(get_tag_code(n, k))(int_val);
    end;
end;
end

@ @<Fetch a register@>=
begin scan_register_num;
case m of
int_val:cur_val:=count(cur_val);
attr_val:cur_val:=attribute(cur_val);
dimen_val:cur_val:=dimen(cur_val);
glue_val: cur_val:=skip(cur_val);
mu_val: cur_val:=mu_skip(cur_val);
end; {there are no other cases}
cur_val_level:=m;
end

@ @<Complain that \.{\\the} can't do this; give zero result@>=
begin print_err("You can't use `"); print_cmd_chr(cur_cmd,cur_chr);
@.You can't use x after ...@>
print("' after "); print_esc("the");
help1("I'm forgetting what you said and using zero instead.");
error;
if level<>tok_val then scanned_result(0)(dimen_val)
else scanned_result(0)(int_val);
end

@ @<Complain that |texlib| can't do this; give zero result@>=
begin print_err("You can't use `"); print_cmd_chr(cmd,m);
print("' as tex library index");
help1("I'm forgetting what you said and using zero instead.");
error;
if level<>tok_val then scanned_result(0)(dimen_val)
else scanned_result(0)(int_val);
end


@ When a |glue_val| changes to a |dimen_val|, we use the width component
of the glue; there is no need to decrease the reference count, since it
has not yet been increased.  When a |dimen_val| changes to an |int_val|,
we use scaled points so that the value doesn't actually change. And when a
|mu_val| changes to a |glue_val|, the value doesn't change either.

@<Convert \(c)|cur_val| to a lower level@>=
begin if cur_val_level=glue_val then cur_val:=width(cur_val)
else if cur_val_level=mu_val then mu_error;
decr(cur_val_level);
end

@ If |cur_val| points to a glue specification at this point, the reference
count for the glue does not yet include the reference by |cur_val|.
If |negative| is |true|, |cur_val_level| is known to be |<=mu_val|.

@<Fix the reference count, if any, ...@>=
if negative then
  if cur_val_level>=glue_val then
    begin cur_val:=new_spec(cur_val);
    @<Negate all three glue components of |cur_val|@>;
    end
  else negate(cur_val)
else if (cur_val_level>=glue_val)and(cur_val_level<=mu_val) then
  add_glue_ref(cur_val)

@ @<Negate all three...@>=
begin negate(width(cur_val));
negate(stretch(cur_val));
negate(shrink(cur_val));
end

@ Our next goal is to write the |scan_int| procedure, which scans anything that
\TeX\ treats as an integer. But first we might as well look at some simple
applications of |scan_int| that have already been made inside of
|scan_something_internal|.

@
@d dir_T=0
@d dir_L=1
@d dir_B=2
@d dir_R=3
@d dir_eq_end(#)==(#)
@d dir_eq(#)==(#)=dir_eq_end
@d dir_ne_end(#)==(#)
@d dir_ne(#)==(#)<>dir_ne_end
@d dir_opposite_end(#)==((#) mod 4)
@d dir_opposite(#)==(((#)+2) mod 4)=dir_opposite_end
@d dir_parallel_end(#)==((#) mod 2)
@d dir_parallel(#)==((#) mod 2)=dir_parallel_end
@d dir_orthogonal_end(#)==(# mod 2)
@d dir_orthogonal(#)==((#) mod 2)<>dir_orthogonal_end
@d dir_next_end(#)==((#) mod 4)
@d dir_next(#)==(((#)+3) mod 4)=dir_next_end
@d dir_prev_end(#)==((#) mod 4)
@d dir_prev(#)==(((#)+1) mod 4)=dir_prev_end

{box directions}
@d dir_TL_=0
@d dir_TR_=1
@d dir_LT_=2
@d dir_LB_=3
@d dir_BL_=4
@d dir_BR_=5
@d dir_RT_=6
@d dir_RB_=7

{font directions}
@d dir__LT= 0
@d dir__LL= 1
@d dir__LB= 2
@d dir__LR= 3
@d dir__RT= 4
@d dir__RL= 5
@d dir__RB= 6
@d dir__RR= 7
@d dir__TT= 8
@d dir__TL= 9
@d dir__TB=10
@d dir__TR=11
@d dir__BT=12
@d dir__BL=13
@d dir__BB=14
@d dir__BR=15

@d is_mirrored(#)==dir_opposite(dir_primary[#])(dir_tertiary[#])
@d is_rotated(#)==dir_parallel(dir_secondary[#])(dir_tertiary[#])
@d font_direction(#)==(# mod 16)
@d box_direction(#)==(# div 4)

@d scan_single_dir(#)==begin
if scan_keyword("T") then #:=dir_T
else if scan_keyword("L") then #:=dir_L
else if scan_keyword("B") then #:=dir_B
else if scan_keyword("R") then #:=dir_R
else begin
  print_err("Bad direction"); cur_val:=0;
  goto exit;
  end
end

@<Declare procedures that scan restricted classes of integers@>=
procedure scan_direction;
var d1,d2,d3: integer;
begin
get_x_token;
if cur_cmd=assign_dir then begin
  cur_val:=eqtb[cur_chr].int;
  goto exit;
  end
else back_input;
scan_single_dir(d1);
scan_single_dir(d2);
if dir_parallel(d1)(d2) then begin
  print_err("Bad direction"); cur_val:=0;
  goto exit;
  end;
scan_single_dir(d3);
cur_val:=d1*8+dir_rearrange[d2]*4+d3;
exit:
end;

@ It is nice to have routines that say what they do, so the original
|scan_eight_bit_int| is superceded by |scan_register_num| and
|scan_mark_num|. It may become split up even further in the future.

@<Declare procedures that scan restricted classes of integers@>=
procedure scan_register_num;
begin scan_int;
if (cur_val<0)or(cur_val>biggest_reg) then
  begin print_err("Bad register code");
@.Bad register code@>
  help2("A register number must be between 0 and 65535.")@/
    ("I changed this one to zero."); int_error(cur_val); cur_val:=0;
  end;
end;
procedure scan_mark_num;
begin scan_int;
if (cur_val<0)or(cur_val>biggest_mark) then
  begin print_err("Bad marks code");
@.Bad marks code@>
  help2("A marks class must be between 0 and 65535.")@/
    ("I changed this one to zero."); int_error(cur_val); cur_val:=0;
  end;
end;

@ @<Declare procedures that scan restricted classes of integers@>=
procedure scan_char_num;
begin scan_int;
if (cur_val<0)or(cur_val>biggest_char) then
  begin print_err("Bad character code");
@.Bad character code@>
  help2("A character number must be between 0 and biggest_char.")@/
    ("I changed this one to zero."); int_error(cur_val); cur_val:=0;
  end;
end;

@ While we're at it, we might as well deal with similar routines that
will be needed later.

@<Declare procedures that scan restricted classes of integers@>=
procedure scan_four_bit_int;
begin scan_int;
if (cur_val<0)or(cur_val>15) then
  begin print_err("Bad number");
@.Bad number@>
  help2("Since I expected to read a number between 0 and 15,")@/
    ("I changed this one to zero."); int_error(cur_val); cur_val:=0;
  end;
end;
procedure scan_math_family_int;
begin scan_int;
if (cur_val<0)or(cur_val>255) then
  begin print_err("Bad number");
@.Bad number@>
  help2("Since I expected to read a number between 0 and 255,")@/
    ("I changed this one to zero."); int_error(cur_val); cur_val:=0;
  end;
end;

@ @<Declare procedures that scan restricted classes of integers@>=
procedure scan_real_fifteen_bit_int;
begin scan_int;
if (cur_val<0)or(cur_val>@'77777) then
  begin print_err("Bad mathchar");
@.Bad mathchar@>
  help2("A mathchar number must be between 0 and 32767.")@/
    ("I changed this one to zero."); int_error(cur_val); cur_val:=0;
  end;
end;
procedure scan_fifteen_bit_int;
begin scan_int;
if (cur_val<0)or(cur_val>@'77777) then
  begin print_err("Bad mathchar");
@.Bad mathchar@>
  help2("A mathchar number must be between 0 and 32767.")@/
    ("I changed this one to zero."); int_error(cur_val); cur_val:=0;
  end;
cur_val := ((cur_val div @"1000) * @"1000000) +
           (((cur_val mod @"1000) div @"100) * @"10000) +
           (cur_val mod @"100);
end;
procedure scan_big_fifteen_bit_int;
begin scan_int;
if (cur_val<0)or(cur_val>@"7FFFFFF) then
  begin print_err("Bad extended mathchar");
@.Bad mathchar@>
  help2("An extended mathchar number must be between 0 and ""7FFFFFF.")@/
    ("I changed this one to zero."); int_error(cur_val); cur_val:=0;
  end;
end;


@ @<Declare procedures that scan restricted classes of integers@>=
procedure scan_twenty_seven_bit_int;
begin scan_int;
if (cur_val<0)or(cur_val>@'777777777) then
  begin print_err("Bad delimiter code");
@.Bad delimiter code@>
  help2("A numeric delimiter code must be between 0 and 2^{27}-1.")@/
    ("I changed this one to zero."); int_error(cur_val); cur_val:=0;
  end;
cur_val1 := (((cur_val mod @"1000) div @"100) * @"10000) +
            (cur_val mod @"100);
cur_val := cur_val div @"1000;
cur_val := ((cur_val div @"1000) * @"1000000) +
           (((cur_val mod @"1000) div @"100) * @"10000) +
           (cur_val mod @"100);
end;

procedure scan_fifty_one_bit_int;
var iiii:integer;
begin scan_int;
if (cur_val<0)or(cur_val>@'777777777) then
  begin print_err("Bad delimiter code");
@.Bad delimiter code@>
  help2("A numeric delimiter (first part) must be between 0 and 2^{27}-1.")
    ("I changed this one to zero."); int_error(cur_val); cur_val:=0;
  end;
iiii:=cur_val;
scan_int;
if (cur_val<0)or(cur_val>@"FFFFFF) then
  begin print_err("Bad delimiter code");
@.Bad delimiter code@>
help2("A numeric delimiter (second part) must be between 0 and 2^{24}-1.")@/
    ("I changed this one to zero."); int_error(cur_val); cur_val:=0;
  end;
cur_val1:=cur_val;
cur_val:=iiii;
end;


procedure scan_string_argument;
var s:integer;
begin
scan_left_brace;
get_x_token;
while (cur_cmd<>right_brace) do
  begin
  if (cur_cmd=letter) or (cur_cmd=other_char) then begin
    str_room(1); append_char(cur_chr);
    end
  else if (cur_cmd=spacer) then begin
    str_room(1); append_char(" ");
    end
  else begin
    print("Bad token appearing in string argument");
    end;
  get_x_token;
  end;
s:=make_string;
if str_eq_str("mi",s) then s:="mi";
if str_eq_str("mo",s) then s:="mo";
if str_eq_str("mn",s) then s:="mn";
cur_val:=s;
end;

@ An integer number can be preceded by any number of spaces and `\.+' or
`\.-' signs. Then comes either a decimal constant (i.e., radix 10), an
octal constant (i.e., radix 8, preceded by~\.\'), a hexadecimal constant
(radix 16, preceded by~\."), an alphabetic constant (preceded by~\.\`), or
an internal variable. After scanning is complete,
|cur_val| will contain the answer, which must be at most
$2^{31}-1=2147483647$ in absolute value. The value of |radix| is set to
10, 8, or 16 in the cases of decimal, octal, or hexadecimal constants,
otherwise |radix| is set to zero. An optional space follows a constant.

@d octal_token=other_token+"'" {apostrophe, indicates an octal constant}
@d hex_token=other_token+"""" {double quote, indicates a hex constant}
@d alpha_token=other_token+"`" {reverse apostrophe, precedes alpha constants}
@d point_token=other_token+"." {decimal point}
@d continental_point_token=other_token+"," {decimal point, Eurostyle}

@<Glob...@>=
@!radix:small_number; {|scan_int| sets this to 8, 10, 16, or zero}

@ We initialize the following global variables just in case |expand|
comes into action before any of the basic scanning routines has assigned
them a value.

@<Set init...@>=
cur_val:=0; cur_val_level:=int_val; radix:=0; cur_order:=0;

@ The |scan_int| routine is used also to scan the integer part of a
fraction; for example, the `\.3' in `\.{3.14159}' will be found by
|scan_int|. The |scan_dimen| routine assumes that |cur_tok=point_token|
after the integer part of such a fraction has been scanned by |scan_int|,
and that the decimal point has been backed up to be scanned again.

@p procedure scan_int; {sets |cur_val| to an integer}
label done;
var negative:boolean; {should the answer be negated?}
@!m:integer; {|@t$2^{31}$@> div radix|, the threshold of danger}
@!d:small_number; {the digit just scanned}
@!vacuous:boolean; {have no digits appeared?}
@!OK_so_far:boolean; {has an error message been issued?}
begin radix:=0; OK_so_far:=true;@/
@<Get the next non-blank non-sign token; set |negative| appropriately@>;
if cur_tok=alpha_token then @<Scan an alphabetic character code into |cur_val|@>
else if (cur_cmd>=min_internal)and(cur_cmd<=max_internal) then
  scan_something_internal(int_val,false)
else @<Scan a numeric constant@>;
if negative then negate(cur_val);
end;

@ @<Get the next non-blank non-sign token...@>=
negative:=false;
repeat @<Get the next non-blank non-call token@>;
if cur_tok=other_token+"-" then
  begin negative := not negative; cur_tok:=other_token+"+";
  end;
until cur_tok<>other_token+"+"

@ A space is ignored after an alphabetic character constant, so that
such constants behave like numeric ones.

@<Scan an alphabetic character code into |cur_val|@>=
begin get_token; {suppress macro expansion}
if cur_tok<cs_token_flag then
  begin cur_val:=cur_chr;
  if cur_cmd<=right_brace then
    if cur_cmd=right_brace then incr(align_state)
    else decr(align_state);
  end
else if cur_tok<cs_token_flag+null_cs then
  cur_val:=cur_tok-cs_token_flag-active_base
else begin {the value of a csname in this context is its name}
  if single_letter(text(cur_tok-cs_token_flag)) then
    cur_val:=pool_to_unichar(str_start_macro(text(cur_tok-cs_token_flag)))
  else
    cur_val:=too_big_char;
end;
if cur_val>biggest_char then
  begin print_err("Improper alphabetic constant");
@.Improper alphabetic constant@>
  help2("A one-character control sequence belongs after a ` mark.")@/
    ("So I'm essentially inserting \0 here.");
  cur_val:="0"; back_error;
  end
else @<Scan an optional space@>;
end

@ @<Scan an optional space@>=
begin get_x_token; if cur_cmd<>spacer then back_input;
end

@ @<Scan a numeric constant@>=
begin radix:=10; m:=214748364;
if cur_tok=octal_token then
  begin radix:=8; m:=@'2000000000; get_x_token;
  end
else if cur_tok=hex_token then
  begin radix:=16; m:=@'1000000000; get_x_token;
  end;
vacuous:=true; cur_val:=0;@/
@<Accumulate the constant until |cur_tok| is not a suitable digit@>;
if vacuous then @<Express astonishment that no number was here@>
else if cur_cmd<>spacer then back_input;
end

@ @d infinity==@'17777777777 {the largest positive value that \TeX\ knows}
@d zero_token=other_token+"0" {zero, the smallest digit}
@d A_token=letter_token+"A" {the smallest special hex digit}
@d other_A_token=other_token+"A" {special hex digit of type |other_char|}

@<Accumulate the constant...@>=
loop@+  begin if (cur_tok<zero_token+radix)and(cur_tok>=zero_token)and
    (cur_tok<=zero_token+9) then d:=cur_tok-zero_token
  else if radix=16 then
    if (cur_tok<=A_token+5)and(cur_tok>=A_token) then d:=cur_tok-A_token+10
    else if (cur_tok<=other_A_token+5)and(cur_tok>=other_A_token) then
      d:=cur_tok-other_A_token+10
    else goto done
  else goto done;
  vacuous:=false;
  if (cur_val>=m)and((cur_val>m)or(d>7)or(radix<>10)) then
    begin if OK_so_far then
      begin print_err("Number too big");
@.Number too big@>
      help2("I can only go up to 2147483647='17777777777=""7FFFFFFF,")@/
        ("so I'm using that number instead of yours.");
      error; cur_val:=infinity; OK_so_far:=false;
      end;
    end
  else cur_val:=cur_val*radix+d;
  get_x_token;
  end;
done:

@ @<Express astonishment...@>=
begin print_err("Missing number, treated as zero");
@.Missing number...@>
help3("A number should have been here; I inserted `0'.")@/
  ("(If you can't figure out why I needed to see a number,")@/
  ("look up `weird error' in the index to The TeXbook.)");
@:TeXbook}{\sl The \TeX book@>
back_error;
end

@ The |scan_dimen| routine is similar to |scan_int|, but it sets |cur_val| to
a |scaled| value, i.e., an integral number of sp. One of its main tasks
is therefore to interpret the abbreviations for various kinds of units and
to convert measurements to scaled points.

There are three parameters: |mu| is |true| if the finite units must be
`\.{mu}', while |mu| is |false| if `\.{mu}' units are disallowed;
|inf| is |true| if the infinite units `\.{fil}', `\.{fill}', `\.{filll}'
are permitted; and |shortcut| is |true| if |cur_val| already contains
an integer and only the units need to be considered.

The order of infinity that was found in the case of infinite glue is returned
in the global variable |cur_order|.

@<Glob...@>=
@!cur_order:glue_ord; {order of infinity found by |scan_dimen|}

@ Constructions like `\.{-\'77 pt}' are legal dimensions, so |scan_dimen|
may begin with |scan_int|. This explains why it is convenient to use
|scan_int| also for the integer part of a decimal fraction.

Several branches of |scan_dimen| work with |cur_val| as an integer and
with an auxiliary fraction |f|, so that the actual quantity of interest is
$|cur_val|+|f|/2^{16}$. At the end of the routine, this ``unpacked''
representation is put into the single word |cur_val|, which suddenly
switches significance from |integer| to |scaled|.

@d attach_fraction=88 {go here to pack |cur_val| and |f| into |cur_val|}
@d attach_sign=89 {go here when |cur_val| is correct except perhaps for sign}
@d scan_normal_dimen==scan_dimen(false,false,false)

@p procedure scan_dimen(@!mu,@!inf,@!shortcut:boolean);
  {sets |cur_val| to a dimension}
label done, done1, done2, found, not_found, attach_fraction, attach_sign;
var negative:boolean; {should the answer be negated?}
@!f:integer; {numerator of a fraction whose denominator is $2^{16}$}
@<Local variables for dimension calculations@>@;
begin f:=0; arith_error:=false; cur_order:=normal; negative:=false;
if not shortcut then
  begin @<Get the next non-blank non-sign...@>;
  if (cur_cmd>=min_internal)and(cur_cmd<=max_internal) then
    @<Fetch an internal dimension and |goto attach_sign|,
      or fetch an internal integer@>
  else  begin back_input;
    if cur_tok=continental_point_token then cur_tok:=point_token;
    if cur_tok<>point_token then scan_int
    else  begin radix:=10; cur_val:=0;
      end;
    if cur_tok=continental_point_token then cur_tok:=point_token;
    if (radix=10)and(cur_tok=point_token) then @<Scan decimal fraction@>;
    end;
  end;
if cur_val<0 then {in this case |f=0|}
  begin negative := not negative; negate(cur_val);
  end;
@<Scan units and set |cur_val| to $x\cdot(|cur_val|+f/2^{16})$, where there
  are |x| sp per unit; |goto attach_sign| if the units are internal@>;
@<Scan an optional space@>;
attach_sign: if arith_error or(abs(cur_val)>=@'10000000000) then
  @<Report that this dimension is out of range@>;
if negative then negate(cur_val);
end;

@ @<Fetch an internal dimension and |goto attach_sign|...@>=
if mu then
  begin scan_something_internal(mu_val,false);
  @<Coerce glue to a dimension@>;
  if cur_val_level=mu_val then goto attach_sign;
  if cur_val_level<>int_val then mu_error;
  end
else  begin scan_something_internal(dimen_val,false);
  if cur_val_level=dimen_val then goto attach_sign;
  end

@ @<Local variables for dimension calculations@>=
@!num,@!denom:1..65536; {conversion ratio for the scanned units}
@!k,@!kk:small_number; {number of digits in a decimal fraction}
@!p,@!q:pointer; {top of decimal digit stack}
@!v:scaled; {an internal dimension}
@!save_cur_val:integer; {temporary storage of |cur_val|}

@ The following code is executed when |scan_something_internal| was
called asking for |mu_val|, when we really wanted a ``mudimen'' instead
of ``muglue.''

@<Coerce glue to a dimension@>=
if cur_val_level>=glue_val then
  begin v:=width(cur_val); delete_glue_ref(cur_val); cur_val:=v;
  end

@ When the following code is executed, we have |cur_tok=point_token|, but this
token has been backed up using |back_input|; we must first discard it.

It turns out that a decimal point all by itself is equivalent to `\.{0.0}'.
Let's hope people don't use that fact.

@<Scan decimal fraction@>=
begin k:=0; p:=null; get_token; {|point_token| is being re-scanned}
loop@+  begin get_x_token;
  if (cur_tok>zero_token+9)or(cur_tok<zero_token) then goto done1;
  if k<17 then {digits for |k>=17| cannot affect the result}
    begin q:=get_avail; link(q):=p; info(q):=cur_tok-zero_token;
    p:=q; incr(k);
    end;
  end;
done1: for kk:=k downto 1 do
  begin dig[kk-1]:=info(p); q:=p; p:=link(p); free_avail(q);
  end;
f:=round_decimals(k);
if cur_cmd<>spacer then back_input;
end

@ Now comes the harder part: At this point in the program, |cur_val| is a
nonnegative integer and $f/2^{16}$ is a nonnegative fraction less than 1;
we want to multiply the sum of these two quantities by the appropriate
factor, based on the specified units, in order to produce a |scaled|
result, and we want to do the calculation with fixed point arithmetic that
does not overflow.

@<Scan units and set |cur_val| to $x\cdot(|cur_val|+f/2^{16})$...@>=
if inf then @<Scan for \(f)\.{fil} units; |goto attach_fraction| if found@>;
@<Scan for \(u)units that are internal dimensions;
  |goto attach_sign| with |cur_val| set if found@>;
if mu then @<Scan for \(m)\.{mu} units and |goto attach_fraction|@>;
if scan_keyword("true") then @<Adjust \(f)for the magnification ratio@>;
@.true@>
if scan_keyword("pt") then goto attach_fraction; {the easy case}
@.pt@>
@<Scan for \(a)all other units and adjust |cur_val| and |f| accordingly;
  |goto done| in the case of scaled points@>;
attach_fraction: if cur_val>=@'40000 then arith_error:=true
else cur_val:=cur_val*unity+f;
done:

@ In traditional TeX, a specification like `\.{filllll}' or `\.{fill L L
L}' will lead to two error messages (one for each additional keyword
\.{"l"}). 

Not so for luatex, it just parses the construct in reverse.

@<Scan for \(f)\.{fil} units...@>=
if scan_keyword("filll") then begin cur_order:=filll; goto attach_fraction; end
else if scan_keyword("fill") then begin cur_order:=fill; goto attach_fraction; end
else if scan_keyword("fil") then begin cur_order:=fil; goto attach_fraction; end
else if scan_keyword("fi") then begin cur_order:=sfi; goto attach_fraction; end

@ @<Scan for \(u)units that are internal dimensions...@>=
save_cur_val:=cur_val;
@<Get the next non-blank non-call...@>;
if (cur_cmd<min_internal)or(cur_cmd>max_internal) then back_input
else  begin if mu then
    begin scan_something_internal(mu_val,false); @<Coerce glue...@>;
    if cur_val_level<>mu_val then mu_error;
    end
  else scan_something_internal(dimen_val,false);
  v:=cur_val; goto found;
  end;
if mu then goto not_found;
if scan_keyword("em") then v:=(@<The em width for |cur_font|@>)
@.em@>
else if scan_keyword("ex") then v:=(@<The x-height for |cur_font|@>)
@.ex@>
else if scan_keyword("px") then v:=pdf_px_dimen
@.px@>
else goto not_found;
@<Scan an optional space@>;
found:cur_val:=nx_plus_y(save_cur_val,v,xn_over_d(v,f,@'200000));
goto attach_sign;
not_found:

@ @<Scan for \(m)\.{mu} units and |goto attach_fraction|@>=
if scan_keyword("mu") then goto attach_fraction
@.mu@>
else  begin print_err("Illegal unit of measure ("); print("mu inserted)");
@.Illegal unit of measure@>
  help4("The unit of measurement in math glue must be mu.")@/
    ("To recover gracefully from this error, it's best to")@/
    ("delete the erroneous units; e.g., type `2' to delete")@/
    ("two letters. (See Chapter 27 of The TeXbook.)");
@:TeXbook}{\sl The \TeX book@>
  error; goto attach_fraction;
  end

@ @<Adjust \(f)for the magnification ratio@>=
begin prepare_mag;
if mag<>1000 then
  begin cur_val:=xn_over_d(cur_val,1000,mag);
  f:=(1000*f+@'200000*remainder) div mag;
  cur_val:=cur_val+(f div @'200000); f:=f mod @'200000;
  end;
end

@ The necessary conversion factors can all be specified exactly as
fractions whose numerator and denominator add to 32768 or less.
According to the definitions here, $\rm2660\,dd\approx1000.33297\,mm$;
this agrees well with the value $\rm1000.333\,mm$ cited by Bosshard
@^Bosshard, Hans Rudolf@>
in {\sl Technische Grundlagen zur Satzherstellung\/} (Bern, 1980).
The Didot point has been newly standardized in 1978;
it's now exactly $\rm 1\,nd=0.375\,mm$.
Conversion uses the equation $0.375=21681/20320/72.27\cdot25.4$.
The new Cicero follows the new Didot point; $\rm 1\,nc=12\,nd$.  These
would lead to the ratios $21681/20320$ and $65043/5080$, respectively.
The closest approximations supported by the algorithm would be
$11183/10481$ and $1370/107$.  In order to maintain the
relation $\rm 1\,nc=12\,nd$, we pick the ratio $685/642$ for $\rm nd$,
however.

@d set_conversion_end(#)== denom:=#; end
@d set_conversion(#)==@+begin num:=#; set_conversion_end

@<Scan for \(a)all other units and adjust |cur_val| and |f|...@>=
if scan_keyword("in") then set_conversion(7227)(100)
@.in@>
else if scan_keyword("pc") then set_conversion(12)(1)
@.pc@>
else if scan_keyword("cm") then set_conversion(7227)(254)
@.cm@>
else if scan_keyword("mm") then set_conversion(7227)(2540)
@.mm@>
else if scan_keyword("bp") then set_conversion(7227)(7200)
@.bp@>
else if scan_keyword("dd") then set_conversion(1238)(1157)
@.dd@>
else if scan_keyword("cc") then set_conversion(14856)(1157)
@.cc@>
else if scan_keyword("nd") then set_conversion(685)(642)
@.nd@>
else if scan_keyword("nc") then set_conversion(1370)(107)
@.nc@>
else if scan_keyword("sp") then goto done
@.sp@>
else @<Complain about unknown unit and |goto done2|@>;
cur_val:=xn_over_d(cur_val,num,denom);
f:=(num*f+@'200000*remainder) div denom;@/
cur_val:=cur_val+(f div @'200000); f:=f mod @'200000;
done2:

@ @<Complain about unknown unit...@>=
begin print_err("Illegal unit of measure ("); print("pt inserted)");
@.Illegal unit of measure@>
help6("Dimensions can be in units of em, ex, in, pt, pc,")@/
  ("cm, mm, dd, cc, nd, nc, bp, or sp; but yours is a new one!")@/
  ("I'll assume that you meant to say pt, for printer's points.")@/
  ("To recover gracefully from this error, it's best to")@/
  ("delete the erroneous units; e.g., type `2' to delete")@/
  ("two letters. (See Chapter 27 of The TeXbook.)");
@:TeXbook}{\sl The \TeX book@>
error; goto done2;
end


@ @<Report that this dimension is out of range@>=
begin print_err("Dimension too large");
@.Dimension too large@>
help2("I can't work with sizes bigger than about 19 feet.")@/
  ("Continue and I'll use the largest value I can.");@/
error; cur_val:=max_dimen; arith_error:=false;
end

@ The final member of \TeX's value-scanning trio is |scan_glue|, which
makes |cur_val| point to a glue specification. The reference count of that
glue spec will take account of the fact that |cur_val| is pointing to~it.

The |level| parameter should be either |glue_val| or |mu_val|.

Since |scan_dimen| was so much more complex than |scan_int|, we might expect
|scan_glue| to be even worse. But fortunately, it is very simple, since
most of the work has already been done.

@p procedure scan_glue(@!level:small_number);
  {sets |cur_val| to a glue spec pointer}
label exit;
var negative:boolean; {should the answer be negated?}
@!q:pointer; {new glue specification}
@!mu:boolean; {does |level=mu_val|?}
begin mu:=(level=mu_val); @<Get the next non-blank non-sign...@>;
if (cur_cmd>=min_internal)and(cur_cmd<=max_internal) then
  begin scan_something_internal(level,negative);
  if cur_val_level>=glue_val then
    begin if cur_val_level<>level then mu_error;
    return;
    end;
  if cur_val_level=int_val then scan_dimen(mu,false,true)
  else if level=mu_val then mu_error;
  end
else  begin back_input; scan_dimen(mu,false,false);
  if negative then negate(cur_val);
  end;
@<Create a new glue specification whose width is |cur_val|; scan for its
  stretch and shrink components@>;
exit:end;
@#
@<Declare procedures needed for expressions@>@;

@ @<Create a new glue specification whose width is |cur_val|...@>=
q:=new_spec(zero_glue); width(q):=cur_val;
if scan_keyword("plus") then
@.plus@>
  begin scan_dimen(mu,true,false);
  stretch(q):=cur_val; stretch_order(q):=cur_order;
  end;
if scan_keyword("minus") then
@.minus@>
  begin scan_dimen(mu,true,false);
  shrink(q):=cur_val; shrink_order(q):=cur_order;
  end;
cur_val:=q

@ Here's a similar procedure that returns a pointer to a rule node. This
routine is called just after \TeX\ has seen \.{\\hrule} or \.{\\vrule};
therefore |cur_cmd| will be either |hrule| or |vrule|. The idea is to store
the default rule dimensions in the node, then to override them if
`\.{height}' or `\.{width}' or `\.{depth}' specifications are
found (in any order).

@d default_rule=26214 {0.4\thinspace pt}

@p function scan_rule_spec:pointer;
label reswitch;
var q:pointer; {the rule node being created}
begin q:=new_rule; {|width|, |depth|, and |height| all equal |null_flag| now}
if cur_cmd=vrule then begin
  width(q):=default_rule;
  rule_dir(q):=body_direction;
  end
else begin
  height(q):=default_rule; depth(q):=0;
  rule_dir(q):=text_direction;
end;
reswitch: if scan_keyword("width") then
@.width@>
  begin scan_normal_dimen; width(q):=cur_val; goto reswitch;
  end;
if scan_keyword("height") then
@.height@>
  begin scan_normal_dimen; height(q):=cur_val; goto reswitch;
  end;
if scan_keyword("depth") then
@.depth@>
  begin scan_normal_dimen; depth(q):=cur_val; goto reswitch;
  end;
scan_rule_spec:=q;
end;

@* \[27] Building token lists.
The token lists for macros and for other things like \.{\\mark} and \.{\\output}
and \.{\\write} are produced by a procedure called |scan_toks|.

Before we get into the details of |scan_toks|, let's consider a much
simpler task, that of converting the current string into a token list.
The |str_toks| function does this; it classifies spaces as type |spacer|
and everything else as type |other_char|.

The token list created by |str_toks| begins at |link(temp_token_head)| and ends
at the value |p| that is returned. (If |p=temp_token_head|, the list is empty.)

|lua_str_toks| is almost identical, but it also escapes the three
symbols that |lua| considers special while scanning a literal string

@d unicode_incr(#)==if str_pool[#]>=@"F0 then #:=#+4 else if str_pool[#]>=@"E0 
     then #:=#+3 else if str_pool[#]>=@"C0 then #:=#+2 else incr(#)


@p @t\4@>@<Declare \eTeX\ procedures for token lists@>@;@/
function lua_str_toks(@!b:pool_pointer):pointer;
  {changes the string |str_pool[b..pool_ptr]| to a token list}
var p:pointer; {tail of the token list}
@!q:pointer; {new node being added to the token list via |store_new_token|}
@!t:halfword; {token being appended}
@!k:pool_pointer; {index into |str_pool|}
begin
p:=temp_token_head; link(p):=null; k:=b;
while k<pool_ptr do
  begin t:=pool_to_unichar(k);
  if t=" " then t:=space_token
  else
    begin
     if (t="\") or (t="""") or (t="'") or (t=10) or (t=13) then
          fast_store_new_token(other_token+"\");
     if (t=10) then
       t:="n";
     if (t=13) then
       t:="r";
    t:=other_token+t;
    end;
  fast_store_new_token(t);
  unicode_incr(k);
  end;
pool_ptr:=b; lua_str_toks:=p;
end;

function str_toks(@!b:pool_pointer):pointer;
  {changes the string |str_pool[b..pool_ptr]| to a token list}
var p:pointer; {tail of the token list}
@!q:pointer; {new node being added to the token list via |store_new_token|}
@!t:halfword; {token being appended}
@!k:pool_pointer; {index into |str_pool|}
begin
p:=temp_token_head; link(p):=null; k:=b;
while k<pool_ptr do
  begin t:=pool_to_unichar(k);
  if t=" " then t:=space_token
  else t:=other_token+t;
  fast_store_new_token(t);
  unicode_incr(k);
  end;
pool_ptr:=b; str_toks:=p;
end;

@ The main reason for wanting |str_toks| is the next function,
|the_toks|, which has similar input/output characteristics.

This procedure is supposed to scan something like `\.{\\skip\\count12}',
i.e., whatever can follow `\.{\\the}', and it constructs a token list
containing something like `\.{-3.0pt minus 0.5fill}'.

@p function the_toks:pointer;
label exit;
var old_setting:0..max_selector; {holds |selector| setting}
@!p,@!q,@!r:pointer; {used for copying a token list}
@!b:pool_pointer; {base of temporary string}
@!c:small_number; {value of |cur_chr|}
begin @<Handle \.{\\unexpanded} or \.{\\detokenize} and |return|@>;@/
get_x_token; scan_something_internal(tok_val,false);
if cur_val_level>=ident_val then begin
  @<Copy the token list@>;
  the_toks:=p;
  end
else begin old_setting:=selector; selector:=new_string; b:=pool_ptr;
  case cur_val_level of
  int_val:print_int(cur_val);
  attr_val:print_int(cur_val);
  dir_val:print_dir(cur_val);
  dimen_val:begin print_scaled(cur_val); print("pt");
    end;
  glue_val: begin print_spec(cur_val,"pt"); delete_glue_ref(cur_val);
    end;
  mu_val: begin print_spec(cur_val,"mu"); delete_glue_ref(cur_val);
    end;
  end; {there are no other cases}
  selector:=old_setting; the_toks:=str_toks(b);
  end;
exit:end;

function the_scanned_result:str_number;
var old_setting:0..max_selector; {holds |selector| setting}
begin
old_setting:=selector; selector:=new_string;
if cur_val_level>=ident_val then begin
  if cur_val<>null then begin
    show_token_list(link(cur_val),null,pool_size-pool_ptr);
    the_scanned_result:=make_string;
    end
  else
    the_scanned_result:="";
  end
else begin
    case cur_val_level of
    int_val:print_int(cur_val);
    attr_val:print_int(cur_val);
    dir_val:print_dir(cur_val);
    dimen_val:begin print_scaled(cur_val); print("pt");
      end;
    glue_val: begin print_spec(cur_val,"pt"); delete_glue_ref(cur_val);
      end;
    mu_val: begin print_spec(cur_val,"mu"); delete_glue_ref(cur_val);
      end;
    end; {there are no other cases}
    the_scanned_result:=make_string;
  end;
selector:=old_setting;
end;

@ @<Copy the token list@>=
begin p:=temp_token_head; link(p):=null;
if cur_val_level=ident_val then store_new_token(cs_token_flag+cur_val)
else if cur_val<>null then
  begin r:=link(cur_val); {do not copy the reference count}
  while r<>null do
    begin fast_store_new_token(info(r)); r:=link(r);
    end;
  end;
end

@ Here's part of the |expand| subroutine that we are now ready to complete:

@p procedure ins_the_toks;
var junk:pointer;
begin junk:=the_toks; ins_list(link(temp_token_head));
end;

@ The primitives \.{\\number}, \.{\\romannumeral}, \.{\\string}, \.{\\meaning},
\.{\\fontname}, and \.{\\jobname} are defined as follows.

\eTeX\ adds \.{\\eTeXrevision} such that |job_name_code| remains last.

\pdfTeX\ adds \.{\\eTeXrevision}, \.{\\pdftexrevision}, \.{\\pdftexbanner},
\.{\\pdffontname}, \.{\\pdffontobjnum}, \.{\\pdffontsize}, and \.{\\pdfpageref}
such that |job_name_code| remains last.

@d number_code=0 {command code for \.{\\number}}
@d roman_numeral_code=1 {command code for \.{\\romannumeral}}
@d string_code=2 {command code for \.{\\string}}
@d meaning_code=3 {command code for \.{\\meaning}}
@d font_name_code=4 {command code for \.{\\fontname}}
@d etex_code=5 {command code for \.{\\eTeXVersion}}
@d omega_code=6 {command code for \.{\\OmegaVersion}}
@d aleph_code=7 {command code for \.{\\AlephVersion}}
@d format_name_code=8 {command code for \.{\\AlephVersion}}
@d pdftex_first_expand_code = 9 {base for \pdfTeX's command codes}
@d pdftex_revision_code     = pdftex_first_expand_code + 0 {command code for \.{\\pdftexrevision}}
@d pdftex_banner_code       = pdftex_first_expand_code + 1 {command code for \.{\\pdftexbanner}}
@d pdf_font_name_code       = pdftex_first_expand_code + 2 {command code for \.{\\pdffontname}}
@d pdf_font_objnum_code     = pdftex_first_expand_code + 3 {command code for \.{\\pdffontobjnum}}
@d pdf_font_size_code       = pdftex_first_expand_code + 4 {command code for \.{\\pdffontsize}}
@d pdf_page_ref_code        = pdftex_first_expand_code + 5 {command code for \.{\\pdfpageref}}
@d pdf_xform_name_code      = pdftex_first_expand_code + 6 {command code for \.{\\pdfxformname}}
@d left_margin_kern_code    = pdftex_first_expand_code + 7 {command code for \.{\\leftmarginkern}}
@d right_margin_kern_code   = pdftex_first_expand_code + 8 {command code for \.{\\rightmarginkern}}
@d pdf_creation_date_code   = pdftex_first_expand_code + 9 {command code for \.{\\pdfcreationdate}}
@d uniform_deviate_code     = pdftex_first_expand_code + 10 {command code for \.{\\uniformdeviate}}
@d normal_deviate_code      = pdftex_first_expand_code + 11 {command code for \.{\\normaldeviate}}
@d pdf_insert_ht_code       = pdftex_first_expand_code + 12 {command code for \.{\\pdfinsertht}}
@d pdf_ximage_bbox_code     = pdftex_first_expand_code + 13 {command code for \.{\\pdfximagebbox}}
@d lua_code                 = pdftex_first_expand_code + 14 {command code for \.{\\directlua}}
@d lua_escape_string_code   = pdftex_first_expand_code + 15 {command code for \.{\\luaescapestring}}
@d pdf_colorstack_init_code = pdftex_first_expand_code + 16 {command code for \.{\\pdfcolorstackinit}}
@d luatex_revision_code     = pdftex_first_expand_code + 17 {command code for \.{\\luatexrevision}}
@d luatex_date_code         = pdftex_first_expand_code + 18 {command code for \.{\\luatexdate}}
@d pdftex_convert_codes     = pdftex_first_expand_code + 19 {end of \pdfTeX's command codes}
@d job_name_code=pdftex_convert_codes {command code for \.{\\jobname}}


@<Put each...@>=
primitive("number",convert,number_code);@/
@!@:number_}{\.{\\number} primitive@>
primitive("romannumeral",convert,roman_numeral_code);@/
@!@:roman_numeral_}{\.{\\romannumeral} primitive@>
primitive("string",convert,string_code);@/
@!@:string_}{\.{\\string} primitive@>
primitive("meaning",convert,meaning_code);@/
@!@:meaning_}{\.{\\meaning} primitive@>
primitive("eTeXVersion",convert,etex_code);@/
@!@:omega_version_}{\.{\\OmegaVersion} primitive@>
primitive("OmegaVersion",convert,omega_code);@/
@!@:omega_version_}{\.{\\OmegaVersion} primitive@>
primitive("AlephVersion",convert,aleph_code);@/
@!@:aleph_version_}{\.{\\AlephVersion} primitive@>
primitive("fontname",convert,font_name_code);@/
@!@:font_name_}{\.{\\fontname} primitive@>
primitive("pdftexrevision",convert,pdftex_revision_code);@/
@!@:pdftex_revision_}{\.{\\pdftexrevision} primitive@>
primitive("luatexrevision",convert,luatex_revision_code);@/
@!@:luatex_revision_}{\.{\\luatexrevision} primitive@>
primitive("luatexdatestamp",convert,luatex_date_code);@/
@!@:luatex_date_}{\.{\\luatexdatestamp} primitive@>
primitive("pdftexbanner",convert,pdftex_banner_code);@/
@!@:pdftex_banner_}{\.{\\pdftexbanner} primitive@>
primitive("pdffontname",convert,pdf_font_name_code);@/
@!@:pdf_font_name_}{\.{\\pdffontname} primitive@>
primitive("pdffontobjnum",convert,pdf_font_objnum_code);@/
@!@:pdf_font_objnum_}{\.{\\pdffontobjnum} primitive@>
primitive("pdffontsize",convert,pdf_font_size_code);@/
@!@:pdf_font_size_}{\.{\\pdffontsize} primitive@>
primitive("pdfpageref",convert,pdf_page_ref_code);@/
@!@:pdf_page_ref_}{\.{\\pdfpageref} primitive@>
primitive("leftmarginkern",convert,left_margin_kern_code);@/
@!@:left_margin_kern_}{\.{\\leftmarginkern} primitive@>
primitive("rightmarginkern",convert,right_margin_kern_code);@/
@!@:right_margin_kern_}{\.{\\rightmarginkern} primitive@>
primitive("pdfxformname",convert,pdf_xform_name_code);@/
@!@:pdf_xform_name_}{\.{\\pdfxformname} primitive@>
primitive("pdfcreationdate",convert,pdf_creation_date_code);@/
@!@:pdf_creation_date_}{\.{\\pdfcreationdate} primitive@>
primitive("pdfuniformdeviate",convert,uniform_deviate_code);@/
@!@:uniform_deviate_}{\.{\\pdfuniformdeviate} primitive@>
primitive("pdfcolorstackinit",convert,pdf_colorstack_init_code);@/
@!@:pdf_colorstack_init_}{\.{\\pdfcolorstackinit} primitive@>
primitive("pdfnormaldeviate",convert,normal_deviate_code);@/
@!@:normal_deviate_}{\.{\\pdfnormaldeviate} primitive@>
primitive("directlua",convert,lua_code);@/
@!@:lua_}{\.{\\directlua} primitive@>
primitive("luaescapestring",convert,lua_escape_string_code);@/
@!@:lua_}{\.{\\luaescapestring} primitive@>
@#
primitive("jobname",convert,job_name_code);@/
@!@:job_name_}{\.{\\jobname} primitive@>
primitive("formatname",convert,format_name_code);@/
@!@:format_name_}{\.{\\formatname} primitive@>
primitive("pdfinsertht",convert,pdf_insert_ht_code);@/
@!@:pdf_insert_ht_}{\.{\\pdfinsertht} primitive@>
primitive("pdfximagebbox",convert,pdf_ximage_bbox_code);@/
@!@:pdf_ximage_bbox_}{\.{\\pdfximagebbox} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
convert: case chr_code of
  number_code: print_esc("number");
  roman_numeral_code: print_esc("romannumeral");
  string_code: print_esc("string");
  meaning_code: print_esc("meaning");
  etex_code: print_esc("eTeXVersion");
  omega_code: print_esc("OmegaVersion");
  aleph_code: print_esc("AlephVersion");
  font_name_code: print_esc("fontname");
  pdftex_revision_code: print_esc("pdftexrevision");
  luatex_revision_code: print_esc("luatexrevision");
  luatex_date_code:     print_esc("luatexdatestamp");
  pdftex_banner_code:   print_esc("pdftexbanner");
  pdf_font_name_code:   print_esc("pdffontname");
  pdf_font_objnum_code: print_esc("pdffontobjnum");
  pdf_font_size_code:   print_esc("pdffontsize");
  pdf_page_ref_code:    print_esc("pdfpageref");
  left_margin_kern_code:    print_esc("leftmarginkern");
  right_margin_kern_code:   print_esc("rightmarginkern");
  pdf_xform_name_code:  print_esc("pdfxformname");
  pdf_creation_date_code: print_esc("pdfcreationdate");
  pdf_colorstack_init_code: print_esc("pdfcolorstackinit");
  uniform_deviate_code:   print_esc("pdfuniformdeviate");
  normal_deviate_code:    print_esc("pdfnormaldeviate");
  pdf_insert_ht_code: print_esc("pdfinsertht");
  pdf_ximage_bbox_code:    print_esc("pdfximagebbox");
  lua_code:                print_esc("directlua");
  lua_escape_string_code:  print_esc("luaescapestring");
  @/@<Cases of |convert| for |print_cmd_chr|@>@/
  othercases print_esc("jobname")
  endcases;

@ The procedure |conv_toks| uses |str_toks| to insert the token list
for |convert| functions into the scanner; `\.{\\outer}' control sequences
are allowed to follow `\.{\\string}' and `\.{\\meaning}'.

The extra temp string |u| is needed because |pdf_scan_ext_toks| incorporates
any pending string in its output. In order to save such a pending string,
we have to create a temporary string that is destroyed immediately after.

@d save_cur_string==if str_start[str_ptr]<pool_ptr then u:=make_string
@d restore_cur_string==if u<>0 then begin decr(str_ptr); u:=0; end

@p procedure conv_toks;
label exit;
var old_setting:0..max_selector; {holds |selector| setting}
p, q: pointer;
@!c:number_code..job_name_code; {desired type of conversion}
@!save_scanner_status:small_number; {|scanner_status| upon entry}
@!save_def_ref: pointer; {|def_ref| upon entry, important if inside `\.{\\message}'}
@!save_warning_index: pointer;
@!bool: boolean; {temp boolean}
@!i: integer; {first temp integer}
@!j: integer; {second temp integer}
@!b:pool_pointer; {base of temporary string}
@!s: str_number; {first temp string}
@!u: str_number; {third temp string}
@!junk: pointer;
begin
c:=cur_chr;
u:=0; { will become non-nil if a string is already being built}
j:=0; i:=0;
@<Scan the argument for command |c|@>;
old_setting:=selector; selector:=new_string; b:=pool_ptr;
@<Print the result of command |c|@>;
selector:=old_setting; junk:=str_toks(b); ins_list(link(temp_token_head));
exit:
end;

@ @<Scan the argument for command |c|@>=
case c of
number_code,roman_numeral_code: scan_int;
string_code, meaning_code: begin save_scanner_status:=scanner_status;
  scanner_status:=normal; get_token; scanner_status:=save_scanner_status;
  end;
etex_code: do_nothing;
omega_code: do_nothing;
aleph_code: do_nothing;
font_name_code: scan_font_ident;
pdftex_revision_code: do_nothing;
luatex_revision_code: do_nothing;
luatex_date_code: do_nothing;
pdftex_banner_code: do_nothing;
pdf_font_name_code, pdf_font_objnum_code, pdf_font_size_code: begin
    scan_font_ident;
    if cur_val = null_font then
        pdf_error("font", "invalid font identifier");
    if c <> pdf_font_size_code then begin
        pdf_check_vf_cur_val;
        if not font_used(cur_val) then
            pdf_init_font_cur_val;
    end;
end;
pdf_page_ref_code: begin
    scan_int;
    if cur_val <= 0 then
        pdf_error("pageref", "invalid page number");
end;
left_margin_kern_code, right_margin_kern_code: begin
    scan_int;
    if (box(cur_val) = null) or (type(box(cur_val)) <> hlist_node) then
        pdf_error("marginkern", "a non-empty hbox expected")
end;
pdf_xform_name_code: begin
    scan_int;
    pdf_check_obj(obj_type_xform, cur_val);
end;
pdf_creation_date_code:
  begin
    b := pool_ptr;
    getcreationdate;
    junk := str_toks(b);
    ins_list(link(temp_token_head));
    return;
  end;
job_name_code: if job_name=0 then open_log_file;
pdf_colorstack_init_code:
  begin
    bool := scan_keyword("page");
    if scan_keyword("direct") then
        cur_val := direct_always
    else
        if scan_keyword("page") then
            cur_val := direct_page
        else
            cur_val := set_origin;
    save_scanner_status := scanner_status;
    save_warning_index := warning_index;
    save_def_ref := def_ref;
    save_cur_string;
    scan_pdf_ext_toks;
    s := tokens_to_string(def_ref);
    delete_token_ref(def_ref);
    def_ref := save_def_ref;
    warning_index := save_warning_index;
    scanner_status := save_scanner_status;
    cur_val := newcolorstack(s, cur_val, bool);
    flush_str(s);
    cur_val_level := int_val;
    if cur_val < 0 then begin
        print_err("Too many color stacks");
@.Too many color stacks@>
        help2("The number of color stacks is limited to 32768.")@/
        ("I'll use the default color stack 0 here.");
        error;
        cur_val := 0;
       restore_cur_string;
    end;
  end;
uniform_deviate_code:     scan_int;
normal_deviate_code:      do_nothing;
lua_escape_string_code:
  begin
	u:=0;
    { check if a string is already being built}
    if str_start_macro(str_ptr)<pool_ptr then u:=make_string;
    save_scanner_status := scanner_status;
    save_def_ref := def_ref;
    save_warning_index := warning_index;
    scan_pdf_ext_toks;
    s := tokens_to_string(def_ref);
    delete_token_ref(def_ref);
    def_ref := save_def_ref;
    warning_index := save_warning_index;
    scanner_status := save_scanner_status;
    junk := lua_str_toks(str_start_macro(s));
	ins_list(link(temp_token_head));
    flush_str(s);
	if u<>0 then begin decr(str_ptr); u:=0; end; 
    return;
  end;
lua_code:
  begin
	u:=0;
    { check if a string is already being built}
    if str_start_macro(str_ptr)<pool_ptr then u:=make_string;
    save_scanner_status := scanner_status;
    save_def_ref := def_ref;
    save_warning_index := warning_index;
	scan_register_num;
	i := cur_val;
    scan_pdf_ext_toks;
    s := def_ref;
    warning_index := save_warning_index;
    def_ref := save_def_ref;
    scanner_status := save_scanner_status;
    luacstrings:=0;
    luatokencall(i,s);
    delete_token_ref(s);
	if u<>0 then begin
      if str_ptr=u+1 then 
        decr(str_ptr)
      else begin {copy old string to the top location}
         i:=0;
	     str_room(length(u));
         while i<length(u) do
           str_pool[pool_ptr+i]:=str_pool[str_start_macro(u)+i];
        end;
    end; 
	if luacstrings>0 then
	  lua_string_start;
    return;
  end;
pdf_insert_ht_code: scan_register_num;
pdf_ximage_bbox_code: begin
    scan_int;
    pdf_check_obj(obj_type_ximage, cur_val);
    i := obj_data_ptr(cur_val);
    scan_int;
    j := cur_val;
    if (j < 1) or (j > 4) then
        pdf_error("pdfximagebbox", "invalid parameter");
    end;
@<Cases of `Scan the argument for command |c|'@>
end {there are no other cases}

@ @<Print the result of command |c|@>=
case c of
number_code: print_int(cur_val);
roman_numeral_code: print_roman_int(cur_val);
string_code:if cur_cs<>0 then sprint_cs(cur_cs)
  else print(cur_chr);
meaning_code: print_meaning;
etex_code: print(eTeX_version_string);
omega_code: print(Omega_version_string);
aleph_code: print(Aleph_version_string);
font_name_code: begin
  append_string(font_name(cur_val));
  if font_size(cur_val)<>font_dsize(cur_val) then
    begin print(" at "); print_scaled(font_size(cur_val));
    print("pt");
    end;
  end;
pdftex_revision_code: print(pdftex_revision);
luatex_revision_code: print(luatex_revision);
luatex_date_code:   print_int(luatex_date_info);
pdftex_banner_code: print(pdftex_banner);
pdf_font_name_code, pdf_font_objnum_code: begin
    set_ff(cur_val);
    if c = pdf_font_name_code then
        print_int(obj_info(pdf_font_num(ff)))
    else
        print_int(pdf_font_num(ff));
end;
pdf_font_size_code: begin
    print_scaled(font_size(cur_val));
    print("pt");
end;
pdf_page_ref_code: print_int(get_obj(obj_type_page, cur_val, false));
left_margin_kern_code: begin
    p := list_ptr(box(cur_val));
    if (p <> null) and (not is_char_node(p)) and
       (type(p) = glue_node) and (subtype(p) = left_skip_code + 1) then
       p := vlink(p);
    if (p <> null) and (not is_char_node(p)) and
       (type(p) = margin_kern_node) and (subtype(p) = left_side) then
        print_scaled(width(p))
    else
        print("0");
    print("pt");
end;
right_margin_kern_code: begin
    q := list_ptr(box(cur_val));
    p := null;
    if q <> null then begin
        p := prev_rightmost(q, null);
        if (p <> null) and (not is_char_node(p)) and
           (type(p) = glue_node) and (subtype(p) = right_skip_code + 1) then
           p := prev_rightmost(q, p);
    end;
    if (p <> null) and (not is_char_node(p)) and
       (type(p) = margin_kern_node) and (subtype(p) = right_side) then
        print_scaled(width(p))
    else
        print("0");
    print("pt");
end;
pdf_xform_name_code: print_int(obj_info(cur_val));
pdf_colorstack_init_code: print_int(cur_val);
uniform_deviate_code:     print_int(unif_rand(cur_val));
normal_deviate_code:      print_int(norm_rand);
pdf_insert_ht_code: begin
    i := qi(cur_val);
    p := page_ins_head;
    while i >= subtype(vlink(p)) do
        p := vlink(p);
    if subtype(p) = i then
        print_scaled(height(p))
    else
        print("0");
    print("pt");
end;
pdf_ximage_bbox_code: begin
    case j of
    1: print_scaled(epdf_orig_x(i));
    2: print_scaled(epdf_orig_y(i));
    3: print_scaled(epdf_orig_x(i) + image_width(i));
    4: print_scaled(epdf_orig_y(i) + image_height(i));
    endcases;
    print("pt");
end;
format_name_code: print(format_name);
job_name_code: print(job_name);
@/@<Cases of `Print the result of command |c|'@>@/
end {there are no other cases}

@ 
@p function is_convert(c:halfword):boolean;
begin
  is_convert:=(c=convert);
end;

function the_convert_string (c:halfword):str_number;
var old_setting:0..max_selector; {saved |selector| setting}
	is_known:boolean;
begin
  old_setting:=selector; 
  selector:=new_string;
  is_known:=true;
  case c of
  etex_code:            print(eTeX_version_string);
  omega_code:           print(Omega_version_string);
  aleph_code:           print(Aleph_version_string);
  pdftex_revision_code: print(pdftex_revision);
  luatex_revision_code: print(luatex_revision);
  luatex_date_code:     print_int(luatex_date_info);
  pdftex_banner_code:   print(pdftex_banner);
  normal_deviate_code:  print_int(norm_rand);
  format_name_code:     print(format_name);
  job_name_code:        print(job_name);
@/@<Cases of `Print the result of command |c|'@>@/
  othercases            is_known:=false
  end;
  if is_known then
    the_convert_string := make_string
  else
    the_convert_string := 0;
  selector:=old_setting;
end;

@ Now we can't postpone the difficulties any longer; we must bravely tackle
|scan_toks|. This function returns a pointer to the tail of a new token
list, and it also makes |def_ref| point to the reference count at the
head of that list.

There are two boolean parameters, |macro_def| and |xpand|. If |macro_def|
is true, the goal is to create the token list for a macro definition;
otherwise the goal is to create the token list for some other \TeX\
primitive: \.{\\mark}, \.{\\output}, \.{\\everypar}, \.{\\lowercase},
\.{\\uppercase}, \.{\\message}, \.{\\errmessage}, \.{\\write}, or
\.{\\special}. In the latter cases a left brace must be scanned next; this
left brace will not be part of the token list, nor will the matching right
brace that comes at the end. If |xpand| is false, the token list will
simply be copied from the input using |get_token|. Otherwise all expandable
tokens will be expanded until unexpandable tokens are left, except that
the results of expanding `\.{\\the}' are not expanded further.
If both |macro_def| and |xpand| are true, the expansion applies
only to the macro body (i.e., to the material following the first
|left_brace| character).

The value of |cur_cs| when |scan_toks| begins should be the |eqtb|
address of the control sequence to display in ``runaway'' error
messages.

@p function scan_toks(@!macro_def,@!xpand:boolean):pointer;
label found,done,done1,done2;
var t:halfword; {token representing the highest parameter number}
@!s:halfword; {saved token}
@!p:pointer; {tail of the token list being built}
@!q:pointer; {new node being added to the token list via |store_new_token|}
@!unbalance:halfword; {number of unmatched left braces}
@!hash_brace:halfword; {possible `\.{\#\{}' token}
begin if macro_def then scanner_status:=defining
@+else scanner_status:=absorbing;
warning_index:=cur_cs; p:=get_avail; def_ref:=p; token_ref_count(def_ref):=0;
p:=def_ref; hash_brace:=0; t:=zero_token;
if macro_def then @<Scan and build the parameter part of the macro definition@>
else scan_left_brace; {remove the compulsory left brace}
@<Scan and build the body of the token list; |goto found| when finished@>;
found: scanner_status:=normal;
if hash_brace<>0 then store_new_token(hash_brace);
scan_toks:=p;
end;

@ @<Scan and build the parameter part...@>=
begin loop begin get_token; {set |cur_cmd|, |cur_chr|, |cur_tok|}
  if cur_tok<right_brace_limit then goto done1;
  if cur_cmd=mac_param then
    @<If the next character is a parameter number, make |cur_tok|
      a |match| token; but if it is a left brace, store
      `|left_brace|, |end_match|', set |hash_brace|, and |goto done|@>;
  store_new_token(cur_tok);
  end;
done1: store_new_token(end_match_token);
if cur_cmd=right_brace then
  @<Express shock at the missing left brace; |goto found|@>;
done: end

@ @<Express shock...@>=
begin print_err("Missing { inserted"); incr(align_state);
@.Missing \{ inserted@>
help2("Where was the left brace? You said something like `\def\a}',")@/
  ("which I'm going to interpret as `\def\a{}'."); error; goto found;
end

@ @<If the next character is a parameter number...@>=
begin s:=match_token+cur_chr; get_token;
if cur_cmd=left_brace then
  begin hash_brace:=cur_tok;
  store_new_token(cur_tok); store_new_token(end_match_token);
  goto done;
  end;
if t=zero_token+9 then
  begin print_err("You already have nine parameters");
@.You already have nine...@>
  help1("I'm going to ignore the # sign you just used."); error;
  end
else  begin incr(t);
  if cur_tok<>t then
    begin print_err("Parameters must be numbered consecutively");
@.Parameters...consecutively@>
    help2("I've inserted the digit you should have used after the #.")@/
      ("Type `1' to delete what you did use."); back_error;
    end;
  cur_tok:=s;
  end;
end

@ @<Scan and build the body of the token list; |goto found| when finished@>=
unbalance:=1;
loop@+  begin if xpand then @<Expand the next part of the input@>
  else get_token;
  if cur_tok<right_brace_limit then
    if cur_cmd<right_brace then incr(unbalance)
    else  begin decr(unbalance);
      if unbalance=0 then goto found;
      end
  else if cur_cmd=mac_param then
    if macro_def then @<Look for parameter number or \.{\#\#}@>;
  store_new_token(cur_tok);
  end

@ Here we insert an entire token list created by |the_toks| without
expanding it further.

@<Expand the next part of the input@>=
begin loop begin get_filtered_next;
  if cur_cmd>=call then
    if info(link(cur_chr))=protected_token then
      begin cur_cmd:=relax; cur_chr:=no_expand_flag;
      end;
  if cur_cmd<=max_command then goto done2;
  if cur_cmd<>the then expand
  else  begin q:=the_toks;
    if link(temp_token_head)<>null then
      begin link(p):=link(temp_token_head); p:=q;
      end;
    end;
  end;
done2: x_token
end

@ @<Look for parameter number...@>=
begin s:=cur_tok;
if xpand then get_x_token else get_token;
if cur_cmd<>mac_param then
  if (cur_tok<=zero_token)or(cur_tok>t) then
    begin print_err("Illegal parameter number in definition of ");
@.Illegal parameter number...@>
    sprint_cs(warning_index);
    help3("You meant to type ## instead of #, right?")@/
    ("Or maybe a } was forgotten somewhere earlier, and things")@/
    ("are all screwed up? I'm going to assume that you meant ##.");
    back_error; cur_tok:=s;
    end
  else cur_tok:=out_param_token-"0"+cur_chr;
end

@ Another way to create a token list is via the \.{\\read} command. The
sixteen files potentially usable for reading appear in the following
global variables. The value of |read_open[n]| will be |closed| if
stream number |n| has not been opened or if it has been fully read;
|just_open| if an \.{\\openin} but not a \.{\\read} has been done;
and |normal| if it is open and ready to read the next line.

@d closed=2 {not open, or at end of file}
@d just_open=1 {newly opened, first line not yet read}

@<Glob...@>=
@!read_file:array[0..15] of alpha_file; {used for \.{\\read}}
@!read_open:array[0..16] of normal..closed; {state of |read_file[n]|}

@ @<Set init...@>=
for k:=0 to 16 do begin 
    read_open[k]:=closed;
end;

@ The |read_toks| procedure constructs a token list like that for any
macro definition, and makes |cur_val| point to it. Parameter |r| points
to the control sequence that will receive this token list.

@p procedure read_toks(@!n:integer;@!r:pointer;@!j:halfword);
label done;
var p:pointer; {tail of the token list}
@!q:pointer; {new node being added to the token list via |store_new_token|}
@!s:integer; {saved value of |align_state|}
@!m:small_number; {stream number}
begin scanner_status:=defining; warning_index:=r;
p:=get_avail; def_ref:=p; token_ref_count(def_ref):=0;
p:=def_ref; {the reference count}
store_new_token(end_match_token);
if (n<0)or(n>15) then m:=16@+else m:=n;
s:=align_state; align_state:=1000000; {disable tab marks, etc.}
repeat @<Input and store tokens from the next line of the file@>;
until align_state=1000000;
cur_val:=def_ref; scanner_status:=normal; align_state:=s;
end;

@ @<Input and store tokens from the next line of the file@>=
begin_file_reading; name:=m+1;
if read_open[m]=closed then @<Input for \.{\\read} from the terminal@>
else if read_open[m]=just_open then @<Input the first line of |read_file[m]|@>
else @<Input the next line of |read_file[m]|@>;
limit:=last;
if end_line_char_inactive then decr(limit)
else  buffer[limit]:=end_line_char;
first:=limit+1; loc:=start; state:=new_line;@/
@<Handle \.{\\readline} and |goto done|@>;@/
loop@+  begin get_token;
  if cur_tok=0 then goto done;
    {|cur_cmd=cur_chr=0| will occur at the end of the line}
  if align_state<1000000 then {unmatched `\.\}' aborts the line}
    begin repeat get_token; until cur_tok=0;
    align_state:=1000000; goto done;
    end;
  store_new_token(cur_tok);
  end;
done: end_file_reading

@ Here we input on-line into the |buffer| array, prompting the user explicitly
if |n>=0|.  The value of |n| is set negative so that additional prompts
will not be given in the case of multi-line input.

@<Input for \.{\\read} from the terminal@>=
if interaction>nonstop_mode then
  if n<0 then prompt_input("")
  else  begin wake_up_terminal;
    print_ln; sprint_cs(r); prompt_input("="); n:=-1;
    end
else fatal_error("*** (cannot \read from terminal in nonstop modes)")
@.cannot \\read@>

@ The first line of a file must be treated specially, since |lua_input_ln|
must be told not to start with |get|.
@^system dependencies@>

@<Input the first line of |read_file[m]|@>=
begin if lua_input_ln(read_file[m],(m+1),false) then read_open[m]:=normal
else  begin lua_a_close_in(read_file[m],(m+1)); read_open[m]:=closed;
  end;
end

@ An empty line is appended at the end of a |read_file|.
@^empty line at end of file@>

@<Input the next line of |read_file[m]|@>=
begin if not lua_input_ln(read_file[m],(m+1),true) then
  begin lua_a_close_in(read_file[m],(m+1)); read_open[m]:=closed;
  if align_state<>1000000 then
    begin runaway;
    print_err("File ended within "); print_esc("read");
@.File ended within \\read@>
    help1("This \read has unbalanced braces.");
    align_state:=1000000; error;
    end;
  end;
end

@* \[28] Conditional processing.
We consider now the way \TeX\ handles various kinds of \.{\\if} commands.

@d unless_code=32 {amount added for `\.{\\unless}' prefix}
@#
@d if_char_code=0 { `\.{\\if}' }
@d if_cat_code=1 { `\.{\\ifcat}' }
@d if_int_code=2 { `\.{\\ifnum}' }
@d if_dim_code=3 { `\.{\\ifdim}' }
@d if_odd_code=4 { `\.{\\ifodd}' }
@d if_vmode_code=5 { `\.{\\ifvmode}' }
@d if_hmode_code=6 { `\.{\\ifhmode}' }
@d if_mmode_code=7 { `\.{\\ifmmode}' }
@d if_inner_code=8 { `\.{\\ifinner}' }
@d if_void_code=9 { `\.{\\ifvoid}' }
@d if_hbox_code=10 { `\.{\\ifhbox}' }
@d if_vbox_code=11 { `\.{\\ifvbox}' }
@d ifx_code=12 { `\.{\\ifx}' }
@d if_eof_code=13 { `\.{\\ifeof}' }
@d if_true_code=14 { `\.{\\iftrue}' }
@d if_false_code=15 { `\.{\\iffalse}' }
@d if_case_code=16 { `\.{\\ifcase}' }
@d if_primitive_code=21 { `\.{\\ifprimitive}' }

@<Put each...@>=
primitive("if",if_test,if_char_code);
@!@:if_char_}{\.{\\if} primitive@>
primitive("ifcat",if_test,if_cat_code);
@!@:if_cat_code_}{\.{\\ifcat} primitive@>
primitive("ifnum",if_test,if_int_code);
@!@:if_int_}{\.{\\ifnum} primitive@>
primitive("ifdim",if_test,if_dim_code);
@!@:if_dim_}{\.{\\ifdim} primitive@>
primitive("ifodd",if_test,if_odd_code);
@!@:if_odd_}{\.{\\ifodd} primitive@>
primitive("ifvmode",if_test,if_vmode_code);
@!@:if_vmode_}{\.{\\ifvmode} primitive@>
primitive("ifhmode",if_test,if_hmode_code);
@!@:if_hmode_}{\.{\\ifhmode} primitive@>
primitive("ifmmode",if_test,if_mmode_code);
@!@:if_mmode_}{\.{\\ifmmode} primitive@>
primitive("ifinner",if_test,if_inner_code);
@!@:if_inner_}{\.{\\ifinner} primitive@>
primitive("ifvoid",if_test,if_void_code);
@!@:if_void_}{\.{\\ifvoid} primitive@>
primitive("ifhbox",if_test,if_hbox_code);
@!@:if_hbox_}{\.{\\ifhbox} primitive@>
primitive("ifvbox",if_test,if_vbox_code);
@!@:if_vbox_}{\.{\\ifvbox} primitive@>
primitive("ifx",if_test,ifx_code);
@!@:ifx_}{\.{\\ifx} primitive@>
primitive("ifeof",if_test,if_eof_code);
@!@:if_eof_}{\.{\\ifeof} primitive@>
primitive("iftrue",if_test,if_true_code);
@!@:if_true_}{\.{\\iftrue} primitive@>
primitive("iffalse",if_test,if_false_code);
@!@:if_false_}{\.{\\iffalse} primitive@>
primitive("ifcase",if_test,if_case_code);
@!@:if_case_}{\.{\\ifcase} primitive@>
primitive("ifprimitive",if_test,if_primitive_code);
@!@:if_primitive_}{\.{\\ifprimitive} primitive@>
primitive("ifpdfprimitive",if_test,if_primitive_code);
@!@:if_primitive_}{\.{\\ifpdfprimitive} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
if_test: begin if chr_code>=unless_code then print_esc("unless");
case chr_code mod unless_code of
  if_cat_code:print_esc("ifcat");
  if_int_code:print_esc("ifnum");
  if_dim_code:print_esc("ifdim");
  if_odd_code:print_esc("ifodd");
  if_vmode_code:print_esc("ifvmode");
  if_hmode_code:print_esc("ifhmode");
  if_mmode_code:print_esc("ifmmode");
  if_inner_code:print_esc("ifinner");
  if_void_code:print_esc("ifvoid");
  if_hbox_code:print_esc("ifhbox");
  if_vbox_code:print_esc("ifvbox");
  ifx_code:print_esc("ifx");
  if_eof_code:print_esc("ifeof");
  if_true_code:print_esc("iftrue");
  if_false_code:print_esc("iffalse");
  if_case_code:print_esc("ifcase");
  if_primitive_code:print_esc("ifprimitive");
  @/@<Cases of |if_test| for |print_cmd_chr|@>@/
  othercases print_esc("if")
  endcases;
end;

@ Conditions can be inside conditions, and this nesting has a stack
that is independent of the |save_stack|.

Four global variables represent the top of the condition stack:
|cond_ptr| points to pushed-down entries, if any; |if_limit| specifies
the largest code of a |fi_or_else| command that is syntactically legal;
|cur_if| is the name of the current type of conditional; and |if_line|
is the line number at which it began.

If no conditions are currently in progress, the condition stack has the
special state |cond_ptr=null|, |if_limit=normal|, |cur_if=0|, |if_line=0|.
Otherwise |cond_ptr| points to a two-word node; the |type|, |subtype|, and
|link| fields of the first word contain |if_limit|, |cur_if|, and
|cond_ptr| at the next level, and the second word contains the
corresponding |if_line|.

@d if_node==49
@d if_node_size=2 {number of words in stack entry for conditionals}
@d if_limit_subtype(#)==subtype(#+1)
@d if_limit_type(#)==type(#+1)
@d if_line_field(#)==vlink(#+1)
@d if_code=1 {code for \.{\\if...} being evaluated}
@d fi_code=2 {code for \.{\\fi}}
@d else_code=3 {code for \.{\\else}}
@d or_code=4 {code for \.{\\or}}

@<Glob...@>=
@!cond_ptr:pointer; {top of the condition stack}
@!if_limit:normal..or_code; {upper bound on |fi_or_else| codes}
@!cur_if:small_number; {type of conditional being worked on}
@!if_line:integer; {line where that conditional began}

@ @<Set init...@>=
cond_ptr:=null; if_limit:=normal; cur_if:=0; if_line:=0;

@ @<Put each...@>=
primitive("fi",fi_or_else,fi_code);
@!@:fi_}{\.{\\fi} primitive@>
text(frozen_fi):="fi"; eqtb[frozen_fi]:=eqtb[cur_val];
primitive("or",fi_or_else,or_code);
@!@:or_}{\.{\\or} primitive@>
primitive("else",fi_or_else,else_code);
@!@:else_}{\.{\\else} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
fi_or_else: if chr_code=fi_code then print_esc("fi")
  else if chr_code=or_code then print_esc("or")
  else print_esc("else");

@ When we skip conditional text, we keep track of the line number
where skipping began, for use in error messages.

@<Glob...@>=
@!skip_line:integer; {skipping began here}

@ Here is a procedure that ignores text until coming to an \.{\\or},
\.{\\else}, or \.{\\fi} at level zero of $\.{\\if}\ldots\.{\\fi}$
nesting. After it has acted, |cur_chr| will indicate the token that
was found, but |cur_tok| will not be set (because this makes the
procedure run faster).

@p procedure pass_text;
label done;
var l:integer; {level of $\.{\\if}\ldots\.{\\fi}$ nesting}
@!save_scanner_status:small_number; {|scanner_status| upon entry}
begin save_scanner_status:=scanner_status; scanner_status:=skipping; l:=0;
skip_line:=line;
loop@+  begin get_filtered_next;
  if cur_cmd=fi_or_else then
    begin if l=0 then goto done;
    if cur_chr=fi_code then decr(l);
    end
  else if cur_cmd=if_test then incr(l);
  end;
done: scanner_status:=save_scanner_status;
if tracing_ifs>0 then show_cur_cmd_chr;
end;

@ When we begin to process a new \.{\\if}, we set |if_limit:=if_code|; then
if\/ \.{\\or} or \.{\\else} or \.{\\fi} occurs before the current \.{\\if}
condition has been evaluated, \.{\\relax} will be inserted.
For example, a sequence of commands like `\.{\\ifvoid1\\else...\\fi}'
would otherwise require something after the `\.1'.

@<Push the condition stack@>=
begin p:=new_node(if_node,0); vlink(p):=cond_ptr; 
if_limit_type(p):=if_limit;
if_limit_subtype(p):=cur_if; 
if_line_field(p):=if_line;
cond_ptr:=p; cur_if:=cur_chr; if_limit:=if_code; if_line:=line;
end

@ @<Pop the condition stack@>=
begin if if_stack[in_open]=cond_ptr then if_warning;
  {conditionals possibly not properly nested with files}
p:=cond_ptr;
if_line:=if_line_field(p);
cur_if:=if_limit_subtype(p); 
if_limit:=if_limit_type(p); 
cond_ptr:=vlink(p);
flush_node(p);
end

@ Here's a procedure that changes the |if_limit| code corresponding to
a given value of |cond_ptr|.

@p procedure change_if_limit(@!l:small_number;@!p:pointer);
label exit;
var q:pointer;
begin if p=cond_ptr then if_limit:=l {that's the easy case}
else  begin q:=cond_ptr;
  loop@+  begin if q=null then confusion("if");
@:this can't happen if}{\quad if@>
    if vlink(q)=p then
      begin if_limit_type(q):=l; return;
      end;
    q:=vlink(q);
    end;
  end;
exit:end;

@ A condition is started when the |expand| procedure encounters
an |if_test| command; in that case |expand| reduces to |conditional|,
which is a recursive procedure.
@^recursion@>

@p procedure conditional;
label exit,common_ending;
var b:boolean; {is the condition true?}
@!r:"<"..">"; {relation to be evaluated}
@!m,@!n,@!s:integer; {to be tested against the second operand}
@!p,@!q:pointer; {for traversing token lists in \.{\\ifx} tests}
@!save_scanner_status:small_number; {|scanner_status| upon entry}
@!save_cond_ptr:pointer; {|cond_ptr| corresponding to this conditional}
@!this_if:small_number; {type of this conditional}
@!is_unless:boolean; {was this if preceded by `\.{\\unless}' ?}
begin b:= false; {default is false, just in case}
if tracing_ifs>0 then if tracing_commands<=1 then show_cur_cmd_chr;
@<Push the condition stack@>;@+save_cond_ptr:=cond_ptr;
is_unless:=(cur_chr>=unless_code); this_if:=cur_chr mod unless_code;@/
@<Either process \.{\\ifcase} or set |b| to the value of a boolean condition@>;
if is_unless then b:=not b;
if tracing_commands>1 then @<Display the value of |b|@>;
if b then
  begin change_if_limit(else_code,save_cond_ptr);
  return; {wait for \.{\\else} or \.{\\fi}}
  end;
@<Skip to \.{\\else} or \.{\\fi}, then |goto common_ending|@>;
common_ending: if cur_chr=fi_code then @<Pop the condition stack@>
else if_limit:=fi_code; {wait for \.{\\fi}}
exit:end;

@ In a construction like `\.{\\if\\iftrue abc\\else d\\fi}', the first
\.{\\else} that we come to after learning that the \.{\\if} is false is
not the \.{\\else} we're looking for. Hence the following curious
logic is needed.

@ @<Skip to \.{\\else} or \.{\\fi}...@>=
loop@+  begin pass_text;
  if cond_ptr=save_cond_ptr then
    begin if cur_chr<>or_code then goto common_ending;
    print_err("Extra "); print_esc("or");
@.Extra \\or@>
    help1("I'm ignoring this; it doesn't match any \if.");
    error;
    end
  else if cur_chr=fi_code then @<Pop the condition stack@>;
  end

@ @<Either process \.{\\ifcase} or set |b|...@>=
case this_if of
if_char_code, if_cat_code: @<Test if two characters match@>;
if_int_code, if_dim_code: @<Test relation between integers or dimensions@>;
if_odd_code: @<Test if an integer is odd@>;
if_vmode_code: b:=(abs(mode)=vmode);
if_hmode_code: b:=(abs(mode)=hmode);
if_mmode_code: b:=(abs(mode)=mmode);
if_inner_code: b:=(mode<0);
if_void_code, if_hbox_code, if_vbox_code: @<Test box register status@>;
ifx_code: @<Test if two tokens match@>;
if_eof_code: begin scan_four_bit_int; b:=(read_open[cur_val]=closed);
  end;
if_true_code: b:=true;
if_false_code: b:=false;
@/@<Cases for |conditional|@>@/
if_case_code: @<Select the appropriate case
  and |return| or |goto common_ending|@>;
if_primitive_code: begin
  save_scanner_status:=scanner_status;
  scanner_status:=normal;
  get_filtered_next;
  scanner_status:=save_scanner_status;
  m := prim_lookup(text(cur_cs));
  b :=((cur_cmd<>undefined_cs) and
       (m<>undefined_primitive) and
       (cur_cmd=get_prim_eq_type(m)) and
       (cur_chr=get_prim_equiv(m)));
  end;
{there are no other cases, but for -Wall: }
othercases
  b:=false;
endcases

@ @<Display the value of |b|@>=
begin begin_diagnostic;
if b then print("{true}")@+else print("{false}");
end_diagnostic(false);
end

@ Here we use the fact that |"<"|, |"="|, and |">"| are consecutive ASCII
codes.
@^ASCII code@>

@<Test relation between integers or dimensions@>=
begin if this_if=if_int_code then scan_int@+else scan_normal_dimen;
n:=cur_val; @<Get the next non-blank non-call...@>;
if (cur_tok>=other_token+"<")and(cur_tok<=other_token+">") then
  r:=cur_tok-other_token
else  begin print_err("Missing = inserted for ");
@.Missing = inserted@>
  print_cmd_chr(if_test,this_if);
  help1("I was expecting to see `<', `=', or `>'. Didn't.");
  back_error; r:="=";
  end;
if this_if=if_int_code then scan_int@+else scan_normal_dimen;
case r of
"<": b:=(n<cur_val);
"=": b:=(n=cur_val);
">": b:=(n>cur_val);
othercases b:=false; {can't happen}
end;
end

@ @<Test if an integer is odd@>=
begin scan_int; b:=odd(cur_val);
end

@ @<Test box register status@>=
begin scan_register_num; p:=box(cur_val);
if this_if=if_void_code then b:=(p=null)
else if p=null then b:=false
else if this_if=if_hbox_code then b:=(type(p)=hlist_node)
else b:=(type(p)=vlist_node);
end

@ An active character will be treated as category 13 following
\.{\\if\\noexpand} or following \.{\\ifcat\\noexpand}. We use the fact that
active characters have the smallest tokens, among all control sequences.

The |(biggest_char-number_active_chars)| part is needed because only the
bottom two planes are present as active characters in |eqtb|.

@d get_x_token_or_active_char==@t@>@;
  begin get_x_token;
  if cur_cmd=relax then if cur_chr=no_expand_flag then
    begin cur_cmd:=active_char;
    cur_chr:=cur_tok-cs_token_flag-active_base+(biggest_char-number_active_chars);
    end;
  end

@<Test if two characters match@>=
begin get_x_token_or_active_char;
if (cur_cmd>active_char)or(cur_chr>biggest_char) then {not a character}
  begin m:=relax; n:=too_big_char;
  end
else  begin m:=cur_cmd; n:=cur_chr;
  end;
get_x_token_or_active_char;
if (cur_cmd>active_char)or(cur_chr>biggest_char) then
  begin cur_cmd:=relax; cur_chr:=too_big_char;
  end;
if this_if=if_char_code then b:=(n=cur_chr)@+else b:=(m=cur_cmd);
end

@ Note that `\.{\\ifx}' will declare two macros different if one is \\{long}
or \\{outer} and the other isn't, even though the texts of the macros are
the same.

We need to reset |scanner_status|, since \.{\\outer} control sequences
are allowed, but we might be scanning a macro definition or preamble.

@<Test if two tokens match@>=
begin save_scanner_status:=scanner_status; scanner_status:=normal;
get_filtered_next; n:=cur_cs; p:=cur_cmd; q:=cur_chr;
get_filtered_next; if cur_cmd<>p then b:=false
else if cur_cmd<call then b:=(cur_chr=q)
else @<Test if two macro texts match@>;
scanner_status:=save_scanner_status;
end

@ Note also that `\.{\\ifx}' decides that macros \.{\\a} and \.{\\b} are
different in examples like this:
$$\vbox{\halign{\.{#}\hfil&\qquad\.{#}\hfil\cr
  {}\\def\\a\{\\c\}&
  {}\\def\\c\{\}\cr
  {}\\def\\b\{\\d\}&
  {}\\def\\d\{\}\cr}}$$

@<Test if two macro texts match@>=
begin p:=link(cur_chr); q:=link(equiv(n)); {omit reference counts}
if p=q then b:=true
else begin while (p<>null)and(q<>null) do
    if info(p)<>info(q) then p:=null
    else  begin p:=link(p); q:=link(q);
      end;
  b:=((p=null)and(q=null));
  end;
end

@ @<Select the appropriate case and |return| or |goto common_ending|@>=
begin scan_int; n:=cur_val; {|n| is the number of cases to pass}
if tracing_commands>1 then
  begin begin_diagnostic; print("{case "); print_int(n); print_char("}");
  end_diagnostic(false);
  end;
while n<>0 do
  begin pass_text;
  if cond_ptr=save_cond_ptr then
    if cur_chr=or_code then decr(n)
    else goto common_ending
  else if cur_chr=fi_code then @<Pop the condition stack@>;
  end;
change_if_limit(or_code,save_cond_ptr);
return; {wait for \.{\\or}, \.{\\else}, or \.{\\fi}}
end

@ The processing of conditionals is complete except for the following
code, which is actually part of |expand|. It comes into play when
\.{\\or}, \.{\\else}, or \.{\\fi} is scanned.

@<Terminate the current conditional and skip to \.{\\fi}@>=
begin if tracing_ifs>0 then if tracing_commands<=1 then show_cur_cmd_chr;
if cur_chr>if_limit then
  if if_limit=if_code then insert_relax {condition not yet evaluated}
  else  begin print_err("Extra "); print_cmd_chr(fi_or_else,cur_chr);
@.Extra \\or@>
@.Extra \\else@>
@.Extra \\fi@>
    help1("I'm ignoring this; it doesn't match any \if.");
    error;
    end
else  begin while cur_chr<>fi_code do pass_text; {skip to \.{\\fi}}
  @<Pop the condition stack@>;
  end;
end

@* \[29] File names.
It's time now to fret about file names.  Besides the fact that different
operating systems treat files in different ways, we must cope with the
fact that completely different naming conventions are used by different
groups of people. The following programs show what is required for one
particular operating system; similar routines for other systems are not
difficult to devise.
@^fingers@>
@^system dependencies@>

\TeX\ assumes that a file name has three parts: the name proper; its
``extension''; and a ``file area'' where it is found in an external file
system.  The extension of an input file or a write file is assumed to be
`\.{.tex}' unless otherwise specified; it is `\.{.log}' on the
transcript file that records each run of \TeX; it is `\.{.tfm}' on the font
metric files that describe characters in the fonts \TeX\ uses; it is
`\.{.dvi}' on the output files that specify typesetting information; and it
is `\.{.fmt}' on the format files written by \.{INITEX} to initialize \TeX.
The file area can be arbitrary on input files, but files are usually
output to the user's current area.  If an input file cannot be
found on the specified area, \TeX\ will look for it on a special system
area; this special area is intended for commonly used input files like
\.{webmac.tex}.

Simple uses of \TeX\ refer only to file names that have no explicit
extension or area. For example, a person usually says `\.{\\input} \.{paper}'
or `\.{\\font\\tenrm} \.= \.{helvetica}' instead of `\.{\\input}
\.{paper.new}' or `\.{\\font\\tenrm} \.= \.{<csd.knuth>test}'. Simple file
names are best, because they make the \TeX\ source files portable;
whenever a file name consists entirely of letters and digits, it should be
treated in the same way by all implementations of \TeX. However, users
need the ability to refer to other files in their environment, especially
when responding to error messages concerning unopenable files; therefore
we want to let them use the syntax that appears in their favorite
operating system.

The following procedures don't allow spaces to be part of
file names; but some users seem to like names that are spaced-out.
System-dependent changes to allow such things should probably
be made with reluctance, and only when an entire file name that
includes spaces is ``quoted'' somehow.

@ In order to isolate the system-dependent aspects of file names, the
@^system dependencies@>
system-independent parts of \TeX\ are expressed in terms
of three system-dependent
procedures called |begin_name|, |more_name|, and |end_name|. In
essence, if the user-specified characters of the file name are $c_1\ldots c_n$,
the system-independent driver program does the operations
$$|begin_name|;\,|more_name|(c_1);\,\ldots\,;|more_name|(c_n);
\,|end_name|.$$
These three procedures communicate with each other via global variables.
Afterwards the file name will appear in the string pool as three strings
called |cur_name|\penalty10000\hskip-.05em,
|cur_area|, and |cur_ext|; the latter two are null (i.e.,
|""|), unless they were explicitly specified by the user.

Actually the situation is slightly more complicated, because \TeX\ needs
to know when the file name ends. The |more_name| routine is a function
(with side effects) that returns |true| on the calls |more_name|$(c_1)$,
\dots, |more_name|$(c_{n-1})$. The final call |more_name|$(c_n)$
returns |false|; or, it returns |true| and the token following $c_n$ is
something like `\.{\\hbox}' (i.e., not a character). In other words,
|more_name| is supposed to return |true| unless it is sure that the
file name has been completely scanned; and |end_name| is supposed to be able
to finish the assembly of |cur_name|, |cur_area|, and |cur_ext| regardless of
whether $|more_name|(c_n)$ returned |true| or |false|.

@<Glob...@>=
@!cur_name:str_number; {name of file just scanned}
@!cur_area:str_number; {file area just scanned, or \.{""}}
@!cur_ext:str_number; {file extension just scanned, or \.{""}}

@ The file names we shall deal with for illustrative purposes have the
following structure:  If the name contains `\.>' or `\.:', the file area
consists of all characters up to and including the final such character;
otherwise the file area is null.  If the remaining file name contains
`\..', the file extension consists of all such characters from the first
remaining `\..' to the end, otherwise the file extension is null.
@^system dependencies@>

We can scan such file names easily by using two global variables that keep track
of the occurrences of area and extension delimiters:

@<Glob...@>=
@!area_delimiter:pool_pointer; {the most recent `\.>' or `\.:', if any}
@!ext_delimiter:pool_pointer; {the relevant `\..', if any}

@ Input files that can't be found in the user's area may appear in a standard
system area called |TEX_area|. Font metric files whose areas are not given
explicitly are assumed to appear in a standard system area called
|TEX_font_area|.  $\Omega$'s compiled translation process files whose areas
are not given explicitly are assumed to appear in a standard system area
called |OMEGA_ocp_area|.  These system area names will, of course, vary
from place to place.
@^system dependencies@>

@d TEX_area=="TeXinputs:"
@.TeXinputs@>
@d TEX_font_area=="TeXfonts:"
@.TeXfonts@>
@d OMEGA_ocp_area=="OmegaOCPs:"
@.OmegaOCPs@>

@ Here now is the first of the system-dependent routines for file name scanning.
@^system dependencies@>

@p procedure begin_name;
begin area_delimiter:=0; ext_delimiter:=0;
end;

@ And here's the second. The string pool might change as the file name is
being scanned, since a new \.{\\csname} might be entered; therefore we keep
|area_delimiter| and |ext_delimiter| relative to the beginning of the current
string, instead of assigning an absolute address like |pool_ptr| to them.
@^system dependencies@>

@p function more_name(@!c:ASCII_code):boolean;
begin if c=" " then more_name:=false
else  begin str_room(1); append_char(c); {contribute |c| to the current string}
  if (c=">")or(c=":") then
    begin area_delimiter:=cur_length; ext_delimiter:=0;
    end
  else if (c=".")and(ext_delimiter=0) then ext_delimiter:=cur_length;
  more_name:=true;
  end;
end;

@ The third.
@^system dependencies@>

@p procedure end_name;
begin if str_ptr+3>(max_strings+string_offset) then
  overflow("number of strings",max_strings-init_str_ptr);
@:TeX capacity exceeded number of strings}{\quad number of strings@>
if area_delimiter=0 then cur_area:=""
else  begin cur_area:=str_ptr;
  str_start_macro(str_ptr+1):=str_start_macro(str_ptr)+area_delimiter; incr(str_ptr);
  end;
if ext_delimiter=0 then
  begin cur_ext:=""; cur_name:=make_string;
  end
else  begin cur_name:=str_ptr;
  str_start_macro(str_ptr+1):=str_start_macro(str_ptr)+ext_delimiter-area_delimiter-1;
  incr(str_ptr); cur_ext:=make_string;
  end;
end;

@ Conversely, here is a routine that takes three strings and prints a file
name that might have produced them. (The routine is system dependent, because
some operating systems put the file area last instead of first.)
@^system dependencies@>

@<Basic printing...@>=
procedure print_file_name(@!n,@!a,@!e:integer);
begin slow_print(a); slow_print(n); slow_print(e);
end;

@ Another system-dependent routine is needed to convert three internal
\TeX\ strings
into the |nameoffile| value that is used to open files. The present code
allows both lowercase and uppercase letters in the file name.
@^system dependencies@>

@d append_to_name(#)==begin c:=#; incr(k);
  if k<=file_name_size then nameoffile[k]:=xchr[c];
  end

@p procedure pack_file_name(@!n,@!a,@!e:str_number);
var k:integer; {number of positions filled in |nameoffile|}
@!c: ASCII_code; {character being packed}
@!j:pool_pointer; {index into |str_pool|}
begin k:=0;
for j:=str_start_macro(a) to str_start_macro(a+1)-1 do append_to_name(so(str_pool[j]));
for j:=str_start_macro(n) to str_start_macro(n+1)-1 do append_to_name(so(str_pool[j]));
for j:=str_start_macro(e) to str_start_macro(e+1)-1 do append_to_name(so(str_pool[j]));
if k<=file_name_size then namelength:=k@+else namelength:=file_name_size;
for k:=namelength+1 to file_name_size do nameoffile[k]:=' ';
end;

@ A messier routine is also needed, since format file names must be scanned
before \TeX's string mechanism has been initialized. We shall use the
global variable |TEX_format_default| to supply the text for default system areas
and extensions related to format files.
@^system dependencies@>

@d format_default_length=20 {length of the |TEX_format_default| string}
@d format_area_length=11 {length of its area part}
@d format_ext_length=4 {length of its `\.{.fmt}' part}
@d format_extension=".fmt" {the extension, as a \.{WEB} constant}

@<Glob...@>=
@!TEX_format_default:packed array[1..format_default_length] of char;

@ @<Set init...@>=
TEX_format_default:='TeXformats:plain.fmt';
@.TeXformats@>
@.plain@>
@^system dependencies@>

@ @<Check the ``constant'' values for consistency@>=
if format_default_length>file_name_size then bad:=31;

@ Here is the messy routine that was just mentioned. It sets |nameoffile|
from the first |n| characters of |TEX_format_default|, followed by
|buffer[a..b]|, followed by the last |format_ext_length| characters of
|TEX_format_default|.

We dare not give error messages here, since \TeX\ calls this routine before
the |error| routine is ready to roll. Instead, we simply drop excess characters,
since the error will be detected in another way when a strange file name
isn't found.
@^system dependencies@>

@p procedure pack_buffered_name(@!n:integer;@!a,@!b:integer);
var k:integer; {number of positions filled in |nameoffile|}
@!c: ASCII_code; {character being packed}
@!j:integer; {index into |buffer| or |TEX_format_default|}
begin if n+b-a+1+format_ext_length>file_name_size then
  b:=a+file_name_size-n-1-format_ext_length;
k:=0;
for j:=1 to n do append_to_name(TEX_format_default[j]);
for j:=a to b do append_to_name(buffer[j]);
for j:=format_default_length-format_ext_length+1 to format_default_length do
  append_to_name(TEX_format_default[j]);
if k<=file_name_size then namelength:=k@+else namelength:=file_name_size;
for k:=namelength+1 to file_name_size do nameoffile[k]:=' ';
end;

@ Here is the only place we use |pack_buffered_name|. This part of the program
becomes active when a ``virgin'' \TeX\ is trying to get going, just after
the preliminary initialization, or when the user is substituting another
format file by typing `\.\&' after the initial `\.{**}' prompt.  The buffer
contains the first line of input in |buffer[loc..(last-1)]|, where
|loc<last| and |buffer[loc]<>" "|.

@<Declare the function called |open_fmt_file|@>=
function open_fmt_file:boolean;
label found,exit;
var j:0..buf_size; {the first space after the format file name}
begin j:=loc;
if buffer[loc]="&" then
  begin incr(loc); j:=loc; buffer[last]:=" ";
  while buffer[j]<>" " do incr(j);
  pack_buffered_name(0,loc,j-1); {try first without the system file area}
  if w_open_in(fmt_file) then goto found;
  pack_buffered_name(format_area_length,loc,j-1);
    {now try the system format file area}
  if w_open_in(fmt_file) then goto found;
  wake_up_terminal;
  wterm_ln('Sorry, I can''t find that format;',' will try PLAIN.');
@.Sorry, I can't find...@>
  update_terminal;
  end;
  {now pull out all the stops: try for the system \.{plain} file}
pack_buffered_name(format_default_length-format_ext_length,1,0);
if not w_open_in(fmt_file) then
  begin wake_up_terminal;
  wterm_ln('I can''t find the PLAIN format file!');
@.I can't find PLAIN...@>
@.plain@>
  open_fmt_file:=false; return;
  end;
found:loc:=j; open_fmt_file:=true;
exit:end;

@ Operating systems often make it possible to determine the exact name (and
possible version number) of a file that has been opened. The following routine,
which simply makes a \TeX\ string from the value of |nameoffile|, should
ideally be changed to deduce the full name of file~|f|, which is the file
most recently opened, if it is possible to do this in a \PASCAL\ program.
@^system dependencies@>

This routine might be called after string memory has overflowed, hence
we dare not use `|str_room|'.

@d a_make_name_string(#)==make_name_string
@d b_make_name_string(#)==make_name_string
@d w_make_name_string(#)==make_name_string

@p function make_name_string:str_number;
var k:1..file_name_size; {index into |nameoffile|}
begin if (pool_ptr+namelength>pool_size)or(str_ptr=max_strings)or
 (cur_length>0) then
  make_name_string:="?"
else  begin for k:=1 to namelength do append_char(nameoffile[k]);
  make_name_string:=make_string;
  end;
end;

@ Now let's consider the ``driver''
routines by which \TeX\ deals with file names
in a system-independent manner.  First comes a procedure that looks for a
file name in the input by calling |get_x_token| for the information.

@p procedure scan_file_name;
label done;
begin name_in_progress:=true; begin_name;
@<Get the next non-blank non-call...@>;
loop@+begin if (cur_cmd>other_char)or(cur_chr>biggest_char) then {not a character}
    begin back_input; goto done;
    end;
  if not more_name(cur_chr) then goto done;
  get_x_token;
  end;
done: end_name; name_in_progress:=false;
end;

@ The global variable |name_in_progress| is used to prevent recursive
use of |scan_file_name|, since the |begin_name| and other procedures
communicate via global variables. Recursion would arise only by
devious tricks like `\.{\\input\\input f}'; such attempts at sabotage
must be thwarted. Furthermore, |name_in_progress| prevents \.{\\input}
@^recursion@>
from being initiated when a font size specification is being scanned.

Another global variable, |job_name|, contains the file name that was first
\.{\\input} by the user. This name is extended by `\.{.log}' and `\.{.dvi}'
and `\.{.fmt}' in the names of \TeX's output files.

@<Glob...@>=
@!name_in_progress:boolean; {is a file name being scanned?}
@!job_name:str_number; {principal file name}
@!log_opened:boolean; {has the transcript file been opened?}

@ Initially |job_name=0|; it becomes nonzero as soon as the true name is known.
We have |job_name=0| if and only if the `\.{log}' file has not been opened,
except of course for a short time just after |job_name| has become nonzero.

@<Initialize the output...@>=
job_name:=0; name_in_progress:=false; log_opened:=false;

@ Here is a routine that manufactures the output file names, assuming that
|job_name<>0|. It ignores and changes the current settings of |cur_area|
and |cur_ext|.

@d pack_cur_name==pack_file_name(cur_name,cur_area,cur_ext)

@p procedure pack_job_name(@!s:str_number); {|s = ".log"|, |".dvi"|, or
  |format_extension|}
begin cur_area:=""; cur_ext:=s;
cur_name:=job_name; pack_cur_name;
end;

@ If some trouble arises when \TeX\ tries to open a file, the following
routine calls upon the user to supply another file name. Parameter~|s|
is used in the error message to identify the type of file; parameter~|e|
is the default extension if none is given. Upon exit from the routine,
variables |cur_name|, |cur_area|, |cur_ext|, and |nameoffile| are
ready for another attempt at file opening.

@p procedure prompt_file_name(@!s,@!e:str_number);
label done;
var k:0..buf_size; {index into |buffer|}
begin if interaction=scroll_mode then wake_up_terminal;
if s="input file name" then print_err("I can't find file `")
@.I can't find file x@>
else print_err("I can't write on file `");
@.I can't write on file x@>
print_file_name(cur_name,cur_area,cur_ext); print("'.");
if e=".tex" then show_context;
print_nl("Please type another "); print(s);
@.Please type...@>
if interaction<scroll_mode then
  fatal_error("*** (job aborted, file error in nonstop mode)");
@.job aborted, file error...@>
clear_terminal; prompt_input(": "); @<Scan file name in the buffer@>;
if cur_ext="" then cur_ext:=e;
pack_cur_name;
end;

@ @<Scan file name in the buffer@>=
begin begin_name; k:=first;
while (buffer[k]=" ")and(k<last) do incr(k);
loop@+  begin if k=last then goto done;
  if not more_name(buffer[k]) then goto done;
  incr(k);
  end;
done:end_name;
end

@ Here's an example of how these conventions are used. Whenever it is time to
ship out a box of stuff, we shall use the macro |ensure_dvi_open|.

@d ensure_dvi_open==if output_file_name=0 then
  begin if job_name=0 then open_log_file;
  pack_job_name(".dvi");
  while not lua_b_open_out(dvi_file) do
    prompt_file_name("file name for output",".dvi");
  dvi_file:=name_file_pointer	;
  output_file_name:=b_make_name_string(dvi_file);
  end

@<Glob...@>=
@!dvi_file: byte_file; {the device-independent output goes here}
@!output_file_name: str_number; {full name of the output file}
@!log_name:str_number; {full name of the log file}

@ @<Initialize the output...@>=output_file_name:=0;

@ The |open_log_file| routine is used to open the transcript file and to help
it catch up to what has previously been printed on the terminal.

@p procedure open_log_file;
var old_setting:0..max_selector; {previous |selector| setting}
@!k:0..buf_size; {index into |months| and |buffer|}
@!l:0..buf_size; {end of first input line}
@!months:packed array [1..36] of char; {abbreviations of month names}
begin old_setting:=selector;
if job_name=0 then job_name:="texput";
@.texput@>
pack_job_name(".log");
while not lua_a_open_out(addressof(log_file),0) do @<Try to get a different log file name@>;
log_file := name_file_pointer;
log_name:=a_make_name_string(log_file);
selector:=log_only; log_opened:=true;
if not callback_defined(start_run_callback) then begin
  @<Print the banner line, including the date and time@>;
  input_stack[input_ptr]:=cur_input; {make sure bottom level is in memory}
  print_nl("**");
@.**@>
  l:=input_stack[0].limit_field; {last position of first line}
  if buffer[l]=end_line_char then decr(l); { TODO: multichar endlinechar}
  for k:=1 to l do print(buffer[k]);
  print_ln; {now the transcript file contains the first line of input}
  end
else begin
  flush_loggable_info;
end;
selector:=old_setting+2; {|log_only| or |term_and_log|}
end;

@ Sometimes |open_log_file| is called at awkward moments when \TeX\ is
unable to print error messages or even to |show_context|.
The |prompt_file_name| routine can result in a |fatal_error|, but the |error|
routine will not be invoked because |log_opened| will be false.

The normal idea of |batch_mode| is that nothing at all should be written
on the terminal. However, in the unusual case that
no log file could be opened, we make an exception and allow
an explanatory message to be seen.

Incidentally, the program always refers to the log file as a `\.{transcript
file}', because some systems cannot use the extension `\.{.log}' for
this file.

@<Try to get a different log file name@>=
begin selector:=term_only;
prompt_file_name("transcript file name",".log");
end

@ @<Print the banner...@>=
begin wlog(banner);
slow_print(format_ident); print("  ");
print_int(day); print_char(" ");
months:='JANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC';
for k:=3*month-2 to 3*month do wlog(months[k]);
print_char(" "); print_int(year); print_char(" ");
print_two(time div 60); print_char(":"); print_two(time mod 60);
end

@ Let's turn now to the procedure that is used to initiate file reading
when an `\.{\\input}' command is being processed.

@p procedure start_input; {\TeX\ will \.{\\input} something}
label done;
var temp_str:str_number;
begin scan_file_name; {set |cur_name| to desired file name}
if cur_ext="" then cur_ext:=".tex";
pack_cur_name;
loop@+  begin begin_file_reading; {set up |cur_file| and new level of input}
  if lua_a_open_in(cur_file,0) then goto done;
  end_file_reading; {remove the level that didn't work}
  prompt_file_name("input file name",".tex");
  end;
done: 
cur_file := name_file_pointer;
name:=a_make_name_string(cur_file);
if job_name=0 then
  begin job_name:=cur_name; open_log_file;
  end; {|open_log_file| doesn't |show_context|, so |limit|
    and |loc| needn't be set to meaningful values yet}
if tracefilenames then begin
  if term_offset+length(name)>max_print_line-2 then print_ln
  else if (term_offset>0)or(file_offset>0) then print_char(" ");
  print_char("("); 
  slow_print(name); 
end;
incr(open_parens); 
update_terminal;
state:=new_line;
if name=str_ptr-1 then {we can conserve string pool space now}
  begin flush_string; name:=cur_name;
  end;
@<Read the first line of the new file@>;
end;

@ Here we have to remember to tell the |lua_input_ln| routine not to
start with a |get|. If the file is empty, it is considered to
contain a single blank line.
@^system dependencies@>
@^empty line at end of file@>

@<Read the first line...@>=
begin line:=1;
if lua_input_ln(cur_file,0,false) then do_nothing;
firm_up_the_line;
if end_line_char_inactive then decr(limit)
else  buffer[limit]:=end_line_char;
first:=limit+1; loc:=start;
end

@* \[30] Font metric data and OCPS.
\TeX\ gets its knowledge about fonts from font metric files, also called
\.{TFM} files; the `\.T' in `\.{TFM}' stands for \TeX,
but other programs know about them too.
@:TFM files}{\.{TFM} files@>
@^font metric files@>

@ When the user defines \.{\\font\\f}, say, \TeX\ assigns an internal number
to the user's font~\.{\\f}. Adding this number to |font_id_base| gives the
|eqtb| location of a ``frozen'' control sequence that will always select
the font.

@<Types...@>=
@!internal_font_number=integer; {|font| in a |char_node|}
@!font_index=integer; {index into |font_info|}

@ @<Glob...@>=
@!font_bytes:integer;

@ \TeX\ always knows at least one font, namely the null font. It has no
characters, and its seven parameters are all equal to zero.

@<Initialize table...@>=
create_null_font;
font_bytes:=0;

@ @<Put each...@>=
primitive("nullfont",set_font,null_font);
@!@:null_font_}{\.{\\nullfont} primitive@>
text(frozen_null_font):="nullfont"; eqtb[frozen_null_font]:=eqtb[cur_val];

@ @<The em width for |cur_font|@>=quad(cur_font)

@ @<The x-height for |cur_font|@>=x_height(cur_font)

@ Before we forget about the format of these tables, let's deal with two
of \TeX's basic scanning routines related to font information.

@<Declare procedures that scan font-related stuff@>=
procedure scan_font_ident;
var f:internal_font_number;
@!m:halfword;
begin @<Get the next non-blank non-call...@>;
if (cur_cmd=def_font) or (cur_cmd=letterspace_font) then f:=cur_font
else if cur_cmd=set_font then begin 
  f:=cur_chr; 
  set_font_touched(f,1);
  end
else if cur_cmd=def_family then begin 
  m:=cur_chr; scan_math_family_int; f:=equiv(m+cur_val);
  set_font_touched(f,1);
  end
else  begin print_err("Missing font identifier");
@.Missing font identifier@>
  help2("I was looking for a control sequence whose")@/
  ("current meaning has been defined by \font.");
  back_error; f:=null_font;
  end;
cur_val:=f;
end;

@ The following routine is used to implement `\.{\\fontdimen} |n| |f|'.
The boolean parameter |writing| is set |true| if the calling program
intends to change the parameter value.

@<Declare procedures that scan font-related stuff@>=
procedure set_font_dimen;forward;
procedure get_font_dimen;forward;

@ @p
procedure set_font_dimen;
label exit;
var f:internal_font_number;
@!n:integer; {the parameter number}
begin scan_int; n:=cur_val; scan_font_ident; f:=cur_val;
  if n<=0 then
    @<Issue a font parameter error message, and return@>
  else begin
    if n>font_params(f) then
      if font_touched(f) then @<Issue a font parameter error message, and return@>
      else @<Increase the number of parameters in the font@>;
    end;
  scan_optional_equals; scan_normal_dimen;
  set_font_param(f,n,cur_val);
exit:
end;
@#
procedure get_font_dimen;
label exit;
var f:internal_font_number;
@!n:integer; {the parameter number}
begin scan_int; n:=cur_val; scan_font_ident; f:=cur_val;
  cur_val:=0; { initialize return value }
  if n<=0 then 
    @<Issue a font parameter error message, and return@>
  else begin
    if n>font_params(f) then
      if font_touched(f) then @<Issue a font parameter error message, and return@>
      else @<Increase the number of parameters in the font@>;
    end;
  cur_val:=font_param(f,n);
exit:
  scanned_result(cur_val)(dimen_val);
end;

@ @<Issue a font parameter error message, and return@>=
begin print_err("Font "); print_esc(font_id_text(f));
  print(" has only "); print_int(font_params(f));
  print(" fontdimen parameters");
@.Font x has only...@>
  help2("To increase the number of font parameters, you must")@/
    ("use \fontdimen immediately after the \font is loaded.");
  error;
  return;
end

@ @<Increase the number of parameters...@>=
begin repeat
  set_font_param(f,(font_params(f)+1),0);
until n=font_params(f);
end


@ When \TeX\ wants to typeset a character that doesn't exist, the
character node is not created; thus the output routine can assume
that characters exist when it sees them. The following procedure
prints a warning message unless the user has suppressed it.

@p procedure char_warning(@!f:internal_font_number;@!c:integer);
var old_setting: integer; {saved value of |tracing_online|}
begin if tracing_lost_chars>0 then
 begin old_setting:=tracing_online;
 if tracing_lost_chars>1 then tracing_online:=1;
  begin begin_diagnostic;
  print_nl("Missing character: There is no ");
@.Missing character@>
  print(c); print(" (");
  print_int(c); print(") in font "); 
  print_font_name(f);
  print_char("!"); end_diagnostic(false);
  end;
 tracing_online:=old_setting;
 end;
end;

@
@<Types...@>=
@!active_index=0..active_mem_size;

@
@d active_ocp(#)==active_info[#].hh.b0
@d active_counter(#)==active_info[#].hh.b1
@d active_lstack_no(#)==active_info[#+1].sc

@<Glob...@>=
@!active_info:array[active_index] of memory_word;
@!active_min_ptr:active_index; {first unused word of |active_info|}
@!active_max_ptr:active_index; {last unused word of |active_info|}
@!active_real:active_index;
@!holding:array[active_index] of ocp_list_index;

@
@<Initialize table...@>=
active_min_ptr:=0;
active_real:=0;

@
@p
function is_last_ocp(llstack_no:scaled; counter:integer):integer;
begin
active_min_ptr:=equiv(ocp_active_min_ptr_base);
active_max_ptr:=equiv(ocp_active_max_ptr_base);
active_real:=active_min_ptr;
while (active_real < active_max_ptr) and
      (active_lstack_no(active_real) < llstack_no) do begin
  active_real:=active_real+2;
  end;
while (active_real < active_max_ptr) and
      (active_lstack_no(active_real) = llstack_no) and
      (active_counter(active_real) <= counter) do begin
  active_real:=active_real+2;
  end;
is_last_ocp := (active_real=active_max_ptr);
end;

procedure print_active_ocps;
var i:integer;
begin
print_nl("Active ocps: [");
i:=active_min_ptr;
while i<active_max_ptr do begin
  print("(");
  print_scaled(active_lstack_no(i));
  print(",");
  print_int(active_counter(i));
  print(",");
  print_esc(ocp_id_text(active_ocp(i)));
  print(")");
  if i<>(active_max_ptr-2) then print(",");
  i:=i+2;
  end;
print("]");
end;

procedure add_ocp_stack(min_index:integer; min_value:scaled);
var p:ocp_lstack_index;
    llstack_no:scaled;
    counter:integer;
	m:scaled;
begin
m:=min_value; { TH: whatever this is ..}
p:=ocp_list_lstack(holding[min_index]);
llstack_no:=ocp_list_lstack_no(holding[min_index]);
counter:=0;
while not (is_null_ocp_lstack(p)) do begin
  active_ocp(active_max_ptr):=ocp_lstack_ocp(p);
  active_counter(active_max_ptr):=counter;
  active_lstack_no(active_max_ptr):=llstack_no;
  p:=ocp_lstack_lnext(p);
  active_max_ptr:=active_max_ptr+2;
  incr(counter);  {no overflow problem}
  end;
end;

procedure active_compile;
var i:integer;
    min_index:integer;
    min_stack_ocp:scaled;
    old_min:scaled;
    max_active:integer;
    stack_value:scaled;
begin
active_min_ptr:=active_max_ptr;
min_stack_ocp:=ocp_maxint;
max_active:=equiv(ocp_active_number_base)-1;
min_index:=max_active; {TH I hope ... }
for i:=max_active downto 0 do begin
  holding[i]:=ocp_list_list[equiv(ocp_active_base+i)];
  stack_value:=ocp_list_lstack_no(holding[i]);
  if stack_value<min_stack_ocp then begin
    min_index:=i;
    min_stack_ocp:=stack_value;
    end;
  end;
while min_stack_ocp<ocp_maxint do begin
  add_ocp_stack(min_index, min_stack_ocp);
  old_min:=min_stack_ocp;
  min_stack_ocp:=ocp_maxint;
  for i:=max_active downto 0 do begin
    stack_value:=ocp_list_lstack_no(holding[i]);
    while old_min=stack_value do begin
      holding[i]:=ocp_list_lnext(holding[i]);
      stack_value:=ocp_list_lstack_no(holding[i]);
      end;
    if stack_value<min_stack_ocp then begin
      min_index:=i;
      min_stack_ocp:=stack_value;
      end;
    end;
  end;
end;

@ Here we begin the \.{OCP} file handling.

@<Glob...@>=
@!ocp_file:byte_file;

@ So that is what \.{OCP} files hold.

When the user defines \.{\\ocp\\f}, say, \TeX\ assigns an internal number
to the user's ocp~\.{\\f}. Adding this number to |ocp_id_base| gives the
|eqtb| location of a ``frozen'' control sequence that will always select
the ocp.

@<Types...@>=
@!internal_ocp_number=ocp_base..ocp_biggest;
@!ocp_index=integer;

@ Here now is the array of ocp arrays.

@<Glob...@>=
@!ocp_ptr:internal_ocp_number; {largest internal ocp number in use}
@!ocp_buffer:^real_eight_bits; {byte buffer for ocp files}
@!ocp_size:integer; {total size of the ocp file}
@!ocp_cur:integer; {index into |ocp_buffer|}

@ @<Set init...@>=
ocp_buffer:=0; ocp_size:=0; ocp_cur:=0;

@ Besides the arrays just enumerated, we have two directory arrays that
make it easy to get at the individual entries in |ocp_info|.
The beginning of the info for the |j|-th state in the |i|-th ocp is at
location |ocp_info[ocp_state_base[i]+j]| and the |k|-th entry is in
location |ocp_info[ocp_info[ocp_state_base[i]+j]+k]|.
(These formulas assume that |min_quarterword| has already been 
added to |i|, |j| and |k|, since $\Omega$ stores its quarterwords that way.)

@d ocp_info_end(#)==#]
@d ocp_info(#)==ocp_tables[#,ocp_info_end
@d offset_ocp_file_size=0
@d offset_ocp_name=1
@d offset_ocp_area=offset_ocp_name+1
@d offset_ocp_external=offset_ocp_area+1
@d offset_ocp_external_arg=offset_ocp_external+1
@d offset_ocp_input=offset_ocp_external_arg+1
@d offset_ocp_output=offset_ocp_input+1
@d offset_ocp_no_tables=offset_ocp_output+1
@d offset_ocp_no_states=offset_ocp_no_tables+1
@d offset_ocp_table_base=offset_ocp_no_states+1
@d offset_ocp_state_base=offset_ocp_table_base+1
@d offset_ocp_info=offset_ocp_state_base+1
@d ocp_file_size(#)==ocp_info(#)(offset_ocp_file_size)
@d ocp_name(#)==ocp_info(#)(offset_ocp_name)
@d ocp_area(#)==ocp_info(#)(offset_ocp_area)
@d ocp_external(#)==ocp_info(#)(offset_ocp_external)
@d ocp_external_arg(#)==ocp_info(#)(offset_ocp_external_arg)
@d ocp_input(#)==ocp_info(#)(offset_ocp_input)
@d ocp_output(#)==ocp_info(#)(offset_ocp_output)
@d ocp_no_tables(#)==ocp_info(#)(offset_ocp_no_tables)
@d ocp_no_states(#)==ocp_info(#)(offset_ocp_no_states)
@d ocp_table_base(#)==ocp_info(#)(offset_ocp_table_base)
@d ocp_state_base(#)==ocp_info(#)(offset_ocp_state_base)

@ $\Omega$ always knows at least one ocp, namely the null ocp.
It does nothing.

@<Initialize table...@>=
ocp_ptr:=null_ocp; 
allocate_ocp_table(null_ocp,17);
ocp_file_size(null_ocp):=17;
ocp_name(null_ocp):="nullocp"; ocp_area(null_ocp):="";
ocp_external(null_ocp):=0; ocp_external_arg(null_ocp):=0;
ocp_input(null_ocp):=1; ocp_output(null_ocp):=1;
ocp_no_tables(null_ocp):=0;
ocp_no_states(null_ocp):=1;
ocp_table_base(f):=offset_ocp_info;
ocp_state_base(f):=offset_ocp_info;
ocp_info(null_ocp)(offset_ocp_info) := offset_ocp_info+2;  {number of entries}
ocp_info(null_ocp)(offset_ocp_info+1) := offset_ocp_info+5;  {number of entries}
ocp_info(null_ocp)(offset_ocp_info+2) := 23;  {|OTP_LEFT_START|}
ocp_info(null_ocp)(offset_ocp_info+3) := 3;  {|OTP_RIGHT_CHAR|}
ocp_info(null_ocp)(offset_ocp_info+4) := 36;  {|OTP_STOP|}


@ @<Put each...@>=
primitive("nullocp", set_ocp, null_ocp);
text(frozen_null_ocp) := "nullocp";
eqtb[frozen_null_ocp] := eqtb[cur_val];
geq_define(ocp_active_number_base, data, 0);
geq_define(ocp_active_min_ptr_base, data, 0);
geq_define(ocp_active_max_ptr_base, data, 0);

@ Of course we want to define macros that suppress the detail of how ocp
information is actually packed, so that we don't have to write things like
$$\hbox{|ocp_info[k+ocp_info[j+ocp_state_base[i]]]|}$$
too often. The \.{WEB} definitions here make |ocp_state_entry(i)(j)(k)| 
(|ocp_table_entry(i)(j)(k)|) the |k|-th word in the |j|-th state (table)
of the |i|-th ocp.
@^inner loop@>

@d ocp_state_end(#)==#]
@d ocp_state_one(#)==#*2]+ocp_state_end
@d ocp_state_entry(#)==ocp_tables[#,ocp_tables[#,ocp_state_base(#)+ocp_state_one

@d ocp_state_no_end(#)==#*2+1]
@d ocp_state_no(#)==ocp_tables[#,ocp_state_base(#)+ocp_state_no_end

@d ocp_table_end(#)==#]
@d ocp_table_one(#)==#*2]+ocp_table_end
@d ocp_table_entry(#)==ocp_tables[#,ocp_tables[#,ocp_table_base(#)+ocp_table_one

@d ocp_table_no_end(#)==#*2+1]
@d ocp_table_no(#)==ocp_tables[#,ocp_table_base(#)+ocp_table_no_end

@ $\Omega$ checks the information of a \.{OCP} file for validity as the
file is being read in, so that no further checks will be needed when
typesetting is going on. The somewhat tedious subroutine that does this
is called |read_ocp_info|. It has three parameters: the user ocp
identifier~|u|, and the file name and area strings |nom| and |aire|.

The subroutine opens and closes a global file variable called |ocp_file|.
It returns the value of the internal ocp number that was just loaded.
If an error is detected, an error message is issued and no ocp
information is stored; |null_ocp| is returned in this case.

@d bad_ocp=11 {label for |read_ocp_info|}
@d ocp_abort(#)==begin print("OCP file error (");
 print(#); print(")"); print_ln; goto bad_ocp end
 {do this when the \.{OCP} data is wrong}

@p function read_ocp_info(@!u:pointer;@!nom,@!aire,@!ext:str_number;
                          @!external_ocp:boolean)
  :internal_ocp_number; {input a \.{OCP} file}
label done,bad_ocp,not_found;
var 
@!file_opened:boolean; {was |ocp_file| successfully opened?}
@!k:integer;
@!res:boolean;
@!callback_id:integer;
@!fnam:str_number;
@!f:internal_ocp_number; {the new ocp's number}
@!g:internal_ocp_number; {the number to return}
@!ocpword:integer;
@!ocpmem_run_ptr:ocp_index;
@!ocp_length,real_ocp_length:integer; {length of ocp file}
@!previous_address:ocp_index;
@!temp_ocp_input:integer;
@!temp_ocp_output:integer;
@!temp_ocp_no_tables:integer;
@!temp_ocp_no_states:integer;
@!i,new_offset,room_for_tables,room_for_states:integer;
begin g:=null_ocp; f:=null_ocp;@/ 
@<Read and check the ocp data; |ocp_abort| if the \.{OCP} file is
  malformed; if there's no room for this ocp, say so and |goto
  done|; otherwise |incr(ocp_ptr)| and |goto done|@>;
bad_ocp: @<Report that the ocp won't be loaded@>;
done: 
ocp_name(f):=nom; ocp_area(f):=aire;
read_ocp_info:=g;
end;

@ $\Omega$ does not give precise details about why it
rejects a particular \.{OCP} file.

@d start_ocp_error_message==print_err("Translation process "); 
   sprint_cs(u); print_char("="); print_file_name(nom,aire,"");

@<Report that the ocp won't be loaded@>=
start_ocp_error_message;
@.Translation process x=xx not loadable...@>
if file_opened then print(" not loadable: Bad ocp file")
else print(" not loadable: ocp file not found");
help2("I wasn't able to read the data for this ocp,")@/
("so I will ignore the ocp specification.");
error

@ @<Read and check the ocp data...@>=
if external_ocp then 
  @<Check |ocp_file| exists@>
else begin
  @<Open |ocp_file| for input@>;
  @<Read the {\.{OCP}} file@>;
  end;

@ @<Check |ocp_file| exists@>=
begin
file_opened:=false;
pack_file_name(nom,aire,ext);
b_test_in;
if namelength=0 then ocp_abort("opening file");
f :=ocp_ptr+1;
allocate_ocp_table(f,13);
ocp_file_size(f):=13;
for i:=1 to namelength do begin
  append_char(nameoffile[i]);
  end;
ocp_external(f):=make_string;
scan_string_argument;
ocp_external_arg(f):=cur_val;
ocp_name(f):=""; ocp_area(f):="";
ocp_state_base(f):=0; ocp_table_base(f):=0;
ocp_input(f):=1; ocp_output(f):=1;
ocp_info(f)(offset_ocp_info):=0;
ocp_ptr:=f; g:=f;
goto done;
end

@ @<Open |ocp_file| for input@>=
file_opened:=false;
pack_file_name(nom,aire,".ocp");
if ocp_buffer<>0 then libcfree(ocp_buffer);
ocp_cur:=0; ocp_buffer:=0; ocp_size:=0;
callback_id:=callback_defined(find_ocp_file_callback);
if callback_id>0 then begin
  res := run_callback(callback_id,'S->s',stringcast(nameoffile+1), addressof(fnam));
  if (res)and(fnam<>0)and(length(fnam)>0) then begin
    @<Fixup |nameoffile| after callback@>;
    end;
  end;
callback_id:=callback_defined(read_ocp_file_callback);
if callback_id>0 then begin
  res := run_callback(callback_id,'S->bSd',stringcast(nameoffile+1),
          addressof(file_opened), addressof(ocp_buffer),addressof(ocp_size));
  if not res         then ocp_abort("callback error");
  if not file_opened then ocp_abort("opening file");
  if not ocp_size    then ocp_abort("checking size");
  end
else begin
  if not ocp_open_in(ocp_file) then ocp_abort("opening file");
  file_opened:=true;
  res := read_ocp_file(ocp_file,addressof(ocp_buffer),addressof(ocp_size));
  b_close(ocp_file);
  if not ocp_size then ocp_abort("checking size");
  if not res      then ocp_abort("reading file");
end


@ Note: A malformed \.{OCP} file might be shorter than it claims to be;
thus |eof(ocp_file)| might be true when |read_ocp_info| refers to
|ocp_file^| or when it says |get(ocp_file)|. If such circumstances
cause system error messages, you will have to defeat them somehow,
for example by defining |ocpget| to be `\ignorespaces|begin get(ocp_file);|
|if eof(ocp_file) then ocp_abort; end|\unskip'.
@^system dependencies@>

@d add_to_ocp_info(#)==begin ocp_tables[f,ocpmem_run_ptr]:=#;
  incr(ocpmem_run_ptr);
  end
@d ocpget==incr(ocp_cur)
@d ocpbyte==ocp_buffer[ocp_cur]
@d ocp_read(#)==begin ocpword:=ocpbyte;
  if ocpword>127 then ocp_abort("checking first octet");
  ocpget; ocpword:=ocpword*@'400+ocpbyte;
  ocpget; ocpword:=ocpword*@'400+ocpbyte;
  ocpget; ocpword:=ocpword*@'400+ocpbyte;
  #:=ocpword;
  end
@d ocp_read_all(#)==begin ocpget; ocp_read(#); end
@d ocp_read_info==begin ocp_read_all(ocpword);
  add_to_ocp_info(ocpword);
  end

@ @<Read the {\.{OCP}} file@>=
begin
f :=ocp_ptr+1;
ocpmem_run_ptr:=offset_ocp_info;
ocp_read(ocp_length);
real_ocp_length:=ocp_length-7;
ocp_read_all(temp_ocp_input);
ocp_read_all(temp_ocp_output);
ocp_read_all(temp_ocp_no_tables);
ocp_read_all(room_for_tables);
ocp_read_all(temp_ocp_no_states);
ocp_read_all(room_for_states);
if real_ocp_length <>
   (temp_ocp_no_tables + room_for_tables +
    temp_ocp_no_states + room_for_states) then
  ocp_abort("checking size");
real_ocp_length:=real_ocp_length+12+
   temp_ocp_no_states+temp_ocp_no_tables;
allocate_ocp_table(f,real_ocp_length);
ocp_external(f):=0;
ocp_external_arg(f):=0;
ocp_file_size(f):=real_ocp_length;
ocp_input(f):=temp_ocp_input;
ocp_output(f):=temp_ocp_output;
ocp_no_tables(f):=temp_ocp_no_tables;
ocp_no_states(f):=temp_ocp_no_states;
ocp_table_base(f):=ocpmem_run_ptr;
if ocp_no_tables(f) <> 0 then begin
  previous_address:=ocpmem_run_ptr+2*(ocp_no_tables(f));
  for i:=1 to ocp_no_tables(f) do begin
    add_to_ocp_info(previous_address);
    ocp_read_all(new_offset);
    add_to_ocp_info(new_offset);
    previous_address:=previous_address+new_offset;
    end
  end;
if room_for_tables <> 0 then begin
  for i:=1 to room_for_tables do begin
    ocp_read_info;
    end
  end;
ocp_state_base(f):=ocpmem_run_ptr;
if ocp_no_states(f) <> 0 then begin
  previous_address:=ocpmem_run_ptr+2*(ocp_no_states(f));
  for i:=1 to ocp_no_states(f) do begin
    add_to_ocp_info(previous_address);
    ocp_read_all(new_offset);
    add_to_ocp_info(new_offset);
    previous_address:=previous_address+new_offset;
    end;
  end;
if room_for_states <> 0 then begin
  for i:=1 to room_for_states do begin
    ocp_read_info;
    end
  end;
ocp_ptr:=f; g:=f;
goto done;
end

@ Before we forget about the format of these tables, let's deal with 
$\Omega$'s basic scanning routine related to ocp information.

@<Declare procedures that scan ocp-related stuff@>=
procedure scan_ocp_ident;
var f:internal_ocp_number;
begin @<Get the next non-blank non-call...@>;
if cur_cmd=set_ocp then f:=cur_chr
else  begin print_err("Missing ocp identifier");
@.Missing ocp identifier@>
  help2("I was looking for a control sequence whose")@/
  ("current meaning has been defined by \ocp.");
  back_error; f:=null_ocp;
  end;
cur_val:=f;
end;


@ Here we begin the \.{OCP} list handling.


@<Types...@>=
@!internal_ocp_list_number=ocp_list_base..ocp_list_biggest;
@!ocp_list_index=integer; {index into |ocp_list_info|}
@!ocp_lstack_index=integer; {index into |ocp_lstack_info|}

@ Here now is the array of ocp arrays.
@d ocp_list_lnext(#)==ocp_list_info[#].hh.b0
@d ocp_list_lstack(#)==ocp_list_info[#].hh.b1
@d ocp_list_lstack_no(#)==ocp_list_info[#+1].sc
@d ocp_lstack_lnext(#)==ocp_lstack_info[#].hh.b0
@d ocp_lstack_ocp(#)==ocp_lstack_info[#].hh.b1
@d make_null_ocp_list==make_ocp_list_node(0,ocp_maxint,0)
@d is_null_ocp_list(#)==ocp_list_lstack_no(#)=ocp_maxint
@d make_null_ocp_lstack==0
@d is_null_ocp_lstack(#)==#=0
@d add_before_op=1
@d add_after_op=2
@d remove_before_op=3
@d remove_after_op=4

@<Glob...@>=
@!ocp_list_info:array[ocp_list_index] of memory_word;
  {the big collection of ocp list data}
@!ocp_listmem_ptr:ocp_list_index; {first unused word of |ocp_list_info|}
@!ocp_listmem_run_ptr:ocp_list_index; {temp unused word of |ocp_list_info|}
@!ocp_lstack_info:array[ocp_lstack_index] of memory_word;
  {the big collection of ocp lstack data}
@!ocp_lstackmem_ptr:ocp_lstack_index; {first unused word of |ocp_lstack_info|}
@!ocp_lstackmem_run_ptr:ocp_lstack_index; {temp unused word of |ocp_lstack_info|}
@!ocp_list_ptr:internal_ocp_list_number; {largest internal ocp list number in use}
@!ocp_list_list:array[internal_ocp_list_number] of ocp_list_index;

@
@<Initialize table...@>=
ocp_listmem_ptr:=2;
ocp_list_lstack(0):=0;
ocp_list_lstack_no(0):=ocp_maxint;
ocp_list_lnext(0):=0;
ocp_list_ptr:=null_ocp_list;
ocp_list_list[null_ocp_list]:=0;
ocp_lstackmem_ptr:=1;

@ $\Omega$ always knows at least one ocp list, namely the null ocp list.

@ @<Put each...@>=
primitive("nullocplist", set_ocp_list, null_ocp_list);
text(frozen_null_ocp_list) := "nullocplist"; 
eqtb[frozen_null_ocp_list] := eqtb[cur_val];

@ @p function make_ocp_list_node(llstack:ocp_lstack_index; 
                                 llstack_no:scaled; 
                                 llnext:ocp_list_index):ocp_list_index;
var p:ocp_list_index;
begin 
p:=ocp_listmem_run_ptr;
ocp_list_lstack(p):=llstack;
ocp_list_lstack_no(p):=llstack_no;
ocp_list_lnext(p):=llnext;
ocp_listmem_run_ptr:=ocp_listmem_run_ptr+2;
if ocp_listmem_run_ptr>=ocp_list_size then
  overflow("ocp_list_size",ocp_list_size);
make_ocp_list_node:=p;
end;

function make_ocp_lstack_node(locp:internal_ocp_number;
                              llnext:ocp_lstack_index) : ocp_lstack_index;
var p:ocp_lstack_index;
begin 
p:=ocp_lstackmem_run_ptr;
ocp_lstack_ocp(p):=locp;
ocp_lstack_lnext(p):=llnext;
incr(ocp_lstackmem_run_ptr);
if ocp_lstackmem_run_ptr>=ocp_stack_size then
  overflow("ocp_stack_size",ocp_stack_size);
make_ocp_lstack_node:=p;
end;

function copy_ocp_lstack(llstack:ocp_lstack_index):ocp_lstack_index;
var result:ocp_lstack_index;
begin
if is_null_ocp_lstack(llstack) then
  result:=make_null_ocp_lstack
else
  result:=make_ocp_lstack_node(ocp_lstack_ocp(llstack),
                               copy_ocp_lstack(ocp_lstack_lnext(llstack)));
copy_ocp_lstack:=result;
end;

function copy_ocp_list(list:ocp_list_index):ocp_list_index;
var result:ocp_list_index;
begin
if is_null_ocp_list(list) then
  result:=make_null_ocp_list
else
  result:=make_ocp_list_node(copy_ocp_lstack(ocp_list_lstack(list)),
                             ocp_list_lstack_no(list),
                             copy_ocp_list(ocp_list_lnext(list)));
copy_ocp_list:=result;
end;

function ocp_ensure_lstack(list:ocp_list_index; llstack_no:scaled):
   ocp_list_index;
var p:ocp_list_index;
    q:ocp_list_index;
begin
p:=list;
if is_null_ocp_list(p) then begin
  ocp_list_lstack_no(p) := llstack_no;
  ocp_list_lnext(p) := make_null_ocp_list;
  end
else if ocp_list_lstack_no(p) > llstack_no then begin
  ocp_list_lnext(p):= 
    make_ocp_list_node(ocp_list_lstack(p),
                       ocp_list_lstack_no(p),
                       ocp_list_lnext(p));
  ocp_list_lstack(p):=0;
  ocp_list_lstack_no(p):=llstack_no;
  end
else begin
  q:=ocp_list_lnext(p);
  while (not (is_null_ocp_list(q))) and 
         ocp_list_lstack_no(q) <= llstack_no do begin
    p:=q; q:=ocp_list_lnext(q);
    end;
  if ocp_list_lstack_no(p) < llstack_no then begin
    ocp_list_lnext(p) := make_ocp_list_node(0, llstack_no, q);
    p := ocp_list_lnext(p);
    end;
  end;
ocp_ensure_lstack := p;
end;

procedure ocp_apply_add(list_entry:ocp_list_index;
                        lbefore:boolean;
                        locp:internal_ocp_number);
var p:ocp_lstack_index;
    q:ocp_lstack_index;
begin
p := ocp_list_lstack(list_entry);
if lbefore or (p=0) then begin
  ocp_list_lstack(list_entry) := make_ocp_lstack_node(locp, p);
  end
else begin
  q:=ocp_lstack_lnext(p);
  while q<>0 do begin
    p:=q; q:=ocp_lstack_lnext(q);
    end;
  ocp_lstack_lnext(p):=make_ocp_lstack_node(locp,0);
  end;
end;

procedure ocp_apply_remove(list_entry:ocp_list_index;
                           lbefore:boolean);
var p:ocp_lstack_index;
    q:ocp_lstack_index;
    r:ocp_lstack_index;
begin
p := ocp_list_lstack(list_entry);
if p=0 then begin
  print_err("warning: stack entry already empty"); print_ln
  end
else begin
  q := ocp_lstack_lnext(p);
  if lbefore or (q=0) then
    ocp_list_lstack(list_entry) := q
  else begin
    r:=ocp_lstack_lnext(q);
    while r <> 0 do begin
      p:=q; q:=r; r:=ocp_lstack_lnext(r);
      end;
    ocp_lstack_lnext(p) := 0; 
    end
  end;
end;

procedure scan_scaled; {sets |cur_val| to a scaled value}
label done, done1, done2, found, not_found, attach_fraction;
var negative:boolean; {should the answer be negated?}
@!f:integer; {numerator of a fraction whose denominator is $2^{16}$}
@!k,@!kk:small_number; {number of digits in a decimal fraction}
@!p,@!q:pointer; {top of decimal digit stack}
begin f:=0; arith_error:=false; negative:=false;
@<Get the next non-blank non-sign...@>;
back_input;
if cur_tok=continental_point_token then cur_tok:=point_token;
if cur_tok<>point_token then scan_int
else  begin radix:=10; cur_val:=0;
  end;
if cur_tok=continental_point_token then cur_tok:=point_token;
if (radix=10)and(cur_tok=point_token) then @<Scan decimal fraction@>;
if cur_val<0 then {in this case |f=0|}
  begin negative := not negative; negate(cur_val);
  end;
if cur_val>@'40000 then arith_error:=true
else cur_val := cur_val*unity +f;
if arith_error or(abs(cur_val)>=@'10000000000) then
begin print_err("Stack number too large"); error;
end;
if negative then negate(cur_val);
end;

procedure print_ocp_lstack(lstack_entry:ocp_lstack_index);
var p:ocp_lstack_index;
begin
p:=lstack_entry;
while (p<>0) do begin
  print_esc(ocp_id_text(ocp_lstack_ocp(p)));
  p:=ocp_lstack_lnext(p);
  if (p<>0) then print(",");
  end;
end;

procedure print_ocp_list(list_entry:ocp_list_index);
var p:ocp_list_index;
begin
print("["); p:=list_entry;
while not (is_null_ocp_list(p)) do begin
  print("(");
  print_scaled(ocp_list_lstack_no(p));
  print(" : ");
  print_ocp_lstack(ocp_list_lstack(p));
  print(")");
  p:=ocp_list_lnext(p);
  if not (is_null_ocp_list(p)) then print(", ");
  end;
print("]");
end;

function scan_ocp_list: ocp_list_index;
var llstack_no:scaled; 
    lop:quarterword;
    lstack_entry:ocp_list_index;
    other_list:ocp_list_index;
    ocp_ident:internal_ocp_number;
    result:ocp_list_index;
begin
get_r_token; 
if cur_cmd = set_ocp_list then
  result := copy_ocp_list(ocp_list_list[cur_chr])
else if cur_cmd <> ocp_list_op then begin
  print_err("Bad ocp list specification");
@.Bad ocp list specification@>
  help1("I was looking for a ocp list specification.");
  error;
  result := make_null_ocp_list;
  end
else begin
  lop:=cur_chr;
  scan_scaled; llstack_no:=cur_val;
  if (llstack_no<=0) or (llstack_no>=ocp_maxint) then begin
    print_err("Stack numbers must be between 0 and 4096 (exclusive)");
    error;
    result := make_null_ocp_list;
    end
  else begin
    if lop <= add_after_op then begin
      scan_ocp_ident; ocp_ident:=cur_val;
      end;
    other_list:=scan_ocp_list;
    lstack_entry:=ocp_ensure_lstack(other_list, llstack_no);
    if lop <= add_after_op then
      ocp_apply_add(lstack_entry, (lop=add_before_op), ocp_ident)
    else
      ocp_apply_remove(lstack_entry, (lop=remove_before_op));
    result:=other_list;
    end;
  end;
scan_ocp_list:=result;
end;

function read_ocp_list: internal_ocp_list_number;
var f:internal_ocp_list_number;
    g:internal_ocp_list_number;
begin
g:=null_ocp_list;
f:=ocp_list_ptr+1;
ocp_listmem_run_ptr:=ocp_listmem_ptr;
ocp_lstackmem_run_ptr:=ocp_lstackmem_ptr;
ocp_list_list[f]:=scan_ocp_list;
ocp_list_ptr:=f;
ocp_listmem_ptr:=ocp_listmem_run_ptr;
ocp_lstackmem_ptr:=ocp_lstackmem_run_ptr;
g:=f;
read_ocp_list:=g;
end;

procedure scan_ocp_list_ident;
var f:internal_ocp_list_number;
begin @<Get the next non-blank non-call...@>;
if cur_cmd=set_ocp_list then f:=cur_chr
else  begin print_err("Missing ocp list identifier");
@.Missing ocp list identifier@>
  help2("I was looking for a control sequence whose")@/
  ("current meaning has been defined by \ocplist.");
  back_error; f:=null_ocp_list;
  end;
cur_val:=f;
end;


@* \[31] Device-independent file format.
The most important output produced by a run of \TeX\ is the ``device
independent'' (\.{DVI}) file that specifies where characters and rules
are to appear on printed pages. The form of these files was designed by
David R. Fuchs in 1979. Almost any reasonable typesetting device can be
@^Fuchs, David Raymond@>
@:DVI_files}{\.{DVI} files@>
driven by a program that takes \.{DVI} files as input, and dozens of such
\.{DVI}-to-whatever programs have been written. Thus, it is possible to
print the output of \TeX\ on many different kinds of equipment, using \TeX\
as a device-independent ``front end.''

A \.{DVI} file is a stream of 8-bit bytes, which may be regarded as a
series of commands in a machine-like language. The first byte of each command
is the operation code, and this code is followed by zero or more bytes
that provide parameters to the command. The parameters themselves may consist
of several consecutive bytes; for example, the `|set_rule|' command has two
parameters, each of which is four bytes long. Parameters are usually
regarded as nonnegative integers; but four-byte-long parameters,
and shorter parameters that denote distances, can be
either positive or negative. Such parameters are given in two's complement
notation. For example, a two-byte-long distance parameter has a value between
$-2^{15}$ and $2^{15}-1$. As in \.{TFM} files, numbers that occupy
more than one byte position appear in BigEndian order.

A \.{DVI} file consists of a ``preamble,'' followed by a sequence of one
or more ``pages,'' followed by a ``postamble.'' The preamble is simply a
|pre| command, with its parameters that define the dimensions used in the
file; this must come first.  Each ``page'' consists of a |bop| command,
followed by any number of other commands that tell where characters are to
be placed on a physical page, followed by an |eop| command. The pages
appear in the order that \TeX\ generated them. If we ignore |nop| commands
and \\{fnt\_def} commands (which are allowed between any two commands in
the file), each |eop| command is immediately followed by a |bop| command,
or by a |post| command; in the latter case, there are no more pages in the
file, and the remaining bytes form the postamble.  Further details about
the postamble will be explained later.

Some parameters in \.{DVI} commands are ``pointers.'' These are four-byte
quantities that give the location number of some other byte in the file;
the first byte is number~0, then comes number~1, and so on. For example,
one of the parameters of a |bop| command points to the previous |bop|;
this makes it feasible to read the pages in backwards order, in case the
results are being directed to a device that stacks its output face up.
Suppose the preamble of a \.{DVI} file occupies bytes 0 to 99. Now if the
first page occupies bytes 100 to 999, say, and if the second
page occupies bytes 1000 to 1999, then the |bop| that starts in byte 1000
points to 100 and the |bop| that starts in byte 2000 points to 1000. (The
very first |bop|, i.e., the one starting in byte 100, has a pointer of~$-1$.)

@ The \.{DVI} format is intended to be both compact and easily interpreted
by a machine. Compactness is achieved by making most of the information
implicit instead of explicit. When a \.{DVI}-reading program reads the
commands for a page, it keeps track of several quantities: (a)~The current
font |f| is an integer; this value is changed only
by \\{fnt} and \\{fnt\_num} commands. (b)~The current position on the page
is given by two numbers called the horizontal and vertical coordinates,
|h| and |v|. Both coordinates are zero at the upper left corner of the page;
moving to the right corresponds to increasing the horizontal coordinate, and
moving down corresponds to increasing the vertical coordinate. Thus, the
coordinates are essentially Cartesian, except that vertical directions are
flipped; the Cartesian version of |(h,v)| would be |(h,-v)|.  (c)~The
current spacing amounts are given by four numbers |w|, |x|, |y|, and |z|,
where |w| and~|x| are used for horizontal spacing and where |y| and~|z|
are used for vertical spacing. (d)~There is a stack containing
|(h,v,w,x,y,z)| values; the \.{DVI} commands |push| and |pop| are used to
change the current level of operation. Note that the current font~|f| is
not pushed and popped; the stack contains only information about
positioning.

The values of |h|, |v|, |w|, |x|, |y|, and |z| are signed integers having up
to 32 bits, including the sign. Since they represent physical distances,
there is a small unit of measurement such that increasing |h| by~1 means
moving a certain tiny distance to the right. The actual unit of
measurement is variable, as explained below; \TeX\ sets things up so that
its \.{DVI} output is in sp units, i.e., scaled points, in agreement with
all the |scaled| dimensions in \TeX's data structures.

@ Here is a list of all the commands that may appear in a \.{DVI} file. Each
command is specified by its symbolic name (e.g., |bop|), its opcode byte
(e.g., 139), and its parameters (if any). The parameters are followed
by a bracketed number telling how many bytes they occupy; for example,
`|p[4]|' means that parameter |p| is four bytes long.

\yskip\hang|set_char_0| 0. Typeset character number~0 from font~|f|
such that the reference point of the character is at |(h,v)|. Then
increase |h| by the width of that character. Note that a character may
have zero or negative width, so one cannot be sure that |h| will advance
after this command; but |h| usually does increase.

\yskip\hang\\{set\_char\_1} through \\{set\_char\_127} (opcodes 1 to 127).
Do the operations of |set_char_0|; but use the character whose number
matches the opcode, instead of character~0.

\yskip\hang|set1| 128 |c[1]|. Same as |set_char_0|, except that character
number~|c| is typeset. \TeX82 uses this command for characters in the
range |128<=c<256|.

\yskip\hang|@!set2| 129 |c[2]|. Same as |set1|, except that |c|~is two
bytes long, so it is in the range |0<=c<65536|. \TeX82 never uses this
command, but it should come in handy for extensions of \TeX\ that deal
with oriental languages.
@^oriental characters@>@^Chinese characters@>@^Japanese characters@>

\yskip\hang|@!set3| 130 |c[3]|. Same as |set1|, except that |c|~is three
bytes long, so it can be as large as $2^{24}-1$. Not even the Chinese
language has this many characters, but this command might prove useful
in some yet unforeseen extension.

\yskip\hang|@!set4| 131 |c[4]|. Same as |set1|, except that |c|~is four
bytes long. Imagine that.

\yskip\hang|set_rule| 132 |a[4]| |b[4]|. Typeset a solid black rectangle
of height~|a| and width~|b|, with its bottom left corner at |(h,v)|. Then
set |h:=h+b|. If either |a<=0| or |b<=0|, nothing should be typeset. Note
that if |b<0|, the value of |h| will decrease even though nothing else happens.
See below for details about how to typeset rules so that consistency with
\MF\ is guaranteed.

\yskip\hang|@!put1| 133 |c[1]|. Typeset character number~|c| from font~|f|
such that the reference point of the character is at |(h,v)|. (The `put'
commands are exactly like the `set' commands, except that they simply put out a
character or a rule without moving the reference point afterwards.)

\yskip\hang|@!put2| 134 |c[2]|. Same as |set2|, except that |h| is not changed.

\yskip\hang|@!put3| 135 |c[3]|. Same as |set3|, except that |h| is not changed.

\yskip\hang|@!put4| 136 |c[4]|. Same as |set4|, except that |h| is not changed.

\yskip\hang|put_rule| 137 |a[4]| |b[4]|. Same as |set_rule|, except that
|h| is not changed.

\yskip\hang|nop| 138. No operation, do nothing. Any number of |nop|'s
may occur between \.{DVI} commands, but a |nop| cannot be inserted between
a command and its parameters or between two parameters.

\yskip\hang|bop| 139 $c_0[4]$ $c_1[4]$ $\ldots$ $c_9[4]$ $p[4]$. Beginning
of a page: Set |(h,v,w,x,y,z):=(0,0,0,0,0,0)| and set the stack empty. Set
the current font |f| to an undefined value.  The ten $c_i$ parameters hold
the values of \.{\\count0} $\ldots$ \.{\\count9} in \TeX\ at the time
\.{\\shipout} was invoked for this page; they can be used to identify
pages, if a user wants to print only part of a \.{DVI} file. The parameter
|p| points to the previous |bop| in the file; the first
|bop| has $p=-1$.

\yskip\hang|eop| 140.  End of page: Print what you have read since the
previous |bop|. At this point the stack should be empty. (The \.{DVI}-reading
programs that drive most output devices will have kept a buffer of the
material that appears on the page that has just ended. This material is
largely, but not entirely, in order by |v| coordinate and (for fixed |v|) by
|h|~coordinate; so it usually needs to be sorted into some order that is
appropriate for the device in question.)

\yskip\hang|push| 141. Push the current values of |(h,v,w,x,y,z)| onto the
top of the stack; do not change any of these values. Note that |f| is
not pushed.

\yskip\hang|pop| 142. Pop the top six values off of the stack and assign
them respectively to |(h,v,w,x,y,z)|. The number of pops should never
exceed the number of pushes, since it would be highly embarrassing if the
stack were empty at the time of a |pop| command.

\yskip\hang|right1| 143 |b[1]|. Set |h:=h+b|, i.e., move right |b| units.
The parameter is a signed number in two's complement notation, |-128<=b<128|;
if |b<0|, the reference point moves left.

\yskip\hang|right2| 144 |b[2]|. Same as |right1|, except that |b| is a
two-byte quantity in the range |-32768<=b<32768|.

\yskip\hang|right3| 145 |b[3]|. Same as |right1|, except that |b| is a
three-byte quantity in the range |@t$-2^{23}$@><=b<@t$2^{23}$@>|.

\yskip\hang|right4| 146 |b[4]|. Same as |right1|, except that |b| is a
four-byte quantity in the range |@t$-2^{31}$@><=b<@t$2^{31}$@>|.

\yskip\hang|w0| 147. Set |h:=h+w|; i.e., move right |w| units. With luck,
this parameterless command will usually suffice, because the same kind of motion
will occur several times in succession; the following commands explain how
|w| gets particular values.

\yskip\hang|w1| 148 |b[1]|. Set |w:=b| and |h:=h+b|. The value of |b| is a
signed quantity in two's complement notation, |-128<=b<128|. This command
changes the current |w|~spacing and moves right by |b|.

\yskip\hang|@!w2| 149 |b[2]|. Same as |w1|, but |b| is two bytes long,
|-32768<=b<32768|.

\yskip\hang|@!w3| 150 |b[3]|. Same as |w1|, but |b| is three bytes long,
|@t$-2^{23}$@><=b<@t$2^{23}$@>|.

\yskip\hang|@!w4| 151 |b[4]|. Same as |w1|, but |b| is four bytes long,
|@t$-2^{31}$@><=b<@t$2^{31}$@>|.

\yskip\hang|x0| 152. Set |h:=h+x|; i.e., move right |x| units. The `|x|'
commands are like the `|w|' commands except that they involve |x| instead
of |w|.

\yskip\hang|x1| 153 |b[1]|. Set |x:=b| and |h:=h+b|. The value of |b| is a
signed quantity in two's complement notation, |-128<=b<128|. This command
changes the current |x|~spacing and moves right by |b|.

\yskip\hang|@!x2| 154 |b[2]|. Same as |x1|, but |b| is two bytes long,
|-32768<=b<32768|.

\yskip\hang|@!x3| 155 |b[3]|. Same as |x1|, but |b| is three bytes long,
|@t$-2^{23}$@><=b<@t$2^{23}$@>|.

\yskip\hang|@!x4| 156 |b[4]|. Same as |x1|, but |b| is four bytes long,
|@t$-2^{31}$@><=b<@t$2^{31}$@>|.

\yskip\hang|down1| 157 |a[1]|. Set |v:=v+a|, i.e., move down |a| units.
The parameter is a signed number in two's complement notation, |-128<=a<128|;
if |a<0|, the reference point moves up.

\yskip\hang|@!down2| 158 |a[2]|. Same as |down1|, except that |a| is a
two-byte quantity in the range |-32768<=a<32768|.

\yskip\hang|@!down3| 159 |a[3]|. Same as |down1|, except that |a| is a
three-byte quantity in the range |@t$-2^{23}$@><=a<@t$2^{23}$@>|.

\yskip\hang|@!down4| 160 |a[4]|. Same as |down1|, except that |a| is a
four-byte quantity in the range |@t$-2^{31}$@><=a<@t$2^{31}$@>|.

\yskip\hang|y0| 161. Set |v:=v+y|; i.e., move down |y| units. With luck,
this parameterless command will usually suffice, because the same kind of motion
will occur several times in succession; the following commands explain how
|y| gets particular values.

\yskip\hang|y1| 162 |a[1]|. Set |y:=a| and |v:=v+a|. The value of |a| is a
signed quantity in two's complement notation, |-128<=a<128|. This command
changes the current |y|~spacing and moves down by |a|.

\yskip\hang|@!y2| 163 |a[2]|. Same as |y1|, but |a| is two bytes long,
|-32768<=a<32768|.

\yskip\hang|@!y3| 164 |a[3]|. Same as |y1|, but |a| is three bytes long,
|@t$-2^{23}$@><=a<@t$2^{23}$@>|.

\yskip\hang|@!y4| 165 |a[4]|. Same as |y1|, but |a| is four bytes long,
|@t$-2^{31}$@><=a<@t$2^{31}$@>|.

\yskip\hang|z0| 166. Set |v:=v+z|; i.e., move down |z| units. The `|z|' commands
are like the `|y|' commands except that they involve |z| instead of |y|.

\yskip\hang|z1| 167 |a[1]|. Set |z:=a| and |v:=v+a|. The value of |a| is a
signed quantity in two's complement notation, |-128<=a<128|. This command
changes the current |z|~spacing and moves down by |a|.

\yskip\hang|@!z2| 168 |a[2]|. Same as |z1|, but |a| is two bytes long,
|-32768<=a<32768|.

\yskip\hang|@!z3| 169 |a[3]|. Same as |z1|, but |a| is three bytes long,
|@t$-2^{23}$@><=a<@t$2^{23}$@>|.

\yskip\hang|@!z4| 170 |a[4]|. Same as |z1|, but |a| is four bytes long,
|@t$-2^{31}$@><=a<@t$2^{31}$@>|.

\yskip\hang|fnt_num_0| 171. Set |f:=0|. Font 0 must previously have been
defined by a \\{fnt\_def} instruction, as explained below.

\yskip\hang\\{fnt\_num\_1} through \\{fnt\_num\_63} (opcodes 172 to 234). Set
|f:=1|, \dots, \hbox{|f:=63|}, respectively.

\yskip\hang|fnt1| 235 |k[1]|. Set |f:=k|. \TeX82 uses this command for font
numbers in the range |64<=k<256|.

\yskip\hang|@!fnt2| 236 |k[2]|. Same as |fnt1|, except that |k|~is two
bytes long, so it is in the range |0<=k<65536|. \TeX82 never generates this
command, but large font numbers may prove useful for specifications of
color or texture, or they may be used for special fonts that have fixed
numbers in some external coding scheme.

\yskip\hang|@!fnt3| 237 |k[3]|. Same as |fnt1|, except that |k|~is three
bytes long, so it can be as large as $2^{24}-1$.

\yskip\hang|@!fnt4| 238 |k[4]|. Same as |fnt1|, except that |k|~is four
bytes long; this is for the really big font numbers (and for the negative ones).

\yskip\hang|xxx1| 239 |k[1]| |x[k]|. This command is undefined in
general; it functions as a $(k+2)$-byte |nop| unless special \.{DVI}-reading
programs are being used. \TeX82 generates |xxx1| when a short enough
\.{\\special} appears, setting |k| to the number of bytes being sent. It
is recommended that |x| be a string having the form of a keyword followed
by possible parameters relevant to that keyword.

\yskip\hang|@!xxx2| 240 |k[2]| |x[k]|. Like |xxx1|, but |0<=k<65536|.

\yskip\hang|@!xxx3| 241 |k[3]| |x[k]|. Like |xxx1|, but |0<=k<@t$2^{24}$@>|.

\yskip\hang|xxx4| 242 |k[4]| |x[k]|. Like |xxx1|, but |k| can be ridiculously
large. \TeX82 uses |xxx4| when sending a string of length 256 or more.

\yskip\hang|fnt_def1| 243 |k[1]| |c[4]| |s[4]| |d[4]| |a[1]| |l[1]| |n[a+l]|.
Define font |k|, where |0<=k<256|; font definitions will be explained shortly.

\yskip\hang|@!fnt_def2| 244 |k[2]| |c[4]| |s[4]| |d[4]| |a[1]| |l[1]| |n[a+l]|.
Define font |k|, where |0<=k<65536|.

\yskip\hang|@!fnt_def3| 245 |k[3]| |c[4]| |s[4]| |d[4]| |a[1]| |l[1]| |n[a+l]|.
Define font |k|, where |0<=k<@t$2^{24}$@>|.

\yskip\hang|@!fnt_def4| 246 |k[4]| |c[4]| |s[4]| |d[4]| |a[1]| |l[1]| |n[a+l]|.
Define font |k|, where |@t$-2^{31}$@><=k<@t$2^{31}$@>|.

\yskip\hang|pre| 247 |i[1]| |num[4]| |den[4]| |mag[4]| |k[1]| |x[k]|.
Beginning of the preamble; this must come at the very beginning of the
file. Parameters |i|, |num|, |den|, |mag|, |k|, and |x| are explained below.

\yskip\hang|post| 248. Beginning of the postamble, see below.

\yskip\hang|post_post| 249. Ending of the postamble, see below.

\yskip\noindent Commands 250--255 are undefined at the present time.

@ @d set_char_0=0 {typeset character 0 and move right}
@d set1=128 {typeset a character and move right}
@d set_rule=132 {typeset a rule and move right}
@d put1==133 {typeset a character without moving}
@d put_rule=137 {typeset a rule}
@d nop=138 {no operation}
@d bop=139 {beginning of page}
@d eop=140 {ending of page}
@d push=141 {save the current positions}
@d pop=142 {restore previous positions}
@d right1==143 {move right}
@d right4==146 {move right, 4 bytes}
@d w0=147 {move right by |w|}
@d w1=148 {move right and set |w|}
@d x0=152 {move right by |x|}
@d x1=153 {move right and set |x|}
@d down1=157 {move down}
@d down4=160 {move down, 4 bytes}
@d y0=161 {move down by |y|}
@d y1=162 {move down and set |y|}
@d z0=166 {move down by |z|}
@d z1=167 {move down and set |z|}
@d fnt_num_0=171 {set current font to 0}
@d fnt1=235 {set current font}
@d xxx1=239 {extension to \.{DVI} primitives}
@d xxx4=242 {potentially long extension to \.{DVI} primitives}
@d fnt_def1=243 {define the meaning of a font number}
@d pre=247 {preamble}
@d post=248 {postamble beginning}
@d post_post=249 {postamble ending}

@ The preamble contains basic information about the file as a whole. As
stated above, there are six parameters:
$$\hbox{|@!i[1]| |@!num[4]| |@!den[4]| |@!mag[4]| |@!k[1]| |@!x[k]|.}$$
The |i| byte identifies \.{DVI} format; currently this byte is always set
to~2. (The value |i=3| is currently used for an extended format that
allows a mixture of right-to-left and left-to-right typesetting.
Some day we will set |i=4|, when \.{DVI} format makes another
incompatible change---perhaps in the year 2048.)

The next two parameters, |num| and |den|, are positive integers that define
the units of measurement; they are the numerator and denominator of a
fraction by which all dimensions in the \.{DVI} file could be multiplied
in order to get lengths in units of $10^{-7}$ meters. Since $\rm 7227{pt} =
254{cm}$, and since \TeX\ works with scaled points where there are $2^{16}$
sp in a point, \TeX\ sets
$|num|/|den|=(254\cdot10^5)/(7227\cdot2^{16})=25400000/473628672$.
@^sp@>

The |mag| parameter is what \TeX\ calls \.{\\mag}, i.e., 1000 times the
desired magnification. The actual fraction by which dimensions are
multiplied is therefore $|mag|\cdot|num|/1000|den|$. Note that if a \TeX\
source document does not call for any `\.{true}' dimensions, and if you
change it only by specifying a different \.{\\mag} setting, the \.{DVI}
file that \TeX\ creates will be completely unchanged except for the value
of |mag| in the preamble and postamble. (Fancy \.{DVI}-reading programs allow
users to override the |mag|~setting when a \.{DVI} file is being printed.)

Finally, |k| and |x| allow the \.{DVI} writer to include a comment, which is not
interpreted further. The length of comment |x| is |k|, where |0<=k<256|.

@d id_byte=2 {identifies the kind of \.{DVI} files described here}

@ Font definitions for a given font number |k| contain further parameters
$$\hbox{|c[4]| |s[4]| |d[4]| |a[1]| |l[1]| |n[a+l]|.}$$
The four-byte value |c| is the check sum that \TeX\ found in the \.{TFM}
file for this font; |c| should match the check sum of the font found by
programs that read this \.{DVI} file.
@^check sum@>

Parameter |s| contains a fixed-point scale factor that is applied to
the character widths in font |k|; font dimensions in \.{TFM} files and
other font files are relative to this quantity, which is called the
``at size'' elsewhere in this documentation. The value of |s| is
always positive and less than $2^{27}$. It is given in the same units
as the other \.{DVI} dimensions, i.e., in sp when \TeX82 has made the
file.  Parameter |d| is similar to |s|; it is the ``design size,'' and
(like~|s|) it is given in \.{DVI} units. Thus, font |k| is to be used
at $|mag|\cdot s/1000d$ times its normal size.

The remaining part of a font definition gives the external name of the font,
which is an ASCII string of length |a+l|. The number |a| is the length
of the ``area'' or directory, and |l| is the length of the font name itself;
the standard local system font area is supposed to be used when |a=0|.
The |n| field contains the area in its first |a| bytes.

Font definitions must appear before the first use of a particular font number.
Once font |k| is defined, it must not be defined again; however, we
shall see below that font definitions appear in the postamble as well as
in the pages, so in this sense each font number is defined exactly twice,
if at all. Like |nop| commands, font definitions can
appear before the first |bop|, or between an |eop| and a |bop|.

@ Sometimes it is desirable to make horizontal or vertical rules line up
precisely with certain features in characters of a font. It is possible to
guarantee the correct matching between \.{DVI} output and the characters
generated by \MF\ by adhering to the following principles: (1)~The \MF\
characters should be positioned so that a bottom edge or left edge that is
supposed to line up with the bottom or left edge of a rule appears at the
reference point, i.e., in row~0 and column~0 of the \MF\ raster. This
ensures that the position of the rule will not be rounded differently when
the pixel size is not a perfect multiple of the units of measurement in
the \.{DVI} file. (2)~A typeset rule of height $a>0$ and width $b>0$
should be equivalent to a \MF-generated character having black pixels in
precisely those raster positions whose \MF\ coordinates satisfy
|0<=x<@t$\alpha$@>b| and |0<=y<@t$\alpha$@>a|, where $\alpha$ is the number
of pixels per \.{DVI} unit.
@:METAFONT}{\MF@>
@^alignment of rules with characters@>
@^rules aligning with characters@>

@ The last page in a \.{DVI} file is followed by `|post|'; this command
introduces the postamble, which summarizes important facts that \TeX\ has
accumulated about the file, making it possible to print subsets of the data
with reasonable efficiency. The postamble has the form
$$\vbox{\halign{\hbox{#\hfil}\cr
  |post| |p[4]| |num[4]| |den[4]| |mag[4]| |l[4]| |u[4]| |s[2]| |t[2]|\cr
  $\langle\,$font definitions$\,\rangle$\cr
  |post_post| |q[4]| |i[1]| 223's$[{\G}4]$\cr}}$$
Here |p| is a pointer to the final |bop| in the file. The next three
parameters, |num|, |den|, and |mag|, are duplicates of the quantities that
appeared in the preamble.

Parameters |l| and |u| give respectively the height-plus-depth of the tallest
page and the width of the widest page, in the same units as other dimensions
of the file. These numbers might be used by a \.{DVI}-reading program to
position individual ``pages'' on large sheets of film or paper; however,
the standard convention for output on normal size paper is to position each
page so that the upper left-hand corner is exactly one inch from the left
and the top. Experience has shown that it is unwise to design \.{DVI}-to-printer
software that attempts cleverly to center the output; a fixed position of
the upper left corner is easiest for users to understand and to work with.
Therefore |l| and~|u| are often ignored.

Parameter |s| is the maximum stack depth (i.e., the largest excess of
|push| commands over |pop| commands) needed to process this file. Then
comes |t|, the total number of pages (|bop| commands) present.

The postamble continues with font definitions, which are any number of
\\{fnt\_def} commands as described above, possibly interspersed with |nop|
commands. Each font number that is used in the \.{DVI} file must be defined
exactly twice: Once before it is first selected by a \\{fnt} command, and once
in the postamble.

@ The last part of the postamble, following the |post_post| byte that
signifies the end of the font definitions, contains |q|, a pointer to the
|post| command that started the postamble.  An identification byte, |i|,
comes next; this currently equals~2, as in the preamble.

The |i| byte is followed by four or more bytes that are all equal to
the decimal number 223 (i.e., @'337 in octal). \TeX\ puts out four to seven of
these trailing bytes, until the total length of the file is a multiple of
four bytes, since this works out best on machines that pack four bytes per
word; but any number of 223's is allowed, as long as there are at least four
of them. In effect, 223 is a sort of signature that is added at the very end.
@^Fuchs, David Raymond@>

This curious way to finish off a \.{DVI} file makes it feasible for
\.{DVI}-reading programs to find the postamble first, on most computers,
even though \TeX\ wants to write the postamble last. Most operating
systems permit random access to individual words or bytes of a file, so
the \.{DVI} reader can start at the end and skip backwards over the 223's
until finding the identification byte. Then it can back up four bytes, read
|q|, and move to byte |q| of the file. This byte should, of course,
contain the value 248 (|post|); now the postamble can be read, so the
\.{DVI} reader can discover all the information needed for typesetting the
pages. Note that it is also possible to skip through the \.{DVI} file at
reasonably high speed to locate a particular page, if that proves
desirable. This saves a lot of time, since \.{DVI} files used in production
jobs tend to be large.

Unfortunately, however, standard \PASCAL\ does not include the ability to
@^system dependencies@>
access a random position in a file, or even to determine the length of a file.
Almost all systems nowadays provide the necessary capabilities, so \.{DVI}
format has been designed to work most efficiently with modern operating systems.
But if \.{DVI} files have to be processed under the restrictions of standard
\PASCAL, one can simply read them from front to back, since the necessary
header information is present in the preamble and in the font definitions.
(The |l| and |u| and |s| and |t| parameters, which appear only in the
postamble, are ``frills'' that are handy but not absolutely necessary.)

@* \[32] Shipping pages out.
After considering \TeX's eyes and stomach, we come now to the bowels.
@^bowels@>

The |ship_out| procedure is given a pointer to a box; its mission is
to describe that box in \.{DVI} form, outputting a ``page'' to |dvi_file|.
The \.{DVI} coordinates $(h,v)=(0,0)$ should correspond to the upper left
corner of the box being shipped.

Since boxes can be inside of boxes inside of boxes, the main work of
|ship_out| is done by two mutually recursive routines, |hlist_out|
and |vlist_out|, which traverse the hlists and vlists inside of horizontal
and vertical boxes.

As individual pages are being processed, we need to accumulate
information about the entire set of pages, since such statistics must be
reported in the postamble. The global variables |total_pages|, |max_v|,
|max_h|, |max_push|, and |last_bop| are used to record this information.

The variable |doing_leaders| is |true| while leaders are being output.
The variable |dead_cycles| contains the number of times an output routine
has been initiated since the last |ship_out|.

A few additional global variables are also defined here for use in
|vlist_out| and |hlist_out|. They could have been local variables, but
that would waste stack space when boxes are deeply nested, since the
values of these variables are not needed during recursive calls.
@^recursion@>

@<Glob...@>=
@!total_pages:integer; {the number of pages that have been shipped out}
@!max_v:scaled; {maximum height-plus-depth of pages shipped so far}
@!max_h:scaled; {maximum width of pages shipped so far}
@!max_push:integer; {deepest nesting of |push| commands encountered so far}
@!last_bop:integer; {location of previous |bop| in the \.{DVI} output}
@!dead_cycles:integer; {recent outputs that didn't ship anything out}
@!doing_leaders:boolean; {are we inside a leader box?}
@#
@!c,@!f:integer; {character and font in current |char_node|}
@!oval,@!ocmd:integer; {used by |out_cmd| for generating
  |set|, |fnt| and |fnt_def| commands}
@!rule_ht,@!rule_dp,@!rule_wd:scaled; {size of current rule being output}
@!g:pointer; {current glue specification}
@!lq,@!lr:integer; {quantities used in calculations for leaders}

@ @<Set init...@>=
total_pages:=0; max_v:=0; max_h:=0; max_push:=0; last_bop:=-1;
doing_leaders:=false; dead_cycles:=0; cur_s:=-1;

@ The \.{DVI} bytes are output to a buffer instead of being written directly
to the output file. This makes it possible to reduce the overhead of
subroutine calls, thereby measurably speeding up the computation, since
output of \.{DVI} bytes is part of \TeX's inner loop. And it has another
advantage as well, since we can change instructions in the buffer in order to
make the output more compact. For example, a `|down2|' command can be
changed to a `|y2|', thereby making a subsequent `|y0|' command possible,
saving two bytes.

The output buffer is divided into two parts of equal size; the bytes found
in |dvi_buf[0..half_buf-1]| constitute the first half, and those in
|dvi_buf[half_buf..dvi_buf_size-1]| constitute the second. The global
variable |dvi_ptr| points to the position that will receive the next
output byte. When |dvi_ptr| reaches |dvi_limit|, which is always equal
to one of the two values |half_buf| or |dvi_buf_size|, the half buffer that
is about to be invaded next is sent to the output and |dvi_limit| is
changed to its other value. Thus, there is always at least a half buffer's
worth of information present, except at the very beginning of the job.

Bytes of the \.{DVI} file are numbered sequentially starting with 0;
the next byte to be generated will be number |dvi_offset+dvi_ptr|.
A byte is present in the buffer only if its number is |>=dvi_gone|.

@<Types...@>=
@!dvi_index=0..dvi_buf_size; {an index into the output buffer}

@ Some systems may find it more efficient to make |dvi_buf| a |packed|
array, since output of four bytes at once may be facilitated.
@^system dependencies@>

@<Glob...@>=
@!dvi_buf:array[dvi_index] of real_eight_bits; {buffer for \.{DVI} output}
@!half_buf:dvi_index; {half of |dvi_buf_size|}
@!dvi_limit:dvi_index; {end of the current half buffer}
@!dvi_ptr:dvi_index; {the next available buffer address}
@!dvi_offset:integer; {|dvi_buf_size| times the number of times the
  output buffer has been fully emptied}
@!dvi_gone:integer; {the number of bytes already output to |dvi_file|}

@ Initially the buffer is all in one piece; we will output half of it only
after it first fills up.

@<Set init...@>=
half_buf:=dvi_buf_size div 2; dvi_limit:=dvi_buf_size; dvi_ptr:=0;
dvi_offset:=0; dvi_gone:=0;

@ The actual output of |dvi_buf[a..b]| to |dvi_file| is performed by calling
|write_dvi(a,b)|. For best results, this procedure should be optimized to
run as fast as possible on each particular system, since it is part of
\TeX's inner loop. It is safe to assume that |a| and |b+1| will both be
multiples of 4 when |write_dvi(a,b)| is called; therefore it is possible on
many machines to use efficient methods to pack four bytes per word and to
output an array of words with one system call.
@^system dependencies@>
@^inner loop@>
@^defecation@>

@p procedure write_dvi(@!a,@!b:dvi_index);
var k:dvi_index;
begin for k:=a to b do write(dvi_file,dvi_buf[k]);
end;

@ To put a byte in the buffer without paying the cost of invoking a procedure
each time, we use the macro |dvi_out|.

@d dvi_out(#)==@+begin dvi_buf[dvi_ptr]:=#; incr(dvi_ptr);
  if dvi_ptr=dvi_limit then dvi_swap;
  end

@p procedure dvi_swap; {outputs half of the buffer}
begin if dvi_limit=dvi_buf_size then
  begin write_dvi(0,half_buf-1); dvi_limit:=half_buf;
  dvi_offset:=dvi_offset+dvi_buf_size; dvi_ptr:=0;
  end
else  begin write_dvi(half_buf,dvi_buf_size-1); dvi_limit:=dvi_buf_size;
  end;
dvi_gone:=dvi_gone+half_buf;
end;

@ Here is how we clean out the buffer when \TeX\ is all through; |dvi_ptr|
will be a multiple of~4.

@<Empty the last bytes out of |dvi_buf|@>=
if dvi_limit=half_buf then write_dvi(half_buf,dvi_buf_size-1);
if dvi_ptr>0 then write_dvi(0,dvi_ptr-1)

@ The |dvi_four| procedure outputs four bytes in two's complement notation,
without risking arithmetic overflow.

@p procedure dvi_four(@!x:integer);
begin if x>=0 then dvi_out(x div @'100000000)
else  begin x:=x+@'10000000000;
  x:=x+@'10000000000;
  dvi_out((x div @'100000000) + 128);
  end;
x:=x mod @'100000000; dvi_out(x div @'200000);
x:=x mod @'200000; dvi_out(x div @'400);
dvi_out(x mod @'400);
end;

@ A mild optimization of the output is performed by the |dvi_pop|
routine, which issues a |pop| unless it is possible to cancel a
`|push| |pop|' pair. The parameter to |dvi_pop| is the byte address
following the old |push| that matches the new |pop|.

@p procedure dvi_pop(@!l:integer);
begin if (l=dvi_offset+dvi_ptr)and(dvi_ptr>0) then decr(dvi_ptr)
else dvi_out(pop);
end;

@ Here's a procedure that outputs a font definition. $\Omega$ allows
more than 256 different fonts per job, so the right font definition 
command must be selected.

@d Incr_Decr(#) == #
@d Incr(#) == #:=#+Incr_Decr {increase a variable}
@d Decr(#) == #:=#-Incr_Decr {decrease a variable}

@d dvi_debug_out(#)==begin
dvi_out(#);
end

@d out_cmd ==
begin
if (oval<@"100)and(oval>=0) then begin
  if (ocmd<>set1)or(oval>127) then
  if (ocmd=fnt1)and(oval<64) then Incr(oval)(fnt_num_0) @+ else dvi_debug_out(ocmd);
  end
else
  begin if (oval<@"10000)and(oval>=0) then dvi_debug_out(ocmd+1) @+ else @;
    begin if (oval<@"1000000)and(oval>=0) then dvi_debug_out(ocmd+2) @+ else @;
      begin dvi_debug_out(ocmd+3);
      if oval>=0 then dvi_debug_out(oval div @"1000000)
      else  begin Incr(oval)(@"40000000); Incr(oval)(@"40000000);
        dvi_debug_out((oval div @"1000000) + 128); oval:=oval mod @"1000000;
        end;
      dvi_debug_out(oval div @"10000); oval:=oval mod @"10000;
      end;
    dvi_debug_out(oval div @"10000); oval:=oval mod @"10000;
    end;
  dvi_debug_out(oval div @"100); oval:=oval mod @"100;
  end;
dvi_debug_out(oval)
end

@p procedure dvi_font_def(@!f:internal_font_number);
var k:pool_pointer; {index into |str_pool|}
fa:^packed_ASCII_code;
begin
oval:=f-font_base-1; ocmd:= fnt_def1; out_cmd;@/
dvi_out(font_check_0(f));
dvi_out(font_check_1(f));
dvi_out(font_check_2(f));
dvi_out(font_check_3(f));@/
dvi_four(font_size(f));
dvi_four(font_dsize(f));@/
dvi_out(strlen(font_area(f)));
dvi_out(strlen(font_name(f)));
@<Output the font name whose internal number is |f|@>;
end;

@ @<Output the font name whose internal number is |f|@>=
fa := get_font_name(f); k := 0;
while fa[k]<>0 do begin dvi_out(fa[k]); incr(k); end;
fa := get_font_area(f); k := 0;
while fa[k]<>0 do begin dvi_out(fa[k]); incr(k); end

@ Versions of \TeX\ intended for small computers might well choose to omit
the ideas in the next few parts of this program, since it is not really
necessary to optimize the \.{DVI} code by making use of the |w0|, |x0|,
|y0|, and |z0| commands. Furthermore, the algorithm that we are about to
describe does not pretend to give an optimum reduction in the length
of the \.{DVI} code; after all, speed is more important than compactness.
But the method is surprisingly effective, and it takes comparatively little
time.

We can best understand the basic idea by first considering a simpler problem
that has the same essential characteristics. Given a sequence of digits,
say $3\,1\,4\,1\,5\,9\,2\,6\,5\,3\,5\,8\,9$, we want to assign subscripts
$d$, $y$, or $z$ to each digit so as to maximize the number of ``$y$-hits''
and ``$z$-hits''; a $y$-hit is an instance of two appearances of the same
digit with the subscript $y$, where no $y$'s intervene between the two
appearances, and a $z$-hit is defined similarly. For example, the sequence
above could be decorated with subscripts as follows:
$$3_z\,1_y\,4_d\,1_y\,5_y\,9_d\,2_d\,6_d\,5_y\,3_z\,5_y\,8_d\,9_d.$$
There are three $y$-hits ($1_y\ldots1_y$ and $5_y\ldots5_y\ldots5_y$) and
one $z$-hit ($3_z\ldots3_z$); there are no $d$-hits, since the two appearances
of $9_d$ have $d$'s between them, but we don't count $d$-hits so it doesn't
matter how many there are. These subscripts are analogous to the \.{DVI}
commands called \\{down}, $y$, and $z$, and the digits are analogous to
different amounts of vertical motion; a $y$-hit or $z$-hit corresponds to
the opportunity to use the one-byte commands |y0| or |z0| in a \.{DVI} file.

\TeX's method of assigning subscripts works like this: Append a new digit,
say $\delta$, to the right of the sequence. Now look back through the
sequence until one of the following things happens: (a)~You see
$\delta_y$ or $\delta_z$, and this was the first time you encountered a
$y$ or $z$ subscript, respectively.  Then assign $y$ or $z$ to the new
$\delta$; you have scored a hit. (b)~You see $\delta_d$, and no $y$
subscripts have been encountered so far during this search.  Then change
the previous $\delta_d$ to $\delta_y$ (this corresponds to changing a
command in the output buffer), and assign $y$ to the new $\delta$; it's
another hit.  (c)~You see $\delta_d$, and a $y$ subscript has been seen
but not a $z$.  Change the previous $\delta_d$ to $\delta_z$ and assign
$z$ to the new $\delta$. (d)~You encounter both $y$ and $z$ subscripts
before encountering a suitable $\delta$, or you scan all the way to the
front of the sequence. Assign $d$ to the new $\delta$; this assignment may
be changed later.

The subscripts $3_z\,1_y\,4_d\ldots\,$ in the example above were, in fact,
produced by this procedure, as the reader can verify. (Go ahead and try it.)

@ In order to implement such an idea, \TeX\ maintains a stack of pointers
to the \\{down}, $y$, and $z$ commands that have been generated for the
current page. And there is a similar stack for \\{right}, |w|, and |x|
commands. These stacks are called the down stack and right stack, and their
top elements are maintained in the variables |down_ptr| and |right_ptr|.

Each entry in these stacks contains four fields: The |width| field is
the amount of motion down or to the right; the |location| field is the
byte number of the \.{DVI} command in question (including the appropriate
|dvi_offset|); the |vlink| field points to the next item below this one
on the stack; and the |vinfo| field encodes the options for possible change
in the \.{DVI} command.

@d movement_node=48
@d movement_node_size=3 {number of words per entry in the down and right stacks}
@d location(#)==vmem(#+1).int {\.{DVI} byte number for a movement command}

@<Glob...@>=
@!down_ptr,@!right_ptr:pointer; {heads of the down and right stacks}

@ @<Set init...@>=
down_ptr:=null; right_ptr:=null;

@ Here is a subroutine that produces a \.{DVI} command for some specified
downward or rightward motion. It has two parameters: |w| is the amount
of motion, and |o| is either |down1| or |right1|. We use the fact that
the command codes have convenient arithmetic properties: |y1-down1=w1-right1|
and |z1-down1=x1-right1|.

@d dvi_set(#)==oval:=#; ocmd:=set1; out_cmd
@d dvi_put(#)==oval:=#; ocmd:=put1; out_cmd
@d dvi_set_rule_end(#)==dvi_four(#)
@d dvi_set_rule(#)==dvi_out(set_rule); dvi_four(#); dvi_set_rule_end
@d dvi_put_rule_end(#)==dvi_four(#)
@d dvi_put_rule(#)==dvi_out(put_rule); dvi_four(#); dvi_put_rule_end
@d dvi_right(#)==dvi_out(right4); dvi_four(#);
@d dvi_left(#)==dvi_out(right4); dvi_four(-#);
@d dvi_down(#)==dvi_out(down4); dvi_four(#);
@d dvi_up(#)==dvi_out(down4); dvi_four(-#);

@p procedure movement(@!w:scaled;@!o:eight_bits);
label exit,found,not_found,2,1;
var mstate:small_number; {have we seen a |y| or |z|?}
@!p,@!q:pointer; {current and top nodes on the stack}
@!k:integer; {index into |dvi_buf|, modulo |dvi_buf_size|}
begin
case box_direction(dvi_direction) of
  dir_TL_: begin
    end;
  dir_TR_: begin
    if o=right1 then negate(w);
    end;
  dir_LT_: begin
    if o=right1 then o:=down1
    else o:=right1;
    end;
  dir_LB_: begin
    if o=right1 then begin
      o:=down1; negate(w);
      end
    else o:=right1;
    end;
  dir_BL_: begin
    if o=down1 then negate(w);
    end;
  dir_BR_: begin
    negate(w);
    end;
  dir_RT_: begin
    if o=right1 then o:=down1
    else begin o:=right1; negate(w);
      end;
    end;
  dir_RB_: begin
    if o=right1 then o:=down1 else o:=right1;
    negate(w);
    end;
  end;
if false then begin
q:=new_node(movement_node,0); {new node for the top of the stack}
width(q):=w; location(q):=dvi_offset+dvi_ptr;
if o=down1 then
  begin vlink(q):=down_ptr; down_ptr:=q;
  end
else  begin vlink(q):=right_ptr; right_ptr:=q;
  end;
@<Look at the other stack entries until deciding what sort of \.{DVI} command
  to generate; |goto found| if node |p| is a ``hit''@>;
end;
@<Generate a |down| or |right| command for |w| and |return|@>;
found: @<Generate a |y0| or |z0| command in order to reuse a previous
  appearance of~|w|@>;
exit:end;

@ The |vinfo| fields in the entries of the down stack or the right stack
have six possible settings: |y_here| or |z_here| mean that the \.{DVI}
command refers to |y| or |z|, respectively (or to |w| or |x|, in the
case of horizontal motion); |yz_OK| means that the \.{DVI} command is
\\{down} (or \\{right}) but can be changed to either |y| or |z| (or
to either |w| or |x|); |y_OK| means that it is \\{down} and can be changed
to |y| but not |z|; |z_OK| is similar; and |d_fixed| means it must stay
\\{down}.

The four settings |yz_OK|, |y_OK|, |z_OK|, |d_fixed| would not need to
be distinguished from each other if we were simply solving the
digit-subscripting problem mentioned above. But in \TeX's case there is
a complication because of the nested structure of |push| and |pop|
commands. Suppose we add parentheses to the digit-subscripting problem,
redefining hits so that $\delta_y\ldots \delta_y$ is a hit if all $y$'s between
the $\delta$'s are enclosed in properly nested parentheses, and if the
parenthesis level of the right-hand $\delta_y$ is deeper than or equal to
that of the left-hand one. Thus, `(' and `)' correspond to `|push|'
and `|pop|'. Now if we want to assign a subscript to the final 1 in the
sequence
$$2_y\,7_d\,1_d\,(\,8_z\,2_y\,8_z\,)\,1$$
we cannot change the previous $1_d$ to $1_y$, since that would invalidate
the $2_y\ldots2_y$ hit. But we can change it to $1_z$, scoring a hit
since the intervening $8_z$'s are enclosed in parentheses.

The program below removes movement nodes that are introduced after a |push|,
before it outputs the corresponding |pop|.

@d y_here=1 {|vinfo| when the movement entry points to a |y| command}
@d z_here=2 {|vinfo| when the movement entry points to a |z| command}
@d yz_OK=3 {|vinfo| corresponding to an unconstrained \\{down} command}
@d y_OK=4 {|vinfo| corresponding to a \\{down} that can't become a |z|}
@d z_OK=5 {|vinfo| corresponding to a \\{down} that can't become a |y|}
@d d_fixed=6 {|vinfo| corresponding to a \\{down} that can't change}

@ When the |movement| procedure gets to the label |found|, the value of
|vinfo(p)| will be either |y_here| or |z_here|. If it is, say, |y_here|,
the procedure generates a |y0| command (or a |w0| command), and marks
all |vinfo| fields between |q| and |p| so that |y| is not OK in that range.

@<Generate a |y0| or |z0| command...@>=
vinfo(q):=vinfo(p);
if vinfo(q)=y_here then
  begin dvi_out(o+y0-down1); {|y0| or |w0|}
  while vlink(q)<>p do
    begin q:=vlink(q);
    case vinfo(q) of
    yz_OK: vinfo(q):=z_OK;
    y_OK: vinfo(q):=d_fixed;
    othercases do_nothing
    endcases;
    end;
  end
else  begin dvi_out(o+z0-down1); {|z0| or |x0|}
  while vlink(q)<>p do
    begin q:=vlink(q);
    case vinfo(q) of
    yz_OK: vinfo(q):=y_OK;
    z_OK: vinfo(q):=d_fixed;
    othercases do_nothing
    endcases;
    end;
  end

@ @<Generate a |down| or |right|...@>=
if abs(w)>=@'40000000 then
  begin dvi_out(o+3); {|down4| or |right4|}
  dvi_four(w); return;
  end;
if abs(w)>=@'100000 then
  begin dvi_out(o+2); {|down3| or |right3|}
  if w<0 then w:=w+@'100000000;
  dvi_out(w div @'200000); w:=w mod @'200000; goto 2;
  end;
if abs(w)>=@'200 then
  begin dvi_out(o+1); {|down2| or |right2|}
  if w<0 then w:=w+@'200000;
  goto 2;
  end;
dvi_out(o); {|down1| or |right1|}
if w<0 then w:=w+@'400;
goto 1;
2: dvi_out(w div @'400);
1: dvi_out(w mod @'400); return

@ As we search through the stack, we are in one of three states,
|y_seen|, |z_seen|, or |none_seen|, depending on whether we have
encountered |y_here| or |z_here| nodes. These states are encoded as
multiples of 6, so that they can be added to the |info| fields for quick
decision-making.
@^inner loop@>

@d none_seen=0 {no |y_here| or |z_here| nodes have been encountered yet}
@d y_seen=6 {we have seen |y_here| but not |z_here|}
@d z_seen=12 {we have seen |z_here| but not |y_here|}

@<Look at the other stack entries until deciding...@>=
p:=vlink(q); mstate:=none_seen;
while p<>null do
  begin if width(p)=w then @<Consider a node with matching width;
    |goto found| if it's a hit@>
  else  case mstate+vinfo(p) of
    none_seen+y_here: mstate:=y_seen;
    none_seen+z_here: mstate:=z_seen;
    y_seen+z_here,z_seen+y_here: goto not_found;
    othercases do_nothing
    endcases;
  p:=vlink(p);
  end;
not_found:

@ We might find a valid hit in a |y| or |z| byte that is already gone
from the buffer. But we can't change bytes that are gone forever; ``the
moving finger writes, $\ldots\,\,$.''

@<Consider a node with matching width...@>=
case mstate+vinfo(p) of
none_seen+yz_OK,none_seen+y_OK,z_seen+yz_OK,z_seen+y_OK:@t@>@;@/
  if location(p)<dvi_gone then goto not_found
  else @<Change buffered instruction to |y| or |w| and |goto found|@>;
none_seen+z_OK,y_seen+yz_OK,y_seen+z_OK:@t@>@;@/
  if location(p)<dvi_gone then goto not_found
  else @<Change buffered instruction to |z| or |x| and |goto found|@>;
none_seen+y_here,none_seen+z_here,y_seen+z_here,z_seen+y_here: goto found;
othercases do_nothing
endcases

@ @<Change buffered instruction to |y| or |w| and |goto found|@>=
begin k:=location(p)-dvi_offset;
if k<0 then k:=k+dvi_buf_size;
dvi_buf[k]:=dvi_buf[k]+y1-down1;
vinfo(p):=y_here; goto found;
end

@ @<Change buffered instruction to |z| or |x| and |goto found|@>=
begin k:=location(p)-dvi_offset;
if k<0 then k:=k+dvi_buf_size;
dvi_buf[k]:=dvi_buf[k]+z1-down1;
vinfo(p):=z_here; goto found;
end

@ In case you are wondering when all the movement nodes are removed from
\TeX's memory, the answer is that they are recycled just before
|hlist_out| and |vlist_out| finish outputting a box. This restores the
down and right stacks to the state they were in before the box was output,
except that some |vinfo|'s may have become more restrictive.

@p procedure prune_movements(@!l:integer);
  {delete movement nodes with |location>=l|}
label done,exit;
var p:pointer; {node being deleted}
begin while down_ptr<>null do
  begin if location(down_ptr)<l then goto done;
  p:=down_ptr; down_ptr:=vlink(p); flush_node(p);
  end;
done: while right_ptr<>null do
  begin if location(right_ptr)<l then return;
  p:=right_ptr; right_ptr:=vlink(p); flush_node(p);
  end;
exit:end;

@ The actual distances by which we want to move might be computed as the
sum of several separate movements. For example, there might be several
glue nodes in succession, or we might want to move right by the width of
some box plus some amount of glue. More importantly, the baselineskip
distances are computed in terms of glue together with the depth and
height of adjacent boxes, and we want the \.{DVI} file to lump these
three quantities together into a single motion.

Therefore, \TeX\ maintains two pairs of global variables: |dvi_h| and |dvi_v|
are the |h| and |v| coordinates corresponding to the commands actually
output to the \.{DVI} file, while |cur_h| and |cur_v| are the coordinates
corresponding to the current state of the output routines. Coordinate
changes will accumulate in |cur_h| and |cur_v| without being reflected
in the output, until such a change becomes necessary or desirable; we
can call the |movement| procedure whenever we want to make |dvi_h=cur_h|
or |dvi_v=cur_v|.

The current font reflected in the \.{DVI} output is called |dvi_f|;
there is no need for a `\\{cur\_f}' variable.

The depth of nesting of |hlist_out| and |vlist_out| is called |cur_s|;
this is essentially the depth of |push| commands in the \.{DVI} output.

@d synch_h==if cur_h<>dvi_h then
    begin movement(cur_h-dvi_h,right1); dvi_h:=cur_h;
    end
@d synch_v==if cur_v<>dvi_v then
    begin movement(cur_v-dvi_v,down1); dvi_v:=cur_v;
    end

@<Glob...@>=
@!dvi_h,@!dvi_v:scaled; {a \.{DVI} reader program thinks we are here}
@!cur_h,@!cur_v:scaled; {\TeX\ thinks we are here}
@!dvi_f:internal_font_number; {the current font}
@!cur_s:integer; {current depth of output box nesting, initially $-1$}

@ @<Calculate DVI page dimensions and margins@>=
if page_width > 0 then
    cur_page_width := page_width
else
    cur_page_width := width(p) + 2*(h_offset + one_inch);
if page_height > 0 then
    cur_page_height := page_height
else
    cur_page_height := height(p) + depth(p) + 2*(v_offset + one_inch);
if page_bottom_offset <> 0 then
    cur_bottom_offset := page_bottom_offset
else
    cur_bottom_offset := 2*one_inch;
if page_right_offset <> 0 then
    cur_right_offset := page_right_offset
else
    cur_right_offset :=  2*one_inch


@ @<Initialize variables as |ship_out| begins@>=
dvi_h:=0; dvi_v:=0; cur_h:=0; cur_v:=0; dvi_f:=null_font;
@<Calculate DVI page dimensions and margins@>;
ensure_dvi_open;
if total_pages=0 then
  begin dvi_out(pre); dvi_out(id_byte); {output the preamble}
@^preamble of \.{DVI} file@>
  dvi_four(25400000); dvi_four(473628672); {conversion ratio for sp}
  prepare_mag; dvi_four(mag); {magnification factor is frozen}
  old_setting:=selector; selector:=new_string;
  print(" LuaTeX output "); print_int(year); print_char(".");
  print_two(month); print_char("."); print_two(day);
  print_char(":"); print_two(time div 60);
  print_two(time mod 60);
  selector:=old_setting; dvi_out(cur_length);
  for s:=str_start_macro(str_ptr) to pool_ptr-1 do dvi_out(so(str_pool[s]));
  pool_ptr:=str_start_macro(str_ptr); {flush the current string}
  end

@ When |hlist_out| is called, its duty is to output the box represented
by the |hlist_node| pointed to by |temp_ptr|. The reference point of that
box has coordinates |(cur_h,cur_v)|.

Similarly, when |vlist_out| is called, its duty is to output the box represented
by the |vlist_node| pointed to by |temp_ptr|. The reference point of that
box has coordinates |(cur_h,cur_v)|.
@^recursion@>

@p procedure@?vlist_out; forward; {|hlist_out| and |vlist_out| are mutually
  recursive}

@ The recursive procedures |hlist_out| and |vlist_out| each have local variables
|save_h| and |save_v| to hold the values of |dvi_h| and |dvi_v| just before
entering a new level of recursion.  In effect, the values of |save_h| and
|save_v| on \TeX's run-time stack correspond to the values of |h| and |v|
that a \.{DVI}-reading program will push onto its coordinate stack.

@d move_past=13 {go to this label when advancing past glue or a rule}
@d fin_rule=14 {go to this label to finish processing a rule}
@d next_p=15 {go to this label when finished with node |p|}

@p @t\4@>@<Declare procedures needed in |hlist_out|, |vlist_out|@>@t@>@/
procedure hlist_out; {output an |hlist_node| box}
label move_past, fin_rule, next_p;
var base_line: scaled; {the baseline coordinate for this box}
c_wd,c_ht,c_dp: scaled;
  {the real width, height and depth of the character}
edge_v: scaled;
edge_h: scaled;
effective_horizontal: scaled;
basepoint_horizontal: scaled;
basepoint_vertical: scaled;
saving_h: scaled;
saving_v: scaled;
save_direction: integer;
dir_ptr,dir_tmp:pointer;
dvi_dir_h,dvi_dir_ptr,dvi_temp_ptr:integer;
@!left_edge: scaled; {the left coordinate for this box}
@!save_h,@!save_v: scaled; {what |dvi_h| and |dvi_v| should pop to}
@!this_box: pointer; {pointer to containing box}
@!g_order: glue_ord; {applicable order of infinity for glue}
@!g_sign: normal..shrinking; {selects type of glue}
@!p,q:pointer; {current position in the hlist}
@!save_loc:integer; {\.{DVI} byte location upon entry}
@!leader_box:pointer; {the leader box being replicated}
@!leader_wd:scaled; {width of leader box being replicated}
@!lx:scaled; {extra space between leader boxes}
@!outer_doing_leaders:boolean; {were we doing leaders?}
@!edge:scaled; {right edge of sub-box or leader space}
@!glue_temp:real; {glue value before rounding}
@!cur_glue:real; {glue seen so far}
@!cur_g:scaled; {rounded equivalent of |cur_glue| times the glue ratio}
begin cur_g:=0; cur_glue:=float_constant(0);
this_box:=temp_ptr; g_order:=glue_order(this_box);
g_sign:=glue_sign(this_box); p:=list_ptr(this_box);
save_direction:=dvi_direction;
dvi_direction:=box_dir(this_box);
@<DIR: Initialize |dir_ptr| for |ship_out|@>;
saving_h:=dvi_h; saving_v:=dvi_v;
incr(cur_s);
if cur_s>0 then dvi_out(push);
if cur_s>max_push then max_push:=cur_s;
save_loc:=dvi_offset+dvi_ptr; base_line:=cur_v; left_edge:=cur_h;
while p<>null do @<Output node |p| for |hlist_out| and move to the next node,
  maintaining the condition |cur_v=base_line|@>;
cur_h:=saving_h; cur_v:=saving_v;
synch_h; synch_v;
prune_movements(save_loc);
if cur_s>0 then dvi_pop(save_loc);
decr(cur_s);
dvi_direction:=save_direction;
@<DIR: Reset |dir_ptr|@>;
end;

@ This is a cacheing attempt

@d charinfo_width(#)==#.ci_wd
@d charinfo_height(#)==#.ci_ht
@d charinfo_depth(#)==#.ci_dp

@<Types...@>=
charinfo_short = packed record@;@/
  @!ci_wd:scaled;
  @!ci_ht:scaled;
  @!ci_dp:scaled;
  end;

@ @<Glob...@>=
ci:charinfo_short;

@ We ought to give special care to the efficiency of one part of |hlist_out|,
since it belongs to \TeX's inner loop. When a |char_node| is encountered,
we save a little time by processing several nodes in succession until
reaching a non-|char_node|. The program uses the fact that |set_char_0=0|.
@^inner loop@>

@<Output node |p| for |hlist_out|...@>=
if is_char_node(p) then
  begin synch_h; synch_v;
  repeat f:=font(p); c:=character(p);
  ci := char_info_short(f,c);
  if f<>dvi_f then @<Change font |dvi_f| to |f|@>;
  if is_rotated(dvi_direction) then begin
    c_ht:=charinfo_width(ci) div 2;
    c_wd:=charinfo_height(ci)+charinfo_depth(ci);
    c_dp:=0;
    end
  else begin
    c_ht:=charinfo_height(ci);
    c_dp:=charinfo_depth(ci);
    c_wd:=charinfo_width(ci);
    end;
  cur_h:=cur_h+c_wd;
  if (font_natural_dir(f)<>-1) then begin
    case font_direction(dvi_direction) of
    dir__LT,dir__LB: begin
      dvi_set(c);
      end;
    dir__RT,dir__RB: begin
      dvi_put(c);
      dvi_left(c_wd);
      end;
    dir__TL,dir__TR: begin
      dvi_put(c);
      dvi_down(c_wd);
      end;
    dir__BL,dir__BR: begin
      dvi_put(c);
      dvi_up(c_wd);
      end;
    dir__LL,dir__LR: begin
      dvi_put(c);
      dvi_right(c_wd);
      end;
    dir__RL,dir__RR: begin
      dvi_put(c);
      dvi_left(c_wd);
      end;
    dir__TT,dir__TB: begin
      dvi_put(c);
      dvi_down(c_wd);
      end;
    dir__BT,dir__BB: begin
      dvi_put(c);
      dvi_up(c_wd);
      end;
    end;
  end else begin
    case font_direction(dvi_direction) of
    dir__LT: begin
      dvi_set(c);
      end;
    dir__LB: begin
      dvi_down(c_ht);
      dvi_set(c);
      dvi_up(c_ht);
      end;
    dir__RT: begin
      dvi_left(c_wd);
      dvi_put(c);
      end;
    dir__RB: begin
      dvi_left(c_wd);
      dvi_down(c_ht);
      dvi_put(c);
      dvi_up(c_ht);
      end;
    dir__TL: begin
      dvi_down(c_wd);
      dvi_left(c_ht);
      dvi_put(c);
      dvi_right(c_ht);
      end;
    dir__TR: begin
      dvi_down(c_wd);
      dvi_left(c_dp);
      dvi_put(c);
      dvi_right(c_dp);
      end;
    dir__BL: begin
      dvi_left(c_ht);
      dvi_put(c);
      dvi_right(c_ht);
      dvi_up(c_wd);
      end;
    dir__BR: begin
      dvi_left(c_dp);
      dvi_put(c);
      dvi_right(c_dp);
      dvi_up(c_wd);
      end;
    dir__LL,dir__LR: begin
      dvi_down(c_ht);
      dvi_put(c);
      dvi_up(c_ht);
      dvi_right(c_wd);
      end;
    dir__RL,dir__RR: begin
      dvi_left(c_wd);
      dvi_down(c_ht);
      dvi_put(c);
      dvi_up(c_ht);
      end;
    dir__TT,dir__TB: begin
      dvi_down(c_wd);
      dvi_left(c_ht);
      dvi_put(c);
      dvi_right(c_ht);
      end;
    dir__BT,dir__BB: begin
      dvi_left(c_ht);
      dvi_put(c);
      dvi_right(c_ht);
      dvi_up(c_wd);
      end;
     end;
    end;
  p:=vlink(p);
  until not is_char_node(p);
  dvi_h:=cur_h;
  end
else @<Output the non-|char_node| |p| for |hlist_out|
    and move to the next node@>

@ @<Change font |dvi_f| to |f|@>=
begin if not font_used(f) then
  begin dvi_font_def(f); set_font_used(f,true);
  end;
oval:=f-font_base-1; ocmd:=fnt1; out_cmd;@/
dvi_f:=f;
end

@ @<Output the non-|char_node| |p| for |hlist_out|...@>=
begin case type(p) of
hlist_node,vlist_node:@<Output a box in an hlist@>;
rule_node: begin
  if not (dir_orthogonal(dir_primary[rule_dir(p)])(dir_primary[dvi_direction]))
    then begin
    rule_ht:=height(p); rule_dp:=depth(p); rule_wd:=width(p);
    end
  else begin
    rule_ht:=width(p) div 2;
    rule_dp:=width(p) div 2;
    rule_wd:=height(p)+depth(p);
    end;
  goto fin_rule;
  end;
whatsit_node: @<Output the whatsit node |p| in an hlist@>;
glue_node: @<Move right or output leaders@>;
disc_node: if vlink(no_break(p))<>null then begin
  vlink(tlink(no_break(p))):=vlink(p);
  q:=vlink(no_break(p)); 
  vlink(no_break(p)):=null;
  vlink(p):=q; 
  end;
margin_kern_node,kern_node:cur_h:=cur_h+width(p);
math_node:cur_h:=cur_h+surround(p);
othercases do_nothing
endcases;@/
goto next_p;
fin_rule: @<Output a rule in an hlist@>;
move_past: cur_h:=cur_h+rule_wd;
next_p:p:=vlink(p);
end

@ @<Output a box in an hlist@>=
begin
if not (dir_orthogonal(dir_primary[box_dir(p)])(dir_primary[dvi_direction]))
  then begin
  effective_horizontal:=width(p);
  basepoint_vertical:=0;
  if dir_opposite(dir_secondary[box_dir(p)])(dir_secondary[dvi_direction]) then
    basepoint_horizontal:=width(p)
  else
    basepoint_horizontal:=0;
  end
else begin
  effective_horizontal:=height(p)+depth(p);
  if not (is_mirrored(box_dir(p))) then
    if dir_eq(dir_primary[box_dir(p)])(dir_secondary[dvi_direction]) then
      basepoint_horizontal:=height(p)
    else
      basepoint_horizontal:=depth(p)
  else
    if dir_eq(dir_primary[box_dir(p)])(dir_secondary[dvi_direction]) then
      basepoint_horizontal:=depth(p)
    else
      basepoint_horizontal:=height(p);
  if dir_eq(dir_secondary[box_dir(p)])(dir_primary[dvi_direction]) then
    basepoint_vertical:= -(width(p) div 2)
  else
    basepoint_vertical:= (width(p) div 2);
  end;
if not (is_mirrored(dvi_direction)) then
  basepoint_vertical := basepoint_vertical + shift_amount(p)
    {shift the box `down'}
else
  basepoint_vertical := basepoint_vertical - shift_amount(p);
    {shift the box `up'}
if list_ptr(p)=null then cur_h:=cur_h + effective_horizontal
else begin
  temp_ptr:=p; edge:=cur_h; cur_h:=cur_h + basepoint_horizontal;
  edge_v:=cur_v; cur_v:=base_line + basepoint_vertical;
  synch_h; synch_v; save_h:=dvi_h; save_v:=dvi_v;
  if type(p)=vlist_node then vlist_out@+else hlist_out;
  dvi_h:=save_h; dvi_v:=save_v;
  cur_h:=edge+effective_horizontal; cur_v:=base_line;
  end
end

@ @<Output a rule in an hlist@>=
if is_running(rule_ht) then rule_ht:=height(this_box);
if is_running(rule_dp) then rule_dp:=depth(this_box);
rule_ht:=rule_ht+rule_dp; {this is the rule thickness}
if (rule_ht>0)and(rule_wd>0) then {we don't output empty rules}
  begin synch_h; cur_v:=base_line+rule_dp; synch_v;
  case font_direction(dvi_direction) of
  dir__LT: begin
    dvi_set_rule(rule_ht)(rule_wd);
    end;
  dir__LB: begin
    dvi_down(rule_ht);
    dvi_set_rule(rule_ht)(rule_wd);
    dvi_up(rule_ht);
    end;
  dir__RT: begin
    dvi_left(rule_wd);
    dvi_put_rule(rule_ht)(rule_wd);
    end;
  dir__RB: begin
    dvi_left(rule_wd);
    dvi_down(rule_ht);
    dvi_put_rule(rule_ht)(rule_wd);
    dvi_up(rule_ht);
    end;
  dir__TL: begin
    dvi_down(rule_wd);
    dvi_left(rule_ht);
    dvi_set_rule(rule_wd)(rule_ht);
    end;
  dir__TR: begin
    dvi_down(rule_wd);
    dvi_put_rule(rule_wd)(rule_ht);
    end;
  dir__BL: begin
    dvi_left(rule_ht);
    dvi_set_rule(rule_wd)(rule_ht);
    dvi_up(rule_wd);
    end;
  dir__BR: begin
    dvi_put_rule(rule_wd)(rule_ht);
    dvi_up(rule_wd);
    end;
  end;
  cur_v:=base_line; dvi_h:=dvi_h+rule_wd;
  end

@ @d billion==float_constant(1000000000)
@d vet_glue(#)== glue_temp:=#;
  if glue_temp>billion then
           glue_temp:=billion
  else if glue_temp<-billion then
           glue_temp:=-billion

@<Move right or output leaders@>=
begin g:=glue_ptr(p); rule_wd:=width(g)-cur_g;
if g_sign<>normal then
  begin if g_sign=stretching then
    begin if stretch_order(g)=g_order then
      begin cur_glue:=cur_glue+stretch(g);
      vet_glue(float(glue_set(this_box))*cur_glue);
@^real multiplication@>
      cur_g:=round(glue_temp);
      end;
    end
  else if shrink_order(g)=g_order then
      begin cur_glue:=cur_glue-shrink(g);
      vet_glue(float(glue_set(this_box))*cur_glue);
      cur_g:=round(glue_temp);
      end;
  end;
rule_wd:=rule_wd+cur_g;

if subtype(p)>=a_leaders then
  @<Output leaders in an hlist, |goto fin_rule| if a rule
    or to |next_p| if done@>;
goto move_past;
end

@ @<Output leaders in an hlist...@>=
begin leader_box:=leader_ptr(p);
if type(leader_box)=rule_node then
  begin rule_ht:=height(leader_box); rule_dp:=depth(leader_box);
  goto fin_rule;
  end;
if not (dir_orthogonal(dir_primary[box_dir(leader_box)])(dir_primary[dvi_direction]))
  then leader_wd:=width(leader_box)
else
  leader_wd:=height(leader_box)+depth(leader_box);
if (leader_wd>0)and(rule_wd>0) then
  begin rule_wd:=rule_wd+10; {compensate for floating-point rounding}
  edge:=cur_h+rule_wd; lx:=0;
  @<Let |cur_h| be the position of the first box, and set |leader_wd+lx|
    to the spacing between corresponding parts of boxes@>;
  while cur_h+leader_wd<=edge do
    @<Output a leader box at |cur_h|,
      then advance |cur_h| by |leader_wd+lx|@>;
  cur_h:=edge-10; goto next_p;
  end;
end

@ The calculations related to leaders require a bit of care. First, in the
case of |a_leaders| (aligned leaders), we want to move |cur_h| to
|left_edge| plus the smallest multiple of |leader_wd| for which the result
is not less than the current value of |cur_h|; i.e., |cur_h| should become
$|left_edge|+|leader_wd|\times\lceil
(|cur_h|-|left_edge|)/|leader_wd|\rceil$.  The program here should work in
all cases even though some implementations of \PASCAL\ give nonstandard
results for the |div| operation when |cur_h| is less than |left_edge|.

In the case of |c_leaders| (centered leaders), we want to increase |cur_h|
by half of the excess space not occupied by the leaders; and in the
case of |x_leaders| (expanded leaders) we increase |cur_h|
by $1/(q+1)$ of this excess space, where $q$ is the number of times the
leader box will be replicated. Slight inaccuracies in the division might
accumulate; half of this rounding error is placed at each end of the leaders.

@<Let |cur_h| be the position of the first box, ...@>=
if subtype(p)=a_leaders then
  begin save_h:=cur_h;
  cur_h:=left_edge+leader_wd*((cur_h-left_edge)@!div leader_wd);
  if cur_h<save_h then cur_h:=cur_h+leader_wd;
  end
else  begin lq:=rule_wd div leader_wd; {the number of box copies}
  lr:=rule_wd mod leader_wd; {the remaining space}
  if subtype(p)=c_leaders then cur_h:=cur_h+(lr div 2)
  else  begin lx:=lr div (lq+1);
    cur_h:=cur_h+((lr-(lq-1)*lx) div 2);
    end;
  end

@ The `\\{synch}' operations here are intended to decrease the number of
bytes needed to specify horizontal and vertical motion in the \.{DVI} output.

@<Output a leader box at |cur_h|, ...@>=
begin
if not (dir_orthogonal(dir_primary[box_dir(leader_box)])(dir_primary[dvi_direction]))
  then begin
  basepoint_vertical:=0;
 if dir_opposite(dir_secondary[box_dir(leader_box)])(dir_secondary[dvi_direction]) then
    basepoint_horizontal:=width(leader_box)
  else
    basepoint_horizontal:=0;
  end
else begin
  if not (is_mirrored(box_dir(leader_box))) then
    if dir_eq(dir_primary[box_dir(leader_box)])(dir_secondary[dvi_direction]) then
      basepoint_horizontal:=height(leader_box)
    else
      basepoint_horizontal:=depth(leader_box)
  else
    if dir_eq(dir_primary[box_dir(leader_box)])(dir_secondary[dvi_direction]) then
      basepoint_horizontal:=depth(leader_box)
    else
      basepoint_horizontal:=height(leader_box);
  if dir_eq(dir_secondary[box_dir(leader_box)])(dir_primary[dvi_direction]) then
    basepoint_vertical:= -(width(leader_box) div 2)
  else
    basepoint_vertical:= (width(leader_box) div 2);
  end;
if not (is_mirrored(dvi_direction)) then
  basepoint_vertical := basepoint_vertical + shift_amount(leader_box)
    {shift the box `down'}
else
  basepoint_vertical := basepoint_vertical - shift_amount(leader_box);
    {shift the box `up'}
temp_ptr:=leader_box;
edge_h:=cur_h; cur_h:=cur_h + basepoint_horizontal;
edge_v:=cur_v; cur_v:=base_line + basepoint_vertical;
synch_h; synch_v; save_h:=dvi_h; save_v:=dvi_v;
outer_doing_leaders:=doing_leaders; doing_leaders:=true;
if type(leader_box)=vlist_node then vlist_out@+else hlist_out;
doing_leaders:=outer_doing_leaders;
dvi_h:=save_h; dvi_v:=save_v;
cur_h:=edge_h+leader_wd+lx; cur_v:=base_line;
end

@ The |vlist_out| routine is similar to |hlist_out|, but a bit simpler.

@p procedure vlist_out; {output a |vlist_node| box}
label move_past, fin_rule, next_p;
var left_edge: scaled; {the left coordinate for this box}
@!top_edge: scaled; {the top coordinate for this box}
@!save_h,@!save_v: scaled; {what |dvi_h| and |dvi_v| should pop to}
@!this_box: pointer; {pointer to containing box}
@!g_order: glue_ord; {applicable order of infinity for glue}
@!g_sign: normal..shrinking; {selects type of glue}
@!p:pointer; {current position in the vlist}
@!save_loc:integer; {\.{DVI} byte location upon entry}
@!leader_box:pointer; {the leader box being replicated}
@!leader_ht:scaled; {height of leader box being replicated}
@!lx:scaled; {extra space between leader boxes}
@!outer_doing_leaders:boolean; {were we doing leaders?}
@!edge:scaled; {bottom boundary of leader space}
@!glue_temp:real; {glue value before rounding}
@!cur_glue:real; {glue seen so far}
@!cur_g:scaled; {rounded equivalent of |cur_glue| times the glue ratio}
@!save_direction: integer;
@!effective_vertical: scaled;
@!basepoint_horizontal: scaled;
@!basepoint_vertical: scaled;
@!edge_v: scaled;
@!saving_v: scaled;
@!saving_h: scaled;
begin cur_g:=0; cur_glue:=float_constant(0);
this_box:=temp_ptr; g_order:=glue_order(this_box);
g_sign:=glue_sign(this_box); p:=list_ptr(this_box);
{pdfassert(p<>0);}
saving_v:=dvi_v; saving_h:=dvi_h;
save_direction:=dvi_direction;
dvi_direction:=box_dir(this_box);
incr(cur_s);
if cur_s>0 then dvi_out(push);
if cur_s>max_push then max_push:=cur_s;
save_loc:=dvi_offset+dvi_ptr; left_edge:=cur_h; cur_v:=cur_v-height(this_box);
top_edge:=cur_v;
while p<>null do @<Output node |p| for |vlist_out| and move to the next node,
  maintaining the condition |cur_h=left_edge|@>;
cur_v:=saving_v; cur_h:=saving_h;
synch_v; synch_h;
prune_movements(save_loc);
if cur_s>0 then dvi_pop(save_loc);
decr(cur_s);
dvi_direction:=save_direction;
end;

@ @<Output node |p| for |vlist_out|...@>=
begin if is_char_node(p) then begin print_font_and_char(p); confusion("vlistout"); end
@:this can't happen vlistout}{\quad vlistout@>
else @<Output the non-|char_node| |p| for |vlist_out|@>;
next_p:p:=vlink(p);
end

@ @<Output the non-|char_node| |p| for |vlist_out|@>=
begin case type(p) of
hlist_node,vlist_node:@<Output a box in a vlist@>;
rule_node: begin
  if not (dir_orthogonal(dir_primary[rule_dir(p)])(dir_primary[dvi_direction]))
    then begin
    rule_ht:=height(p); rule_dp:=depth(p); rule_wd:=width(p);
    end
  else begin
    rule_ht:=width(p) div 2;
    rule_dp:=width(p) div 2;
    rule_wd:=height(p)+depth(p);
    end;
  goto fin_rule;
  end;
whatsit_node: @<Output the whatsit node |p| in a vlist@>;
glue_node: @<Move down or output leaders@>;
kern_node:cur_v:=cur_v+width(p);
othercases do_nothing
endcases;@/
goto next_p;
fin_rule: @<Output a rule in a vlist, |goto next_p|@>;
move_past: cur_v:=cur_v+rule_ht;
end

@ The |synch_v| here allows the \.{DVI} output to use one-byte commands
for adjusting |v| in most cases, since the baselineskip distance will
usually be constant.

@<Output a box in a vlist@>=
begin
if not (dir_orthogonal(dir_primary[box_dir(p)])(dir_primary[dvi_direction]))
  then begin
  effective_vertical:=height(p)+depth(p);
  if (type(p)=hlist_node) and (is_mirrored(box_dir(p))) then
    basepoint_vertical:=depth(p)
  else
    basepoint_vertical:=height(p);
  if dir_opposite(dir_secondary[box_dir(p)])(dir_secondary[dvi_direction]) then
    basepoint_horizontal:=width(p)
  else
    basepoint_horizontal:=0;
  end
else begin
  effective_vertical:=width(p);
  if not (is_mirrored(box_dir(p))) then
    if dir_eq(dir_primary[box_dir(p)])(dir_secondary[dvi_direction]) then
      basepoint_horizontal:=height(p)
    else
      basepoint_horizontal:=depth(p)
  else
    if dir_eq(dir_primary[box_dir(p)])(dir_secondary[dvi_direction]) then
      basepoint_horizontal:=depth(p)
    else
      basepoint_horizontal:=height(p);
  if dir_eq(dir_secondary[box_dir(p)])(dir_primary[dvi_direction]) then
    basepoint_vertical:=0
  else
    basepoint_vertical:=width(p);
  end;
basepoint_horizontal := basepoint_horizontal + shift_amount(p);
  {shift the box `right'}
if list_ptr(p)=null then begin
  cur_v:=cur_v+effective_vertical;
  end
else  begin
  synch_h; synch_v; edge_v:=cur_v;
  cur_h:=left_edge + basepoint_horizontal;
  cur_v:=cur_v + basepoint_vertical;
  synch_h; synch_v; save_h:=dvi_h; save_v:=dvi_v;
  temp_ptr:=p;
  if type(p)=vlist_node then vlist_out@+else hlist_out;
  dvi_h:=save_h; dvi_v:=save_v;
  cur_h:=left_edge; cur_v:=edge_v + effective_vertical;
  end
end

@ @<Output a rule in a vlist...@>=
if is_running(rule_wd) then rule_wd:=width(this_box);
rule_ht:=rule_ht+rule_dp; {this is the rule thickness}
cur_v:=cur_v+rule_ht;
if (rule_ht>0)and(rule_wd>0) then {we don't output empty rules}
  begin synch_h; synch_v;
  case font_direction(dvi_direction) of
  dir__LT: begin
    dvi_put_rule(rule_ht)(rule_wd);
    end;
  dir__LB: begin
    dvi_down(rule_ht);
    dvi_put_rule(rule_ht)(rule_wd);
    dvi_up(rule_ht);
    end;
  dir__RT: begin
    dvi_left(rule_wd);
    dvi_set_rule(rule_ht)(rule_wd);
    end;
  dir__RB: begin
    dvi_down(rule_ht);
    dvi_left(rule_wd);
    dvi_set_rule(rule_ht)(rule_wd);
    dvi_up(rule_ht);
    end;
  dir__TL: begin
    dvi_down(rule_wd);
    dvi_left(rule_ht);
    dvi_set_rule(rule_wd)(rule_ht);
    dvi_up(rule_wd);
    end;
  dir__TR: begin
    dvi_down(rule_wd);
    dvi_put_rule(rule_wd)(rule_ht);
    dvi_up(rule_wd);
    end;
  dir__BL: begin
    dvi_left(rule_ht);
    dvi_set_rule(rule_wd)(rule_ht);
    end;
  dir__BR: begin
    dvi_put_rule(rule_wd)(rule_ht);
    end;
  end;
  end;
goto next_p

@ @<Move down or output leaders@>=
begin g:=glue_ptr(p); rule_ht:=width(g)-cur_g;
if g_sign<>normal then
  begin if g_sign=stretching then
    begin if stretch_order(g)=g_order then
      begin cur_glue:=cur_glue+stretch(g);
      vet_glue(float(glue_set(this_box))*cur_glue);
@^real multiplication@>
      cur_g:=round(glue_temp);
      end;
    end
  else if shrink_order(g)=g_order then
      begin cur_glue:=cur_glue-shrink(g);
      vet_glue(float(glue_set(this_box))*cur_glue);
      cur_g:=round(glue_temp);
      end;
  end;
rule_ht:=rule_ht+cur_g;
if subtype(p)>=a_leaders then
  @<Output leaders in a vlist, |goto fin_rule| if a rule
    or to |next_p| if done@>;
goto move_past;
end

@ @<Output leaders in a vlist...@>=
begin leader_box:=leader_ptr(p);
if type(leader_box)=rule_node then
  begin rule_wd:=width(leader_box); rule_dp:=0;
  goto fin_rule;
  end;
if not (dir_orthogonal(dir_primary[box_dir(leader_box)])(dir_primary[dvi_direction]))
  then leader_ht:=height(leader_box)+depth(leader_box)
else
  leader_ht:=width(leader_box);
if (leader_ht>0)and(rule_ht>0) then
  begin rule_ht:=rule_ht+10; {compensate for floating-point rounding}
  edge:=cur_v+rule_ht; lx:=0;
  @<Let |cur_v| be the position of the first box, and set |leader_ht+lx|
    to the spacing between corresponding parts of boxes@>;
  while cur_v+leader_ht<=edge do
    @<Output a leader box at |cur_v|,
      then advance |cur_v| by |leader_ht+lx|@>;
  cur_v:=edge-10; goto next_p;
  end;
end

@ @<Let |cur_v| be the position of the first box, ...@>=
if subtype(p)=a_leaders then
  begin save_v:=cur_v;
  cur_v:=top_edge+leader_ht*((cur_v-top_edge)@!div leader_ht);
  if cur_v<save_v then cur_v:=cur_v+leader_ht;
  end
else  begin lq:=rule_ht div leader_ht; {the number of box copies}
  lr:=rule_ht mod leader_ht; {the remaining space}
  if subtype(p)=c_leaders then cur_v:=cur_v+(lr div 2)
  else  begin lx:=lr div (lq+1);
    cur_v:=cur_v+((lr-(lq-1)*lx) div 2);
    end;
  end

@ When we reach this part of the program, |cur_v| indicates the top of a
leader box, not its baseline.

@<Output a leader box at |cur_v|, ...@>=
begin
if not (dir_orthogonal(dir_primary[box_dir(leader_box)])(dir_primary[dvi_direction]))
  then begin
  effective_vertical:=height(leader_box)+depth(leader_box);
  if (type(leader_box)=hlist_node) and (is_mirrored(box_dir(leader_box))) then
    basepoint_vertical:=depth(leader_box)
  else
    basepoint_vertical:=height(leader_box);
  if dir_opposite(dir_secondary[box_dir(leader_box)])(dir_secondary[dvi_direction]) then
    basepoint_horizontal:=width(leader_box)
  else
    basepoint_horizontal:=0;
  end
else begin
  effective_vertical:=width(leader_box);
  if not (is_mirrored(box_dir(leader_box))) then
    if dir_eq(dir_primary[box_dir(leader_box)])(dir_secondary[dvi_direction]) then
      basepoint_horizontal:=height(leader_box)
    else
      basepoint_horizontal:=depth(leader_box)
  else
    if dir_eq(dir_primary[box_dir(leader_box)])(dir_secondary[dvi_direction]) then
      basepoint_horizontal:=depth(leader_box)
    else
      basepoint_horizontal:=height(leader_box);
  if dir_eq(dir_secondary[box_dir(leader_box)])(dir_primary[dvi_direction]) then
    basepoint_vertical:= width(leader_box)
  else
    basepoint_vertical:= 0;
  end;
basepoint_horizontal := basepoint_horizontal + shift_amount(leader_box);
  {shift the box `right'}
temp_ptr:=leader_box;
cur_h:=left_edge + basepoint_horizontal;
edge_v:=cur_v ;
cur_v:=cur_v + basepoint_vertical;
synch_h; synch_v; save_h:=dvi_h; save_v:=dvi_v;
outer_doing_leaders:=doing_leaders; doing_leaders:=true;
if type(leader_box)=vlist_node then vlist_out@+else hlist_out;
doing_leaders:=outer_doing_leaders;
dvi_h:=save_h; dvi_v:=save_v;
cur_h:=left_edge; cur_v:=edge_v+leader_ht+lx;
end

@ The |hlist_out| and |vlist_out| procedures are now complete, so we are
ready for the |dvi_ship_out| routine that gets them started in the first place.

@p procedure dvi_ship_out(@!p:pointer); {output the box |p|}
label done;
var page_loc:integer; {location of the current |bop|}
@!j,@!k:0..9; {indices to first ten count registers}
@!s:pool_pointer; {index into |str_pool|}
@!old_setting:0..max_selector; {saved |selector| setting}
pre_callback_id:integer;
post_callback_id:integer;
ret:boolean;
begin 
pre_callback_id:=callback_defined(start_page_number_callback);	
post_callback_id:=callback_defined(stop_page_number_callback);	
if (tracing_output>0)and(pre_callback_id=0) then
  begin print_nl(""); print_ln;
  print("Completed box being shipped out");
@.Completed box...@>
  end;
if pre_callback_id>0 then
  ret:=run_callback(pre_callback_id,'->')
else begin
  if term_offset>max_print_line-9 then print_ln
  else if (term_offset>0)or(file_offset>0) then print_char(" ");
  print_char("["); j:=9;
  while (count(j)=0)and(j>0) do decr(j);
  for k:=0 to j do
    begin print_int(count(k));
    if k<j then print_char(".");
    end;
  end;
update_terminal;
if (tracing_output>0)and(post_callback_id=0) then 
  begin print_char("]");
  begin_diagnostic; show_box(p); end_diagnostic(true);
  end;
@<Ship box |p| out@>;
if (tracing_output<=0)and(post_callback_id=0) then 
  print_char("]");
dead_cycles:=0;
update_terminal; {progress report}
@<Flush the box from memory, showing statistics if requested@>;
if post_callback_id>0 then 
  ret:=run_callback(post_callback_id,'->');
end;

@ @<Flush the box from memory, showing statistics if requested@>=
@!stat if (tracing_stats>1)and(pre_callback_id=0) then
  begin print_nl("Memory usage before: ");
@.Memory usage...@>
  print_int(var_used); print_char("&");
  print_int(dyn_used); print_char(";");
  end;
tats@/
flush_node_list(p);
@!stat if (tracing_stats>1)and(post_callback_id=0) then
  begin print(" after: ");
  print_int(var_used); print_char("&");
  print_int(dyn_used); print_ln;
  end;
tats

@ @<Ship box |p| out@>=
@<Update the values of |max_h| and |max_v|; but if the page is too large,
  |goto done|@>;
@<Initialize variables as |ship_out| begins@>;
page_loc:=dvi_offset+dvi_ptr;
dvi_out(bop);
for k:=0 to 9 do dvi_four(count(k));
dvi_four(last_bop); last_bop:=page_loc;
dvi_direction:=page_direction;
case box_direction(dvi_direction) of
dir_TL_,dir_LT_: begin
  end;
dir_TR_,dir_RT_: begin
  dvi_right(cur_page_width-cur_right_offset);
  dvi_h:=-cur_right_offset;
  end;
dir_RB_,dir_BR_: begin
  dvi_right(cur_page_width-cur_right_offset);
  dvi_down(cur_page_height-cur_bottom_offset);
  dvi_h:=-cur_right_offset;
  dvi_v:=-cur_bottom_offset;
  end;
dir_BL_,dir_LB_: begin
  dvi_down(cur_page_height-cur_bottom_offset);
  dvi_v:=-cur_bottom_offset;
  end;
end;
cur_h:=h_offset;
cur_v:=height(p)+v_offset;
case box_direction(dvi_direction) of
dir_TL_: begin
  dvi_down(cur_v);
  dvi_right(cur_h);
  end;
dir_TR_: begin
  dvi_down(cur_v);
  dvi_right(-cur_h);
  end;
dir_LT_: begin
  dvi_right(cur_v);
  dvi_down(cur_h);
  end;
dir_LB_: begin
  dvi_right(cur_v);
  dvi_down(-cur_h);
  end;
dir_BL_: begin
  dvi_down(-cur_v);
  dvi_right(cur_h);
  end;
dir_BR_: begin
  dvi_down(-cur_v);
  dvi_right(-cur_h);
  end;
dir_RT_: begin
  dvi_right(-cur_v);
  dvi_down(cur_h);
  end;
dir_RB_: begin
  dvi_right(-cur_v);
  dvi_down(-cur_h);
  end;
end;
dvi_h:=cur_h;
dvi_v:=cur_v;
temp_ptr:=p;
if type(p)=vlist_node then vlist_out@+else hlist_out;
dvi_out(eop); incr(total_pages); cur_s:=-1;
done:

@ Sometimes the user will generate a huge page because other error messages
are being ignored. Such pages are not output to the \.{dvi} file, since they
may confuse the printing software.

@<Update the values of |max_h| and |max_v|; but if the page is too large...@>=
if (height(p)>max_dimen)or@|(depth(p)>max_dimen)or@|
   (height(p)+depth(p)+v_offset>max_dimen)or@|
   (width(p)+h_offset>max_dimen) then
  begin print_err("Huge page cannot be shipped out");
@.Huge page...@>
  help2("The page just created is more than 18 feet tall or")@/
   ("more than 18 feet wide, so I suspect something went wrong.");
  error;
  if tracing_output<=0 then
    begin begin_diagnostic;
    print_nl("The following box has been deleted:");
@.The following...deleted@>
    show_box(p);
    end_diagnostic(true);
    end;
  goto done;
  end;
if height(p)+depth(p)+v_offset>max_v then max_v:=height(p)+depth(p)+v_offset;
if width(p)+h_offset>max_h then max_h:=width(p)+h_offset

@ At the end of the program, we must finish things off by writing the
post\-amble. If |total_pages=0|, the \.{DVI} file was never opened.
If |total_pages>=65536|, the \.{DVI} file will lie.

An integer variable |k| will be declared for use by this routine.

@<Finish the \.{DVI} file@>=
while cur_s>-1 do
  begin if cur_s>0 then dvi_out(pop)
  else  begin dvi_out(eop); incr(total_pages);
    end;
  decr(cur_s);
  end;
if total_pages=0 then begin 
  if callback_id=0 then
    print_nl("No pages of output.")
  else
    res:=run_callback(callback_id,'->');
  end
@.No pages of output@>
else  begin dvi_out(post); {beginning of the postamble}
  dvi_four(last_bop); last_bop:=dvi_offset+dvi_ptr-5; {|post| location}
  dvi_four(25400000); dvi_four(473628672); {conversion ratio for sp}
  prepare_mag; dvi_four(mag); {magnification factor}
  dvi_four(max_v); dvi_four(max_h);@/
  dvi_out(max_push div 256); dvi_out(max_push mod 256);@/
  dvi_out((total_pages div 256) mod 256); dvi_out(total_pages mod 256);@/
  @<Output the font definitions for all fonts that were used@>;
  dvi_out(post_post); dvi_four(last_bop); dvi_out(id_byte);@/
  k:=4+((dvi_buf_size-dvi_ptr) mod 4); {the number of 223's}
  while k>0 do
    begin dvi_out(223); decr(k);
    end;
  @<Empty the last bytes out of |dvi_buf|@>;
  if callback_id=0 then begin
    print_nl("Output written on "); slow_print(output_file_name);
@.Output written on x@>
    print(" ("); print_int(total_pages); print(" page");
    if total_pages<>1 then print_char("s");
    print(", "); print_int(dvi_offset+dvi_ptr); print(" bytes).");
    end
  else
    res:=run_callback(callback_id,'->');
  b_close(dvi_file);
  end

@ @<Output the font definitions...@>=
k := max_font_id;
while k>0 do
  begin if font_used(k) then dvi_font_def(k);
  decr(k);
  end


@* \[32a] \pdfTeX\ basic.

Initialize \pdfTeX's parameters to some useful default value.
Helpful in case one forgets to set them during initex run.

@<Initialize table entries...@>=
pdf_h_origin := one_inch;
pdf_v_origin := one_inch;
pdf_compress_level := 9;
pdf_objcompresslevel := 0;
pdf_decimal_digits := 3;
pdf_image_resolution := 72;
pdf_minor_version := 4;
pdf_gamma := 1000;
pdf_image_gamma := 2200;
pdf_image_hicolor := 1;
pdf_image_apply_gamma := 0;
pdf_px_dimen := one_bp;
pdf_draftmode := 0;

@ The subroutines define the corresponding macros so we can use them
in C.

@d flushable(#) == (# = str_ptr - 1)

@d is_valid_char(#) == char_exists(f,#)

@p function get_pdf_compress_level: integer;
begin
    get_pdf_compress_level := pdf_compress_level;
end;

function get_nullfont: internal_font_number;
begin
    get_nullfont := null_font;
end;

function get_escape_char: integer;
begin
    get_escape_char := escape_char;
end;

function get_undefined_control_sequence: integer;
begin
    get_undefined_control_sequence := undefined_control_sequence;
end;

function get_fontbase: internal_font_number;
begin
    get_fontbase := font_base;
end;

function get_nullcs: pointer;
begin
    get_nullcs := null_cs;
end;

function get_nullptr: pointer;
begin
    get_nullptr := null;
end;

function get_tex_int(code: integer): integer;
begin
    get_tex_int := int_par(code);
end;

function get_tex_dimen(code: integer): scaled;
begin
    get_tex_dimen := dimen_par(code);
end;

function get_x_height(f: internal_font_number): scaled;
begin
    get_x_height := x_height(f);
end;

function get_charwidth(f: internal_font_number; c: integer): scaled;
begin
    if is_valid_char(c) then
        get_charwidth := char_width(f,c)
    else
        get_charwidth := 0;
end;

function get_charheight(f: internal_font_number; c: integer): scaled;
begin
    if is_valid_char(c) then
        get_charheight := char_height(f,c)
    else
        get_charheight := 0;
end;

function get_chardepth(f: internal_font_number; c: integer): scaled;
begin
    if is_valid_char(c) then
        get_chardepth := char_depth(f,c)
    else
        get_chardepth := 0;
end;

function get_quad(f: internal_font_number): scaled;
begin
    get_quad := quad(f);
end;

function get_slant(f: internal_font_number): scaled;
begin
    get_slant := slant(f);
end;

function new_dummy_font: internal_font_number;
begin
    new_dummy_font := read_font_info(null_cs, "dummy", "", -1000, -1);
end;

function get_hash_size: integer;
begin
  get_hash_size:= hash_size;
end;

function get_eqtb_size: integer;
begin
  get_eqtb_size:= eqtb_size;
end;

function get_hash_base: integer;
begin
  get_hash_base:= hash_base;
end;

function get_active_base: integer;
begin
  get_active_base:= active_base;
end;

function get_cur_font: internal_font_number;
begin
  get_cur_font:= cur_font;
end;

procedure set_cur_font (f: internal_font_number);
var a:small_number;
begin
  a:=0;
  define(cur_font_loc,data,f);
end;

function get_current_name: str_number;
begin
  get_current_name:= name;
end;


@ Helper for debugging purposes

@p procedure short_display_n(@!p, m:integer); {prints highlights of list |p|}
var i: integer;
begin
i := 0;
font_in_short_display:=null_font;
if p = null then
    return;
while p<>null do
  begin if is_char_node(p) then
    begin if p<=max_halfword then
      begin if font(p)<>font_in_short_display then
        begin if not is_valid_font(font(p)) then
          print_char("*")
@.*\relax@>
        else print_font_identifier(font(p));
        print_char(" "); font_in_short_display:=font(p);
        end;
      print(qo(character(p)));
      end;
    end
  else begin
      if (type(p) = glue_node) or
         (type(p) = disc_node) or
         (type(p) = penalty_node) or
         ((type(p) = kern_node) and (subtype(p) = explicit)) then
         incr(i);
      if i >= m then
         return;
      if (type(p) = disc_node) then begin
          print("|");
          short_display(vlink(pre_break(p)));
          print("|");
          short_display(vlink(post_break(p)));
          print("|");
        end
        else
            @<Print a short indication of the contents of node |p|@>;
  end;
  p:=vlink(p);
  if p = null then
      return;
  end;
  update_terminal;
end;

@ Sometimes it is neccesary to allocate memory for PDF output that cannot
be deallocated then, so we use |pdf_mem| for this purpose.

@<Constants...@>=
@!inf_pdf_mem_size = 10000; {min size of the |pdf_mem| array}
@!sup_pdf_mem_size = 10000000; {max size of the |pdf_mem| array}

@ @<Glob...@>=
@!pdf_mem_size: integer;
@!pdf_mem: ^integer;
@!pdf_mem_ptr: integer;

@ @<Set init...@>=
pdf_mem_ptr := 1; {the first word is not used so we can use zero as a value for testing
whether a pointer to |pdf_mem| is valid}
pdf_mem_size := inf_pdf_mem_size; {allocated size of |pdf_mem| array}

@ We use |pdf_get_mem| to allocate memory in |pdf_mem|

@p function pdf_get_mem(s: integer): integer; {allocate |s| words in |pdf_mem|}
var a: integer;
begin
    if s > sup_pdf_mem_size - pdf_mem_ptr then
        overflow("PDF memory size (pdf_mem_size)", pdf_mem_size);
    if pdf_mem_ptr + s > pdf_mem_size then begin
        a := 0.2 * pdf_mem_size;
        if pdf_mem_ptr + s > pdf_mem_size + a then
            pdf_mem_size := pdf_mem_ptr + s
        else if pdf_mem_size < sup_pdf_mem_size - a then
            pdf_mem_size := pdf_mem_size + a
        else
            pdf_mem_size := sup_pdf_mem_size;
        pdf_mem := xreallocarray(pdf_mem, integer, pdf_mem_size);
    end;
    pdf_get_mem := pdf_mem_ptr;
    pdf_mem_ptr := pdf_mem_ptr + s;
end;

@* \[32b] \pdfTeX\ output low-level subroutines.
We use the similiar subroutines to handle the output buffer for
PDF output. When compress is used, the state of writing to buffer
is held in |zip_write_state|. We must write the header of PDF
output file in initialization to ensure that it will be the first
written bytes.

@<Constants...@>=
@!pdf_op_buf_size = 16384; {size of the PDF output buffer}
@!inf_pdf_os_buf_size = 1; {initial value of |pdf_os_buf_size|}
@!sup_pdf_os_buf_size = 5000000; {arbitrary upper hard limit of |pdf_os_buf_size|}
@!pdf_os_max_objs = 100; {maximum number of objects in object stream}

@ The following macros are similar as for \.{DVI} buffer handling

@d pdf_offset == (pdf_gone + pdf_ptr) {the file offset of last byte in PDF
buffer that |pdf_ptr| points to}

@d no_zip == 0 {no \.{ZIP} compression}
@d zip_writing == 1 {\.{ZIP} compression being used}
@d zip_finish == 2 {finish \.{ZIP} compression}

@d pdf_quick_out(#) == {output a byte to PDF buffer without checking of
overflow}
begin
    pdf_buf[pdf_ptr] := #;
    incr(pdf_ptr);
end

@d pdf_room(#) == {make sure that there are at least |n| bytes free in PDF buffer}
begin
    if pdf_os_mode and (# + pdf_ptr > pdf_buf_size) then
        pdf_os_get_os_buf(#)
    else if not pdf_os_mode and (# > pdf_buf_size) then
        overflow("PDF output buffer", pdf_op_buf_size)
    else if not pdf_os_mode and (# + pdf_ptr > pdf_buf_size) then
        pdf_flush;
end

@d pdf_out(#) == {do the same as |pdf_quick_out| and flush the PDF
buffer if necessary}
begin
    pdf_room(1);
    pdf_quick_out(#);
end

@<Glob...@>=
@!pdf_file: byte_file; {the PDF output file}
@!pdf_buf: ^real_eight_bits; {pointer to the PDF output buffer or PDF object stream buffer}
@!pdf_buf_size: integer; {end of PDF output buffer or PDF object stream buffer}
@!pdf_ptr: integer; {pointer to the first unused byte in the PDF buffer or object stream buffer}
@!pdf_op_buf: ^real_eight_bits; {the PDF output buffer}
@!pdf_os_buf: ^real_eight_bits; {the PDF object stream buffer}
@!pdf_os_buf_size: integer; {current size of the PDF object stream buffer, grows dynamically}
@!pdf_os_objnum: ^integer; {array of object numbers within object stream}
@!pdf_os_objoff: ^integer; {array of object offsets within object stream}
@!pdf_os_objidx: pointer; {pointer into |pdf_os_objnum| and |pdf_os_objoff|}
@!pdf_os_cntr: integer; {counter for object stream objects}
@!pdf_op_ptr: integer; {store for PDF buffer |pdf_ptr| while inside object streams}
@!pdf_os_ptr: integer; {store for object stream |pdf_ptr| while outside object streams}
@!pdf_os_mode: boolean; {true if producing object stream}
@!pdf_os_enable: boolean; {true if object streams are globally enabled}
@!pdf_os_cur_objnum: integer; {number of current object stream object}
@!pdf_gone: integer; {number of bytes that were flushed to output}
@!pdf_save_offset: integer; {to save |pdf_offset|}
@!zip_write_state: integer; {which state of compression we are in}
@!fixed_pdf_minor_version: integer; {fixed minor part of the PDF version}
@!fixed_pdf_objcompresslevel: integer; {fixed level for activating PDF object streams}
@!pdf_minor_version_written: boolean; {flag if the PDF version has been written}
@!fixed_pdfoutput: integer; {fixed output format}
@!fixed_pdfoutput_set: boolean; {|fixed_pdfoutput| has been set?}
@!fixed_gamma: integer;
@!fixed_image_gamma: integer;
@!fixed_image_hicolor: boolean;
@!fixed_image_apply_gamma: integer;
@!epochseconds: integer;
@!microseconds: integer;
@!fixed_pdf_draftmode: integer; {fixed \\pdfdraftmode}
@!fixed_pdf_draftmode_set: boolean; {|fixed_pdf_draftmode| has been set?}


@ @<Set init...@>=
pdf_gone := 0;
pdf_os_mode := false;
pdf_ptr := 0;
pdf_op_ptr := 0;
pdf_os_ptr := 0;
pdf_os_cur_objnum := 0;
pdf_os_cntr := 0;
pdf_buf_size := pdf_op_buf_size;
pdf_os_buf_size := inf_pdf_os_buf_size;
pdf_buf := pdf_op_buf;
pdf_seek_write_length := false;
zip_write_state := no_zip;
pdf_minor_version_written := false;
fixed_pdfoutput_set := false;
fixed_pdf_draftmode_set := false;

@ @p
function fix_int(val, min, max: integer): integer;
begin
    if val < min then
        fix_int := min
    else if val > max then
        fix_int := max
    else
        fix_int := val;
end;

@ This ensures that |pdfminorversion| is set only before any bytes have
been written to the generated PDF file. Here also the PDF file is opened
by |ensure_pdf_open| and the PDF header is written.

@p procedure check_pdfminorversion;
begin
    if not pdf_minor_version_written then begin
        pdf_minor_version_written := true;
        if (pdf_minor_version < 0) or (pdf_minor_version > 9) then begin
            print_err("pdfTeX error (illegal pdfminorversion)");
            print_ln;
            help2 ("The pdfminorversion must be between 0 and 9.")@/
                ("I changed this to 4.");
            int_error (pdf_minor_version);
            pdf_minor_version := 4;
        end;
        fixed_pdf_minor_version := pdf_minor_version;
        fixed_gamma             := fix_int(pdf_gamma, 0, 1000000);
        fixed_image_gamma       := fix_int(pdf_image_gamma, 0, 1000000);
        fixed_image_hicolor     := fix_int(pdf_image_hicolor, 0, 1);
        fixed_image_apply_gamma := fix_int(pdf_image_apply_gamma, 0, 1);
        fixed_pdf_objcompresslevel := fix_int(pdf_objcompresslevel, 0, 3);
        fixed_pdf_draftmode     := fix_int(pdf_draftmode, 0, 1);
		fixed_replace_font      := fix_int(pdf_replace_font, 0, 1);
        if (fixed_pdf_minor_version >= 5) and (fixed_pdf_objcompresslevel > 0) then
            pdf_os_enable := true
        else begin
            if fixed_pdf_objcompresslevel > 0 then begin
                pdf_warning("Object streams", "\pdfobjcompresslevel > 0 requires \pdfminorversion > 4. Object streams disabled now.", true, true);
                fixed_pdf_objcompresslevel := 0;
            end;
            pdf_os_enable := false;
        end;
        ensure_pdf_open;
        fix_pdfoutput;
        pdf_print("%PDF-1.");
        pdf_print_int_ln(fixed_pdf_minor_version);
        pdf_print("%");
        pdf_out(208); {'P' + 128}
        pdf_out(212); {'T' + 128}
        pdf_out(197); {'E' + 128}
        pdf_out(216); {'X' + 128}
        pdf_print_nl;
    end
    else begin
        if fixed_pdf_minor_version <> pdf_minor_version then
            pdf_error("setup",
               "\pdfminorversion cannot be changed after data is written to the PDF file");
    end;
end;

@ Checks that we have a name for the generated PDF file and that it's open.

@p procedure ensure_pdf_open;
begin
    if output_file_name <> 0 then
        return;
    if job_name = 0 then
        open_log_file;
    pack_job_name(".pdf");
	if fixed_pdf_draftmode = 0 then
    while not lua_b_open_out(pdf_file) do
        prompt_file_name("file name for output",".pdf");
    pdf_file:=name_file_pointer;
    output_file_name := b_make_name_string(pdf_file);
end;

@ The PDF buffer is flushed by calling |pdf_flush|, which checks the
variable |zip_write_state| and will compress the buffer before flushing if
neccesary. We call |pdf_begin_stream| to begin a stream  and |pdf_end_stream|
to finish it. The stream contents will be compressed if compression is turn on.

@p procedure pdf_flush; {flush out the |pdf_buf|}
begin
    if not pdf_os_mode then begin
        case zip_write_state of
            no_zip: if pdf_ptr > 0 then begin
                if fixed_pdf_draftmode = 0 then write_pdf(0, pdf_ptr - 1);
                pdf_gone := pdf_gone + pdf_ptr;
                pdf_last_byte := pdf_buf[pdf_ptr - 1];
            end;
            zip_writing:
                if fixed_pdf_draftmode = 0 then write_zip(false);
            zip_finish: begin
                if fixed_pdf_draftmode = 0 then write_zip(true);
                zip_write_state := no_zip;
            end;
        end;
        pdf_ptr := 0;
    end;
end;

procedure pdf_begin_stream; {begin a stream}
begin
    pdf_print_ln("/Length           ");
    pdf_seek_write_length := true; {fill in length at |pdf_end_stream| call}
    pdf_stream_length_offset := pdf_offset - 11;
    pdf_stream_length := 0;
    if pdf_compress_level > 0 then begin
        pdf_print_ln("/Filter /FlateDecode");
        pdf_print_ln(">>");
        pdf_print_ln("stream");
        pdf_flush;
        zip_write_state := zip_writing;
    end
    else begin
        pdf_print_ln(">>");
        pdf_print_ln("stream");
        pdf_save_offset := pdf_offset;
    end;
end;

procedure pdf_end_stream; {end a stream}
begin
    if zip_write_state = zip_writing then
        zip_write_state := zip_finish
    else
        pdf_stream_length := pdf_offset - pdf_save_offset;
    pdf_flush;
    if pdf_seek_write_length then
        write_stream_length(pdf_stream_length, pdf_stream_length_offset);
    pdf_seek_write_length := false;
    if pdf_last_byte <> pdf_new_line_char then
        pdf_out(pdf_new_line_char);
    pdf_print_ln("endstream");
    pdf_end_obj;
end;

@ Basic printing procedures for PDF output are very similiar to \TeX\ basic
printing ones but the output is going to PDF buffer. Subroutines with
suffix |_ln| append a new-line character to the PDF output.

@d pdf_new_line_char == 10 {new-line character for UNIX platforms}

@d pdf_print_nl == {output a new-line character to PDF buffer}
pdf_out(pdf_new_line_char)

@d pdf_print_ln(#) == {print out a string to PDF buffer followed by
a new-line character}
begin
    pdf_print(#);
    pdf_print_nl;
end

@d pdf_print_int_ln(#) == {print out an integer to PDF buffer followed by
a new-line character}
begin
    pdf_print_int(#);
    pdf_print_nl;
end

@<Declare procedures that need to be declared forward for \pdfTeX@>=
procedure pdf_error(t, p: str_number);
begin
    normalize_selector;
    print_err("pdfTeX error");
    if t <> 0 then begin
        print(" (");
        print(t);
        print(")");
    end;
    print(": "); print(p);
    succumb;
end;

procedure pdf_warning(t, p: str_number; prepend_nl, append_nl: boolean);
begin
    if interaction = error_stop_mode then
        wake_up_terminal;
    if prepend_nl then
        print_ln;
    print("pdfTeX warning");
    if t <> 0 then begin
        print(" (");
        print(t);
        print(")");
    end;
    print(": "); print(p);
    if append_nl then
        print_ln;
	if history=spotless then history:=warning_issued;
end;

procedure pdf_os_get_os_buf(s: integer); {check that |s| bytes more
fit into |pdf_os_buf|; increase it if required}
var a: integer;
begin
    if s > sup_pdf_os_buf_size - pdf_ptr then
        overflow("PDF object stream buffer", pdf_os_buf_size);
    if pdf_ptr + s > pdf_os_buf_size then begin
        a := 0.2 * pdf_os_buf_size;
        if pdf_ptr + s > pdf_os_buf_size + a then
            pdf_os_buf_size := pdf_ptr + s
        else if pdf_os_buf_size < sup_pdf_os_buf_size - a then
            pdf_os_buf_size := pdf_os_buf_size + a
        else
            pdf_os_buf_size := sup_pdf_os_buf_size;
        pdf_os_buf := xreallocarray(pdf_os_buf, real_eight_bits, pdf_os_buf_size);
        pdf_buf := pdf_os_buf;
        pdf_buf_size := pdf_os_buf_size;
    end;
end;

procedure remove_last_space;
begin
    if (pdf_ptr > 0) and (pdf_buf[pdf_ptr - 1] = 32) then
        decr(pdf_ptr);
end;

function str_in_str(s, r: str_number; i: integer): boolean;
  {test equality of strings}
label not_found; {loop exit}
var j, k: pool_pointer; {running indices}
begin
    str_in_str := false;
    if length(s) < i + length(r) then
        return;
    j := i + str_start_macro(s);
    k := str_start_macro(r);
    while (j < str_start_macro(s + 1)) and (k < str_start_macro(r + 1)) do begin
        if str_pool[j] <> str_pool[k] then
            return;
        incr(j);
        incr(k);
    end;
    str_in_str := true;
end;

function tokens_to_string(p: pointer): str_number; {return a string from tokens
list}
var old_setting:integer;
begin
    if selector = new_string then
        pdf_error("tokens", "tokens_to_string() called while selector = new_string");
    old_setting:=selector; selector:=new_string;
    show_token_list(link(p),null,pool_size-pool_ptr);
    selector:=old_setting;
    last_tokens_string := make_string;
    tokens_to_string := last_tokens_string;
end;


@ To print |scaled| value to PDF output we need some subroutines to ensure
accurary.

@d max_integer == @"7FFFFFFF {$2^{31}-1$}
@d call_func(#) == begin if # <> 0 then do_nothing end


@<Glob...@>=
@!one_hundred_inch: scaled; {scaled value corresponds to 100in}
@!one_inch: scaled; {scaled value corresponds to 1in (rounded!)}
@!one_hundred_bp: scaled; {scaled value corresponds to 100bp}
@!one_bp: scaled; {scaled value corresponds to 1bp (rounded!)}
@!ten_pow: array[0..9] of integer; {$10^0..10^9$}
@!scaled_out: integer; {amount of |scaled| that was taken out in
|divide_scaled|}
@!init_pdf_output: boolean;

@ @<Set init...@>=
one_hundred_inch := 7227 * 65536; {exact, 473628672}
one_inch := (one_hundred_inch + 50) div 100; {rounded to 4736287}
one_hundred_bp := one_hundred_inch div 72; {exact, 6578176}
one_bp := (one_hundred_bp + 50) div 100; {rounded to 65782}
ten_pow[0] := 1;
for i := 1 to 9 do
    ten_pow[i] := 10*ten_pow[i - 1];
init_pdf_output := false;


@ The function |divide_scaled| divides |s| by |m| using |dd| decimal
digits of precision. It is defined in C because it is a good candidate
for optimizations that are not possible in pascal.

@<Declare procedures that need to be declared forward for \pdfTeX@>=
function round_xn_over_d(@!x:scaled; @!n,@!d:integer):scaled;
var positive:boolean; {was |x>=0|?}
@!t,@!u,@!v:nonnegative_integer; {intermediate quantities}
begin if x>=0 then positive:=true
else  begin negate(x); positive:=false;
  end;
t:=(x mod @'100000)*n;
u:=(x div @'100000)*n+(t div @'100000);
v:=(u mod d)*@'100000 + (t mod @'100000);
if u div d>=@'100000 then arith_error:=true
else u:=@'100000*(u div d) + (v div d);
v := v mod d;
if 2*v >= d then
    incr(u);
if positive then
    round_xn_over_d := u
else
    round_xn_over_d := -u;
end;

@ Next subroutines are needed for controling spacing in PDF page description.
For a given character |c| from a font |f|,
the procedure |adv_char_width| advances |pdf_h|
by {\it about\/} the amount |w|, which is the character width.
But we cannot simply add |w| to |pdf_h|.
Instead we have to bring the required shift into the same raster,
on which also the \.{/Widths} array values,
as they appear in the PDF file, are based.
The |scaled_out| value is the |w| value moved into this raster.
The \.{/Widths} values are used by the PDF reader independently
to update its positions.
So one has to be sure, that calculations are properly synchronized.
Currently the \.{/Widths} array values are output
with one digit after the decimal point,
therefore the raster on which |adv_char_width| is operating
is $1/10000$ of the |pdf_font_size|.

For PK fonts things are more complicated,
as we have to deal with scaling bitmaps as well.

@p
procedure adv_char_width(f: internal_font_number; c: integer); {update |pdf_h|
by character width |w| from font |f|}
var w, s_out: scaled;
    s: integer;
begin
    w := char_width(f,c);
    if hasfmentry(f) then begin
        if pdf_cur_Tm_a = 1000 then begin
            call_func(divide_scaled_n(w, pdf_font_size(f), 10000.0));
            pdf_delta_h := pdf_delta_h + scaled_out;
        end
        else begin
            s := divide_scaled_n(round_xn_over_d(w, 1000, pdf_cur_Tm_a),
                                 pdf_font_size(f), 10000.0);
            s_out := round_xn_over_d(round_xn_over_d(pdf_font_size(f), abs(s), 10000),
                                     pdf_cur_Tm_a, 1000);
            if s < 0 then
                s_out := -s_out;
            pdf_delta_h := pdf_delta_h + s_out;
        end;
    end else
        pdf_delta_h := pdf_delta_h + get_pk_char_width(f, w);
end;

procedure pdf_print_bp(s: scaled); {print scaled as |bp|}
begin
    pdf_print_real(divide_scaled(s, one_hundred_bp, fixed_decimal_digits + 2),
                   fixed_decimal_digits);
end;

procedure pdf_print_mag_bp(s: scaled); {take |mag| into account}
begin
    prepare_mag;
    if mag <> 1000 then
        s := round_xn_over_d(s, mag, 1000);
    pdf_print_bp(s);
end;

@* \[32c] PDF page description.

@d pdf_h_offset == (h_offset + pdf_h_origin)
@d pdf_v_offset == (v_offset + pdf_v_origin)
@d pdf_x(#) == ((#) - pdf_h_offset + one_inch) {convert $x$-coordinate from \.{DVI} to PDF}
@d pdf_y(#) == (cur_page_height - (#) - pdf_v_offset + one_inch) {convert $y$-coordinate from \.{DVI} to PDF}

@<Glob...@>=
@!pdf_f: internal_font_number; {the current font in PDF output page}
@!pdf_h: scaled; {current horizontal coordinate in PDF output page}
@!pdf_v: scaled; {current vertical coordinate in PDF output page}
@!pdf_tj_start_h: scaled; {horizontal coordinate in PDF output page just before \.{TJ} array start}
@!cur_delta_h: scaled; {horizontal |cur_h| offset from |pdf_tj_start_h|}
@!pdf_delta_h: scaled; {horizontal offset from |pdf_tj_start_h|}
@!pdf_origin_h: scaled; {current horizontal origin in PDF output page}
@!pdf_origin_v: scaled; {current vertical origin in PDF output page}
@!pdf_doing_string: boolean; {we are writing string to PDF file?}
@!pdf_doing_text: boolean; {we are writing text section to PDF file?}
@!min_bp_val: scaled;
@!min_font_val: scaled; {(TJ array system)}
@!fixed_pk_resolution: integer;
@!fixed_decimal_digits: integer;
@!fixed_gen_tounicode: integer;
@!fixed_replace_font: integer;
@!pk_scale_factor: integer;
@!pdf_output_option: integer;
@!pdf_output_value: integer;
@!pdf_draftmode_option: integer;
@!pdf_draftmode_value: integer;
@!pdf_cur_Tm_a: integer; {value |a| of the current text matrix, i.e.,
                          the current horizontal scaling factor}
@!pdf_cur_Tm_c: integer; {value |c| of the current text matrix, i.e., slant (skew, obliqueness)}
@!pdf_last_f: internal_font_number; {last font in PDF output page}
@!pdf_last_fs: internal_font_number; {last font size in PDF output page}

@ Following procedures implement low-level subroutines to convert \TeX{}
internal structures to PDF page description.

@p procedure pdf_set_origin(h, v: scaled); {set the origin to |h|, |v|}
begin
    if (abs(h - pdf_origin_h) >= min_bp_val) or
        (abs(v - pdf_origin_v) >= min_bp_val) then begin
        pdf_print("1 0 0 1 ");
        pdf_print_bp(h - pdf_origin_h);
        pdf_origin_h := pdf_origin_h + scaled_out;
        pdf_out(" ");
        pdf_print_bp(pdf_origin_v - v);
        pdf_origin_v := pdf_origin_v - scaled_out;
        pdf_print_ln(" cm");
    end;
    pdf_h := pdf_origin_h;
    pdf_tj_start_h := pdf_h;
    pdf_v := pdf_origin_v;
end;

procedure pdf_set_origin_temp(h, v: scaled); {set the origin to |h|, |v| inside group}
begin
    if (abs(h - pdf_origin_h) >= min_bp_val) or
        (abs(v - pdf_origin_v) >= min_bp_val) then begin
        pdf_print("1 0 0 1 ");
        pdf_print_bp(h - pdf_origin_h);
        pdf_out(" ");
        pdf_print_bp(pdf_origin_v - v);
        pdf_print_ln(" cm");
    end;
end;

procedure pdf_end_string; {end the current string}
begin
    if pdf_doing_string then begin
        pdf_print(")]TJ");
        pdf_doing_string := false;
    end;
end;

procedure pdf_end_string_nl; {end the current string, with new-line}
begin
    if pdf_doing_string then begin
        pdf_print_ln(")]TJ");
        pdf_doing_string := false;
    end;
end;

procedure pdf_set_textmatrix(v, v_out: scaled; f: internal_font_number);
{set the next starting point to |cur_h|, |cur_v|}
var pdf_new_Tm_a, pdf_new_Tm_c: integer; {values |a| and |c| of the new text matrix}
begin
    pdf_out(" ");
    if f = pdf_f then begin
        pdf_new_Tm_a := pdf_cur_Tm_a;
        pdf_new_Tm_c := pdf_cur_Tm_c;
    end else begin
        if pdf_font_auto_expand(f) then
            pdf_new_Tm_a := 1000 + pdf_font_expand_ratio(f)
        else
            pdf_new_Tm_a := 1000;
        pdf_new_Tm_c := 0 * font_slant(f); {don't activate it yet, needs fixing writefont.c etc.}
    end;
    if (pdf_new_Tm_a <> 1000) or (pdf_cur_Tm_a <> 1000)
    or (pdf_new_Tm_c <> 0) or (pdf_cur_Tm_c <> 0)
    then begin
        pdf_print_real(pdf_new_Tm_a, 3);
        pdf_print(" 0 ");
        pdf_print_real(pdf_new_Tm_c, 3);
        pdf_print(" 1 ");
        pdf_print_bp(cur_h - pdf_origin_h);
        pdf_h := pdf_origin_h + scaled_out;
        pdf_out(" ");
        pdf_print_bp(pdf_origin_v - cur_v);
        pdf_v := pdf_origin_v - scaled_out;
        pdf_print(" Tm");
        pdf_cur_Tm_a := pdf_new_Tm_a;
        pdf_cur_Tm_c := pdf_new_Tm_c;
        pdfassert(pdf_cur_Tm_a > 0);
    end else begin
        pdf_print_bp(cur_h - pdf_tj_start_h); {works only for unexpanded fonts}
        pdf_h := pdf_tj_start_h + scaled_out;
        pdf_out(" ");
        pdf_print_real(v, fixed_decimal_digits); {use |v| and |v_out| to avoid duplicate calculation}
        pdf_v := pdf_v - v_out;
        pdf_print(" Td");
    end;
    pdf_tj_start_h := pdf_h;
    pdf_delta_h := 0;
end;

procedure pdf_use_font(f: internal_font_number; fontnum: integer);
{mark |f| as a used font; set |font_used(f)|, |pdf_font_size(f)| and |pdf_font_num(f)|}
begin
    call_func(divide_scaled(font_size(f), one_hundred_bp, 6));
    set_pdf_font_size(f,scaled_out);
    set_font_used(f,true);
    pdfassert((fontnum > 0) or ((fontnum < 0) and (pdf_font_num(-fontnum) > 0)));
    set_pdf_font_num(f,fontnum);
    if pdf_move_chars > 0 then begin
        pdf_warning(0,"Primitive \pdfmovechars is obsolete.",true, true);
        pdf_move_chars := 0; {warn only once}
    end;
end;

@ To set PDF font we need to find out fonts with the same name, because \TeX\
can load the same font several times for various sizes. For such fonts we
define only one font resource. The array |pdf_font_num| holds the object
number of font resource. A negative value of an entry of |pdf_font_num|
indicates that the corresponding font shares the font resource with the font

@d pdf_print_resname_prefix ==
if pdf_resname_prefix <> 0 then
    pdf_print(pdf_resname_prefix)

@p procedure pdf_init_font(f: internal_font_number);
{create a font object}
var k, b: internal_font_number;
    i: integer;
begin
    pdfassert(not font_used(f));

    {if |f| is auto expanded then ensure the base font is initialized}
    if pdf_font_auto_expand(f) and (pdf_font_blink(f) <> null_font) then begin
        b := pdf_font_blink(f);
	    {TODO: reinstate this check. disabled because wide fonts font have fmentries}
        if false and (not hasfmentry(b)) then
            pdf_error("font expansion", "auto expansion is only possible with scalable fonts");
        if not font_used(b) then
            pdf_init_font(b);
        set_font_map(f,font_map(b));
    end;

    {check whether |f| can share the font object with some |k|: we have 2 cases
    here: 1) |f| and |k| have the same tfm name (so they have been loaded at
    different sizes, eg 'cmr10' and 'cmr10 at 11pt'); 2) |f| has been auto
    expanded from |k|}
    if hasfmentry(f) or true then begin
        i := head_tab[obj_type_font];
        while i <> 0 do begin
            k := obj_info(i);
            if font_shareable(f,k) then
            begin
                pdfassert(pdf_font_num(k) <> 0);
                if pdf_font_num(k) < 0 then
                    pdf_use_font(f, pdf_font_num(k))
                else
                    pdf_use_font(f, -k);
                return;
            end;
            i := obj_link(i);
        end;
    end;

    {create a new font object for |f|}
    pdf_create_obj(obj_type_font, f);
    pdf_use_font(f, obj_ptr);
end;

procedure pdf_init_font_cur_val;
begin
    pdf_init_font(cur_val);
end;

procedure pdf_set_font(f: internal_font_number);
{set the actual font on PDF page}
label found, found1;
var p: pointer;
    k: internal_font_number;
begin
    if not font_used(f) then
        pdf_init_font(f);
    set_ff(f); {set |ff| to the tfm number of the font sharing the font object
                with |f|; |ff| is either |f| or some font with the same tfm name
                at different size and/or expansion}
    k := ff;
    p := pdf_font_list;
    while p <> null do begin
        set_ff(info(p));
        if ff = k then
            goto found;
        p := link(p);
    end;
    pdf_append_list(f)(pdf_font_list); {|f| not found in |pdf_font_list|, append it now}
found:
    if (k = pdf_last_f) and (font_size(f) = pdf_last_fs) then
        return;
    pdf_print("/F");
    pdf_print_int(k);
    pdf_print_resname_prefix;
    pdf_out(" ");
    pdf_print_real(divide_scaled(font_size(f), one_hundred_bp, 6), 4);
    pdf_print(" Tf");
    pdf_last_f := k;
    pdf_last_fs := font_size(f);
end;

procedure pdf_begin_text; {begin a text section}
begin
    pdf_set_origin(0, cur_page_height);
    pdf_print_ln("BT");
    pdf_doing_text := true;
    pdf_f := null_font;
    pdf_last_f := null_font;
    pdf_last_fs := 0;
    pdf_doing_string := false;
    pdf_cur_Tm_a := 1000;
    pdf_cur_Tm_c := 0;
end;

@ @p
procedure pdf_begin_string(f: internal_font_number); {begin to draw a string}
var s_out, v, v_out: scaled;
    s: integer;
begin s_out:=0;
    if not pdf_doing_text then
        pdf_begin_text;
    if f <> pdf_f then begin
        pdf_end_string;
        pdf_set_font(f);
    end;
    if pdf_cur_Tm_a = 1000 then begin
        s := divide_scaled_n(cur_h - (pdf_tj_start_h + pdf_delta_h), pdf_font_size(f), 1000.0);
        s_out := scaled_out;
    end
    else begin
        s := divide_scaled_n(round_xn_over_d(cur_h - (pdf_tj_start_h + pdf_delta_h), 1000,
                                             pdf_cur_Tm_a), pdf_font_size(f), 1000.0);
        if abs(s) < @'100000 then begin
            s_out := round_xn_over_d(round_xn_over_d(pdf_font_size(f), abs(s), 1000),
                                     pdf_cur_Tm_a, 1000);
            if s < 0 then
                s_out := -s_out;
        end;
        {no need to calculate |s_out| when |abs(s) >= @'100000|, since the text
         matrix will be reset below}
    end;
    if abs(cur_v - pdf_v) >= min_bp_val then begin
        v := divide_scaled(pdf_v - cur_v, one_hundred_bp,
                           fixed_decimal_digits + 2);
        v_out := scaled_out;
    end
    else begin
        v := 0;
        v_out := 0;
    end;
    if (f <> pdf_f) or (v <> 0) or (abs(s) >= @'100000) then begin
        pdf_end_string;
        pdf_set_textmatrix(v, v_out, f);
        pdf_f := f;
        s := 0;
    end;
    if not pdf_doing_string then begin
        pdf_print(" [");
        if s = 0 then
            pdf_out("(");
    end;
    if s <> 0 then begin
        if pdf_doing_string then
            pdf_out(")");
        pdf_print_int(-s);
        pdf_out("(");
        pdf_delta_h := pdf_delta_h + s_out;
    end;
    pdf_doing_string := true;
end;

procedure pdf_end_text; {end a text section}
begin
    if pdf_doing_text then begin
        pdf_end_string_nl;
        pdf_print_ln("ET");
        pdf_doing_text := false;
    end;
end;

procedure pdf_set_rule(x, y, w, h: scaled); {draw a rule}
begin
    pdf_end_text;
    pdf_print_ln("q");
    if h <= one_bp then begin
        pdf_set_origin_temp(x, y - (h + 1)/2);
        pdf_print("[]0 d 0 J ");
        pdf_print_bp(h); pdf_print(" w 0 0 m ");
        pdf_print_bp(w); pdf_print_ln(" 0 l S");
    end
    else if w <= one_bp then begin
        pdf_set_origin_temp(x + (w + 1)/2, cur_v);
        pdf_print("[]0 d 0 J ");
        pdf_print_bp(w); pdf_print(" w 0 0 m 0 ");
        pdf_print_bp(h); pdf_print_ln(" l S");
    end
    else begin
        pdf_set_origin_temp(x, y);
        pdf_print("0 0 ");
        pdf_print_bp(w); pdf_out(" ");
        pdf_print_bp(h); pdf_print_ln(" re f");
    end;
    pdf_print_ln("Q");
end;

procedure pdf_rectangle(left, top, right, bottom: scaled); {output a
rectangle specification to PDF file}
begin
    prepare_mag;
    pdf_print("/Rect [");
    pdf_print_mag_bp(pdf_x(left)); pdf_out(" ");
    pdf_print_mag_bp(pdf_y(bottom)); pdf_out(" ");
    pdf_print_mag_bp(pdf_x(right)); pdf_out(" ");
    pdf_print_mag_bp(pdf_y(top));
    pdf_print_ln("]");
end;

procedure literal(s: str_number; literal_mode: integer; warn: boolean);
var j: pool_pointer; {current character code position}
begin
    j:=str_start_macro(s);
    if literal_mode = scan_special then begin
        if not (str_in_str(s, "PDF:", 0) or str_in_str(s, "pdf:", 0)) then begin
            if warn and not (str_in_str(s, "SRC:", 0)
                or str_in_str(s, "src:", 0)
                or (length(s) = 0)) then
                    print_nl("Non-PDF special ignored!");
            return;
        end;
        j := j + length("PDF:");
        if str_in_str(s, "direct:", length("PDF:")) then begin
            j := j + length("direct:");
            literal_mode := direct_always; end
        else if str_in_str(s, "page:", length("PDF:")) then begin
            j := j + length("page:");
            literal_mode := direct_page; end
        else
            literal_mode := set_origin;
    end;
    case literal_mode of
    set_origin: begin
        pdf_end_text;
        pdf_set_origin(cur_h, cur_v);
        end;
    direct_page:
        pdf_end_text;
    direct_always:
        pdf_end_string_nl;
    othercases confusion("literal1")
    endcases;
    while j<str_start_macro(s+1) do begin
       pdf_out(str_pool[j]);
       incr(j);
    end;
    pdf_print_nl;
end;

procedure latelua(lua_id: quarterword; s: str_number);
var b, j: pool_pointer; {current character code position}
begin
    j:=str_start_macro(s);
    b := pool_ptr;
    luacall(lua_id,(s-string_offset));
    while b<pool_ptr do begin
       pdf_out(str_pool[b]);
       incr(b);
    end;
    pdf_print_nl;
end;

@* \[32d] The cross-reference table.

The cross-reference table |obj_tab| is an array of |obj_tab_size| of
|tab_entry|. Each entry contains five integer fields and represents an object
in PDF file whose object number is the index of this entry in |obj_tab|.
Objects in |obj_tab| maybe linked into list; objects in such a linked list have
the same type.

@<Types...@>=
@!obj_entry = record@;@/
    int0, int1, int2, int3, int4: integer;
end;

@ The first field contains information representing identifier of this object.
It is usally a number for most of object types, but it may be a string number
for named destination or named thread.

The second field of |obj_entry| contains link to the next
object in |obj_tab| if this object is linked in a list.

The third field holds the byte offset of the object in the output PDF file,
or its byte offset within an object stream.
Objects that have been not written yet have this field set to zero. However
sometimes we have to use this field to store some info before the object is
written out.

The fourth field holds the object number of the object stream, into which
the object is included.

The last field usually represents the pointer to some auxiliary data
structure depending on the object type; however it may be used as a counter as
well.

@d obj_info(#) == obj_tab[#].int0 {information representing identifier of this object}
@d obj_link(#) == obj_tab[#].int1 {link to the next entry in linked list}
@d obj_offset(#) == obj_tab[#].int2 {byte offset for this object in PDF output file, or object stream number for this object}
@d obj_os_idx(#) == obj_tab[#].int3 {index of this object in object stream}
@d obj_aux(#) == obj_tab[#].int4 {auxiliary pointer}
@d is_obj_written(#) == (obj_offset(#) <> 0)

@# {types of objects}
@d obj_type_others              == 0 {objects which are not linked in any list}
@d obj_type_page                == 1 {index of linked list of Page objects}
@d obj_type_pages               == 2 {index of linked list of Pages objects}
@d obj_type_font                == 3 {index of linked list of Fonts objects}
@d obj_type_outline             == 4 {index of linked list of outline objects}
@d obj_type_dest                == 5 {index of linked list of destination objects}
@d obj_type_obj                 == 6 {index of linked list of raw objects}
@d obj_type_xform               == 7 {index of linked list of XObject forms}
@d obj_type_ximage              == 8 {index of linked list of XObject image}
@d obj_type_thread              == 9 {index of linked list of num article threads}
@d head_tab_max                 == obj_type_thread {max index of |head_tab|}

@# {max number of kids for balanced trees}
@d pages_tree_kids_max     == 6 {max number of kids of Pages tree node}
@d name_tree_kids_max      == 6 {max number of kids of node of name tree for
name destinations}

@# {when a whatsit node representing annotation is created, words |1..3| are
width, height and depth of this annotation; after shipping out words |1..4|
are rectangle specification of annotation. For whatsit node representing
destination |pdf_left| and |pdf_top| are used for some types of destinations}

@# {coordinates of destinations/threads/annotations (in whatsit node)}
@d pdf_left(#)             == vmem(# + 2).sc
@d pdf_top(#)              == vmem(# + 3).sc
@d pdf_right(#)            == vmem(# + 4).sc
@d pdf_bottom(#)           == vmem(# + 5).sc

@# {dimension of destinations/threads/annotations (in whatsit node)}
@d pdf_width(#)            == vmem(# + 2).sc
@d pdf_height(#)           == vmem(# + 3).sc
@d pdf_depth(#)            == vmem(# + 4).sc

@# {data structure for \.{\\pdfliteral}}
@d pdf_literal_data(#)     == vlink(#+2) {data}
@d pdf_literal_mode(#)     == vinfo(#+2) {mode of resetting the text matrix
                              while writing data to the page stream}
@# {modes of setting the current transformation matrix (CTM)}
@d set_origin              == 0 {end text (ET) if needed, set CTM to current point}
@d direct_page             == 1 {end text (ET) if needed, but don't change the CTM}
@d direct_always           == 2 {don't end text, don't change the CTM}
@d scan_special            == 3 {look into special text}

@# {data structure for \.{\\pdfcolorstack}}
@d pdf_colorstack_node_size == 4
@d pdf_colorstack_stack(#)  == vlink(#+2) {stack number}
@d pdf_colorstack_cmd(#)    == vinfo(#+2) {command: set, push, pop, current}
@d pdf_colorstack_data(#)   == vlink(#+3) {data}

@# {color stack commands}
@d colorstack_set          == 0
@d colorstack_push         == 1
@d colorstack_data         == 1 { last value where data field is set }
@d colorstack_pop          == 2
@d colorstack_current      == 3

@# {data structure for \.{\\pdfsetmatrix}}
@d pdf_setmatrix_node_size == 3
@d pdf_setmatrix_data(#)   == vlink(#+2) {data}

@# {data structure for \.{\\pdsave}}
@d pdf_save_node_size      == 3

@# {data structure for \.{\\pdfrestore}}
@d pdf_restore_node_size   == 3


@# {data structure for \.{\\latelua}}
@d late_lua_data(#)        == vlink(#+2) {data}
@d late_lua_reg(#)         == vinfo(#+2) {register id}

@# {data structure for \.{\\pdfobj} and \.{\\pdfrefobj}}
@d pdf_refobj_node_size    == 3 {size of whatsit node representing the raw object}
@d pdf_obj_objnum(#)       == vinfo(# + 2) {number of the raw object}
@d obj_data_ptr            == obj_aux {pointer to |pdf_mem|}
@d pdfmem_obj_size         == 4 {size of memory in |pdf_mem| which |obj_data_ptr| holds}
@d obj_obj_data(#)         == pdf_mem[obj_data_ptr(#) + 0] {object data}
@d obj_obj_is_stream(#)    == pdf_mem[obj_data_ptr(#) + 1] {will this object
                              be written as a stream instead of a dictionary?}
@d obj_obj_stream_attr(#)  == pdf_mem[obj_data_ptr(#) + 2] {additional
                              object attributes for streams}
@d obj_obj_is_file(#)      == pdf_mem[obj_data_ptr(#) + 3] {data should be
                              read from an external file?}

@# {data structure for \.{\\pdfxform} and \.{\\pdfrefxform}}
@d pdf_refxform_node_size  == 6 {size of whatsit node for xform; words 1..3 are
                              form dimensions}
@d pdf_xform_objnum(#)     == vinfo(# + 4) {object number}
@d pdfmem_xform_size       == 6 {size of memory in |pdf_mem| which
                              |obj_data_ptr| holds}
@d obj_xform_width(#)      == pdf_mem[obj_data_ptr(#) + 0]
@d obj_xform_height(#)     == pdf_mem[obj_data_ptr(#) + 1]
@d obj_xform_depth(#)      == pdf_mem[obj_data_ptr(#) + 2]
@d obj_xform_box(#)        == pdf_mem[obj_data_ptr(#) + 3] {this field holds
                              pointer to the corresponding box}
@d obj_xform_attr(#)       == pdf_mem[obj_data_ptr(#) + 4] {additional xform
                              attributes}
@d obj_xform_resources(#)  == pdf_mem[obj_data_ptr(#) + 5] {additional xform
                              Resources}

@# {data structure for \.{\\pdfximage} and \.{\\pdfrefximage}}
@d pdf_refximage_node_size == 6 {size of whatsit node for ximage; words 2..4
                               are image dimensions}
@d pdf_ximage_ref(#)       == vinfo(# + 5) {image reference number}

@# {data structure of annotations; words 1..4 represent the coordinates of
    the annotation}
@d obj_annot_ptr           == obj_aux {pointer to corresponding whatsit node}
@d pdf_annot_node_size     == 8 {size of whatsit node representing annotation}
@d pdf_annot_data(#)       == vinfo(# + 6) {raw data of general annotations}
@d pdf_link_attr(#)        == vinfo(# + 6) {attributes of link annotations}
@d pdf_link_action(#)      == vlink(# + 6) {pointer to action structure}
@d pdf_annot_objnum(#)     == vmem(# + 7).int {object number of corresponding object}
@d pdf_link_objnum(#)      == vmem(# + 7).int {object number of corresponding object}

@# {types of actions}
@d pdf_action_page         == 0 {GoTo action}
@d pdf_action_goto         == 1 {GoTo action}
@d pdf_action_thread       == 2 {Thread action}
@d pdf_action_user         == 3 {user-defined action}

@# {data structure of actions}
@d pdf_action_size         == 4 {size of action structure in |mem|}
@d action_node         == 45
@d pdf_action_type(#)      == type(#+1) {action type}
@d pdf_action_named_id(#)  == subtype(#+1) {identifier is type of name}
@d pdf_action_id(#)        == vlink(#+1) {destination/thread name identifier}
@d pdf_action_file(#)      == vinfo(# + 2) {file name for external action}
@d pdf_action_new_window(#) == vlink(# + 2) {open a new window?}
@d pdf_action_tokens(#)    == vinfo(# + 3) {specification of GoTo page or user action}
@d pdf_action_refcount(#)  == vlink(# + 3) {counter of references to this action}

@# {data structure of outlines; it's not able to write out outline entries
before all outline entries are defined, so memory allocated for outline
entries can't not be deallocated and will stay in memory. For this reason we
will store data of outline entries in |pdf_mem| instead of |mem|}

@d pdfmem_outline_size     == 8 {size of memory in |pdf_mem| which
|obj_outline_ptr| points to}
@d obj_outline_count        == obj_info{count of all opened children}
@d obj_outline_ptr          == obj_aux {pointer to |pdf_mem|}
@d obj_outline_title(#)     == pdf_mem[obj_outline_ptr(#)]
@d obj_outline_parent(#)    == pdf_mem[obj_outline_ptr(#) + 1]
@d obj_outline_prev(#)      == pdf_mem[obj_outline_ptr(#) + 2]
@d obj_outline_next(#)      == pdf_mem[obj_outline_ptr(#) + 3]
@d obj_outline_first(#)     == pdf_mem[obj_outline_ptr(#) + 4]
@d obj_outline_last(#)      == pdf_mem[obj_outline_ptr(#) + 5]
@d obj_outline_action_objnum(#) == pdf_mem[obj_outline_ptr(#) + 6] {object number of
action}
@d obj_outline_attr(#)      == pdf_mem[obj_outline_ptr(#) + 7]

@# {types of destinations}
@d pdf_dest_xyz             == 0
@d pdf_dest_fit             == 1
@d pdf_dest_fith            == 2
@d pdf_dest_fitv            == 3
@d pdf_dest_fitb            == 4
@d pdf_dest_fitbh           == 5
@d pdf_dest_fitbv           == 6
@d pdf_dest_fitr            == 7

@# {data structure of destinations}
@d obj_dest_ptr             == obj_aux {pointer to |pdf_dest_node|}
@d pdf_dest_node_size       == 8 {size of whatsit node for destination;
words |1..4| hold dest dimensions, word |6| identifier type, subtype
and identifier of destination, word |6| the corresponding object number}
@d pdf_dest_type(#)          == type(# + 6) {type of destination}
@d pdf_dest_named_id(#)      == subtype(# + 6) {is named identifier?}
@d pdf_dest_id(#)            == vlink(# + 6) {destination identifier}
@d pdf_dest_xyz_zoom(#)      == vinfo(# + 7) {zoom factor for |destxyz| destination}
@d pdf_dest_objnum(#)        == vlink(# + 7) {object number of corresponding
object}

@# {data structure of threads; words 1..4 represent the coordinates of the
    corners}
@d pdf_thread_node_size      == 8
@d pdf_thread_named_id(#)    == subtype(# + 6) {is a named identifier}
@d pdf_thread_id(#)          == vlink(# + 6) {thread identifier}
@d pdf_thread_attr(#)        == vinfo(# + 7) {attributes of thread}
@d obj_thread_first          == obj_aux {pointer to the first bead}

@# {data structure of beads}
@d pdfmem_bead_size         == 5 {size of memory in |pdf_mem| which
                                  |obj_bead_ptr| points to}
@d obj_bead_ptr             == obj_aux {pointer to |pdf_mem|}
@d obj_bead_rect(#)         == pdf_mem[obj_bead_ptr(#)]
@d obj_bead_page(#)         == pdf_mem[obj_bead_ptr(#) + 1]
@d obj_bead_next(#)         == pdf_mem[obj_bead_ptr(#) + 2]
@d obj_bead_prev(#)         == pdf_mem[obj_bead_ptr(#) + 3]
@d obj_bead_attr(#)         == pdf_mem[obj_bead_ptr(#) + 4]
@d obj_bead_data            == obj_bead_rect {pointer to the corresponding
whatsit node; |obj_bead_rect| is needed only when the bead rectangle has
been written out and after that |obj_bead_data| is not needed any more
so we can use this field for both}

@<Constants...@>=
@!inf_obj_tab_size = 1000; {min size of the cross-reference table for PDF output}
@!sup_obj_tab_size = 8388607; {max size of the cross-reference table for PDF output}
@!inf_dest_names_size = 1000; {min size of the destination names table for PDF output}
@!sup_dest_names_size = 131072; {max size of the destination names table for PDF output}
@!inf_pk_dpi = 72; {min PK pixel density value from \.{texmf.cnf}}
@!sup_pk_dpi = 8000; {max PK pixel density value from \.{texmf.cnf}}
@!pdf_objtype_max = head_tab_max;

@ @<Glob...@>=
@!obj_tab_size:integer;
@!obj_tab:^obj_entry;
@!head_tab: array[1..head_tab_max] of integer;
@!pages_tail: integer;
@!obj_ptr: integer; {user objects counter}
@!sys_obj_ptr: integer; {system objects counter, including object streams}
@!pdf_last_pages: integer; {pointer to most recently generated pages object}
@!pdf_last_page: integer; {pointer to most recently generated page object}
@!pdf_last_stream: integer; {pointer to most recently generated stream}
@!pdf_stream_length: integer; {length of most recently generated stream}
@!pdf_stream_length_offset: integer; {file offset of the last stream length}
@!pdf_seek_write_length: boolean; {flag whether to seek back and write \.{/Length}}
@!pdf_last_byte: integer; {byte most recently written to PDF file; for \.{endstream} in new line}
@!pdf_append_list_arg: integer; {for use with |pdf_append_list|}
@!ff: integer; {for use with |set_ff|}
@!pdf_box_spec_media: integer;
@!pdf_box_spec_crop: integer;
@!pdf_box_spec_bleed: integer;
@!pdf_box_spec_trim: integer;
@!pdf_box_spec_art: integer;

@ @<Set init...@>=
obj_ptr := 0;
sys_obj_ptr := 0;
obj_tab_size := inf_obj_tab_size; {allocated size of |obj_tab| array}
dest_names_size := inf_dest_names_size; {allocated size of |dest_names| array}
for k := 1 to head_tab_max do
    head_tab[k] := 0;
pdf_box_spec_media  := 1;
pdf_box_spec_crop   := 2;
pdf_box_spec_bleed  := 3;
pdf_box_spec_trim   := 4;
pdf_box_spec_art    := 5;

@ Here we implement subroutines for work with objects and related things.
Some of them are used in former parts too, so we need to declare them
forward.

@d pdf_append_list_end(#) == # := append_ptr(#, pdf_append_list_arg); end
@d pdf_append_list(#) == begin pdf_append_list_arg := #; pdf_append_list_end
@d set_ff(#) == begin
    if pdf_font_num(#) < 0 then
        ff := -pdf_font_num(#)
    else
        ff := #;
end

@<Declare procedures that need to be declared forward for \pdfTeX@>=
procedure append_dest_name(s: str_number; n: integer);
var a: integer;
begin
    if pdf_dest_names_ptr = sup_dest_names_size then
        overflow("number of destination names (dest_names_size)", dest_names_size);
    if pdf_dest_names_ptr = dest_names_size then begin
        a := 0.2 * dest_names_size;
        if dest_names_size < sup_dest_names_size - a then
            dest_names_size := dest_names_size + a
        else
            dest_names_size := sup_dest_names_size;
        dest_names := xreallocarray(dest_names, dest_name_entry, dest_names_size);
    end;
    dest_names[pdf_dest_names_ptr].objname := s;
    dest_names[pdf_dest_names_ptr].objnum := n;
    incr(pdf_dest_names_ptr);
end;

procedure pdf_create_obj(t, i: integer); {create an object with type |t| and
identifier |i|}
label done;
var a, p, q: integer;
begin
    if sys_obj_ptr = sup_obj_tab_size then
        overflow("indirect objects table size", obj_tab_size);
    if sys_obj_ptr = obj_tab_size then begin
        a := 0.2 * obj_tab_size;
        if obj_tab_size < sup_obj_tab_size - a then
            obj_tab_size := obj_tab_size + a
        else
            obj_tab_size := sup_obj_tab_size;
        obj_tab := xreallocarray(obj_tab, obj_entry, obj_tab_size);
    end;
    incr(sys_obj_ptr);
    obj_ptr := sys_obj_ptr;
    obj_info(obj_ptr) := i;
    obj_offset(obj_ptr) := 0;
    obj_aux(obj_ptr) := 0;
    avl_put_obj(obj_ptr, t);
    if t = obj_type_page then begin
        p := head_tab[t];
        {find the right position to insert newly created object}@/
        if (p = 0) or (obj_info(p) < i) then begin
            obj_link(obj_ptr) := p;
            head_tab[t] := obj_ptr;
        end
        else begin
            while p <> 0 do begin
                if obj_info(p) < i then
                    goto done;
                q := p;
                p := obj_link(p);
            end;
done:
            obj_link(q) := obj_ptr;
            obj_link(obj_ptr) := p;
        end;
    end
    else if t <> obj_type_others then begin
        obj_link(obj_ptr) := head_tab[t];
        head_tab[t] := obj_ptr;
        if (t = obj_type_dest) and (i < 0) then
            append_dest_name(-obj_info(obj_ptr), obj_ptr);
    end;
end;

function pdf_new_objnum: integer; {create a new object and return its number}
begin
    pdf_create_obj(obj_type_others, 0);
    pdf_new_objnum := obj_ptr;
end;

procedure pdf_os_switch(pdf_os: boolean); {switch between PDF stream and object stream mode}
begin
    if pdf_os and pdf_os_enable then begin
        if not pdf_os_mode then begin {back up PDF stream variables}
            pdf_op_ptr := pdf_ptr;
            pdf_ptr := pdf_os_ptr;
            pdf_buf := pdf_os_buf;
            pdf_buf_size := pdf_os_buf_size;
            pdf_os_mode := true; {switch to object stream}
        end;
    end else begin
        if pdf_os_mode then begin {back up object stream variables}
            pdf_os_ptr := pdf_ptr;
            pdf_ptr := pdf_op_ptr;
            pdf_buf := pdf_op_buf;
            pdf_buf_size := pdf_op_buf_size;
            pdf_os_mode := false; {switch to PDF stream}
        end;
    end;
end;

procedure pdf_os_prepare_obj(i: integer; pdf_os_level: integer); {create new \.{/ObjStm} object
if required, and set up cross reference info}
begin
    pdf_os_switch((pdf_os_level > 0) and (fixed_pdf_objcompresslevel >= pdf_os_level));
    if pdf_os_mode then begin
        if pdf_os_cur_objnum = 0 then begin
            pdf_os_cur_objnum := pdf_new_objnum;
            decr(obj_ptr); {object stream is not accessible to user}
            incr(pdf_os_cntr); {only for statistics}
            pdf_os_objidx := 0;
            pdf_ptr := 0; {start fresh object stream}
        end else
            incr(pdf_os_objidx);
        obj_os_idx(i) := pdf_os_objidx;
        obj_offset(i) := pdf_os_cur_objnum;
        pdf_os_objnum[pdf_os_objidx] := i;
        pdf_os_objoff[pdf_os_objidx] := pdf_ptr;
    end else begin
        obj_offset(i) := pdf_offset;
        obj_os_idx(i) := -1; {mark it as not included in object stream}
    end;
end;

procedure pdf_begin_obj(i: integer; pdf_os_level: integer); {begin a PDF object}
begin
    check_pdfminorversion;
    pdf_os_prepare_obj(i, pdf_os_level);
    if not pdf_os_mode then begin
        pdf_print_int(i);
        pdf_print_ln(" 0 obj");
    end else if pdf_compress_level = 0 then begin
        pdf_print("% "); {debugging help}
        pdf_print_int(i);
        pdf_print_ln(" 0 obj");
    end;
end;

procedure pdf_new_obj(t, i: integer; pdf_os: integer); {begin a new PDF object}
begin
    pdf_create_obj(t, i);
    pdf_begin_obj(obj_ptr, pdf_os);
end;

procedure pdf_end_obj; {end a PDF object}
begin
    if pdf_os_mode then begin
        if pdf_os_objidx = pdf_os_max_objs - 1 then
            pdf_os_write_objstream;
    end else
        pdf_print_ln("endobj"); {end a PDF object}
end;

procedure pdf_begin_dict(i: integer; pdf_os_level: integer); {begin a PDF dictionary object}
begin
    check_pdfminorversion;
    pdf_os_prepare_obj(i, pdf_os_level);
    if not pdf_os_mode then begin
        pdf_print_int(i);
        pdf_print(" 0 obj ");
    end else if pdf_compress_level = 0 then begin
        pdf_print("% "); {debugging help}
        pdf_print_int(i);
        pdf_print_ln(" 0 obj");
    end;
    pdf_print_ln("<<");
end;

procedure pdf_new_dict(t, i: integer; pdf_os: integer); {begin a new PDF dictionary object}
begin
    pdf_create_obj(t, i);
    pdf_begin_dict(obj_ptr, pdf_os);
end;

procedure pdf_end_dict; {end a PDF dictionary object}
begin
    if pdf_os_mode then begin
        pdf_print_ln(">>");
        if pdf_os_objidx = pdf_os_max_objs - 1 then
            pdf_os_write_objstream;
    end else
        pdf_print_ln(">> endobj");
end;

@ Write out an accumulated object stream.
First the object number and byte offset pairs are generated
and appended to the ready buffered object stream.
By this the value of \.{/First} can be calculated.
Then a new \.{/ObjStm} object is generated, and everything is
copied to the PDF output buffer, where also compression is done.
When calling this procedure, |pdf_os_mode| must be |true|.

@<Declare procedures that need to be declared forward for \pdfTeX@>=
procedure pdf_os_write_objstream;
var i, j, p, q: pointer;
begin
    if pdf_os_cur_objnum = 0 then {no object stream started}
        return;
    p := pdf_ptr;
    i := 0;
    j := 0;
    while i <= pdf_os_objidx do begin {assemble object number and byte offset pairs}
        pdf_print_int(pdf_os_objnum[i]);
        pdf_print(" ");
        pdf_print_int(pdf_os_objoff[i]);
        if j = 9 then begin {print out in groups of ten for better readability}
            pdf_out(pdf_new_line_char);
            j := 0;
        end else begin
            pdf_print(" ");
            incr(j);
        end;
        incr(i);
    end;
    pdf_buf[pdf_ptr - 1] := pdf_new_line_char; {no risk of flush, as we are in |pdf_os_mode|}
    q := pdf_ptr;
    pdf_begin_dict(pdf_os_cur_objnum, 0); {switch to PDF stream writing}
    pdf_print_ln("/Type /ObjStm");
    pdf_print("/N ");
    pdf_print_int_ln(pdf_os_objidx + 1);
    pdf_print("/First ");
    pdf_print_int_ln(q - p);
    pdf_begin_stream;
    pdf_room(q - p); {should always fit into the PDF output buffer}
    i := p;
    while i < q do begin {write object number and byte offset pairs}
        pdf_quick_out(pdf_os_buf[i]);
        incr(i);
    end;
    i := 0;
    while i < p do begin
        q := i + pdf_buf_size;
        if q > p then q := p;
        pdf_room(q - i);
        while i < q do begin {write the buffered objects}
            pdf_quick_out(pdf_os_buf[i]);
            incr(i);
        end;
    end;
    pdf_end_stream;
    pdf_os_cur_objnum := 0; {to force object stream generation next time}
end;

@ @<Declare procedures that need to be declared forward for \pdfTeX@>=
function append_ptr(p: pointer; i: integer): pointer; {appends a pointer with
info |i| to the end of linked list with head |p|}
var q: pointer;
begin
    append_ptr := p;
    fast_get_avail(q);
    info(q) := i;
    link(q) := null;
    if p = null then begin
        append_ptr := q;
        return;
    end;
    while link(p) <> null do
        p := link(p);
    link(p) := q;
end;

function pdf_lookup_list(p: pointer; i: integer): pointer; {looks up for pointer
with info |i| in list |p|}
begin
    pdf_lookup_list := null;
    while p <> null do begin
        if info(p) = i then begin
            pdf_lookup_list := p;
            return;
        end;
        p := link(p);
    end;
end;

@ @<Glob...@>=
@!pdf_image_procset: integer; {collection of image types used in current page/form}
@!pdf_text_procset: boolean; {mask of used ProcSet's in the current page/form}

@ Subroutines to print out various PDF objects

@p procedure pdf_print_fw_int(n, w: integer); {print out an integer with
fixed width; used for outputting cross-reference table}
var k: integer; {$0\le k\le23$}
begin
    k := 0;
    repeat dig[k] := n mod 10; n := n div 10; incr(k);
    until k = w;
    pdf_room(k);
    while k > 0 do begin
        decr(k);
        pdf_quick_out("0" + dig[k]);
    end;
end;

procedure pdf_out_bytes(n, w: integer); {print out an integer as
a number of bytes; used for outputting \.{/XRef} cross-reference stream}
var k: integer;
byte: array[0..3] of integer; {digits in a number being output}
begin
    k := 0;
    repeat byte[k] := n mod 256; n := n div 256; incr(k);
    until k = w;
    pdf_room(k);
    while k > 0 do begin
        decr(k);
        pdf_quick_out(byte[k]);
    end;
end;

procedure pdf_int_entry(s: str_number; v: integer); {print out an entry in
dictionary with integer value to PDF buffer}
begin
    pdf_out("/");
    pdf_print(s);
    pdf_out(" ");
    pdf_print_int(v);
end;

procedure pdf_int_entry_ln(s: str_number; v: integer);
begin
    pdf_int_entry(s, v);
    pdf_print_nl;
end;

procedure pdf_indirect(s: str_number; o: integer); {print out an indirect
entry in dictionary}
begin
    pdf_out("/");
    pdf_print(s);
    pdf_out(" ");
    pdf_print_int(o);
    pdf_print(" 0 R");
end;

procedure pdf_indirect_ln(s: str_number; o: integer);
begin
    pdf_indirect(s, o);
    pdf_print_nl;
end;

procedure pdf_print_str_ln(s: str_number); {print out |s| as string in PDF
output}
begin
    pdf_print_str(s);
    pdf_print_nl;
end;

procedure pdf_str_entry(s, v: str_number); {print out an entry in
dictionary with string value to PDF buffer}
begin
    if v = 0 then
        return;
    pdf_out("/");
    pdf_print(s);
    pdf_out(" ");
    pdf_print_str(v);
end;

procedure pdf_str_entry_ln(s, v: str_number);
begin
    if v = 0 then
        return;
    pdf_str_entry(s, v);
    pdf_print_nl;
end;

@* \[32e] Font processing.

As \pdfTeX{} should also act as a back-end driver, it needs to support virtual
fonts too. Information about virtual fonts can be found in the source of some
\.{DVI}-related programs.

Whenever we want to write out a character in a font to PDF output, we
should check whether the used character is a virtual or read character.
The |has_packet()| C macro checks for this condition. 

@ The following code typesets a character to PDF output.

@p procedure output_one_char(ffi:internal_font_number;c:integer);
begin
  if has_packet(ffi,c) then 
      do_vf_packet(ffi, c)
  else begin
      pdf_begin_string(ffi);
      pdf_print_char(ffi, c);
      adv_char_width(ffi, c);
  end;
end;

@ @<Declare procedures that need to be declared forward for \pdfTeX@>=
procedure pdf_check_vf_cur_val; forward;
procedure pdf_create_font_obj; forward;
procedure pdf_init_font_cur_val; forward;
procedure scan_pdf_ext_toks; forward;

@ Here come some subroutines to deal with expanded fonts for HZ-algorithm.

@d set_char_and_font(#) ==
if is_char_node(#) then begin
    c := character(#);
    f := font(#);
end

@p
function get_default_hyphen_char:integer;
begin
	get_default_hyphen_char:=default_hyphen_char; 
end;
@#
function get_default_skew_char:integer;
begin
	get_default_skew_char:=default_skew_char; 
end;
@#

procedure copy_expand_params(k, f: internal_font_number; e: integer);
{set expansion-related parameters for an expanded font |k|, based on the base
font |f| and the expansion amount |e|}
begin
    set_pdf_font_expand_ratio(k,e);
    set_pdf_font_step(k,pdf_font_step(f));
    set_pdf_font_auto_expand(k, pdf_font_auto_expand(f));
    set_pdf_font_blink(k,f);
end;

function tfm_lookup(s: str_number; fs: scaled): internal_font_number;
{looks up for a TFM with name |s| loaded at |fs| size; if found then flushes |s|}
label exit;
var k: internal_font_number;
begin
    if fs <> 0 then begin
        for k := 1 to max_font_id do
            if cmp_font_name(k, s) and (font_size(k) = fs) then begin
                flush_str(s);
                tfm_lookup := k;
                return;
            end;
    end
    else begin
        for k := 1 to max_font_id do
            if cmp_font_name(k, s) then begin
	            flush_string; {|font_name|}
                flush_str(s);
                tfm_lookup := k;
                return;
            end else flush_string;
    end;
    tfm_lookup := null_font;
exit:
end;

function load_expand_font(f: internal_font_number; e: integer): internal_font_number;
{loads font |f| expanded by |e| thousandths into font memory; |e| is nonzero
and is a multiple of |pdf_font_step(f)|}
label found;
var s: str_number; {font name}
    k: internal_font_number;
begin
    s := expand_font_name(f, e);
    k := tfm_lookup(s, font_size(f));
    if k = null_font then begin
        if pdf_font_auto_expand(f) then begin
            k := auto_expand_font(f, e);
	        font_id_text(k) := font_id_text(f);
            end
        else
           k := read_font_info(null_cs, s, "", font_size(f), font_natural_dir(f)); 
    end;
    copy_expand_params(k, f, e);
    load_expand_font := k;
end;

function fix_expand_value(f: internal_font_number; e: integer): integer;
{return the multiple of |pdf_font_step(f)| that is nearest to |e|}
var step: integer;
    max_expand: integer;
    neg: boolean;
begin
    fix_expand_value := 0;
    if e = 0 then
        return;
    if e < 0 then begin
        e := -e;
        neg := true;
        max_expand := -pdf_font_expand_ratio(pdf_font_shrink(f));
    end
    else begin
        neg := false;
        max_expand := pdf_font_expand_ratio(pdf_font_stretch(f));
    end;
    if e > max_expand then
        e :=  max_expand
    else begin
        step := pdf_font_step(f);
        if e mod step > 0 then
            e := step*round_xn_over_d(e, 1, step);
    end;
    if neg then
        e := -e;
    fix_expand_value := e;
end;

function get_expand_font(f: internal_font_number; e: integer): internal_font_number;
{look up and create if not found an expanded version of |f|; |f| is an
expandable font; |e| is nonzero and is a multiple of |pdf_font_step(f)|}
var k: internal_font_number;
begin
    k := pdf_font_elink(f);
    while k <> null_font do begin
        if pdf_font_expand_ratio(k) = e then begin
            get_expand_font := k;
            return;
        end;
        k := pdf_font_elink(k);
    end;
    k := load_expand_font(f, e);
    set_pdf_font_elink(k,pdf_font_elink(f));
    set_pdf_font_elink(f,k);
    {|wterm_ln('get_expand_font ', e:1, ': ',f:1, ' became ', k:1);|}
    get_expand_font := k;
end;

function expand_font(f: internal_font_number; e: integer): internal_font_number;
{looks up for font |f| expanded by |e| thousandths, |e| is an arbitrary value
between max stretch and max shrink of |f|; if not found then creates it}
begin
    expand_font := f;
    if e = 0 then
        return;
    e := fix_expand_value(f, e);
    if e = 0 then
        return;
    if pdf_font_elink(f) = null_font then
        pdf_error("font expansion", "uninitialized pdf_font_elink");
    expand_font := get_expand_font(f, e);
end;

procedure set_expand_params(f: internal_font_number; auto_expand: boolean;
                            font_stretch, font_shrink, font_step, expand_ratio: integer);
{expand a font with given parameters}
begin
    set_pdf_font_step(f, font_step);
    set_pdf_font_auto_expand(f, auto_expand);
    if font_stretch > 0 then
        set_pdf_font_stretch(f,get_expand_font(f, font_stretch));
    if font_shrink > 0 then
        set_pdf_font_shrink(f, get_expand_font(f, -font_shrink));
    if expand_ratio <> 0 then
        set_pdf_font_expand_ratio(f,expand_ratio);
end;

procedure read_expand_font; {read font expansion spec and load expanded font}
var font_shrink, font_stretch, font_step: integer;
    f: internal_font_number;
    auto_expand: boolean;
begin
    {read font expansion parameters}
    scan_font_ident;
    f := cur_val;
    if f = null_font then
        pdf_error("font expansion", "invalid font identifier");
    if pdf_font_blink(f) <> null_font then
        pdf_error("font expansion", "\pdffontexpand cannot be used this way (the base font has been expanded or letter-spaced)");
    scan_optional_equals;
    scan_int;
    font_stretch := fix_int(cur_val, 0, 1000);
    scan_int;
    font_shrink := fix_int(cur_val, 0, 500);
    scan_int;
    font_step := fix_int(cur_val, 0, 100);
    if font_step = 0 then
        pdf_error("font expansion", "invalid step");
    font_stretch := font_stretch - font_stretch mod font_step;
    if font_stretch < 0 then
        font_stretch := 0;
    font_shrink := font_shrink - font_shrink mod font_step;
    if font_shrink < 0 then
        font_shrink := 0;
    if (font_stretch = 0) and (font_shrink = 0) then
        pdf_error("font expansion", "invalid limit(s)");
    auto_expand := false;
    if scan_keyword("autoexpand") then begin
        auto_expand := true;
        @<Scan an optional space@>; 
    end;

    {check if the font can be expanded}
    if (pdf_font_expand_ratio(f) <> 0) then
        pdf_error("font expansion", "this font has been expanded by another font so it cannot be used now");
    if (pdf_font_step(f) <> 0) then
    {this font has been expanded, ensure the expansion parameters are identical}
    begin
        if (pdf_font_step(f) <> font_step) or
           ((pdf_font_stretch(f) = null_font) and (font_stretch <> 0)) or
           ((pdf_font_stretch(f) <> null_font) and
            (pdf_font_expand_ratio(pdf_font_stretch(f)) <> font_stretch)) or
           ((pdf_font_shrink(f) = null_font) and (font_shrink <> 0)) or
           ((pdf_font_shrink(f) <> null_font) and
            (pdf_font_expand_ratio(pdf_font_shrink(f)) <> -font_shrink)) or
           (pdf_font_auto_expand(f) <> auto_expand)
        then
            pdf_error("font expansion", "font has been expanded with different parameters");
    end
    else begin
        if font_used(f) then
            pdf_warning("font expansion", "font should be expanded before its first use",
                        true, true);
        set_expand_params(f, auto_expand, font_stretch, font_shrink, font_step, 0);
        if font_type(f) = virtual_font_type then
            vf_expand_local_fonts(f);
    end;
end;

procedure new_letterspaced_font(a: small_number);
{letter-space a font by creating a virtual font}
var u:pointer; {user's font identifier}
@!t:str_number; {name for the frozen font identifier}
@!old_setting:0..max_selector; {holds |selector| setting}
@!f, k:internal_font_number;
begin
    get_r_token; u:=cur_cs;
    if u>=hash_base then t:=text(u)
    else if u=null_cs then t:="FONT"
    else  begin old_setting:=selector; selector:=new_string;
      print("FONT"); print(u-active_base); selector:=old_setting;
    @.FONTx@>
      str_room(1); t:=make_string;
      end;
    define(u,set_font,null_font); scan_optional_equals; scan_font_ident;
    k := cur_val;
    scan_int;
    f := letter_space_font(u, k, fix_int(cur_val, -1000, 1000));
    equiv(u):=f; eqtb[font_id_base+f]:=eqtb[u]; font_id_text(f):=t;
end;

@ We need to hold information about used characters in each font for partial
downloading.

@<Types...@>=
char_map_array = array[0..32] of eight_bits; {move chars in range 0..32}
fm_entry_ptr = ^integer;

@ @<Glob...@>=
@!pdf_font_list: pointer; {list of used fonts in current page}
@!pdf_resname_prefix: str_number; {global prefix of resources name}
@!last_tokens_string: str_number; {the number of the most recently string
created by |tokens_to_string|}

@ @<Set init...@>=
pdf_resname_prefix := 0;
last_tokens_string := 0;

@ Reading VF files is done in C, using the procedure |do_vf()|

@* \[32f] PDF shipping out.
To ship out a \TeX\ box to PDF page description we need to implement
|pdf_hlist_out|, |pdf_vlist_out| and |pdf_ship_out|, which are equivalent to
the \TeX' original |hlist_out|, |vlist_out| and |ship_out| resp. But first we
need to declare some procedures needed in |pdf_hlist_out| and |pdf_vlist_out|.

@<Declare procedures needed in |pdf_hlist_out|, |pdf_vlist_out|@>=
procedure pdf_out_literal(p:pointer);
var old_setting:0..max_selector; {holds print |selector|}
    s: str_number;
begin
    old_setting:=selector; selector:=new_string;
    show_token_list(link(pdf_literal_data(p)),null,pool_size-pool_ptr);
    selector:=old_setting;
    s := make_string;
    literal(s, pdf_literal_mode(p), false);
    flush_str(s);
end;

procedure pdf_out_colorstack(p:pointer);
var old_setting: 0..max_selector; {holds print |selector|}
    s: str_number;
    cmd: integer;
    stack_no: integer;
    literal_mode: integer;
begin
    cmd := pdf_colorstack_cmd(p);
    stack_no := pdf_colorstack_stack(p);
    literal_mode := 0;
    if stack_no >= colorstackused then begin
        print_nl("");
        print("Color stack ");
        print_int(stack_no);
        print(" is not initialized for use!");
        print_nl("");
        return;
    end;
    case cmd of
    colorstack_set, colorstack_push: begin
        old_setting:=selector; selector:=new_string;
        show_token_list(link(pdf_colorstack_data(p)),null,pool_size-pool_ptr);
        selector:=old_setting;
        s := make_string;
        if cmd = colorstack_set then
            literal_mode := colorstackset(stack_no, s)
        else
            literal_mode := colorstackpush(stack_no, s);
        if length(s) > 0 then
            literal(s, literal_mode, false);
        flush_str(s);
        return;
    end;
    colorstack_pop: literal_mode := colorstackpop(stack_no);
    colorstack_current: literal_mode := colorstackcurrent(stack_no);
    othercases do_nothing
    endcases;
    if cur_length > 0 then begin
        s := make_string;
        literal(s, literal_mode, false);
        flush_str(s);
    end
end;

procedure pdf_out_colorstack_startpage;
var i: integer;
    max: integer;
    start_status: integer;
    literal_mode: integer;
    s: str_number;
begin
    i := 0;
    max := colorstackused;
    while i < max do begin
        start_status := colorstackskippagestart(i);
        if start_status = 0 then begin
            literal_mode := colorstackcurrent(i);
            if cur_length > 0 then begin
                s := make_string;
                literal(s, literal_mode, false);
                flush_str(s);
            end;
        end;
        incr(i);
    end;
end;

procedure pdf_out_setmatrix(p:pointer);
var old_setting:0..max_selector; {holds print |selector|}
    s: str_number;
begin
    old_setting:=selector; selector:=new_string;
    show_token_list(link(pdf_setmatrix_data(p)),null,pool_size-pool_ptr);
    selector:=old_setting;
    str_room(7);
    str_pool[pool_ptr] := 0; { make C string for pdfsetmatrix }
    pdfsetmatrix(str_start[str_ptr], cur_h, cur_page_height - cur_v);
    str_room(7);
    append_char(" ");
    append_char("0");
    append_char(" ");
    append_char("0");
    append_char(" ");
    append_char("c");
    append_char("m");
    s := make_string;
    literal(s, set_origin, false);
    flush_str(s);
end;

procedure pdf_out_save;
begin
    checkpdfsave(cur_h, cur_v);
    literal("q", set_origin, false);
end;

procedure pdf_out_restore;
begin
    checkpdfrestore(cur_h, cur_v);
    literal("Q", set_origin, false);
end;

procedure pdf_special(p: pointer);
var old_setting:0..max_selector; {holds print |selector|}
    s: str_number;
begin
    old_setting:=selector; selector:=new_string;
    show_token_list(link(write_tokens(p)),null,pool_size-pool_ptr);
    selector:=old_setting;
    s := make_string;
    literal(s, scan_special, true);
    flush_str(s);
end;

procedure do_late_lua(p: pointer);
var old_setting:0..max_selector; {holds print |selector|}
    s: str_number;
begin
    old_setting:=selector; selector:=new_string;
    show_token_list(link(late_lua_data(p)),null,pool_size-pool_ptr);
    selector:=old_setting;
    s := make_string;
    latelua(late_lua_reg(p), s);
    flush_str(s);
end;

procedure pdf_print_toks(p: pointer); {print tokens list |p|}
var s: str_number;
begin
    s := tokens_to_string(p);
    if length(s) > 0 then
        pdf_print(s);
    flush_str(s);
end;

procedure pdf_print_toks_ln(p: pointer); {print tokens list |p|}
var s: str_number;
begin
    s := tokens_to_string(p);
    if length(s) > 0 then begin
        pdf_print_ln(s);
    end;
    flush_str(s);
end;

@ Similiar to |vlist_out|, |pdf_vlist_out| needs to be declared forward

@p procedure@?pdf_vlist_out; forward;

@ The implementation of procedure |pdf_hlist_out| is similiar to |hlist_out|

@p @t\4@>@<Declare procedures needed in |pdf_hlist_out|, |pdf_vlist_out|@>@t@>@/

procedure pdf_hlist_out; {output an |hlist_node| box}
label move_past, fin_rule, next_p;
var base_line: scaled; {the baseline coordinate for this box}
c_wd,c_ht,c_dp: scaled;
  {the real width, height and depth of the character}
w: scaled; { temporary value for directional width calculation }
dir_nest: integer; { for tracking nested direction nodes }
edge_v: scaled;
edge_h: scaled;
effective_horizontal: scaled;
basepoint_horizontal: scaled;
basepoint_vertical: scaled;
saving_h: scaled;
saving_v: scaled;
save_direction: integer;
dvi_ptr,dir_ptr,dir_tmp:pointer;
@!left_edge: scaled; {the left coordinate for this box}
@!save_h: scaled; {what |cur_h| should pop to}
@!this_box: pointer; {pointer to containing box}
@!g_order: glue_ord; {applicable order of infinity for glue}
@!g_sign: normal..shrinking; {selects type of glue}
@!p,q:pointer; {current position in the hlist}
@!leader_box:pointer; {the leader box being replicated}
@!leader_wd:scaled; {width of leader box being replicated}
@!lx:scaled; {extra space between leader boxes}
@!outer_doing_leaders:boolean; {were we doing leaders?}
@!edge:scaled; {right edge of sub-box or leader space}
@!prev_p:pointer; {one step behind |p|}
@!glue_temp:real; {glue value before rounding}
@!cur_glue:real; {glue seen so far}
@!save_cur_glue:real; { saved version, for direction switch }
@!cur_g:scaled; {rounded equivalent of |cur_glue| times the glue ratio}
@!save_cur_g:scaled; { saved version, for direction switch }
@!i: small_number; {index to scan |pdf_link_stack|}
begin cur_g:=0; cur_glue:=float_constant(0);
this_box:=temp_ptr; g_order:=glue_order(this_box);
g_sign:=glue_sign(this_box); p:=list_ptr(this_box);
save_direction:=dvi_direction;
dvi_direction:=box_dir(this_box);
dvi_ptr:=0;  lx:=0;
@<DIR: Initialize |dir_ptr| for |ship_out|@>;
saving_h:=cur_h; saving_v:=cur_v;
incr(cur_s);
base_line:=cur_v;
left_edge:=cur_h;
prev_p:=this_box+list_offset;
@<Create link annotations for the current hbox if needed@>;
while p<>null do
    @<Output node |p| for |pdf_hlist_out| and move to the next node,
    maintaining the condition |cur_v=base_line|@>;
cur_h:=saving_h; cur_v:=saving_v;
decr(cur_s);
dvi_direction:=save_direction;
@<DIR: Reset |dir_ptr|@>;
end;

@ @<Create link annotations for the current hbox if needed@>=
for i := 1 to pdf_link_stack_ptr do begin
    pdfassert(is_running(pdf_width(pdf_link_stack[i].link_node)));
    if (pdf_link_stack[i].nesting_level = cur_s) then
        append_link(this_box, left_edge, base_line, i);
end

@ 

@d pdf_dvicmd_set(#)==output_one_char(f,#)
@d pdf_dvicmd_put(#)==output_one_char(f,#); cur_h:=cur_h-c_wd
@d pdf_dvicmd_right(#)==cur_h := cur_h + #
@d pdf_dvicmd_left(#)== cur_h := cur_h - #
@d pdf_dvicmd_down(#)== cur_v := cur_v - #
@d pdf_dvicmd_up(#)==   cur_v := cur_v + #
@d pdf_dvicmd_h(#)==case box_direction(dvi_direction) of
  dir_TL_: begin cur_h := cur_h + #;  end;
  dir_TR_: begin cur_h := cur_h - #;  end;
  dir_LT_: begin do_nothing; {if o=right1 then o:=down1 else o:=right1;}  end;
  dir_LB_: begin do_nothing; {if o=right1 then begin o:=down1; negate(w); end else o:=right1;} end;
  dir_BL_: begin do_nothing; {if o=down1 then negate(w); } end;
  dir_BR_: begin do_nothing; {  negate(w);} end;
  dir_RT_: begin do_nothing; {if o=right1 then o:=down1 else begin o:=right1; negate(w); end;} end;
  dir_RB_: begin do_nothing; {if o=right1 then o:=down1 else o:=right1;  negate(w);} end;
  end


@<Output node |p| for |pdf_hlist_out|...@>=
begin
if is_char_node(p) then 
  begin
  repeat f:=font(p); c:=character(p);
  ci := char_info_short (f,c);
  {|writeln('hlist_out: a char node ', c:1 , ' in font ',f:1);|}
  if is_valid_char(c) then begin
  if is_rotated(dvi_direction) then begin
    c_ht:=charinfo_width(ci) div 2;
    c_dp:=0;
    c_wd:=charinfo_height(ci)+charinfo_depth(ci);
    end
  else begin
    c_ht:=charinfo_height(ci);
    c_dp:=charinfo_depth(ci);
    c_wd:=charinfo_width(ci);
    end;
  if (font_natural_dir(f)<>-1) then
    case font_direction(dvi_direction) of
    dir__LT,dir__LB: begin
      if x_displace(p)<>0 then pdf_dvicmd_right(x_displace(p));
      if y_displace(p)<>0 then pdf_dvicmd_up(-y_displace(p));
      pdf_dvicmd_set(c);
      if x_displace(p)<>0 then pdf_dvicmd_left(x_displace(p)); 
      if y_displace(p)<>0 then pdf_dvicmd_down(-y_displace(p));
      end;
    dir__RT,dir__RB: begin
      if x_displace(p)<>0 then pdf_dvicmd_left(x_displace(p));
      if y_displace(p)<>0 then pdf_dvicmd_up(-y_displace(p));
      pdf_dvicmd_left(c_wd);
      pdf_dvicmd_put(c);
      if x_displace(p)<>0 then pdf_dvicmd_right(x_displace(p));
      if y_displace(p)<>0 then pdf_dvicmd_down(-y_displace(p));
      end;
    dir__TL,dir__TR: begin
      pdf_dvicmd_put(c);
      pdf_dvicmd_down(c_wd);
      end;
    dir__BL,dir__BR: begin
      pdf_dvicmd_put(c);
      pdf_dvicmd_up(c_wd);
      end;
    dir__LL,dir__LR: begin
      pdf_dvicmd_put(c);
      pdf_dvicmd_right(c_wd);
      end;
    dir__RL,dir__RR: begin
      pdf_dvicmd_put(c);
      pdf_dvicmd_left(c_wd);
      end;
    dir__TT,dir__TB: begin
      pdf_dvicmd_put(c);
      pdf_dvicmd_down(c_wd);
      end;
    dir__BT,dir__BB: begin
      pdf_dvicmd_put(c);
      pdf_dvicmd_up(c_wd);
      end;
    end
  else
    case font_direction(dvi_direction) of
    dir__LT: begin
	  if x_displace(p)<>0 then pdf_dvicmd_right(x_displace(p));
	  if y_displace(p)<>0 then pdf_dvicmd_up(-y_displace(p));
      pdf_dvicmd_set(c);
	  if x_displace(p)<>0 then pdf_dvicmd_left(x_displace(p));
	  if y_displace(p)<>0 then pdf_dvicmd_down(-y_displace(p));
      end;
    dir__LB: begin
      pdf_dvicmd_down(c_ht);
      pdf_dvicmd_set(c);
      pdf_dvicmd_up(c_ht);
      end;
    dir__RT: begin
	  if x_displace(p)<>0 then pdf_dvicmd_left(x_displace(p));
	  if y_displace(p)<>0 then pdf_dvicmd_up(-y_displace(p));
      pdf_dvicmd_left(c_wd);
      pdf_dvicmd_put(c);
	  if x_displace(p)<>0 then pdf_dvicmd_right(x_displace(p));
	  if y_displace(p)<>0 then pdf_dvicmd_down(-y_displace(p));
      end;
    dir__RB: begin
      pdf_dvicmd_left(c_wd);
      pdf_dvicmd_down(c_ht);
      pdf_dvicmd_put(c);
      pdf_dvicmd_up(c_ht);
      end;
    dir__TL: begin
      pdf_dvicmd_down(c_wd);
      pdf_dvicmd_left(c_ht);
      pdf_dvicmd_put(c);
      pdf_dvicmd_right(c_ht);
      end;
    dir__TR: begin
      pdf_dvicmd_down(c_wd);
      pdf_dvicmd_left(c_dp);
      pdf_dvicmd_put(c);
      pdf_dvicmd_right(c_dp);
      end;
    dir__BL: begin
      pdf_dvicmd_left(c_ht);
      pdf_dvicmd_put(c);
      pdf_dvicmd_right(c_ht);
      pdf_dvicmd_up(c_wd);
      end;
    dir__BR: begin
      pdf_dvicmd_left(c_dp);
      pdf_dvicmd_put(c);
      pdf_dvicmd_right(c_dp);
      pdf_dvicmd_up(c_wd);
      end;
    dir__LL,dir__LR: begin
      pdf_dvicmd_down(c_ht);
      pdf_dvicmd_put(c);
      pdf_dvicmd_up(c_ht);
      pdf_dvicmd_right(c_wd);
      end;
    dir__RL,dir__RR: begin
      pdf_dvicmd_left(c_wd);
      pdf_dvicmd_down(c_ht);
      pdf_dvicmd_put(c);
      pdf_dvicmd_up(c_ht);
      end;
    dir__TT,dir__TB: begin
      pdf_dvicmd_down(c_wd);
      pdf_dvicmd_left(c_ht);
      pdf_dvicmd_put(c);
      pdf_dvicmd_right(c_ht);
      end;
    dir__BT,dir__BB: begin
      pdf_dvicmd_left(c_ht);
      pdf_dvicmd_put(c);
      pdf_dvicmd_right(c_ht);
      pdf_dvicmd_up(c_wd);
      end;
    end;
    cur_h:=cur_h+c_wd;
  end
  else
    char_warning(f, c);
  prev_p:=p;
  p:=vlink(p);
  until not is_char_node(p);
  end
else @<Output the non-|char_node| |p| for |pdf_hlist_out|
    and move to the next node@>;
end

@ @<Output the non-|char_node| |p| for |pdf_hlist_out|...@>=
begin case type(p) of
hlist_node,vlist_node:@<(\pdfTeX) Output a box in an hlist@>;
disc_node: if vlink(no_break(p))<>null then begin
  q:=tail_of_list (vlink(no_break(p))); {TODO, this should be a tlink}
  vlink(q):=vlink(p);
  q:=vlink(no_break(p)); 
  vlink(no_break(p)):=null;
  vlink(p):=q; 
  end;
rule_node: begin 
  if not (dir_orthogonal(dir_primary[rule_dir(p)])(dir_primary[dvi_direction]))
    then begin
    rule_ht:=height(p); rule_dp:=depth(p); rule_wd:=width(p);
    end
  else begin
    rule_ht:=width(p) div 2;
    rule_dp:=width(p) div 2;
    rule_wd:=height(p)+depth(p);
    end;
  goto fin_rule;
  end;
whatsit_node: @<Output the whatsit node |p| in |pdf_hlist_out|@>;
glue_node: @<(\pdfTeX) Move right or output leaders@>;
margin_kern_node,kern_node: pdf_dvicmd_h(width(p));
math_node: pdf_dvicmd_h(surround(p));
othercases do_nothing
endcases;@/
goto next_p;
fin_rule: @<(\pdfTeX) Output a rule in an hlist@>;
move_past: pdf_dvicmd_h(rule_wd);
next_p:prev_p:=p; p:=vlink(p);
end

@ @<(\pdfTeX) Output a box in an hlist@>=
begin
if not (dir_orthogonal(dir_primary[box_dir(p)])(dir_primary[dvi_direction]))
  then begin
  effective_horizontal:=width(p);
  basepoint_vertical:=0;
  if dir_opposite(dir_secondary[box_dir(p)])(dir_secondary[dvi_direction]) then
    basepoint_horizontal:=width(p)
  else
    basepoint_horizontal:=0;
  end
else begin
  effective_horizontal:=height(p)+depth(p);
  if not (is_mirrored(box_dir(p))) then
    if dir_eq(dir_primary[box_dir(p)])(dir_secondary[dvi_direction]) then
      basepoint_horizontal:=height(p)
    else
      basepoint_horizontal:=depth(p)
  else
    if dir_eq(dir_primary[box_dir(p)])(dir_secondary[dvi_direction]) then
      basepoint_horizontal:=depth(p)
    else
      basepoint_horizontal:=height(p);
  if dir_eq(dir_secondary[box_dir(p)])(dir_primary[dvi_direction]) then
    basepoint_vertical:= -(width(p) div 2)
  else
    basepoint_vertical:= (width(p) div 2);
  end;
if not (is_mirrored(dvi_direction)) then
  basepoint_vertical := basepoint_vertical + shift_amount(p)
    {shift the box `down'}
else
  basepoint_vertical := basepoint_vertical - shift_amount(p);
    {shift the box `up'}
if list_ptr(p)=null then begin pdf_dvicmd_h(effective_horizontal); end
else begin
  temp_ptr:=p; 
  edge:=cur_h; pdf_dvicmd_h(basepoint_horizontal);
  edge_v:=cur_v; cur_v:=base_line + basepoint_vertical;
  if type(p)=vlist_node then pdf_vlist_out@+else pdf_hlist_out;
  cur_h:=edge; pdf_dvicmd_h(effective_horizontal);
  cur_v:=base_line;
  end
end

@ @<(\pdfTeX) Output a rule in an hlist@>=
if is_running(rule_ht) then rule_ht:=height(this_box);
if is_running(rule_dp) then rule_dp:=depth(this_box);
rule_ht:=rule_ht+rule_dp; {this is the rule thickness}
if (rule_ht>0)and(rule_wd>0) then {we don't output empty rules}
  begin cur_v:=base_line+rule_dp;
  case font_direction(dvi_direction) of
  dir__LT: begin
 	pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
    end;
  dir__LB: begin
    pdf_dvicmd_down(rule_ht);
	pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
    pdf_dvicmd_up(rule_ht);
    end;
  dir__RT: begin
    pdf_dvicmd_left(rule_wd);
  	pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
	pdf_dvicmd_right(rule_wd);
    end;
  dir__RB: begin
    pdf_dvicmd_left(rule_wd);
    pdf_dvicmd_down(rule_ht);
    pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
	pdf_dvicmd_left(rule_wd);
    pdf_dvicmd_up(rule_ht);
    end;
  dir__TL: begin
    pdf_dvicmd_down(rule_wd);
    pdf_dvicmd_left(rule_ht);
    pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
    end;
  dir__TR: begin
    pdf_dvicmd_down(rule_wd);
    pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
    pdf_dvicmd_left(rule_ht);
    end;
  dir__BL: begin
    pdf_dvicmd_left(rule_ht);
	pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
    pdf_dvicmd_up(rule_wd);
    end;
  dir__BR: begin
    pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
	pdf_dvicmd_left(rule_ht);
    pdf_dvicmd_up(rule_wd);
    end;
  end;
  {|cur_h:=cur_h+rule_wd;|}{|dir__RT| is corrected elsewhere}
  cur_v:=base_line;
  end

@ @<(\pdfTeX) Move right or output leaders@>=
begin g:=glue_ptr(p); rule_wd:=width(g)-cur_g;
if g_sign<>normal then
  begin if g_sign=stretching then
    begin if stretch_order(g)=g_order then
      begin cur_glue:=cur_glue+stretch(g);
      vet_glue(float(glue_set(this_box))*cur_glue);
@^real multiplication@>
      cur_g:=round(glue_temp);
      end;
    end
  else if shrink_order(g)=g_order then
      begin cur_glue:=cur_glue-shrink(g);
      vet_glue(float(glue_set(this_box))*cur_glue);
      cur_g:=round(glue_temp);
      end;
  end;
rule_wd:=rule_wd+cur_g;
if subtype(p)>=a_leaders then
  @<(\pdfTeX) Output leaders in an hlist, |goto fin_rule| if a rule
    or to |next_p| if done@>;
goto move_past;
end

@ @<(\pdfTeX) Output leaders in an hlist...@>=
begin leader_box:=leader_ptr(p);
if type(leader_box)=rule_node then
  begin rule_ht:=height(leader_box); rule_dp:=depth(leader_box);
  goto fin_rule;
  end;
if not (dir_orthogonal(dir_primary[box_dir(leader_box)])(dir_primary[dvi_direction]))
  then leader_wd:=width(leader_box)
else
  leader_wd:=height(leader_box)+depth(leader_box);
if (leader_wd>0)and(rule_wd>0) then
  begin
  edge:=cur_h+rule_wd;
  {TODO this double |case| is a hack, and not quite the proper
   solution, but it produces the correct output for |xleaders|
   in TRT mode, which is important for KASHIDAH fills.}
  case box_direction(dvi_direction) of
  dir_TR_,dir_RT_: begin
    edge:=cur_h;
    cur_h:=cur_h-rule_wd;
    end;
  end;
  @<Let |cur_h| be the position of the first box, and set |leader_wd+lx|
    to the spacing between corresponding parts of boxes@>;
  while cur_h+leader_wd<=edge do
    @<(\pdfTeX) Output a leader box at |cur_h|,
      then advance |cur_h| by |leader_wd+lx|@>;
  case box_direction(dvi_direction) of
  dir_TR_,dir_RT_: cur_h:=cur_h-rule_wd;
  end;
  goto next_p;
  end;
end

@ @<(\pdfTeX) Output a leader box at |cur_h|, ...@>=
begin
if not (dir_orthogonal(dir_primary[box_dir(leader_box)])(dir_primary[dvi_direction]))
  then begin
  basepoint_vertical:=0;
 if dir_opposite(dir_secondary[box_dir(leader_box)])(dir_secondary[dvi_direction]) then begin
    basepoint_horizontal:=width(leader_box)
    end
  else
    basepoint_horizontal:=0;
  end
else begin
  if not (is_mirrored(box_dir(leader_box))) then
    if dir_eq(dir_primary[box_dir(leader_box)])(dir_secondary[dvi_direction]) then
      basepoint_horizontal:=height(leader_box)
    else
      basepoint_horizontal:=depth(leader_box)
  else
    if dir_eq(dir_primary[box_dir(leader_box)])(dir_secondary[dvi_direction]) then
      basepoint_horizontal:=depth(leader_box)
    else
      basepoint_horizontal:=height(leader_box);
  if dir_eq(dir_secondary[box_dir(leader_box)])(dir_primary[dvi_direction]) then
    basepoint_vertical:= -(width(leader_box) div 2)
  else
    basepoint_vertical:= (width(leader_box) div 2);
  end;
if not (is_mirrored(dvi_direction)) then
  basepoint_vertical := basepoint_vertical + shift_amount(leader_box)
    {shift the box `down'}
else
  basepoint_vertical := basepoint_vertical - shift_amount(leader_box);
    {shift the box `up'}
temp_ptr:=leader_box;
edge_h:=cur_h; cur_h:=cur_h + basepoint_horizontal;
edge_v:=cur_v; cur_v:=base_line + basepoint_vertical;
outer_doing_leaders:=doing_leaders; doing_leaders:=true;
if type(leader_box)=vlist_node then pdf_vlist_out@+else pdf_hlist_out;
doing_leaders:=outer_doing_leaders;
cur_h:=edge_h+leader_wd+lx; cur_v:=base_line;
end

@ The |pdf_vlist_out| routine is similar to |pdf_hlist_out|, but a bit simpler.
@p procedure pdf_vlist_out; {output a |pdf_vlist_node| box}
label move_past, fin_rule, next_p;
var left_edge: scaled; {the left coordinate for this box}
@!top_edge: scaled; {the top coordinate for this box}
@!save_v: scaled; {what |cur_v| should pop to}
@!this_box: pointer; {pointer to containing box}
@!g_order: glue_ord; {applicable order of infinity for glue}
@!g_sign: normal..shrinking; {selects type of glue}
@!p:pointer; {current position in the vlist}
@!leader_box:pointer; {the leader box being replicated}
@!leader_ht:scaled; {height of leader box being replicated}
@!lx:scaled; {extra space between leader boxes}
@!outer_doing_leaders:boolean; {were we doing leaders?}
@!edge:scaled; {bottom boundary of leader space}
@!glue_temp:real; {glue value before rounding}
@!cur_glue:real; {glue seen so far}
@!cur_g:scaled; {rounded equivalent of |cur_glue| times the glue ratio}
@!save_direction: integer;
@!effective_vertical: scaled;
@!basepoint_horizontal: scaled;
@!basepoint_vertical: scaled;
@!edge_v: scaled;
@!saving_v: scaled;
@!saving_h: scaled;
begin cur_g:=0; cur_glue:=float_constant(0);
this_box:=temp_ptr; g_order:=glue_order(this_box);
g_sign:=glue_sign(this_box); p:=list_ptr(this_box);
{pdfassert(p<>0);}
saving_v:=cur_v; saving_h:=cur_h;
{|writeln(''); writeln('vlist_out: left edge: ', cur_h:1 , '');|}
save_direction:=dvi_direction;
dvi_direction:=box_dir(this_box);
incr(cur_s);
left_edge:=cur_h; cur_v:=cur_v-height(this_box); top_edge:=cur_v;
@<Create thread for the current vbox if needed@>;
while p<>null do
    @<Output node |p| for |pdf_vlist_out| and move to the next node,
    maintaining the condition |cur_h=left_edge|@>;
cur_v:=saving_v; cur_h:=saving_h;
decr(cur_s);
dvi_direction:=save_direction;
end;

@ @<Create thread for the current vbox if needed@>=
if (last_thread <> null) and is_running(pdf_thread_dp) and
    (pdf_thread_level = cur_s) then
    append_thread(this_box, left_edge, top_edge + height(this_box))

@ @<Output node |p| for |pdf_vlist_out|...@>=
begin if is_char_node(p) then confusion("pdfvlistout")
@:this can't happen pdfvlistout}{\quad pdfvlistout@>
else @<Output the non-|char_node| |p| for |pdf_vlist_out|@>;
next_p:p:=vlink(p);
end

@ @<Output the non-|char_node| |p| for |pdf_vlist_out|@>=
begin case type(p) of
hlist_node,vlist_node:@<(\pdfTeX) Output a box in a vlist@>;
rule_node: begin
  if not (dir_orthogonal(dir_primary[rule_dir(p)])(dir_primary[dvi_direction]))
    then begin
    rule_ht:=height(p); rule_dp:=depth(p); rule_wd:=width(p);
    end
  else begin
    rule_ht:=width(p) div 2;
    rule_dp:=width(p) div 2;
    rule_wd:=height(p)+depth(p);
    end;
  goto fin_rule;
  end;
whatsit_node: @<Output the whatsit node |p| in |pdf_vlist_out|@>;
glue_node: @<(\pdfTeX) Move down or output leaders@>;
kern_node:cur_v:=cur_v+width(p);
othercases do_nothing
endcases;@/
goto next_p;
fin_rule: @<(\pdfTeX) Output a rule in a vlist, |goto next_p|@>;
move_past: cur_v:=cur_v+rule_ht;
end

@ TODO: the direct test to switch between |width(p)| and |-width(p)|
is definately wrong, because it does not nest properly. But at least
it fixes a very obvious problem that otherwise occured with
\.{\\pardir TLT} in a document with \.{\\bodydir TRT}, and so it
will have to do for now.

@<(\pdfTeX) Output a box in a vlist@>=
begin
if not (dir_orthogonal(dir_primary[box_dir(p)])(dir_primary[dvi_direction]))
  then begin
  effective_vertical:=height(p)+depth(p);
  if (type(p)=hlist_node) and (is_mirrored(box_dir(p))) then
    basepoint_vertical:=depth(p)
  else
    basepoint_vertical:=height(p);
  if dir_opposite(dir_secondary[box_dir(p)])(dir_secondary[dvi_direction]) then begin
    if dvi_direction=dir_TL_ then
      basepoint_horizontal:=width(p) 
    else
      basepoint_horizontal:=-width(p);
    end
  else
    basepoint_horizontal:=0;
  end
else begin
  effective_vertical:=width(p);
  if not (is_mirrored(box_dir(p))) then
    if dir_eq(dir_primary[box_dir(p)])(dir_secondary[dvi_direction]) then
      basepoint_horizontal:=height(p)
    else
      basepoint_horizontal:=depth(p)
  else
    if dir_eq(dir_primary[box_dir(p)])(dir_secondary[dvi_direction]) then
      basepoint_horizontal:=depth(p)
    else
      basepoint_horizontal:=height(p);
  if dir_eq(dir_secondary[box_dir(p)])(dir_primary[dvi_direction]) then
    basepoint_vertical:=0
  else
    basepoint_vertical:=width(p);
  end;
basepoint_horizontal := basepoint_horizontal + shift_amount(p);
if list_ptr(p)=null then begin
  cur_v:=cur_v+effective_vertical;
  end
else  begin 
  edge_v:=cur_v;
  cur_h:=left_edge + basepoint_horizontal;
  cur_v:=cur_v + basepoint_vertical; 
  temp_ptr:=p;
  if type(p)=vlist_node then pdf_vlist_out@+else pdf_hlist_out;
  cur_h:=left_edge; cur_v:=edge_v + effective_vertical;
  end
end

@ @<(\pdfTeX) Output a rule in a vlist...@>=
if is_running(rule_wd) then rule_wd:=width(this_box);
rule_ht:=rule_ht+rule_dp; {this is the rule thickness}
cur_v:=cur_v+rule_ht;
if (rule_ht>0)and(rule_wd>0) then {we don't output empty rules}
  begin
  case font_direction(dvi_direction) of
  dir__LT: begin
    pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
    {|pdf_dvicmd_left(rule_wd);|}
    end;
  dir__LB: begin
    pdf_dvicmd_down(rule_ht);
    pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
	pdf_dvicmd_left(rule_wd);
    pdf_dvicmd_up(rule_ht);
    end;
  dir__RT: begin
    pdf_dvicmd_left(rule_wd);
    pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
    pdf_dvicmd_left(rule_wd);
    end;
  dir__RB: begin
    pdf_dvicmd_down(rule_ht);
    pdf_dvicmd_left(rule_wd);
    pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
    pdf_dvicmd_up(rule_ht);
    end;
  dir__TL: begin
    pdf_dvicmd_down(rule_wd);
    pdf_dvicmd_left(rule_ht);
    pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
    pdf_dvicmd_up(rule_wd);
    end;
  dir__TR: begin
    pdf_dvicmd_down(rule_wd);
    pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
    pdf_dvicmd_left(rule_wd);
    pdf_dvicmd_up(rule_wd);
    end;
  dir__BL: begin
    pdf_dvicmd_left(rule_ht);
    pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
    end;
  dir__BR: begin
    pdf_set_rule(cur_h, cur_v, rule_wd, rule_ht);
    pdf_dvicmd_left(rule_wd);
    end;
  end;
  end;
goto next_p

@ @<(\pdfTeX) Move down or output leaders@>=
begin g:=glue_ptr(p); rule_ht:=width(g)-cur_g;
if g_sign<>normal then
  begin if g_sign=stretching then
    begin if stretch_order(g)=g_order then
      begin cur_glue:=cur_glue+stretch(g);
      vet_glue(float(glue_set(this_box))*cur_glue);
@^real multiplication@>
      cur_g:=round(glue_temp);
      end;
    end
  else if shrink_order(g)=g_order then
      begin cur_glue:=cur_glue-shrink(g);
      vet_glue(float(glue_set(this_box))*cur_glue);
      cur_g:=round(glue_temp);
      end;
  end;
rule_ht:=rule_ht+cur_g;
if subtype(p)>=a_leaders then
  @<(\pdfTeX) Output leaders in a vlist, |goto fin_rule| if a rule
    or to |next_p| if done@>;
goto move_past;
end

@ @<(\pdfTeX) Output leaders in a vlist...@>=
begin leader_box:=leader_ptr(p);
if type(leader_box)=rule_node then
  begin rule_wd:=width(leader_box); rule_dp:=0;
  goto fin_rule;
  end;
leader_ht:=height(leader_box)+depth(leader_box);
if (leader_ht>0)and(rule_ht>0) then
  begin rule_ht:=rule_ht+10; {compensate for floating-point rounding}
  edge:=cur_v+rule_ht; lx:=0;
  @<Let |cur_v| be the position of the first box, and set |leader_ht+lx|
    to the spacing between corresponding parts of boxes@>;
  while cur_v+leader_ht<=edge do
    @<(\pdfTeX) Output a leader box at |cur_v|,
      then advance |cur_v| by |leader_ht+lx|@>;
  cur_v:=edge-10; goto next_p;
  end;
end

@ @<(\pdfTeX) Output a leader box at |cur_v|, ...@>=
begin cur_h:=left_edge+shift_amount(leader_box);
cur_v:=cur_v+height(leader_box); save_v:=cur_v;
temp_ptr:=leader_box;
outer_doing_leaders:=doing_leaders; doing_leaders:=true;
if type(leader_box)=vlist_node then pdf_vlist_out@+else pdf_hlist_out;
doing_leaders:=outer_doing_leaders;
cur_h:=left_edge;
cur_v:=save_v-height(leader_box)+leader_ht+lx;
end

@ |fix_pdfoutput| freezes |pdfoutput| when something has been written to
the output.

@p procedure fix_pdfoutput;
begin
    if not fixed_pdfoutput_set then begin
        fixed_pdfoutput := pdf_output;
        fixed_pdfoutput_set := true;
    end
    else if fixed_pdfoutput <> pdf_output then
        pdf_error("setup",
            "\pdfoutput can only be changed before anything is written to the output");
    if fixed_pdfoutput_set then fix_pdf_draftmode;
end;

@ |fix_pdf_draftmode| freezes |pdfdraftmode| when something has been written to
the output and also switches somes things off when draftmode is on.
@p procedure fix_pdf_draftmode;
begin
    if not fixed_pdf_draftmode_set then begin
        fixed_pdf_draftmode := pdf_draftmode;
        fixed_pdf_draftmode_set := true;
    end
    else if fixed_pdf_draftmode <> pdf_draftmode then
        pdf_error("setup",
            "\pdfdraftmode can only be changed before anything is written to the output");
    if fixed_pdf_draftmode_set and fixed_pdf_draftmode > 0 then begin
        fixed_pdf_draftmode_set := true;
        pdf_compress_level := 0;
        fixed_pdf_objcompresslevel := 0;
    end;
end;

@ |pdf_ship_out| is used instead of |ship_out| to shipout a box to PDF
output. If |shipping_page| is not set then the output will be a Form object,
otherwise it will be a Page object.

@p procedure pdf_ship_out(p: pointer; shipping_page: boolean); {output the box |p|}
label done, done1;
var i,j,k:integer; {general purpose accumulators}
save_font_list: pointer; {to save |pdf_font_list| during flushing pending forms}
save_obj_list: pointer; {to save |pdf_obj_list|}
save_ximage_list: pointer; {to save |pdf_ximage_list|}
save_xform_list: pointer; {to save |pdf_xform_list|}
save_image_procset: integer;  {to save |pdf_image_procset|}
save_text_procset: integer;  {to save |pdf_text_procset|}
save_cur_page_height: scaled; {to save |cur_page_height| during flushing pending forms}
pdf_last_resources: integer; {pointer to most recently generated Resources object}
pre_callback_id:integer;
post_callback_id:integer;
ret:boolean;
begin 
pre_callback_id:=callback_defined(start_page_number_callback);	
post_callback_id:=callback_defined(stop_page_number_callback);	
if (tracing_output>0)and(pre_callback_id=0) then
  begin print_nl(""); print_ln;
  print("Completed box being shipped out");
@.Completed box...@>
  end;
if not init_pdf_output then begin
    @<Initialize variables for \.{PDF} output@>;
    init_pdf_output := true;
end;
is_shipping_page := shipping_page;
if shipping_page then begin
  if pre_callback_id>0 then 
    ret:=run_callback(pre_callback_id,'->')
  else begin
    if term_offset>max_print_line-9 then print_ln
    else if (term_offset>0)or(file_offset>0) then print_char(" ");
    print_char("["); j:=9;
    while (count(j)=0)and(j>0) do decr(j);
    for k:=0 to j do
      begin print_int(count(k));
      if k<j then print_char(".");
      end;
    end;
  update_terminal;
end;
if (tracing_output>0)and(post_callback_id=0) then
  begin if shipping_page then print_char("]");
  begin_diagnostic; show_box(p); end_diagnostic(true);
  end;
@<(\pdfTeX) Ship box |p| out@>;
if (tracing_output<=0)and(post_callback_id=0) and shipping_page then
  print_char("]");
dead_cycles:=0;
update_terminal; {progress report}
@<Flush the box from memory, showing statistics if requested@>;
if post_callback_id>0 then 
  ret:=run_callback(post_callback_id,'->');
end;

@ @<(\pdfTeX) Ship box |p| out@>=
@<Update the values of |max_h| and |max_v|; but if the page is too large,
  |goto done|@>;
@<Initialize variables as |pdf_ship_out| begins@>;
if type(p)=vlist_node then pdf_vlist_out@+else pdf_hlist_out;
if shipping_page then
    incr(total_pages);
cur_s:=-1;
@<Finish shipping@>;
done:

@ @<Initialize variables as |pdf_ship_out| begins@>=
fix_pdfoutput;
temp_ptr:=p;
prepare_mag;
pdf_last_resources := pdf_new_objnum;
@<Reset resource lists@>;
dvi_direction:=page_direction;
@<Calculate PDF page dimensions and margins@>;
if not shipping_page then begin
    pdf_begin_dict(pdf_cur_form, 0);
    pdf_last_stream := pdf_cur_form;
    @<Write out Form stream header@>;
end
else begin
    pdf_last_page := get_obj(obj_type_page, total_pages + 1, 0);
    obj_aux(pdf_last_page) := 1; {mark that this page has beed created}
    pdf_new_dict(obj_type_others, 0, 0);
    pdf_last_stream := obj_ptr;
    @<Reset PDF mark lists@>;
end;
@<Start stream of page/form contents@>

@ @<Reset resource lists@>=
pdf_font_list := null;
pdf_obj_list := null;
pdf_xform_list := null;
pdf_ximage_list := null;
pdf_text_procset := false;
pdf_image_procset := 0

@ @<Reset PDF mark lists@>=
pdf_annot_list := null;
pdf_link_list := null;
pdf_dest_list := null;
pdf_bead_list := null;
last_thread := null

@ @<Calculate PDF page dimensions and margins@>=
if is_shipping_page then begin
    if page_width > 0 then
        cur_page_width := page_width
    else
        cur_page_width := width(p) + 2 * pdf_h_offset;
    if page_height > 0 then
        cur_page_height := page_height
    else
        cur_page_height := height(p) + depth(p) + 2 * pdf_v_offset;
    if page_bottom_offset <> 0 then
        cur_bottom_offset := page_bottom_offset
    else
        cur_bottom_offset := one_inch;
    if page_right_offset <> 0 then
        cur_right_offset := page_right_offset
    else
        cur_right_offset :=  one_inch;
    cur_h := pdf_h_offset;
    cur_v := height(p) + pdf_v_offset;
    case box_direction(dvi_direction) of
        dir_TL_,dir_LT_: begin end;
        dir_TR_,dir_RT_: begin cur_h:=cur_page_width-cur_right_offset; end;
        dir_RB_,dir_BR_: begin cur_h:=cur_page_width-cur_right_offset; cur_v:=-cur_bottom_offset; end;
        dir_BL_,dir_LB_: begin cur_v:=-cur_bottom_offset; end; 
    end;
end
else begin
   cur_page_width := width(p);
   cur_page_height := height(p) + depth(p);
   cur_h := 0;
   cur_v := height(p);
end;
pdf_origin_h := 0;
pdf_origin_v := cur_page_height;

@ Here we write out the header for Form.

@<Write out Form stream header@>=
pdf_print_ln("/Type /XObject");
pdf_print_ln("/Subtype /Form");
if obj_xform_attr(pdf_cur_form) <> null then begin
    pdf_print_toks_ln(obj_xform_attr(pdf_cur_form));
    delete_toks(obj_xform_attr(pdf_cur_form));
end;
pdf_print("/BBox [");
pdf_print("0 0 ");
pdf_print_bp(cur_page_width); pdf_out(" ");
pdf_print_bp(cur_page_height); pdf_print_ln("]");
pdf_print_ln("/FormType 1");
pdf_print_ln("/Matrix [1 0 0 1 0 0]");
pdf_indirect_ln("Resources", pdf_last_resources)

@ @<Start stream of page/form contents@>=
pdf_begin_stream;
if shipping_page then begin
    @<Adjust transformation matrix for the magnification ratio@>;
end;
pdfshipoutbegin(shipping_page);
if shipping_page then
    pdf_out_colorstack_startpage;


@ @<Adjust transformation matrix for the magnification ratio@>=
prepare_mag;
if mag <> 1000 then begin
    pdf_print_real(mag, 3);
    pdf_print(" 0 0 ");
    pdf_print_real(mag, 3);
    pdf_print_ln(" 0 0 cm");
end

@ @<Finish shipping@>=
@<Finish stream of page/form contents@>;
if shipping_page then begin
    @<Write out page object@>;
end;
@<Write out resource lists@>;
if shipping_page then begin
    @<Write out pending PDF marks@>;
end;
@<Write out resources dictionary@>;
@<Flush resource lists@>;
if shipping_page then begin
    @<Flush PDF mark lists@>;
end

@ @<Finish stream of page/form contents@>=
pdf_end_text;
pdfshipoutend(shipping_page);
pdf_end_stream

@ @<Write out resource lists@>=
@<Write out pending raw objects@>;
@<Write out pending forms@>;
@<Write out pending images@>

@ @<Write out resources dictionary@>=
pdf_begin_dict(pdf_last_resources, 1);
@<Print additional resources@>;
@<Generate font resources@>;
@<Generate XObject resources@>;
@<Generate ProcSet@>;
pdf_end_dict

@ @<Print additional resources@>=
if shipping_page then begin
    if pdf_page_resources <> null then
        pdf_print_toks_ln(pdf_page_resources);
end
else begin
    if obj_xform_resources(pdf_cur_form) <> null then begin
        pdf_print_toks_ln(obj_xform_resources(pdf_cur_form));
        delete_toks(obj_xform_resources(pdf_cur_form));
    end;
end

@ In the end of shipping out a page we reset all the lists holding objects
have been created during the page shipping.

@d delete_toks(#) == begin delete_token_ref(#); # := null; end

@<Flush resource lists@>=
flush_list(pdf_font_list);
flush_list(pdf_obj_list);
flush_list(pdf_xform_list);
flush_list(pdf_ximage_list)

@ @<Flush PDF mark lists@>=
flush_list(pdf_annot_list);
flush_list(pdf_link_list);
flush_list(pdf_dest_list);
flush_list(pdf_bead_list)

@ @<Generate font resources@>=
if pdf_font_list <> null then begin
    pdf_print("/Font << ");
    k := pdf_font_list;
    while k <> null do begin
        pdf_print("/F");
        set_ff(info(k));
        pdf_print_int(ff);
        pdf_print_resname_prefix;
        pdf_out(" ");
        pdf_print_int(pdf_font_num(ff));
        pdf_print(" 0 R ");
        k := link(k);
    end;
    pdf_print_ln(">>");
    pdf_text_procset := true;
end

@ @<Generate XObject resources@>=
if (pdf_xform_list <> null) or (pdf_ximage_list <> null) then begin
    pdf_print("/XObject << ");
    k := pdf_xform_list;
    while k <> null do begin
        pdf_print("/Fm");
        pdf_print_int(obj_info(info(k)));
        pdf_print_resname_prefix;
        pdf_out(" ");
        pdf_print_int(info(k));
        pdf_print(" 0 R ");
        k := link(k);
    end;
    k := pdf_ximage_list;
    while k <> null do begin
        pdf_print("/Im");
        pdf_print_int(image_index(obj_data_ptr(info(k))));
        pdf_print_resname_prefix;
        pdf_out(" ");
        pdf_print_int(info(k));
        pdf_print(" 0 R ");
        update_image_procset(obj_data_ptr(info(k)));
        k := link(k);
    end;
    pdf_print_ln(">>");
end

@ @<Generate ProcSet@>=
pdf_print("/ProcSet [ /PDF");
if pdf_text_procset then
    pdf_print(" /Text");
if check_image_b(pdf_image_procset) then
    pdf_print(" /ImageB");
if check_image_c(pdf_image_procset) then
    pdf_print(" /ImageC");
if check_image_i(pdf_image_procset) then
    pdf_print(" /ImageI");
pdf_print_ln(" ]")

@ @<Write out page object@>=
pdf_begin_dict(pdf_last_page, 1);
pdf_print_ln("/Type /Page");
pdf_indirect_ln("Contents", pdf_last_stream);
pdf_indirect_ln("Resources", pdf_last_resources);
pdf_print("/MediaBox [0 0 ");
pdf_print_mag_bp(cur_page_width); pdf_out(" ");
pdf_print_mag_bp(cur_page_height);
pdf_print_ln("]");
if pdf_page_attr <> null then
    pdf_print_toks_ln(pdf_page_attr);
@<Generate parent pages object@>;
@<Generate array of annotations or beads in page@>;
pdf_end_dict

@ @<Generate parent pages object@>=
if total_pages mod pages_tree_kids_max = 1 then begin
    pdf_create_obj(obj_type_pages, pages_tree_kids_max);
    pdf_last_pages := obj_ptr;
end;
pdf_indirect_ln("Parent", pdf_last_pages)

@ @<Generate array of annotations or beads in page@>=
if (pdf_annot_list <> null) or (pdf_link_list <> null) then begin
    pdf_print("/Annots [ ");
    k := pdf_annot_list;
    while k <> null do begin
        pdf_print_int(info(k));
        pdf_print(" 0 R ");
        k := link(k);
    end;
    k := pdf_link_list;
    while k <> null do begin
        pdf_print_int(info(k));
        pdf_print(" 0 R ");
        k := link(k);
    end;
    pdf_print_ln("]");
end;
if pdf_bead_list <> null then begin
    k := pdf_bead_list;
    pdf_print("/B [ ");
    while k <> null do begin
        pdf_print_int(info(k));
        pdf_print(" 0 R ");
        k := link(k);
    end;
    pdf_print_ln("]");
end

@ @<Declare procedures needed in |pdf_hlist_out|, |pdf_vlist_out|@>=
procedure pdf_write_obj(n: integer); {write a raw PDF object}
var s: str_number;
    f: byte_file;
    data_size:integer; {total size of the data file}
    data_cur:integer; {index into |data_buffer|}
    data_buffer:^real_eight_bits; {byte buffer for data files}
    file_opened:boolean;
    k:integer;
    res:boolean;
	fnam: str_number;
    callback_id:integer;
begin
    s := tokens_to_string(obj_obj_data(n));
    delete_toks(obj_obj_data(n));
    if obj_obj_is_stream(n) > 0 then begin
        pdf_begin_dict(n, 0);
        if obj_obj_stream_attr(n) <> null then begin
            pdf_print_toks_ln(obj_obj_stream_attr(n));
            delete_toks(obj_obj_stream_attr(n));
        end;
        pdf_begin_stream;
    end
    else
        pdf_begin_obj(n, 1);
    if obj_obj_is_file(n) > 0 then begin
        data_size:=0; data_cur:=0; data_buffer:=0;
        pack_file_name(s,"","");
	    callback_id:=callback_defined(find_data_file_callback);
	    if callback_id>0 then begin
    	  res := run_callback(callback_id,'S->s',stringcast(nameoffile+1),addressof(fnam));
	      if (res)and(fnam<>0)and(length(fnam)>0) then begin
	        @<Fixup |nameoffile| after callback@>;
		 	end;
          end;
		callback_id:=callback_defined(read_data_file_callback);
        if callback_id>0 then begin
          file_opened := false;
          res := run_callback(callback_id,'S->bSd',stringcast(nameoffile+1),
                  addressof(file_opened), addressof(data_buffer),addressof(data_size));
          if not file_opened then pdf_error("ext5", "cannot open file for embedding");
          end
        else begin
          if not tex_b_open_in(f) then 
             pdf_error("ext5", "cannot open file for embedding");
          res := read_data_file(f,addressof(data_buffer),addressof(data_size));
          b_close(f);
        end;
        if not data_size then pdf_error("ext5", "empty file for embedding");
        if not res       then pdf_error("ext5", "error reading file for embedding");
        print("<<");
        print(s);
        while data_cur<data_size do begin
            pdf_out(data_buffer[data_cur]);
            incr(data_cur);
            end;
	    if data_buffer<>0 then libcfree(data_buffer);
        print(">>");
    end
    else if obj_obj_is_stream(n) > 0 then
        pdf_print(s)
    else
        pdf_print_ln(s);
    if obj_obj_is_stream(n) > 0 then
        pdf_end_stream
    else
        pdf_end_obj;
    flush_str(s);
end;

@ @<Write out pending raw objects@>=
if pdf_obj_list <> null then begin
    k := pdf_obj_list;
    while k <> null do begin
        if not is_obj_written(info(k)) then
            pdf_write_obj(info(k));
        k := link(k);
    end;
end

@ When flushing pending forms we need to save and restore resource lists
(|pdf_font_list|, |pdf_obj_list|, |pdf_xform_list| and |pdf_ximage_list|),
which are also used by page shipping.
Saving and restoring |cur_page_height| is needed for proper
writing out pending PDF marks.

@<Write out pending forms@>=
if pdf_xform_list <> null then begin
    k := pdf_xform_list;
    while k <> null do begin
        if not is_obj_written(info(k)) then begin
            pdf_cur_form := info(k);
            @<Save resource lists@>;
            @<Reset resource lists@>;
            save_cur_page_height := cur_page_height;
            pdf_ship_out(obj_xform_box(pdf_cur_form), false);
            cur_page_height := save_cur_page_height;
            @<Restore resource lists@>;
        end;
        k := link(k);
    end;
end

@ @<Save resource lists@>=
save_font_list := pdf_font_list;
save_obj_list := pdf_obj_list;
save_xform_list := pdf_xform_list;
save_ximage_list := pdf_ximage_list;
save_text_procset := pdf_text_procset;
save_image_procset := pdf_image_procset

@ @<Restore resource lists@>=
pdf_font_list := save_font_list;
pdf_obj_list := save_obj_list;
pdf_xform_list := save_xform_list;
pdf_ximage_list := save_ximage_list;
pdf_text_procset := save_text_procset;
pdf_image_procset := save_image_procset

@ @<Declare procedures needed in |pdf_hlist_out|, |pdf_vlist_out|@>=
procedure pdf_write_image(n: integer); {write an image}
begin
    pdf_begin_dict(n, 0);
    if fixed_pdf_draftmode = 0 then write_image(obj_data_ptr(n));
end;

@ @<Write out pending images@>=
if pdf_ximage_list <> null then begin
    k := pdf_ximage_list;
    while k <> null do begin
        if not is_obj_written(info(k)) then
            pdf_write_image(info(k));
        k := link(k);
    end;
end

@ @<Write out pending PDF marks@>=
pdf_origin_h := 0;
pdf_origin_v := cur_page_height;
@<Write out PDF annotations@>;
@<Write out PDF link annotations@>;
@<Write out PDF mark destinations@>;
@<Write out PDF bead rectangle specifications@>

@ @<Write out PDF annotations@>=
if pdf_annot_list <> null then begin
    k := pdf_annot_list;
    while k <> null do begin
        i := obj_annot_ptr(info(k)); {|i| points to |pdf_annot_node|}
        pdf_begin_dict(info(k), 1);
        pdf_print_ln("/Type /Annot");
        pdf_print_toks_ln(pdf_annot_data(i));
        pdf_rectangle(pdf_left(i), pdf_top(i), pdf_right(i), pdf_bottom(i));
        pdf_end_dict;
        k := link(k);
    end;
end

@ @<Write out PDF link annotations@>=
if pdf_link_list <> null then begin
k := pdf_link_list;
while k <> null do begin
    i := obj_annot_ptr(info(k));
    pdf_begin_dict(info(k), 1);
    pdf_print_ln("/Type /Annot");
    if pdf_link_attr(i) <> null then
        pdf_print_toks_ln(pdf_link_attr(i));
    pdf_rectangle(pdf_left(i), pdf_top(i), pdf_right(i), pdf_bottom(i));
    if pdf_action_type(pdf_link_action(i)) <> pdf_action_user
    then begin
        pdf_print_ln("/Subtype /Link");
        pdf_print("/A ");
    end;
    write_action(pdf_link_action(i));
    pdf_end_dict;
    k := link(k);
    end;
    @<Flush |pdf_start_link_node|'s created by |append_link|@>;
end

@ @<Flush |pdf_start_link_node|'s created by |append_link|@>=
k := pdf_link_list;
while k <> null do begin
    i := obj_annot_ptr(info(k));
    {nodes with |subtype = pdf_link_data_node| were created by |append_link| and
     must be flushed here, as they are not linked in any list}
    if subtype(i) = pdf_link_data_node then
        flush_node(i);
    k := link(k);
end

@ @<Write out PDF mark destinations@>=
if pdf_dest_list <> null then begin
    k := pdf_dest_list;
    while k <> null do begin
        if is_obj_written(info(k)) then
            pdf_error("ext5",
                "destination has been already written (this shouldn't happen)")
        else begin
            i := obj_dest_ptr(info(k));
            if pdf_dest_named_id(i) > 0 then begin
                pdf_begin_dict(info(k), 1);
                pdf_print("/D ");
            end
            else
                pdf_begin_obj(info(k), 1);
            pdf_out("["); pdf_print_int(pdf_last_page); pdf_print(" 0 R ");
            case pdf_dest_type(i) of
            pdf_dest_xyz: begin
                pdf_print("/XYZ ");
                pdf_print_mag_bp(pdf_x(pdf_left(i))); pdf_out(" ");
                pdf_print_mag_bp(pdf_y(pdf_top(i))); pdf_out(" ");
                if pdf_dest_xyz_zoom(i) = null then
                    pdf_print("null")
                else begin
                    pdf_print_int(pdf_dest_xyz_zoom(i) div 1000);
                    pdf_out(".");
                    pdf_print_int((pdf_dest_xyz_zoom(i) mod 1000));
                end;
            end;
            pdf_dest_fit:
                pdf_print("/Fit");
            pdf_dest_fith: begin
                pdf_print("/FitH ");
                pdf_print_mag_bp(pdf_y(pdf_top(i)));
            end;
            pdf_dest_fitv: begin
                pdf_print("/FitV ");
                pdf_print_mag_bp(pdf_x(pdf_left(i)));
            end;
            pdf_dest_fitb:
                pdf_print("/FitB");
            pdf_dest_fitbh: begin
                pdf_print("/FitBH ");
                pdf_print_mag_bp(pdf_y(pdf_top(i)));
            end;
            pdf_dest_fitbv: begin
                pdf_print("/FitBV ");
                pdf_print_mag_bp(pdf_x(pdf_left(i)));
            end;
            pdf_dest_fitr: begin
                pdf_print("/FitR ");
                pdf_print_rect_spec(i);
            end;
            othercases pdf_error("ext5", "unknown dest type");
            endcases;
            pdf_print_ln("]");
            if pdf_dest_named_id(i) > 0 then
                pdf_end_dict
            else
                pdf_end_obj;
        end;
        k := link(k);
    end;
end

@ @<Declare procedures needed in |pdf_hlist_out|, |pdf_vlist_out|@>=
procedure pdf_print_rect_spec(r: pointer); {prints a rect spec}
begin
    pdf_print_mag_bp(pdf_x(pdf_left(r)));
    pdf_out(" ");
    pdf_print_mag_bp(pdf_y(pdf_bottom(r)));
    pdf_out(" ");
    pdf_print_mag_bp(pdf_x(pdf_right(r)));
    pdf_out(" ");
    pdf_print_mag_bp(pdf_y(pdf_top(r)));
end;

@ @<Write out PDF bead rectangle specifications@>=
if pdf_bead_list <> null then begin
    k := pdf_bead_list;
    while k <> null do begin
        pdf_new_obj(obj_type_others, 0, 1);
        pdf_out("[");
        i := obj_bead_data(info(k)); {pointer to a whatsit or whatsit-like node}
        pdf_print_rect_spec(i);
        if subtype(i) = pdf_thread_data_node then {thanh says it mis be destroyed here}
            flush_node(i);
        pdf_print_ln("]");
        obj_bead_rect(info(k)) := obj_ptr; {rewrite |obj_bead_data|}
        pdf_end_obj;
        k := link(k);
    end;
end

@ In the end we must flush PDF objects that cannot be written out
immediately after shipping out pages.

@ @<Output outlines@>=
if pdf_first_outline <> 0 then begin
    pdf_new_dict(obj_type_others, 0, 1);
    outlines := obj_ptr;
    l := pdf_first_outline; k := 0;
    repeat
        incr(k);
        a := open_subentries(l);
        if obj_outline_count(l) > 0 then
            k := k + a;
        obj_outline_parent(l) := obj_ptr;
        l := obj_outline_next(l);
    until l = 0;
    pdf_print_ln("/Type /Outlines");
    pdf_indirect_ln("First", pdf_first_outline);
    pdf_indirect_ln("Last", pdf_last_outline);
    pdf_int_entry_ln("Count", k);
    pdf_end_dict;
    @<Output PDF outline entries@>;
end
else
    outlines := 0

@ @<Output PDF outline entries@>=
k := head_tab[obj_type_outline];
while k <> 0 do begin
    if obj_outline_parent(k) = pdf_parent_outline then begin
        if obj_outline_prev(k) = 0 then
            pdf_first_outline := k;
        if obj_outline_next(k) = 0 then
            pdf_last_outline := k;
    end;
    pdf_begin_dict(k, 1);
    pdf_indirect_ln("Title", obj_outline_title(k));
    pdf_indirect_ln("A", obj_outline_action_objnum(k));
    if obj_outline_parent(k) <> 0 then
        pdf_indirect_ln("Parent", obj_outline_parent(k));
    if obj_outline_prev(k) <> 0 then
        pdf_indirect_ln("Prev", obj_outline_prev(k));
    if obj_outline_next(k) <> 0 then
        pdf_indirect_ln("Next", obj_outline_next(k));
    if obj_outline_first(k) <> 0 then
        pdf_indirect_ln("First", obj_outline_first(k));
    if obj_outline_last(k) <> 0 then
        pdf_indirect_ln("Last", obj_outline_last(k));
    if obj_outline_count(k) <> 0 then
        pdf_int_entry_ln("Count", obj_outline_count(k));
    if obj_outline_attr(k) <> 0 then begin
        pdf_print_toks_ln(obj_outline_attr(k));
        delete_toks(obj_outline_attr(k));
    end;
    pdf_end_dict;
    k := obj_link(k);
end

@ @<Output article threads@>=
if head_tab[obj_type_thread] <> 0 then begin
    pdf_new_obj(obj_type_others, 0, 1);
    threads := obj_ptr;
    pdf_out("[");
    k := head_tab[obj_type_thread];
    while k <> 0 do begin
        pdf_print_int(k);
        pdf_print(" 0 R ");
        k := obj_link(k);
    end;
    remove_last_space;
    pdf_print_ln("]");
    pdf_end_obj;
    k := head_tab[obj_type_thread];
    while k <> 0 do begin
        out_thread(k);
        k := obj_link(k);
    end;
end
else
    threads := 0

@ Now we are ready to declare our new procedure |ship_out|.  It will call
|pdf_ship_out| if the integer parameter |pdf_output| is positive; otherwise it
will call |dvi_ship_out|, which is the \TeX\ original |ship_out|.

@p procedure ship_out(p:pointer); {output the box |p|}
begin
    fix_pdfoutput;
    if pdf_output > 0 then
        pdf_ship_out(p, true)
    else
        dvi_ship_out(p);
end;

@ @<Initialize variables for \.{PDF} output@>=
check_pdfminorversion;
prepare_mag;
fixed_decimal_digits := fix_int(pdf_decimal_digits, 0, 4);
min_bp_val :=
    divide_scaled(one_hundred_bp, ten_pow[fixed_decimal_digits + 2], 0);
if pdf_pk_resolution = 0 then {if not set from format file or by user}
    pdf_pk_resolution := pk_dpi; {take it from \.{texmf.cnf}}
fixed_pk_resolution := fix_int(pdf_pk_resolution, 72, 8000);
pk_scale_factor :=
    divide_scaled(72, fixed_pk_resolution, 5 + fixed_decimal_digits);
if not callback_defined(read_pk_file_callback) then begin
  if pdf_pk_mode <> null then begin
    kpseinitprog('PDFTEX', fixed_pk_resolution,
                   makecstring(tokens_to_string(pdf_pk_mode)), nil);
    flush_string;
  end else
    kpseinitprog('PDFTEX', fixed_pk_resolution, nil, nil);
  if not kpsevarvalue('MKTEXPK') then
     kpsesetprogramenabled (kpsepkformat, 1, kpsesrccmdline);
  end;
set_job_id(year, month, day, time);
if (pdf_unique_resname > 0) and (pdf_resname_prefix = 0) then
    pdf_resname_prefix := get_resname_prefix

@ Finishing the PDF output file.

The following procedures sort the table of destination names
@p function str_less_str(s1, s2: str_number): boolean; {compare two strings}
var c1, c2: pool_pointer;
    l, i: integer;
begin
    c1 := str_start_macro(s1);
    c2 := str_start_macro(s2);
    if length(s1) < length(s2) then
        l := length(s1)
    else
        l := length(s2);
    i := 0;
    while (i < l) and (str_pool[c1 + i] = str_pool[c2 + i]) do
        incr(i);
    if ((i < l) and (str_pool[c1 + i] < str_pool[c2 + i])) or
        ((i = l) and (length(s1) < length(s2))) then
        str_less_str := true
    else
        str_less_str := false;
end;

procedure sort_dest_names(l, r: integer); {sorts |dest_names| by names}
var i, j: integer;
    s: str_number;
    e: dest_name_entry;
begin
    i := l;
    j := r;
    s := dest_names[(l + r) div 2].objname;
    repeat
        while str_less_str(dest_names[i].objname, s) do
            incr(i);
        while str_less_str(s, dest_names[j].objname) do
            decr(j);
        if i <= j then begin
            e := dest_names[i];
            dest_names[i] := dest_names[j];
            dest_names[j] := e;
            incr(i);
            decr(j);
        end;
    until i > j;
    if l < j then
        sort_dest_names(l, j);
    if i < r then
        sort_dest_names(i, r);
end;

@  Now the finish of PDF output file. At this moment all Page objects
are already written completely to PDF output file.

@<Finish the PDF file@>=
if total_pages=0 then begin
	if callback_id=0 then
      print_nl("No pages of output.")
    else
      res:=run_callback(callback_id,'->');
  @.No pages of output@>
    if pdf_gone > 0 then
        garbage_warning;
end
else begin
    if fixed_pdf_draftmode = 0 then begin
    pdf_flush; {to make sure that the output file name has been already
    created}
    if total_pages mod pages_tree_kids_max <> 0 then
        obj_info(pdf_last_pages) := total_pages mod pages_tree_kids_max;
    {last pages object may have less than |pages_tree_kids_max| children}
    flush_jbig2_page0_objects; {flush page 0 objects from JBIG2 images, if any}
    @<Check for non-existing pages@>;
    @<Reverse the linked list of Page and Pages objects@>;
    @<Check for non-existing destinations@>;
    @<Output fonts definition@>;
    @<Output pages tree@>;
    @<Output outlines@>;
    @<Output name tree@>;
    @<Output article threads@>;
    @<Output the catalog object@>;
    pdf_print_info; {last candidate for object stream}
    if pdf_os_enable then begin
        pdf_os_switch(true);
        pdf_os_write_objstream;
        pdf_flush;
        pdf_os_switch(false);
        @<Output the cross-reference stream dictionary@>;
        pdf_flush;
    end else begin
        @<Output the |obj_tab|@>;
    end;
    @<Output the trailer@>;
    pdf_flush;
	if callback_id=0 then begin
      print_nl("Output written on "); print_file_name(0, output_file_name, 0);
  @.Output written on x@>
      print(" ("); print_int(total_pages); print(" page");
      if total_pages<>1 then print_char("s");
      print(", "); print_int(pdf_offset); print(" bytes).");
      end
    else
      res:=run_callback(callback_id,'->');
    end;
    libpdffinish;
    if fixed_pdf_draftmode = 0 then b_close(pdf_file)
    else pdf_warning(0, "\pdfdraftmode enabled, not changing output pdf", true, true)
end

@ Destinations that have been referenced but don't exists have
|obj_dest_ptr=null|. Leaving them undefined might cause troubles for
PDF browsers, so we need to fix them.

@p procedure pdf_fix_dest(k: integer);
begin
    if obj_dest_ptr(k) <> null then
        return;
    pdf_warning("dest", "", false, false);
    if obj_info(k) < 0 then begin
        print("name{");
        print(-obj_info(k));
        print("}");
    end
    else begin
        print("num");
        print_int(obj_info(k));
    end;
    print(" has been referenced but does not exist, replaced by a fixed one");
    print_ln; print_ln;
    pdf_begin_obj(k, 1);
    pdf_out("[");
    pdf_print_int(head_tab[obj_type_page]);
    pdf_print_ln(" 0 R /Fit]");
    pdf_end_obj;
end;

@ @<Check for non-existing destinations@>=
k := head_tab[obj_type_dest];
while k <> 0 do begin
    pdf_fix_dest(k);
    k := obj_link(k);
end

@ @<Check for non-existing pages@>=
k := head_tab[obj_type_page];
while obj_aux(k) = 0 do begin
    pdf_warning("dest", "Page ", false, false);
    print_int(obj_info(k));
    print(" has been referenced but does not exist!");
    print_ln; print_ln;
    k := obj_link(k);
end;
head_tab[obj_type_page] := k

@ @<Reverse the linked list of Page and Pages objects@>=
k := head_tab[obj_type_page];
l := 0;
repeat
    i := obj_link(k);
    obj_link(k) := l;
    l := k;
    k := i;
until k = 0;
head_tab[obj_type_page] := l;
k := head_tab[obj_type_pages];
pages_tail := k;
l := 0;
repeat
    i := obj_link(k);
    obj_link(k) := l;
    l := k;
    k := i;
until k = 0;
head_tab[obj_type_pages] := l

@ @<Output fonts definition@>=
for k := 1 to max_font_id do
    if font_used(k) and (pdf_font_num(k) < 0) then begin
        i := -pdf_font_num(k);
        pdfassert(pdf_font_num(i) > 0);
        for j := font_bc(k) to font_ec(k) do
            if pdf_char_marked(k, j) then
                pdf_mark_char(i, j);
        if (pdf_font_attr(i) = 0) and (pdf_font_attr(k) <> 0) then
            set_pdf_font_attr(i, pdf_font_attr(k))
        else if (pdf_font_attr(k) = 0) and (pdf_font_attr(i) <> 0) then
            set_pdf_font_attr(k,pdf_font_attr(i))
        else if (pdf_font_attr(i) <> 0) and (pdf_font_attr(k) <> 0) and
           not str_eq_str(pdf_font_attr(i), pdf_font_attr(k)) then begin
           pdf_warning("\pdffontattr", "fonts ", false, false);
           print_font_identifier(i);
           print(" and ");
           print_font_identifier(k);
           print(" has conflicting attributes"); print_ln; print_ln;
        end;
    end;
fixed_gen_tounicode := pdf_gen_tounicode;
k := head_tab[obj_type_font];
while k <> 0 do begin
    f := obj_info(k);
    pdfassert(pdf_font_num(f) > 0);
    do_pdf_font(k, f);
    k := obj_link(k);
end;
write_fontstuff

@ We will generate in each single step the parents of all Pages/Page objects in
the previous level. These new generated Pages object will create a new level of
Pages tree. We will repeat this until search only one Pages object. This one
will be the Root object.

@<Output pages tree@>=
a := sys_obj_ptr + 1; {all Pages objects whose children are not Page objects
                       should have index greater than |a|}
l := head_tab[obj_type_pages]; {|l| is the index of current Pages object
                                which is being output}
k := head_tab[obj_type_page]; {|k| is the index of current child of |l|}
b := 0;
repeat
    i := 0; {counter of Pages object in current level}
    c := 0; {first Pages object in previous level}
    if obj_link(l) = 0 then
        is_root := true {only Pages object; total pages is
                         not greater than |pages_tree_kids_max|}
    else
        is_root := false;
    repeat
        if not is_root then begin
            if i mod pages_tree_kids_max = 0 then begin {create a new Pages object
                                                         for next level}
                pdf_last_pages := pdf_new_objnum;
                if c = 0 then
                    c := pdf_last_pages;
                obj_link(pages_tail) := pdf_last_pages;
                pages_tail := pdf_last_pages;
                obj_link(pdf_last_pages) := 0;
                obj_info(pdf_last_pages) := obj_info(l);
            end
            else
                obj_info(pdf_last_pages) := obj_info(pdf_last_pages) +
                    obj_info(l);
        end;
        @<Output the current Pages object in this level@>;
        incr(i);
        l := obj_link(l);
    until (l = c);
    b := c;
    if l = 0 then
        goto done;
until false;
done:

@ @<Output the current Pages object in this level@>=
pdf_begin_dict(l, 1);
pdf_print_ln("/Type /Pages");
pdf_int_entry_ln("Count", obj_info(l));
if not is_root then
    pdf_indirect_ln("Parent", pdf_last_pages);
pdf_print("/Kids [");
j := 0;
repeat
    pdf_print_int(k);
    pdf_print(" 0 R ");
    k := obj_link(k);
    incr(j);
until ((l < a) and (j = obj_info(l))) or
    (k = 0) or ((k = b) and (b <> 0)) or
    (j = pages_tree_kids_max);
remove_last_space;
pdf_print_ln("]");
if k = 0 then begin
    k := head_tab[obj_type_pages];
    head_tab[obj_type_pages] := 0;
end;
if is_root and (pdf_pages_attr <> null) then
    pdf_print_toks_ln(pdf_pages_attr);
pdf_end_dict;

@ The name tree is very similiar to Pages tree so its construction should be
certain from Pages tree construction. For intermediate node |obj_info| will be
the first name and |obj_link| will be the last name in \.{\\Limits} array.
Note that |pdf_dest_names_ptr| will be less than |obj_ptr|, so we test if
|k < pdf_dest_names_ptr| then |k| is index of leaf in |dest_names|; else
|k| will be index in |obj_tab| of some intermediate node.

@<Output name tree@>=
if pdf_dest_names_ptr = 0 then begin
    dests := 0;
    goto done1;
end;
sort_dest_names(0, pdf_dest_names_ptr - 1);
names_head := 0;
names_tail := 0;
k := 0; {index of current child of |l|; if |k < pdf_dest_names_ptr|
         then this is pointer to |dest_names| array;
         otherwise it is the pointer to |obj_tab| (object number)}
is_names := true; {flag whether Names or Kids}
b := 0;
repeat
    repeat
        pdf_create_obj(obj_type_others, 0); {create a new node}
        l := obj_ptr;
        if b = 0 then
            b := l; {first in this level}
        if names_head = 0 then begin
            names_head := l;
            names_tail := l;
        end else begin
            obj_link(names_tail) := l;
            names_tail := l;
        end;
        obj_link(names_tail) := 0;
        @<Output the current node in this level@>;
    until b = 0;
    if k = l then begin
        dests := l;
        goto done1;
    end;
until false;
done1:
if (dests <> 0) or (pdf_names_toks <> null) then begin
    pdf_new_dict(obj_type_others, 0, 1);
    if (dests <> 0) then
        pdf_indirect_ln("Dests", dests);
    if pdf_names_toks <> null then begin
        pdf_print_toks_ln(pdf_names_toks);
        delete_toks(pdf_names_toks);
    end;
    pdf_end_dict;
    names_tree := obj_ptr;
end
else
    names_tree := 0

@ @<Output the current node in this level@>=
pdf_begin_dict(l, 1);
j := 0;
if is_names then begin
    obj_info(l) := dest_names[k].objname;
    pdf_print("/Names [");
    repeat
        pdf_print_str(dest_names[k].objname);
        pdf_out(" ");
        pdf_print_int(dest_names[k].objnum);
        pdf_print(" 0 R ");
        incr(j);
        incr(k);
    until (j = name_tree_kids_max) or (k = pdf_dest_names_ptr);
    remove_last_space;
    pdf_print_ln("]");
    obj_aux(l) := dest_names[k - 1].objname;
    if k = pdf_dest_names_ptr then begin
        is_names := false;
        k := names_head;
        b := 0;
    end;
end
else begin
    obj_info(l) := obj_info(k);
    pdf_print("/Kids [");
    repeat
        pdf_print_int(k);
        pdf_print(" 0 R ");
        incr(j);
        obj_aux(l) := obj_aux(k);
        k := obj_link(k);
    until (j = name_tree_kids_max) or (k = b) or (obj_link(k) = 0);
    remove_last_space;
    pdf_print_ln("]");
    if k = b then
        b := 0;
end;
pdf_print("/Limits [");
pdf_print_str(obj_info(l));
pdf_out(" ");
pdf_print_str(obj_aux(l));
pdf_print_ln("]");
pdf_end_dict;

@ @<Output the catalog object@>=
pdf_new_dict(obj_type_others, 0, 1);
root := obj_ptr;
pdf_print_ln("/Type /Catalog");
pdf_indirect_ln("Pages", pdf_last_pages);
if threads <> 0 then
    pdf_indirect_ln("Threads", threads);
if outlines <> 0 then
    pdf_indirect_ln("Outlines", outlines);
if names_tree <> 0 then
    pdf_indirect_ln("Names", names_tree);
if pdf_catalog_toks <> null then begin
    pdf_print_toks_ln(pdf_catalog_toks);
    delete_toks(pdf_catalog_toks);
end;
if pdf_catalog_openaction <> 0 then
    pdf_indirect_ln("OpenAction", pdf_catalog_openaction);
pdf_end_dict

@ If the same keys in a dictionary are given several times, then it is not
defined which value is choosen by an application.  Therefore the keys
|/Producer| and |/Creator| are only set if the token list
|pdf_info_toks| converted to a string does not contain these key strings.

@p function substr_of_str(s, t: str_number):boolean;
label continue,exit;
var j, k, kk: pool_pointer; {running indices}
begin
    k:=str_start_macro(t);
    while (k < str_start_macro(t+1) - length(s)) do begin
        j:=str_start_macro(s);
        kk:=k;
        while (j < str_start_macro(s+1)) do begin
            if str_pool[j] <> str_pool[kk] then
                goto continue;
            incr(j);
            incr(kk);
        end;
        substr_of_str:=true;
        return;
        continue: incr(k);
    end;
    substr_of_str:=false;
end;

procedure pdf_print_info; {print info object}
var s: str_number;
    creator_given, producer_given, creationdate_given, moddate_given, trapped_given: boolean;
begin
    s:="";
    pdf_new_dict(obj_type_others, 0, 3); {keep Info readable unless explicitely forced}
    creator_given:=false;
    producer_given:=false;
    creationdate_given:=false;
    moddate_given:=false;
    trapped_given:=false;
    if pdf_info_toks <> null then begin
        s:=tokens_to_string(pdf_info_toks);
        creator_given:=substr_of_str("/Creator", s);
        producer_given:=substr_of_str("/Producer", s);
        creationdate_given:=substr_of_str("/CreationDate", s);
        moddate_given:=substr_of_str("/ModDate", s);
        trapped_given:=substr_of_str("/Trapped", s);
    end;
    if not producer_given then begin
        @<Print the Producer key@>;
    end;
    if pdf_info_toks <> null then begin
        if length(s) > 0 then begin
            pdf_print_ln(s);
        end;
        flush_str(s);
        delete_toks(pdf_info_toks);
    end;
    if not creator_given then
        pdf_str_entry_ln("Creator", "TeX");
    if not creationdate_given then begin
        @<Print the CreationDate key@>;
    end;
    if not moddate_given then begin
        @<Print the ModDate key@>;
    end;
    if not trapped_given then begin
        pdf_print_ln("/Trapped /False");
    end;
    pdf_str_entry_ln("PTEX.Fullbanner", pdftex_banner);
    pdf_end_dict;
end;

@ @<Print the Producer key@>=
pdf_print("/Producer (luaTeX-");
pdf_print_int(luatex_version div 100);
pdf_out(".");
pdf_print_int(luatex_version mod 100);
pdf_out(".");
pdf_print(luatex_revision);
pdf_print_ln(")")

@ @<Print the CreationDate key@>=
print_creation_date;

@ @<Print the ModDate key@>=
print_mod_date;

@ @<Glob...@>=
@!pdftex_banner: str_number;   {the complete banner}

@ @<Output the |obj_tab|@>=
l := 0;
for k := 1 to sys_obj_ptr do
    if obj_offset(k) = 0 then begin
        obj_link(l) := k;
        l := k;
    end;
obj_link(l) := 0;
pdf_save_offset := pdf_offset;
pdf_print_ln("xref");
pdf_print("0 "); pdf_print_int_ln(obj_ptr + 1);
pdf_print_fw_int(obj_link(0), 10);
pdf_print_ln(" 65535 f ");
for k := 1 to obj_ptr do begin
    if obj_offset(k) = 0 then begin
        pdf_print_fw_int(obj_link(k), 10);
        pdf_print_ln(" 00000 f ");
    end
    else begin
        pdf_print_fw_int(obj_offset(k), 10);
        pdf_print_ln(" 00000 n ");
    end;
end

@ @<Output the cross-reference stream dictionary@>=
pdf_new_dict(obj_type_others, 0, 0);
if obj_offset(sys_obj_ptr) > 16777215 then
    xref_offset_width := 4
else if obj_offset(sys_obj_ptr) > 65535 then
    xref_offset_width := 3
else if obj_offset(sys_obj_ptr) > 255 then
    xref_offset_width := 2
else
    xref_offset_width := 1;
l := 0;
for k := 1 to sys_obj_ptr do
    if obj_offset(k) = 0 then begin
        obj_link(l) := k;
        l := k;
    end;
obj_link(l) := 0;
pdf_print_ln("/Type /XRef");
pdf_print("/Index [0 ");
pdf_print_int(obj_ptr);
pdf_print_ln("]");
pdf_int_entry_ln("Size", obj_ptr);
pdf_print("/W [1 ");
pdf_print_int(xref_offset_width);
pdf_print_ln(" 1]");
pdf_indirect_ln("Root", root);
pdf_indirect_ln("Info", obj_ptr - 1);
if pdf_trailer_toks <> null then begin
    pdf_print_toks_ln(pdf_trailer_toks);
    delete_toks(pdf_trailer_toks);
end;
print_ID(output_file_name);
pdf_print_nl;
pdf_begin_stream;
for k := 0 to sys_obj_ptr do begin
    if obj_offset(k) = 0 then begin {a free object}
        pdf_out(0);
        pdf_out_bytes(obj_link(k), xref_offset_width);
        pdf_out(255);
    end else begin
        if obj_os_idx(k) = -1 then begin {object not in object stream}
            pdf_out(1);
            pdf_out_bytes(obj_offset(k), xref_offset_width);
            pdf_out(0);
        end else begin {object in object stream}
            pdf_out(2);
            pdf_out_bytes(obj_offset(k), xref_offset_width);
            pdf_out(obj_os_idx(k));
        end;
    end;
end;
pdf_end_stream;

@ @<Output the trailer@>=
if not pdf_os_enable then begin
    pdf_print_ln("trailer");
    pdf_print("<< ");
    pdf_int_entry_ln("Size", sys_obj_ptr + 1);
    pdf_indirect_ln("Root", root);
    pdf_indirect_ln("Info", sys_obj_ptr);
    if pdf_trailer_toks <> null then begin
        pdf_print_toks_ln(pdf_trailer_toks);
        delete_toks(pdf_trailer_toks);
    end;
    print_ID(output_file_name);
    pdf_print_ln(" >>");
end;
pdf_print_ln("startxref");
if pdf_os_enable then
    pdf_print_int_ln(obj_offset(sys_obj_ptr))
else
    pdf_print_int_ln(pdf_save_offset);
pdf_print_ln("%%EOF")

@* \[33] Packaging.
We're essentially done with the parts of \TeX\ that are concerned with
the input (|get_next|) and the output (|ship_out|). So it's time to
get heavily into the remaining part, which does the real work of typesetting.

After lists are constructed, \TeX\ wraps them up and puts them into boxes.
Two major subroutines are given the responsibility for this task: |hpack|
applies to horizontal lists (hlists) and |vpack| applies to vertical lists
(vlists). The main duty of |hpack| and |vpack| is to compute the dimensions
of the resulting boxes, and to adjust the glue if one of those dimensions
is pre-specified. The computed sizes normally enclose all of the material
inside the new box; but some items may stick out if negative glue is used,
if the box is overfull, or if a \.{\\vbox} includes other boxes that have
been shifted left.

The subroutine call |hpack(p,w,m)| returns a pointer to an |hlist_node|
for a box containing the hlist that starts at |p|. Parameter |w| specifies
a width; and parameter |m| is either `|exactly|' or `|additional|'.  Thus,
|hpack(p,w,exactly)| produces a box whose width is exactly |w|, while
|hpack(p,w,additional)| yields a box whose width is the natural width plus
|w|.  It is convenient to define a macro called `|natural|' to cover the
most common case, so that we can say |hpack(p,natural)| to get a box that
has the natural width of list |p|.

Similarly, |vpack(p,w,m)| returns a pointer to a |vlist_node| for a
box containing the vlist that starts at |p|. In this case |w| represents
a height instead of a width; the parameter |m| is interpreted as in |hpack|.

@d exactly=0 {a box dimension is pre-specified}
@d additional=1 {a box dimension is increased from the natural one}
@d natural==0,additional {shorthand for parameters to |hpack| and |vpack|}

@<Glob...@>=
pack_direction:integer;
spec_direction:integer;

@ The parameters to |hpack| and |vpack| correspond to \TeX's primitives
like `\.{\\hbox} \.{to} \.{300pt}', `\.{\\hbox} \.{spread} \.{10pt}'; note
that `\.{\\hbox}' with no dimension following it is equivalent to
`\.{\\hbox} \.{spread} \.{0pt}'.  The |scan_spec| subroutine scans such
constructions in the user's input, including the mandatory left brace that
follows them, and it puts the specification onto |save_stack| so that the
desired box can later be obtained by executing the following code:
$$\vbox{\halign{#\hfil\cr
|save_ptr:=save_ptr-2;|\cr
|hpack(p,saved(1),saved(0)).|\cr}}$$
Special care is necessary to ensure that the special |save_stack| codes
are placed just below the new group code, because scanning can change
|save_stack| when \.{\\csname} appears.

@p procedure scan_spec(@!c:group_code;@!three_codes:boolean);
  {scans a box specification and left brace}
label found, continue;
var @!s:integer; {temporarily saved value}
i:integer; v:integer;
@!spec_code:exactly..additional;
attr_list:halfword; 
begin s:=0;
if attr_list_cache=cache_disabled then update_attribute_cache; 
attr_list:=attr_list_cache;
if three_codes then begin
  s:=saved(0);
continue:
  if scan_keyword("attr") then begin
    scan_register_num; i:=cur_val;
    scan_optional_equals;
    scan_int; v:=cur_val;
	if (attr_list<>null) and (attr_list=attr_list_cache) then begin
      attr_list:=copy_attribute_list(attr_list_cache);
	  add_node_attr_ref(attr_list); {will be used once}
      end;
    attr_list:=do_set_attribute(attr_list,i,v);
    goto continue;
  end;
  if scan_keyword("dir") then begin
    scan_direction; spec_direction:=cur_val;
    goto continue;
    end;
  end;
if attr_list=attr_list_cache then begin add_node_attr_ref(attr_list); end;
if scan_keyword("to") then spec_code:=exactly
@.to@>
else if scan_keyword("spread") then spec_code:=additional
@.spread@>
else  begin spec_code:=additional; cur_val:=0;
  goto found;
  end;
scan_normal_dimen;
found: if three_codes then begin 
    saved(0):=s; 
    saved(1):=spec_code;
    saved(2):=cur_val;
    saved(3):=spec_direction;
    @<DIR: Adjust |text_dir_ptr| for |scan_spec|@>;
    saved(5):=attr_list;
    save_ptr:=save_ptr+6;
    new_save_level(c); scan_left_brace;
    eq_word_define(dir_base+body_direction_code,spec_direction);
    eq_word_define(dir_base+par_direction_code,spec_direction);
    eq_word_define(dir_base+text_direction_code,spec_direction);
    eq_word_define(int_base+level_local_dir_code,cur_level);
    end 
  else begin
    saved(0):=spec_code; 
    saved(1):=cur_val;
    save_ptr:=save_ptr+2;
    new_save_level(c); scan_left_brace;
  end;
spec_direction:=-1;
end;

@ To figure out the glue setting, |hpack| and |vpack| determine how much
stretchability and shrinkability are present, considering all four orders
of infinity. The highest order of infinity that has a nonzero coefficient
is then used as if no other orders were present.

For example, suppose that the given list contains six glue nodes with
the respective stretchabilities 3pt, 8fill, 5fil, 6pt, $-3$fil, $-8$fill.
Then the total is essentially 2fil; and if a total additional space of 6pt
is to be achieved by stretching, the actual amounts of stretch will be
0pt, 0pt, 15pt, 0pt, $-9$pt, and 0pt, since only `fil' glue will be
considered. (The `fill' glue is therefore not really stretching infinitely
with respect to `fil'; nobody would actually want that to happen.)

The arrays |total_stretch| and |total_shrink| are used to determine how much
glue of each kind is present. A global variable |last_badness| is used
to implement \.{\\badness}.

@<Glob...@>=
@!total_stretch, @!total_shrink: array[glue_ord] of scaled;
  {glue found by |hpack| or |vpack|}
@!last_badness:integer; {badness of the most recently packaged box}

@ If the global variable |adjust_tail| is non-null, the |hpack| routine
also removes all occurrences of |ins_node|, |mark_node|, and |adjust_node|
items and appends the resulting material onto the list that ends at
location |adjust_tail|.

@< Glob...@>=
@!adjust_tail:pointer; {tail of adjustment list}

@ @<Set init...@>=adjust_tail:=null; last_badness:=0;

@ @<Glob...@>=
@!font_expand_ratio: integer; {current expansion ratio}
@!last_leftmost_char: pointer;
@!last_rightmost_char: pointer;

@ @d cal_margin_kern_var(#) ==
begin
    character(cp) := character(#);
    font(cp) := font(#);
    do_subst_font(cp, 1000);
    if font(cp) <> font(#) then
        margin_kern_stretch := margin_kern_stretch + left_pw(#) - left_pw(cp);
    font(cp) := font(#);
    do_subst_font(cp, -1000);
    if font(cp) <> font(#) then
        margin_kern_shrink := margin_kern_shrink + left_pw(cp) - left_pw(#);
end

@ @<Glob...@>=
next_char_p:pointer; {pointer to the next char of an implicit kern}
prev_char_p:pointer; {pointer to the previous char of an implicit kern}

@ This procedure is called repeatedly from inside the line break algorithm.

@p procedure set_prev_char_p(p:pointer);
begin prev_char_p:=p;
end;

@ Here is |hpack|, which is place where we do font substituting when
font expansion is being used. We define some constants used when calling
|hpack| to deal with font expansion.

@d cal_expand_ratio    == 2 {calculate amount for font expansion after breaking
                             paragraph into lines}
@d subst_ex_font       == 3 {substitute fonts}

@d substituted = 3 {|subtype| of kern nodes that should be substituted}

@d left_pw(#) == char_pw(#, left_side)
@d right_pw(#) == char_pw(#, right_side)

@p function char_stretch(p:halfword): scaled;
var k: internal_font_number;
    dw: scaled;
    ef: integer;
    f: internal_font_number; 
    c: integer;
begin
    f := font(p);
    c := character(p);
    char_stretch := 0;
    k := pdf_font_stretch(f);
    ef := get_ef_code(f, c);
    if (k <> null_font) and (ef > 0) then begin
        dw := char_width(k,c) - char_width(f,c);
        if dw > 0 then
            char_stretch := round_xn_over_d(dw, ef, 1000);
    end;
end;

function char_shrink(p:halfword): scaled;
var k: internal_font_number;
    dw: scaled;
    ef: integer;
    f: internal_font_number; 
    c: integer;
begin
    f := font(p);
    c := character(p);
    char_shrink := 0;
    k := pdf_font_shrink(f);
    ef := get_ef_code(f, c);
    if (k <> null_font) and (ef > 0) then begin
        dw := char_width(f,c) - char_width(k,c);
        if dw > 0 then
            char_shrink := round_xn_over_d(dw, ef, 1000);
    end;
end;

function kern_stretch(p: pointer): scaled;
var l, r: pointer;
    d: scaled;
begin
    kern_stretch := 0;
    if (prev_char_p = null) or (vlink(prev_char_p) <> p) or (vlink(p) = null)
    then
        return;
    l := prev_char_p;
    r := vlink(p);
    if not (is_char_node(l) and is_char_node(r) and
            (font(l) = font(r)) and
            (pdf_font_stretch(font(l)) <> null_font))
    then
        return;
    d := get_kern(pdf_font_stretch(font(l)), character(l), character(r));
    kern_stretch := round_xn_over_d(d - width(p),
                                    get_ef_code(font(l), character(l)), 1000);
end;

function kern_shrink(p: pointer): scaled;
var l, r: pointer;
    d: scaled;
begin
    kern_shrink := 0;
    if (prev_char_p = null) or (vlink(prev_char_p) <> p) or (vlink(p) = null)
    then
        return;
    l := prev_char_p;
    r := vlink(p);
    if not (is_char_node(l) and is_char_node(r) and
            (font(l) = font(r)) and
            (pdf_font_shrink(font(l)) <> null_font))
    then
        return;
    d := get_kern(pdf_font_shrink(font(l)), character(l), character(r));
    kern_shrink := round_xn_over_d(width(p) - d,
                                    get_ef_code(font(l), character(l)), 1000);
end;

procedure do_subst_font(p: pointer; ex_ratio: integer);
var f, k: internal_font_number;
    r: pointer;
    ef: integer;
begin
    if not is_char_node(p) and (type(p) = disc_node) then begin
        r := vlink(pre_break(p));
        while r <> null do begin
            if is_char_node(r) then
                do_subst_font(r, ex_ratio);
            r := vlink(r);
        end;
        r := vlink(post_break(p));
        while r <> null do begin
            if is_char_node(r) then
                do_subst_font(r, ex_ratio);
            r := vlink(r);
        end;
        r := vlink(no_break(p));
        while r <> null do begin
            if is_char_node(r) then
                do_subst_font(r, ex_ratio);
            r := vlink(r);
        end;
        return;
    end;
    if is_char_node(p) then
        r := p
    else begin
        {|short_display_n(p, 5);|}
        pdf_error("font expansion", "invalid node type");
	    return;
    end;
    f := font(r);
    ef := get_ef_code(f, character(r));
    if ef = 0 then
        return;
    if (pdf_font_expand_ratio(f)=0) and 
       (pdf_font_stretch(f) <> null_font) and 
       (ex_ratio > 0) then
        k := expand_font(f, ext_xn_over_d(ex_ratio*ef,
                                          pdf_font_expand_ratio(pdf_font_stretch(f)),
                                          1000000))
    else if (pdf_font_expand_ratio(f)=0) and 
            (pdf_font_shrink(f) <> null_font) and (ex_ratio < 0) then
        k := expand_font(f, ext_xn_over_d(ex_ratio*ef,
                                          -pdf_font_expand_ratio(pdf_font_shrink(f)),
                                          1000000))
    else
        k := f;
    if k <> f then begin
        font(r) := k;
        if not is_char_node(p) then begin
            r := lig_ptr(p);
            while r <> null do begin
                font(r) := k;
                r := vlink(r);
            end;
        end;
    end;
end;

function char_pw(p: pointer; side: small_number): scaled;
var f: internal_font_number;
    c: integer;
begin
    char_pw := 0;
    if side = left_side then
        last_leftmost_char := null
    else
        last_rightmost_char := null;
    if p = null then
        return;
    if not is_char_node(p) then 
        return;
    f := font(p);
    if side = left_side then begin
        c := get_lp_code(f, character(p));
        last_leftmost_char := p;
    end
    else begin
        c := get_rp_code(f, character(p));
        last_rightmost_char := p;
    end;
    if c = 0 then
        return;
    char_pw :=
        round_xn_over_d(quad(f), c, 1000);
end;

function new_margin_kern(w: scaled; p: pointer; side: small_number): pointer;
var k,q: pointer;
begin
    k := new_node(margin_kern_node,side);
    width(k) := w;
    if p = null then
        pdf_error("margin kerning", "invalid pointer to marginal char node");
    q := new_char(font(p), character(p)); margin_char(k):=q;
    new_margin_kern := k;
end;

function hpack(@!p:pointer;@!w:scaled;@!m:small_number):pointer;
label reswitch,common_ending,exit;
var r:pointer; {the box node that will be returned}
@!q:pointer; {trails behind |p|}
@!h,@!d,@!x:scaled; {height, depth, and natural width}
@!s:scaled; {shift amount}
@!g:pointer; {points to a glue specification}
@!o:glue_ord; {order of infinity}
@!f:internal_font_number; {the font in a |char_node|}
@!dir_tmp,dir_ptr:pointer; {for managing the direction stack}
@!hpack_dir:integer; {the current direction}
@!disc_level:integer;
pack_interrupt:array[0..255] of halfword;
font_stretch: scaled;
font_shrink: scaled;
k: scaled;
begin last_badness:=0; r:=new_node(hlist_node,min_quarterword);
if pack_direction=-1 then
  box_dir(r):=text_direction
else begin
  box_dir(r):=pack_direction; pack_direction:=-1;
  end;
hpack_dir:=box_dir(r);
dir_ptr:=null;
push_dir(hpack_dir);
q:=r+list_offset; vlink(q):=p;@/
if m = cal_expand_ratio then begin
    prev_char_p := null;
    font_stretch := 0;
    font_shrink := 0;
    font_expand_ratio := 0;
end;
@{
if m = subst_ex_font then begin
  wterm_ln('replacing ', font_expand_ratio:1);
end;
@}
h:=0; @<Clear dimensions to zero@>;
disc_level:=0;
reswitch:
while (p<>null)or(disc_level>0) do begin
  if p=null then begin
     decr(disc_level);
     p:=pack_interrupt[disc_level];
     goto reswitch;
     end;
  @<Examine node |p| in the hlist, taking account of its effect
  on the dimensions of the new box, or moving it to the adjustment list;
  then advance |p| to the next node@>;
  end;
if adjust_tail<>null then vlink(adjust_tail):=null;
if pre_adjust_tail<>null then vlink(pre_adjust_tail):=null;
height(r):=h; depth(r):=d;@/
@<Determine the value of |width(r)| and the appropriate glue setting;
  then |return| or |goto common_ending|@>;
common_ending: @<Finish issuing a diagnostic message
      for an overfull or underfull hbox@>;
exit: 
if (m = cal_expand_ratio) and (font_expand_ratio <> 0) then begin
    font_expand_ratio := fix_int(font_expand_ratio, -1000, 1000);
    q := list_ptr(r);
	list_ptr(r):=null; flush_node(r);
    r:=hpack(q, w, subst_ex_font);
end;
while dir_ptr<>null do pop_dir_node;
hpack:=r;
end;

function filtered_hpack(@!p:pointer;@!qt:pointer;@!w:scaled;@!m:small_number;@!grp:integer):pointer;
var q:pointer;
  d:integer; { a direction }
begin
  new_hyphenation(p,qt);
  call_func(new_ligkern(p,qt)); {don't care about the tail in this case}
  q:=vlink(p);
  q:=lua_hpack_filter(q,w,m,grp);
  filtered_hpack:=hpack(q,w,m);
end;

@ @<Clear dimensions to zero@>=
d:=0; x:=0;
total_stretch[normal]:=0; total_shrink[normal]:=0;
total_stretch[sfi]:=0; total_shrink[sfi]:=0;
total_stretch[fil]:=0; total_shrink[fil]:=0;
total_stretch[fill]:=0; total_shrink[fill]:=0;
total_stretch[filll]:=0; total_shrink[filll]:=0

@ @<Examine node |p| in the hlist, taking account of its effect...@>=
@^inner loop@>
begin while is_char_node(p) do
  @<Incorporate character dimensions into the dimensions of
    the hbox that will contain~it, then move to the next node@>;
if p<>null then
  begin case type(p) of
  hlist_node,vlist_node,rule_node,unset_node:
    @<Incorporate box dimensions into the dimensions of
      the hbox that will contain~it@>;
  ins_node,mark_node,adjust_node: begin if adjust_tail<>null then
    @<Transfer node |p| to the adjustment list@>; end;
  whatsit_node:@<Incorporate a whatsit node into an hbox@>;
  glue_node:@<Incorporate glue into the horizontal totals@>;
    margin_kern_node: begin
    if m = cal_expand_ratio then begin
        f := font(margin_char(p));
        do_subst_font(margin_char(p), 1000);
        if f <> font(margin_char(p)) then
            font_stretch := font_stretch - width(p) -
                char_pw(margin_char(p), subtype(p));
        font(margin_char(p)) := f;
        do_subst_font(margin_char(p), -1000);
        if f <> font(margin_char(p)) then
            font_shrink := font_shrink - width(p) -
                char_pw(margin_char(p), subtype(p));
        font(margin_char(p)) := f;
      end
    else if m = subst_ex_font then begin
            do_subst_font(margin_char(p), font_expand_ratio);
            width(p) := -char_pw(margin_char(p), subtype(p));
      end;
    x := x + width(p);
    end;
  kern_node: begin
    if subtype(p) = normal then begin
        if m = cal_expand_ratio then begin
            font_stretch := font_stretch + kern_stretch(p);
            font_shrink := font_shrink + kern_shrink(p);
        end
        else if m = subst_ex_font then begin
            if font_expand_ratio > 0 then
                k := kern_stretch(p)
            else if font_expand_ratio < 0 then
                k := kern_shrink(p)
            else
                pdfassert(0);
            if k <> 0 then
               width(p) := get_kern(font(prev_char_p),
                                    character(prev_char_p),
                                    character(vlink(p)))
        end;
      end;
    x := x + width(p);
    end;
  math_node: x:=x+surround(p);
  disc_node:
      begin
      if m = subst_ex_font then do_subst_font(p, font_expand_ratio);
      if vlink(no_break(p))<>null then begin
        pack_interrupt[disc_level]:=vlink(p);
        incr(disc_level);
        p:=no_break(p);
        end;
      end;
  othercases do_nothing
  endcases;@/
  p:=vlink(p);
  end;
end


@ The code here implicitly uses the fact that running dimensions are
indicated by |null_flag|, which will be ignored in the calculations
because it is a highly negative number.

@<Incorporate box dimensions into the dimensions of the hbox...@>=
begin
if (type(p)=hlist_node) or (type(p)=vlist_node) then begin
  if dir_orthogonal(dir_primary[box_dir(p)])(dir_primary[hpack_dir]) then begin
    x:=x+height(p)+depth(p);
    s:=shift_amount(p);
    if (width(p) div 2)-s>h then h:=(width(p) div 2)-s;
    if (width(p) div 2)+s>d then d:=(width(p) div 2)+s;
    end
  else if (type(p)=hlist_node) and (is_mirrored(hpack_dir)) then begin
    x:=x+width(p);
    s:=shift_amount(p);
    if depth(p)-s>h then h:=depth(p)-s;
    if height(p)+s>d then d:=height(p)+s;
    end
  else begin
    x:=x+width(p);
    s:=shift_amount(p);
    if height(p)-s>h then h:=height(p)-s;
    if depth(p)+s>d then d:=depth(p)+s;
    end
  end
else begin
  x:=x+width(p);
  if type(p)>=rule_node then s:=0 @+else s:=shift_amount(p);
  if height(p)-s>h then h:=height(p)-s;
  if depth(p)+s>d then d:=depth(p)+s;
  end;
end

@ The following code is part of \TeX's inner loop; i.e., adding another
character of text to the user's input will cause each of these instructions
to be exercised one more time.
@^inner loop@>

@d add_char_stretch_end(#) == char_stretch(#)
@d add_char_stretch(#) == # := # + add_char_stretch_end

@d add_char_shrink_end(#) == char_shrink(#)
@d add_char_shrink(#) == # := # + add_char_shrink_end

@<Incorporate character dimensions into the dimensions of the hbox...@>=
begin
if m >= cal_expand_ratio then begin
    prev_char_p := p;
    case m of
    cal_expand_ratio: begin
        add_char_stretch(font_stretch)(p);
        add_char_shrink(font_shrink)(p);
    end;
    subst_ex_font:
        do_subst_font(p, font_expand_ratio);
    endcases;
end;
f:=font(p);
if is_rotated(hpack_dir) then begin
  x:=x+glyph_height(p)+glyph_depth(p);@/
  s:=glyph_width(p) div 2;@+if s>h then h:=s;@+if s>d then d:=s;
  end
else if dir_opposite(dir_tertiary[hpack_dir])(dir_tertiary[box_dir(r)])
  then begin
  x:=x+glyph_width(p);@/
  s:=glyph_depth(p);@+if s>h then h:=s;
  s:=glyph_height(p);@+if s>d then d:=s;
  end
else begin
  x:=x+glyph_width(p);@/
  s:=glyph_height(p);@+if s>h then h:=s;
  s:=glyph_depth(p);@+if s>d then d:=s;
  end;
p:=vlink(p);
end

@ Although node |q| is not necessarily the immediate predecessor of node |p|,
it always points to some node in the list preceding |p|. Thus, we can delete
nodes by moving |q| when necessary. The algorithm takes linear time, and the
extra computation does not intrude on the inner loop unless it is necessary
to make a deletion.
@^inner loop@>

@<Glob...@>=
@!pre_adjust_tail: pointer;

@ @<Set init...@>=
pre_adjust_tail := null;

@ Materials in \.{\\vadjust} used with \.{pre} keyword will be appended to
|pre_adjust_tail| instead of |adjust_tail|.

@d update_adjust_list(#) == begin
    vlink(#) := adjust_ptr(p);
    while vlink(#) <> null do
        # := vlink(#);
end

@<Transfer node |p| to the adjustment list@>=
begin while vlink(q)<>p do q:=vlink(q);
    if type(p) = adjust_node then begin
        if adjust_pre(p) <> 0 then
            update_adjust_list(pre_adjust_tail)
        else
            update_adjust_list(adjust_tail);
        p := vlink(p); 
        adjust_ptr(vlink(q)):=null; flush_node(vlink(q));
    end
else  begin vlink(adjust_tail):=p; adjust_tail:=p; p:=vlink(p);
  end;
vlink(q):=p; p:=q;
end

@ @<Incorporate glue into the horizontal totals@>=
begin g:=glue_ptr(p); x:=x+width(g);@/
o:=stretch_order(g); total_stretch[o]:=total_stretch[o]+stretch(g);
o:=shrink_order(g); total_shrink[o]:=total_shrink[o]+shrink(g);
if subtype(p)>=a_leaders then
  begin g:=leader_ptr(p);
  if height(g)>h then h:=height(g);
  if depth(g)>d then d:=depth(g);
  end;
end

@ When we get to the present part of the program, |x| is the natural width
of the box being packaged.

@<Determine the value of |width(r)| and the appropriate glue setting...@>=
if m=additional then w:=x+w;
width(r):=w; x:=w-x; {now |x| is the excess to be made up}
if x=0 then
  begin glue_sign(r):=normal; glue_order(r):=normal;
  set_glue_ratio_zero(glue_set(r));
  return;
  end
else if x>0 then @<Determine horizontal glue stretch setting, then |return|
    or \hbox{|goto common_ending|}@>
else @<Determine horizontal glue shrink setting, then |return|
    or \hbox{|goto common_ending|}@>

@ If |hpack| is called with |m=cal_expand_ratio| we calculate
|font_expand_ratio| and return without checking for overfull or underfull box.

@<Determine horizontal glue stretch setting...@>=
begin @<Determine the stretch order@>;
if (m = cal_expand_ratio) and (o = normal) and (font_stretch > 0) then begin
    font_expand_ratio := divide_scaled_n(x, font_stretch, 1000.0);
    return;
end;
glue_order(r):=o; glue_sign(r):=stretching;
if total_stretch[o]<>0 then glue_set(r):=unfloat(x/total_stretch[o])
@^real division@>
else  begin glue_sign(r):=normal;
  set_glue_ratio_zero(glue_set(r)); {there's nothing to stretch}
  end;
if o=normal then if list_ptr(r)<>null then
  @<Report an underfull hbox and |goto common_ending|, if this box
    is sufficiently bad@>;
return;
end

@ @<Determine the stretch order@>=
if total_stretch[filll]<>0 then o:=filll
else if total_stretch[fill]<>0 then o:=fill
else if total_stretch[fil]<>0 then o:=fil
else if total_stretch[sfi]<>0 then o:=sfi
else o:=normal

@ @<Report an underfull hbox and |goto common_ending|, if...@>=
begin last_badness:=badness(x,total_stretch[normal]);
if last_badness>hbadness then
  begin print_ln;
  if last_badness>100 then print_nl("Underfull")@+else print_nl("Loose");
  print(" \hbox (badness "); print_int(last_badness);
@.Underfull \\hbox...@>
@.Loose \\hbox...@>
  goto common_ending;
  end;
end

@ In order to provide a decent indication of where an overfull or underfull
box originated, we use a global variable |pack_begin_line| that is
set nonzero only when |hpack| is being called by the paragraph builder
or the alignment finishing routine.

@<Glob...@>=
@!pack_begin_line:integer; {source file line where the current paragraph
  or alignment began; a negative value denotes alignment}

@ @<Set init...@>=
pack_begin_line:=0;

@ @<Finish issuing a diagnostic message for an overfull or underfull hbox@>=
if output_active then print(") has occurred while \output is active")
else  begin if pack_begin_line<>0 then
    begin if pack_begin_line>0 then print(") in paragraph at lines ")
    else print(") in alignment at lines ");
    print_int(abs(pack_begin_line));
    print("--");
    end
  else print(") detected at line ");
  print_int(line);
  end;
print_ln;@/
font_in_short_display:=null_font; short_display(list_ptr(r)); print_ln;@/
begin_diagnostic; show_box(r); end_diagnostic(true)

@ @<Determine horizontal glue shrink setting...@>=
begin @<Determine the shrink order@>;
if (m = cal_expand_ratio) and (o = normal) and (font_shrink > 0) then begin
    font_expand_ratio := divide_scaled_n(x, font_shrink, 1000.0);
    return;
end;
glue_order(r):=o; glue_sign(r):=shrinking;
if total_shrink[o]<>0 then glue_set(r):=unfloat((-x)/total_shrink[o])
@^real division@>
else  begin glue_sign(r):=normal;
  set_glue_ratio_zero(glue_set(r)); {there's nothing to shrink}
  end;
if (total_shrink[o]<-x)and(o=normal)and(list_ptr(r)<>null) then
  begin last_badness:=1000000;
  set_glue_ratio_one(glue_set(r)); {use the maximum shrinkage}
  @<Report an overfull hbox and |goto common_ending|, if this box
    is sufficiently bad@>;
  end
else if o=normal then if list_ptr(r)<>null then
  @<Report a tight hbox and |goto common_ending|, if this box
    is sufficiently bad@>;
return;
end

@ @<Determine the shrink order@>=
if total_shrink[filll]<>0 then o:=filll
else if total_shrink[fill]<>0 then o:=fill
else if total_shrink[fil]<>0 then o:=fil
else if total_shrink[sfi]<>0 then o:=sfi
else o:=normal

@ @<Report an overfull hbox and |goto common_ending|, if...@>=
if (-x-total_shrink[normal]>hfuzz)or(hbadness<100) then
  begin if (overfull_rule>0)and(-x-total_shrink[normal]>hfuzz) then
    begin while vlink(q)<>null do q:=vlink(q);
    vlink(q):=new_rule;  rule_dir(vlink(q)):=box_dir(r);
    width(vlink(q)):=overfull_rule;
    end;
  print_ln; print_nl("Overfull \hbox (");
@.Overfull \\hbox...@>
  print_scaled(-x-total_shrink[normal]); print("pt too wide");
  goto common_ending;
  end

@ @<Report a tight hbox and |goto common_ending|, if...@>=
begin last_badness:=badness(-x,total_shrink[normal]);
if last_badness>hbadness then
  begin print_ln; print_nl("Tight \hbox (badness "); print_int(last_badness);
@.Tight \\hbox...@>
  goto common_ending;
  end;
end

@ The |vpack| subroutine is actually a special case of a slightly more
general routine called |vpackage|, which has four parameters. The fourth
parameter, which is |max_dimen| in the case of |vpack|, specifies the
maximum depth of the page box that is constructed. The depth is first
computed by the normal rules; if it exceeds this limit, the reference
point is simply moved down until the limiting depth is attained.

@d vpack(#)==vpackage(#,max_dimen) {special case of unconstrained depth}

@p function vpackage(@!p:pointer;@!h:scaled;@!m:small_number;@!l:scaled):
  pointer;
label common_ending, exit;
var r:pointer; {the box node that will be returned}
@!w,@!d,@!x:scaled; {width, depth, and natural height}
@!s:scaled; {shift amount}
@!g:pointer; {points to a glue specification}
@!o:glue_ord; {order of infinity}
begin last_badness:=0; 
{pdfassert(p<>0);}
r:=new_node(vlist_node,0);
if pack_direction=-1 then
  box_dir(r):=body_direction
else begin
  box_dir(r):=pack_direction; pack_direction:=-1;
  end;
subtype(r):=min_quarterword; shift_amount(r):=0;
list_ptr(r):=p;@/
w:=0; @<Clear dimensions to zero@>;
while p<>null do @<Examine node |p| in the vlist, taking account of its effect
  on the dimensions of the new box; then advance |p| to the next node@>;
width(r):=w;
if d>l then
  begin x:=x+d-l; depth(r):=l;
  end
else depth(r):=d;
@<Determine the value of |height(r)| and the appropriate glue setting;
  then |return| or |goto common_ending|@>;
common_ending: @<Finish issuing a diagnostic message
      for an overfull or underfull vbox@>;
exit: vpackage:=r;
end;

function filtered_vpackage(@!p:pointer;@!h:scaled;@!m:small_number;@!l:scaled;@!grp:integer):pointer;
var q:pointer;
begin
  q:=p;
  q:=lua_vpack_filter(q,h,m,l,grp);
  filtered_vpackage:=vpackage(q,h,m,l);
end;

@ @<Examine node |p| in the vlist, taking account of its effect...@>=
begin if is_char_node(p) then confusion("vpack")
@:this can't happen vpack}{\quad vpack@>
else  case type(p) of
  hlist_node,vlist_node,rule_node,unset_node:
    @<Incorporate box dimensions into the dimensions of
      the vbox that will contain~it@>;
  whatsit_node:@<Incorporate a whatsit node into a vbox@>;
  glue_node: @<Incorporate glue into the vertical totals@>;
  kern_node: begin x:=x+d+width(p); d:=0;
    end;
  othercases do_nothing
  endcases;
p:=vlink(p);
end

@ @<Incorporate box dimensions into the dimensions of the vbox...@>=
begin
if (type(p)=hlist_node) or (type(p)=vlist_node) then begin
  if dir_orthogonal(dir_primary[box_dir(p)])(dir_primary[box_dir(r)]) then begin
    x:=x+d+(width(p) div 2); d:=width(p) div 2;
    s:=shift_amount(p);
    if depth(p)+height(p)+s>w then w:=depth(p)+height(p)+s;
    end
  else if (type(p)=hlist_node) and (is_mirrored(box_dir(p))) then begin
    x:=x+d+depth(p); d:=height(p);
    s:=shift_amount(p);
    if width(p)+s>w then w:=width(p)+s;
    end
  else begin
    x:=x+d+height(p); d:=depth(p);
    s:=shift_amount(p);
    if width(p)+s>w then w:=width(p)+s;
    end
  end  
else
  begin x:=x+d+height(p); d:=depth(p);
  if type(p)>=rule_node then s:=0 @+else s:=shift_amount(p);
  if width(p)+s>w then w:=width(p)+s;
  end;
end

@ @<Incorporate glue into the vertical totals@>=
begin x:=x+d; d:=0;@/
g:=glue_ptr(p); x:=x+width(g);@/
o:=stretch_order(g); total_stretch[o]:=total_stretch[o]+stretch(g);
o:=shrink_order(g); total_shrink[o]:=total_shrink[o]+shrink(g);
if subtype(p)>=a_leaders then
  begin g:=leader_ptr(p);
  if width(g)>w then w:=width(g);
  end;
end

@ When we get to the present part of the program, |x| is the natural height
of the box being packaged.

@<Determine the value of |height(r)| and the appropriate glue setting...@>=
if m=additional then h:=x+h;
height(r):=h; x:=h-x; {now |x| is the excess to be made up}
if x=0 then
  begin glue_sign(r):=normal; glue_order(r):=normal;
  set_glue_ratio_zero(glue_set(r));
  return;
  end
else if x>0 then @<Determine vertical glue stretch setting, then |return|
    or \hbox{|goto common_ending|}@>
else @<Determine vertical glue shrink setting, then |return|
    or \hbox{|goto common_ending|}@>

@ @<Determine vertical glue stretch setting...@>=
begin @<Determine the stretch order@>;
glue_order(r):=o; glue_sign(r):=stretching;
if total_stretch[o]<>0 then glue_set(r):=unfloat(x/total_stretch[o])
@^real division@>
else  begin glue_sign(r):=normal;
  set_glue_ratio_zero(glue_set(r)); {there's nothing to stretch}
  end;
if o=normal then if list_ptr(r)<>null then
  @<Report an underfull vbox and |goto common_ending|, if this box
    is sufficiently bad@>;
return;
end

@ @<Report an underfull vbox and |goto common_ending|, if...@>=
begin last_badness:=badness(x,total_stretch[normal]);
if last_badness>vbadness then
  begin print_ln;
  if last_badness>100 then print_nl("Underfull")@+else print_nl("Loose");
  print(" \vbox (badness "); print_int(last_badness);
@.Underfull \\vbox...@>
@.Loose \\vbox...@>
  goto common_ending;
  end;
end

@ @<Finish issuing a diagnostic message for an overfull or underfull vbox@>=
if output_active then print(") has occurred while \output is active")
else  begin if pack_begin_line<>0 then {it's actually negative}
    begin print(") in alignment at lines ");
    print_int(abs(pack_begin_line));
    print("--");
    end
  else print(") detected at line ");
  print_int(line);
  print_ln;@/
  end;
begin_diagnostic; show_box(r); end_diagnostic(true)

@ @<Determine vertical glue shrink setting...@>=
begin @<Determine the shrink order@>;
glue_order(r):=o; glue_sign(r):=shrinking;
if total_shrink[o]<>0 then glue_set(r):=unfloat((-x)/total_shrink[o])
@^real division@>
else  begin glue_sign(r):=normal;
  set_glue_ratio_zero(glue_set(r)); {there's nothing to shrink}
  end;
if (total_shrink[o]<-x)and(o=normal)and(list_ptr(r)<>null) then
  begin last_badness:=1000000;
  set_glue_ratio_one(glue_set(r)); {use the maximum shrinkage}
  @<Report an overfull vbox and |goto common_ending|, if this box
    is sufficiently bad@>;
  end
else if o=normal then if list_ptr(r)<>null then
  @<Report a tight vbox and |goto common_ending|, if this box
    is sufficiently bad@>;
return;
end

@ @<Report an overfull vbox and |goto common_ending|, if...@>=
if (-x-total_shrink[normal]>vfuzz)or(vbadness<100) then
  begin print_ln; print_nl("Overfull \vbox (");
@.Overfull \\vbox...@>
  print_scaled(-x-total_shrink[normal]); print("pt too high");
  goto common_ending;
  end

@ @<Report a tight vbox and |goto common_ending|, if...@>=
begin last_badness:=badness(-x,total_shrink[normal]);
if last_badness>vbadness then
  begin print_ln; print_nl("Tight \vbox (badness "); print_int(last_badness);
@.Tight \\vbox...@>
  goto common_ending;
  end;
end

@ When a box is being appended to the current vertical list, the
baselineskip calculation is handled by the |append_to_vlist| routine.

@p procedure append_to_vlist(@!b:pointer);
var d:scaled; {deficiency of space between baselines}
@!p:pointer; {a new glue specification}
begin if prev_depth>ignore_depth then
  begin
  if (type(b)=hlist_node) and (is_mirrored(box_dir(b))) then
    d:=width(baseline_skip)-prev_depth-depth(b)
  else
    d:=width(baseline_skip)-prev_depth-height(b);
  if d<line_skip_limit then p:=new_param_glue(line_skip_code)
  else  begin p:=new_skip_param(baseline_skip_code);
    width(temp_ptr):=d; {|temp_ptr=glue_ptr(p)|}
    end;
  vlink(tail):=p; tail:=p;
  end;
vlink(tail):=b; tail:=b;
if (type(b)=hlist_node) and (is_mirrored(box_dir(b))) then 
  prev_depth:=height(b)
else
  prev_depth:=depth(b);
end;

@* \[34] Data structures for math mode.
When \TeX\ reads a formula that is enclosed between \.\$'s, it constructs an
{\sl mlist}, which is essentially a tree structure representing that
formula.  An mlist is a linear sequence of items, but we can regard it as
a tree structure because mlists can appear within mlists. For example, many
of the entries can be subscripted or superscripted, and such ``scripts''
are mlists in their own right.

An entire formula is parsed into such a tree before any of the actual
typesetting is done, because the current style of type is usually not
known until the formula has been fully scanned. For example, when the
formula `\.{\$a+b \\over c+d\$}' is being read, there is no way to tell
that `\.{a+b}' will be in script size until `\.{\\over}' has appeared.

During the scanning process, each element of the mlist being built is
classified as a relation, a binary operator, an open parenthesis, etc.,
or as a construct like `\.{\\sqrt}' that must be built up. This classification
appears in the mlist data structure.

After a formula has been fully scanned, the mlist is converted to an hlist
so that it can be incorporated into the surrounding text. This conversion is
controlled by a recursive procedure that decides all of the appropriate
styles by a ``top-down'' process starting at the outermost level and working
in towards the subformulas. The formula is ultimately pasted together using
combinations of horizontal and vertical boxes, with glue and penalty nodes
inserted as necessary.

An mlist is represented internally as a linked list consisting chiefly
of ``noads'' (pronounced ``no-adds''), to distinguish them from the somewhat
similar ``nodes'' in hlists and vlists. Certain kinds of ordinary nodes are
allowed to appear in mlists together with the noads; \TeX\ tells the difference
by means of the |type| field, since a noad's |type| is always greater than
that of a node. An mlist does not contain character nodes, hlist nodes, vlist
nodes, math nodes or unset nodes; in particular, each mlist item appears in the
variable-size part of |mem|, so the |type| field is always present.

@ Each noad is five or more words long. The first word contains the
|type| and |subtype| and |link| fields that are already so familiar to
us; the second contains the attribute list pointer, and the third,
fourth an fifth words are called the noad's |nucleus|, |subscr|, and
|supscr| fields. (This use of a combined attribute list is temporary. 
Eventually, each of fields need their own list)

Consider, for example, the simple formula `\.{\$x\^2\$}', which would be
parsed into an mlist containing a single element called an |ord_noad|.
The |nucleus| of this noad is a representation of `\.x', the |subscr| is
empty, and the |supscr| is a representation of `\.2'.

The |nucleus|, |subscr|, and |supscr| fields are further broken into
subfields. If |p| points to a noad, and if |q| is one of its principal
fields (e.g., |q=subscr(p)|), there are several possibilities for the
subfields, depending on the |math_type| of |q|.

\yskip\hang|math_type(q)=math_char| means that |fam(q)| refers to one of
the sixteen font families, and |character(q)| is the number of a character
within a font of that family, as in a character node.

\yskip\hang|math_type(q)=math_text_char| is similar, but the character is
unsubscripted and unsuperscripted and it is followed immediately by another
character from the same font. (This |math_type| setting appears only
briefly during the processing; it is used to suppress unwanted italic
corrections.)

\yskip\hang|math_type(q)=empty| indicates a field with no value (the
corresponding attribute of noad |p| is not present).

\yskip\hang|math_type(q)=sub_box| means that |vinfo(q)| points to a box
node (either an |hlist_node| or a |vlist_node|) that should be used as the
value of the field.  The |shift_amount| in the subsidiary box node is the
amount by which that box will be shifted downward.

\yskip\hang|math_type(q)=sub_mlist| means that |vinfo(q)| points to
an mlist; the mlist must be converted to an hlist in order to obtain
the value of this field.

\yskip\noindent In the latter case, we might have |vinfo(q)=null|. This
is not the same as |math_type(q)=empty|; for example, `\.{\$P\_\{\}\$}'
and `\.{\$P\$}' produce different results (the former will not have the
``italic correction'' added to the width of |P|, but the ``script skip''
will be added).

The definitions of subfields given here are a little wasteful of space,
since a quarterword is being used for the |math_type| although only three
bits would be needed. However, there are hardly ever many noads present at
once, since they are soon converted to nodes that take up even more space,
so we can afford to represent them in whatever way simplifies the
programming.

I tried exchanging |mcharacter()| and |math_type()| so that a character 
could use the full Unicode range, but for some reason that does not work
properly. TH

@d noad_size=5 {number of words in a normal noad}
@d nucleus(#)==#+2 {the |nucleus| field of a noad}
@d supscr(#)==#+3 {the |supscr| field of a noad}
@d subscr(#)==#+4 {the |subscr| field of a noad}
@d math_type==vlink {a |quarterword| in |mem|}
@d fam(#)==type(#) {a |quarterword| in |mem|}
@d mcharacter(#)==subtype(#)
@d math_char=1 {|math_type| when the attribute is simple}
@d sub_box=2 {|math_type| when the attribute is a box}
@d sub_mlist=3 {|math_type| when the attribute is a formula}
@d math_text_char=4 {|math_type| when italic correction is dubious}

@ Each portion of a formula is classified as Ord, Op, Bin, Rel, Ope,
Clo, Pun, or Inn, for purposes of spacing and line breaking. An
|ord_noad|, |op_noad|, |bin_noad|, |rel_noad|, |open_noad|, |close_noad|,
|punct_noad|, or |inner_noad| is used to represent portions of the various
types. For example, an `\.=' sign in a formula leads to the creation of a
|rel_noad| whose |nucleus| field is a representation of an equals sign
(usually |fam=0|, |character=@'75|).  A formula preceded by \.{\\mathrel}
also results in a |rel_noad|.  When a |rel_noad| is followed by an
|op_noad|, say, and possibly separated by one or more ordinary nodes (not
noads), \TeX\ will insert a penalty node (with the current |rel_penalty|)
just after the formula that corresponds to the |rel_noad|, unless there
already was a penalty immediately following; and a ``thick space'' will be
inserted just before the formula that corresponds to the |op_noad|.

A noad of type |ord_noad|, |op_noad|, \dots, |inner_noad| usually
has a |subtype=normal|. The only exception is that an |op_noad| might
have |subtype=limits| or |no_limits|, if the normal positioning of
limits has been overridden for this operator.

@d ord_noad=unset_node+3 {|type| of a noad classified Ord}
@d op_noad=ord_noad+1 {|type| of a noad classified Op}
@d bin_noad=ord_noad+2 {|type| of a noad classified Bin}
@d rel_noad=ord_noad+3 {|type| of a noad classified Rel}
@d open_noad=ord_noad+4 {|type| of a noad classified Ope}
@d close_noad=ord_noad+5 {|type| of a noad classified Clo}
@d punct_noad=ord_noad+6 {|type| of a noad classified Pun}
@d inner_noad=ord_noad+7 {|type| of a noad classified Inn}
@d limits=1 {|subtype| of |op_noad| whose scripts are to be above, below}
@d no_limits=2 {|subtype| of |op_noad| whose scripts are to be normal}

@ A |radical_noad| is five words long; the fifth word is the |left_delimiter|
field, which usually represents a square root sign.

A |fraction_noad| is six words long; it has a |right_delimiter| field
as well as a |left_delimiter|.

Delimiter fields are of type |four_quarters|, and they have four subfields
called |small_fam|, |small_char|, |large_fam|, |large_char|. These subfields
represent variable-size delimiters by giving the ``small'' and ``large''
starting characters, as explained in Chapter~17 of {\sl The \TeX book}.
@:TeXbook}{\sl The \TeX book@>

A |fraction_noad| is actually quite different from all other noads. Not
only does it have six words, it has |thickness|, |denominator|, and
|numerator| fields instead of |nucleus|, |subscr|, and |supscr|. The
|thickness| is a scaled value that tells how thick to make a fraction
rule; however, the special value |default_code| is used to stand for the
|default_rule_thickness| of the current size. The |numerator| and
|denominator| point to mlists that define a fraction; we always have
$$\hbox{|math_type(numerator)=math_type(denominator)=sub_mlist|}.$$ The
|left_delimiter| and |right_delimiter| fields specify delimiters that will
be placed at the left and right of the fraction. In this way, a
|fraction_noad| is able to represent all of \TeX's operators \.{\\over},
\.{\\atop}, \.{\\above}, \.{\\overwithdelims}, \.{\\atopwithdelims}, and
 \.{\\abovewithdelims}.

@d left_delimiter(#)==#+5 {first delimiter field of a noad}
@d right_delimiter(#)==#+6 {second delimiter field of a fraction noad}
@d radical_noad=inner_noad+1 {|type| of a noad for square roots}
@d radical_noad_size=6 {number of |mem| words in a radical noad}
@d fraction_noad=radical_noad+1 {|type| of a noad for generalized fractions}
@d fraction_noad_size=7 {number of |mem| words in a fraction noad}
@d small_fam(#)==vmem(#).qqqq.b0 {|fam| for ``small'' delimiter}
@d small_char(#)==vmem(#).qqqq.b1 {|character| for ``small'' delimiter}
@d large_fam(#)==vmem(#).qqqq.b2 {|fam| for ``large'' delimiter}
@d large_char(#)==vmem(#).qqqq.b3 {|character| for ``large'' delimiter}
@d thickness(#)==vmem(#+2).sc {|thickness| field in a fraction noad}
@d default_code==@'10000000000 {denotes |default_rule_thickness|}
@d numerator==supscr {|numerator| field in a fraction noad}
@d denominator==subscr {|denominator| field in a fraction noad}

@ The global variable |empty_field| is set up for initialization of empty
fields in new noads. Similarly, |null_delimiter| is for the initialization
of delimiter fields.

@<Glob...@>=
@!empty_field:two_halves;
@!null_delimiter:four_quarters;

@ @<Set init...@>=
empty_field.rh:=empty; empty_field.lh:=null;@/
null_delimiter.b0:=0; null_delimiter.b1:=min_quarterword;@/
null_delimiter.b2:=0; null_delimiter.b3:=min_quarterword;

@ The |new_noad| function creates an |ord_noad| that is completely null.

@p function new_noad:pointer;
var p:pointer;
begin p:=new_node(ord_noad,normal);
vmem(nucleus(p)).hh:=empty_field;
vmem(subscr(p)).hh:=empty_field;
vmem(supscr(p)).hh:=empty_field;
new_noad:=p;
end;

@ A few more kinds of noads will complete the set: An |under_noad| has its
nucleus underlined; an |over_noad| has it overlined. An |accent_noad| places
an accent over its nucleus; the accent character appears as
|fam(accent_chr(p))| and |mcharacter(accent_chr(p))|. A |vcenter_noad|
centers its nucleus vertically with respect to the axis of the formula;
in such noads we always have |math_type(nucleus(p))=sub_box|.

And finally, we have |left_noad| and |right_noad| types, to implement
\TeX's \.{\\left} and \.{\\right} as well as \eTeX's \.{\\middle}.
The |nucleus| of such noads is
replaced by a |delimiter| field; thus, for example, `\.{\\left(}' produces
a |left_noad| such that |delimiter(p)| holds the family and character
codes for all left parentheses. A |left_noad| never appears in an mlist
except as the first element, and a |right_noad| never appears in an mlist
except as the last element; furthermore, we either have both a |left_noad|
and a |right_noad|, or neither one is present. The |subscr| and |supscr|
fields are always |empty| in a |left_noad| and a |right_noad|.

@d under_noad=fraction_noad+1 {|type| of a noad for underlining}
@d over_noad=under_noad+1 {|type| of a noad for overlining}
@d accent_noad=over_noad+1 {|type| of a noad for accented subformulas}
@d accent_noad_size=6 {number of |mem| words in an accent noad}
@d accent_chr(#)==#+5 {the |accent_chr| field of an accent noad}
@d vcenter_noad=accent_noad+1 {|type| of a noad for \.{\\vcenter}}
@d left_noad=vcenter_noad+1 {|type| of a noad for \.{\\left}}
@d right_noad=left_noad+1 {|type| of a noad for \.{\\right}}
@d delimiter==nucleus {|delimiter| field in left and right noads}
@d middle_noad==1 {|subtype| of right noad representing \.{\\middle}}
@d scripts_allowed(#)==(type(#)>=ord_noad)and(type(#)<left_noad)

@ Math formulas can also contain instructions like \.{\\textstyle} that
override \TeX's normal style rules. A |style_node| is inserted into the
data structure to record such instructions; it is three words long, so it
is considered a node instead of a noad. The |subtype| is either |display_style|
or |text_style| or |script_style| or |script_script_style|. The
second and third words of a |style_node| are not used, but they are
present because a |choice_node| is converted to a |style_node|.

\TeX\ uses even numbers 0, 2, 4, 6 to encode the basic styles
|display_style|, \dots, |script_script_style|, and adds~1 to get the
``cramped'' versions of these styles. This gives a numerical order that
is backwards from the convention of Appendix~G in {\sl The \TeX book\/};
i.e., a smaller style has a larger numerical value.
@:TeXbook}{\sl The \TeX book@>

@d style_node=unset_node+1 {|type| of a style node}
@d style_node_size=4 {number of words in a style node}
@d display_style=0 {|subtype| for \.{\\displaystyle}}
@d text_style=2 {|subtype| for \.{\\textstyle}}
@d script_style=4 {|subtype| for \.{\\scriptstyle}}
@d script_script_style=6 {|subtype| for \.{\\scriptscriptstyle}}
@d cramped=1 {add this to an uncramped style if you want to cramp it}

@p function new_style(@!s:small_number):pointer; {create a style node}
var p:pointer; {the new node}
begin p:=new_node(style_node,s);
new_style:=p;
end;

@ Finally, the \.{\\mathchoice} primitive creates a |choice_node|, which
has special subfields |display_mlist|, |text_mlist|, |script_mlist|,
and |script_script_mlist| pointing to the mlists for each style.

@d choice_node=unset_node+2 {|type| of a choice node}
@d display_mlist(#)==vinfo(#+2) {mlist to be used in display style}
@d text_mlist(#)==vlink(#+2) {mlist to be used in text style}
@d script_mlist(#)==vinfo(#+3) {mlist to be used in script style}
@d script_script_mlist(#)==vlink(#+3) {mlist to be used in scriptscript style}

@p function new_choice:pointer; {create a choice node}
var p:pointer; {the new node}
begin p:=new_node(choice_node,0); {the |subtype| is not used}
new_choice:=p;
end;

@ Let's consider now the previously unwritten part of |show_node_list|
that displays the things that can only be present in mlists; this
program illustrates how to access the data structures just defined.

In the context of the following program, |p| points to a node or noad that
should be displayed, and the current string contains the ``recursion history''
that leads to this point. The recursion history consists of a dot for each
outer level in which |p| is subsidiary to some node, or in which |p| is
subsidiary to the |nucleus| field of some noad; the dot is replaced by
`\.\_' or `\.\^' or `\./' or `\.\\' if |p| is descended from the |subscr|
or |supscr| or |denominator| or |numerator| fields of noads. For example,
the current string would be `\.{.\^.\_/}' if |p| points to the |ord_noad| for
|x| in the (ridiculous) formula
`\.{\$\\sqrt\{a\^\{\\mathinner\{b\_\{c\\over x+y\}\}\}\}\$}'.

@<Cases of |show_node_list| that arise...@>=
style_node:print_style(subtype(p));
choice_node:@<Display choice node |p|@>;
ord_noad,op_noad,bin_noad,rel_noad,open_noad,close_noad,punct_noad,inner_noad,
  radical_noad,over_noad,under_noad,vcenter_noad,accent_noad,
  left_noad,right_noad:@<Display normal noad |p|@>;
fraction_noad:@<Display fraction noad |p|@>;

@ Here are some simple routines used in the display of noads.

@<Declare procedures needed for displaying the elements of mlists@>=
procedure print_fam_and_char(@!p:pointer); {prints family and character}
begin print_esc("fam"); print_int(fam(p)); print_char(" ");
print(qo(mcharacter(p)));
end;
@#
procedure print_delimiter(@!p:pointer); {prints a delimiter as 24-bit hex value}
{TH: FIX to do: print 48-bit integer where needed!}
var a:integer; {accumulator}
begin a:=small_fam(p)*256+qo(small_char(p));
a:=a*@"1000+large_fam(p)*256+qo(large_char(p));
if a<0 then print_int(a) {this should never happen}
else print_hex(a);
end;

@ The next subroutine will descend to another level of recursion when a
subsidiary mlist needs to be displayed. The parameter |c| indicates what
character is to become part of the recursion history. An empty mlist is
distinguished from a field with |math_type(p)=empty|, because these are
not equivalent (as explained above).
@^recursion@>

@<Declare procedures needed for displaying...@>=
procedure@?show_info; forward;@t\2@>@?{|show_node_list(vinfo(temp_ptr))|}
procedure print_subsidiary_data(@!p:pointer;@!c:ASCII_code);
  {display a noad field}
begin if cur_length>=depth_threshold then
  begin if math_type(p)<>empty then print(" []");
  end
else  begin append_char(c); {include |c| in the recursion history}
  temp_ptr:=p; {prepare for |show_info| if recursion is needed}
  case math_type(p) of
  math_char: begin print_ln; print_current_string; print_fam_and_char(p);
    end;
  sub_box: show_info; {recursive call}
  sub_mlist: if vinfo(p)=null then
      begin print_ln; print_current_string; print("{}");
      end
    else show_info; {recursive call}
  othercases do_nothing {|empty|}
  endcases;@/
  flush_char; {remove |c| from the recursion history}
  end;
end;

@ The inelegant introduction of |show_info| in the code above seems better
than the alternative of using \PASCAL's strange |forward| declaration for a
procedure with parameters. The \PASCAL\ convention about dropping parameters
from a post-|forward| procedure is, frankly, so intolerable to the author
of \TeX\ that he would rather stoop to communication via a global temporary
variable. (A similar stoopidity occurred with respect to |hlist_out| and
|vlist_out| above, and it will occur with respect to |mlist_to_hlist| below.)
@^Knuth, Donald Ervin@>
@:PASCAL}{\PASCAL@>

@p procedure show_info; {the reader will kindly forgive this}
begin show_node_list(vinfo(temp_ptr));
end;

@ @<Declare procedures needed for displaying...@>=
procedure print_style(@!c:integer);
begin case c div 2 of
0: print_esc("displaystyle"); {|display_style=0|}
1: print_esc("textstyle"); {|text_style=2|}
2: print_esc("scriptstyle"); {|script_style=4|}
3: print_esc("scriptscriptstyle"); {|script_script_style=6|}
othercases print("Unknown style!")
endcases;
end;

@ @<Display choice node |p|@>=
begin print_esc("mathchoice");
append_char("D"); show_node_list(display_mlist(p)); flush_char;
append_char("T"); show_node_list(text_mlist(p)); flush_char;
append_char("S"); show_node_list(script_mlist(p)); flush_char;
append_char("s"); show_node_list(script_script_mlist(p)); flush_char;
end

@ @<Display normal noad |p|@>=
begin case type(p) of
ord_noad: print_esc("mathord");
op_noad: print_esc("mathop");
bin_noad: print_esc("mathbin");
rel_noad: print_esc("mathrel");
open_noad: print_esc("mathopen");
close_noad: print_esc("mathclose");
punct_noad: print_esc("mathpunct");
inner_noad: print_esc("mathinner");
over_noad: print_esc("overline");
under_noad: print_esc("underline");
vcenter_noad: print_esc("vcenter");
radical_noad: begin
  {TH: TODO print oradical where needed and fix otherwise} 
  print_esc("radical"); print_delimiter(left_delimiter(p));
  end;
accent_noad: begin print_esc("accent"); print_fam_and_char(accent_chr(p));
  end;
left_noad: begin print_esc("left"); print_delimiter(nucleus(p));
  end;
right_noad: begin if subtype(p)=normal then print_esc("right")
  else print_esc("middle");
  print_delimiter(nucleus(p));
  end;
end;
if type(p)<left_noad then
  begin if subtype(p)<>normal then
    if subtype(p)=limits then print_esc("limits")
    else print_esc("nolimits");
  print_subsidiary_data(nucleus(p),".");
  end;
print_subsidiary_data(supscr(p),"^");
print_subsidiary_data(subscr(p),"_");
end

@ @<Display fraction noad |p|@>=
begin print_esc("fraction, thickness ");
if thickness(p)=default_code then print("= default")
else print_scaled(thickness(p));
if (small_fam(left_delimiter(p))<>0)or@+
  (small_char(left_delimiter(p))<>min_quarterword)or@|
  (large_fam(left_delimiter(p))<>0)or@|
  (large_char(left_delimiter(p))<>min_quarterword) then
  begin print(", left-delimiter "); print_delimiter(left_delimiter(p));
  end;
if (small_fam(right_delimiter(p))<>0)or@|
  (small_char(right_delimiter(p))<>min_quarterword)or@|
  (large_fam(right_delimiter(p))<>0)or@|
  (large_char(right_delimiter(p))<>min_quarterword) then
  begin print(", right-delimiter "); print_delimiter(right_delimiter(p));
  end;
print_subsidiary_data(numerator(p),"\");
print_subsidiary_data(denominator(p),"/");
end

@* \[35] Subroutines for math mode.
In order to convert mlists to hlists, i.e., noads to nodes, we need several
subroutines that are conveniently dealt with now.

Let us first introduce the macros that make it easy to get at the parameters and
other font information. A size code, which is a multiple of 16, is added to a
family number to get an index into the table of internal font numbers
for each combination of family and size.  (Be alert: Size codes get
larger as the type gets smaller.)

@<Basic printing procedures@>=
procedure print_size(@!s:integer);
begin if s=0 then print_esc("textfont")
else if s=script_size then print_esc("scriptfont")
else print_esc("scriptscriptfont");
end;

@ Before an mlist is converted to an hlist, \TeX\ makes sure that
the fonts in family~2 have enough parameters to be math-symbol
fonts, and that the fonts in family~3 have enough parameters to be
math-extension fonts. The math-symbol parameters are referred to by using the
following macros, which take a size code as their parameter; for example,
|num1(cur_size)| gives the value of the |num1| parameter for the current size.
@^parameters for symbols@>
@^font parameters@>

@d mathsy_end(#)==
@d mathsy(#)==font_param(fam_fnt(2+cur_size),#) mathsy_end
@d math_x_height==mathsy(5) {height of `\.x'}
@d math_quad==mathsy(6) {\.{18mu}}
@d num1==mathsy(8) {numerator shift-up in display styles}
@d num2==mathsy(9) {numerator shift-up in non-display, non-\.{\\atop}}
@d num3==mathsy(10) {numerator shift-up in non-display \.{\\atop}}
@d denom1==mathsy(11) {denominator shift-down in display styles}
@d denom2==mathsy(12) {denominator shift-down in non-display styles}
@d sup1==mathsy(13) {superscript shift-up in uncramped display style}
@d sup2==mathsy(14) {superscript shift-up in uncramped non-display}
@d sup3==mathsy(15) {superscript shift-up in cramped styles}
@d sub1==mathsy(16) {subscript shift-down if superscript is absent}
@d sub2==mathsy(17) {subscript shift-down if superscript is present}
@d sup_drop==mathsy(18) {superscript baseline below top of large box}
@d sub_drop==mathsy(19) {subscript baseline below bottom of large box}
@d delim1==mathsy(20) {size of \.{\\atopwithdelims} delimiters
  in display styles}
@d delim2==mathsy(21) {size of \.{\\atopwithdelims} delimiters in non-displays}
@d axis_height==mathsy(22) {height of fraction lines above the baseline}
@d total_mathsy_params=22

@ The math-extension parameters have similar macros, but the size code is
omitted (since it is always |cur_size| when we refer to such parameters).
@^parameters for symbols@>
@^font parameters@>

@d mathex(#)==font_param(fam_fnt(3+cur_size),#)
@d default_rule_thickness==mathex(8) {thickness of \.{\\over} bars}
@d big_op_spacing1==mathex(9) {minimum clearance above a displayed op}
@d big_op_spacing2==mathex(10) {minimum clearance below a displayed op}
@d big_op_spacing3==mathex(11) {minimum baselineskip above displayed op}
@d big_op_spacing4==mathex(12) {minimum baselineskip below displayed op}
@d big_op_spacing5==mathex(13) {padding above and below displayed limits}
@d total_mathex_params=13

@ We also need to compute the change in style between mlists and their
subsidiaries. The following macros define the subsidiary style for
an overlined nucleus (|cramped_style|), for a subscript or a superscript
(|sub_style| or |sup_style|), or for a numerator or denominator (|num_style|
or |denom_style|).

@d cramped_style(#)==2*(# div 2)+cramped {cramp the style}
@d sub_style(#)==2*(# div 4)+script_style+cramped {smaller and cramped}
@d sup_style(#)==2*(# div 4)+script_style+(# mod 2) {smaller}
@d num_style(#)==#+2-2*(# div 6) {smaller unless already script-script}
@d denom_style(#)==2*(# div 2)+cramped+2-2*(# div 6) {smaller, cramped}

@ When the style changes, the following piece of program computes associated
information:

@<Set up the values of |cur_size| and |cur_mu|, based on |cur_style|@>=
begin if cur_style<script_style then cur_size:=text_size
else cur_size:=script_size*((cur_style-text_style) div 2);
cur_mu:=x_over_n(math_quad(cur_size),18);
end

@ Here is a function that returns a pointer to a rule node having a given
thickness |t|. The rule will extend horizontally to the boundary of the vlist
that eventually contains it.

@p function fraction_rule(@!t:scaled):pointer;
  {construct the bar for a fraction}
var p:pointer; {the new node}
begin p:=new_rule; rule_dir(p):=math_direction;
height(p):=t; depth(p):=0; fraction_rule:=p;
end;

@ The |overbar| function returns a pointer to a vlist box that consists of
a given box |b|, above which has been placed a kern of height |k| under a
fraction rule of thickness |t| under additional space of height |t|.

@p function overbar(@!b:pointer;@!k,@!t:scaled):pointer;
var p,@!q:pointer; {nodes being constructed}
begin p:=new_kern(k); vlink(p):=b; q:=fraction_rule(t); vlink(q):=p;
p:=new_kern(t); vlink(p):=q;
pack_direction:=math_direction; overbar:=vpack(p,natural);
end;

@ The |var_delimiter| function, which finds or constructs a sufficiently
large delimiter, is the most interesting of the auxiliary functions that
currently concern us. Given a pointer |d| to a delimiter field in some noad,
together with a size code |s| and a vertical distance |v|, this function
returns a pointer to a box that contains the smallest variant of |d| whose
height plus depth is |v| or more. (And if no variant is large enough, it
returns the largest available variant.) In particular, this routine will
construct arbitrarily large delimiters from extensible components, if
|d| leads to such characters.

The value returned is a box whose |shift_amount| has been set so that
the box is vertically centered with respect to the axis in the given size.
If a built-up symbol is returned, the height of the box before shifting
will be the height of its topmost component.

@p@t\4@>@<Declare subprocedures for |var_delimiter|@>
function var_delimiter(@!d:pointer;@!s:integer;@!v:scaled):pointer;
label found,continue;
var b:pointer; {the box that will be constructed}
@!f,@!g: internal_font_number; {best-so-far and tentative font codes}
@!c,@!x,@!y: integer; {best-so-far and tentative character codes}
@!cc: integer; { a temporary character code for extensibles }
@!m,@!n: integer; {the number of extensible pieces}
@!u: scaled; {height-plus-depth of a tentative character}
@!w: scaled; {largest height-plus-depth so far}
@!z: integer; {runs through font family members}
@!large_attempt: boolean; {are we trying the ``large'' variant?}
begin f:=null_font; c:=0; w:=0; large_attempt:=false;
z:=small_fam(d); x:=small_char(d);
loop@+  begin @<Look at the variants of |(z,x)|; set |f| and |c| whenever
    a better character is found; |goto found| as soon as a
    large enough variant is encountered@>;
  if large_attempt then goto found; {there were none large enough}
  large_attempt:=true; z:=large_fam(d); x:=large_char(d);
  end;
found: if f<>null_font then
  @<Make variable |b| point to a box for |(f,c)|@>
else  begin b:=new_null_box;
  width(b):=null_delimiter_space; {use this width if no delimiter was found}
  end;
z:=cur_size; cur_size:=s;
shift_amount(b):=half(height(b)-depth(b)) - axis_height(cur_size);
cur_size:=z;
var_delimiter:=b;
end;

@ The search process is complicated slightly by the facts that some of the
characters might not be present in some of the fonts, and they might not
be probed in increasing order of height.

@<Look at the variants of |(z,x)|; set |f| and |c|...@>=
if (z<>0)or(x<>min_quarterword) then
  begin z:=z+s+script_size;
  repeat z:=z-script_size; g:=fam_fnt(z);
  if g<>null_font then
    @<Look at the list of characters starting with |x| in
      font |g|; set |f| and |c| whenever
      a better character is found; |goto found| as soon as a
      large enough variant is encountered@>;
  until z<script_size;
  end

@ @<Look at the list of characters starting with |x|...@>=
begin y:=x;
if (y>=font_bc(g))and(y<=font_ec(g)) then
  begin continue:
  if char_exists(g,y) then
    begin if char_tag(g,y)=ext_tag then
      begin f:=g; c:=y; goto found;
      end;
    u:=char_height(g,y)+char_depth(g,y);
    if u>w then
      begin f:=g; c:=y; w:=u;
      if u>=v then goto found;
      end;
    if char_tag(g,y)=list_tag then
      begin y:=char_remainder(g,y); goto continue;
      end;
    end;
  end;
end

@ Here is a subroutine that creates a new box, whose list contains a
single character, and whose width includes the italic correction for
that character. The height or depth of the box will be negative, if
the height or depth of the character is negative; thus, this routine
may deliver a slightly different result than |hpack| would produce.

@<Declare subprocedures for |var_delimiter|@>=
function char_box(@!f:internal_font_number;@!c:quarterword):pointer;
var @!b,@!p:pointer; {the new box and its character node}
begin 
b:=new_null_box; ci:=char_info_short(f,c);
width(b):=charinfo_width(ci)+char_italic(f,c);
height(b):=charinfo_height(ci); depth(b):=charinfo_depth(ci);
p:=new_char(f,c); list_ptr(b):=p; char_box:=b;
end;

@ When the following code is executed, |char_tag(q)| will be equal to
|ext_tag| if and only if a built-up symbol is supposed to be returned.

@<Make variable |b| point to a box for |(f,c)|@>=
if char_tag(f,c)=ext_tag then
  @<Construct an extensible character in a new box |b|,
    using recipe |rem_byte(q)| and font |f|@>
else b:=char_box(f,c)

@ When we build an extensible character, it's handy to have the
following subroutine, which puts a given character on top
of the characters already in box |b|:

@<Declare subprocedures for |var_delimiter|@>=
procedure stack_into_box(@!b:pointer;@!f:internal_font_number;
  @!c:quarterword);
var p:pointer; {new node placed into |b|}
begin p:=char_box(f,c); vlink(p):=list_ptr(b); list_ptr(b):=p;
height(b):=height(p);
end;

@ Another handy subroutine computes the height plus depth of
a given character:

@<Declare subprocedures for |var_delimiter|@>=
function height_plus_depth(@!f:internal_font_number;@!c:quarterword):scaled;
begin
height_plus_depth:=char_height(f,c)+char_depth(f,c);
end;

@ @<Construct an extensible...@>=
begin b:=new_null_box;
type(b):=vlist_node;
@<Compute the minimum suitable height, |w|, and the corresponding
  number of extension steps, |n|; also set |width(b)|@>;
cc:=ext_bot(f,c);
if cc<>min_quarterword then stack_into_box(b,f,cc);
cc:=ext_rep(f,c);
for m:=1 to n do stack_into_box(b,f,cc);
cc:=ext_mid(f,c);
if cc<>min_quarterword then
  begin stack_into_box(b,f,cc); cc:=ext_rep(f,c);
  for m:=1 to n do stack_into_box(b,f,cc);
  end;
cc:=ext_top(f,c);
if cc<>min_quarterword then stack_into_box(b,f,cc);
depth(b):=w-height(b);
end

@ The width of an extensible character is the width of the repeatable
module. If this module does not have positive height plus depth,
we don't use any copies of it, otherwise we use as few as possible
(in groups of two if there is a middle part).

@<Compute the minimum suitable height, |w|, and...@>=
cc:=ext_rep(f,c); u:=height_plus_depth(f,cc);
w:=0; width(b):=char_width(f,cc)+char_italic(f,cc);@/
cc:=ext_bot(f,c);@+if cc<>min_quarterword then w:=w+height_plus_depth(f,cc);
cc:=ext_mid(f,c);@+if cc<>min_quarterword then w:=w+height_plus_depth(f,cc);
cc:=ext_top(f,c);@+if cc<>min_quarterword then w:=w+height_plus_depth(f,cc);
n:=0;
if u>0 then while w<v do
  begin w:=w+u; incr(n);
  if (ext_mid(f,c))<>min_quarterword then w:=w+u;
  end

@ The next subroutine is much simpler; it is used for numerators and
denominators of fractions as well as for displayed operators and
their limits above and below. It takes a given box~|b| and
changes it so that the new box is centered in a box of width~|w|.
The centering is done by putting \.{\\hss} glue at the left and right
of the list inside |b|, then packaging the new box; thus, the
actual box might not really be centered, if it already contains
infinite glue.

The given box might contain a single character whose italic correction
has been added to the width of the box; in this case a compensating
kern is inserted.

@p function rebox(@!b:pointer;@!w:scaled):pointer;
var p,q:pointer; {temporary registers for list manipulation}
@!f:internal_font_number; {font in a one-character box}
@!v:scaled; {width of a character without italic correction}
begin if (width(b)<>w)and(list_ptr(b)<>null) then
  begin if type(b)=vlist_node then b:=hpack(b,natural);
  p:=list_ptr(b);
  if (is_char_node(p))and(vlink(p)=null) then
    begin f:=font(p); v:=char_width(f,character(p));
    if v<>width(b) then begin 
       q:=new_kern(width(b)-v); vlink(p):=q;
       end;
    end;
  list_ptr(b):=null; flush_node(b);
  b:=new_glue(ss_glue); vlink(b):=p;
  while vlink(p)<>null do p:=vlink(p);
  q:=new_glue(ss_glue); vlink(p):=q;
  rebox:=hpack(b,w,exactly);
  end
else  begin width(b):=w; rebox:=b;
  end;
end;

@ Here is a subroutine that creates a new glue specification from another
one that is expressed in `\.{mu}', given the value of the math unit.

@d mu_mult(#)==nx_plus_y(n,#,xn_over_d(#,f,@'200000))

@p function math_glue(@!g:pointer;@!m:scaled):pointer;
var p:pointer; {the new glue specification}
@!n:integer; {integer part of |m|}
@!f:scaled; {fraction part of |m|}
begin n:=x_over_n(m,@'200000); f:=remainder;@/
if f<0 then
  begin decr(n); f:=f+@'200000;
  end;
p:=new_node(glue_spec_node,0);
width(p):=mu_mult(width(g)); {convert \.{mu} to \.{pt}}
stretch_order(p):=stretch_order(g);
if stretch_order(p)=normal then stretch(p):=mu_mult(stretch(g))
else stretch(p):=stretch(g);
shrink_order(p):=shrink_order(g);
if shrink_order(p)=normal then shrink(p):=mu_mult(shrink(g))
else shrink(p):=shrink(g);
math_glue:=p;
end;

@ The |math_kern| subroutine removes |mu_glue| from a kern node, given
the value of the math unit.

@p procedure math_kern(@!p:pointer;@!m:scaled);
var @!n:integer; {integer part of |m|}
@!f:scaled; {fraction part of |m|}
begin if subtype(p)=mu_glue then
  begin n:=x_over_n(m,@'200000); f:=remainder;@/
  if f<0 then
    begin decr(n); f:=f+@'200000;
    end;
  width(p):=mu_mult(width(p)); subtype(p):=explicit;
  end;
end;

@ Sometimes it is necessary to destroy an mlist. The following
subroutine empties the current list, assuming that |abs(mode)=mmode|.

@p procedure flush_math;
begin flush_node_list(vlink(head)); flush_node_list(incompleat_noad);
vlink(head):=null; tail:=head; incompleat_noad:=null;
end;

@* \[36] Typesetting math formulas.
\TeX's most important routine for dealing with formulas is called
|mlist_to_hlist|.  After a formula has been scanned and represented as an
mlist, this routine converts it to an hlist that can be placed into a box
or incorporated into the text of a paragraph. There are three implicit
parameters, passed in global variables: |cur_mlist| points to the first
node or noad in the given mlist (and it might be |null|); |cur_style| is a
style code; and |mlist_penalties| is |true| if penalty nodes for potential
line breaks are to be inserted into the resulting hlist. After
|mlist_to_hlist| has acted, |vlink(temp_head)| points to the translated hlist.

Since mlists can be inside mlists, the procedure is recursive. And since this
is not part of \TeX's inner loop, the program has been written in a manner
that stresses compactness over efficiency.
@^recursion@>

@<Glob...@>=
@!cur_mlist:pointer; {beginning of mlist to be translated}
@!cur_style:integer; {style code at current place in the list}
@!cur_size:integer; {size code corresponding to |cur_style|}
@!cur_mu:scaled; {the math unit width corresponding to |cur_size|}
@!mlist_penalties:boolean; {should |mlist_to_hlist| insert penalties?}

@ The recursion in |mlist_to_hlist| is due primarily to a subroutine
called |clean_box| that puts a given noad field into a box using a given
math style; |mlist_to_hlist| can call |clean_box|, which can call
|mlist_to_hlist|.
@^recursion@>

The box returned by |clean_box| is ``clean'' in the
sense that its |shift_amount| is zero.

@p procedure@?mlist_to_hlist; forward;@t\2@>@/
function clean_box(@!p:pointer;@!s:integer):pointer;
label found;
var q:pointer; {beginning of a list to be boxed}
@!save_style:integer; {|cur_style| to be restored}
@!x:pointer; {box to be returned}
@!r:pointer; {temporary pointer}
begin 
case math_type(p) of
math_char: begin cur_mlist:=new_noad; vmem(nucleus(cur_mlist)):=vmem(p);
  end;
sub_box: begin q:=vinfo(p); goto found;
  end;
sub_mlist: cur_mlist:=vinfo(p);
othercases begin q:=new_null_box; goto found;
  end
endcases;@/
save_style:=cur_style; cur_style:=s; mlist_penalties:=false;@/
mlist_to_hlist; q:=vlink(temp_head); {recursive call}
cur_style:=save_style; {restore the style}
@<Set up the values of |cur_size| and |cur_mu|, based on |cur_style|@>;
found: if is_char_node(q)or(q=null) then x:=hpack(q,natural)
  else if (vlink(q)=null)and(type(q)<=vlist_node)and(shift_amount(q)=0) then
    x:=q {it's already clean}
  else x:=hpack(q,natural);
@<Simplify a trivial box@>;
clean_box:=x;
end;

@ Here we save memory space in a common case.

@<Simplify a trivial box@>=
q:=list_ptr(x);
if is_char_node(q) then
  begin r:=vlink(q);
  if r<>null then if vlink(r)=null then if not is_char_node(r) then
   if type(r)=kern_node then {unneeded italic correction}
    begin flush_node(r); vlink(q):=null;
    end;
  end

@ It is convenient to have a procedure that converts a |math_char|
field to an ``unpacked'' form. The |fetch| routine sets |cur_f| and |cur_c|
to the font code and character code of a given noad field. 
It also takes care of issuing error messages for
nonexistent characters; in such cases, |char_exists(cur_f,cur_c)| will be |false|
after |fetch| has acted, and the field will also have been reset to |empty|.

@p procedure fetch(@!a:pointer); {unpack the |math_char| field |a|}
begin cur_c:=mcharacter(a); cur_f:=fam_fnt(fam(a)+cur_size);
if cur_f=null_font then
  @<Complain about an undefined family@>
else  begin 
  if not(char_exists(cur_f,cur_c)) then
    begin char_warning(cur_f,qo(cur_c));
    math_type(a):=empty;
    end;
  end;
end;

@ @<Complain about an undefined family@>=
begin print_err(""); print_size(cur_size); print_char(" ");
print_int(fam(a)); print(" is undefined (character ");
print(qo(cur_c)); print_char(")");
help4("Somewhere in the math formula just ended, you used the")@/
("stated character from an undefined font family. For example,")@/
("plain TeX doesn't allow \it or \sl in subscripts. Proceed,")@/
("and I'll try to forget that I needed that character.");
error; math_type(a):=empty;
end

@ The outputs of |fetch| are placed in global variables.

@<Glob...@>=
@!cur_f:internal_font_number; {the |font| field of a |math_char|}
@!cur_c:quarterword; {the |character| field of a |math_char|}

@ We need to do a lot of different things, so |mlist_to_hlist| makes two
passes over the given mlist.

The first pass does most of the processing: It removes ``mu'' spacing from
glue, it recursively evaluates all subsidiary mlists so that only the
top-level mlist remains to be handled, it puts fractions and square roots
and such things into boxes, it attaches subscripts and superscripts, and
it computes the overall height and depth of the top-level mlist so that
the size of delimiters for a |left_noad| and a |right_noad| will be known.
The hlist resulting from each noad is recorded in that noad's |new_hlist|
field, an integer field that replaces the |nucleus| or |thickness|.
@^recursion@>

The second pass eliminates all noads and inserts the correct glue and
penalties between nodes.

@d new_hlist(#)==vmem(nucleus(#)).int {the translation of an mlist}

@ Here is the overall plan of |mlist_to_hlist|, and the list of its
local variables.

@d done_with_noad=80 {go here when a noad has been fully translated}
@d done_with_node=81 {go here when a node has been fully converted}
@d check_dimensions=82 {go here to update |max_h| and |max_d|}
@d delete_q=83 {go here to delete |q| and move to the next node}

@p@t\4@>@<Declare math construction procedures@>
procedure mlist_to_hlist;
label reswitch, check_dimensions, done_with_noad, done_with_node, delete_q,
  done;
var mlist:pointer; {beginning of the given list}
@!penalties:boolean; {should penalty nodes be inserted?}
@!style:integer; {the given style}
@!save_style:integer; {holds |cur_style| during recursion}
@!q:pointer; {runs through the mlist}
@!r:pointer; {the most recent noad preceding |q|}
@!r_type:integer; {the |type| of noad |r|, or |op_noad| if |r=null|}
@!t:integer; {the effective |type| of noad |q| during the second pass}
@!p,@!x,@!y,@!z: pointer; {temporary registers for list construction}
@!pen:integer; {a penalty to be inserted}
@!s:integer; {the size of a noad to be deleted}
@!max_hl,@!max_d:scaled; {maximum height and depth of the list translated so far}
@!delta:scaled; {offset between subscript and superscript}
begin mlist:=cur_mlist; penalties:=mlist_penalties;
style:=cur_style; {tuck global parameters away as local variables}
q:=mlist; r:=null; r_type:=op_noad; max_hl:=0; max_d:=0; x:=null; p:=null;
@<Set up the values of |cur_size| and |cur_mu|, based on |cur_style|@>;
while q<>null do @<Process node-or-noad |q| as much as possible in preparation
    for the second pass of |mlist_to_hlist|, then move to the next
    item in the mlist@>;
@<Convert \(a)a final |bin_noad| to an |ord_noad|@>;
@<Make a second pass over the mlist, removing all noads and inserting the
  proper spacing and penalties@>;
end;

@ We use the fact that no character nodes appear in an mlist, hence
the field |type(q)| is always present.

@<Process node-or-noad...@>=
begin @<Do first-pass processing based on |type(q)|; |goto done_with_noad|
  if a noad has been fully processed, |goto check_dimensions| if it
  has been translated into |new_hlist(q)|, or |goto done_with_node|
  if a node has been fully processed@>;
check_dimensions: z:=hpack(new_hlist(q),natural);
if height(z)>max_hl then max_hl:=height(z);
if depth(z)>max_d then max_d:=depth(z);
list_ptr(z):=null; flush_node(z);
done_with_noad: r:=q; r_type:=type(r);
if r_type=right_noad then
  begin r_type:=left_noad; cur_style:=style; @<Set up the values...@>;
  end;
done_with_node: q:=vlink(q);
end

@ One of the things we must do on the first pass is change a |bin_noad| to
an |ord_noad| if the |bin_noad| is not in the context of a binary operator.
The values of |r| and |r_type| make this fairly easy.

@<Do first-pass processing...@>=
reswitch: delta:=0;
case type(q) of
bin_noad: case r_type of
  bin_noad,op_noad,rel_noad,open_noad,punct_noad,left_noad:
    begin type(q):=ord_noad; goto reswitch;
    end;
  othercases do_nothing
  endcases;
rel_noad,close_noad,punct_noad,right_noad: begin@t@>@;@/
  @<Convert \(a)a final |bin_noad| to an |ord_noad|@>;
  if type(q)=right_noad then goto done_with_noad;
  end;
@t\4@>@<Cases for noads that can follow a |bin_noad|@>@;
@t\4@>@<Cases for nodes that can appear in an mlist, after which we
  |goto done_with_node|@>@;
othercases confusion("mlist1")
@:this can't happen mlist1}{\quad mlist1@>
endcases;@/
@<Convert \(n)|nucleus(q)| to an hlist and attach the sub/superscripts@>

@ @<Convert \(a)a final |bin_noad| to an |ord_noad|@>=
if r_type=bin_noad then type(r):=ord_noad

@ @<Cases for nodes that can appear in an mlist...@>=
style_node: begin cur_style:=subtype(q);
  @<Set up the values of |cur_size| and |cur_mu|, based on |cur_style|@>;
  goto done_with_node;
  end;
choice_node: @<Change this node to a style node followed by the correct choice,
   then |goto done_with_node|@>;
ins_node,mark_node,adjust_node,
  whatsit_node,penalty_node,disc_node: goto done_with_node;
rule_node: begin if height(q)>max_hl then max_hl:=height(q);
  if depth(q)>max_d then max_d:=depth(q); goto done_with_node;
  end;
glue_node: begin @<Convert \(m)math glue to ordinary glue@>;
  goto done_with_node;
  end;
kern_node: begin math_kern(q,cur_mu); goto done_with_node;
  end;

@ @d choose_mlist(#)==begin p:=#(q); #(q):=null;@+end

@<Change this node to a style node...@>=
begin case cur_style div 2 of
0: choose_mlist(display_mlist); {|display_style=0|}
1: choose_mlist(text_mlist); {|text_style=2|}
2: choose_mlist(script_mlist); {|script_style=4|}
3: choose_mlist(script_script_mlist); {|script_script_style=6|}
end; {there are no other cases}
flush_node_list(display_mlist(q));
flush_node_list(text_mlist(q));
flush_node_list(script_mlist(q));
flush_node_list(script_script_mlist(q));@/
type(q):=style_node; subtype(q):=cur_style; width(q):=0; depth(q):=0;
if p<>null then
  begin z:=vlink(q); vlink(q):=p;
  while vlink(p)<>null do p:=vlink(p);
  vlink(p):=z;
  end;
goto done_with_node;
end

@ Conditional math glue (`\.{\\nonscript}') results in a |glue_node|
pointing to |zero_glue|, with |subtype(q)=cond_math_glue|; in such a case
the node following will be eliminated if it is a glue or kern node and if the
current size is different from |text_size|. Unconditional math glue
(`\.{\\muskip}') is converted to normal glue by multiplying the dimensions
by |cur_mu|.
@!@:non_script_}{\.{\\nonscript} primitive@>

@<Convert \(m)math glue to ordinary glue@>=
if subtype(q)=mu_glue then
  begin x:=glue_ptr(q);
  y:=math_glue(x,cur_mu); delete_glue_ref(x); glue_ptr(q):=y;
  subtype(q):=normal;
  end
else if (cur_size<>text_size)and(subtype(q)=cond_math_glue) then
  begin p:=vlink(q);
  if p<>null then if (type(p)=glue_node)or(type(p)=kern_node) then
      begin vlink(q):=vlink(p); vlink(p):=null; flush_node_list(p);
      end;
  end

@ @<Cases for noads that can follow a |bin_noad|@>=
left_noad: goto done_with_noad;
fraction_noad: begin make_fraction(q); goto check_dimensions;
  end;
op_noad: begin delta:=make_op(q);
  if subtype(q)=limits then goto check_dimensions;
  end;
ord_noad: make_ord(q);
open_noad,inner_noad: do_nothing;
radical_noad: make_radical(q);
over_noad: make_over(q);
under_noad: make_under(q);
accent_noad: make_math_accent(q);
vcenter_noad: make_vcenter(q);

@ Most of the actual construction work of |mlist_to_hlist| is done
by procedures with names
like |make_fraction|, |make_radical|, etc. To illustrate
the general setup of such procedures, let's begin with a couple of
simple ones.

@<Declare math...@>=
procedure make_over(@!q:pointer);
var p:pointer;
begin p:=overbar(clean_box(nucleus(q),cramped_style(cur_style)),@|
  	  3*default_rule_thickness,default_rule_thickness);
vinfo(nucleus(q)):=p;
math_type(nucleus(q)):=sub_box;
end;

@ @<Declare math...@>=
procedure make_under(@!q:pointer);
var p,@!x,@!y,@!r: pointer; {temporary registers for box construction}
@!delta:scaled; {overall height plus depth}
begin x:=clean_box(nucleus(q),cur_style);
p:=new_kern(3*default_rule_thickness); vlink(x):=p;
r:=fraction_rule(default_rule_thickness); vlink(p):=r;
pack_direction:=math_direction; y:=vpack(x,natural);
delta:=height(y)+depth(y)+default_rule_thickness;
height(y):=height(x); depth(y):=delta-height(y);
vinfo(nucleus(q)):=y; math_type(nucleus(q)):=sub_box;
end;

@ @<Declare math...@>=
procedure make_vcenter(@!q:pointer);
var v:pointer; {the box that should be centered vertically}
@!delta:scaled; {its height plus depth}
begin v:=vinfo(nucleus(q));
if type(v)<>vlist_node then confusion("vcenter");
@:this can't happen vcenter}{\quad vcenter@>
delta:=height(v)+depth(v);
height(v):=axis_height(cur_size)+half(delta);
depth(v):=delta-height(v);
end;

@ According to the rules in the \.{DVI} file specifications, we ensure alignment
@^square roots@>
between a square root sign and the rule above its nucleus by assuming that the
baseline of the square-root symbol is the same as the bottom of the rule. The
height of the square-root symbol will be the thickness of the rule, and the
depth of the square-root symbol should exceed or equal the height-plus-depth
of the nucleus plus a certain minimum clearance~|clr|. The symbol will be
placed so that the actual clearance is |clr| plus half the excess.

@<Declare math...@>=
procedure make_radical(@!q:pointer);
var x,@!y,@!p:pointer; {temporary registers for box construction}
@!delta,@!clr:scaled; {dimensions involved in the calculation}
begin x:=clean_box(nucleus(q),cramped_style(cur_style));
if cur_style<text_style then {display style}
  clr:=default_rule_thickness+(abs(math_x_height(cur_size)) div 4)
else  begin clr:=default_rule_thickness; clr:=clr + (abs(clr) div 4);
  end;
y:=var_delimiter(left_delimiter(q),cur_size,height(x)+depth(x)+clr+
  default_rule_thickness);
delta:=depth(y)-(height(x)+depth(x)+clr);
if delta>0 then clr:=clr+half(delta); {increase the actual clearance}
shift_amount(y):=-(height(x)+clr);
p:=overbar(x,clr,height(y)); vlink(y):=p;
p:=hpack(y,natural); vinfo(nucleus(q)):=p; 
math_type(nucleus(q)):=sub_box;
end;

@ Slants are not considered when placing accents in math mode. The accenter is
centered over the accentee, and the accent width is treated as zero with
respect to the size of the final box.

@<Declare math...@>=
procedure make_math_accent(@!q:pointer);
label done;
var p,@!x,@!y:pointer; {temporary registers for box construction}
@!c:quarterword; {accent character}
@!f:internal_font_number; {its font}
@!s:scaled; {amount to skew the accent to the right}
@!h:scaled; {height of character being accented}
@!delta:scaled; {space to remove between accent and accentee}
@!w:scaled; {width of the accentee, not including sub/superscripts}
begin fetch(accent_chr(q));
if char_exists(cur_f,cur_c) then
  begin c:=cur_c; f:=cur_f;@/
  @<Compute the amount of skew@>;
  x:=clean_box(nucleus(q),cramped_style(cur_style)); w:=width(x); h:=height(x);
  @<Switch to a larger accent if available and appropriate@>;
  if h<x_height(f) then delta:=h@+else delta:=x_height(f);
  if (math_type(supscr(q))<>empty)or(math_type(subscr(q))<>empty) then
    if math_type(nucleus(q))=math_char then
      @<Swap the subscript and superscript into box |x|@>;
  y:=char_box(f,c);
  shift_amount(y):=s+half(w-width(y));
  width(y):=0; p:=new_kern(-delta); vlink(p):=x; vlink(y):=p;
  pack_direction:=math_direction;
  y:=vpack(y,natural); width(y):=width(x);
  if height(y)<h then @<Make the height of box |y| equal to |h|@>;
  vinfo(nucleus(q)):=y;
  math_type(nucleus(q)):=sub_box;
  end;
end;

@ @<Make the height of box |y|...@>=
begin p:=new_kern(h-height(y)); vlink(p):=list_ptr(y); list_ptr(y):=p;
height(y):=h;
end

@ @<Switch to a larger accent if available and appropriate@>=
loop@+  begin if char_tag(f,c)<>list_tag then goto done;
  y:=char_remainder(f,c);
  if not char_exists(f,y) then goto done;
  if char_width(f,y)>w then goto done;
  c:=y;
  end;
done:

@ @<Compute the amount of skew@>=
s:=0;
if math_type(nucleus(q))=math_char then
  begin fetch(nucleus(q));
  s := get_kern(cur_f,cur_c,skew_char(cur_f));
  end

@ @<Swap the subscript and superscript into box |x|@>=
begin flush_node_list(x); x:=new_noad;
vmem(nucleus(x)):=vmem(nucleus(q));
vmem(supscr(x)):=vmem(supscr(q));
vmem(subscr(x)):=vmem(subscr(q));@/
vmem(supscr(q)).hh:=empty_field;
vmem(subscr(q)).hh:=empty_field;@/
math_type(nucleus(q)):=sub_mlist; vinfo(nucleus(q)):=x;
x:=clean_box(nucleus(q),cur_style); delta:=delta+height(x)-h; h:=height(x);
end

@ The |make_fraction| procedure is a bit different because it sets
|new_hlist(q)| directly rather than making a sub-box.

@<Declare math...@>=
procedure make_fraction(@!q:pointer);
var p,@!v,@!x,@!y,@!z:pointer; {temporary registers for box construction}
@!delta,@!delta1,@!delta2,@!shift_up,@!shift_down,@!clr:scaled;
  {dimensions for box calculations}
begin if thickness(q)=default_code then thickness(q):=default_rule_thickness;
@<Create equal-width boxes |x| and |z| for the numerator and denominator,
  and compute the default amounts |shift_up| and |shift_down| by which they
  are displaced from the baseline@>;
if thickness(q)=0 then @<Adjust \(s)|shift_up| and |shift_down| for the case
  of no fraction line@>
else @<Adjust \(s)|shift_up| and |shift_down| for the case of a fraction line@>;
@<Construct a vlist box for the fraction, according to |shift_up| and
  |shift_down|@>;
@<Put the \(f)fraction into a box with its delimiters, and make |new_hlist(q)|
  point to it@>;
end;

@ @<Create equal-width boxes |x| and |z| for the numerator and denom...@>=
x:=clean_box(numerator(q),num_style(cur_style)); 
z:=clean_box(denominator(q),denom_style(cur_style));
vinfo(numerator(q)):=null;
vinfo(denominator(q)):=null;
if width(x)<width(z) then x:=rebox(x,width(z))
else z:=rebox(z,width(x));
if cur_style<text_style then {display style}
  begin shift_up:=num1(cur_size); shift_down:=denom1(cur_size);
  end
else  begin shift_down:=denom2(cur_size);
  if thickness(q)<>0 then shift_up:=num2(cur_size)
  else shift_up:=num3(cur_size);
  end

@ The numerator and denominator must be separated by a certain minimum
clearance, called |clr| in the following program. The difference between
|clr| and the actual clearance is |2delta|.

@<Adjust \(s)|shift_up| and |shift_down| for the case of no fraction line@>=
begin if cur_style<text_style then clr:=7*default_rule_thickness
else clr:=3*default_rule_thickness;
delta:=half(clr-((shift_up-depth(x))-(height(z)-shift_down)));
if delta>0 then
  begin shift_up:=shift_up+delta;
  shift_down:=shift_down+delta;
  end;
end

@ In the case of a fraction line, the minimum clearance depends on the actual
thickness of the line.

@<Adjust \(s)|shift_up| and |shift_down| for the case of a fraction line@>=
begin if cur_style<text_style then clr:=3*thickness(q)
else clr:=thickness(q);
delta:=half(thickness(q));
delta1:=clr-((shift_up-depth(x))-(axis_height(cur_size)+delta));
delta2:=clr-((axis_height(cur_size)-delta)-(height(z)-shift_down));
if delta1>0 then shift_up:=shift_up+delta1;
if delta2>0 then shift_down:=shift_down+delta2;
end

@ @<Construct a vlist box for the fraction...@>=
v:=new_null_box; type(v):=vlist_node;
height(v):=shift_up+height(x); depth(v):=depth(z)+shift_down;
width(v):=width(x); {this also equals |width(z)|}
if thickness(q)=0 then
  begin p:=new_kern((shift_up-depth(x))-(height(z)-shift_down));
  vlink(p):=z;
  end
else  begin y:=fraction_rule(thickness(q));@/
  p:=new_kern((axis_height(cur_size)-delta)-@|(height(z)-shift_down));@/
  vlink(y):=p; vlink(p):=z;@/
  p:=new_kern((shift_up-depth(x))-(axis_height(cur_size)+delta));
  vlink(p):=y;
  end;
vlink(x):=p; list_ptr(v):=x

@ @<Put the \(f)fraction into a box with its delimiters...@>=
if cur_style<text_style then delta:=delim1(cur_size)
else delta:=delim2(cur_size);
x:=var_delimiter(left_delimiter(q), cur_size, delta); vlink(x):=v;@/
z:=var_delimiter(right_delimiter(q), cur_size, delta); vlink(v):=z;@/
y:=hpack(x,natural); 
new_hlist(q):=y

@ If the nucleus of an |op_noad| is a single character, it is to be
centered vertically with respect to the axis, after first being enlarged
(via a character list in the font) if we are in display style.  The normal
convention for placing displayed limits is to put them above and below the
operator in display style.

The italic correction is removed from the character if there is a subscript
and the limits are not being displayed. The |make_op|
routine returns the value that should be used as an offset between
subscript and superscript.

After |make_op| has acted, |subtype(q)| will be |limits| if and only if
the limits have been set above and below the operator. In that case,
|new_hlist(q)| will already contain the desired final box.

@<Declare math...@>=
function make_op(@!q:pointer):scaled;
var delta:scaled; {offset between subscript and superscript}
@!p,@!v,@!x,@!y,@!z:pointer; {temporary registers for box construction}
@!c:quarterword; {register for character examination}
@!shift_up,@!shift_down:scaled; {dimensions for box calculation}
begin if (subtype(q)=normal)and(cur_style<text_style) then
  subtype(q):=limits;
if math_type(nucleus(q))=math_char then
  begin fetch(nucleus(q));
  if (cur_style<text_style)and(char_tag(cur_f,cur_c)=list_tag) then {make it larger}
    begin c:=char_remainder(cur_f,cur_c);
    if char_exists(cur_f,c) then
      begin cur_c:=c; mcharacter(nucleus(q)):=c;
      end;
    end;
  delta:=char_italic(cur_f,cur_c); x:=clean_box(nucleus(q),cur_style);
  if (math_type(subscr(q))<>empty)and(subtype(q)<>limits) then
    width(x):=width(x)-delta; {remove italic correction}
  shift_amount(x):=half(height(x)-depth(x)) - axis_height(cur_size);
    {center vertically}
  math_type(nucleus(q)):=sub_box; vinfo(nucleus(q)):=x;
  end
else delta:=0;
if subtype(q)=limits then
  @<Construct a box with limits above and below it, skewed by |delta|@>;
make_op:=delta;
end;

@ The following program builds a vlist box |v| for displayed limits. The
width of the box is not affected by the fact that the limits may be skewed.

@<Construct a box with limits above and below it...@>=
begin x:=clean_box(supscr(q),sup_style(cur_style));
y:=clean_box(nucleus(q),cur_style);
z:=clean_box(subscr(q),sub_style(cur_style));
v:=new_null_box; type(v):=vlist_node; width(v):=width(y);
if width(x)>width(v) then width(v):=width(x);
if width(z)>width(v) then width(v):=width(z);
x:=rebox(x,width(v)); y:=rebox(y,width(v)); z:=rebox(z,width(v));@/
shift_amount(x):=half(delta); shift_amount(z):=-shift_amount(x);
height(v):=height(y); depth(v):=depth(y);
@<Attach the limits to |y| and adjust |height(v)|, |depth(v)| to
  account for their presence@>;
new_hlist(q):=v;
end

@ We use |shift_up| and |shift_down| in the following program for the
amount of glue between the displayed operator |y| and its limits |x| and
|z|. The vlist inside box |v| will consist of |x| followed by |y| followed
by |z|, with kern nodes for the spaces between and around them.

@<Attach the limits to |y| and adjust |height(v)|, |depth(v)|...@>=
if math_type(supscr(q))=empty then
  begin list_ptr(x):=null; flush_node(x); list_ptr(v):=y;
  end
else  begin shift_up:=big_op_spacing3-depth(x);
  if shift_up<big_op_spacing1 then shift_up:=big_op_spacing1;
  p:=new_kern(shift_up); vlink(p):=y; vlink(x):=p;@/
  p:=new_kern(big_op_spacing5); vlink(p):=x; list_ptr(v):=p;
  height(v):=height(v)+big_op_spacing5+height(x)+depth(x)+shift_up;
  end;
if math_type(subscr(q))=empty then begin list_ptr(z):=null; flush_node(z); end
else  begin shift_down:=big_op_spacing4-height(z);
  if shift_down<big_op_spacing2 then shift_down:=big_op_spacing2;
  p:=new_kern(shift_down); vlink(y):=p; vlink(p):=z;@/
  p:=new_kern(big_op_spacing5); vlink(z):=p;
  depth(v):=depth(v)+big_op_spacing5+height(z)+depth(z)+shift_down;
  end

@ A ligature found in a math formula does not create a ligature, because
there is no question of hyphenation afterwards; the ligature will simply be
stored in an ordinary |glyph_node|, after residing in an |ord_noad|.

The |math_type| is converted to |math_text_char| here if we would not want to
apply an italic correction to the current character unless it belongs
to a math font (i.e., a font with |space=0|).

No boundary characters enter into these ligatures.

@<Declare math...@>=
procedure make_ord(@!q:pointer);
label restart,exit;
var a:integer; { the left-side character for lig/kern testing }
@!p,@!r:pointer; {temporary registers for list manipulation}
k:scaled; { a kern }
lig:liginfo; { a ligature }
begin restart:@t@>@;@/
if math_type(subscr(q))=empty then if math_type(supscr(q))=empty then
 if math_type(nucleus(q))=math_char then
  begin p:=vlink(q);
  if p<>null then if (type(p)>=ord_noad)and(type(p)<=punct_noad) then
    if math_type(nucleus(p))=math_char then
    if fam(nucleus(p))=fam(nucleus(q)) then
      begin math_type(nucleus(q)):=math_text_char;
      fetch(nucleus(q)); a:=cur_c;
      if (has_kern(cur_f,a))or(has_lig(cur_f,a)) then
        begin cur_c:=mcharacter(nucleus(p));
          @<If character |a| has a kern with |cur_c|, attach
            the kern after~|q|; or if it has a ligature with |cur_c|, combine
            noads |q| and~|p| appropriately; then |return| if the cursor has
            moved past a noad, or |goto restart|@>;
        end;
      end;
  end;
exit:end;

@ Note that a ligature between an |ord_noad| and another kind of noad
is replaced by an |ord_noad|, when the two noads collapse into one.
But we could make a parenthesis (say) change shape when it follows
certain letters. Presumably a font designer will define such
ligatures only when this convention makes sense.

\chardef\?='174 % vertical line to indicate character retention

@<If character |a| has a kern with |cur_c|, ...@>=
begin
if disable_lig=0 and has_lig(cur_f,a) then begin
  lig:=get_ligature(cur_f,a,cur_c);
  if is_valid_ligature(lig) then begin
	check_interrupt; {allow a way out of infinite ligature loop}
    case lig_type(lig) of
    qi(1),qi(5): mcharacter(nucleus(q)):=lig_replacement(lig); {\.{=:\?}, \.{=:\?>}}
    qi(2),qi(6): mcharacter(nucleus(p)):=lig_replacement(lig); {\.{\?=:}, \.{\?=:>}}
    qi(3),qi(7),qi(11):begin r:=new_noad; {\.{\?=:\?}, \.{\?=:\?>}, \.{\?=:\?>>}}
      mcharacter(nucleus(r)):=lig_replacement(lig);
      fam(nucleus(r)):=fam(nucleus(q));@/
      vlink(q):=r; vlink(r):=p;
      if lig_type(lig)<qi(11) then math_type(nucleus(r)):=math_char
      else math_type(nucleus(r)):=math_text_char; {prevent combination}
      end;
    othercases begin vlink(q):=vlink(p);
      mcharacter(nucleus(q)):=lig_replacement(lig); {\.{=:}}
      vmem(subscr(q)):=vmem(subscr(p)); vmem(supscr(q)):=vmem(supscr(p));@/
      flush_node(p);
      end
    endcases;
    if lig_type(lig)>qi(3) then return;
    math_type(nucleus(q)):=math_char; goto restart;
    end;
  end;
if disable_kern=0 and has_kern(cur_f,a) then begin
  k:=get_kern(cur_f,a,cur_c);
  if k<>0 then begin 
    p:=new_kern(k); vlink(p):=vlink(q); vlink(q):=p; return;
	end;
  end;
end

@ When we get to the following part of the program, we have ``fallen through''
from cases that did not lead to |check_dimensions| or |done_with_noad| or
|done_with_node|. Thus, |q|~points to a noad whose nucleus may need to be
converted to an hlist, and whose subscripts and superscripts need to be
appended if they are present.

If |nucleus(q)| is not a |math_char|, the variable |delta| is the amount
by which a superscript should be moved right with respect to a subscript
when both are present.
@^subscripts@>
@^superscripts@>

@<Convert \(n)|nucleus(q)| to an hlist and attach the sub/superscripts@>=
case math_type(nucleus(q)) of
math_char, math_text_char:
  @<Create a character node |p| for |nucleus(q)|, possibly followed
  by a kern node for the italic correction, and set |delta| to the
  italic correction if a subscript is present@>;
empty: p:=null;
sub_box: p:=vinfo(nucleus(q));
sub_mlist: begin cur_mlist:=vinfo(nucleus(q)); save_style:=cur_style;
  mlist_penalties:=false; mlist_to_hlist; {recursive call}
@^recursion@>
  cur_style:=save_style; @<Set up the values...@>;
  p:=hpack(vlink(temp_head),natural);
  end;
othercases confusion("mlist2")
@:this can't happen mlist2}{\quad mlist2@>
endcases;@/
new_hlist(q):=p;
if (math_type(subscr(q))=empty)and(math_type(supscr(q))=empty) then
  goto check_dimensions;
make_scripts(q,delta)

@ @<Create a character node |p| for |nucleus(q)|...@>=
begin fetch(nucleus(q));
if char_exists(cur_f,cur_c) then
  begin delta:=char_italic(cur_f,cur_c); p:=new_glyph(cur_f,cur_c);
  if (math_type(nucleus(q))=math_text_char)and(space(cur_f)<>0) then
    delta:=0; {no italic correction in mid-word of text font}
  if (math_type(subscr(q))=empty)and(delta<>0) then
    begin x:=new_kern(delta); vlink(p):=x; delta:=0;
    end;
  end
else p:=null;
end

@ The purpose of |make_scripts(q,delta)| is to attach the subscript and/or
superscript of noad |q| to the list that starts at |new_hlist(q)|,
given that subscript and superscript aren't both empty. The superscript
will appear to the right of the subscript by a given distance |delta|.

We set |shift_down| and |shift_up| to the minimum amounts to shift the
baseline of subscripts and superscripts based on the given nucleus.

@<Declare math...@>=
procedure make_scripts(@!q:pointer;@!delta:scaled);
var p,@!x,@!y,@!z:pointer; {temporary registers for box construction}
@!shift_up,@!shift_down,@!clr:scaled; {dimensions in the calculation}
@!t:integer; {subsidiary size code}
begin p:=new_hlist(q);
if is_char_node(p) then
  begin shift_up:=0; shift_down:=0;
  end
else  begin z:=hpack(p,natural);
  t:=cur_size;
  if cur_style<script_style
  then cur_size:=script_size@+else cur_size:=script_script_size;
  shift_up:=height(z)-sup_drop(cur_size);
  shift_down:=depth(z)+sub_drop(cur_size);
  cur_size:=t;
  list_ptr(z):=null; flush_node(z);
  end;
if math_type(supscr(q))=empty then
  @<Construct a subscript box |x| when there is no superscript@>
else  begin @<Construct a superscript box |x|@>;
  if math_type(subscr(q))=empty then shift_amount(x):=-shift_up
  else @<Construct a sub/superscript combination box |x|, with the
    superscript offset by |delta|@>;
  end;
if new_hlist(q)=null then new_hlist(q):=x
else  begin p:=new_hlist(q);
  while vlink(p)<>null do p:=vlink(p);
  vlink(p):=x;
  end;
end;

@ When there is a subscript without a superscript, the top of the subscript
should not exceed the baseline plus four-fifths of the x-height.

@<Construct a subscript box |x| when there is no superscript@>=
begin x:=clean_box(subscr(q),sub_style(cur_style));
width(x):=width(x)+script_space;
if shift_down<sub1(cur_size) then shift_down:=sub1(cur_size);
clr:=height(x)-(abs(math_x_height(cur_size)*4) div 5);
if shift_down<clr then shift_down:=clr;
shift_amount(x):=shift_down;
end

@ The bottom of a superscript should never descend below the baseline plus
one-fourth of the x-height.

@<Construct a superscript box |x|@>=
begin x:=clean_box(supscr(q),sup_style(cur_style));
width(x):=width(x)+script_space;
if odd(cur_style) then clr:=sup3(cur_size)
else if cur_style<text_style then clr:=sup1(cur_size)
else clr:=sup2(cur_size);
if shift_up<clr then shift_up:=clr;
clr:=depth(x)+(abs(math_x_height(cur_size)) div 4);
if shift_up<clr then shift_up:=clr;
end

@ When both subscript and superscript are present, the subscript must be
separated from the superscript by at least four times |default_rule_thickness|.
If this condition would be violated, the subscript moves down, after which
both subscript and superscript move up so that the bottom of the superscript
is at least as high as the baseline plus four-fifths of the x-height.

@<Construct a sub/superscript combination box |x|...@>=
begin y:=clean_box(subscr(q),sub_style(cur_style));
width(y):=width(y)+script_space;
if shift_down<sub2(cur_size) then shift_down:=sub2(cur_size);
clr:=4*default_rule_thickness-
  ((shift_up-depth(x))-(height(y)-shift_down));
if clr>0 then
  begin shift_down:=shift_down+clr;
  clr:=(abs(math_x_height(cur_size)*4) div 5)-(shift_up-depth(x));
  if clr>0 then
    begin shift_up:=shift_up+clr;
    shift_down:=shift_down-clr;
    end;
  end;
shift_amount(x):=delta; {superscript is |delta| to the right of the subscript}
p:=new_kern((shift_up-depth(x))-(height(y)-shift_down)); vlink(x):=p; vlink(p):=y;
pack_direction:=math_direction;
x:=vpack(x,natural); shift_amount(x):=shift_down;
end

@ We have now tied up all the loose ends of the first pass of |mlist_to_hlist|.
The second pass simply goes through and hooks everything together with the
proper glue and penalties. It also handles the |left_noad| and |right_noad| that
might be present, since |max_hl| and |max_d| are now known. Variable |p| points
to a node at the current end of the final hlist.

@<Make a second pass over the mlist, ...@>=
p:=temp_head; vlink(p):=null; q:=mlist; r_type:=0; cur_style:=style;
@<Set up the values of |cur_size| and |cur_mu|, based on |cur_style|@>;
while q<>null do
  begin @<If node |q| is a style node, change the style and |goto delete_q|;
    otherwise if it is not a noad, put it into the hlist,
    advance |q|, and |goto done|; otherwise set |s| to the size
    of noad |q|, set |t| to the associated type (|ord_noad..
    inner_noad|), and set |pen| to the associated penalty@>;
  @<Append inter-element spacing based on |r_type| and |t|@>;
  @<Append any |new_hlist| entries for |q|, and any appropriate penalties@>;
  if type(q)=right_noad then t:=open_noad;
  r_type:=t;
  delete_q: r:=q; q:=vlink(q); 
  flush_node(r); {|r| had better be a noad-like thing }
  done: end

@ Just before doing the big |case| switch in the second pass, the program
sets up default values so that most of the branches are short.

@<If node |q| is a style node, change the style...@>=
t:=ord_noad; s:=noad_size; pen:=inf_penalty;
case type(q) of
op_noad,open_noad,close_noad,punct_noad,inner_noad: t:=type(q);
bin_noad: begin t:=bin_noad; pen:=bin_op_penalty;
  end;
rel_noad: begin t:=rel_noad; pen:=rel_penalty;
  end;
ord_noad,vcenter_noad,over_noad,under_noad: do_nothing;
radical_noad: s:=radical_noad_size;
accent_noad: s:=accent_noad_size;
fraction_noad: begin t:=inner_noad; s:=fraction_noad_size;
  end;
left_noad,right_noad: t:=make_left_right(q,style,max_d,max_hl);
style_node: @<Change the current style and |goto delete_q|@>;
whatsit_node,penalty_node,rule_node,disc_node,adjust_node,ins_node,mark_node,
 glue_node,kern_node:@t@>@;@/
  begin vlink(p):=q; p:=q; q:=vlink(q); vlink(p):=null; goto done;
  end;
othercases confusion("mlist3")
@:this can't happen mlist3}{\quad mlist3@>
endcases

@ The |make_left_right| function constructs a left or right delimiter of
the required size and returns the value |open_noad| or |close_noad|. The
|right_noad| and |left_noad| will both be based on the original |style|,
so they will have consistent sizes.

We use the fact that |right_noad-left_noad=close_noad-open_noad|.

@<Declare math...@>=
function make_left_right(@!q:pointer;@!style:integer;
  @!max_d,@!max_hv:scaled):small_number;
var delta,@!delta1,@!delta2:scaled; {dimensions used in the calculation}
tmp:pointer;
begin cur_style:=style; @<Set up the values...@>;
delta2:=max_d+axis_height(cur_size);
delta1:=max_hv+max_d-delta2;
if delta2>delta1 then delta1:=delta2; {|delta1| is max distance from axis}
delta:=(delta1 div 500)*delimiter_factor;
delta2:=delta1+delta1-delimiter_shortfall;
if delta<delta2 then delta:=delta2;
tmp:=var_delimiter(delimiter(q),cur_size,delta);
new_hlist(q):=tmp; 
make_left_right:=type(q)-(left_noad-open_noad); {|open_noad| or |close_noad|}
end;

@ @<Change the current style and |goto delete_q|@>=
begin cur_style:=subtype(q); s:=style_node_size;
@<Set up the values of |cur_size| and |cur_mu|, based on |cur_style|@>;
goto delete_q;
end

@ The inter-element spacing in math formulas depends on a $8\times8$ table that
\TeX\ preloads as a 64-digit string. The elements of this string have the
following significance:
$$\vbox{\halign{#\hfil\cr
\.0 means no space;\cr
\.1 means a conditional thin space (\.{\\nonscript\\mskip\\thinmuskip});\cr
\.2 means a thin space (\.{\\mskip\\thinmuskip});\cr
\.3 means a conditional medium space
  (\.{\\nonscript\\mskip\\medmuskip});\cr
\.4 means a conditional thick space
  (\.{\\nonscript\\mskip\\thickmuskip});\cr
\.* means an impossible case.\cr}}$$
This is all pretty cryptic, but {\sl The \TeX book\/} explains what is
supposed to happen, and the string makes it happen.
@:TeXbook}{\sl The \TeX book@>

A global variable |magic_offset| is computed so that if |a| and |b| are
in the range |ord_noad..inner_noad|, then |str_pool[a*8+b+magic_offset]|
is the digit for spacing between noad types |a| and |b|.

If \PASCAL\ had provided a good way to preload constant arrays, this part of
the program would not have been so strange.
@:PASCAL}{\PASCAL@>

@d math_spacing=@;@/
@t\hskip-35pt@>
"0234000122*4000133**3**344*0400400*000000234000111*1111112341011"
@t$ \hskip-35pt$@>

@<Glob...@>=
@!magic_offset:integer; {used to find inter-element spacing}

@ @<Compute the magic offset@>=
magic_offset:=str_start_macro(math_spacing)-9*ord_noad

@ @<Append inter-element spacing based on |r_type| and |t|@>=
if r_type>0 then {not the first noad}
  begin case so(str_pool[r_type*8+t+magic_offset]) of
  "0": x:=0;
  "1": if cur_style<script_style then x:=thin_mu_skip_code@+else x:=0;
  "2": x:=thin_mu_skip_code;
  "3": if cur_style<script_style then x:=med_mu_skip_code@+else x:=0;
  "4": if cur_style<script_style then x:=thick_mu_skip_code@+else x:=0;
  othercases confusion("mlist4")
@:this can't happen mlist4}{\quad mlist4@>
  endcases;
  if x<>0 then
    begin y:=math_glue(glue_par(x),cur_mu);
    z:=new_glue(y); glue_ref_count(y):=null; vlink(p):=z; p:=z;@/
    subtype(z):=x+1; {store a symbolic subtype}
    end;
  end

@ We insert a penalty node after the hlist entries of noad |q| if |pen|
is not an ``infinite'' penalty, and if the node immediately following |q|
is not a penalty node or a |rel_noad| or absent entirely.

@<Append any |new_hlist| entries for |q|, and any appropriate penalties@>=
if new_hlist(q)<>null then
  begin vlink(p):=new_hlist(q);
  repeat p:=vlink(p);
  until vlink(p)=null;
  end;
if penalties then if vlink(q)<>null then if pen<inf_penalty then
  begin r_type:=type(vlink(q));
  if r_type<>penalty_node then if r_type<>rel_noad then
    begin z:=new_penalty(pen); vlink(p):=z; p:=z;
    end;
  end

@* \[37] Alignment.
It's sort of a miracle whenever \.{\\halign} and \.{\\valign} work, because
they cut across so many of the control structures of \TeX.

Therefore the
present page is probably not the best place for a beginner to start reading
this program; it is better to master everything else first.

Let us focus our thoughts on an example of what the input might be, in order
to get some idea about how the alignment miracle happens. The example doesn't
do anything useful, but it is sufficiently general to indicate all of the
special cases that must be dealt with; please do not be disturbed by its
apparent complexity and meaninglessness.
$$\vbox{\halign{\.{#}\hfil\cr
{}\\tabskip 2pt plus 3pt\cr
{}\\halign to 300pt\{u1\#v1\&\cr
\hskip 50pt\\tabskip 1pt plus 1fil u2\#v2\&\cr
\hskip 50pt u3\#v3\\cr\cr
\hskip 25pt a1\&\\omit a2\&\\vrule\\cr\cr
\hskip 25pt \\noalign\{\\vskip 3pt\}\cr
\hskip 25pt b1\\span b2\\cr\cr
\hskip 25pt \\omit\&c2\\span\\omit\\cr\}\cr}}$$
Here's what happens:

\yskip
(0) When `\.{\\halign to 300pt\{}' is scanned, the |scan_spec| routine
places the 300pt dimension onto the |save_stack|, and an |align_group|
code is placed above it. This will make it possible to complete the alignment
when the matching `\.\}' is found.

(1) The preamble is scanned next. Macros in the preamble are not expanded,
@^preamble@>
except as part of a tabskip specification. For example, if \.{u2} had been
a macro in the preamble above, it would have been expanded, since \TeX\
must look for `\.{minus...}' as part of the tabskip glue. A ``preamble list''
is constructed based on the user's preamble; in our case it contains the
following seven items:
$$\vbox{\halign{\.{#}\hfil\qquad&(#)\hfil\cr
{}\\glue 2pt plus 3pt&the tabskip preceding column 1\cr
{}\\alignrecord, width $-\infty$&preamble info for column 1\cr
{}\\glue 2pt plus 3pt&the tabskip between columns 1 and 2\cr
{}\\alignrecord, width $-\infty$&preamble info for column 2\cr
{}\\glue 1pt plus 1fil&the tabskip between columns 2 and 3\cr
{}\\alignrecord, width $-\infty$&preamble info for column 3\cr
{}\\glue 1pt plus 1fil&the tabskip following column 3\cr}}$$
These ``alignrecord'' entries have the same size as an |unset_node|,
since they will later be converted into such nodes. These alignrecord
nodes have no |depth| field; this is split into |u_part| and |v_part|,
and they point to token lists for the templates of the alignment. For
example, the |u_part| field in the first alignrecord points to the
token list `\.{u1}', i.e., the template preceding the `\.\#' for
column~1.  Furthermore, They have a |span_ptr| instead of a |node_attr|
field, and these |span_ptr| fields are initially set to the value
|end_span|, for reasons explained below.

(2) \TeX\ now looks at what follows the \.{\\cr} that ended the preamble.
It is not `\.{\\noalign}' or `\.{\\omit}', so this input is put back to
be read again, and the template `\.{u1}' is fed to the scanner. Just
before reading `\.{u1}', \TeX\ goes into restricted horizontal mode.
Just after reading `\.{u1}', \TeX\ will see `\.{a1}', and then (when the
{\.\&} is sensed) \TeX\ will see `\.{v1}'. Then \TeX\ scans an |endv|
token, indicating the end of a column. At this point an |unset_node| is
created, containing the contents of the current hlist (i.e., `\.{u1a1v1}').
The natural width of this unset node replaces the |width| field of the
alignrecord for column~1; in general, the alignrecords will record the
maximum natural width that has occurred so far in a given column.

(3) Since `\.{\\omit}' follows the `\.\&', the templates for column~2
are now bypassed. Again \TeX\ goes into restricted horizontal mode and
makes an |unset_node| from the resulting hlist; but this time the
hlist contains simply `\.{a2}'. The natural width of the new unset box
is remembered in the |width| field of the alignrecord for column~2.

(4) A third |unset_node| is created for column 3, using essentially the
mechanism that worked for column~1; this unset box contains `\.{u3\\vrule
v3}'. The vertical rule in this case has running dimensions that will later
extend to the height and depth of the whole first row, since each |unset_node|
in a row will eventually inherit the height and depth of its enclosing box.

(5) The first row has now ended; it is made into a single unset box
comprising the following seven items:
$$\vbox{\halign{\hbox to 325pt{\qquad\.{#}\hfil}\cr
{}\\glue 2pt plus 3pt\cr
{}\\unsetbox for 1 column: u1a1v1\cr
{}\\glue 2pt plus 3pt\cr
{}\\unsetbox for 1 column: a2\cr
{}\\glue 1pt plus 1fil\cr
{}\\unsetbox for 1 column: u3\\vrule v3\cr
{}\\glue 1pt plus 1fil\cr}}$$
The width of this unset row is unimportant, but it has the correct height
and depth, so the correct baselineskip glue will be computed as the row
is inserted into a vertical list.

(6) Since `\.{\\noalign}' follows the current \.{\\cr}, \TeX\ appends
additional material (in this case \.{\\vskip 3pt}) to the vertical list.
While processing this material, \TeX\ will be in internal vertical
mode, and |no_align_group| will be on |save_stack|.

(7) The next row produces an unset box that looks like this:
$$\vbox{\halign{\hbox to 325pt{\qquad\.{#}\hfil}\cr
{}\\glue 2pt plus 3pt\cr
{}\\unsetbox for 2 columns: u1b1v1u2b2v2\cr
{}\\glue 1pt plus 1fil\cr
{}\\unsetbox for 1 column: {\rm(empty)}\cr
{}\\glue 1pt plus 1fil\cr}}$$
The natural width of the unset box that spans columns 1~and~2 is stored
in a ``span node,'' which we will explain later; the |span_ptr| field of the
alignrecord for column~1 now points to the new span node, and the |span_ptr|
of the span node points to |end_span|.

(8) The final row produces the unset box
$$\vbox{\halign{\hbox to 325pt{\qquad\.{#}\hfil}\cr
{}\\glue 2pt plus 3pt\cr
{}\\unsetbox for 1 column: {\rm(empty)}\cr
{}\\glue 2pt plus 3pt\cr
{}\\unsetbox for 2 columns: u2c2v2\cr
{}\\glue 1pt plus 1fil\cr}}$$
A new span node is attached to the alignrecord for column 2.

(9) The last step is to compute the true column widths and to change all the
unset boxes to hboxes, appending the whole works to the vertical list that
encloses the \.{\\halign}. The rules for deciding on the final widths of
each unset column box will be explained below.

\yskip\noindent
Note that as \.{\\halign} is being processed, we fearlessly give up control
to the rest of \TeX. At critical junctures, an alignment routine is
called upon to step in and do some little action, but most of the time
these routines just lurk in the background. It's something like
post-hypnotic suggestion.

@ We have mentioned that alignrecords contain no |height| or |depth| fields.
Their |glue_sign| and |glue_order| are pre-empted as well, since it
is necessary to store information about what to do when a template ends.
This information is called the |extra_info| field.

@d align_record_node=34
@d u_part(#)==vlink(#+depth_offset) {pointer to \<u_j> token list}
@d v_part(#)==vinfo(#+depth_offset) {pointer to \<v_j> token list}
@d span_ptr(#)==vinfo(#+1) {column spanning list}
@d extra_info(#)==vinfo(#+list_offset) {info to remember during template}

@ Alignments can occur within alignments, so a small stack is used to access
the alignrecord information. At each level we have a |preamble| pointer,
indicating the beginning of the preamble list; a |cur_align| pointer,
indicating the current position in the preamble list; a |cur_span| pointer,
indicating the value of |cur_align| at the beginning of a sequence of
spanned columns; a |cur_loop| pointer, indicating the tabskip glue before
an alignrecord that should be copied next if the current list is extended;
and the |align_state| variable, which indicates the nesting of braces so
that \.{\\cr} and \.{\\span} and tab marks are properly intercepted.
There also are pointers |cur_head| and |cur_tail| to the head and tail
of a list of adjustments being moved out from horizontal mode to
vertical~mode, and alike |cur_pre_head| and |cur_pre_tail| for pre-adjust 
lists.

The current values of these nine quantities appear in global variables;
when they have to be pushed down, they are stored in 6-word nodes, and
|align_ptr| points to the topmost such node.

@d preamble==vlink(align_head) {the current preamble list}
@d align_stack_node=47 

@<Glob...@>=
@!cur_align:pointer; {current position in preamble list}
@!cur_span:pointer; {start of currently spanned columns in preamble list}
@!cur_loop:pointer; {place to copy when extending a periodic preamble}
@!align_ptr:pointer; {most recently pushed-down alignment stack node}
@!cur_head,@!cur_tail:pointer; {adjustment list pointers}
@!cur_pre_head,@!cur_pre_tail:pointer; {pre-adjustment list pointers}

@ The |align_state| and |preamble| variables are initialized elsewhere.

@<Set init...@>=
align_ptr:=null; cur_align:=null; cur_span:=null; cur_loop:=null;
cur_head:=null; cur_tail:=null;
cur_pre_head:=null; cur_pre_tail:=null;

@ Alignment stack maintenance is handled by a pair of trivial routines
called |push_alignment| and |pop_alignment|.

@p procedure push_alignment;
var p:pointer; {the new alignment stack node}
begin p:=new_node(align_stack_node,0);
vinfo(p+1):=align_ptr;       vlink(p+1):=cur_align;
vinfo(p+2):=preamble;        vlink(p+2):=cur_span;
vinfo(p+3):=cur_loop;        vlink(p+3):=align_state;
vinfo(p+4):=cur_head;        vlink(p+4):=cur_tail;
vinfo(p+5):=cur_pre_head;    vlink(p+5):=cur_pre_tail;
align_ptr:=p;
cur_head:=new_node(temp_node,0);
end;
@#
procedure pop_alignment;
var p:pointer; {the top alignment stack node}
begin flush_node(cur_head); 
p:=align_ptr;
cur_pre_tail:=vlink(p+5); cur_pre_head:=vinfo(p+5);
cur_tail    :=vlink(p+4); cur_head    :=vinfo(p+4);
align_state :=vlink(p+3); cur_loop    :=vinfo(p+3);
cur_span    :=vlink(p+2); preamble    :=vinfo(p+2);
cur_align   :=vlink(p+1); align_ptr   :=vinfo(p+1);
flush_node(p);
end;

@ \TeX\ has eight procedures that govern alignments: |init_align| and
|fin_align| are used at the very beginning and the very end; |init_row| and
|fin_row| are used at the beginning and end of individual rows; |init_span|
is used at the beginning of a sequence of spanned columns (possibly involving
only one column); |init_col| and |fin_col| are used at the beginning and
end of individual columns; and |align_peek| is used after \.{\\cr} to see
whether the next item is \.{\\noalign}.

We shall consider these routines in the order they are first used during
the course of a complete \.{\\halign}, namely |init_align|, |align_peek|,
|init_row|, |init_span|, |init_col|, |fin_col|, |fin_row|, |fin_align|.

@ When \.{\\halign} or \.{\\valign} has been scanned in an appropriate
mode, \TeX\ calls |init_align|, whose task is to get everything off to a
good start. This mostly involves scanning the preamble and putting its
information into the preamble list.
@^preamble@>

@p @t\4@>@<Declare the procedure called |get_preamble_token|@>@t@>@/
procedure@?align_peek; forward;@t\2@>@/
procedure@?normal_paragraph; forward;@t\2@>@/
procedure init_align;
label done, done1, done2, continue;
var save_cs_ptr:pointer; {|warning_index| value for error messages}
@!p,r:pointer; {for short-term temporary use}
begin save_cs_ptr:=cur_cs; {\.{\\halign} or \.{\\valign}, usually}
push_alignment; align_state:=-1000000; {enter a new alignment level}
@<Check for improper alignment in displayed math@>;
push_nest; {enter a new semantic level}
@<Change current mode to |-vmode| for \.{\\halign}, |-hmode| for \.{\\valign}@>;
scan_spec(align_group,false);@/
@<Scan the preamble and record it in the |preamble| list@>;
new_save_level(align_group);
if every_cr<>null then begin_token_list(every_cr,every_cr_text);
align_peek; {look for \.{\\noalign} or \.{\\omit}}
end;

@ In vertical modes, |prev_depth| already has the correct value. But
if we are in |mmode| (displayed formula mode), we reach out to the
enclosing vertical mode for the |prev_depth| value that produces the
correct baseline calculations.

@<Change current mode...@>=
if mode=mmode then
  begin mode:=-vmode; prev_depth:=nest[nest_ptr-2].aux_field.sc;
  end
else if mode>0 then negate(mode)

@ When \.{\\halign} is used as a displayed formula, there should be
no other pieces of mlists present.

@<Check for improper alignment in displayed math@>=
if (mode=mmode)and((tail<>head)or(incompleat_noad<>null)) then
  begin print_err("Improper "); print_esc("halign"); print(" inside $$'s");
@.Improper \\halign...@>
  help3("Displays can use special alignments (like \eqalignno)")@/
  ("only if nothing but the alignment itself is between $$'s.")@/
  ("So I've deleted the formulas that preceded this alignment.");
  error; flush_math;
  end

@ @<Scan the preamble and record it in the |preamble| list@>=
preamble:=null; cur_align:=align_head; cur_loop:=null; scanner_status:=aligning;
warning_index:=save_cs_ptr; align_state:=-1000000;
  {at this point, |cur_cmd=left_brace|}
loop@+  begin @<Append the current tabskip glue to the preamble list@>;
  if cur_cmd=car_ret then goto done; {\.{\\cr} ends the preamble}
  @<Scan preamble text until |cur_cmd| is |tab_mark| or |car_ret|,
    looking for changes in the tabskip glue; append an
    alignrecord to the preamble list@>;
  end;
done: scanner_status:=normal

@ @<Append the current tabskip glue to the preamble list@>=
r:=new_param_glue(tab_skip_code); vlink(cur_align):=r;
cur_align:=vlink(cur_align)

@ @<Scan preamble text until |cur_cmd| is |tab_mark| or |car_ret|...@>=
@<Scan the template \<u_j>, putting the resulting token list in |hold_token_head|@>;
r:=new_node(align_record_node,0); vlink(cur_align):=r;
cur_align:=vlink(cur_align); {a new alignrecord}
span_ptr(cur_align):=end_span; width(cur_align):=null_flag;
u_part(cur_align):=link(hold_token_head);
@<Scan the template \<v_j>, putting the resulting token list in |hold_token_head|@>;
v_part(cur_align):=link(hold_token_head)

@ We enter `\.{\\span}' into |eqtb| with |tab_mark| as its command code,
and with |span_code| as the command modifier. This makes \TeX\ interpret it
essentially the same as an alignment delimiter like `\.\&', yet it is
recognizably different when we need to distinguish it from a normal delimiter.
It also turns out to be useful to give a special |cr_code| to `\.{\\cr}',
and an even larger |cr_cr_code| to `\.{\\crcr}'.

The end of a template is represented by two ``frozen'' control sequences
called \.{\\endtemplate}. The first has the command code |end_template|, which
is |>outer_call|, so it will not easily disappear in the presence of errors.
The |get_x_token| routine converts the first into the second, which has |endv|
as its command code.

@d span_code=special_char {distinct from any character}
@d cr_code=span_code+1 {distinct from |span_code| and from any character}
@d cr_cr_code=cr_code+1 {this distinguishes \.{\\crcr} from \.{\\cr}}
@d end_template_token==cs_token_flag+frozen_end_template

@<Put each of \TeX's primitives into the hash table@>=
primitive("span",tab_mark,span_code);@/
@!@:span_}{\.{\\span} primitive@>
primitive("cr",car_ret,cr_code);
@!@:cr_}{\.{\\cr} primitive@>
text(frozen_cr):="cr"; eqtb[frozen_cr]:=eqtb[cur_val];@/
primitive("crcr",car_ret,cr_cr_code);
@!@:cr_cr_}{\.{\\crcr} primitive@>
text(frozen_end_template):="endtemplate"; text(frozen_endv):="endtemplate";
eq_type(frozen_endv):=endv; equiv(frozen_endv):=null_list;
eq_level(frozen_endv):=level_one;@/
eqtb[frozen_end_template]:=eqtb[frozen_endv];
eq_type(frozen_end_template):=end_template;

@ @<Cases of |print_cmd_chr|...@>=
tab_mark: if chr_code=span_code then print_esc("span")
  else chr_cmd("alignment tab character ");
car_ret: if chr_code=cr_code then print_esc("cr")
  else print_esc("crcr");

@ The preamble is copied directly, except that \.{\\tabskip} causes a change
to the tabskip glue, thereby possibly expanding macros that immediately
follow it. An appearance of \.{\\span} also causes such an expansion.

Note that if the preamble contains `\.{\\global\\tabskip}', the `\.{\\global}'
token survives in the preamble and the `\.{\\tabskip}' defines new
tabskip glue (locally).

@<Declare the procedure called |get_preamble_token|@>=
procedure get_preamble_token;
label restart;
begin restart: get_token;
while (cur_chr=span_code)and(cur_cmd=tab_mark) do
  begin get_token; {this token will be expanded once}
  if cur_cmd>max_command then
    begin expand; get_token;
    end;
  end;
if cur_cmd=endv then
  fatal_error("(interwoven alignment preambles are not allowed)");
@.interwoven alignment preambles...@>
if (cur_cmd=assign_glue)and(cur_chr=glue_base+tab_skip_code) then
  begin scan_optional_equals; scan_glue(glue_val);
  if global_defs>0 then geq_define(glue_base+tab_skip_code,glue_ref,cur_val)
  else eq_define(glue_base+tab_skip_code,glue_ref,cur_val);
  goto restart;
  end;
end;

@ Spaces are eliminated from the beginning of a template.

@<Scan the template \<u_j>...@>=
p:=hold_token_head; link(p):=null;
loop@+  begin get_preamble_token;
  if cur_cmd=mac_param then goto done1;
  if (cur_cmd<=car_ret)and(cur_cmd>=tab_mark)and(align_state=-1000000) then
   if (p=hold_token_head)and(cur_loop=null)and(cur_cmd=tab_mark)
    then cur_loop:=cur_align
   else  begin print_err("Missing # inserted in alignment preamble");
@.Missing \# inserted...@>
    help3("There should be exactly one # between &'s, when an")@/
    ("\halign or \valign is being set up. In this case you had")@/
    ("none, so I've put one in; maybe that will work.");
    back_error; goto done1;
    end
  else if (cur_cmd<>spacer)or(p<>hold_token_head) then
    begin r:=get_avail; link(p):=r; p:=link(p); info(p):=cur_tok;
    end;
  end;
done1:

@ @<Scan the template \<v_j>...@>=
p:=hold_token_head; link(p):=null;
loop@+  begin continue: get_preamble_token;
  if (cur_cmd<=car_ret)and(cur_cmd>=tab_mark)and(align_state=-1000000) then
    goto done2;
  if cur_cmd=mac_param then
    begin print_err("Only one # is allowed per tab");
@.Only one \# is allowed...@>
    help3("There should be exactly one # between &'s, when an")@/
    ("\halign or \valign is being set up. In this case you had")@/
    ("more than one, so I'm ignoring all but the first.");
    error; goto continue;
    end;
  r:=get_avail; link(p):=r; p:=link(p); info(p):=cur_tok;
  end;
done2: r:=get_avail; link(p):=r; p:=link(p);
info(p):=end_template_token {put \.{\\endtemplate} at the end}

@ The tricky part about alignments is getting the templates into the
scanner at the right time, and recovering control when a row or column
is finished.

We usually begin a row after each \.{\\cr} has been sensed, unless that
\.{\\cr} is followed by \.{\\noalign} or by the right brace that terminates
the alignment. The |align_peek| routine is used to look ahead and do
the right thing; it either gets a new row started, or gets a \.{\\noalign}
started, or finishes off the alignment.

@<Declare the procedure called |align_peek|@>=
procedure align_peek;
label restart;
begin restart: align_state:=1000000;
repeat get_x_or_protected;
until cur_cmd<>spacer;
if cur_cmd=no_align then
  begin scan_left_brace; new_save_level(no_align_group);
  if mode=-vmode then normal_paragraph;
  end
else if cur_cmd=right_brace then fin_align
else if (cur_cmd=car_ret)and(cur_chr=cr_cr_code) then
  goto restart {ignore \.{\\crcr}}
else  begin init_row; {start a new row}
  init_col; {start a new column and replace what we peeked at}
  end;
end;

@ To start a row (i.e., a `row' that rhymes with `dough' but not with `bough'),
we enter a new semantic level, copy the first tabskip glue, and change
from internal vertical mode to restricted horizontal mode or vice versa.
The |space_factor| and |prev_depth| are not used on this semantic level,
but we clear them to zero just to be tidy.

@p @t\4@>@<Declare the procedure called |init_span|@>@t@>@/
procedure init_row;
begin push_nest; mode:=(-hmode-vmode)-mode;
if mode=-hmode then space_factor:=0 @+else prev_depth:=0;
tail_append(new_glue(glue_ptr(preamble)));
subtype(tail):=tab_skip_code+1;@/
cur_align:=vlink(preamble); cur_tail:=cur_head; cur_pre_tail:=cur_pre_head;
init_span(cur_align);
end;

@ The parameter to |init_span| is a pointer to the alignrecord where the
next column or group of columns will begin. A new semantic level is
entered, so that the columns will generate a list for subsequent packaging.

@<Declare the procedure called |init_span|@>=
procedure init_span(@!p:pointer);
begin push_nest;
if mode=-hmode then space_factor:=1000
else  begin prev_depth:=ignore_depth; normal_paragraph;
  end;
cur_span:=p;
end;

@ When a column begins, we assume that |cur_cmd| is either |omit| or else
the current token should be put back into the input until the \<u_j>
template has been scanned.  (Note that |cur_cmd| might be |tab_mark| or
|car_ret|.)  We also assume that |align_state| is approximately 1000000 at
this time.  We remain in the same mode, and start the template if it is
called for.

@p procedure init_col;
begin extra_info(cur_align):=cur_cmd;
if cur_cmd=omit then align_state:=0
else  begin back_input; begin_token_list(u_part(cur_align),u_template);
  end; {now |align_state=1000000|}
end;

@ The scanner sets |align_state| to zero when the \<u_j> template ends. When
a subsequent \.{\\cr} or \.{\\span} or tab mark occurs with |align_state=0|,
the scanner activates the following code, which fires up the \<v_j> template.
We need to remember the |cur_chr|, which is either |cr_cr_code|, |cr_code|,
|span_code|, or a character code, depending on how the column text has ended.

This part of the program had better not be activated when the preamble
to another alignment is being scanned, or when no alignment preamble is active.

@p procedure insert_vj_template;
begin if (scanner_status=aligning) or (cur_align=null) then
  fatal_error("(interwoven alignment preambles are not allowed)");
@.interwoven alignment preambles...@>
cur_cmd:=extra_info(cur_align); extra_info(cur_align):=cur_chr;
if cur_cmd=omit then begin_token_list(omit_template,v_template)
else begin_token_list(v_part(cur_align),v_template);
align_state:=1000000;
end;

@ The token list |omit_template| just referred to is a constant token
list that contains the special control sequence \.{\\endtemplate} only.

@<Initialize the special...@>=
info(omit_template):=end_template_token; {|link(omit_template)=null|}

@ When the |endv| command at the end of a \<v_j> template comes through the
scanner, things really start to happen; and it is the |fin_col| routine
that makes them happen. This routine returns |true| if a row as well as a
column has been finished.

@p function fin_col:boolean;
label exit;
var p:pointer; {the alignrecord after the current one}
@!q,@!r:pointer; {temporary pointers for list manipulation}
@!s:pointer; {a new span node}
@!u:pointer; {a new unset box}
@!w:scaled; {natural width}
@!o:glue_ord; {order of infinity}
@!n:halfword; {span counter}
begin if cur_align=null then confusion("endv");
q:=vlink(cur_align);@+if q=null then confusion("endv");
@:this can't happen endv}{\quad endv@>
if align_state<500000 then
  fatal_error("(interwoven alignment preambles are not allowed)");
@.interwoven alignment preambles...@>
p:=vlink(q);
@<If the preamble list has been traversed, check that the row has ended@>;
if extra_info(cur_align)<>span_code then
  begin unsave; new_save_level(align_group);@/
  @<Package an unset box for the current column and record its width@>;
  @<Copy the tabskip glue between columns@>;
  if extra_info(cur_align)>=cr_code then
    begin fin_col:=true; return;
    end;
  init_span(p);
  end;
align_state:=1000000;
repeat get_x_or_protected;
until cur_cmd<>spacer;
cur_align:=p;
init_col; fin_col:=false;
exit: end;

@ @<If the preamble list has been traversed, check that the row has ended@>=
if (p=null)and(extra_info(cur_align)<cr_code) then
 if cur_loop<>null then @<Lengthen the preamble periodically@>
 else  begin print_err("Extra alignment tab has been changed to ");
@.Extra alignment tab...@>
  print_esc("cr");
  help3("You have given more \span or & marks than there were")@/
  ("in the preamble to the \halign or \valign now in progress.")@/
  ("So I'll assume that you meant to type \cr instead.");
  extra_info(cur_align):=cr_code; error;
  end

@ @<Lengthen the preamble...@>=
begin r:=new_node(align_record_node,0); vlink(q):=r; p:=vlink(q); {a new alignrecord}
span_ptr(p):=end_span; width(p):=null_flag; cur_loop:=vlink(cur_loop);
@<Copy the templates from node |cur_loop| into node |p|@>;
cur_loop:=vlink(cur_loop);
r:=new_glue(glue_ptr(cur_loop)); vlink(p):=r;
end

@ @<Copy the templates from node |cur_loop| into node |p|@>=
q:=hold_token_head; r:=u_part(cur_loop);
while r<>null do
  begin s:=get_avail; link(q):=s; q:=link(q); info(q):=info(r); r:=link(r);
  end;
link(q):=null; u_part(p):=link(hold_token_head);
q:=hold_token_head; r:=v_part(cur_loop);
while r<>null do
  begin s:=get_avail; link(q):=s; q:=link(q); info(q):=info(r); r:=link(r);
  end;
link(q):=null; v_part(p):=link(hold_token_head)

@ @<Copy the tabskip glue...@>=
tail_append(new_glue(glue_ptr(vlink(cur_align))));
subtype(tail):=tab_skip_code+1

@ @<Package an unset...@>=
begin if mode=-hmode then
  begin adjust_tail:=cur_tail; pre_adjust_tail:=cur_pre_tail;
  u:=filtered_hpack(head,tail,natural,align_set_group); w:=width(u);
  cur_tail:=adjust_tail; adjust_tail:=null;
  cur_pre_tail:=pre_adjust_tail; pre_adjust_tail:=null;
  end
else  begin u:=filtered_vpackage(vlink(head),natural,0,align_set_group); w:=height(u);
  end;
n:=min_quarterword; {this represents a span count of 1}
if cur_span<>cur_align then @<Update width entry for spanned columns@>
else if w>width(cur_align) then width(cur_align):=w;
type(u):=unset_node; span_count(u):=n;@/
@<Determine the stretch order@>;
glue_order(u):=o; glue_stretch(u):=total_stretch[o];@/
@<Determine the shrink order@>;
glue_sign(u):=o; glue_shrink(u):=total_shrink[o];@/
pop_nest; vlink(tail):=u; tail:=u;
end

@ A span node is a 3-word record containing |width|, |span_span|, and
|span_ptr| fields. The |span_span| field indicates the number of
spanned columns; the |span_ptr| field points to a span node for the same
starting column, having a greater extent of spanning, or to
|end_span|, which has the largest possible |span_span| field; the |width|
field holds the largest natural width corresponding to a particular
set of spanned columns.

A list of the maximum widths so far, for spanned columns starting at a
given column, begins with the |span_ptr| field of the alignrecord for
that column. The code has to make sure that there is room for
|span_ptr| in both the alignrecord and the span nodes, which is why
|span_ptr| replaces |node_attr|.
@^data structure assumptions@>

The |new_span_node| function is defined in |texnodes.c|.

@d span_node==41
@d span_node_size==3 {number of |mem| words for a span node}
@d span_span(#)==vlink(#+1) {that is normally |alink| }

@<Initialize the special list heads...@>=
span_span(end_span):=max_quarterword+1; span_ptr(end_span):=null;

@ @<Update width entry for spanned columns@>=
begin q:=cur_span;
repeat incr(n); q:=vlink(vlink(q));
until q=cur_align;
if n>max_quarterword then confusion("too many spans"); {this can happen, but won't}
@^system dependencies@>
@:this can't happen too many spans}{\quad too many spans@>
q:=cur_span;
while span_span(span_ptr(q))<n do begin 
  q:=span_ptr(q);
  end;
if span_span(span_ptr(q))>n then begin
  s:=new_span_node(span_ptr(q),n,w); 
  span_ptr(q):=s; 
  end
else if width(span_ptr(q))<w then width(span_ptr(q)):=w;
end

@ At the end of a row, we append an unset box to the current vlist (for
\.{\\halign}) or the current hlist (for \.{\\valign}). This unset box
contains the unset boxes for the columns, separated by the tabskip glue.
Everything will be set later.

@p procedure fin_row;
var p:pointer; {the new unset box}
begin if mode=-hmode then
  begin p:=filtered_hpack(head,tail,natural,fin_row_group);
  pop_nest;
  if cur_pre_head <> cur_pre_tail then
      append_list(cur_pre_head)(cur_pre_tail);
  append_to_vlist(p);
  if cur_head <> cur_tail then
      append_list(cur_head)(cur_tail);
  end
else  begin p:=filtered_vpackage(vlink(head),natural,max_depth,fin_row_group); 
  pop_nest; vlink(tail):=p; tail:=p; space_factor:=1000;
  end;
type(p):=unset_node; glue_stretch(p):=0;
if every_cr<>null then begin_token_list(every_cr,every_cr_text);
align_peek;
end; {note that |glue_shrink(p)=0| since |glue_shrink==shift_amount|}

@ Finally, we will reach the end of the alignment, and we can breathe a
sigh of relief that memory hasn't overflowed. All the unset boxes will now be
set so that the columns line up, taking due account of spanned columns.

@p procedure@?do_assignments; forward;@t\2@>@/
procedure@?resume_after_display; forward;@t\2@>@/
procedure@?build_page; forward;@t\2@>@/
procedure fin_align;
var @!p,@!q,@!r,@!s,@!u,@!v,@!rr: pointer; {registers for the list operations}
@!t,@!w:scaled; {width of column}
@!o:scaled; {shift offset for unset boxes}
@!n:halfword; {matching span amount}
@!rule_save:scaled; {temporary storage for |overfull_rule|}
@!aux_save:memory_word; {temporary storage for |aux|}
begin if cur_group<>align_group then confusion("align1");
@:this can't happen align}{\quad align@>
unsave; {that |align_group| was for individual entries}
if cur_group<>align_group then confusion("align0");
unsave; {that |align_group| was for the whole alignment}
if nest[nest_ptr-1].mode_field=mmode then o:=display_indent
  else o:=0;
@<Go through the preamble list, determining the column widths and
  changing the alignrecords to dummy unset boxes@>;
@<Package the preamble list, to determine the actual tabskip glue amounts,
  and let |p| point to this prototype box@>;
@<Set the glue in all the unset boxes of the current list@>;
flush_node_list(p); pop_alignment;
@<Insert the \(c)current list into its environment@>;
end;@/
@t\4@>@<Declare the procedure called |align_peek|@>

@ It's time now to dismantle the preamble list and to compute the column
widths. Let $w_{ij}$ be the maximum of the natural widths of all entries
that span columns $i$ through $j$, inclusive. The alignrecord for column~$i$
contains $w_{ii}$ in its |width| field, and there is also a linked list of
the nonzero $w_{ij}$ for increasing $j$, accessible via the |info| field;
these span nodes contain the value $j-i-1+|min_quarterword|$ in their
|link| fields. The values of $w_{ii}$ were initialized to |null_flag|, which
we regard as $-\infty$.

The final column widths are defined by the formula
$$w_j=\max_{1\L i\L j}\biggl( w_{ij}-\sum_{i\L k<j}(t_k+w_k)\biggr),$$
where $t_k$ is the natural width of the tabskip glue between columns
$k$ and~$k+1$. However, if $w_{ij}=-\infty$ for all |i| in the range
|1<=i<=j| (i.e., if every entry that involved column~|j| also involved
column~|j+1|), we let $w_j=0$, and we zero out the tabskip glue after
column~|j|.

\TeX\ computes these values by using the following scheme: First $w_1=w_{11}$.
Then replace $w_{2j}$ by $\max(w_{2j},w_{1j}-t_1-w_1)$, for all $j>1$.
Then $w_2=w_{22}$. Then replace $w_{3j}$ by $\max(w_{3j},w_{2j}-t_2-w_2)$
for all $j>2$; and so on. If any $w_j$ turns out to be $-\infty$, its
value is changed to zero and so is the next tabskip.

@<Go through the preamble list,...@>=
q:=vlink(preamble);
repeat flush_list(u_part(q)); flush_list(v_part(q));
p:=vlink(vlink(q));
if width(q)=null_flag then
  @<Nullify |width(q)| and the tabskip glue following this column@>;
if span_ptr(q)<>end_span then
  @<Merge the widths in the span nodes of |q| with those of |p|,
    destroying the span nodes of |q|@>;
type(q):=unset_node; span_count(q):=min_quarterword; height(q):=0;
depth(q):=0; glue_order(q):=normal; glue_sign(q):=normal;
glue_stretch(q):=0; glue_shrink(q):=0; q:=p;
until q=null

@ @<Nullify |width(q)| and the tabskip glue following this column@>=
begin width(q):=0; r:=vlink(q); s:=glue_ptr(r);
if s<>zero_glue then
  begin add_glue_ref(zero_glue); delete_glue_ref(s);
  glue_ptr(r):=zero_glue;
  end;
end

@ Merging of two span-node lists is a typical exercise in the manipulation of
linearly linked data structures. The essential invariant in the following
|repeat| loop is that we want to dispense with node |r|, in |q|'s list,
and |u| is its successor; all nodes of |p|'s list up to and including |s|
have been processed, and the successor of |s| matches |r| or precedes |r|
or follows |r|, according as |link(r)=n| or |link(r)>n| or |link(r)<n|.

@<Merge the widths...@>=
begin t:=width(q)+width(glue_ptr(vlink(q)));
r:=span_ptr(q); s:=end_span; span_ptr(s):=p; n:=min_quarterword+1;
repeat width(r):=width(r)-t; u:=span_ptr(r);
while span_span(r)>n do
  begin s:=span_ptr(s); n:=span_span(span_ptr(s))+1;
  end;
if span_span(r)<n then
  begin span_ptr(r):=span_ptr(s); span_ptr(s):=r; decr(span_span(r)); s:=r;
  end
else  begin if width(r)>width(span_ptr(s)) then width(span_ptr(s)):=width(r);
  flush_node(r);
  end;
r:=u;
until r=end_span;
end

@ Now the preamble list has been converted to a list of alternating unset
boxes and tabskip glue, where the box widths are equal to the final
column sizes. In case of \.{\\valign}, we change the widths to heights,
so that a correct error message will be produced if the alignment is
overfull or underfull.

@<Package the preamble list...@>=
save_ptr:=save_ptr-2; pack_begin_line:=-mode_line;
if mode=-vmode then
  begin rule_save:=overfull_rule;
  overfull_rule:=0; {prevent rule from being packaged}
  p:=hpack(preamble,saved(1),saved(0)); 
  overfull_rule:=rule_save;
  end
else  begin q:=vlink(preamble);
  repeat height(q):=width(q); width(q):=0; q:=vlink(vlink(q));
  until q=null;
  p:=filtered_vpackage(preamble,saved(1),saved(0),max_depth,preamble_group);
  q:=vlink(preamble);
  repeat width(q):=height(q); height(q):=0; q:=vlink(vlink(q));
  until q=null;
  end;
pack_begin_line:=0

@ @<Set the glue in all the unset...@>=
q:=vlink(head); s:=head;
while q<>null do
  begin if not is_char_node(q) then
    if type(q)=unset_node then
      @<Set the unset box |q| and the unset boxes in it@>
    else if type(q)=rule_node then
      @<Make the running dimensions in rule |q| extend to the
        boundaries of the alignment@>;
  s:=q; q:=vlink(q);
  end

@ @<Make the running dimensions in rule |q| extend...@>=
begin if is_running(width(q)) then width(q):=width(p);
if is_running(height(q)) then height(q):=height(p);
if is_running(depth(q)) then depth(q):=depth(p);
if o<>0 then
  begin r:=vlink(q); vlink(q):=null; q:=hpack(q,natural);
  shift_amount(q):=o; vlink(q):=r; vlink(s):=q;
  end;
end

@ The unset box |q| represents a row that contains one or more unset boxes,
depending on how soon \.{\\cr} occurred in that row.

@<Set the unset box |q| and the unset boxes in it@>=
begin if mode=-vmode then
  begin type(q):=hlist_node; width(q):=width(p);
  end
else  begin type(q):=vlist_node; height(q):=height(p);
  end;
glue_order(q):=glue_order(p); glue_sign(q):=glue_sign(p);
glue_set(q):=glue_set(p); shift_amount(q):=o;
r:=vlink(list_ptr(q)); s:=vlink(list_ptr(p));
repeat @<Set the glue in node |r| and change it from an unset node@>;
r:=vlink(vlink(r)); s:=vlink(vlink(s));
until r=null;
end

@ A box made from spanned columns will be followed by tabskip glue nodes and
by empty boxes as if there were no spanning. This permits perfect alignment
of subsequent entries, and it prevents values that depend on floating point
arithmetic from entering into the dimensions of any boxes.

@<Set the glue in node |r|...@>=
n:=span_count(r); t:=width(s); w:=t; u:=hold_head;
while n>min_quarterword do
  begin decr(n);
  @<Append tabskip glue and an empty box to list |u|,
    and update |s| and |t| as the prototype nodes are passed@>;
  end;
if mode=-vmode then
  @<Make the unset node |r| into an |hlist_node| of width |w|,
    setting the glue as if the width were |t|@>
else @<Make the unset node |r| into a |vlist_node| of height |w|,
    setting the glue as if the height were |t|@>;
shift_amount(r):=0;
if u<>hold_head then {append blank boxes to account for spanned nodes}
  begin vlink(u):=vlink(r); vlink(r):=vlink(hold_head); r:=u;
  end

@ @<Append tabskip glue and an empty box to list |u|...@>=
s:=vlink(s); v:=glue_ptr(s); vlink(u):=new_glue(v); u:=vlink(u);
subtype(u):=tab_skip_code+1; t:=t+width(v);
if glue_sign(p)=stretching then
  begin if stretch_order(v)=glue_order(p) then
    t:=t+round(float(glue_set(p))*stretch(v));
@^real multiplication@>
  end
else if glue_sign(p)=shrinking then
  begin if shrink_order(v)=glue_order(p) then
    t:=t-round(float(glue_set(p))*shrink(v));
  end;
s:=vlink(s); rr:=new_null_box; vlink(u):=rr; u:=vlink(u); t:=t+width(s);
if mode=-vmode then width(u):=width(s)@+else
  begin type(u):=vlist_node; height(u):=width(s);
  end

@ @<Make the unset node |r| into an |hlist_node| of width |w|...@>=
begin height(r):=height(q); depth(r):=depth(q);
if t=width(r) then
  begin glue_sign(r):=normal; glue_order(r):=normal;
  set_glue_ratio_zero(glue_set(r));
  end
else if t>width(r) then
  begin glue_sign(r):=stretching;
  if glue_stretch(r)=0 then set_glue_ratio_zero(glue_set(r))
  else glue_set(r):=unfloat((t-width(r))/glue_stretch(r));
@^real division@>
  end
else  begin glue_order(r):=glue_sign(r); glue_sign(r):=shrinking;
  if glue_shrink(r)=0 then set_glue_ratio_zero(glue_set(r))
  else if (glue_order(r)=normal)and(width(r)-t>glue_shrink(r)) then
    set_glue_ratio_one(glue_set(r))
  else glue_set(r):=unfloat((width(r)-t)/glue_shrink(r));
  end;
width(r):=w; type(r):=hlist_node;
end

@ @<Make the unset node |r| into a |vlist_node| of height |w|...@>=
begin width(r):=width(q);
if t=height(r) then
  begin glue_sign(r):=normal; glue_order(r):=normal;
  set_glue_ratio_zero(glue_set(r));
  end
else if t>height(r) then
  begin glue_sign(r):=stretching;
  if glue_stretch(r)=0 then set_glue_ratio_zero(glue_set(r))
  else glue_set(r):=unfloat((t-height(r))/glue_stretch(r));
@^real division@>
  end
else  begin glue_order(r):=glue_sign(r); glue_sign(r):=shrinking;
  if glue_shrink(r)=0 then set_glue_ratio_zero(glue_set(r))
  else if (glue_order(r)=normal)and(height(r)-t>glue_shrink(r)) then
    set_glue_ratio_one(glue_set(r))
  else glue_set(r):=unfloat((height(r)-t)/glue_shrink(r));
  end;
height(r):=w; type(r):=vlist_node;
end

@ We now have a completed alignment, in the list that starts at |head|
and ends at |tail|. This list will be merged with the one that encloses
it. (In case the enclosing mode is |mmode|, for displayed formulas,
we will need to insert glue before and after the display; that part of the
program will be deferred until we're more familiar with such operations.)

@<Insert the \(c)current list into its environment@>=
aux_save:=aux; p:=vlink(head); q:=tail; pop_nest;
if mode=mmode then @<Finish an alignment in a display@>
else  begin aux:=aux_save; vlink(tail):=p;
  if p<>null then tail:=q;
  if mode=vmode then begin check_filter('alignment'); build_page; end;
  end

@* \[38] Breaking paragraphs into lines.
We come now to what is probably the most interesting algorithm of \TeX:
the mechanism for choosing the ``best possible'' breakpoints that yield
the individual lines of a paragraph. \TeX's line-breaking algorithm takes
a given horizontal list and converts it to a sequence of boxes that are
appended to the current vertical list. In the course of doing this, it
creates a special data structure containing three kinds of records that are
not used elsewhere in \TeX. Such nodes are created while a paragraph is
being processed, and they are destroyed afterwards; thus, the other parts
of \TeX\ do not need to know anything about how line-breaking is done.

The method used here is based on an approach devised by Michael F. Plass and
@^Plass, Michael Frederick@>
@^Knuth, Donald Ervin@>
the author in 1977, subsequently generalized and improved by the same two
people in 1980. A detailed discussion appears in {\sl SOFTWARE---Practice
\AM\ Experience \bf11} (1981), 1119--1184, where it is shown that the
line-breaking problem can be regarded as a special case of the problem of
computing the shortest path in an acyclic network. The cited paper includes
numerous examples and describes the history of line breaking as it has been
practiced by printers through the ages. The present implementation adds two
new ideas to the algorithm of 1980: memory space requirements are considerably
reduced by using smaller records for inactive nodes than for active ones,
and arithmetic overflow is avoided by using ``delta distances'' instead of
keeping track of the total distance from the beginning of the paragraph to the
current point.

@ The |line_break| procedure should be invoked only in horizontal mode; it
leaves that mode and places its output into the current vlist of the
enclosing vertical mode (or internal vertical mode).
There is one explicit parameter:  |d| is true for partial paragraphs
preceding display math mode; in this case the amount of additional
penalty inserted before the final line is |display_widow_penalty|
instead of |widow_penalty|.

There are also a number of implicit parameters: The hlist to be broken
starts at |vlink(head)|, and it is nonempty. The value of |prev_graf| in the
enclosing semantic level tells where the paragraph should begin in the
sequence of line numbers, in case hanging indentation or \.{\\parshape}
are in use; |prev_graf| is zero unless this paragraph is being continued
after a displayed formula.  Other implicit parameters, such as the
|par_shape_ptr| and various penalties to use for hyphenation, etc., appear
in |eqtb|.

After |line_break| has acted, it will have updated the current vlist and the
value of |prev_graf|. Furthermore, the global variable |just_box| will
point to the final box created by |line_break|, so that the width of this
line can be ascertained when it is necessary to decide whether to use
|above_display_skip| or |above_display_short_skip| before a displayed formula.

@<Glob...@>=
@!just_box:pointer; {the |hlist_node| for the last line of the new paragraph}
@!paragraph_dir:integer; {main direction of paragraph}
@!line_break_dir:integer; {current direction within paragraph}
@!line_break_context:integer; {the surrounding state for |line_break| calls}
@!break_c_htdp:quarterword; {height-depth entry in |char_info|}
@!temp_no_whatsits:integer; {used when closing group}
@!temp_no_dirs:integer; {used when closing group}
@!temporary_dir:integer;
@!dir_ptr,@!dir_tmp,@!dir_rover:pointer;

@ @<Set init...@>=
temp_no_whatsits:=0; temp_no_dirs:=0; temporary_dir:=0;
dir_ptr:=null; dir_tmp:=null; dir_rover:=null;
line_break_context := bottom_level;

@ In it's complete form, |line_break| is a rather lengthy
procedure---sort of a small world unto itself---we must build it up
little by little. Below you see only te general outline.

The main task performed here is to move the list from |head| to
|temp_head| and go into the enclosing semantic level. We also append
the \.{\\parfillskip} glue to the end of the paragraph, removing a
space (or other glue node) if it was there, since spaces usually
precede blank lines and instances of `\.{\$\$}'. The |par_fill_skip|
is preceded by an infinite penalty, so it will never be considered as
a potential breakpoint.

That code assumes that a |glue_node| and a |penalty_node| occupy the
same number of |mem|~words.
@^data structure assumptions@>

Most other processing is delegated to external functions.

@p procedure line_break(@!d:boolean);
var final_par_glue:pointer;
start_of_par:pointer;
begin pack_begin_line:=mode_line; {this is for over/underfull box messages}
vlink(temp_head):=vlink(head);
new_hyphenation(temp_head, tail);
if (not is_char_node(vlink(head))) and ((type(vlink(head))=whatsit_node)
   and (subtype(vlink(head))=local_par_node)) then 
  paragraph_dir:=local_par_dir(vlink(head)) 
else
  paragraph_dir:=0;
line_break_dir:=paragraph_dir;
tail:=new_ligkern(temp_head,tail);
if is_char_node(tail) then new_tail_append(new_penalty(inf_penalty))
else if type(tail)<>glue_node then new_tail_append(new_penalty(inf_penalty))
else begin 
  type(tail):=penalty_node; 
  delete_glue_ref(glue_ptr(tail));
  if leader_ptr(tail)<>null then
    flush_node_list(leader_ptr(tail));
  penalty(tail):=inf_penalty;
  end;
final_par_glue:=new_param_glue(par_fill_skip_code);
couple_nodes(tail,final_par_glue);
if not output_active then 
  lua_node_filter(pre_linebreak_filter_callback,
	line_break_context,temp_head,addressof(tail));
last_line_fill:=vlink(tail);
pop_nest;
start_of_par:=tail;
ext_do_line_break(d,pretolerance,tracing_paragraphs,tolerance,emergency_stretch,
		   looseness,hyphen_penalty,ex_hyphen_penalty,
		   pdf_adjust_spacing, par_shape_ptr, adj_demerits,
		   pdf_protrude_chars, line_penalty, last_line_fit, 
		   double_hyphen_demerits, final_hyphen_demerits,
		   hang_indent, hsize, hang_after, left_skip, right_skip,
		   pdf_each_line_height,pdf_each_line_depth,
		   pdf_first_line_height, pdf_last_line_depth,
		   inter_line_penalties_ptr, inter_line_penalty,
		   club_penalty, club_penalties_ptr,
		   display_widow_penalties_ptr,widow_penalties_ptr,
		   display_widow_penalty, widow_penalty,
		   broken_penalty, final_par_glue);
if not output_active then 
  lua_node_filter(post_linebreak_filter_callback,
	line_break_context,start_of_par,addressof(tail));
pack_begin_line:=0;
end;
@#
@t\4@>@<Declare \eTeX\ procedures for use by |main_control|@>

@ It is possible that the user wants to interfere at some point.  

The choice between |check_head_filter| and |check_contrib_filter| is not
quite clear to me yet, but it seems that the latter is the better choice.

@d check_head_filter(#)==if (not output_active) and (vlink(head)<>null) then
lua_node_filter_s(buildpage_filter_callback,#,head,addressof(tail))

@d check_contrib_filter(#)==if (not output_active) and (vlink(contrib_head)<>null) then
lua_node_filter_s(buildpage_filter_callback,#,contrib_head,addressof(garbage))

@d check_filter==check_head_filter

@* \[39] Breaking paragraphs into lines, continued.

Hyphenation and line breaking are now all handled in C. Only the
section heads are kept here.

@* \[40] Pre-hyphenation.

@* \[41] Post-hyphenation.

@* \[42] Hyphenation.

@ When \TeX\ has scanned `\.{\\hyphenation}', it calls on a procedure named
|new_hyph_exceptions| to do the right thing.

@p procedure new_hyph_exceptions; {enters new exceptions}
var p:halfword; {just to catch the return value of |scan_toks|}
begin p:=scan_toks(false,true);
load_tex_hyphenation(language,def_ref);
flush_list(def_ref); 
end;

@ Similarly, when \TeX\ has scanned `\.{\\patterns}', it calls on a
procedure named |new_patterns|.

@p procedure new_patterns; {initializes the hyphenation pattern data}
var p:halfword; {just to catch the return value of |scan_toks|}
begin p:=scan_toks(false,true);
load_tex_patterns(language,def_ref);
flush_list(def_ref); 
end;

@ `\.{\\prehyphenchar}', sets the |pre_break| character, and
`\.{\\posthyphenchar}' the |post_break| character. Their respective
defaults are ascii hyphen ("-") and zero (nul).

@p procedure new_pre_hyphen_char;
begin scan_optional_equals; scan_int;
   set_pre_hyphen_char(language,cur_val);
end;
@#
procedure new_post_hyphen_char;
begin scan_optional_equals; scan_int;
   set_post_hyphen_char(language,cur_val);
end;

@* \[43] Initializing the hyphenation tables.

None of the trie-related stuff is applicable any more in luatex.

@* \[44] Breaking vertical lists into pages.
The |vsplit| procedure, which implements \TeX's \.{\\vsplit} operation,
is considerably simpler than |line_break| because it doesn't have to
worry about hyphenation, and because its mission is to discover a single
break instead of an optimum sequence of breakpoints.  But before we get
into the details of |vsplit|, we need to consider a few more basic things.

@ A subroutine called |prune_page_top| takes a pointer to a vlist and
returns a pointer to a modified vlist in which all glue, kern, and penalty nodes
have been deleted before the first box or rule node. However, the first
box or rule is actually preceded by a newly created glue node designed so that
the topmost baseline will be at distance |split_top_skip| from the top,
whenever this is possible without backspacing.

When the second argument |s| is |false| the deleted nodes are destroyed,
otherwise they are collected in a list starting at |split_disc|.

@d discard_or_move = 60
@p function prune_page_top(@!p:pointer;@!s:boolean):pointer;
var prev_p:pointer; {lags one step behind |p|}
@!q,@!r:pointer; {temporary variables for list manipulation}
begin prev_p:=temp_head; vlink(temp_head):=p; r:=null;
while p<>null do
  case type(p) of
  hlist_node,vlist_node,rule_node:@<Insert glue for |split_top_skip|
    and set~|p:=null|@>;
  whatsit_node,mark_node,ins_node: begin
    prev_p:=p; p:=vlink(prev_p);
    end;
  glue_node,kern_node,penalty_node: begin
    q:=p; p:=vlink(q); vlink(q):=null;
    vlink(prev_p):=p;
    if s then
      begin if split_disc=null then split_disc:=q else vlink(r):=q;
      r:=q;
      end
    else flush_node_list(q);
    end;
  othercases confusion("pruning")
@:this can't happen pruning}{\quad pruning@>
  endcases;
prune_page_top:=vlink(temp_head);
end;

@ @<Insert glue for |split_top_skip|...@>=
begin q:=new_skip_param(split_top_skip_code); vlink(prev_p):=q; vlink(q):=p;
  {now |temp_ptr=glue_ptr(q)|}
if width(temp_ptr)>height(p) then width(temp_ptr):=width(temp_ptr)-height(p)
else width(temp_ptr):=0;
p:=null;
end

@ The next subroutine finds the best place to break a given vertical list
so as to obtain a box of height~|h|, with maximum depth~|d|.
A pointer to the beginning of the vertical list is given,
and a pointer to the optimum breakpoint is returned. The list is effectively
followed by a forced break, i.e., a penalty node with the |eject_penalty|;
if the best break occurs at this artificial node, the value |null| is returned.

@<Glob...@>=
@!active_height:array[1..9] of scaled;
  {distance from first active node to~|cur_p|}

@ An array of six |scaled| distances is used to keep track of the height
from the beginning of the list to the current place, just as in |line_break|.
In fact, we use one of the same arrays, only changing its name to reflect
its new significance.

@d do_all_six(#)==#(1);#(2);#(3);#(4);#(5);#(6);#(7)

@d cur_height==active_height[1] {the natural height}
@d set_height_zero(#)==active_height[#]:=0 {initialize the height to zero}
@#
@d update_heights=90 {go here to record glue in the |active_height| table}
@d awful_bad=@'7777777777 { more than a billion demerits }

@p function vert_break(@!p:pointer; @!h,@!d:scaled):pointer;
  {finds optimum page break}
label done,not_found,update_heights;
var prev_p:pointer; {if |p| is a glue node, |type(prev_p)| determines
  whether |p| is a legal breakpoint}
@!q,@!r:pointer; {glue specifications}
@!pi:integer; {penalty value}
@!b:integer; {badness at a trial breakpoint}
@!least_cost:integer; {the smallest badness plus penalties found so far}
@!best_place:pointer; {the most recent break that leads to |least_cost|}
@!prev_dp:scaled; {depth of previous box in the list}
@!t:small_number; {|type| of the node following a kern}
begin prev_p:=p; {an initial glue node is not a legal breakpoint}
least_cost:=awful_bad; do_all_six(set_height_zero); prev_dp:=0;
best_place:=null; pi:=0;
loop@+  begin @<If node |p| is a legal breakpoint, check if this break is
    the best known, and |goto done| if |p| is null or
    if the page-so-far is already too full to accept more stuff@>;
  prev_p:=p; p:=vlink(prev_p);
  end;
done: vert_break:=best_place;
end;

@ A global variable |best_height_plus_depth| will be set to the natural size
of the box that corresponds to the optimum breakpoint found by |vert_break|.
(This value is used by the insertion-splitting algorithm of the page builder.)

@<Glob...@>=
@!best_height_plus_depth:scaled; {height of the best box, without stretching or
  shrinking}

@ A subtle point to be noted here is that the maximum depth~|d| might be
negative, so |cur_height| and |prev_dp| might need to be corrected even
after a glue or kern node.

@<If node |p| is a legal breakpoint, check...@>=
if p=null then pi:=eject_penalty
else  @<Use node |p| to update the current height and depth measurements;
    if this node is not a legal breakpoint, |goto not_found|
    or |update_heights|,
    otherwise set |pi| to the associated penalty at the break@>;
@<Check if node |p| is a new champion breakpoint; then \(go)|goto done|
  if |p| is a forced break or if the page-so-far is already too full@>;
if (type(p)<glue_node)or(type(p)>kern_node) then goto not_found;
update_heights: @<Update the current height and depth measurements with
  respect to a glue or kern node~|p|@>;
not_found: if prev_dp>d then
    begin cur_height:=cur_height+prev_dp-d;
    prev_dp:=d;
    end;

@ @<Use node |p| to update the current height and depth measurements...@>=
case type(p) of
hlist_node,vlist_node,rule_node: begin@t@>@;@/
  cur_height:=cur_height+prev_dp+height(p); prev_dp:=depth(p);
  goto not_found;
  end;
whatsit_node:@<Process whatsit |p| in |vert_break| loop, |goto not_found|@>;
glue_node: if precedes_break(prev_p) then pi:=0
  else goto update_heights;
kern_node: begin if vlink(p)=null then t:=penalty_node
  else t:=type(vlink(p));
  if t=glue_node then pi:=0@+else goto update_heights;
  end;
penalty_node: pi:=penalty(p);
mark_node,ins_node: goto not_found;
othercases confusion("vertbreak")
@:this can't happen vertbreak}{\quad vertbreak@>
endcases

@ @d deplorable==100000 {more than |inf_bad|, but less than |awful_bad|}

@<Check if node |p| is a new champion breakpoint; then \(go)...@>=
if pi<inf_penalty then
  begin @<Compute the badness, |b|, using |awful_bad|
    if the box is too full@>;
  if b<awful_bad then
    if pi<=eject_penalty then b:=pi
    else if b<inf_bad then b:=b+pi
      else b:=deplorable;
  if b<=least_cost then
    begin best_place:=p; least_cost:=b;
    best_height_plus_depth:=cur_height+prev_dp;
    end;
  if (b=awful_bad)or(pi<=eject_penalty) then goto done;
  end

@ @<Compute the badness, |b|, using |awful_bad| if the box is too full@>=
if cur_height<h then
  if (active_height[3]<>0) or (active_height[4]<>0) or
    (active_height[5]<>0) or (active_height[6]<>0) then b:=0
  else b:=badness(h-cur_height,active_height[2])
else if cur_height-h>active_height[7] then b:=awful_bad
else b:=badness(cur_height-h,active_height[7])

@ Vertical lists that are subject to the |vert_break| procedure should not
contain infinite shrinkability, since that would permit any amount of
information to ``fit'' on one page.

@<Update the current height and depth measurements with...@>=
if type(p)=kern_node then q:=p
else  begin q:=glue_ptr(p);
  active_height[2+stretch_order(q)]:=@|
    active_height[2+stretch_order(q)]+stretch(q);@/
  active_height[7]:=active_height[7]+shrink(q);
  if (shrink_order(q)<>normal)and(shrink(q)<>0) then
    begin@t@>@;@/
    print_err("Infinite glue shrinkage found in box being split");@/
@.Infinite glue shrinkage...@>
    help4("The box you are \vsplitting contains some infinitely")@/
      ("shrinkable glue, e.g., `\vss' or `\vskip 0pt minus 1fil'.")@/
      ("Such glue doesn't belong there; but you can safely proceed,")@/
      ("since the offensive shrinkability has been made finite.");
    error; r:=new_spec(q); shrink_order(r):=normal; delete_glue_ref(q);
    glue_ptr(p):=r; q:=r;
    end;
  end;
cur_height:=cur_height+prev_dp+width(q); prev_dp:=0

@ Now we are ready to consider |vsplit| itself. Most of
its work is accomplished by the two subroutines that we have just considered.

Given the number of a vlist box |n|, and given a desired page height |h|,
the |vsplit| function finds the best initial segment of the vlist and
returns a box for a page of height~|h|. The remainder of the vlist, if
any, replaces the original box, after removing glue and penalties and
adjusting for |split_top_skip|. Mark nodes in the split-off box are used to
set the values of |split_first_mark| and |split_bot_mark|; we use the
fact that |split_first_mark(x)=null| if and only if |split_bot_mark(x)=null|.

The original box becomes ``void'' if and only if it has been entirely
extracted.  The extracted box is ``void'' if and only if the original
box was void (or if it was, erroneously, an hlist box).

@p function vsplit(@!n:halfword; @!h:scaled):pointer;
  {extracts a page of height |h| from box |n|}
label exit,done;
var v:pointer; {the box to be split}
vdir:integer; {the direction of the box to be split}
p:pointer; {runs through the vlist}
q:pointer; {points to where the break occurs}
i:halfword; {for traversing marks lists}
begin v:=box(n); vdir:=box_dir(v);
flush_node_list(split_disc); split_disc:=null;
for i:=0 to biggest_used_mark do begin
  delete_split_first_mark(i);
  delete_split_bot_mark(i);
end;
@<Dispense with trivial cases of void or bad boxes@>;
q:=vert_break(list_ptr(v),h,split_max_depth);
@<Look at all the marks in nodes before the break, and set the final
  link to |null| at the break@>;
q:=prune_page_top(q,saving_vdiscards>0);
p:=list_ptr(v); list_ptr(v):=null; flush_node(v);
pack_direction:=vdir;
if q=null then box(n):=null {the |eq_level| of the box stays the same}
else box(n):=filtered_vpackage(q,0,additional,max_depth,split_keep_group);
vsplit:=filtered_vpackage(p,h,exactly,split_max_depth,split_off_group);
exit: end;

@ @<Dispense with trivial cases of void or bad boxes@>=
if v=null then
  begin vsplit:=null; return;
  end;
if type(v)<>vlist_node then
  begin print_err(""); print_esc("vsplit"); print(" needs a ");
  print_esc("vbox");
@:vsplit_}{\.{\\vsplit needs a \\vbox}@>
  help2("The box you are trying to split is an \hbox.")@/
  ("I can't split such a box, so I'll leave it alone.");
  error; vsplit:=null; return;
  end

@ It's possible that the box begins with a penalty node that is the
``best'' break, so we must be careful to handle this special case correctly.

@<Look at all the marks...@>=
p:=list_ptr(v);
if p=q then list_ptr(v):=null
else loop@+begin if type(p)=mark_node then
    if split_first_mark(mark_class(p))=null then
      begin split_first_mark(mark_class(p)):=mark_ptr(p);
      split_bot_mark(mark_class(p)):=split_first_mark(mark_class(p));
      token_ref_count(split_first_mark(mark_class(p))):=@|
        token_ref_count(split_first_mark(mark_class(p)))+2;
      end
    else  begin delete_token_ref(split_bot_mark(mark_class(p)));
      split_bot_mark(mark_class(p)):=mark_ptr(p);
      add_token_ref(split_bot_mark(mark_class(p)));
      end;
  if vlink(p)=q then
    begin vlink(p):=null; goto done;
    end;
  p:=vlink(p);
  end;
done:

@* \[45] The page builder.
When \TeX\ appends new material to its main vlist in vertical mode, it uses
a method something like |vsplit| to decide where a page ends, except that
the calculations are done ``on line'' as new items come in.
The main complication in this process is that insertions must be put
into their boxes and removed from the vlist, in a more-or-less optimum manner.

We shall use the term ``current page'' for that part of the main vlist that
is being considered as a candidate for being broken off and sent to the
user's output routine. The current page starts at |vlink(page_head)|, and
it ends at |page_tail|.  We have |page_head=page_tail| if this list is empty.
@^current page@>

Utter chaos would reign if the user kept changing page specifications
while a page is being constructed, so the page builder keeps the pertinent
specifications frozen as soon as the page receives its first box or
insertion.  The global variable |page_contents| is |empty| when the
current page contains only mark nodes and content-less whatsit nodes; it
is |inserts_only| if the page contains only insertion nodes in addition to
marks and whatsits.  Glue nodes, kern nodes, and penalty nodes are
discarded until a box or rule node appears, at which time |page_contents|
changes to |box_there|.  As soon as |page_contents| becomes non-|empty|,
the current |vsize| and |max_depth| are squirreled away into |page_goal|
and |page_max_depth|; the latter values will be used until the page has
been forwarded to the user's output routine. The \.{\\topskip} adjustment
is made when |page_contents| changes to |box_there|.

Although |page_goal| starts out equal to |vsize|, it is decreased by the
scaled natural height-plus-depth of the insertions considered so far, and by
the \.{\\skip} corrections for those insertions. Therefore it represents
the size into which the non-inserted material should fit, assuming that
all insertions in the current page have been made.

The global variables |best_page_break| and |least_page_cost| correspond
respectively to the local variables |best_place| and |least_cost| in the
|vert_break| routine that we have already studied; i.e., they record the
location and value of the best place currently known for breaking the
current page. The value of |page_goal| at the time of the best break is
stored in |best_size|.

@d inserts_only=1
  {|page_contents| when an insert node has been contributed, but no boxes}
@d box_there=2 {|page_contents| when a box or rule has been contributed}

@<Glob...@>=
@!page_tail:pointer; {the final node on the current page}
@!page_contents:empty..box_there; {what is on the current page so far?}
@!page_max_depth:scaled; {maximum box depth on page being built}
@!best_page_break:pointer; {break here to get the best page known so far}
@!least_page_cost:integer; {the score for this currently best page}
@!best_size:scaled; {its |page_goal|}

@ The page builder has another data structure to keep track of insertions.
This is a list of four-word nodes, starting and ending at |page_ins_head|.
That is, the first element of the list is node |r@t$_1$@>=vlink(page_ins_head)|;
node $r_j$ is followed by |r@t$_{j+1}$@>=vlink(r@t$_j$@>)|; and if there are
|n| items we have |r@t$_{n+1}$@>=page_ins_head|. The |subtype| field of
each node in this list refers to an insertion number; for example, `\.{\\insert
250}' would correspond to a node whose |subtype| is |qi(250)|
(the same as the |subtype| field of the relevant |ins_node|). These |subtype|
fields are in increasing order, and |subtype(page_ins_head)=
qi(255)|, so |page_ins_head| serves as a convenient sentinel
at the end of the list. A record is present for each insertion number that
appears in the current page.

The |type| field in these nodes distinguishes two possibilities that
might occur as we look ahead before deciding on the optimum page break.
If |type(r)=inserting_node|, then |height(r)| contains the total of the
height-plus-depth dimensions of the box and all its inserts seen so far.
If |type(r)=split_up_node|, then no more insertions will be made into this box,
because at least one previous insertion was too big to fit on the current
page; |broken_ptr(r)| points to the node where that insertion will be
split, if \TeX\ decides to split it, |broken_ins(r)| points to the
insertion node that was tentatively split, and |height(r)| includes also the
natural height plus depth of the part that would be split off.

In both cases, |last_ins_ptr(r)| points to the last |ins_node|
encountered for box |qo(subtype(r))| that would be at least partially
inserted on the next page; and |best_ins_ptr(r)| points to the last
such |ins_node| that should actually be inserted, to get the page with
minimum badness among all page breaks considered so far. We have
|best_ins_ptr(r)=null| if and only if no insertion for this box should
be made to produce this optimum page.

The data structure definitions here use the fact that the |@!height| field
appears in the fourth word of a box node.
@^data structure assumptions@>

@d inserting_node=37 {an insertion class that has not yet overflowed}
@d split_up_node=38 {an overflowed insertion class}
@d broken_ptr(#)==vlink(#+2)
  {an insertion for this class will break here if anywhere}
@d broken_ins(#)==vinfo(#+2) {this insertion might break at |broken_ptr|}
@d last_ins_ptr(#)==vlink(#+3) {the most recent insertion for this |subtype|}
@d best_ins_ptr(#)==vinfo(#+3) {the optimum most recent insertion}

@<Initialize the special list heads...@>=
subtype(page_ins_head):=qi(255);
type(page_ins_head):=split_up_node; vlink(page_ins_head):=page_ins_head;

@ An array |page_so_far| records the heights and depths of everything
on the current page. This array contains six |scaled| numbers, like the
similar arrays already considered in |line_break| and |vert_break|; and it
also contains |page_goal| and |page_depth|, since these values are
all accessible to the user via |set_page_dimen| commands. The
value of |page_so_far[1]| is also called |page_total|.  The stretch
and shrink components of the \.{\\skip} corrections for each insertion are
included in |page_so_far|, but the natural space components of these
corrections are not, since they have been subtracted from |page_goal|.

The variable |page_depth| records the depth of the current page; it has been
adjusted so that it is at most |page_max_depth|. The variable
|last_glue| points to the glue specification of the most recent node
contributed from the contribution list, if this was a glue node; otherwise
|last_glue=max_halfword|. (If the contribution list is nonempty,
however, the value of |last_glue| is not necessarily accurate.)
The variables |last_penalty|, |last_kern|, and |last_node_type|
are similar.  And
finally, |insert_penalties| holds the sum of the penalties associated with
all split and floating insertions.

@d page_goal==page_so_far[0] {desired height of information on page being built}
@d page_total==page_so_far[1] {height of the current page}
@d page_shrink==page_so_far[6] {shrinkability of the current page}
@d page_depth==page_so_far[7] {depth of the current page}

@<Glob...@>=
@!page_so_far:array [0..7] of scaled; {height and glue of the current page}
@!last_glue:pointer; {used to implement \.{\\lastskip}}
@!last_penalty:integer; {used to implement \.{\\lastpenalty}}
@!last_kern:scaled; {used to implement \.{\\lastkern}}
@!last_node_type:integer; {used to implement \.{\\lastnodetype}}
@!insert_penalties:integer; {sum of the penalties for held-over insertions}

@ @<Put each...@>=
primitive("pagegoal",set_page_dimen,0);
@!@:page_goal_}{\.{\\pagegoal} primitive@>
primitive("pagetotal",set_page_dimen,1);
@!@:page_total_}{\.{\\pagetotal} primitive@>
primitive("pagestretch",set_page_dimen,2);
@!@:page_stretch_}{\.{\\pagestretch} primitive@>
primitive("pagefilstretch",set_page_dimen,3);
@!@:page_fil_stretch_}{\.{\\pagefilstretch} primitive@>
primitive("pagefillstretch",set_page_dimen,4);
@!@:page_fill_stretch_}{\.{\\pagefillstretch} primitive@>
primitive("pagefilllstretch",set_page_dimen,5);
@!@:page_filll_stretch_}{\.{\\pagefilllstretch} primitive@>
primitive("pageshrink",set_page_dimen,6);
@!@:page_shrink_}{\.{\\pageshrink} primitive@>
primitive("pagedepth",set_page_dimen,7);
@!@:page_depth_}{\.{\\pagedepth} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
set_page_dimen: case chr_code of
0: print_esc("pagegoal");
1: print_esc("pagetotal");
2: print_esc("pagestretch");
3: print_esc("pagefilstretch");
4: print_esc("pagefillstretch");
5: print_esc("pagefilllstretch");
6: print_esc("pageshrink");
othercases print_esc("pagedepth")
endcases;

@ @d print_plus_end(#)==print(#);@+end
@d print_plus(#)==if page_so_far[#]<>0 then
  begin print(" plus "); print_scaled(page_so_far[#]); print_plus_end

@p procedure print_totals;
begin print_scaled(page_total);
print_plus(2)("");
print_plus(3)("fil");
print_plus(4)("fill");
print_plus(5)("filll");
if page_shrink<>0 then
  begin print(" minus "); print_scaled(page_shrink);
  end;
end;

@ @<Show the status of the current page@>=
if page_head<>page_tail then
  begin print_nl("### current page:");
  if output_active then print(" (held over for next output)");
@.held over for next output@>
  show_box(vlink(page_head));
  if page_contents>empty then
    begin print_nl("total height "); print_totals;
@:total_height}{\.{total height}@>
    print_nl(" goal height "); print_scaled(page_goal);
@.goal height@>
    r:=vlink(page_ins_head);
    while r<>page_ins_head do
      begin print_ln; print_esc("insert"); t:=qo(subtype(r));
      print_int(t); print(" adds ");
      t:=x_over_n(height(r),1000)*count(t); print_scaled(t);
      if type(r)=split_up_node then
        begin q:=page_head; t:=0;
        repeat q:=vlink(q);
        if (type(q)=ins_node)and(subtype(q)=subtype(r)) then incr(t);
        until q=broken_ins(r);
        print(", #"); print_int(t); print(" might split");
        end;
      r:=vlink(r);
      end;
    end;
  end

@ Here is a procedure that is called when the |page_contents| is changing
from |empty| to |inserts_only| or |box_there|.

@d set_page_so_far_zero(#)==page_so_far[#]:=0

@p procedure freeze_page_specs(@!s:small_number);
begin page_contents:=s;
page_goal:=vsize; page_max_depth:=max_depth;
page_depth:=0; do_all_six(set_page_so_far_zero);
least_page_cost:=awful_bad;
@!stat if tracing_pages>0 then
  begin begin_diagnostic;
  print_nl("%% goal height="); print_scaled(page_goal);
@.goal height@>
  print(", max depth="); print_scaled(page_max_depth);
  end_diagnostic(false);
  end;@;@+tats@;@/
end;

@ Pages are built by appending nodes to the current list in \TeX's
vertical mode, which is at the outermost level of the semantic nest. This
vlist is split into two parts; the ``current page'' that we have been
talking so much about already, and the ``contribution list'' that receives
new nodes as they are created.  The current page contains everything that
the page builder has accounted for in its data structures, as described
above, while the contribution list contains other things that have been
generated by other parts of \TeX\ but have not yet been
seen by the page builder.
The contribution list starts at |vlink(contrib_head)|, and it ends at the
current node in \TeX's vertical mode.

When \TeX\ has appended new material in vertical mode, it calls the procedure
|build_page|, which tries to catch up by moving nodes from the contribution
list to the current page. This procedure will succeed in its goal of
emptying the contribution list, unless a page break is discovered, i.e.,
unless the current page has grown to the point where the optimum next
page break has been determined. In the latter case, the nodes after the
optimum break will go back onto the contribution list, and control will
effectively pass to the user's output routine.

We make |type(page_head)=glue_node|, so that an initial glue node on
the current page will not be considered a valid breakpoint.

@<Initialize the special list...@>=
type(page_head):=glue_node; subtype(page_head):=normal;

@ The global variable |output_active| is true during the time the
user's output routine is driving \TeX.

@<Glob...@>=
@!output_active:boolean; {are we in the midst of an output routine?}

@ @<Set init...@>=
output_active:=false; insert_penalties:=0;

@ The page builder is ready to start a fresh page if we initialize
the following state variables. (However, the page insertion list is initialized
elsewhere.)

@<Start a new current page@>=
page_contents:=empty; page_tail:=page_head; vlink(page_head):=null;@/
last_glue:=max_halfword; last_penalty:=0; last_kern:=0;
last_node_type:=-1;
page_depth:=0; page_max_depth:=0

@ At certain times box 255 is supposed to be void (i.e., |null|),
or an insertion box is supposed to be ready to accept a vertical list.
If not, an error message is printed, and the following subroutine
flushes the unwanted contents, reporting them to the user.

@p procedure box_error(@!n:eight_bits);
begin error; begin_diagnostic;
print_nl("The following box has been deleted:");
@.The following...deleted@>
show_box(box(n)); end_diagnostic(true);
flush_node_list(box(n)); box(n):=null;
end;

@ The following procedure guarantees that a given box register
does not contain an \.{\\hbox}.

@p procedure ensure_vbox(@!n:eight_bits);
var p:pointer; {the box register contents}
begin p:=box(n);
if p<>null then if type(p)=hlist_node then
  begin print_err("Insertions can only be added to a vbox");
@.Insertions can only...@>
  help3("Tut tut: You're trying to \insert into a")@/
    ("\box register that now contains an \hbox.")@/
    ("Proceed, and I'll discard its present contents.");
  box_error(n);
  end;
end;

@ \TeX\ is not always in vertical mode at the time |build_page|
is called; the current mode reflects what \TeX\ should return to, after
the contribution list has been emptied. A call on |build_page| should
be immediately followed by `|goto big_switch|', which is \TeX's central
control point.

@d contribute=80 {go here to link a node into the current page}

@p @t\4@>@<Declare the procedure called |fire_up|@>@;@/
procedure build_page; {append contributions to the current page}
label exit,done,done1,continue,contribute,update_heights;
var p:pointer; {the node being appended}
@!q,@!r:pointer; {nodes being examined}
@!b,@!c:integer; {badness and cost of current page}
@!pi:integer; {penalty to be added to the badness}
@!n:min_quarterword..255; {insertion box number}
@!delta,@!h,@!w:scaled; {sizes used for insertion calculations}
begin pi:=0;
if (vlink(contrib_head)=null)or output_active then return;
repeat continue: p:=vlink(contrib_head);@/
@<Update the values of |last_glue|, |last_penalty|, and |last_kern|@>;
@<Move node |p| to the current page; if it is time for a page break,
  put the nodes following the break back onto the contribution list,
  and |return| to the user's output routine if there is one@>;
until vlink(contrib_head)=null;
@<Make the contribution list empty by setting its tail to |contrib_head|@>;
exit:end;

@ @d contrib_tail==nest[0].tail_field {tail of the contribution list}

@<Make the contribution list empty...@>=
if nest_ptr=0 then tail:=contrib_head {vertical mode}
else contrib_tail:=contrib_head {other modes}

@ @<Update the values of |last_glue|...@>=
if last_glue<>max_halfword then delete_glue_ref(last_glue);
last_penalty:=0; last_kern:=0;
last_node_type:=type(p)+1;
if type(p)=glue_node then
  begin last_glue:=glue_ptr(p); add_glue_ref(last_glue);
  end
else  begin last_glue:=max_halfword;
  if type(p)=penalty_node then last_penalty:=penalty(p)
  else if type(p)=kern_node then last_kern:=width(p);
  end

@ The code here is an example of a many-way switch into routines that
merge together in different places. Some people call this unstructured
programming, but the author doesn't see much wrong with it, as long as
@^Knuth, Donald Ervin@>
the various labels have a well-understood meaning.

@<Move node |p| to the current page; ...@>=
@<If the current page is empty and node |p| is to be deleted, |goto done1|;
  otherwise use node |p| to update the state of the current page;
  if this node is an insertion, |goto contribute|; otherwise if this node
  is not a legal breakpoint, |goto contribute| or |update_heights|;
  otherwise set |pi| to the penalty associated with this breakpoint@>;
@<Check if node |p| is a new champion breakpoint; then \(if)if it is time for
  a page break, prepare for output, and either fire up the user's
  output routine and |return| or ship out the page and |goto done|@>;
if (type(p)<glue_node)or(type(p)>kern_node) then goto contribute;
update_heights:@<Update the current page measurements with respect to the
  glue or kern specified by node~|p|@>;
contribute: @<Make sure that |page_max_depth| is not exceeded@>;
@<Link node |p| into the current page and |goto done|@>;
done1:@<Recycle node |p|@>;
done:

@ @<Link node |p| into the current page and |goto done|@>=
vlink(page_tail):=p; page_tail:=p;
vlink(contrib_head):=vlink(p); vlink(p):=null; goto done

@ @<Recycle node |p|@>=
vlink(contrib_head):=vlink(p); vlink(p):=null;
if saving_vdiscards>0 then
  begin if page_disc=null then page_disc:=p@+else vlink(tail_page_disc):=p;
  tail_page_disc:=p;
  end
else flush_node_list(p)

@ The title of this section is already so long, it seems best to avoid
making it more accurate but still longer, by mentioning the fact that a
kern node at the end of the contribution list will not be contributed until
we know its successor.

@<If the current page is empty...@>=
case type(p) of
hlist_node,vlist_node,rule_node: if page_contents<box_there then
    @<Initialize the current page, insert the \.{\\topskip} glue
      ahead of |p|, and |goto continue|@>
  else @<Prepare to move a box or rule node to the current page,
    then |goto contribute|@>;
whatsit_node: @<Prepare to move whatsit |p| to the current page,
                     then |goto contribute|@>;
glue_node: if page_contents<box_there then goto done1
  else if precedes_break(page_tail) then pi:=0
  else goto update_heights;
kern_node: if page_contents<box_there then goto done1
  else if vlink(p)=null then return
  else if type(vlink(p))=glue_node then pi:=0
  else goto update_heights;
penalty_node: if page_contents<box_there then goto done1@+else pi:=penalty(p);
mark_node: goto contribute;
ins_node: @<Append an insertion to the current page and |goto contribute|@>;
othercases confusion("page")
@:this can't happen page}{\quad page@>
endcases

@ @<Initialize the current page, insert the \.{\\topskip} glue...@>=
begin if page_contents=empty then freeze_page_specs(box_there)
else page_contents:=box_there;
q:=new_skip_param(top_skip_code); {now |temp_ptr=glue_ptr(q)|}
if (type(p)=hlist_node) and (is_mirrored(body_direction)) then begin
  if width(temp_ptr)>depth(p) then width(temp_ptr):=width(temp_ptr)-depth(p)
  else width(temp_ptr):=0;
  end
else begin
  if width(temp_ptr)>height(p) then width(temp_ptr):=width(temp_ptr)-height(p)
  else width(temp_ptr):=0;
  end;
vlink(q):=p; vlink(contrib_head):=q; goto continue;
end

@ @<Prepare to move a box or rule node to the current page...@>=
begin
if (type(p)=hlist_node) and (is_mirrored(body_direction)) then begin
  page_total:=page_total+page_depth+depth(p);
  page_depth:=height(p);
  end
else begin
  page_total:=page_total+page_depth+height(p);
  page_depth:=depth(p);
  end;
goto contribute;
end

@ @<Make sure that |page_max_depth| is not exceeded@>=
if page_depth>page_max_depth then
  begin page_total:=@|
    page_total+page_depth-page_max_depth;@/
  page_depth:=page_max_depth;
  end;

@ @<Update the current page measurements with respect to the glue...@>=
if type(p)=kern_node then q:=p
else begin q:=glue_ptr(p);
if stretch_order(q)>1 then
  page_so_far[1+stretch_order(q)]:=@|
    page_so_far[1+stretch_order(q)]+stretch(q)@/
else
  page_so_far[2+stretch_order(q)]:=@|
    page_so_far[2+stretch_order(q)]+stretch(q);@/
  page_shrink:=page_shrink+shrink(q);
  if (shrink_order(q)<>normal)and(shrink(q)<>0) then
    begin@t@>@;@/
    print_err("Infinite glue shrinkage found on current page");@/
@.Infinite glue shrinkage...@>
    help4("The page about to be output contains some infinitely")@/
      ("shrinkable glue, e.g., `\vss' or `\vskip 0pt minus 1fil'.")@/
      ("Such glue doesn't belong there; but you can safely proceed,")@/
      ("since the offensive shrinkability has been made finite.");
    error;
    r:=new_spec(q); shrink_order(r):=normal; delete_glue_ref(q);
    glue_ptr(p):=r; q:=r;
    end;
  end;
page_total:=page_total+page_depth+width(q); page_depth:=0

@ @<Check if node |p| is a new champion breakpoint; then \(if)...@>=
if pi<inf_penalty then
  begin @<Compute the badness, |b|, of the current page,
    using |awful_bad| if the box is too full@>;
  if b<awful_bad then
    if pi<=eject_penalty then c:=pi
    else  if b<inf_bad then c:=b+pi+insert_penalties
      else c:=deplorable
  else c:=b;
  if insert_penalties>=10000 then c:=awful_bad;
  @!stat if tracing_pages>0 then @<Display the page break cost@>;@+tats@;@/
  if c<=least_page_cost then
    begin best_page_break:=p; best_size:=page_goal;
    least_page_cost:=c;
    r:=vlink(page_ins_head);
    while r<>page_ins_head do
      begin best_ins_ptr(r):=last_ins_ptr(r);
      r:=vlink(r);
      end;
    end;
  if (c=awful_bad)or(pi<=eject_penalty) then
    begin fire_up(p); {output the current page at the best place}
    if output_active then return; {user's output routine will act}
    goto done; {the page has been shipped out by default output routine}
    end;
  end

@ @<Display the page break cost@>=
begin begin_diagnostic; print_nl("%");
print(" t="); print_totals;@/
print(" g="); print_scaled(page_goal);@/
print(" b=");
if b=awful_bad then print_char("*")@+else print_int(b);
@.*\relax@>
print(" p="); print_int(pi);
print(" c=");
if c=awful_bad then print_char("*")@+else print_int(c);
if c<=least_page_cost then print_char("#");
end_diagnostic(false);
end

@ @<Compute the badness, |b|, of the current page...@>=
if page_total<page_goal then
  if (page_so_far[3]<>0) or (page_so_far[4]<>0) or@|
    (page_so_far[5]<>0) then b:=0
  else b:=badness(page_goal-page_total,page_so_far[2])
else if page_total-page_goal>page_shrink then b:=awful_bad
else b:=badness(page_total-page_goal,page_shrink)

@ @<Append an insertion to the current page and |goto contribute|@>=
begin if page_contents=empty then freeze_page_specs(inserts_only);
n:=subtype(p); r:=page_ins_head;
while n>=subtype(vlink(r)) do r:=vlink(r);
n:=qo(n);
if subtype(r)<>qi(n) then
  @<Create a page insertion node with |subtype(r)=qi(n)|, and
    include the glue correction for box |n| in the
    current page state@>;
if type(r)=split_up_node then insert_penalties:=insert_penalties+float_cost(p)
else  begin last_ins_ptr(r):=p;
  delta:=page_goal-page_total-page_depth+page_shrink;
    {this much room is left if we shrink the maximum}
  if count(n)=1000 then h:=height(p)
  else h:=x_over_n(height(p),1000)*count(n); {this much room is needed}
  if ((h<=0)or(h<=delta))and(height(p)+height(r)<=dimen(n)) then
    begin page_goal:=page_goal-h; height(r):=height(r)+height(p);
    end
  else @<Find the best way to split the insertion, and change
    |type(r)| to |split_up_node|@>;
  end;
goto contribute;
end

@ We take note of the value of \.{\\skip} |n| and the height plus depth
of \.{\\box}~|n| only when the first \.{\\insert}~|n| node is
encountered for a new page. A user who changes the contents of \.{\\box}~|n|
after that first \.{\\insert}~|n| had better be either extremely careful
or extremely lucky, or both.

@<Create a page insertion node...@>=
begin q:=new_node(inserting_node,n); vlink(q):=vlink(r); vlink(r):=q; r:=q;
ensure_vbox(n);
if box(n)=null then height(r):=0
else height(r):=height(box(n))+depth(box(n));
best_ins_ptr(r):=null;@/
q:=skip(n);
if count(n)=1000 then h:=height(r)
else h:=x_over_n(height(r),1000)*count(n);
page_goal:=page_goal-h-width(q);@/
if stretch_order(q)>1 then
  page_so_far[1+stretch_order(q)]:=@|page_so_far[1+stretch_order(q)]+stretch(q)@/
else
  page_so_far[2+stretch_order(q)]:=@|page_so_far[2+stretch_order(q)]+stretch(q);@/
page_shrink:=page_shrink+shrink(q);
if (shrink_order(q)<>normal)and(shrink(q)<>0) then
  begin print_err("Infinite glue shrinkage inserted from "); print_esc("skip");
@.Infinite glue shrinkage...@>
  print_int(n);
  help3("The correction glue for page breaking with insertions")@/
    ("must have finite shrinkability. But you may proceed,")@/
    ("since the offensive shrinkability has been made finite.");
  error;
  end;
end

@ Here is the code that will split a long footnote between pages, in an
emergency. The current situation deserves to be recapitulated: Node |p|
is an insertion into box |n|; the insertion will not fit, in its entirety,
either because it would make the total contents of box |n| greater than
\.{\\dimen} |n|, or because it would make the incremental amount of growth
|h| greater than the available space |delta|, or both. (This amount |h| has
been weighted by the insertion scaling factor, i.e., by \.{\\count} |n|
over 1000.) Now we will choose the best way to break the vlist of the
insertion, using the same criteria as in the \.{\\vsplit} operation.

@<Find the best way to split the insertion...@>=
begin if count(n)<=0 then w:=max_dimen
else  begin w:=page_goal-page_total-page_depth;
  if count(n)<>1000 then w:=x_over_n(w,count(n))*1000;
  end;
if w>dimen(n)-height(r) then w:=dimen(n)-height(r);
q:=vert_break(ins_ptr(p),w,depth(p));
height(r):=height(r)+best_height_plus_depth;
@!stat if tracing_pages>0 then @<Display the insertion split cost@>;@+tats@;@/
if count(n)<>1000 then
  best_height_plus_depth:=x_over_n(best_height_plus_depth,1000)*count(n);
page_goal:=page_goal-best_height_plus_depth;
type(r):=split_up_node; broken_ptr(r):=q; broken_ins(r):=p;
if q=null then insert_penalties:=insert_penalties+eject_penalty
else if type(q)=penalty_node then insert_penalties:=insert_penalties+penalty(q);
end

@ @<Display the insertion split cost@>=
begin begin_diagnostic; print_nl("% split"); print_int(n);
@.split@>
print(" to "); print_scaled(w);
print_char(","); print_scaled(best_height_plus_depth);@/
print(" p=");
if q=null then print_int(eject_penalty)
else if type(q)=penalty_node then print_int(penalty(q))
else print_char("0");
end_diagnostic(false);
end

@ When the page builder has looked at as much material as could appear before
the next page break, it makes its decision. The break that gave minimum
badness will be used to put a completed ``page'' into box 255, with insertions
appended to their other boxes.

We also set the values of |top_mark|, |first_mark|, and |bot_mark|. The
program uses the fact that |bot_mark(x)<>null| implies |first_mark(x)<>null|;
it also knows that |bot_mark(x)=null| implies |top_mark(x)=first_mark(x)=null|.

The |fire_up| subroutine prepares to output the current page at the best
place; then it fires up the user's output routine, if there is one,
or it simply ships out the page. There is one parameter, |c|, which represents
the node that was being contributed to the page when the decision to
force an output was made.

@<Declare the procedure called |fire_up|@>=
procedure fire_up(@!c:pointer);
label exit;
var p,@!q,@!r,@!s:pointer; {nodes being examined and/or changed}
@!prev_p:pointer; {predecessor of |p|}
@!n:min_quarterword..255; {insertion box number}
@!wait:boolean; {should the present insertion be held over?}
@!save_vbadness:integer; {saved value of |vbadness|}
@!save_vfuzz: scaled; {saved value of |vfuzz|}
@!save_split_top_skip: pointer; {saved value of |split_top_skip|}
@!i: halfword; { for looping through the marks}
begin @<Set the value of |output_penalty|@>;
for i:=0 to biggest_used_mark do begin
  if bot_mark(i)<>null then
    begin if top_mark(i)<>null then delete_token_ref(top_mark(i));
    top_mark(i):=bot_mark(i); add_token_ref(top_mark(i));
    delete_first_mark(i);
    end;
  end;
@<Put the \(o)optimal current page into box 255, update |first_mark| and
  |bot_mark|, append insertions to their boxes, and put the
  remaining nodes back on the contribution list@>;
for i:=0 to biggest_used_mark do begin
  if (top_mark(i)<>null)and(first_mark(i)=null) then
    begin first_mark(i):=top_mark(i); add_token_ref(top_mark(i));
    end;
  end;
if output_routine<>null then
  if dead_cycles>=max_dead_cycles then
    @<Explain that too many dead cycles have occurred in a row@>
  else @<Fire up the user's output routine and |return|@>;
@<Perform the default output routine@>;
exit:end;

@ @<Set the value of |output_penalty|@>=
if type(best_page_break)=penalty_node then
  begin geq_word_define(int_base+output_penalty_code,penalty(best_page_break));
  penalty(best_page_break):=inf_penalty;
  end
else geq_word_define(int_base+output_penalty_code,inf_penalty)

@ As the page is finally being prepared for output,
pointer |p| runs through the vlist, with |prev_p| trailing behind;
pointer |q| is the tail of a list of insertions that
are being held over for a subsequent page.

@<Put the \(o)optimal current page into box 255...@>=
if c=best_page_break then best_page_break:=null; {|c| not yet linked in}
@<Ensure that box 255 is empty before output@>;
insert_penalties:=0; {this will count the number of insertions held over}
save_split_top_skip:=split_top_skip;
if holding_inserts<=0 then
  @<Prepare all the boxes involved in insertions to act as queues@>;
q:=hold_head; vlink(q):=null; prev_p:=page_head; p:=vlink(prev_p);
while p<>best_page_break do
  begin if type(p)=ins_node then
    begin if holding_inserts<=0 then
       @<Either insert the material specified by node |p| into the
         appropriate box, or hold it for the next page;
         also delete node |p| from the current page@>;
    end
  else if type(p)=mark_node then @<Update the values of
    |first_mark| and |bot_mark|@>;
  prev_p:=p; p:=vlink(prev_p);
  end;
split_top_skip:=save_split_top_skip;
@<Break the current page at node |p|, put it in box~255,
  and put the remaining nodes on the contribution list@>;
@<Delete \(t)the page-insertion nodes@>

@ @<Ensure that box 255 is empty before output@>=
if box(255)<>null then
  begin print_err(""); print_esc("box"); print("255 is not void");
@:box255}{\.{\\box255 is not void}@>
  help2("You shouldn't use \box255 except in \output routines.")@/
    ("Proceed, and I'll discard its present contents.");
  box_error(255);
  end

@ @<Update the values of |first_mark| and |bot_mark|@>=
begin if first_mark(mark_class(p))=null then
  begin first_mark(mark_class(p)):=mark_ptr(p);
  add_token_ref(first_mark(mark_class(p)));
  end;
if bot_mark(mark_class(p))<>null then delete_token_ref(bot_mark(mark_class(p)));
bot_mark(mark_class(p)):=mark_ptr(p); add_token_ref(bot_mark(mark_class(p)));
end;

@ When the following code is executed, the current page runs from node
|vlink(page_head)| to node |prev_p|, and the nodes from |p| to |page_tail|
are to be placed back at the front of the contribution list. Furthermore
the heldover insertions appear in a list from |vlink(hold_head)| to |q|; we
will put them into the current page list for safekeeping while the user's
output routine is active.  We might have |q=hold_head|; and |p=null| if
and only if |prev_p=page_tail|. Error messages are suppressed within
|vpackage|, since the box might appear to be overfull or underfull simply
because the stretch and shrink from the \.{\\skip} registers for inserts
are not actually present in the box.

@<Break the current page at node |p|, put it...@>=
if p<>null then
  begin if vlink(contrib_head)=null then
    if nest_ptr=0 then tail:=page_tail
    else contrib_tail:=page_tail;
  vlink(page_tail):=vlink(contrib_head);
  vlink(contrib_head):=p;
  vlink(prev_p):=null;
  end;
save_vbadness:=vbadness; vbadness:=inf_bad;
save_vfuzz:=vfuzz; vfuzz:=max_dimen; {inhibit error messages}
pack_direction:=body_direction;
box(255):=filtered_vpackage(vlink(page_head),best_size,exactly,page_max_depth,output_group);
vbadness:=save_vbadness; vfuzz:=save_vfuzz;
if last_glue<>max_halfword then delete_glue_ref(last_glue);
@<Start a new current page@>; {this sets |last_glue:=max_halfword|}
if q<>hold_head then
  begin vlink(page_head):=vlink(hold_head); page_tail:=q;
  end

@ If many insertions are supposed to go into the same box, we want to know
the position of the last node in that box, so that we don't need to waste time
when linking further information into it. The |last_ins_ptr| fields of the
page insertion nodes are therefore used for this purpose during the
packaging phase.

@<Prepare all the boxes involved in insertions to act as queues@>=
begin r:=vlink(page_ins_head);
while r<>page_ins_head do
  begin if best_ins_ptr(r)<>null then
    begin n:=qo(subtype(r)); ensure_vbox(n);
    if box(n)=null then box(n):=new_null_box;
    p:=box(n)+list_offset;
    while vlink(p)<>null do p:=vlink(p);
    last_ins_ptr(r):=p;
    end;
  r:=vlink(r);
  end;
end

@ @<Delete \(t)the page-insertion nodes@>=
r:=vlink(page_ins_head);
while r<>page_ins_head do
  begin q:=vlink(r); flush_node(r); r:=q;
  end;
vlink(page_ins_head):=page_ins_head

@ We will set |best_ins_ptr:=null| and package the box corresponding to
insertion node~|r|, just after making the final insertion into that box.
If this final insertion is `|split_up_node|', the remainder after splitting
and pruning (if any) will be carried over to the next page.

@<Either insert the material specified by node |p| into...@>=
begin r:=vlink(page_ins_head);
while subtype(r)<>subtype(p) do r:=vlink(r);
if best_ins_ptr(r)=null then wait:=true
else  begin wait:=false; s:=last_ins_ptr(r); vlink(s):=ins_ptr(p);
  if best_ins_ptr(r)=p then
    @<Wrap up the box specified by node |r|, splitting node |p| if
    called for; set |wait:=true| if node |p| holds a remainder after
    splitting@>
  else  begin while vlink(s)<>null do s:=vlink(s);
    last_ins_ptr(r):=s;
    end;
  end;
@<Either append the insertion node |p| after node |q|, and remove it
  from the current page, or delete |node(p)|@>;
end

@ @<Wrap up the box specified by node |r|, splitting node |p| if...@>=
begin if type(r)=split_up_node then
  if (broken_ins(r)=p)and(broken_ptr(r)<>null) then
    begin while vlink(s)<>broken_ptr(r) do s:=vlink(s);
    vlink(s):=null;
    split_top_skip:=split_top_ptr(p);
    ins_ptr(p):=prune_page_top(broken_ptr(r),false);
    if ins_ptr(p)<>null then
      begin temp_ptr:=vpack(ins_ptr(p),natural);
      height(p):=height(temp_ptr)+depth(temp_ptr);
      list_ptr(temp_ptr):=null; flush_node(temp_ptr); wait:=true;
      end;
    end;
best_ins_ptr(r):=null;
n:=qo(subtype(r));
temp_ptr:=list_ptr(box(n));
list_ptr(box(n)):=null; flush_node(box(n));
pack_direction:=body_direction;
box(n):=vpack(temp_ptr,natural);
end

@ @<Either append the insertion node |p|...@>=
vlink(prev_p):=vlink(p); vlink(p):=null;
if wait then
  begin vlink(q):=p; q:=p; incr(insert_penalties);
  end
else  begin ins_ptr(p):=null; flush_node(p);
  end;
p:=prev_p

@ The list of heldover insertions, running from |vlink(page_head)| to
|page_tail|, must be moved to the contribution list when the user has
specified no output routine.

@<Perform the default output routine@>=
begin if vlink(page_head)<>null then
  begin if vlink(contrib_head)=null then
    if nest_ptr=0 then tail:=page_tail@+else contrib_tail:=page_tail
  else vlink(page_tail):=vlink(contrib_head);
  vlink(contrib_head):=vlink(page_head);
  vlink(page_head):=null; page_tail:=page_head;
  end;
flush_node_list(page_disc); page_disc:=null;
ship_out(box(255)); box(255):=null;
end

@ @<Explain that too many dead cycles have occurred in a row@>=
begin print_err("Output loop---"); print_int(dead_cycles);
@.Output loop...@>
print(" consecutive dead cycles");
help3("I've concluded that your \output is awry; it never does a")@/
("\shipout, so I'm shipping \box255 out myself. Next time")@/
("increase \maxdeadcycles if you want me to be more patient!"); error;
end

@ @<Fire up the user's output routine and |return|@>=
begin output_active:=true;
incr(dead_cycles);
push_nest; mode:=-vmode; prev_depth:=ignore_depth; mode_line:=-line;
begin_token_list(output_routine,output_text);
new_save_level(output_group); normal_paragraph;
scan_left_brace;
return;
end

@ When the user's output routine finishes, it has constructed a vlist
in internal vertical mode, and \TeX\ will do the following:

@<Resume the page builder after an output routine has come to an end@>=
begin if (loc<>null) or
 ((token_type<>output_text)and(token_type<>backed_up)) then
  @<Recover from an unbalanced output routine@>;
end_token_list; {conserve stack space in case more outputs are triggered}
end_graf; unsave; output_active:=false; insert_penalties:=0;@/
@<Ensure that box 255 is empty after output@>;
if tail<>head then {current list goes after heldover insertions}
  begin vlink(page_tail):=vlink(head);
  page_tail:=tail;
  end;
if vlink(page_head)<>null then {and both go before heldover contributions}
  begin if vlink(contrib_head)=null then contrib_tail:=page_tail;
  vlink(page_tail):=vlink(contrib_head);
  vlink(contrib_head):=vlink(page_head);
  vlink(page_head):=null; page_tail:=page_head;
  end;
flush_node_list(page_disc); page_disc:=null;
pop_nest; build_page;
end

@ @<Recover from an unbalanced output routine@>=
begin print_err("Unbalanced output routine");
@.Unbalanced output routine@>
help2("Your sneaky output routine has problematic {'s and/or }'s.")@/
("I can't handle that very well; good luck."); error;
repeat get_token;
until loc=null;
end {loops forever if reading from a file, since |null=min_halfword<=0|}

@ @<Ensure that box 255 is empty after output@>=
if box(255)<>null then
  begin print_err("Output routine didn't use all of ");
  print_esc("box"); print_int(255);
@.Output routine didn't use...@>
  help3("Your \output commands should empty \box255,")@/
    ("e.g., by saying `\shipout\box255'.")@/
    ("Proceed; I'll discard its present contents.");
  box_error(255);
  end

@* \[46] The chief executive.
We come now to the |main_control| routine, which contains the master
switch that causes all the various pieces of \TeX\ to do their things,
in the right order.

In a sense, this is the grand climax of the program: It applies all the
tools that we have worked so hard to construct. In another sense, this is
the messiest part of the program: It necessarily refers to other pieces
of code all over the place, so that a person can't fully understand what is
going on without paging back and forth to be reminded of conventions that
are defined elsewhere. We are now at the hub of the web, the central nervous
system that touches most of the other parts and ties them together.
@^brain@>

The structure of |main_control| itself is quite simple. There's a label
called |big_switch|, at which point the next token of input is fetched
using |get_x_token|. Then the program branches at high speed into one of
about 100 possible directions, based on the value of the current
mode and the newly fetched command code; the sum |abs(mode)+cur_cmd|
indicates what to do next. For example, the case `|vmode+letter|' arises
when a letter occurs in vertical mode (or internal vertical mode); this
case leads to instructions that initialize a new paragraph and enter
horizontal mode.

The big |case| statement that contains this multiway switch has been labeled
|reswitch|, so that the program can |goto reswitch| when the next token
has already been fetched. Most of the cases are quite short; they call
an ``action procedure'' that does the work for that case, and then they
either |goto reswitch| or they ``fall through'' to the end of the |case|
statement, which returns control back to |big_switch|. Thus, |main_control|
is not an extremely large procedure, in spite of the multiplicity of things
it must do; it is small enough to be handled by \PASCAL\ compilers that put
severe restrictions on procedure size.
@!@^action procedure@>

One case is singled out for special treatment, because it accounts for most
of \TeX's activities in typical applications. The process of reading simple
text and converting it into |char_node| records, while looking for ligatures
and kerns, is part of \TeX's ``inner loop''; the whole program runs
efficiently when its inner loop is fast, so this part has been written
with particular care.

@ We shall concentrate first on the inner loop of |main_control|, deferring
consideration of the other cases until later.
@^inner loop@>

@d big_switch=60 {go here to branch on the next token of input}

@p @t\4@>@<Declare action procedures for use by |main_control|@>@;
@t\4@>@<Declare the procedure called |handle_right_brace|@>@;
procedure main_control; {governs \TeX's activities}
label big_switch,reswitch,continue,exit;
var@!t,k:integer; {general-purpose temporary variables}
p:pointer; {for whatsit nodes and testing whether an auto kern should be inserted}
chr_stack:integer; { to temporarily save an |cur_chr| to be appended }
begin t:=0; {for -Wall}
chr_stack:=-1; 
if every_job<>null then begin_token_list(every_job,every_job_text);
big_switch: get_x_token;@/
reswitch: @<Give diagnostic information, if requested@>;
case abs(mode)+cur_cmd of
hmode+letter,hmode+other_char,hmode+char_given,hmode+char_num: begin 
  if abs(mode)+cur_cmd=hmode+char_num then begin 
    scan_char_num; cur_chr:=cur_val; 
    end;
  if is_last_ocp(current_ocp_lstack,current_ocp_no) then begin
    @<Append character |cur_chr| and the following characters (if~any)
      to the current hlist in the current font; |goto reswitch| when
      a non-character has been fetched@>;
    end
  else begin
    @<Create a buffer with character |cur_chr| and the following
      characters (if~any) and then apply the current active OCP filter
      to this buffer@>;
    end;
  end;
hmode+no_boundary: begin @<Append a |cancel_boundary_node| @>;
  end;
hmode+char_ghost: begin t:=cur_chr; get_x_token;
  if (cur_cmd=letter)or(cur_cmd=other_char)or(cur_cmd=char_given)or
   (cur_cmd=char_num) then begin 
	p:=new_glyph(cur_font,cur_chr);
    if t=0 then begin set_is_leftghost(p); end
    else begin set_is_rightghost(p); end;
    tail_append(p);
    end;
  end;
hmode+spacer,hmode+ex_space,mmode+ex_space: 
if (abs(mode)+cur_cmd=hmode+spacer) and 
   (not (space_factor = 1000)) then
  app_space
else begin
  @<Append a normal inter-word space to the current list@>; 
  end;
@t\4@>@<Cases of |main_control| that are not part of the inner loop@>@;
end; {of the big |case| statement}
goto big_switch;
exit:end;

@ When a new token has just been fetched at |big_switch|, we have an
ideal place to monitor \TeX's activity.
@^debugging@>

@<Give diagnostic information, if requested@>=
if interrupt<>0 then if OK_to_interrupt then
  begin back_input; check_interrupt; goto big_switch;
  end;
if tracing_commands>0 then show_cur_cmd_chr

@ The following part of the program was first written in a structured
manner, according to the philosophy that ``premature optimization is
the root of all evil.'' Then it was rearranged into pieces of
spaghetti so that the most common actions could proceed with little or
no redundancy. And finally, it is replaced by a completely standalone
loop over the node list: luatex does not have a |main+loop| at all.
@^inner loop@>

@<Glob...@>=
@!main_p:pointer; {temporary register for list manipulation}
@!main_s:integer; {space factor value}

@ We leave the |space_factor| unchanged if |sf_code(cur_chr)=0|; otherwise we
set it equal to |sf_code(cur_chr)|, except that it should never change
from a value less than 1000 to a value exceeding 1000. The most common
case is |sf_code(cur_chr)=1000|, so we want that case to be fast.

@d adjust_space_factor==@t@>@;@/
  main_s:=get_sf_code(cur_chr);
  if main_s=1000 then space_factor:=1000
  else if main_s<1000 then
    begin if main_s>0 then space_factor:=main_s;
    end
  else if space_factor<1000 then space_factor:=1000
  else space_factor:=main_s

@<Append character |cur_chr|...@>=
continue: adjust_space_factor;@/
chr_stack:=cur_chr;
tail_append(new_char(cur_font,chr_stack));
get_x_token;
if (cur_cmd=letter)or(cur_cmd=other_char)or
   (cur_cmd=char_given)or(cur_cmd=char_num) then begin 
  if cur_cmd=char_num then begin 
    scan_char_num; cur_chr:=cur_val; 
    end;
  if (chr_stack=ex_hyphen_char)and(cur_chr<>ex_hyphen_char)and(mode>0) then begin 
    tail_append(new_disc); subtype(tail):=automatic_disc; 
    end;
  goto continue;
  end 
else begin
  if (chr_stack=ex_hyphen_char) and (mode>0) then begin 
    tail_append(new_disc); subtype(tail):=automatic_disc; 
    end;
  chr_stack:=-1;
  goto reswitch;
  end

@ The occurrence of blank spaces is almost part of \TeX's inner loop,
@^inner loop@>
since we usually encounter about one space for every five non-blank characters.
Therefore |main_control| gives second-highest priority to ordinary spaces.

When a glue parameter like \.{\\spaceskip} is set to `\.{0pt}', we will
see to it later that the corresponding glue specification is precisely
|zero_glue|, not merely a pointer to some specification that happens
to be full of zeroes. Therefore it is simple to test whether a glue parameter
is zero or~not.

@<Append a normal inter-word space...@>=
if space_skip=zero_glue then
  begin @<Find the glue specification, |main_p|, for
    text spaces in the current font@>;
  temp_ptr:=new_glue(main_p);
  end
else temp_ptr:=new_param_glue(space_skip_code);
vlink(tail):=temp_ptr; tail:=temp_ptr


@ From Knuth: ``Having |font_glue| allocated for each text font saves
both time and memory.''  That may be true, but it also punches through
the API wall for fonts, so I removed that -- Taco. But a bit of caching
is very welcome, which is why I need to have the next two globals:

@<Glob...@>=
space_spec_font:internal_font_number;
space_spec_cache:halfword;

@ @<Set init...@>=
space_spec_font:=0;
space_spec_cache:=zero_glue;

@ @<Find the glue specification...@>=
begin 
if cur_font<>space_spec_font then begin
  if space_spec_cache<>zero_glue then
     delete_glue_ref(space_spec_cache);
  space_spec_cache:=new_spec(zero_glue);
  width(space_spec_cache):=space(cur_font);
  stretch(space_spec_cache):=space_stretch(cur_font);
  shrink(space_spec_cache):=space_shrink(cur_font);
  space_spec_font:=cur_font;
  end;
main_p:=space_spec_cache;
end

@ @<Declare act...@>=
procedure app_space; {handle spaces when |space_factor<>1000|}
var@!q:pointer; {glue node}
begin if (space_factor>=2000)and(xspace_skip<>zero_glue) then
  q:=new_param_glue(xspace_skip_code)
else begin if space_skip<>zero_glue then 
    main_p:=new_spec(space_skip)
  else begin 
    main_p:=new_spec(zero_glue);
    width(main_p):=space(cur_font);
    stretch(main_p):=space_stretch(cur_font);
    shrink(main_p):=space_shrink(cur_font);
  end;
  @<Modify the glue specification in |main_p| according to the space factor@>;
  q:=new_glue(main_p); glue_ref_count(main_p):=null;
  end;
vlink(tail):=q; tail:=q;
end;

@ @<Modify the glue specification in |main_p| according to the space factor@>=
if space_factor>=2000 then width(main_p):=width(main_p)+extra_space(cur_font);
stretch(main_p):=xn_over_d(stretch(main_p),space_factor,1000);
shrink(main_p):=xn_over_d(shrink(main_p),1000,space_factor)

@ Whew---that covers the main loop. We can now proceed at a leisurely
pace through the other combinations of possibilities.

@d any_mode(#)==vmode+#,hmode+#,mmode+# {for mode-independent commands}

@<Cases of |main_control| that are not part of the inner loop@>=
any_mode(relax),vmode+spacer,mmode+spacer,mmode+no_boundary:do_nothing;
any_mode(ignore_spaces): begin
  if cur_chr = 0 then begin
    @<Get the next non-blank non-call...@>;
    goto reswitch;
  end
  else begin
    t:=scanner_status;
    scanner_status:=normal;
    get_filtered_next;
    scanner_status:=t;
    cur_cs  := prim_lookup(text(cur_cs));
    if cur_cs<>undefined_primitive then begin
      cur_cmd := get_prim_eq_type(cur_cs);
      cur_chr := get_prim_equiv(cur_cs);
      cur_tok := (cur_cmd*string_offset)+cur_chr;
      goto reswitch;
      end;
    end;
  end;
vmode+stop: if its_all_over then return; {this is the only way out}
@t\4@>@<Forbidden cases detected in |main_control|@>@+@,any_mode(mac_param):
  report_illegal_case;
@<Math-only cases in non-math modes, or vice versa@>: insert_dollar_sign;
@t\4@>@<Cases of |main_control| that build boxes and lists@>@;
@t\4@>@<Cases of |main_control| that don't depend on |mode|@>@;
@t\4@>@<Cases of |main_control| that are for extensions to \TeX@>@;

@ Here is a list of cases where the user has probably gotten into or out of math
mode by mistake. \TeX\ will insert a dollar sign and rescan the current token.

@d non_math(#)==vmode+#,hmode+#

@<Math-only cases in non-math modes...@>=
non_math(sup_mark), non_math(sub_mark), non_math(math_char_num),
non_math(math_given), non_math(omath_given), 
non_math(math_comp), non_math(delim_num),
non_math(left_right), non_math(above), non_math(radical),
non_math(math_style), non_math(math_choice), non_math(vcenter),
non_math(non_script), non_math(mkern), non_math(limit_switch),
non_math(mskip), non_math(math_accent),
mmode+endv, mmode+par_end, mmode+stop, mmode+vskip, mmode+un_vbox,
mmode+valign, mmode+hrule

@ @<Declare action...@>=
procedure insert_dollar_sign;
begin back_input; cur_tok:=math_shift_token+"$";
print_err("Missing $ inserted");
@.Missing \$ inserted@>
help2("I've inserted a begin-math/end-math symbol since I think")@/
("you left one out. Proceed, with fingers crossed."); ins_error;
end;

@ When erroneous situations arise, \TeX\ usually issues an error message
specific to the particular error. For example, `\.{\\noalign}' should
not appear in any mode, since it is recognized by the |align_peek| routine
in all of its legitimate appearances; a special error message is given
when `\.{\\noalign}' occurs elsewhere. But sometimes the most appropriate
error message is simply that the user is not allowed to do what he or she
has attempted. For example, `\.{\\moveleft}' is allowed only in vertical mode,
and `\.{\\lower}' only in non-vertical modes.  Such cases are enumerated
here and in the other sections referred to under `See also \dots.'

@<Forbidden cases...@>=
vmode+vmove,hmode+hmove,mmode+hmove,any_mode(last_item),

@ The `|you_cant|' procedure prints a line saying that the current command
is illegal in the current mode; it identifies these things symbolically.

@<Declare action...@>=
procedure you_cant;
begin print_err("You can't use `");
@.You can't use x in y mode@>
print_cmd_chr(cur_cmd,cur_chr);
print("' in "); print_mode(mode);
end;

@ @<Declare act...@>=
procedure report_illegal_case;
begin you_cant;
help4("Sorry, but I'm not programmed to handle this case;")@/
("I'll just pretend that you didn't ask for it.")@/
("If you're in the wrong mode, you might be able to")@/
("return to the right one by typing `I}' or `I$' or `I\par'.");@/
error;
end;

@ Some operations are allowed only in privileged modes, i.e., in cases
that |mode>0|. The |privileged| function is used to detect violations
of this rule; it issues an error message and returns |false| if the
current |mode| is negative.

@<Declare act...@>=
function privileged:boolean;
begin if mode>0 then privileged:=true
else  begin report_illegal_case; privileged:=false;
  end;
end;

@ Either \.{\\dump} or \.{\\end} will cause |main_control| to enter the
endgame, since both of them have `|stop|' as their command code.

@<Put each...@>=
primitive("end",stop,0);@/
@!@:end_}{\.{\\end} primitive@>
primitive("dump",stop,1);@/
@!@:dump_}{\.{\\dump} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
stop:if chr_code=1 then print_esc("dump")@+else print_esc("end");

@ We don't want to leave |main_control| immediately when a |stop| command
is sensed, because it may be necessary to invoke an \.{\\output} routine
several times before things really grind to a halt. (The output routine
might even say `\.{\\gdef\\end\{...\}}', to prolong the life of the job.)
Therefore |its_all_over| is |true| only when the current page
and contribution list are empty, and when the last output was not a
``dead cycle.''

@<Declare act...@>=
function its_all_over:boolean; {do this when \.{\\end} or \.{\\dump} occurs}
label exit;
begin if privileged then
  begin if (page_head=page_tail)and(head=tail)and(dead_cycles=0) then
    begin its_all_over:=true; return;
    end;
  back_input; {we will try to end again after ejecting residual material}
  tail_append(new_null_box);
  width(tail):=hsize;
  tail_append(new_glue(fill_glue));
  tail_append(new_penalty(-@'10000000000));@/
  build_page; {append \.{\\hbox to \\hsize\{\}\\vfill\\penalty-'10000000000}}
  end;
its_all_over:=false;
exit:end;

@* \[47] Building boxes and lists.
The most important parts of |main_control| are concerned with \TeX's
chief mission of box-making. We need to control the activities that put
entries on vlists and hlists, as well as the activities that convert
those lists into boxes. All of the necessary machinery has already been
developed; it remains for us to ``push the buttons'' at the right times.

@ As an introduction to these routines, let's consider one of the simplest
cases: What happens when `\.{\\hrule}' occurs in vertical mode, or
`\.{\\vrule}' in horizontal mode or math mode? The code in |main_control|
is short, since the |scan_rule_spec| routine already does most of what is
required; thus, there is no need for a special action procedure.

Note that baselineskip calculations are disabled after a rule in vertical
mode, by setting |prev_depth:=ignore_depth|.

@<Cases of |main_control| that build...@>=
vmode+hrule,hmode+vrule,mmode+vrule: begin tail_append(scan_rule_spec);
  if abs(mode)=vmode then prev_depth:=ignore_depth
  else if abs(mode)=hmode then space_factor:=1000;
  end;

@ The processing of things like \.{\\hskip} and \.{\\vskip} is slightly
more complicated. But the code in |main_control| is very short, since
it simply calls on the action routine |append_glue|. Similarly, \.{\\kern}
activates |append_kern|.

@<Cases of |main_control| that build...@>=
vmode+vskip,hmode+hskip,mmode+hskip,mmode+mskip: append_glue;
any_mode(kern),mmode+mkern: append_kern;

@ The |hskip| and |vskip| command codes are used for control sequences
like \.{\\hss} and \.{\\vfil} as well as for \.{\\hskip} and \.{\\vskip}.
The difference is in the value of |cur_chr|.

@d fil_code=0 {identifies \.{\\hfil} and \.{\\vfil}}
@d fill_code=1 {identifies \.{\\hfill} and \.{\\vfill}}
@d ss_code=2 {identifies \.{\\hss} and \.{\\vss}}
@d fil_neg_code=3 {identifies \.{\\hfilneg} and \.{\\vfilneg}}
@d skip_code=4 {identifies \.{\\hskip} and \.{\\vskip}}
@d mskip_code=5 {identifies \.{\\mskip}}

@<Put each...@>=
primitive("hskip",hskip,skip_code);@/
@!@:hskip_}{\.{\\hskip} primitive@>
primitive("hfil",hskip,fil_code);
@!@:hfil_}{\.{\\hfil} primitive@>
primitive("hfill",hskip,fill_code);@/
@!@:hfill_}{\.{\\hfill} primitive@>
primitive("hss",hskip,ss_code);
@!@:hss_}{\.{\\hss} primitive@>
primitive("hfilneg",hskip,fil_neg_code);@/
@!@:hfil_neg_}{\.{\\hfilneg} primitive@>
primitive("vskip",vskip,skip_code);@/
@!@:vskip_}{\.{\\vskip} primitive@>
primitive("vfil",vskip,fil_code);
@!@:vfil_}{\.{\\vfil} primitive@>
primitive("vfill",vskip,fill_code);@/
@!@:vfill_}{\.{\\vfill} primitive@>
primitive("vss",vskip,ss_code);
@!@:vss_}{\.{\\vss} primitive@>
primitive("vfilneg",vskip,fil_neg_code);@/
@!@:vfil_neg_}{\.{\\vfilneg} primitive@>
primitive("mskip",mskip,mskip_code);@/
@!@:mskip_}{\.{\\mskip} primitive@>
primitive("kern",kern,explicit);
@!@:kern_}{\.{\\kern} primitive@>
primitive("mkern",mkern,mu_glue);@/
@!@:mkern_}{\.{\\mkern} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
hskip: case chr_code of
  skip_code:print_esc("hskip");
  fil_code:print_esc("hfil");
  fill_code:print_esc("hfill");
  ss_code:print_esc("hss");
  othercases print_esc("hfilneg")
  endcases;
vskip: case chr_code of
  skip_code:print_esc("vskip");
  fil_code:print_esc("vfil");
  fill_code:print_esc("vfill");
  ss_code:print_esc("vss");
  othercases print_esc("vfilneg")
  endcases;
mskip: print_esc("mskip");
kern: print_esc("kern");
mkern: print_esc("mkern");

@ All the work relating to glue creation has been relegated to the
following subroutine. It does not call |build_page|, because it is
used in at least one place where that would be a mistake.

@<Declare action...@>=
procedure append_glue;
var s:small_number; {modifier of skip command}
begin s:=cur_chr;
case s of
fil_code: cur_val:=fil_glue;
fill_code: cur_val:=fill_glue;
ss_code: cur_val:=ss_glue;
fil_neg_code: cur_val:=fil_neg_glue;
skip_code: scan_glue(glue_val);
mskip_code: scan_glue(mu_val);
end; {now |cur_val| points to the glue specification}
tail_append(new_glue(cur_val));
if s>=skip_code then
  begin decr(glue_ref_count(cur_val));
  if s>skip_code then subtype(tail):=mu_glue;
  end;
end;

@ @<Declare act...@>=
procedure append_kern;
var s:quarterword; {|subtype| of the kern node}
begin s:=cur_chr; scan_dimen(s=mu_glue,false,false);
tail_append(new_kern(cur_val)); subtype(tail):=s;
end;

@ Many of the actions related to box-making are triggered by the appearance
of braces in the input. For example, when the user says `\.{\\hbox}
\.{to} \.{100pt\{$\langle\,\hbox{hlist}\,\rangle$\}}' in vertical mode,
the information about the box size (100pt, |exactly|) is put onto |save_stack|
with a level boundary word just above it, and |cur_group:=adjusted_hbox_group|;
\TeX\ enters restricted horizontal mode to process the hlist. The right
brace eventually causes |save_stack| to be restored to its former state,
at which time the information about the box size (100pt, |exactly|) is
available once again; a box is packaged and we leave restricted horizontal
mode, appending the new box to the current list of the enclosing mode
(in this case to the current list of vertical mode), followed by any
vertical adjustments that were removed from the box by |hpack|.

The next few sections of the program are therefore concerned with the
treatment of left and right curly braces.

@ If a left brace occurs in the middle of a page or paragraph, it simply
introduces a new level of grouping, and the matching right brace will not have
such a drastic effect. Such grouping affects neither the mode nor the
current list.

@<Cases of |main_control| that build...@>=
non_math(left_brace): begin
  new_save_level(simple_group);
  eq_word_define(int_base+no_local_whatsits_code,0);
  eq_word_define(int_base+no_local_dirs_code,0);
  end;
any_mode(begin_group): begin
  new_save_level(semi_simple_group);
  eq_word_define(int_base+no_local_whatsits_code,0);
  eq_word_define(int_base+no_local_dirs_code,0);
  end;
any_mode(end_group):
  if cur_group=semi_simple_group then begin
    temp_no_whatsits:=no_local_whatsits;
    temp_no_dirs:=no_local_dirs;
    temporary_dir:=text_direction;
    if dir_level(text_dir_ptr)=cur_level then
      @<DIR: Remove from |text_dir_ptr|@>;
    unsave;
    if abs(mode)=hmode then begin
      if temp_no_dirs<>0 then begin
        @<DIR: Add local dir node@>;
        dir_dir(tail):=temporary_dir-64;
        end;
      if temp_no_whatsits<>0 then
        @<LOCAL: Add local paragraph node@>;
      end
    end
  else off_save;

@ We have to deal with errors in which braces and such things are not
properly nested. Sometimes the user makes an error of commission by
inserting an extra symbol, but sometimes the user makes an error of omission.
\TeX\ can't always tell one from the other, so it makes a guess and tries
to avoid getting into a loop.

The |off_save| routine is called when the current group code is wrong. It tries
to insert something into the user's input that will help clean off
the top level.

@<Declare act...@>=
procedure off_save;
var p,q:pointer; {inserted token}
begin if cur_group=bottom_level then
  @<Drop current token and complain that it was unmatched@>
else  begin back_input; p:=get_avail; link(temp_token_head):=p;
  print_err("Missing ");
  @<Prepare to insert a token that matches |cur_group|,
    and print what it is@>;
  print(" inserted"); ins_list(link(temp_token_head));
  help5("I've inserted something that you may have forgotten.")@/
  ("(See the <inserted text> above.)")@/
  ("With luck, this will get me unwedged. But if you")@/
  ("really didn't forget anything, try typing `2' now; then")@/
  ("my insertion and my current dilemma will both disappear.");
  error;
  end;
end;

@ At this point, |link(temp_token_head)=p|, a pointer to an empty one-word node.

@<Prepare to insert a token that matches |cur_group|...@>=
case cur_group of
semi_simple_group: begin info(p):=cs_token_flag+frozen_end_group;
  print_esc("endgroup");
@.Missing \\endgroup inserted@>
  end;
math_shift_group: begin info(p):=math_shift_token+"$"; print_char("$");
@.Missing \$ inserted@>
  end;
math_left_group: begin info(p):=cs_token_flag+frozen_right; q:=get_avail; link(p):=q;
  p:=link(p); info(p):=other_token+"."; print_esc("right.");
@.Missing \\right\hbox{.} inserted@>
@^null delimiter@>
  end;
othercases begin info(p):=right_brace_token+"}"; print_char("}");
@.Missing \} inserted@>
  end
endcases

@ @<Drop current token and complain that it was unmatched@>=
begin print_err("Extra "); print_cmd_chr(cur_cmd,cur_chr);
@.Extra x@>
help1("Things are pretty mixed up, but I think the worst is over.");@/
error;
end

@ The routine for a |right_brace| character branches into many subcases,
since a variety of things may happen, depending on |cur_group|. Some
types of groups are not supposed to be ended by a right brace; error
messages are given in hopes of pinpointing the problem. Most branches
of this routine will be filled in later, when we are ready to understand
them; meanwhile, we must prepare ourselves to deal with such errors.

@<Cases of |main_control| that build...@>=
any_mode(right_brace): handle_right_brace;

@ @<Declare the procedure called |handle_right_brace|@>=
procedure handle_right_brace;
var p,@!q:pointer; {for short-term use}
@!d:scaled; {holds |split_max_depth| in |insert_group|}
@!f:integer; {holds |floating_penalty| in |insert_group|}
begin case cur_group of
simple_group: begin
  temp_no_whatsits:=no_local_whatsits;
  temp_no_dirs:=no_local_dirs;
  temporary_dir:=text_direction;
  if dir_level(text_dir_ptr)=cur_level then
    @<DIR: Remove from |text_dir_ptr|@>;
  unsave;
  if abs(mode)=hmode then begin
    if temp_no_dirs<>0 then begin
      @<DIR: Add local dir node@>;
      dir_dir(tail):=temporary_dir-64;
      end;
    if temp_no_whatsits<>0 then
      @<LOCAL: Add local paragraph node@>;
    end
  end;
bottom_level: begin print_err("Too many }'s");
@.Too many \}'s@>
  help2("You've closed more groups than you opened.")@/
  ("Such booboos are generally harmless, so keep going."); error;
  end;
semi_simple_group,math_shift_group,math_left_group: extra_right_brace;
@t\4@>@<Cases of |handle_right_brace| where a |right_brace| triggers
  a delayed action@>@;
othercases confusion("rightbrace")
@:this can't happen rightbrace}{\quad rightbrace@>
endcases;
end;

@ @<Declare act...@>=
procedure extra_right_brace;
begin print_err("Extra }, or forgotten ");
@.Extra \}, or forgotten x@>
case cur_group of
semi_simple_group: print_esc("endgroup");
math_shift_group: print_char("$");
math_left_group: print_esc("right");
end;@/
help5("I've deleted a group-closing symbol because it seems to be")@/
("spurious, as in `$x}$'. But perhaps the } is legitimate and")@/
("you forgot something else, as in `\hbox{$x}'. In such cases")@/
("the way to recover is to insert both the forgotten and the")@/
("deleted material, e.g., by typing `I$}'."); error;
incr(align_state);
end;

@ Here is where we clear the parameters that are supposed to revert to their
default values after every paragraph and when internal vertical mode is entered.

@<Declare act...@>=
procedure normal_paragraph;
begin if looseness<>0 then eq_word_define(int_base+looseness_code,0);
if hang_indent<>0 then eq_word_define(dimen_base+hang_indent_code,0);
if hang_after<>1 then eq_word_define(int_base+hang_after_code,1);
if par_shape_ptr<>null then eq_define(par_shape_loc,shape_ref,null);
if inter_line_penalties_ptr<>null then
  eq_define(inter_line_penalties_loc,shape_ref,null);
end;

@ Now let's turn to the question of how \.{\\hbox} is treated. We actually
need to consider also a slightly larger context, since constructions like
`\.{\\setbox3=}\penalty0\.{\\hbox...}' and
`\.{\\leaders}\penalty0\.{\\hbox...}' and
`\.{\\lower3.8pt\\hbox...}'
are supposed to invoke quite
different actions after the box has been packaged. Conversely,
constructions like `\.{\\setbox3=}' can be followed by a variety of
different kinds of boxes, and we would like to encode such things in an
efficient way.

In other words, there are two problems: To represent the context of a box,
and to represent its type.

The first problem is solved by putting a ``context code'' on the |save_stack|,
just below the two entries that give the dimensions produced by |scan_spec|.
The context code is either a (signed) shift amount, or it is a large
integer |>=box_flag|, where |box_flag=@t$2^{30}$@>|. Codes |box_flag| through
|box_flag+biggest_reg| represent `\.{\\setbox0}' through
`\.{\\setbox}|biggest_reg|'; codes |box_flag+biggest_reg+1| through
|box_flag+2*biggest_reg| represent `\.{\\global\\setbox0}'
through `\.{\\global\\setbox}|biggest_reg|'; code |box_flag+2*number_regs|
represents `\.{\\shipout}'; and codes |box_flag+2*number_regs+1|
through |box_flag+2*number_regs+3| represent `\.{\\leaders}', `\.{\\cleaders}',
and `\.{\\xleaders}'.

The second problem is solved by giving the command code |make_box| to all
control sequences that produce a box, and by using the following |chr_code|
values to distinguish between them: |box_code|, |copy_code|, |last_box_code|,
|vsplit_code|, |vtop_code|, |vtop_code+vmode|, and |vtop_code+hmode|,
where the latter two are used denote \.{\\vbox} and \.{\\hbox}, respectively.

@d box_flag==@'10000000000 {context code for `\.{\\setbox0}'}
@d global_box_flag==(box_flag+number_regs) {context code for `\.{\\global\\setbox0}'}
@d max_global_box_flag==(global_box_flag+number_regs)
@d ship_out_flag==(max_global_box_flag+1) {context code for `\.{\\shipout}'}
@d leader_flag==ship_out_flag+1 {context code for `\.{\\leaders}'}
@d box_code=0 {|chr_code| for `\.{\\box}'}
@d copy_code=1 {|chr_code| for `\.{\\copy}'}
@d last_box_code=2 {|chr_code| for `\.{\\lastbox}'}
@d vsplit_code=3 {|chr_code| for `\.{\\vsplit}'}
@d vtop_code=4 {|chr_code| for `\.{\\vtop}'}

@<Put each...@>=
primitive("moveleft",hmove,1);
@!@:move_left_}{\.{\\moveleft} primitive@>
primitive("moveright",hmove,0);@/
@!@:move_right_}{\.{\\moveright} primitive@>
primitive("raise",vmove,1);
@!@:raise_}{\.{\\raise} primitive@>
primitive("lower",vmove,0);
@!@:lower_}{\.{\\lower} primitive@>
@#
primitive("box",make_box,box_code);
@!@:box_}{\.{\\box} primitive@>
primitive("copy",make_box,copy_code);
@!@:copy_}{\.{\\copy} primitive@>
primitive("lastbox",make_box,last_box_code);
@!@:last_box_}{\.{\\lastbox} primitive@>
primitive("vsplit",make_box,vsplit_code);
@!@:vsplit_}{\.{\\vsplit} primitive@>
primitive("vtop",make_box,vtop_code);@/
@!@:vtop_}{\.{\\vtop} primitive@>
primitive("vbox",make_box,vtop_code+vmode);
@!@:vbox_}{\.{\\vbox} primitive@>
primitive("hbox",make_box,vtop_code+hmode);@/
@!@:hbox_}{\.{\\hbox} primitive@>
primitive("shipout",leader_ship,a_leaders-1); {|ship_out_flag=leader_flag-1|}
@!@:ship_out_}{\.{\\shipout} primitive@>
primitive("leaders",leader_ship,a_leaders);
@!@:leaders_}{\.{\\leaders} primitive@>
primitive("cleaders",leader_ship,c_leaders);
@!@:c_leaders_}{\.{\\cleaders} primitive@>
primitive("xleaders",leader_ship,x_leaders);
@!@:x_leaders_}{\.{\\xleaders} primitive@>;
primitive("boxdir",assign_box_dir,0);
@!@:box_dir}{\.{\\boxdir} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
hmove: if chr_code=1 then print_esc("moveleft")@+else print_esc("moveright");
vmove: if chr_code=1 then print_esc("raise")@+else print_esc("lower");
make_box: case chr_code of
  box_code: print_esc("box");
  copy_code: print_esc("copy");
  last_box_code: print_esc("lastbox");
  vsplit_code: print_esc("vsplit");
  vtop_code: print_esc("vtop");
  vtop_code+vmode: print_esc("vbox");
  othercases print_esc("hbox")
  endcases;
leader_ship: if chr_code=a_leaders then print_esc("leaders")
  else if chr_code=c_leaders then print_esc("cleaders")
  else if chr_code=x_leaders then print_esc("xleaders")
  else print_esc("shipout");

@ Constructions that require a box are started by calling |scan_box| with
a specified context code. The |scan_box| routine verifies
that a |make_box| command comes next and then it calls |begin_box|.

@<Cases of |main_control| that build...@>=
vmode+hmove,hmode+vmove,mmode+vmove: begin t:=cur_chr;
  scan_normal_dimen;
  if t=0 then scan_box(cur_val)@+else scan_box(-cur_val);
  end;
any_mode(leader_ship): scan_box(leader_flag-a_leaders+cur_chr);
any_mode(make_box): begin_box(0);
any_mode(assign_box_dir): begin scan_register_num;
  cur_box:=box(cur_val);
  scan_optional_equals; scan_direction;
  if cur_box<>null then box_dir(cur_box):=cur_val;
  end;

@ The global variable |cur_box| will point to a newly-made box. If the box
is void, we will have |cur_box=null|. Otherwise we will have
|type(cur_box)=hlist_node| or |vlist_node| or |rule_node|; the |rule_node|
case can occur only with leaders.

@<Glob...@>=
@!cur_box:pointer; {box to be placed into its context}

@ The |box_end| procedure does the right thing with |cur_box|, if
|box_context| represents the context as explained above.

@<Declare act...@>=
procedure box_end(@!box_context:integer);
var p:pointer; {|ord_noad| for new box in math mode}
begin if box_context<box_flag then @<Append box |cur_box| to the current list,
    shifted by |box_context|@>
else if box_context<ship_out_flag then @<Store \(c)|cur_box| in a box register@>
else if cur_box<>null then
  if box_context>ship_out_flag then @<Append a new leader node that
      uses |cur_box|@>
  else ship_out(cur_box);
end;

@ The global variable |adjust_tail| will be non-null if and only if the
current box might include adjustments that should be appended to the
current vertical list.

@<Append box |cur_box| to the current...@>=
begin if cur_box<>null then
  begin shift_amount(cur_box):=box_context;
  if abs(mode)=vmode then
    begin
        if pre_adjust_tail <> null then begin
            if pre_adjust_head <> pre_adjust_tail then
                append_list(pre_adjust_head)(pre_adjust_tail);
            pre_adjust_tail := null;
        end;
        append_to_vlist(cur_box);
        if adjust_tail <> null then begin
            if adjust_head <> adjust_tail then
                append_list(adjust_head)(adjust_tail);
            adjust_tail := null;
        end;
    if mode>0 then begin check_filter('box'); build_page; end;
    end
  else  begin if abs(mode)=hmode then space_factor:=1000
    else  begin p:=new_noad;
      math_type(nucleus(p)):=sub_box;
      vinfo(nucleus(p)):=cur_box; cur_box:=p;
      end;
    vlink(tail):=cur_box; tail:=cur_box;
    end;
  end;
end

@ @<Store \(c)|cur_box| in a box register@>=
if box_context<global_box_flag then
  eq_define(box_base+box_context-box_flag,box_ref,cur_box)
else geq_define(box_base+box_context-global_box_flag,box_ref,cur_box)

@ @<Append a new leader node ...@>=
begin @<Get the next non-blank non-relax...@>;
if ((cur_cmd=hskip)and(abs(mode)<>vmode))or@|
   ((cur_cmd=vskip)and(abs(mode)=vmode))or@|
   ((cur_cmd=mskip)and(abs(mode)=mmode)) then
  begin append_glue; subtype(tail):=box_context-(leader_flag-a_leaders);
  leader_ptr(tail):=cur_box;
  end
else  begin print_err("Leaders not followed by proper glue");
@.Leaders not followed by...@>
  help3("You should say `\leaders <box or rule><hskip or vskip>'.")@/
  ("I found the <box or rule>, but there's no suitable")@/
  ("<hskip or vskip>, so I'm ignoring these leaders."); back_error;
  flush_node_list(cur_box);
  end;
end

@ Now that we can see what eventually happens to boxes, we can consider
the first steps in their creation. The |begin_box| routine is called when
|box_context| is a context specification, |cur_chr| specifies the type of
box desired, and |cur_cmd=make_box|.

@<Declare act...@>=
procedure begin_box(@!box_context:integer);
label exit, done;
var @!p,@!q:pointer; {run through the current list}
@!k:halfword; {0 or |vmode| or |hmode|}
@!n:eight_bits; {a box number}
begin case cur_chr of
box_code: begin scan_register_num; cur_box:=box(cur_val);
  box(cur_val):=null; {the box becomes void, at the same level}
  end;
copy_code: begin scan_register_num; cur_box:=copy_node_list(box(cur_val));
  end;
last_box_code: @<If the current list ends with a box node, delete it from
  the list and make |cur_box| point to it; otherwise set |cur_box:=null|@>;
vsplit_code: @<Split off part of a vertical box, make |cur_box| point to it@>;
othercases @<Initiate the construction of an hbox or vbox, then |return|@>
endcases;@/
box_end(box_context); {in simple cases, we use the box immediately}
exit:end;

@ Note that the condition |not is_char_node(tail)| implies that |head<>tail|,
since |head| is a one-word node.

@<If the current list ends with a box node, delete it...@>=
begin cur_box:=null;
if abs(mode)=mmode then
  begin you_cant; help1("Sorry; this \lastbox will be void."); error;
  end
else if (mode=vmode)and(head=tail) then
  begin you_cant;
  help2("Sorry...I usually can't take things from the current page.")@/
    ("This \lastbox will therefore be void."); error;
  end
else  begin if not is_char_node(tail) then
    if (type(tail)=hlist_node)or(type(tail)=vlist_node) then
      @<Remove the last box, unless it's part of a discretionary@>;
  end;
end

@ @<Remove the last box...@>=
begin q:=head;
repeat p:=q;
if not is_char_node(q) then if type(q)=disc_node then
  begin 
  if p=tail then goto done;
  end;
q:=vlink(p);
until q=tail;
cur_box:=tail; shift_amount(cur_box):=0;
tail:=p; vlink(p):=null;
done:end

@ Here we deal with things like `\.{\\vsplit 13 to 100pt}'.

@<Split off part of a vertical box, make |cur_box| point to it@>=
begin scan_register_num; n:=cur_val;
if not scan_keyword("to") then
@.to@>
  begin print_err("Missing `to' inserted");
@.Missing `to' inserted@>
  help2("I'm working on `\vsplit<box number> to <dimen>';")@/
  ("will look for the <dimen> next."); error;
  end;
scan_normal_dimen;
cur_box:=vsplit(n,cur_val);
end

@ Here is where we enter restricted horizontal mode or internal vertical
mode, in order to make a box.

@<Initiate the construction of an hbox or vbox, then |return|@>=
begin k:=cur_chr-vtop_code; saved(0):=box_context;
case abs(mode) of
vmode: spec_direction:=body_direction;
hmode: spec_direction:=text_direction;
mmode: spec_direction:=math_direction;
end;
if k=hmode then
  if (box_context<box_flag)and(abs(mode)=vmode) then
    scan_spec(adjusted_hbox_group,true)
  else scan_spec(hbox_group,true)
else  begin if k=vmode then scan_spec(vbox_group,true)
  else  begin scan_spec(vtop_group,true); k:=vmode;
    end;
  normal_paragraph;
  end;
push_nest; mode:=-k;
if k=vmode then
  begin prev_depth:=ignore_depth;
  if every_vbox<>null then begin_token_list(every_vbox,every_vbox_text);
  end
else  begin space_factor:=1000;
  if every_hbox<>null then begin_token_list(every_hbox,every_hbox_text);
  end;
return;
end

@ @<Declare act...@>=
procedure scan_box(@!box_context:integer);
  {the next input should specify a box or perhaps a rule}
begin @<Get the next non-blank non-relax...@>;
if cur_cmd=make_box then begin_box(box_context)
else if (box_context>=leader_flag)and((cur_cmd=hrule)or(cur_cmd=vrule)) then
  begin cur_box:=scan_rule_spec; box_end(box_context);
  end
else  begin@t@>@;@/
  print_err("A <box> was supposed to be here");@/
@.A <box> was supposed to...@>
  help3("I was expecting to see \hbox or \vbox or \copy or \box or")@/
  ("something like that. So you might find something missing in")@/
  ("your output. But keep trying; you can fix this later."); back_error;
  end;
end;

@ When the right brace occurs at the end of an \.{\\hbox} or \.{\\vbox} or
\.{\\vtop} construction, the |package| routine comes into action. We might
also have to finish a paragraph that hasn't ended.

@<Cases of |handle...@>=
hbox_group: package(0);
adjusted_hbox_group: begin adjust_tail:=adjust_head;
    pre_adjust_tail:=pre_adjust_head; package(0);
  end;
vbox_group: begin line_break_context:=vbox_group; end_graf; package(0);
  end;
vtop_group: begin line_break_context:=vtop_group; end_graf; package(vtop_code);
  end;

@ @<Declare action...@>=
procedure package(@!c:small_number);
var h:scaled; {height of box}
@!p:pointer; {first node in a box}
@!d:scaled; {max depth}
@!grp:integer;
begin grp:=cur_group;
d:=box_max_depth; unsave; save_ptr:=save_ptr-6;
pack_direction:=saved(3);
if mode=-hmode then cur_box:=filtered_hpack(head,tail,saved(2),saved(1),grp)
else  begin cur_box:=filtered_vpackage(vlink(head),saved(2),saved(1),d,grp);
  if c=vtop_code then @<Readjust the height and depth of |cur_box|,
    for \.{\\vtop}@>;
  end;
if saved(4)<>null then
  @<DIR: Adjust back |text_dir_ptr| for |scan_spec|@>;
replace_attribute_list(cur_box, saved(5)); 
pop_nest; box_end(saved(0));
end;

@ The height of a `\.{\\vtop}' box is inherited from the first item on its list,
if that item is an |hlist_node|, |vlist_node|, or |rule_node|; otherwise
the \.{\\vtop} height is zero.


@<Readjust the height...@>=
begin h:=0; p:=list_ptr(cur_box);
if p<>null then if type(p)<=rule_node then h:=height(p);
depth(cur_box):=depth(cur_box)-h+height(cur_box); height(cur_box):=h;
end

@ Here is a really small patch to add a new primitive called
\.{\\quitvmode}. In vertical modes, it is identical to \.{\\indent},
but in horizontal and math modes it is really a no-op (as opposed to
\.{\\indent}, which executes the |indent_in_hmode| procedure).

A paragraph begins when horizontal-mode material occurs in vertical mode,
or when the paragraph is explicitly started by `\.{\\quitvmode}',
`\.{\\indent}' or `\.{\\noindent}'.

@<Put each...@>=
primitive("indent",start_par,1);
@!@:indent_}{\.{\\indent} primitive@>
primitive("noindent",start_par,0);
@!@:no_indent_}{\.{\\noindent} primitive@>
primitive("quitvmode",start_par,2);
@!@:quit_vmode_}{\.{\\quitvmode} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
start_par: if chr_code=0 then print_esc("noindent")@+ else if chr_code=1 then print_esc("indent")@+ else print_esc("quitvmode");

@ @<Cases of |main_control| that build...@>=
vmode+start_par: new_graf(cur_chr>0);
vmode+letter,vmode+other_char,vmode+char_num,vmode+char_given,
   vmode+char_ghost,
   vmode+math_shift,vmode+un_hbox,vmode+vrule,
   vmode+accent,vmode+discretionary,vmode+hskip,vmode+valign,
   vmode+ex_space,vmode+no_boundary:@t@>@;@/
  begin back_input; new_graf(true);
  end;

@ @<Declare act...@>=
procedure new_graf(@!indented:boolean);
var p,q,dir_graf_tmp:pointer;
begin prev_graf:=0;
if (mode=vmode)or(head<>tail) then begin
  tail_append(new_param_glue(par_skip_code));
  if nest_ptr=0 then
    check_filter('begin_of_par'); 
  end;
push_nest; mode:=hmode; space_factor:=1000; 
@<LOCAL: Add local paragraph node@>;
if indented then begin
  p:=new_null_box; box_dir(p):=par_direction;
  width(p):=par_indent;@+
  tail_append(p);
  end;
q:=tail;
dir_rover:=text_dir_ptr;
while dir_rover<>null do
  begin
  if (vlink(dir_rover)<>null) or (dir_dir(dir_rover)<>par_direction) then
    begin
    dir_graf_tmp:=new_dir(dir_dir(dir_rover));
    vlink(dir_graf_tmp):=vlink(q); vlink(q):=dir_graf_tmp;
    end;
  dir_rover:=vlink(dir_rover);
  end;
q:=head;
while vlink(q)<>null do q:=vlink(q);
tail:=q;
if every_par<>null then begin_token_list(every_par,every_par_text);
if nest_ptr=1 then begin 
  build_page; {put |par_skip| glue on current page}
  end;
end;

@ @<Cases of |main_control| that build...@>=
hmode+start_par,mmode+start_par: if cur_chr<>2 then indent_in_hmode;

@ @<Declare act...@>=
procedure indent_in_hmode;
var p,@!q:pointer;
begin if cur_chr>0 then {\.{\\indent}}
  begin p:=new_null_box; width(p):=par_indent;
  if abs(mode)=hmode then space_factor:=1000
  else  begin q:=new_noad; math_type(nucleus(q)):=sub_box;
    vinfo(nucleus(q)):=p; p:=q;
    end;
  tail_append(p);
  end;
end;

@ A paragraph ends when a |par_end| command is sensed, or when we are in
horizontal mode when reaching the right brace of vertical-mode routines
like \.{\\vbox}, \.{\\insert}, or \.{\\output}.

@<Cases of |main_control| that build...@>=
vmode+par_end: begin normal_paragraph;
  if mode>0 then begin check_filter('vmode_par'); build_page; end;
  end;
hmode+par_end: begin if align_state<0 then off_save; {this tries to
    recover from an alignment that didn't end properly}
  if (mode>0) and (nest[(nest_ptr-1)].mode_field=vmode) then
	  line_break_context:=bottom_level;
  end_graf; {this takes us to the enclosing mode, if |mode>0|}
  if mode=vmode then begin check_filter('hmode_par');  build_page; end;
  end;
hmode+stop,hmode+vskip,hmode+hrule,hmode+un_vbox,hmode+halign: head_for_vmode;

@ @<Declare act...@>=
procedure head_for_vmode;
begin if mode<0 then
  if cur_cmd<>hrule then off_save
  else  begin print_err("You can't use `");
    print_esc("hrule"); print("' here except with leaders");
@.You can't use \\hrule...@>
    help2("To put a horizontal rule in an hbox or an alignment,")@/
      ("you should use \leaders or \hrulefill (see The TeXbook).");
    error;
    end
else  begin back_input; cur_tok:=par_token; back_input; token_type:=inserted;
  end;
end;

@ TODO (BUG?): |dir_save| would have been set by |line_break| by means
of |post_line_break|, but this is not done right now, as it introduces
pretty heavy memory leaks. This means the current code is probably
wrong in some way that relates to in-paragraph displays.
 
@<Declare act...@>=
procedure end_graf;
begin if mode=hmode then
  begin if (head=tail) or (vlink(head)=tail) then pop_nest
        {null paragraphs are ignored, all contain a |local_paragraph| node}
  else line_break(false);
  if dir_save<>null then
    begin flush_node_list(dir_save); dir_save:=null;
    end;
  normal_paragraph;
  error_count:=0;
  end;
end;

@ Insertion and adjustment and mark nodes are constructed by the following
pieces of the program.

@<Cases of |main_control| that build...@>=
any_mode(insert),hmode+vadjust,mmode+vadjust: begin_insert_or_adjust;
any_mode(mark): handle_mark;

@ @<Forbidden...@>=
vmode+vadjust,

@ @<Declare act...@>=
procedure begin_insert_or_adjust;
begin if cur_cmd=vadjust then cur_val:=255
else  begin scan_register_num;
  if cur_val=255 then
    begin print_err("You can't "); print_esc("insert"); print_int(255);
@.You can't \\insert255@>
    help1("I'm changing to \insert0; box 255 is special.");
    error; cur_val:=0;
    end;
  end;
saved(0) := cur_val;
if (cur_cmd = vadjust) and scan_keyword("pre") then
    saved(1) := 1
else
    saved(1) := 0;
save_ptr := save_ptr + 2;
new_save_level(insert_group); scan_left_brace; normal_paragraph;
push_nest; mode:=-vmode; prev_depth:=ignore_depth;
end;

@ @<Cases of |handle...@>=
insert_group: begin
  line_break_context:=insert_group; 
  end_graf; q:=split_top_skip; add_glue_ref(q);
  d:=split_max_depth; f:=floating_penalty; unsave; save_ptr := save_ptr - 2;
  {now |saved(0)| is the insertion number, or 255 for |vadjust|}
  p:=vpack(vlink(head),natural); pop_nest;
  if saved(0)<>255 then
    begin tail_append(new_node(ins_node,saved(0))); 
    height(tail):=height(p)+depth(p); ins_ptr(tail):=list_ptr(p);
    split_top_ptr(tail):=q; depth(tail):=d; float_cost(tail):=f;
    end
  else  begin tail_append(new_node(adjust_node,saved(1))); {the |subtype| is used for |adjust_pre|}
    adjust_ptr(tail):=list_ptr(p); delete_glue_ref(q);
    end;
  list_ptr(p):=null; flush_node(p);
  if nest_ptr=0 then begin check_filter('insert'); build_page; end;
  end;
output_group: @<Resume the page builder...@>;

@ I've renamed the |make_mark| procedure to this, because if the
current chr code is 1, then the actual command was \.{\\clearmarks},
which does not generate a mark node but instead destroys the current
mark tokenlists.

@<Declare act...@>=
procedure handle_mark;
var p:pointer; {new node}
@!c:halfword; {the mark class}
begin if cur_chr=clear_marks_code then begin
    scan_mark_num; c:=cur_val;
    delete_top_mark(c); delete_bot_mark(c); delete_first_mark(c);
    delete_split_first_mark(c); delete_split_bot_mark(c);
  end
else begin
if cur_chr=0 then c:=0
else begin scan_mark_num; c:=cur_val;
  if c > biggest_used_mark then biggest_used_mark := c;
  end;
p:=scan_toks(false,true); 
p:=new_node(mark_node,0); {the |subtype| is not used}
mark_class(p):=c;
mark_ptr(p):=def_ref; vlink(tail):=p; tail:=p;
end;
end;

@ Penalty nodes get into a list via the |break_penalty| command.
@^penalties@>

@<Cases of |main_control| that build...@>=
any_mode(break_penalty): append_penalty;

@ @<Declare action...@>=
procedure append_penalty;
begin scan_int; tail_append(new_penalty(cur_val));
if mode=vmode then begin check_filter('penalty'); build_page; end;
end;

@ The |remove_item| command removes a penalty, kern, or glue node if it
appears at the tail of the current list, using a brute-force linear scan.
Like \.{\\lastbox}, this command is not allowed in vertical mode (except
internal vertical mode), since the current list in vertical mode is sent
to the page builder.  But if we happen to be able to implement it in
vertical mode, we do.

@<Cases of |main_control| that build...@>=
any_mode(remove_item): delete_last;

@ When |delete_last| is called, |cur_chr| is the |type| of node that
will be deleted, if present.

@<Declare action...@>=
procedure delete_last;
label exit;
var @!p,@!q:pointer; {run through the current list}
begin if (mode=vmode)and(tail=head) then
  @<Apologize for inability to do the operation now,
    unless \.{\\unskip} follows non-glue@>
else  begin if not is_char_node(tail) then if type(tail)=cur_chr then
    begin q:=head;
    repeat p:=q;
    if not is_char_node(q) then if type(q)=disc_node then
      begin
      if p=tail then return;
      end;
    q:=vlink(p);
    until q=tail;
    vlink(p):=null; flush_node_list(tail); tail:=p;
    end;
  end;
exit:end;

@ @<Apologize for inability to do the operation...@>=
begin if (cur_chr<>glue_node)or(last_glue<>max_halfword) then
  begin you_cant;
  help2("Sorry...I usually can't take things from the current page.")@/
    ("Try `I\vskip-\lastskip' instead.");
  if cur_chr=kern_node then help_line[0]:=
    ("Try `I\kern-\lastkern' instead.")
  else if cur_chr<>glue_node then help_line[0]:=@|
    ("Perhaps you can make the output routine do it.");
  error;
  end;
end

@ @<Put each...@>=
primitive("unpenalty",remove_item,penalty_node);@/
@!@:un_penalty_}{\.{\\unpenalty} primitive@>
primitive("unkern",remove_item,kern_node);@/
@!@:un_kern_}{\.{\\unkern} primitive@>
primitive("unskip",remove_item,glue_node);@/
@!@:un_skip_}{\.{\\unskip} primitive@>
primitive("unhbox",un_hbox,box_code);@/
@!@:un_hbox_}{\.{\\unhbox} primitive@>
primitive("unhcopy",un_hbox,copy_code);@/
@!@:un_hcopy_}{\.{\\unhcopy} primitive@>
primitive("unvbox",un_vbox,box_code);@/
@!@:un_vbox_}{\.{\\unvbox} primitive@>
primitive("unvcopy",un_vbox,copy_code);@/
@!@:un_vcopy_}{\.{\\unvcopy} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
remove_item: if chr_code=glue_node then print_esc("unskip")
  else if chr_code=kern_node then print_esc("unkern")
  else print_esc("unpenalty");
un_hbox: if chr_code=copy_code then print_esc("unhcopy")
  else print_esc("unhbox");
un_vbox: if chr_code=copy_code then print_esc("unvcopy")
  @<Cases of |un_vbox| for |print_cmd_chr|@>@/
  else print_esc("unvbox");

@ The |un_hbox| and |un_vbox| commands unwrap one of the |number_regs| current boxes.

@<Cases of |main_control| that build...@>=
vmode+un_vbox,hmode+un_hbox,mmode+un_hbox: unpackage;

@ @<Declare act...@>=
procedure unpackage;
label done, exit;
var p:pointer; {the box}
    r: pointer; {to remove marginal kern nodes}
@!c:box_code..copy_code; {should we copy?}
@!s:pointer; {for varmem assignment }
begin if cur_chr>copy_code then @<Handle saved items and |goto done|@>;
c:=cur_chr; scan_register_num; p:=box(cur_val);
if p=null then return;
if (abs(mode)=mmode)or((abs(mode)=vmode)and(type(p)<>vlist_node))or@|
   ((abs(mode)=hmode)and(type(p)<>hlist_node)) then
  begin print_err("Incompatible list can't be unboxed");
@.Incompatible list...@>
  help3("Sorry, Pandora. (You sneaky devil.)")@/
  ("I refuse to unbox an \hbox in vertical mode or vice versa.")@/
  ("And I can't open any boxes in math mode.");@/
  error; return;
  end;
if c=copy_code then begin s:=copy_node_list(list_ptr(p)); vlink(tail):=s; end
else  begin vlink(tail):=list_ptr(p); box(cur_val):=null;
  list_ptr(p):=null; flush_node(p);
  end;
done:
while vlink(tail) <> null do begin
    r := vlink(tail);
    if not is_char_node(r) and (type(r) = margin_kern_node) then begin
        vlink(tail) := vlink(r);
        flush_node(r);
    end;
    tail:=vlink(tail);
end;
exit:end;

@ @<Forbidden...@>=vmode+ital_corr,

@ Italic corrections are converted to kern nodes when the |ital_corr| command
follows a character. In math mode the same effect is achieved by appending
a kern of zero here, since italic corrections are supplied later.

@<Cases of |main_control| that build...@>=
hmode+ital_corr: append_italic_correction;
mmode+ital_corr: tail_append(new_kern(0));

@ @<Declare act...@>=
procedure append_italic_correction;
label exit;
var p:pointer; {|char_node| at the tail of the current list}
@!f:internal_font_number; {the font in the |char_node|}
begin if tail<>head then
  begin if is_char_node(tail) then p:=tail
  else return;
  f:=font(p);
  tail_append(new_kern(char_italic(f,character(p))));
  subtype(tail):=explicit;
  end;
exit:end;

@ Discretionary nodes are easy in the common case `\.{\\-}', but in the
general case we must process three braces full of items.

There are four subtypes of discretionaries, but only the first two are
generated by primitive commands.

@d discretionary_disc=0
@d explicit_disc=1

@<Put each...@>=
primitive("-",discretionary,explicit_disc);
@!@:Single-character primitives -}{\quad\.{\\-}@>
primitive("discretionary",discretionary,discretionary_disc);
@!@:discretionary_}{\.{\\discretionary} primitive@>
primitive("localleftbox",assign_local_box,0);
@!@:assign_local_box}{\.{\\localleftbox} primitive@>
primitive("localrightbox",assign_local_box,1);
@!@:assign_local_box}{\.{\\localrightbox} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
discretionary: if chr_code=explicit_disc then
  print_esc("-")@+else print_esc("discretionary");
assign_local_box: if chr_code=0 then print_esc("localleftbox")
                  else print_esc("localrightbox");

@ @<Cases of |main_control| that build...@>=
hmode+discretionary,mmode+discretionary: append_discretionary;
any_mode(assign_local_box): append_local_box(cur_chr);

@ The space factor does not change when we append a discretionary node,
but it starts out as 1000 in the subsidiary lists.

@<Declare act...@>=
procedure append_local_box(kind:integer);
begin 
incr(save_ptr); saved(-1):=kind; new_save_level(local_box_group);
scan_left_brace; push_nest; mode:=-hmode; space_factor:=1000;
end;

procedure append_discretionary;
var c:integer;
begin tail_append(new_disc);
subtype(tail):=cur_chr;
if cur_chr=explicit_disc then begin 
    c:=get_pre_hyphen_char(cur_lang);
    if c<>0 then begin 
   	  vlink(pre_break(tail)):=new_char(cur_font,c);
      alink(vlink(pre_break(tail))):=pre_break(tail);
   	  tlink(pre_break(tail)):=vlink(pre_break(tail));
      end;
    c:=get_post_hyphen_char(cur_lang);
    if c<>0 then begin
       vlink(post_break(tail)):=new_char(cur_font,c);
       alink(vlink(post_break(tail))):=post_break(tail);
       tlink(post_break(tail)):=vlink(post_break(tail));
       end;
    end
else  begin incr(save_ptr); saved(-1):=0; new_save_level(disc_group);
  scan_left_brace; push_nest; mode:=-hmode; space_factor:=1000;
  end;
end;

@ The three discretionary lists are constructed somewhat as if they were
hboxes. A~subroutine called |build_discretionary| handles the transitions.
(This is sort of fun.)

@<Cases of |handle...@>=
disc_group: build_discretionary;
local_box_group: build_local_box;

@ @<Declare act...@>=
procedure build_local_box;
var p:pointer;
    kind:integer;
begin
unsave;
kind:=saved(-1);
decr(save_ptr);
p:=vlink(head); pop_nest;
p:=hpack(p,natural);
if kind=0 then
  eq_define(local_left_box_base,box_ref,p)
else
  eq_define(local_right_box_base,box_ref,p);
if abs(mode)=hmode then
  @<LOCAL: Add local paragraph node@>;
eq_word_define(int_base+no_local_whatsits_code,no_local_whatsits+1);
end;

procedure build_discretionary;
label done,exit;
var p,@!q:pointer; {for link manipulation}
@!n:integer; {length of discretionary list}
begin unsave;
@<Prune the current list, if necessary, until it contains only
  |char_node|, |kern_node|, |hlist_node|, |vlist_node| and 
  |rule_node| items; set |n| to the length of the list,
  and set |q| to the list's tail@>;
p:=vlink(head); pop_nest;
case saved(-1) of
0: if (n>0) then begin 
   vlink(pre_break(tail)):=p; 
   alink(p):=pre_break(tail);
   tlink(pre_break(tail)):=q; 
   end;
1: if (n>0) then begin
   vlink(post_break(tail)):=p;
   alink(p):=post_break(tail);
   tlink(post_break(tail)):=q; 
   end;
2:@<Attach list |p| to the current list, and record its length;
  then finish up and |return|@>;
end; {there are no other cases}
incr(saved(-1)); new_save_level(disc_group); scan_left_brace;
push_nest; mode:=-hmode; space_factor:=1000;
exit:end;

@ @<Attach list |p| to the current...@>=
begin if (n>0)and(abs(mode)=mmode) then
  begin print_err("Illegal math "); print_esc("discretionary");
@.Illegal math \\disc...@>
  help2("Sorry: The third part of a discretionary break must be")@/
  ("empty, in math formulas. I had to delete your third part.");
  flush_node_list(p); error;
  end
else begin 
  if (n>0) then begin  
    vlink(no_break(tail)):=p;
    alink(p):=no_break(tail);
    tlink(no_break(tail)):=q; 
    end;
  end;
decr(save_ptr); return;
end

@ During this loop, |p=vlink(q)| and there are |n| items preceding |p|.

@<Prune the current list, if necessary...@>=
q:=head; p:=vlink(q); n:=0;
while p<>null do
  begin if not is_char_node(p) then if type(p)<>disc_node then
    if type(p)>rule_node then if type(p)<>kern_node then 
      begin print_err("Improper discretionary list");
@.Improper discretionary list@>
      help1("Discretionary lists must contain only boxes and kerns.");@/
      error;
      begin_diagnostic;
      print_nl("The following discretionary sublist has been deleted:");
@.The following...deleted@>
      show_box(p);
      end_diagnostic(true);
      flush_node_list(p); vlink(q):=null; goto done;
      end;
  q:=p; p:=vlink(q); incr(n);
  end;
done:

@ We need only one more thing to complete the horizontal mode routines, namely
the \.{\\accent} primitive.

@<Cases of |main_control| that build...@>=
hmode+accent: make_accent;

@ The positioning of accents is straightforward but tedious. Given an accent
of width |a|, designed for characters of height |x| and slant |s|;
and given a character of width |w|, height |h|, and slant |t|: We will shift
the accent down by |x-h|, and we will insert kern nodes that have the effect of
centering the accent over the character and shifting the accent to the
right by $\delta={1\over2}(w-a)+h\cdot t-x\cdot s$.  If either character is
absent from the font, we will simply use the other, without shifting.

@<Declare act...@>=
procedure make_accent;
var s,@!t: real; {amount of slant}
@!p,@!q,@!r:pointer; {character, box, and kern nodes}
@!f:internal_font_number; {relevant font}
@!a,@!h,@!x,@!w,@!delta:scaled; {heights and widths, as explained above}
begin scan_char_num; f:=cur_font; p:=new_glyph(f,cur_val);
if p<>null then
  begin x:=x_height(f); s:=slant(f)/float_constant(65536);
@^real division@>
  a:=glyph_width(p);@/
  do_assignments;@/
  @<Create a character node |q| for the next character,
    but set |q:=null| if problems arise@>;
  if q<>null then @<Append the accent with appropriate kerns,
      then set |p:=q|@>;
  vlink(tail):=p; tail:=p; space_factor:=1000;
  end;
end;

@ @<Create a character node |q| for the next...@>=
q:=null; f:=cur_font;
if (cur_cmd=letter)or(cur_cmd=other_char)or(cur_cmd=char_given) then
  q:=new_glyph(f,cur_chr)
else if cur_cmd=char_num then
  begin scan_char_num; q:=new_glyph(f,cur_val);
  end
else back_input

@ The kern nodes appended here must be distinguished from other kerns, lest
they be wiped away by the hyphenation algorithm or by a previous line break.

The two kerns are computed with (machine-dependent) |real| arithmetic, but
their sum is machine-independent; the net effect is machine-independent,
because the user cannot remove these nodes nor access them via \.{\\lastkern}.

@<Append the accent with appropriate kerns...@>=
begin t:=slant(f)/float_constant(65536);
@^real division@>
w:=glyph_width(q); 
h:=glyph_height(q);
if h<>x then {the accent must be shifted up or down}
  begin p:=hpack(p,natural); shift_amount(p):=x-h;
  end;
delta:=round((w-a)/float_constant(2)+h*t-x*s);
@^real multiplication@>
@^real addition@>
r:=new_kern(delta); subtype(r):=acc_kern; vlink(tail):=r; vlink(r):=p;
tail:=new_kern(-a-delta); subtype(tail):=acc_kern; vlink(p):=tail; p:=q;
end

@ When `\.{\\cr}' or `\.{\\span}' or a tab mark comes through the scanner
into |main_control|, it might be that the user has foolishly inserted
one of them into something that has nothing to do with alignment. But it is
far more likely that a left brace or right brace has been omitted, since
|get_next| takes actions appropriate to alignment only when `\.{\\cr}'
or `\.{\\span}' or tab marks occur with |align_state=0|. The following
program attempts to make an appropriate recovery.

@<Cases of |main_control| that build...@>=
any_mode(car_ret), any_mode(tab_mark): align_error;
any_mode(no_align): no_align_error;
any_mode(omit): omit_error;

@ @<Declare act...@>=
procedure align_error;
begin if abs(align_state)>2 then
  @<Express consternation over the fact that no alignment is in progress@>
else  begin back_input;
  if align_state<0 then
    begin print_err("Missing { inserted");
@.Missing \{ inserted@>
    incr(align_state); cur_tok:=left_brace_token+"{";
    end
  else  begin print_err("Missing } inserted");
@.Missing \} inserted@>
    decr(align_state); cur_tok:=right_brace_token+"}";
    end;
  help3("I've put in what seems to be necessary to fix")@/
    ("the current column of the current alignment.")@/
    ("Try to go on, since this might almost work."); ins_error;
  end;
end;

@ @<Express consternation...@>=
begin print_err("Misplaced "); print_cmd_chr(cur_cmd,cur_chr);
@.Misplaced \&@>
@.Misplaced \\span@>
@.Misplaced \\cr@>
if cur_tok=tab_token+"&" then
  begin help6("I can't figure out why you would want to use a tab mark")@/
  ("here. If you just want an ampersand, the remedy is")@/
  ("simple: Just type `I\&' now. But if some right brace")@/
  ("up above has ended a previous alignment prematurely,")@/
  ("you're probably due for more error messages, and you")@/
  ("might try typing `S' now just to see what is salvageable.");
  end
else  begin help5("I can't figure out why you would want to use a tab mark")@/
  ("or \cr or \span just now. If something like a right brace")@/
  ("up above has ended a previous alignment prematurely,")@/
  ("you're probably due for more error messages, and you")@/
  ("might try typing `S' now just to see what is salvageable.");
  end;
error;
end

@ The help messages here contain a little white lie, since \.{\\noalign}
and \.{\\omit} are allowed also after `\.{\\noalign\{...\}}'.

@<Declare act...@>=
procedure no_align_error;
begin print_err("Misplaced "); print_esc("noalign");
@.Misplaced \\noalign@>
help2("I expect to see \noalign only after the \cr of")@/
  ("an alignment. Proceed, and I'll ignore this case."); error;
end;
procedure omit_error;
begin print_err("Misplaced "); print_esc("omit");
@.Misplaced \\omit@>
help2("I expect to see \omit only after tab marks or the \cr of")@/
  ("an alignment. Proceed, and I'll ignore this case."); error;
end;

@ We've now covered most of the abuses of \.{\\halign} and \.{\\valign}.
Let's take a look at what happens when they are used correctly.

@<Cases of |main_control| that build...@>=
vmode+halign,hmode+valign:init_align;
mmode+halign: if privileged then
  if cur_group=math_shift_group then init_align
  else off_save;
vmode+endv,hmode+endv: do_endv;

@ An |align_group| code is supposed to remain on the |save_stack|
during an entire alignment, until |fin_align| removes it.

A devious user might force an |endv| command to occur just about anywhere;
we must defeat such hacks.

@<Declare act...@>=
procedure do_endv;
begin base_ptr:=input_ptr; input_stack[base_ptr]:=cur_input;
while (input_stack[base_ptr].index_field<>v_template) and
      (input_stack[base_ptr].loc_field=null) and
      (input_stack[base_ptr].state_field=token_list) do decr(base_ptr);
if (input_stack[base_ptr].index_field<>v_template) or
      (input_stack[base_ptr].loc_field<>null) or
      (input_stack[base_ptr].state_field<>token_list) then
  fatal_error("(interwoven alignment preambles are not allowed)");
@.interwoven alignment preambles...@>
 if cur_group=align_group then
  begin line_break_context:=align_group; end_graf;
  if fin_col then fin_row;
  end
else off_save;
end;

@ @<Cases of |handle_right_brace|...@>=
align_group: begin back_input; cur_tok:=cs_token_flag+frozen_cr;
  print_err("Missing "); print_esc("cr"); print(" inserted");
@.Missing \\cr inserted@>
  help1("I'm guessing that you meant to end an alignment here.");
  ins_error;
  end;

@ @<Cases of |handle_right_brace|...@>=
no_align_group: begin line_break_context:=no_align_group; end_graf; unsave; align_peek;
  end;

@ Finally, \.{\\endcsname} is not supposed to get through to |main_control|.

@<Cases of |main_control| that build...@>=
any_mode(end_cs_name): cs_error;

@ @<Declare act...@>=
procedure cs_error;
begin print_err("Extra "); print_esc("endcsname");
@.Extra \\endcsname@>
help1("I'm ignoring this, since I wasn't doing a \csname.");
error;
end;

@* \[48] Building math lists.
The routines that \TeX\ uses to create mlists are similar to those we have
just seen for the generation of hlists and vlists. But it is necessary to
make ``noads'' as well as nodes, so the reader should review the
discussion of math mode data structures before trying to make sense out of
the following program.

Here is a little routine that needs to be done whenever a subformula
is about to be processed. The parameter is a code like |math_group|.

@<Declare act...@>=
procedure push_math(@!c:group_code);
begin
if math_direction<>text_direction then dir_math_save:=true;
push_nest; mode:=-mmode; incompleat_noad:=null;
@<DIR: |new_save_level| math@>;
end;

@ We get into math mode from horizontal mode when a `\.\$' (i.e., a
|math_shift| character) is scanned. We must check to see whether this
`\.\$' is immediately followed by another, in case display math mode is
called for.

@<Cases of |main_control| that build...@>=
hmode+math_shift:init_math;

@ @<Declare act...@>=
procedure init_math;
label found,not_found,done;
var w:scaled; {new or partial |pre_display_size|}
@!l:scaled; {new |display_width|}
@!s:scaled; {new |display_indent|}
@!p:pointer; {current node when calculating |pre_display_size|}
@!q:pointer; {glue specification when calculating |pre_display_size|}
@!f:internal_font_number; {font in current |char_node|}
@!n:integer; {scope of paragraph shape specification}
@!v:scaled; {|w| plus possible glue amount}
@!d:scaled; {increment to |v|}
begin get_token; {|get_x_token| would fail on \.{\\ifmmode}\thinspace!}
if (cur_cmd=math_shift)and(mode>0) then @<Go into display math mode@>
else  begin back_input; @<Go into ordinary math mode@>;
  end;
end;

@ @<Go into ordinary math mode@>=
begin push_math(math_shift_group); eq_word_define(int_base+cur_fam_code,-1);
if every_math<>null then begin_token_list(every_math,every_math_text);
end

@ We get into ordinary math mode from display math mode when `\.{\\eqno}' or
`\.{\\leqno}' appears. In such cases |cur_chr| will be 0 or~1, respectively;
the value of |cur_chr| is placed onto |save_stack| for safe keeping.

@<Cases of |main_control| that build...@>=
mmode+eq_no: if privileged then
  if cur_group=math_shift_group then start_eq_no
  else off_save;

@ @<Put each...@>=
primitive("eqno",eq_no,0);
@!@:eq_no_}{\.{\\eqno} primitive@>
primitive("leqno",eq_no,1);
@!@:leq_no_}{\.{\\leqno} primitive@>

@ When \TeX\ is in display math mode, |cur_group=math_shift_group|,
so it is not necessary for the |start_eq_no| procedure to test for
this condition.

@<Declare act...@>=
procedure start_eq_no;
begin saved(0):=cur_chr; incr(save_ptr);
@<Go into ordinary math mode@>;
end;

@ @<Cases of |print_cmd_chr|...@>=
eq_no:if chr_code=1 then print_esc("leqno")@+else print_esc("eqno");

@ @<Forbidden...@>=non_math(eq_no),

@ When we enter display math mode, we need to call |line_break| to
process the partial paragraph that has just been interrupted by the
display. Then we can set the proper values of |display_width| and
|display_indent| and |pre_display_size|.

@<Go into display math mode@>=
begin if head=tail then {`\.{\\noindent\$\$}' or `\.{\$\${ }\$\$}'}
  begin pop_nest; w:=-max_dimen;
  end
else  begin 
  line_break(true);@/
  @<Calculate the natural width, |w|, by which the characters of the
    final line extend to the right of the reference point,
    plus two ems; or set |w:=max_dimen| if the non-blank information
    on that line is affected by stretching or shrinking@>;
  end;
{now we are in vertical mode, working on the list that will contain the display}
@<Calculate the length, |l|, and the shift amount, |s|, of the display lines@>;
push_math(math_shift_group); mode:=mmode;
eq_word_define(int_base+cur_fam_code,-1);@/
eq_word_define(dimen_base+pre_display_size_code,w);
eq_word_define(dimen_base+display_width_code,l);
eq_word_define(dimen_base+display_indent_code,s);
if every_display<>null then begin_token_list(every_display,every_display_text);
if nest_ptr=1 then begin check_contrib_filter('before_display'); build_page; end;
end

@ @<Calculate the natural width, |w|, by which...@>=
v:=shift_amount(just_box)+2*quad(cur_font); w:=-max_dimen;
p:=list_ptr(just_box);
while p<>null do
  begin @<Let |d| be the natural width of node |p|;
    if the node is ``visible,'' |goto found|;
    if the node is glue that stretches or shrinks, set |v:=max_dimen|@>;
  if v<max_dimen then v:=v+d;
  goto not_found;
  found: if v<max_dimen then
    begin v:=v+d; w:=v;
    end
  else  begin w:=max_dimen; goto done;
    end;
  not_found: p:=vlink(p);
  end;
done:

@ @<Let |d| be the natural width of node |p|...@>=
if is_char_node(p) then
  begin f:=font(p); d:=glyph_width(p);
  goto found;
  end;
case type(p) of
hlist_node,vlist_node,rule_node: begin d:=width(p); goto found;
  end;
margin_kern_node: d:=width(p);
kern_node: d:=width(p);
math_node: d:=surround(p);
glue_node:@<Let |d| be the natural width of this glue; if stretching
  or shrinking, set |v:=max_dimen|; |goto found| in the case of leaders@>;
whatsit_node: @<Let |d| be the width of the whatsit |p|@>;
othercases d:=0
endcases

@ We need to be careful that |w|, |v|, and |d| do not depend on any |glue_set|
values, since such values are subject to system-dependent rounding.
System-dependent numbers are not allowed to infiltrate parameters like
|pre_display_size|, since \TeX82 is supposed to make the same decisions on all
machines.

@<Let |d| be the natural width of this glue...@>=
begin q:=glue_ptr(p); d:=width(q);
if glue_sign(just_box)=stretching then
  begin if (glue_order(just_box)=stretch_order(q))and@|
     (stretch(q)<>0) then
    v:=max_dimen;
  end
else if glue_sign(just_box)=shrinking then
  begin if (glue_order(just_box)=shrink_order(q))and@|
     (shrink(q)<>0) then
    v:=max_dimen;
  end;
if subtype(p)>=a_leaders then goto found;
end

@ A displayed equation is considered to be three lines long, so we
calculate the length and offset of line number |prev_graf+2|.

@<Calculate the length, |l|, ...@>=
if par_shape_ptr=null then
  if (hang_indent<>0)and@|
   (((hang_after>=0)and(prev_graf+2>hang_after))or@|
    (prev_graf+1<-hang_after)) then
    begin l:=hsize-abs(hang_indent);
    if hang_indent>0 then s:=hang_indent@+else s:=0;
    end
  else  begin l:=hsize; s:=0;
    end
else  begin n:=vinfo(par_shape_ptr);
  if prev_graf+2>=n then p:=par_shape_ptr+2*n
  else p:=par_shape_ptr+2*(prev_graf+2);
  s:=vmem(p-1).sc; l:=vmem(p).sc;
  end

@ Subformulas of math formulas cause a new level of math mode to be entered,
on the semantic nest as well as the save stack. These subformulas arise in
several ways: (1)~A left brace by itself indicates the beginning of a
subformula that will be put into a box, thereby freezing its glue and
preventing line breaks. (2)~A subscript or superscript is treated as a
subformula if it is not a single character; the same applies to
the nucleus of things like \.{\\underline}. (3)~The \.{\\left} primitive
initiates a subformula that will be terminated by a matching \.{\\right}.
The group codes placed on |save_stack| in these three cases are
|math_group|, |math_group|, and |math_left_group|, respectively.

Here is the code that handles case (1); the other cases are not quite as
trivial, so we shall consider them later.

@<Cases of |main_control| that build...@>=
mmode+left_brace: begin tail_append(new_noad);
  back_input; scan_math(nucleus(tail));
  end;

@ Recall that the |nucleus|, |subscr|, and |supscr| fields in a noad are
broken down into subfields called |math_type| and either |info| or
|(fam,character)|. The job of |scan_math| is to figure out what to place
in one of these principal fields; it looks at the subformula that
comes next in the input, and places an encoding of that subformula
into a given word of |mem|.

@d fam_in_range==((cur_fam>=0)and(cur_fam<256))

@<Declare act...@>=
@t\4@>@<Declare the function called |fin_mlist|@>@t@>@;@/

procedure scan_math(@!p:pointer);
label restart,reswitch,exit;
var c:integer; {math character code}
begin restart:@<Get the next non-blank non-relax...@>;
reswitch:case cur_cmd of
letter,other_char,char_given: begin c:=get_math_code(cur_chr);
   if c=@"8000000 then
      begin @<Treat |cur_chr| as an active character@>;
      goto restart;
      end;
    end;
char_num: begin scan_char_num; cur_chr:=cur_val; cur_cmd:=char_given;
  goto reswitch;
  end;
math_char_num: begin
  if cur_chr=0 then scan_fifteen_bit_int
  else scan_big_fifteen_bit_int;
  c:=cur_val;
  end;
math_given: begin
  c := ((cur_chr div @"1000) * @"1000000) +
         (((cur_chr mod @"1000) div @"100) * @"10000) +
         (cur_chr mod @"100);
  end;
omath_given: begin c:=cur_chr;
  end;
delim_num: begin
  if cur_chr=0 then scan_twenty_seven_bit_int
  else scan_fifty_one_bit_int;
  c:=cur_val;
  end;
othercases @<Scan a subformula enclosed in braces and |return|@>
endcases;@/
math_type(p):=math_char; mcharacter(p):=qi(c mod @"10000);
if (c>=var_code)and fam_in_range then fam(p):=cur_fam
else fam(p):=(c div @"10000) mod @"100;
exit:end;

@ An active character that is an |outer_call| is allowed here.

@<Treat |cur_chr|...@>=
begin cur_cs:=(cur_chr mod number_active_chars)+active_base;
cur_cmd:=eq_type(cur_cs); cur_chr:=equiv(cur_cs);
x_token; back_input;
end

@ The pointer |p| is placed on |save_stack| while a complex subformula
is being scanned.

@<Scan a subformula...@>=
begin back_input; scan_left_brace;@/
saved(0):=p; incr(save_ptr); push_math(math_group); return;
end

@ The simplest math formula is, of course, `\.{\${ }\$}', when no noads are
generated. The next simplest cases involve a single character, e.g.,
`\.{\$x\$}'. Even though such cases may not seem to be very interesting,
the reader can perhaps understand how happy the author was when `\.{\$x\$}'
was first properly typeset by \TeX. The code in this section was used.
@^Knuth, Donald Ervin@>

@<Cases of |main_control| that build...@>=
mmode+letter,mmode+other_char,mmode+char_given:
  set_math_char(get_math_code(cur_chr));
mmode+char_num: begin scan_char_num; cur_chr:=cur_val;
  set_math_char(get_math_code(cur_chr));
  end;
mmode+math_char_num: begin
  if cur_chr=0 then scan_fifteen_bit_int
  else scan_big_fifteen_bit_int;
  set_math_char(cur_val);
  end;
mmode+math_given: begin
  set_math_char(((cur_chr div @"1000) * @"1000000) +
                (((cur_chr mod @"1000) div @"100) * @"10000) +
                (cur_chr mod @"100));
  end;
mmode+omath_given: set_math_char(cur_chr);
mmode+delim_num: begin
  if cur_chr=0 then scan_twenty_seven_bit_int
  else scan_fifty_one_bit_int;
  set_math_char(cur_val);
  end;

@ The |set_math_char| procedure creates a new noad appropriate to a given
math code, and appends it to the current mlist. However, if the math code
is sufficiently large, the |cur_chr| is treated as an active character and
nothing is appended.

@<Declare act...@>=
procedure set_math_char(@!c:integer);
var p:pointer; {the new noad}
begin if c>=@"8000000 then
  @<Treat |cur_chr|...@>
else  begin p:=new_noad; math_type(nucleus(p)):=math_char;
  mcharacter(nucleus(p)):=qi(c mod @"10000);
  fam(nucleus(p)):=(c div @"10000) mod @"100;
  if c>=var_code then
    begin if fam_in_range then fam(nucleus(p)):=cur_fam;
    type(p):=ord_noad;
    end
  else
    type(p):=ord_noad+(c div @"1000000);
  vlink(tail):=p; tail:=p;
  end;
end;

@ Primitive math operators like \.{\\mathop} and \.{\\underline} are given
the command code |math_comp|, supplemented by the noad type that they
generate.

@<Put each...@>=
primitive("mathord",math_comp,ord_noad);
@!@:math_ord_}{\.{\\mathord} primitive@>
primitive("mathop",math_comp,op_noad);
@!@:math_op_}{\.{\\mathop} primitive@>
primitive("mathbin",math_comp,bin_noad);
@!@:math_bin_}{\.{\\mathbin} primitive@>
primitive("mathrel",math_comp,rel_noad);
@!@:math_rel_}{\.{\\mathrel} primitive@>
primitive("mathopen",math_comp,open_noad);
@!@:math_open_}{\.{\\mathopen} primitive@>
primitive("mathclose",math_comp,close_noad);
@!@:math_close_}{\.{\\mathclose} primitive@>
primitive("mathpunct",math_comp,punct_noad);
@!@:math_punct_}{\.{\\mathpunct} primitive@>
primitive("mathinner",math_comp,inner_noad);
@!@:math_inner_}{\.{\\mathinner} primitive@>
primitive("underline",math_comp,under_noad);
@!@:underline_}{\.{\\underline} primitive@>
primitive("overline",math_comp,over_noad);@/
@!@:overline_}{\.{\\overline} primitive@>
primitive("displaylimits",limit_switch,normal);
@!@:display_limits_}{\.{\\displaylimits} primitive@>
primitive("limits",limit_switch,limits);
@!@:limits_}{\.{\\limits} primitive@>
primitive("nolimits",limit_switch,no_limits);
@!@:no_limits_}{\.{\\nolimits} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
math_comp: case chr_code of
  ord_noad: print_esc("mathord");
  op_noad: print_esc("mathop");
  bin_noad: print_esc("mathbin");
  rel_noad: print_esc("mathrel");
  open_noad: print_esc("mathopen");
  close_noad: print_esc("mathclose");
  punct_noad: print_esc("mathpunct");
  inner_noad: print_esc("mathinner");
  under_noad: print_esc("underline");
  othercases print_esc("overline")
  endcases;
limit_switch: if chr_code=limits then print_esc("limits")
  else if chr_code=no_limits then print_esc("nolimits")
  else print_esc("displaylimits");

@ @<Cases of |main_control| that build...@>=
mmode+math_comp: begin tail_append(new_noad);
  type(tail):=cur_chr; scan_math(nucleus(tail));
  end;
mmode+limit_switch: math_limit_switch;

@ @<Declare act...@>=
procedure math_limit_switch;
label exit;
begin if head<>tail then if type(tail)=op_noad then
  begin subtype(tail):=cur_chr; return;
  end;
print_err("Limit controls must follow a math operator");
@.Limit controls must follow...@>
help1("I'm ignoring this misplaced \limits or \nolimits command."); error;
exit:end;

@ Delimiter fields of noads are filled in by the |scan_delimiter| routine.
The first parameter of this procedure is the |mem| address where the
delimiter is to be placed; the second tells if this delimiter follows
\.{\\radical} or not.

@<Declare act...@>=
procedure scan_delimiter(@!p:pointer;@!r:integer);
begin if r=1 then scan_twenty_seven_bit_int
else if r=2 then scan_fifty_one_bit_int
else  begin @<Get the next non-blank non-relax...@>;
  case cur_cmd of
  letter,other_char: begin
    cur_val:=get_del_code_a(cur_chr); cur_val1:=get_del_code_b(cur_chr);
    end;
  delim_num: if cur_chr=0 then scan_twenty_seven_bit_int
             else scan_fifty_one_bit_int;
  othercases begin cur_val:=-1; cur_val1:=-1; end;
  endcases;
  end;
if cur_val<0 then begin @<Report that an invalid delimiter code is being changed
   to null; set~|cur_val:=0|@>;
 cur_val1:=0;
 end;
small_fam(p):=(cur_val div @"10000) mod @"100;
small_char(p):=qi(cur_val mod @"10000);
large_fam(p):=(cur_val1 div @"10000) mod @"100;
large_char(p):=qi(cur_val1 mod @"10000);
end;

@ @<Report that an invalid delimiter...@>=
begin print_err("Missing delimiter (. inserted)");
@.Missing delimiter...@>
help6("I was expecting to see something like `(' or `\{' or")@/
  ("`\}' here. If you typed, e.g., `{' instead of `\{', you")@/
  ("should probably delete the `{' by typing `1' now, so that")@/
  ("braces don't get unbalanced. Otherwise just proceed.")@/
  ("Acceptable delimiters are characters whose \delcode is")@/
  ("nonnegative, or you can use `\delimiter <delimiter code>'.");
back_error; cur_val:=0;
end

@ @<Cases of |main_control| that build...@>=
mmode+radical:math_radical;

@ @<Declare act...@>=
procedure math_radical;
begin tail_append(new_node(radical_noad,normal));
vmem(nucleus(tail)).hh:=empty_field;
vmem(subscr(tail)).hh:=empty_field;
vmem(supscr(tail)).hh:=empty_field;
scan_delimiter(left_delimiter(tail),cur_chr+1);
scan_math(nucleus(tail));
end;

@ @<Cases of |main_control| that build...@>=
mmode+accent,mmode+math_accent:math_ac;

@ @<Declare act...@>=
procedure math_ac;
begin if cur_cmd=accent then
  @<Complain that the user should have said \.{\\mathaccent}@>;
tail_append(new_node(accent_noad,normal));
vmem(nucleus(tail)).hh:=empty_field;
vmem(subscr(tail)).hh:=empty_field;
vmem(supscr(tail)).hh:=empty_field;
math_type(accent_chr(tail)):=math_char;
if cur_chr=0 then scan_fifteen_bit_int
else scan_big_fifteen_bit_int;
mcharacter(accent_chr(tail)):=qi(cur_val mod @"1000);
if (cur_val>=var_code)and fam_in_range then fam(accent_chr(tail)):=cur_fam
else fam(accent_chr(tail)):=(cur_val div @"10000) mod @"100;
scan_math(nucleus(tail));
end;

@ @<Complain that the user should have said \.{\\mathaccent}@>=
begin print_err("Please use "); print_esc("mathaccent");
print(" for accents in math mode");
@.Please use \\mathaccent...@>
help2("I'm changing \accent to \mathaccent here; wish me luck.")@/
  ("(Accents are not the same in formulas as they are in text.)");
error;
end

@ @<Cases of |main_control| that build...@>=
mmode+vcenter: begin scan_spec(vcenter_group,false); normal_paragraph;
  push_nest; mode:=-vmode; prev_depth:=ignore_depth;
  if every_vbox<>null then begin_token_list(every_vbox,every_vbox_text);
  end;

@ @<Cases of |handle...@>=
vcenter_group: begin line_break_context:=vcenter_group; end_graf; unsave; save_ptr:=save_ptr-2;
  p:=vpack(vlink(head),saved(1),saved(0)); pop_nest;
  tail_append(new_noad); type(tail):=vcenter_noad;
  math_type(nucleus(tail)):=sub_box; vinfo(nucleus(tail)):=p;
  end;

@ The routine that inserts a |style_node| holds no surprises.

@<Put each...@>=
primitive("displaystyle",math_style,display_style);
@!@:display_style_}{\.{\\displaystyle} primitive@>
primitive("textstyle",math_style,text_style);
@!@:text_style_}{\.{\\textstyle} primitive@>
primitive("scriptstyle",math_style,script_style);
@!@:script_style_}{\.{\\scriptstyle} primitive@>
primitive("scriptscriptstyle",math_style,script_script_style);
@!@:script_script_style_}{\.{\\scriptscriptstyle} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
math_style: print_style(chr_code);

@ @<Cases of |main_control| that build...@>=
mmode+math_style: tail_append(new_style(cur_chr));
mmode+non_script: begin tail_append(new_glue(zero_glue));
  subtype(tail):=cond_math_glue;
  end;
mmode+math_choice: append_choices;

@ The routine that scans the four mlists of a \.{\\mathchoice} is very
much like the routine that builds discretionary nodes.

@<Declare act...@>=
procedure append_choices;
begin tail_append(new_choice); incr(save_ptr); saved(-1):=0;
push_math(math_choice_group); scan_left_brace;
end;

@ @<Cases of |handle_right_brace|...@>=
math_choice_group: build_choices;

@ @<Declare act...@>=
procedure build_choices;
label exit;
var p:pointer; {the current mlist}
begin @<DIR: |unsave| math@>; p:=fin_mlist(null);
case saved(-1) of
0:display_mlist(tail):=p;
1:text_mlist(tail):=p;
2:script_mlist(tail):=p;
3:begin script_script_mlist(tail):=p; decr(save_ptr); return;
  end;
end; {there are no other cases}
incr(saved(-1)); push_math(math_choice_group); scan_left_brace;
exit:end;

@ Subscripts and superscripts are attached to the previous nucleus by the
@^superscripts@>@^subscripts@>
action procedure called |sub_sup|. We use the facts that |sub_mark=sup_mark+1|
and |subscr(p)=supscr(p)+1|.

@<Cases of |main_control| that build...@>=
mmode+sub_mark,mmode+sup_mark: sub_sup;

@ @<Declare act...@>=
procedure sub_sup;
var t:small_number; {type of previous sub/superscript}
@!p:pointer; {field to be filled by |scan_math|}
begin t:=empty; p:=null;
if tail<>head then if scripts_allowed(tail) then
  begin p:=supscr(tail)+cur_cmd-sup_mark; {|supscr| or |subscr|}
  t:=math_type(p);
  end;
if (p=null)or(t<>empty) then @<Insert a dummy noad to be sub/superscripted@>;
scan_math(p);
end;

@ @<Insert a dummy...@>=
begin tail_append(new_noad);
p:=supscr(tail)+cur_cmd-sup_mark; {|supscr| or |subscr|}
if t<>empty then
  begin if cur_cmd=sup_mark then
    begin print_err("Double superscript");
@.Double superscript@>
    help1("I treat `x^1^2' essentially like `x^1{}^2'.");
    end
  else  begin print_err("Double subscript");
@.Double subscript@>
    help1("I treat `x_1_2' essentially like `x_1{}_2'.");
    end;
  error;
  end;
end

@ An operation like `\.{\\over}' causes the current mlist to go into a
state of suspended animation: |incompleat_noad| points to a |fraction_noad|
that contains the mlist-so-far as its numerator, while the denominator
is yet to come. Finally when the mlist is finished, the denominator will
go into the incompleat fraction noad, and that noad will become the
whole formula, unless it is surrounded by `\.{\\left}' and `\.{\\right}'
delimiters.

@d above_code=0 { `\.{\\above}' }
@d over_code=1 { `\.{\\over}' }
@d atop_code=2 { `\.{\\atop}' }
@d delimited_code=3 { `\.{\\abovewithdelims}', etc.}

@<Put each...@>=
primitive("above",above,above_code);@/
@!@:above_}{\.{\\above} primitive@>
primitive("over",above,over_code);@/
@!@:over_}{\.{\\over} primitive@>
primitive("atop",above,atop_code);@/
@!@:atop_}{\.{\\atop} primitive@>
primitive("abovewithdelims",above,delimited_code+above_code);@/
@!@:above_with_delims_}{\.{\\abovewithdelims} primitive@>
primitive("overwithdelims",above,delimited_code+over_code);@/
@!@:over_with_delims_}{\.{\\overwithdelims} primitive@>
primitive("atopwithdelims",above,delimited_code+atop_code);
@!@:atop_with_delims_}{\.{\\atopwithdelims} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
above: case chr_code of
  over_code:print_esc("over");
  atop_code:print_esc("atop");
  delimited_code+above_code:print_esc("abovewithdelims");
  delimited_code+over_code:print_esc("overwithdelims");
  delimited_code+atop_code:print_esc("atopwithdelims");
  othercases print_esc("above")
  endcases;

@ @<Cases of |main_control| that build...@>=
mmode+above: math_fraction;

@ @<Declare act...@>=
procedure math_fraction;
var c:small_number; {the type of generalized fraction we are scanning}
begin c:=cur_chr;
if incompleat_noad<>null then
  @<Ignore the fraction operation and complain about this ambiguous case@>
else  begin incompleat_noad:=new_node(fraction_noad,normal);
  math_type(numerator(incompleat_noad)):=sub_mlist;
  vinfo(numerator(incompleat_noad)):=vlink(head);
  vmem(denominator(incompleat_noad)).hh:=empty_field;
  vmem(left_delimiter(incompleat_noad)).qqqq:=null_delimiter;
  vmem(right_delimiter(incompleat_noad)).qqqq:=null_delimiter;@/
  vlink(head):=null; tail:=head;
  @<Use code |c| to distinguish between generalized fractions@>;
  end;
end;

@ @<Use code |c|...@>=
if c>=delimited_code then
  begin scan_delimiter(left_delimiter(incompleat_noad),false);
  scan_delimiter(right_delimiter(incompleat_noad),false);
  end;
case c mod delimited_code of
above_code: begin scan_normal_dimen;
  thickness(incompleat_noad):=cur_val;
  end;
over_code: thickness(incompleat_noad):=default_code;
atop_code: thickness(incompleat_noad):=0;
end {there are no other cases}

@ @<Ignore the fraction...@>=
begin if c>=delimited_code then
  begin scan_delimiter(garbage,false); scan_delimiter(garbage,false);
  end;
if c mod delimited_code=above_code then scan_normal_dimen;
print_err("Ambiguous; you need another { and }");
@.Ambiguous...@>
help3("I'm ignoring this fraction specification, since I don't")@/
  ("know whether a construction like `x \over y \over z'")@/
  ("means `{x \over y} \over z' or `x \over {y \over z}'.");
error;
end

@ At the end of a math formula or subformula, the |fin_mlist| routine is
called upon to return a pointer to the newly completed mlist, and to
pop the nest back to the enclosing semantic level. The parameter to
|fin_mlist|, if not null, points to a |right_noad| that ends the
current mlist; this |right_noad| has not yet been appended.

@<Declare the function called |fin_mlist|@>=
function fin_mlist(@!p:pointer):pointer;
var q:pointer; {the mlist to return}
begin if incompleat_noad<>null then @<Compleat the incompleat noad@>
else  begin vlink(tail):=p; q:=vlink(head);
  end;
pop_nest; fin_mlist:=q;
end;

@ @<Compleat...@>=
begin math_type(denominator(incompleat_noad)):=sub_mlist;
vinfo(denominator(incompleat_noad)):=vlink(head);
if p=null then q:=incompleat_noad
else  begin q:=vinfo(numerator(incompleat_noad));
  if (type(q)<>left_noad)or(delim_ptr=null) then confusion("right");
@:this can't happen right}{\quad right@>
  vinfo(numerator(incompleat_noad)):=vlink(delim_ptr);
  vlink(delim_ptr):=incompleat_noad; vlink(incompleat_noad):=p;
  end;
end

@ Now at last we're ready to see what happens when a right brace occurs
in a math formula. Two special cases are simplified here: Braces are effectively
removed when they surround a single Ord without sub/superscripts, or when they
surround an accent that is the nucleus of an Ord atom.

@<Cases of |handle...@>=
math_group: begin @<DIR: |unsave| math@>; decr(save_ptr);@/
  math_type(saved(0)):=sub_mlist; p:=fin_mlist(null); vinfo(saved(0)):=p;
  if p<>null then if vlink(p)=null then
   if type(p)=ord_noad then
    begin if math_type(subscr(p))=empty then
     if math_type(supscr(p))=empty then
      begin vmem(saved(0)).hh:=vmem(nucleus(p)).hh;
      flush_node(p);
      end;
    end
  else if type(p)=accent_noad then if saved(0)=nucleus(tail) then
   if type(tail)=ord_noad then @<Replace the tail of the list by |p|@>;
  end;

@ @<Replace the tail...@>=
begin q:=head; while vlink(q)<>tail do q:=vlink(q);
vlink(q):=p; flush_node(tail); tail:=p;
end

@ We have dealt with all constructions of math mode except `\.{\\left}' and
`\.{\\right}', so the picture is completed by the following sections of
the program.

@<Put each...@>=
primitive("left",left_right,left_noad);
@!@:left_}{\.{\\left} primitive@>
primitive("right",left_right,right_noad);
@!@:right_}{\.{\\right} primitive@>
text(frozen_right):="right"; eqtb[frozen_right]:=eqtb[cur_val];

@ @<Cases of |print_cmd_chr|...@>=
left_right: if chr_code=left_noad then print_esc("left")
@/@<Cases of |left_right| for |print_cmd_chr|@>@/
else print_esc("right");

@ @<Cases of |main_control| that build...@>=
mmode+left_right: math_left_right;

@ @<Declare act...@>=
procedure math_left_right;
var t:small_number; {|left_noad| or |right_noad|}
@!p:pointer; {new noad}
@!q:pointer; {resulting mlist}
begin t:=cur_chr;
if (t<>left_noad)and(cur_group<>math_left_group) then
  @<Try to recover from mismatched \.{\\right}@>
else  begin p:=new_noad; type(p):=t;
  scan_delimiter(delimiter(p),false);
  if t=middle_noad then
    begin type(p):=right_noad; subtype(p):=middle_noad;
    end;
  if t=left_noad then q:=p
  else  begin q:=fin_mlist(p);
    @<DIR: |unsave| math@>; {end of |math_left_group|}
    end;
  if t<>right_noad then
    begin push_math(math_left_group); vlink(head):=q; tail:=p;
    delim_ptr:=p;
    end
  else  begin
    tail_append(new_noad); type(tail):=inner_noad;
    math_type(nucleus(tail)):=sub_mlist;
    vinfo(nucleus(tail)):=q;
    end;
  end;
end;

@ @<Try to recover from mismatch...@>=
begin if cur_group=math_shift_group then
  begin scan_delimiter(garbage,false);
  print_err("Extra ");
  if t=middle_noad then
    begin print_esc("middle");
@.Extra \\middle.@>
    help1("I'm ignoring a \middle that had no matching \left.");
    end
  else  begin print_esc("right");
@.Extra \\right.@>
    help1("I'm ignoring a \right that had no matching \left.");
    end;
  error;
  end
else off_save;
end

@ Here is the only way out of math mode.

@<Cases of |main_control| that build...@>=
mmode+math_shift: if cur_group=math_shift_group then after_math
  else off_save;

@ @<Declare act...@>=
procedure after_math;
var l:boolean; {`\.{\\leqno}' instead of `\.{\\eqno}'}
@!danger:boolean; {not enough symbol fonts are present}
@!m:integer; {|mmode| or |-mmode|}
@!p:pointer; {the formula}
@!a:pointer; {box containing equation number}
@<Local variables for finishing a displayed formula@>@;
begin danger:=false;
@<Check that the necessary fonts for math symbols are present;
  if not, flush the current math lists and set |danger:=true|@>;
m:=mode; l:=false; p:=fin_mlist(null); {this pops the nest}
if mode=-m then {end of equation number}
  begin @<Check that another \.\$ follows@>;
  cur_mlist:=p; cur_style:=text_style; mlist_penalties:=false;
  mlist_to_hlist; a:=hpack(vlink(temp_head),natural);
  @<DIR: |unsave| math@>;
  decr(save_ptr); {now |cur_group=math_shift_group|}
  if saved(0)=1 then l:=true;
  danger:=false;
  @<Check that the necessary fonts for math symbols are present;
    if not, flush the current math lists and set |danger:=true|@>;
  m:=mode; p:=fin_mlist(null);
  end
else a:=null;
if m<0 then @<Finish math in text@>
else  begin if a=null then @<Check that another \.\$ follows@>;
  @<Finish displayed math@>;
  end;
end;

@ @<Check that the necessary fonts...@>=
if (font_params(fam_fnt(2+text_size))<total_mathsy_params)or@|
   (font_params(fam_fnt(2+script_size))<total_mathsy_params)or@|
   (font_params(fam_fnt(2+script_script_size))<total_mathsy_params) then
  begin print_err("Math formula deleted: Insufficient symbol fonts");@/
@.Math formula deleted...@>
  help3("Sorry, but I can't typeset math unless \textfont 2")@/
    ("and \scriptfont 2 and \scriptscriptfont 2 have all")@/
    ("the \fontdimen values needed in math symbol fonts.");
  error; flush_math; danger:=true;
  end
else if (font_params(fam_fnt(3+text_size))<total_mathex_params)or@|
   (font_params(fam_fnt(3+script_size))<total_mathex_params)or@|
   (font_params(fam_fnt(3+script_script_size))<total_mathex_params) then
  begin print_err("Math formula deleted: Insufficient extension fonts");@/
  help3("Sorry, but I can't typeset math unless \textfont 3")@/
    ("and \scriptfont 3 and \scriptscriptfont 3 have all")@/
    ("the \fontdimen values needed in math extension fonts.");
  error; flush_math; danger:=true;
  end

@ The |unsave| is done after everything else here; hence an appearance of
`\.{\\mathsurround}' inside of `\.{\$...\$}' affects the spacing at these
particular \.\$'s. This is consistent with the conventions of
`\.{\$\$...\$\$}', since `\.{\\abovedisplayskip}' inside a display affects the
space above that display.

@<Finish math in text@> =
begin tail_append(new_math(math_surround,before));
if dir_math_save then
  @<Append a begin direction to the tail of the current list@>;
cur_mlist:=p; cur_style:=text_style; mlist_penalties:=(mode>0); mlist_to_hlist;
vlink(tail):=vlink(temp_head);
while vlink(tail)<>null do tail:=vlink(tail);
if dir_math_save then
  @<Append an end direction to the tail of the current list@>;
dir_math_save:=false;
tail_append(new_math(math_surround,after));
space_factor:=1000;
@<DIR: |unsave| math@>;
end

@ \TeX\ gets to the following part of the program when the first `\.\$' ending
a display has been scanned.

@<Check that another \.\$ follows@>=
begin get_x_token;
if cur_cmd<>math_shift then
  begin print_err("Display math should end with $$");
@.Display math...with \$\$@>
  help2("The `$' that I just saw supposedly matches a previous `$$'.")@/
    ("So I shall assume that you typed `$$' both times.");
  back_error;
  end;
end

@ We have saved the worst for last: The fussiest part of math mode processing
occurs when a displayed formula is being centered and placed with an optional
equation number.

@<Local variables for finishing...@>=
@!b:pointer; {box containing the equation}
@!w:scaled; {width of the equation}
@!z:scaled; {width of the line}
@!e:scaled; {width of equation number}
@!q:scaled; {width of equation number plus space to separate from equation}
@!d:scaled; {displacement of equation in the line}
@!s:scaled; {move the line right this much}
@!g1,@!g2:small_number; {glue parameter codes for before and after}
@!r:pointer; {kern node used to position the display}
@!t:pointer; {tail of adjustment list}
@!pre_t:pointer; {tail of pre-adjustment list}

@ At this time |p| points to the mlist for the formula; |a| is either
|null| or it points to a box containing the equation number; and we are in
vertical mode (or internal vertical mode).

@<Finish displayed math@>=
cur_mlist:=p; cur_style:=display_style; mlist_penalties:=false;
mlist_to_hlist; p:=vlink(temp_head);@/
adjust_tail:=adjust_head; pre_adjust_tail:=pre_adjust_head;
b:=hpack(p,natural); p:=list_ptr(b);
t:=adjust_tail; adjust_tail:=null;@/
pre_t:=pre_adjust_tail; pre_adjust_tail:=null;@/
w:=width(b); z:=display_width; s:=display_indent;
if (a=null)or danger then
  begin e:=0; q:=0;
  end
else  begin e:=width(a); q:=e+math_quad(text_size);
  end;
if w+q>z then
  @<Squeeze the equation as much as possible; if there is an equation
    number that should go on a separate line by itself,
    set~|e:=0|@>;
@<Determine the displacement, |d|, of the left edge of the equation, with
  respect to the line size |z|, assuming that |l=false|@>;
@<Append the glue or equation number preceding the display@>;
@<Append the display and perhaps also the equation number@>;
@<Append the glue or equation number following the display@>;
resume_after_display

@ @<Declare act...@>=
procedure resume_after_display;
begin if cur_group<>math_shift_group then confusion("display");
@:this can't happen display}{\quad display@>
@<DIR: |unsave| math@>;
prev_graf:=prev_graf+3;
push_nest; mode:=hmode; space_factor:=1000;
@<LOCAL: Add local paragraph node@>;
@<Scan an optional space@>;
if nest_ptr=1 then begin check_filter('after_display'); build_page; end;
end;

@ The user can force the equation number to go on a separate line
by causing its width to be zero.

@<Squeeze the equation as much as possible...@>=
begin if (e<>0)and((w-total_shrink[normal]+q<=z)or@|
   (total_shrink[sfi]<>0)or(total_shrink[fil]<>0)or
   (total_shrink[fill]<>0)or(total_shrink[filll]<>0)) then
  begin list_ptr(b):=null; flush_node(b);
  b:=hpack(p,z-q,exactly);
  end
else  begin e:=0;
  if w>z then
    begin 
    list_ptr(b):=null; flush_node(b);
    b:=hpack(p,z,exactly);
    end;
  end;
w:=width(b);
end

@ We try first to center the display without regard to the existence of
the equation number. If that would make it too close (where ``too close''
means that the space between display and equation number is less than the
width of the equation number), we either center it in the remaining space
or move it as far from the equation number as possible. The latter alternative
is taken only if the display begins with glue, since we assume that the
user put glue there to control the spacing precisely.

@<Determine the displacement, |d|, of the left edge of the equation...@>=
d:=half(z-w);
if (e>0)and(d<2*e) then {too close}
  begin d:=half(z-w-e);
  if p<>null then if not is_char_node(p) then if type(p)=glue_node then d:=0;
  end

@ If the equation number is set on a line by itself, either before or
after the formula, we append an infinite penalty so that no page break will
separate the display from its number; and we use the same size and
displacement for all three potential lines of the display, even though
`\.{\\parshape}' may specify them differently.

@<Append the glue or equation number preceding the display@>=
tail_append(new_penalty(pre_display_penalty));@/
if (d+s<=pre_display_size)or l then {not enough clearance}
  begin g1:=above_display_skip_code; g2:=below_display_skip_code;
  end
else  begin g1:=above_display_short_skip_code;
  g2:=below_display_short_skip_code;
  end;
if l and(e=0) then {it follows that |type(a)=hlist_node|}
  begin shift_amount(a):=s; append_to_vlist(a);
  tail_append(new_penalty(inf_penalty));
  end
else tail_append(new_param_glue(g1))

@ @<Append the display and perhaps also the equation number@>=
if e<>0 then
  begin r:=new_kern(z-w-e-d);
  if l then
    begin vlink(a):=r; vlink(r):=b; b:=a; d:=0;
    end
  else  begin vlink(b):=r; vlink(r):=a;
    end;
  b:=hpack(b,natural);
  end;
shift_amount(b):=s+d; append_to_vlist(b)

@ @<Append the glue or equation number following the display@>=
if (a<>null)and(e=0)and not l then
  begin tail_append(new_penalty(inf_penalty));
  shift_amount(a):=s+z-width(a);
  append_to_vlist(a);
  g2:=0;
  end;
if t<>adjust_head then {migrating material comes after equation number}
  begin vlink(tail):=vlink(adjust_head); tail:=t;
  end;
if pre_t<>pre_adjust_head then
  begin vlink(tail):=vlink(pre_adjust_head); tail:=pre_t;
  end;
tail_append(new_penalty(post_display_penalty));
if g2>0 then tail_append(new_param_glue(g2))

@ When \.{\\halign} appears in a display, the alignment routines operate
essentially as they do in vertical mode. Then the following program is
activated, with |p| and |q| pointing to the beginning and end of the
resulting list, and with |aux_save| holding the |prev_depth| value.

@<Finish an alignment in a display@>=
begin do_assignments;
if cur_cmd<>math_shift then @<Pontificate about improper alignment in display@>
else @<Check that another \.\$ follows@>;
pop_nest;
tail_append(new_penalty(pre_display_penalty));
tail_append(new_param_glue(above_display_skip_code));
vlink(tail):=p;
if p<>null then tail:=q;
tail_append(new_penalty(post_display_penalty));
tail_append(new_param_glue(below_display_skip_code));
prev_depth:=aux_save.sc; resume_after_display;
end

@ @<Pontificate...@>=
begin print_err("Missing $$ inserted");
@.Missing {\$\$} inserted@>
help2("Displays can use special alignments (like \eqalignno)")@/
  ("only if nothing but the alignment itself is between $$'s.");
back_error;
end

@* \[49] Mode-independent processing.
The long |main_control| procedure has now been fully specified, except for
certain activities that are independent of the current mode. These activities
do not change the current vlist or hlist or mlist; if they change anything,
it is the value of a parameter or the meaning of a control sequence.

Assignments to values in |eqtb| can be global or local. Furthermore, a
control sequence can be defined to be `\.{\\long}', `\.{\\protected}',
or `\.{\\outer}', and it might or might not be expanded. The prefixes
`\.{\\global}', `\.{\\long}', `\.{\\protected}',
and `\.{\\outer}' can occur in any order. Therefore we assign binary numeric
codes, making it possible to accumulate the union of all specified prefixes
by adding the corresponding codes.  (\PASCAL's |set| operations could also
have been used.)

@<Put each...@>=
primitive("long",prefix,1);
@!@:long_}{\.{\\long} primitive@>
primitive("outer",prefix,2);
@!@:outer_}{\.{\\outer} primitive@>
primitive("global",prefix,4);
@!@:global_}{\.{\\global} primitive@>
primitive("def",def,0);
@!@:def_}{\.{\\def} primitive@>
primitive("gdef",def,1);
@!@:gdef_}{\.{\\gdef} primitive@>
primitive("edef",def,2);
@!@:edef_}{\.{\\edef} primitive@>
primitive("xdef",def,3);
@!@:xdef_}{\.{\\xdef} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
prefix: if chr_code=1 then print_esc("long")
  else if chr_code=2 then print_esc("outer")
  @/@<Cases of |prefix| for |print_cmd_chr|@>@/
  else print_esc("global");
def: if chr_code=0 then print_esc("def")
  else if chr_code=1 then print_esc("gdef")
  else if chr_code=2 then print_esc("edef")
  else print_esc("xdef");

@ Every prefix, and every command code that might or might not be prefixed,
calls the action procedure |prefixed_command|. This routine accumulates
a sequence of prefixes until coming to a non-prefix, then it carries out
the command.

@<Cases of |main_control| that don't...@>=
any_mode(toks_register),
any_mode(assign_toks),
any_mode(assign_int),
any_mode(assign_attr),
any_mode(assign_dir),
any_mode(assign_dimen),
any_mode(assign_glue),
any_mode(assign_mu_glue),
any_mode(assign_font_dimen),
any_mode(assign_font_int),
any_mode(set_aux),
any_mode(set_prev_graf),
any_mode(set_page_dimen),
any_mode(set_page_int),
any_mode(set_box_dimen),
any_mode(set_shape),
any_mode(def_code),
any_mode(extdef_code),
any_mode(def_family),
any_mode(set_font),
any_mode(def_font),
any_mode(letterspace_font),
any_mode(register),
any_mode(advance),
any_mode(multiply),
any_mode(divide),
any_mode(prefix),
any_mode(let),
any_mode(shorthand_def),
any_mode(read_to_cs),
any_mode(def),
any_mode(set_box),
any_mode(hyph_data),
any_mode(set_interaction),
any_mode(set_ocp),
any_mode(def_ocp),
any_mode(set_ocp_list),
any_mode(def_ocp_list),
any_mode(clear_ocp_lists),
any_mode(push_ocp_list),
any_mode(pop_ocp_list),
any_mode(ocp_list_op),
any_mode(ocp_trace_level) : prefixed_command;

@ If the user says, e.g., `\.{\\global\\global}', the redundancy is
silently accepted.

@<Declare act...@>=
@t\4@>@<Declare subprocedures for |prefixed_command|@>@t@>@;@/
procedure prefixed_command;
label done,exit;
var a:small_number; {accumulated prefix codes so far}
@!f:internal_font_number; {identifies a font}
@!j:halfword; {index into a \.{\\parshape} specification}
@!p,@!q:pointer; {for temporary short-term use}
@!n:integer; {ditto}
@!e:boolean; {should a definition be expanded? or was \.{\\let} not done?}
begin a:=0;
while cur_cmd=prefix do
  begin if not odd(a div cur_chr) then a:=a+cur_chr;
  @<Get the next non-blank non-relax...@>;
  if cur_cmd<=max_non_prefixed_command then
    @<Discard erroneous prefixes and |return|@>;
  if tracing_commands>2 then show_cur_cmd_chr;
  end;
@<Discard the prefixes \.{\\long} and \.{\\outer} if they are irrelevant@>;
@<Adjust \(f)for the setting of \.{\\globaldefs}@>;
case cur_cmd of
@t\4@>@<Assignments@>@;
othercases confusion("prefix")
@:this can't happen prefix}{\quad prefix@>
endcases;
done: @<Insert a token saved by \.{\\afterassignment}, if any@>;
exit:end;

@ @<Discard erroneous...@>=
begin print_err("You can't use a prefix with `");
@.You can't use a prefix with x@>
print_cmd_chr(cur_cmd,cur_chr); print_char("'");
help1("I'll pretend you didn't say \long or \outer or \global.");
back_error; return;
end

@ @<Discard the prefixes...@>=
if a>=8 then
  begin j:=protected_token; a:=a-8;
  end
else j:=0;
if (cur_cmd<>def)and((a mod 4<>0)or(j<>0)) then
  begin print_err("You can't use `"); print_esc("long"); print("' or `");
  print_esc("outer"); print("' with `");
@.You can't use \\long...@>
  print_cmd_chr(cur_cmd,cur_chr); print_char("'");
  help1("I'll pretend you didn't say \long or \outer here.");
  error;
  end

@ The previous routine does not have to adjust |a| so that |a mod 4=0|,
since the following routines test for the \.{\\global} prefix as follows.

@d global==(a>=4)
@d define(#)==if global then geq_define(#)@+else eq_define(#)
@d word_define(#)==if global then geq_word_define(#)@+else eq_word_define(#)
@d define_math_code(#)==if global 
   then set_math_code(#,level_one)@+else set_math_code(#,cur_level)
@d define_del_code(#)==if global 
   then set_del_code(#,level_one)@+else set_del_code(#,cur_level)
@d define_lc_code(#)==if global 
   then set_lc_code(#,level_one)@+else set_lc_code(#,cur_level)
@d define_uc_code(#)==if global 
   then set_uc_code(#,level_one)@+else set_uc_code(#,cur_level)
@d define_sf_code(#)==if global 
   then set_sf_code(#,level_one)@+else set_sf_code(#,cur_level)
@d define_cat_code(#)==if global 
   then set_cat_code(cat_code_table,#,level_one)@+else set_cat_code(cat_code_table,#,cur_level)

@<Adjust \(f)for the setting of \.{\\globaldefs}@>=
if global_defs<>0 then
  if global_defs<0 then
    begin if global then a:=a-4;
    end
  else  begin if not global then a:=a+4;
    end

@ When a control sequence is to be defined, by \.{\\def} or \.{\\let} or
something similar, the |get_r_token| routine will substitute a special
control sequence for a token that is not redefinable.

@<Declare subprocedures for |prefixed_command|@>=
procedure get_r_token;
label restart;
begin restart: repeat get_token;
until cur_tok<>space_token;
if (cur_cs=0)or(cur_cs>frozen_control_sequence) then
  begin print_err("Missing control sequence inserted");
@.Missing control...@>
  help5("Please don't say `\def cs{...}', say `\def\cs{...}'.")@/
  ("I've inserted an inaccessible control sequence so that your")@/
  ("definition will be completed without mixing me up too badly.")@/
  ("You can recover graciously from this error, if you're")@/
  ("careful; see exercise 27.2 in The TeXbook.");
@:TeXbook}{\sl The \TeX book@>
  if cur_cs=0 then back_input;
  cur_tok:=cs_token_flag+frozen_protection; ins_error; goto restart;
  end;
end;

@ @<Initialize table entries...@>=
text(frozen_protection):="inaccessible";

@ Assignments from Lua need helpers. 

@p function is_int_assign(cmd:halfword):boolean;
begin
  is_int_assign := (cmd=assign_int);
end;
function is_dim_assign(cmd:halfword):boolean;
begin
  is_dim_assign := (cmd=assign_dimen);
end;
procedure assign_internal_int(cmd:halfword;value:integer);
var  a:small_number;
begin
   a:=0;
   word_define(cmd,value);
end;
procedure assign_internal_dim(cmd:halfword;value:integer);
var  a:small_number;
begin
   a:=0;
  word_define(cmd,value);
end;


@ Here's an example of the way many of the following routines operate.
(Unfortunately, they aren't all as simple as this.)

@<Assignments@>=
set_font: define(cur_font_loc,data,cur_chr);

@ When a |def| command has been scanned,
|cur_chr| is odd if the definition is supposed to be global, and
|cur_chr>=2| if the definition is supposed to be expanded.

@<Assignments@>=
def: begin if odd(cur_chr)and not global and(global_defs>=0) then a:=a+4;
  e:=(cur_chr>=2); get_r_token; p:=cur_cs;
  q:=scan_toks(true,e);
  if j<>0 then
    begin q:=get_avail; info(q):=j; link(q):=link(def_ref);
    link(def_ref):=q;
    end;
  define(p,call+(a mod 4),def_ref);
  end;

@ Both \.{\\let} and \.{\\futurelet} share the command code |let|.

@<Put each...@>=
primitive("let",let,normal);@/
@!@:let_}{\.{\\let} primitive@>
primitive("futurelet",let,normal+1);@/
@!@:future_let_}{\.{\\futurelet} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
let: if chr_code<>normal then print_esc("futurelet")@+else print_esc("let");

@ @<Assignments@>=
let:  begin n:=cur_chr;
  get_r_token; p:=cur_cs;
  if n=normal then
    begin repeat get_token;
    until cur_cmd<>spacer;
    if cur_tok=other_token+"=" then
      begin get_token;
      if cur_cmd=spacer then get_token;
      end;
    end
  else  begin get_token; q:=cur_tok; get_token; back_input;
    cur_tok:=q; back_input; {look ahead, then back up}
    end; {note that |back_input| doesn't affect |cur_cmd|, |cur_chr|}
  if cur_cmd>=call then add_token_ref(cur_chr);
  define(p,cur_cmd,cur_chr);
  end;

@ A \.{\\chardef} creates a control sequence whose |cmd| is |char_given|;
a \.{\\mathchardef} creates a control sequence whose |cmd| is |math_given|;
and the corresponding |chr| is the character code or math code. A \.{\\countdef}
or \.{\\dimendef} or \.{\\skipdef} or \.{\\muskipdef} creates a control
sequence whose |cmd| is |assign_int| or \dots\ or |assign_mu_glue|, and the
corresponding |chr| is the |eqtb| location of the internal register in question.

@d char_def_code=0 {|shorthand_def| for \.{\\chardef}}
@d math_char_def_code=1 {|shorthand_def| for \.{\\mathchardef}}
@d omath_char_def_code=2 {|shorthand_def| for \.{\\omathchardef}}
@d count_def_code=3 {|shorthand_def| for \.{\\countdef}}
@d attribute_def_code=4 {|shorthand_def| for \.{\\attributedef}}
@d dimen_def_code=5 {|shorthand_def| for \.{\\dimendef}}
@d skip_def_code=6 {|shorthand_def| for \.{\\skipdef}}
@d mu_skip_def_code=7 {|shorthand_def| for \.{\\muskipdef}}
@d toks_def_code=8 {|shorthand_def| for \.{\\toksdef}}

@<Put each...@>=
primitive("chardef",shorthand_def,char_def_code);@/
@!@:char_def_}{\.{\\chardef} primitive@>
primitive("mathchardef",shorthand_def,math_char_def_code);@/
@!@:math_char_def_}{\.{\\mathchardef} primitive@>
primitive("omathchardef",shorthand_def,omath_char_def_code);@/
@!@:math_char_def_}{\.{\\omathchardef} primitive@>
primitive("countdef",shorthand_def,count_def_code);@/
@!@:count_def_}{\.{\\countdef} primitive@>
primitive("attributedef",shorthand_def,attribute_def_code);@/
@!@:attribute_def_}{\.{\\attributedef} primitive@>
primitive("dimendef",shorthand_def,dimen_def_code);@/
@!@:dimen_def_}{\.{\\dimendef} primitive@>
primitive("skipdef",shorthand_def,skip_def_code);@/
@!@:skip_def_}{\.{\\skipdef} primitive@>
primitive("muskipdef",shorthand_def,mu_skip_def_code);@/
@!@:mu_skip_def_}{\.{\\muskipdef} primitive@>
primitive("toksdef",shorthand_def,toks_def_code);@/
@!@:toks_def_}{\.{\\toksdef} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
shorthand_def: case chr_code of
  char_def_code: print_esc("chardef");
  math_char_def_code: print_esc("mathchardef");
  omath_char_def_code: print_esc("omathchardef");
  count_def_code: print_esc("countdef");
  attribute_def_code: print_esc("attributedef");
  dimen_def_code: print_esc("dimendef");
  skip_def_code: print_esc("skipdef");
  mu_skip_def_code: print_esc("muskipdef");
  othercases print_esc("toksdef")
  endcases;
char_given: begin print_esc("char"); print_hex(chr_code);
  end;
math_given: begin print_esc("mathchar"); print_hex(chr_code);
  end;
omath_given: begin print_esc("omathchar"); print_hex(chr_code);
  end;

@ We temporarily define |p| to be |relax|, so that an occurrence of |p|
while scanning the definition will simply stop the scanning instead of
producing an ``undefined control sequence'' error or expanding the
previous meaning.  This allows, for instance, `\.{\\chardef\\foo=123\\foo}'.

@<Assignments@>=
shorthand_def: begin n:=cur_chr; get_r_token; p:=cur_cs; 
  define(p,relax,too_big_char); scan_optional_equals;
  case n of
  char_def_code: begin scan_char_num; define(p,char_given,cur_val);
    end;
  math_char_def_code: begin scan_real_fifteen_bit_int;
    define(p,math_given,cur_val);
    end;
  omath_char_def_code: begin scan_big_fifteen_bit_int;
    define(p,omath_given,cur_val);
    end;
  othercases begin scan_register_num;
    case n of
    count_def_code: define(p,assign_int,count_base+cur_val);
    attribute_def_code: define(p,assign_attr,attribute_base+cur_val);
    dimen_def_code: define(p,assign_dimen,scaled_base+cur_val);
    skip_def_code: define(p,assign_glue,skip_base+cur_val);
    mu_skip_def_code: define(p,assign_mu_glue,mu_skip_base+cur_val);
    toks_def_code: define(p,assign_toks,toks_base+cur_val);
    end; {there are no other cases}
    end
  endcases;
  end;

@ @<Assignments@>=
read_to_cs: begin j:=cur_chr; scan_int; n:=cur_val;
  if not scan_keyword("to") then
    begin print_err("Missing `to' inserted");
@.Missing `to'...@>
    help2("You should have said `\read<number> to \cs'.")@/
    ("I'm going to look for the \cs now."); error;
    end;
  get_r_token;
  p:=cur_cs; read_toks(n,p,j); define(p,call,cur_val);
  end;

@ The token-list parameters, \.{\\output} and \.{\\everypar}, etc., receive
their values in the following way. (For safety's sake, we place an
enclosing pair of braces around an \.{\\output} list.)

@<Assignments@>=
toks_register,assign_toks: begin q:=cur_cs;
  if cur_cmd=toks_register then
    begin scan_register_num; p:=toks_base+cur_val;
    end
  else p:=cur_chr; {|p=every_par_loc| or |output_routine_loc| or \dots}
  scan_optional_equals;
  @<Get the next non-blank non-relax non-call token@>;
  if cur_cmd<>left_brace then @<If the right-hand side is a token parameter
      or token register, finish the assignment and |goto done|@>;
  back_input; cur_cs:=q; q:=scan_toks(false,false);
  if link(def_ref)=null then {empty list: revert to the default}
    begin define(p,undefined_cs,null); free_avail(def_ref);
    end
  else  begin if p=output_routine_loc then {enclose in curlies}
      begin p:=get_avail; link(q):=p; p:=output_routine_loc; 
      q:=link(q);info(q):=right_brace_token+"}";
      q:=get_avail;      
      info(q):=left_brace_token+"{";
      link(q):=link(def_ref); link(def_ref):=q;
      end;
    define(p,call,def_ref);
    end;
  end;

@ @<If the right-hand side is a token parameter...@>=
begin if cur_cmd=toks_register then
  begin scan_register_num; cur_cmd:=assign_toks; cur_chr:=toks_base+cur_val;
  end;
if cur_cmd=assign_toks then
  begin q:=equiv(cur_chr);
  if q=null then define(p,undefined_cs,null)
  else  begin add_token_ref(q); define(p,call,q);
    end;
  goto done;
  end;
end

@ Similar routines are used to assign values to the numeric parameters.

@<Assignments@>=
assign_int: begin p:=cur_chr; scan_optional_equals; scan_int;
  if p=(int_base+cat_code_table_code) then begin
    if valid_catcode_table(cur_val) then begin
      if cur_val<>cat_code_table then
        word_define(p,cur_val);
      end
    else begin
      print_err("Invalid \catcode table");
      help2("You can only switch to a \catcode table that is initialized")
           ("using \savecatcodetable or \initcatcodetable, or to table 0");
      error;
      end;
    end
  else if (p=new_line_char)and(cur_val>127) then begin
    print_err("Invalid \newlinechar");
    help1("The value for \newlinechar has to be between 0 and 127.");
    error;
    end
  else if p=end_line_char then begin
    if (cur_val<0)or(cur_val>biggest_char) then
      word_define(p,-1)
    else
      word_define(p,13);
    end
  else 
   word_define(p,cur_val);
{If we are defining subparagraph penalty levels while we are
in hmode, then we put out a whatsit immediately, otherwise
we leave it alone.  This mechanism might not be sufficiently
powerful, and some other algorithm, searching down the stack,
might be necessary.  Good first step.}
  if (abs(mode)=hmode) and
     ((p=(int_base+local_inter_line_penalty_code)) or
      (p=(int_base+local_broken_penalty_code))) then begin
    @<LOCAL: Add local paragraph node@>;
    eq_word_define(int_base+no_local_whatsits_code,no_local_whatsits+1);
    local_par_bool:=true;
    end;
  if p=int_base+language_code then word_define(int_base+cur_lang_code,cur_val);
  end;
assign_attr: begin p:=cur_chr; scan_optional_equals; scan_int;
  if (p-attribute_base)>max_used_attr then max_used_attr:=(p-attribute_base);
  attr_list_cache:=cache_disabled;
  word_define(p,cur_val); end;
assign_dir: begin
  @<DIR: Assign direction codes@>
  end;
assign_dimen: begin p:=cur_chr; scan_optional_equals;
  scan_normal_dimen; word_define(p,cur_val);
  end;
assign_glue,assign_mu_glue: begin p:=cur_chr; n:=cur_cmd; scan_optional_equals;
  if n=assign_mu_glue then scan_glue(mu_val)@+else scan_glue(glue_val);
  trap_zero_glue;
  define(p,glue_ref,cur_val);
  end;

@ When a glue register or parameter becomes zero, it will always point to
|zero_glue| because of the following procedure. (Exception: The tabskip
glue isn't trapped while preambles are being scanned.)

@<Declare subprocedures for |prefixed_command|@>=
procedure trap_zero_glue;
begin if (width(cur_val)=0)and(stretch(cur_val)=0)and(shrink(cur_val)=0) then
  begin add_glue_ref(zero_glue);
  delete_glue_ref(cur_val); cur_val:=zero_glue;
  end;
end;

@ The various character code tables are changed by the |def_code| commands,
and the font families are declared by |def_family|.

@<Put each...@>=
primitive("catcode",def_code,cat_code_base);
@!@:cat_code_}{\.{\\catcode} primitive@>
primitive("mathcode",def_code,math_code_base);
@!@:math_code_}{\.{\\mathcode} primitive@>
primitive("lccode",def_code,lc_code_base);
@!@:lc_code_}{\.{\\lccode} primitive@>
primitive("uccode",def_code,uc_code_base);
@!@:uc_code_}{\.{\\uccode} primitive@>
primitive("sfcode",def_code,sf_code_base);
@!@:sf_code_}{\.{\\sfcode} primitive@>
primitive("delcode",def_code,del_code_base);
@!@:del_code_}{\.{\\delcode} primitive@>
primitive("textfont",def_family,math_font_base);
@!@:text_font_}{\.{\\textfont} primitive@>
primitive("scriptfont",def_family,math_font_base+script_size);
@!@:script_font_}{\.{\\scriptfont} primitive@>
primitive("scriptscriptfont",def_family,math_font_base+script_script_size);
@!@:script_script_font_}{\.{\\scriptscriptfont} primitive@>
primitive("omathcode",extdef_code,math_code_base);
@!@:math_code_}{\.{\\omathcode} primitive@>
primitive("odelcode",extdef_code,del_code_base);
@!@:del_code_}{\.{\\odelcode} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
def_code: if chr_code=cat_code_base then print_esc("catcode")
  else if chr_code=math_code_base then print_esc("mathcode")
  else if chr_code=lc_code_base then print_esc("lccode")
  else if chr_code=uc_code_base then print_esc("uccode")
  else if chr_code=sf_code_base then print_esc("sfcode")
  else print_esc("delcode");
extdef_code: if chr_code=math_code_base then print_esc("omathcode")
  else print_esc("odelcode");
def_family: print_size(chr_code-math_font_base);

@ The different types of code values have different legal ranges; the
following program is careful to check each case properly.

@d check_def_code(#)== if ((cur_val<0)and(p<#))or(cur_val>n) then
      begin print_err("Invalid code ("); print_int(cur_val);
      if p<# then print("), should be in the range 0..")
      else print("), should be at most ");
      print_int(n);
      help1("I'm going to use 0 instead of that illegal code value.");@/
      error; cur_val:=0;
     end
@.Invalid code@>


@<Assignments@>=
def_code: begin @<Let |n| be the largest legal code value, based on |cur_chr|@>;
  p:=cur_chr;
  if cur_chr=math_code_base then begin
    scan_char_num; p:= cur_val;
    scan_optional_equals;  
    scan_int;
    check_def_code(math_code_base);
    if cur_val=@"8000 then cur_val:=@"8000000
    else cur_val:=((cur_val div @"1000) * @"1000000) +
                  (((cur_val mod @"1000) div @"100) * @"10000) +
                  (cur_val mod @"100);
    define_math_code(p,cur_val);
    end
  else if cur_chr=lc_code_base then begin
    scan_char_num; p:= cur_val;
    scan_optional_equals;  
    scan_int;
    check_def_code(lc_code_base);
    define_lc_code(p,cur_val);
    end
  else if cur_chr=uc_code_base then begin
    scan_char_num; p:= cur_val;
    scan_optional_equals;  
    scan_int;
    check_def_code(uc_code_base);
    define_uc_code(p,cur_val);
    end
  else if cur_chr=sf_code_base then begin
    scan_char_num; p:= cur_val;
    scan_optional_equals;  
    scan_int;
    check_def_code(sf_code_base);
    define_sf_code(p,cur_val);
    end
  else if cur_chr=cat_code_base then begin
    scan_char_num; p:= cur_val;
    scan_optional_equals;  
    scan_int;
    check_def_code(cat_code_base);
    define_cat_code(p,cur_val);
    end
  else if cur_chr=del_code_base then begin
    scan_char_num; p:= cur_val;
    scan_optional_equals;  
    scan_int;
    check_def_code(del_code_base);
    cur_val1:=cur_val div @"1000;
    cur_val1:=(cur_val1 div @"100)*@"10000 + (cur_val1 mod @"100);
    cur_val:=cur_val mod @"1000;
    cur_val:=(cur_val div @"100)*@"10000 + (cur_val mod @"100);
    define_del_code(p,cur_val1,cur_val);
    end;
  end;
extdef_code: begin 
  if cur_chr=del_code_base then begin
   p:=cur_chr; scan_char_num; p:=p+cur_val; scan_optional_equals;
   scan_int; cur_val1:=cur_val; scan_int; {backwards}
   if (cur_val1>@"FFFFFF) or (cur_val>@"FFFFFF) then
     begin print_err("Invalid code ("); print_int(cur_val1); print(" ");
     print_int(cur_val);
     print("), should be at most ""FFFFFF ""FFFFFF");
     help1("I'm going to use 0 instead of that illegal code value.");@/
     error; cur_val1:=0; cur_val:=0;
     end;
   define_del_code(p,cur_val1,cur_val);
   end
   else begin
   p:=cur_chr; scan_char_num; p:=cur_val; scan_optional_equals;
   scan_int;
   if (cur_val>@"8000000) then
     begin print_err("Invalid code ("); print_int(cur_val);
@.Invalid code@>
     print("), should be at most ");  print_int(@"8000000);
     help1("I'm going to use 0 instead of that illegal code value.");@/
     error; cur_val:=0;
     end;
   define_math_code(p,cur_val);
   end;
  end;

@ @<Let |n| be the largest...@>=
if cur_chr=cat_code_base then n:=max_char_code
else if cur_chr=lc_code_base then n:=biggest_char
else if cur_chr=uc_code_base then n:=biggest_char
else if cur_chr=math_code_base then n:=@'100000
else if cur_chr=sf_code_base then n:=@'77777
else if cur_chr=del_code_base then n:=@'77777777
else n:=biggest_char

@ @<Assignments@>=
def_family: begin p:=cur_chr; scan_math_family_int; p:=p+cur_val;
  scan_optional_equals; scan_font_ident; define(p,data,cur_val);
  end;

@ Next we consider changes to \TeX's numeric registers.

@<Assignments@>=
register,advance,multiply,divide: do_register_command(a);

@ We use the fact that |register<advance<multiply<divide|.

@<Declare subprocedures for |prefixed_command|@>=
procedure do_register_command(@!a:small_number);
label found,exit;
var l,@!q,@!r,@!s:pointer; {for list manipulation}
@!p:int_val..mu_val; {type of register involved}
begin q:=cur_cmd; 
@<Compute the register location |l| and its type |p|; but |return| if invalid@>;
if q=register then scan_optional_equals
else if scan_keyword("by") then do_nothing; {optional `\.{by}'}
arith_error:=false;
if q<multiply then @<Compute result of |register| or
    |advance|, put it in |cur_val|@>
else @<Compute result of |multiply| or |divide|, put it in |cur_val|@>;
if arith_error then
  begin print_err("Arithmetic overflow");
@.Arithmetic overflow@>
  help2("I can't carry out that multiplication or division,")@/
    ("since the result is out of range.");
  error; return;
  end;
if p<glue_val then begin
   if p=attr_val then begin
     if (l-attribute_base)>max_used_attr then max_used_attr:=(l-attribute_base);
     attr_list_cache:=cache_disabled;
     end;
  word_define(l,cur_val);
  end
else  begin trap_zero_glue; define(l,glue_ref,cur_val);
  end;
exit: end;

@ Here we use the fact that the consecutive codes |int_val...mu_val| and
|assign_int..assign_mu_glue| correspond to each other nicely.

@<Compute the register location |l| and its type |p|...@>=
begin l:=0;
if q<>register then
  begin get_x_token;
  if (cur_cmd>=assign_int)and(cur_cmd<=assign_mu_glue) then
    begin l:=cur_chr; p:=cur_cmd-assign_int; goto found;
    end;
  if cur_cmd<>register then
    begin print_err("You can't use `"); print_cmd_chr(cur_cmd,cur_chr);
@.You can't use x after ...@>
    print("' after "); print_cmd_chr(q,0);
    help1("I'm forgetting what you said and not changing anything.");
    error; return;
    end;
  end;
p:=cur_chr; scan_register_num;
case p of
int_val: l:=cur_val+count_base;
attr_val: l:=cur_val+attribute_base;
dimen_val: l:=cur_val+scaled_base;
glue_val: l:=cur_val+skip_base;
mu_val: l:=cur_val+mu_skip_base;
end; {there are no other cases}
end;
found:

@ @<Compute result of |register| or |advance|...@>=
if p<glue_val then
  begin if (p=int_val) or (p=attr_val) then scan_int@+else scan_normal_dimen;
  if q=advance then cur_val:=cur_val+eqtb[l].int;
  end
else  begin scan_glue(p);
  if q=advance then @<Compute the sum of two glue specs@>;
  end

@ @<Compute the sum of two glue specs@>=
begin q:=new_spec(cur_val); r:=equiv(l);
delete_glue_ref(cur_val);
width(q):=width(q)+width(r);
if stretch(q)=0 then stretch_order(q):=normal;
if stretch_order(q)=stretch_order(r) then stretch(q):=stretch(q)+stretch(r)
else if (stretch_order(q)<stretch_order(r))and(stretch(r)<>0) then
  begin stretch(q):=stretch(r); stretch_order(q):=stretch_order(r);
  end;
if shrink(q)=0 then shrink_order(q):=normal;
if shrink_order(q)=shrink_order(r) then shrink(q):=shrink(q)+shrink(r)
else if (shrink_order(q)<shrink_order(r))and(shrink(r)<>0) then
  begin shrink(q):=shrink(r); shrink_order(q):=shrink_order(r);
  end;
cur_val:=q;
end

@ @<Compute result of |multiply| or |divide|...@>=
begin scan_int;
if p<glue_val then
  if q=multiply then
    if (p=int_val)or(p=attr_val) then cur_val:=mult_integers(eqtb[l].int,cur_val)
    else cur_val:=nx_plus_y(eqtb[l].int,cur_val,0)
  else cur_val:=x_over_n(eqtb[l].int,cur_val)
else  begin s:=equiv(l); r:=new_spec(s);
  if q=multiply then
    begin width(r):=nx_plus_y(width(s),cur_val,0);
    stretch(r):=nx_plus_y(stretch(s),cur_val,0);
    shrink(r):=nx_plus_y(shrink(s),cur_val,0);
    end
  else  begin width(r):=x_over_n(width(s),cur_val);
    stretch(r):=x_over_n(stretch(s),cur_val);
    shrink(r):=x_over_n(shrink(s),cur_val);
    end;
  cur_val:=r;
  end;
end

@ The processing of boxes is somewhat different, because we may need
to scan and create an entire box before we actually change the value of the old
one.

@<Assignments@>=
set_box: begin scan_register_num;
  if global then n:=global_box_flag+cur_val@+else n:=box_flag+cur_val;
  scan_optional_equals;
  if set_box_allowed then scan_box(n)
  else begin print_err("Improper "); print_esc("setbox");
@.Improper \\setbox@>
    help2("Sorry, \setbox is not allowed after \halign in a display,")@/
    ("or between \accent and an accented character."); error;
    end;
  end;

@ The |space_factor| or |prev_depth| settings are changed when a |set_aux|
command is sensed. Similarly, |prev_graf| is changed in the presence of
|set_prev_graf|, and |dead_cycles| or |insert_penalties| in the presence of
|set_page_int|. These definitions are always global.

When some dimension of a box register is changed, the change isn't exactly
global; but \TeX\ does not look at the \.{\\global} switch.

@<Assignments@>=
set_aux:alter_aux;
set_prev_graf:alter_prev_graf;
set_page_dimen:alter_page_so_far;
set_page_int:alter_integer;
set_box_dimen:alter_box_dimen;

@ @<Declare subprocedures for |prefixed_command|@>=
procedure alter_aux;
var c:halfword; {|hmode| or |vmode|}
begin if cur_chr<>abs(mode) then report_illegal_case
else  begin c:=cur_chr; scan_optional_equals;
  if c=vmode then
    begin scan_normal_dimen; prev_depth:=cur_val;
    end
  else  begin scan_int;
    if (cur_val<=0)or(cur_val>32767) then
      begin print_err("Bad space factor");
@.Bad space factor@>
      help1("I allow only values in the range 1..32767 here.");
      int_error(cur_val);
      end
    else space_factor:=cur_val;
    end;
  end;
end;

@ @<Declare subprocedures for |prefixed_command|@>=
procedure alter_prev_graf;
var p:0..nest_size; {index into |nest|}
begin nest[nest_ptr]:=cur_list; p:=nest_ptr;
while abs(nest[p].mode_field)<>vmode do decr(p);
scan_optional_equals; scan_int;
if cur_val<0 then
  begin print_err("Bad "); print_esc("prevgraf");
@.Bad \\prevgraf@>
  help1("I allow only nonnegative values here.");
  int_error(cur_val);
  end
else  begin nest[p].pg_field:=cur_val; cur_list:=nest[nest_ptr];
  end;
end;

@ @<Declare subprocedures for |prefixed_command|@>=
procedure alter_page_so_far;
var c:0..7; {index into |page_so_far|}
begin c:=cur_chr; scan_optional_equals; scan_normal_dimen;
page_so_far[c]:=cur_val;
end;

@ @<Declare subprocedures for |prefixed_command|@>=
procedure alter_integer;
var c:small_number;
  {0 for \.{\\deadcycles}, 1 for \.{\\insertpenalties}, etc.}
begin c:=cur_chr; scan_optional_equals; scan_int;
if c=0 then dead_cycles:=cur_val
@/@<Cases for |alter_integer|@>@/
else insert_penalties:=cur_val;
end;

@ @<Declare subprocedures for |prefixed_command|@>=
procedure alter_box_dimen;
var c:small_number; {|width_offset| or |height_offset| or |depth_offset|}
@!b:eight_bits; {box number}
begin c:=cur_chr; scan_register_num; b:=cur_val; scan_optional_equals;
scan_normal_dimen;
if box(b)<>null then vmem(box(b)+c).sc:=cur_val;
end;

@ Paragraph shapes are set up in an obvious way. It needs one word more than in 
\TeX, though.

@d shape_node=54 { storage for shape pointers }

@<Assignments@>=
set_shape: begin q:=cur_chr; scan_optional_equals; scan_int; n:=cur_val;
  if n<=0 then p:=null
  else if q>par_shape_loc then
    begin n:=(cur_val div 2)+1; p:=new_node(shape_node,2*n+1+1); vinfo(p+1):=n;
    n:=cur_val; vmem(p+2).int:=n; {number of penalties}
    for j:=p+3 to p+n+2 do
      begin scan_int; vmem(j).int:=cur_val; {penalty values}
      end;
    if not odd(n) then vmem(p+n+3).int:=0; {unused}
    end
  else  begin p:=new_node(shape_node,2*(n+1)+1); vinfo(p+1):=n;
    for j:=1 to n do
      begin scan_normal_dimen;
      vmem(p+2*j).sc:=cur_val; {indentation}
      scan_normal_dimen;
      vmem(p+2*j+1).sc:=cur_val; {width}
      end;
    end;
  define(q,shape_ref,p);
  end;

@ New language information data is loaded by the |hyph_data| command.

@<Put each...@>=
primitive("hyphenation",hyph_data,0);
@!@:hyphenation_}{\.{\\hyphenation} primitive@>
primitive("patterns",hyph_data,1);
@!@:patterns_}{\.{\\patterns} primitive@>
primitive("prehyphenchar",hyph_data,2);
@!@:prehyphenchar_}{\.{\\prehyphenchar} primitive@>
primitive("posthyphenchar",hyph_data,3);
@!@:posthyphenchar_}{\.{\\posthyphenchar} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
hyph_data: case cur_chr of 
    0: print_esc("hyphenation"); 
    1: print_esc("patterns"); 
    2: print_esc("prehyphenchar"); 
    3: print_esc("posthyphenchar");
    endcases;

@ @<Assignments@>=
hyph_data: begin 
   case cur_chr of 
    0: new_hyph_exceptions; 
    1: new_patterns; 
    2: new_pre_hyphen_char; 
    3: new_post_hyphen_char;
    endcases;
  goto done;
  end;

@ All of \TeX's parameters are kept in |eqtb| except the font information,
the interaction mode, and the hyphenation tables; these are strictly global.

@<Assignments@>=
assign_font_dimen: set_font_dimen;
assign_font_int: begin 
  n:=cur_chr; scan_font_ident; f:=cur_val;
  if n = no_lig_code then set_no_ligatures(f)
  else if n < lp_code_base then begin
    scan_optional_equals; scan_int;
    if n=0 then set_hyphen_char(f,cur_val)@+else set_skew_char(f,cur_val);
  end
  else begin
    scan_char_num; p := cur_val;
    scan_optional_equals; scan_int;
    case n of
    lp_code_base: set_lp_code(f, p, cur_val);
    rp_code_base: set_rp_code(f, p, cur_val);
    ef_code_base: set_ef_code(f, p, cur_val);
    tag_code:     set_tag_code(f, p, cur_val);
    end;
  end;
end;

@ @<Put each...@>=
primitive("hyphenchar",assign_font_int,0);
@!@:hyphen_char_}{\.{\\hyphenchar} primitive@>
primitive("skewchar",assign_font_int,1);
@!@:skew_char_}{\.{\\skewchar} primitive@>
primitive("lpcode",assign_font_int,lp_code_base);
@!@:lp_code_}{\.{\\lpcode} primitive@>
primitive("rpcode",assign_font_int,rp_code_base);
@!@:rp_code_}{\.{\\rpcode} primitive@>
primitive("efcode",assign_font_int,ef_code_base);
@!@:ef_code_}{\.{\\efcode} primitive@>
primitive("tagcode",assign_font_int,tag_code);
@!@:tag_code_}{\.{\\tagcode} primitive@>
primitive("pdfnoligatures",assign_font_int,no_lig_code);
@!@:no_lig_code_}{\.{\\pdfnoligatures} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
assign_font_int: case chr_code of
0: print_esc("hyphenchar");
1: print_esc("skewchar");
lp_code_base: print_esc("lpcode");
rp_code_base: print_esc("rpcode");
ef_code_base: print_esc("efcode");
tag_code: print_esc("tagcode");
no_lig_code: print_esc("pdfnoligatures");
endcases;

@ Here is where the information for a new font gets loaded.

@<Assignments@>=
def_font: def_new_font(a);
letterspace_font: new_letterspaced_font(a);

@ @<Declare subprocedures for |prefixed_command|@>=
procedure def_new_font(@!a:small_number);
var u:pointer; {user's font identifier}
@!s:scaled; {stated ``at'' size, or negative of scaled magnification}
@!f:internal_font_number; {runs through existing fonts}
@!t:str_number; {name for the frozen font identifier}
@!old_setting:0..max_selector; {holds |selector| setting}
@!offset:integer;
@!natural_dir:integer;{the natural direction of the font}
@!flushable_string:str_number; {string not yet referenced}
@!junk:pointer;
begin if job_name=0 then open_log_file;
  {avoid confusing \.{texput} with the font name}
@.texput@>
get_r_token; u:=cur_cs;
if u>=hash_base then t:=text(u)
else if u=null_cs then t:="FONT"
else  begin old_setting:=selector; selector:=new_string;
  print("FONT"); print(u-active_base); selector:=old_setting;
@.FONTx@>
  str_room(1); t:=make_string;
  end;
define(u,set_font,null_font); scan_optional_equals; 
@<Get the next non-blank non-call token@>;
if cur_cmd<>left_brace then begin
  back_input;
  scan_file_name;
  end 
else begin
  back_input;
  junk:=scan_toks(false,true);
  old_setting:=selector; selector:=new_string;
  token_show(def_ref); selector:=old_setting;
  flush_list(def_ref);
  str_room(1);
  cur_name:=make_string;
  cur_ext:=""; 
  cur_area:="";
  end;
@<Scan the font size specification@>;
name_in_progress:=true;
if scan_keyword("offset") then begin
  scan_int;
  offset:=cur_val;
  if (cur_val<0) then begin
    print_err("Illegal offset has been changed to 0");
    help1("The offset must be bigger than 0."); int_error(cur_val);
    offset:=0;
    end
  end
else offset:=0;
if scan_keyword("naturaldir") then begin
  scan_direction;
  natural_dir:=cur_val;
  end
else natural_dir:=-1;
name_in_progress:=false;
if cur_area = "" then
  f:=read_font_info(u,cur_name,"",s,natural_dir)
else
  f:=read_font_info(u,cur_name,cur_area,s,natural_dir);
equiv(u):=f; eqtb[font_id_base+f]:=eqtb[u]; font_id_text(f):=t;
end;

@ @<Scan the font size specification@>=
name_in_progress:=true; {this keeps |cur_name| from being changed}
if scan_keyword("at") then @<Put the \(p)(positive) `at' size into |s|@>
@.at@>
else if scan_keyword("scaled") then
@.scaled@>
  begin scan_int; s:=-cur_val;
  if (cur_val<=0)or(cur_val>32768) then
    begin print_err("Illegal magnification has been changed to 1000");@/
@.Illegal magnification...@>
    help1("The magnification ratio must be between 1 and 32768.");
    int_error(cur_val); s:=-1000;
    end;
  end
else s:=-1000;
name_in_progress:=false

@ @<Put the \(p)(positive) `at' size into |s|@>=
begin scan_normal_dimen; s:=cur_val;
if (s<=0)or(s>=@'1000000000) then
  begin print_err("Improper `at' size (");
  print_scaled(s); print("pt), replaced by 10pt");
@.Improper `at' size...@>
  help2("I can only handle fonts at positive sizes that are")@/
  ("less than 2048pt, so I've changed what you said to 10pt.");
  error; s:=10*unity;
  end;
end


@ @<Cases of |print_cmd_chr|...@>=
set_font:begin print("select font "); print_font_name(chr_code);
  if font_size(chr_code)<>font_dsize(chr_code) then
    begin print(" at "); print_scaled(font_size(chr_code));
    print("pt");
    end;
  end;

@ @<Put each...@>=
primitive("batchmode",set_interaction,batch_mode);
@!@:batch_mode_}{\.{\\batchmode} primitive@>
primitive("nonstopmode",set_interaction,nonstop_mode);
@!@:nonstop_mode_}{\.{\\nonstopmode} primitive@>
primitive("scrollmode",set_interaction,scroll_mode);
@!@:scroll_mode_}{\.{\\scrollmode} primitive@>
primitive("errorstopmode",set_interaction,error_stop_mode);
@!@:error_stop_mode_}{\.{\\errorstopmode} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
set_interaction: case chr_code of
  batch_mode: print_esc("batchmode");
  nonstop_mode: print_esc("nonstopmode");
  scroll_mode: print_esc("scrollmode");
  othercases print_esc("errorstopmode")
  endcases;

@ @<Assignments@>=
set_interaction: new_interaction;

@ @<Declare subprocedures for |prefixed_command|@>=
procedure new_interaction;
begin print_ln;
interaction:=cur_chr;
@<Initialize the print |selector| based on |interaction|@>;
if log_opened then selector:=selector+2;
end;

@ The \.{\\afterassignment} command puts a token into the global
variable |after_token|. This global variable is examined just after
every assignment has been performed.

@<Glob...@>=
@!after_token:halfword; {zero, or a saved token}

@ @<Set init...@>=
after_token:=0;

@ @<Cases of |main_control| that don't...@>=
any_mode(after_assignment):begin get_token; after_token:=cur_tok;
  end;

@ @<Insert a token saved by \.{\\afterassignment}, if any@>=
if after_token<>0 then
  begin cur_tok:=after_token; back_input; after_token:=0;
  end

@ Here is a procedure that might be called `Get the next non-blank non-relax
non-call non-assignment token'.

@<Declare act...@>=
procedure do_assignments;
label exit;
begin loop begin @<Get the next non-blank non-relax...@>;
  if cur_cmd<=max_non_prefixed_command then return;
  set_box_allowed:=false; prefixed_command; set_box_allowed:=true;
  end;
exit:end;

@ @<Cases of |main_control| that don't...@>=
any_mode(after_group):begin get_token; save_for_after(cur_tok);
  end;

@ Files for \.{\\read} are opened and closed by the |in_stream| command.

@<Put each...@>=
primitive("openin",in_stream,1);
@!@:open_in_}{\.{\\openin} primitive@>
primitive("closein",in_stream,0);
@!@:close_in_}{\.{\\closein} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
in_stream: if chr_code=0 then print_esc("closein")
  else print_esc("openin");

@ @<Cases of |main_control| that don't...@>=
any_mode(in_stream): open_or_close_in;

@ @<Declare act...@>=
procedure open_or_close_in;
var c:0..1; {1 for \.{\\openin}, 0 for \.{\\closein}}
@!n:0..15; {stream number}
begin c:=cur_chr; scan_four_bit_int; n:=cur_val;
if read_open[n]<>closed then
  begin lua_a_close_in(read_file[n],(n+1)); read_open[n]:=closed;
  end;
if c<>0 then
  begin scan_optional_equals; scan_file_name;
  if cur_ext="" then cur_ext:=".tex";
  pack_cur_name;
  if lua_a_open_in(read_file[n],(n+1)) then begin
     read_file[n]:= name_file_pointer;
     read_open[n]:=just_open;
     end;
  end;
end;

@ The user can issue messages to the terminal, regardless of the
current mode.

@<Cases of |main_control| that don't...@>=
any_mode(message):issue_message;

@ @<Put each...@>=
primitive("message",message,0);
@!@:message_}{\.{\\message} primitive@>
primitive("errmessage",message,1);
@!@:err_message_}{\.{\\errmessage} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
message: if chr_code=0 then print_esc("message")
  else print_esc("errmessage");

@ @<Declare act...@>=
procedure issue_message;
var old_setting:0..max_selector; {holds |selector| setting}
junk:pointer;
@!c:0..1; {identifies \.{\\message} and \.{\\errmessage}}
@!s:str_number; {the message}
begin c:=cur_chr; junk:=scan_toks(false,true);
old_setting:=selector; selector:=new_string;
token_show(def_ref); selector:=old_setting;
flush_list(def_ref);
str_room(1); s:=make_string;
if c=0 then @<Print string |s| on the terminal@>
else @<Print string |s| as an error message@>;
flush_string;
end;

@ @<Print string |s| on the terminal@>=
begin if term_offset+length(s)>max_print_line-2 then print_ln
else if (term_offset>0)or(file_offset>0) then print_char(" ");
slow_print(s); update_terminal;
end

@ If \.{\\errmessage} occurs often in |scroll_mode|, without user-defined
\.{\\errhelp}, we don't want to give a long help message each time. So we
give a verbose explanation only once.

@<Glob...@>=
@!long_help_seen:boolean; {has the long \.{\\errmessage} help been used?}

@ @<Set init...@>=long_help_seen:=false;

@ @<Print string |s| as an error message@>=
begin print_err(""); slow_print(s);
if err_help<>null then use_err_help:=true
else if long_help_seen then help1("(That was another \errmessage.)")
else  begin if interaction<error_stop_mode then long_help_seen:=true;
  help4("This error message was generated by an \errmessage")@/
  ("command, so I can't give any explicit help.")@/
  ("Pretend that you're Hercule Poirot: Examine all clues,")@/
@^Poirot, Hercule@>
  ("and deduce the truth by order and method.");
  end;
error; use_err_help:=false;
end

@ The |error| routine calls on |give_err_help| if help is requested from
the |err_help| parameter.

@p procedure give_err_help;
begin token_show(err_help);
end;

@ The \.{\\uppercase} and \.{\\lowercase} commands are implemented by
building a token list and then changing the cases of the letters in it.

@<Cases of |main_control| that don't...@>=
any_mode(case_shift):shift_case;

@ @<Put each...@>=
primitive("lowercase",case_shift,lc_code_base);
@!@:lowercase_}{\.{\\lowercase} primitive@>
primitive("uppercase",case_shift,uc_code_base);
@!@:uppercase_}{\.{\\uppercase} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
case_shift:if chr_code=lc_code_base then print_esc("lowercase")
  else print_esc("uppercase");

@ @<Declare act...@>=
procedure shift_case;
var b:pointer; {|lc_code_base| or |uc_code_base|}
@!p:pointer; {runs through the token list}
@!t:halfword; {token}
@!c:halfword; {character code}
@!i:halfword; {inbetween}
begin b:=cur_chr; p:=scan_toks(false,false); p:=link(def_ref);
while p<>null do
  begin @<Change the case of the token in |p|, if a change is appropriate@>;
  p:=link(p);
  end;
back_list(link(def_ref)); free_avail(def_ref); {omit reference count}
end;

@ When the case of a |chr_code| changes, we don't change the |cmd|.
We also change active characters, using the fact that
|cs_token_flag+active_base| is a multiple of~|string_offset|.
@^data structure assumptions@>

@<Change the case of the token in |p|, if a change is appropriate@>=
t:=info(p);
if t<cs_token_flag+null_cs then
  begin 
  c:=t mod string_offset;
  if b=uc_code_base then begin 
     i:=get_uc_code(c);
	 if i<>0 then info(p):=t-c+i; 
     end
  else 
     begin if get_lc_code(c)<>0 then info(p):=t-c+get_lc_code(c); end;
  end

@ We come finally to the last pieces missing from |main_control|, namely the
`\.{\\show}' commands that are useful when debugging.

@<Cases of |main_control| that don't...@>=
any_mode(xray): show_whatever;

@ @d show_code=0 { \.{\\show} }
@d show_box_code=1 { \.{\\showbox} }
@d show_the_code=2 { \.{\\showthe} }
@d show_lists=3 { \.{\\showlists} }

@<Put each...@>=
primitive("show",xray,show_code);
@!@:show_}{\.{\\show} primitive@>
primitive("showbox",xray,show_box_code);
@!@:show_box_}{\.{\\showbox} primitive@>
primitive("showthe",xray,show_the_code);
@!@:show_the_}{\.{\\showthe} primitive@>
primitive("showlists",xray,show_lists);
@!@:show_lists_}{\.{\\showlists} primitive@>

@ @<Cases of |print_cmd_chr|...@>=
xray: case chr_code of
  show_box_code:print_esc("showbox");
  show_the_code:print_esc("showthe");
  show_lists:print_esc("showlists");
  @<Cases of |xray| for |print_cmd_chr|@>@;@/
  othercases print_esc("show")
  endcases;

@ @<Declare act...@>=
procedure show_whatever;
label common_ending;
var p:pointer; {tail of a token list to show}
@!t:small_number; {type of conditional being shown}
@!m:normal..or_code; {upper bound on |fi_or_else| codes}
@!l:integer; {line where that conditional began}
@!n:integer; {level of \.{\\if...\\fi} nesting}
begin case cur_chr of
show_lists: begin begin_diagnostic; show_activities;
  end;
show_box_code: @<Show the current contents of a box@>;
show_code: @<Show the current meaning of a token, then |goto common_ending|@>;
@<Cases for |show_whatever|@>@;@/
othercases @<Show the current value of some parameter or register,
  then |goto common_ending|@>
endcases;@/
@<Complete a potentially long \.{\\show} command@>;
common_ending: if interaction<error_stop_mode then
  begin help0; decr(error_count);
  end
else if tracing_online>0 then
  begin@t@>@;@/
  help3("This isn't an error message; I'm just \showing something.")@/
  ("Type `I\show...' to show more (e.g., \show\cs,")@/
  ("\showthe\count10, \showbox255, \showlists).");
  end
else  begin@t@>@;@/
  help5("This isn't an error message; I'm just \showing something.")@/
  ("Type `I\show...' to show more (e.g., \show\cs,")@/
  ("\showthe\count10, \showbox255, \showlists).")@/
  ("And type `I\tracingonline=1\show...' to show boxes and")@/
  ("lists on your terminal as well as in the transcript file.");
  end;
error;
end;

@ @<Show the current meaning of a token...@>=
begin get_token;
if interaction=error_stop_mode then wake_up_terminal;
print_nl("> ");
if cur_cs<>0 then
  begin sprint_cs(cur_cs); print_char("=");
  end;
print_meaning; goto common_ending;
end

@ @<Cases of |print_cmd_chr|...@>=
undefined_cs: print("undefined");
call,long_call,outer_call,long_outer_call: begin n:=cmd-call;
  if info(link(chr_code))=protected_token then n:=n+4;
  if odd(n div 4) then print_esc("protected");
  if odd(n) then print_esc("long");
  if odd(n div 2) then print_esc("outer");
  if n>0 then print_char(" ");
  print("macro");
  end;
end_template: print_esc("outer endtemplate");

@ @<Show the current contents of a box@>=
begin scan_register_num; begin_diagnostic;
print_nl("> \box"); print_int(cur_val); print_char("=");
if box(cur_val)=null then print("void")
else show_box(box(cur_val));
end

@ @<Show the current value of some parameter...@>=
begin p:=the_toks;
if interaction=error_stop_mode then wake_up_terminal;
print_nl("> "); token_show(temp_token_head);
flush_list(link(temp_token_head)); goto common_ending;
end

@ @<Complete a potentially long \.{\\show} command@>=
end_diagnostic(true); print_err("OK");
@.OK@>
if selector=term_and_log then if tracing_online<=0 then
  begin selector:=term_only; print(" (see the transcript file)");
  selector:=term_and_log;
  end

@* \[50] Dumping and undumping the tables.
After \.{INITEX} has seen a collection of fonts and macros, it
can write all the necessary information on an auxiliary file so
that production versions of \TeX\ are able to initialize their
memory at high speed. The present section of the program takes
care of such output and input. We shall consider simultaneously
the processes of storing and restoring,
so that the inverse relation between them is clear.
@.INITEX@>

The global variable |format_ident| is a string that is printed right
after the |banner| line when \TeX\ is ready to start. For \.{INITEX} this
string says simply `\.{(INITEX)}'; for other versions of \TeX\ it says,
for example, `\.{(preloaded format=plain 82.11.19)}', showing the year,
month, and day that the format file was created. We have |format_ident=0|
before \TeX's tables are loaded.

@<Glob...@>=
@!format_ident:str_number;
@!format_name:str_number; {principal file name}

@ @<Set init...@>=
format_ident:=0;
format_name:="";

@ @<Initialize table entries...@>=
format_ident:=" (INITEX)";

@ @<Declare act...@>=
@!init procedure store_fmt_file;
label found1,found2,done1,done2;
var j,@!k,@!l:integer; {all-purpose indices}
@!p: pointer; {all-purpose pointer}
@!x: integer; {something to dump}
@!w: four_quarters; {four ASCII codes}
begin @<If dumping is not allowed, abort@>;
@<Create the |format_ident|, open the format file,
  and inform the user that dumping has begun@>;
@<Dump constants for consistency check@>;
@<Dump the string pool@>;
@<Dump the dynamic memory@>;
@<Dump the table of equivalents@>;
@<Dump the font information@>;
@<Dump the active ocp information@>;
@<Dump the ocp information@>;
@<Dump the ocp list information@>;
@<Dump the hyphenation tables@>;
@<Dump a couple more things and the closing check word@>;
@<Dump the lua bytecodes@>;
@<Close the format file@>;
end;
tini

@ Corresponding to the procedure that dumps a format file, we have a function
that reads one in. The function returns |false| if the dumped format is
incompatible with the present \TeX\ table sizes, etc.

@d bad_fmt=6666 {go here if the format file is unacceptable}
@d too_small(#)==begin wake_up_terminal;
  wterm_ln('---! Must increase the ',#);
@.Must increase the x@>
  goto bad_fmt;
  end

@p @t\4@>@<Declare the function called |open_fmt_file|@>@;
function load_fmt_file:boolean;
label bad_fmt,exit;
var j,@!k:integer; {all-purpose indices}
@!p: pointer; {all-purpose pointer}
@!x: integer; {something undumped}
@!w: four_quarters; {four ASCII codes}
begin @<Undump constants for consistency check@>;
@<Undump the string pool@>;
@<Undump the dynamic memory@>;
@<Undump the table of equivalents@>;
@<Undump the font information@>;
@<Undump the active ocp information@>;
@<Undump the ocp information@>;
@<Undump the ocp list information@>;
@<Undump the hyphenation tables@>;
@<Undump a couple more things and the closing check word@>;
@<Undump the lua bytecodes@>;
load_fmt_file:=true; return; {it worked!}
bad_fmt: wake_up_terminal;
  wterm_ln('(Fatal format file error; I''m stymied)');
@.Fatal format file error@>
load_fmt_file:=false;
exit:end;

@ The user is not allowed to dump a format file unless |save_ptr=0|.
This condition implies that |cur_level=level_one|, hence
the |xeq_level| array is constant and it need not be dumped.

@<If dumping is not allowed, abort@>=
if save_ptr<>0 then
  begin print_err("You can't dump inside a group");
@.You can't dump...@>
  help1("`{...\dump}' is a no-no."); succumb;
  end

@ Format files consist of |memory_word| items, and we use the following
macros to dump words of different types:

@d dump_wd(#)==begin fmt_file^:=#; put(fmt_file);@+end
@d dump_int(#)==begin fmt_file^.int:=#; put(fmt_file);@+end
@d dump_hh(#)==begin fmt_file^.hh:=#; put(fmt_file);@+end
@d dump_qqqq(#)==begin fmt_file^.qqqq:=#; put(fmt_file);@+end

@<Glob...@>=
@!fmt_file:word_file; {for input or output of format information}

@ The inverse macros are slightly more complicated, since we need to check
the range of the values we are reading in. We say `|undump(a)(b)(x)|' to
read an integer value |x| that is supposed to be in the range |a<=x<=b|.

@d undump_wd(#)==begin get(fmt_file); #:=fmt_file^;@+end
@d undump_int(#)==begin get(fmt_file); #:=fmt_file^.int;@+end
@d undump_hh(#)==begin get(fmt_file); #:=fmt_file^.hh;@+end
@d undump_qqqq(#)==begin get(fmt_file); #:=fmt_file^.qqqq;@+end
@d undump_end_end(#)==#:=x;@+end
@d undump_end(#)==(x>#) then goto bad_fmt@+else undump_end_end
@d undump(#)==begin undump_int(x); if (x<#) or undump_end
@d undump_size_end_end(#)==too_small(#)@+else undump_end_end
@d undump_size_end(#)==if x># then undump_size_end_end
@d undump_size(#)==begin undump_int(x);
  if x<# then goto bad_fmt; undump_size_end

@ The next few sections of the program should make it clear how we use the
dump/undump macros.

@<Dump constants for consistency check@>=
dump_int(@$);@/
dump_int(eqtb_size);@/
dump_int(hash_prime)

@ Sections of a \.{WEB} program that are ``commented out'' still contribute
strings to the string pool; therefore \.{INITEX} and \TeX\ will have
the same strings. (And it is, of course, a good thing that they do.)
@.WEB@>
@^string pool@>

@<Undump constants for consistency check@>=
x:=fmt_file^.int;
if x<>@$ then goto bad_fmt; {check that strings are the same}
undump_int(x);@/
if x<>eqtb_size then goto bad_fmt;
undump_int(x);
if x<>hash_prime then goto bad_fmt

@ @d dump_four_ASCII==
  w.b0:=qi(so(str_pool[k])); w.b1:=qi(so(str_pool[k+1]));
  w.b2:=qi(so(str_pool[k+2])); w.b3:=qi(so(str_pool[k+3]));
  dump_qqqq(w)

@<Dump the string pool@>=
dump_int(pool_ptr);
dump_int(str_ptr);
for k:=string_offset to str_ptr do dump_int(str_start_macro(k));
k:=0;
while k+4<pool_ptr do
  begin dump_four_ASCII; k:=k+4;
  end;
k:=pool_ptr-4; dump_four_ASCII;
print_ln; print_int(str_ptr-string_offset); print(" strings of total length ");
print_int(pool_ptr)

@ @d undump_four_ASCII==
  undump_qqqq(w);
  str_pool[k]:=si(qo(w.b0)); str_pool[k+1]:=si(qo(w.b1));
  str_pool[k+2]:=si(qo(w.b2)); str_pool[k+3]:=si(qo(w.b3))

@<Undump the string pool@>=
undump_size(0)(pool_size)('string pool size')(pool_ptr);
undump_size(0)(max_strings)('max strings')(str_ptr);
for k:=string_offset to str_ptr do undump(0)(pool_ptr)(str_start_macro(k));
k:=0;
while k+4<pool_ptr do
  begin undump_four_ASCII; k:=k+4;
  end;
k:=pool_ptr-4; undump_four_ASCII;
init_str_ptr:=str_ptr; init_pool_ptr:=pool_ptr

@ By sorting the list of available spaces in the variable-size portion of
|mem|, we are usually able to get by without having to dump very much
of the dynamic memory.

We recompute |var_used| and |dyn_used|, so that \.{INITEX} dumps valid
information even when it has not been gathering statistics.

@<Dump the dynamic memory@>=
dump_node_mem;
@#
dump_int(temp_token_head); dump_int(hold_token_head);
dump_int(omit_template); dump_int(null_list);
dump_int(backup_head); dump_int(garbage);
dump_int(fix_mem_min); dump_int(fix_mem_max);
dump_int(fix_mem_end);
dump_int(avail);
dyn_used:=fix_mem_end+1;
for k:=fix_mem_min to fix_mem_end do dump_wd(mem(k));
x:=x+(fix_mem_end+1-fix_mem_min);
p:=avail;
while p<>null do
  begin decr(dyn_used); p:=link(p);
  end;
dump_int(dyn_used);
print_ln; print_int(x);
print(" memory locations dumped; current usage is ");
print_int(var_used); print_char("&"); print_int(dyn_used)

@ @<Undump the dynamic memory@>=
undump_node_mem;
@#
undump_int(temp_token_head); undump_int(hold_token_head);
undump_int(omit_template); undump_int(null_list); 
undump_int(backup_head); undump_int(garbage);
undump_int(fix_mem_min);undump_int(fix_mem_max);
fixmem:= xmallocarray (smemory_word, fix_mem_max+1);
memset (voidcast(fixmem),0,(fix_mem_max+1)*sizeof(smemory_word));
undump_int(fix_mem_end);
undump_int(avail);
for k:=fix_mem_min to fix_mem_end do undump_wd(mem(k));
undump_int(dyn_used)

@ @<Dump the table of equivalents@>=
@<Dump regions 1 to 4 of |eqtb|@>;
@<Dump regions 5 and 6 of |eqtb|@>;
dump_int(par_loc); dump_int(write_loc);@/
dump_math_codes;
dump_text_codes;
@<Dump the hash table@>

@ @<Undump the table of equivalents@>=
@<Undump regions 1 to 6 of |eqtb|@>;
undump(hash_base)(frozen_control_sequence)(par_loc);
par_token:=cs_token_flag+par_loc;@/
undump(hash_base)(frozen_control_sequence)(write_loc);@/
undump_math_codes;
undump_text_codes;
@<Undump the hash table@>

@ The table of equivalents usually contains repeated information, so we dump it
in compressed form: The sequence of $n+2$ values $(n,x_1,\ldots,x_n,m)$ in the
format file represents $n+m$ consecutive entries of |eqtb|, with |m| extra
copies of $x_n$, namely $(x_1,\ldots,x_n,x_n,\ldots,x_n)$.

@<Dump regions 1 to 4 of |eqtb|@>=
k:=active_base;
repeat j:=k;
while j<int_base-1 do
  begin if (equiv(j)=equiv(j+1))and(eq_type(j)=eq_type(j+1))and@|
    (eq_level(j)=eq_level(j+1)) then goto found1;
  incr(j);
  end;
l:=int_base; goto done1; {|j=int_base-1|}
found1: incr(j); l:=j;
while j<int_base-1 do
  begin if (equiv(j)<>equiv(j+1))or(eq_type(j)<>eq_type(j+1))or@|
    (eq_level(j)<>eq_level(j+1)) then goto done1;
  incr(j);
  end;
done1:
dump_int(l-k);
while k<l do
  begin dump_wd(eqtb[k]); incr(k);
  end;
k:=j+1; dump_int(k-l);
until k=int_base

@ @<Dump regions 5 and 6 of |eqtb|@>=
repeat j:=k;
while j<eqtb_size do
  begin if eqtb[j].int=eqtb[j+1].int then goto found2;
  incr(j);
  end;
l:=eqtb_size+1; goto done2; {|j=eqtb_size|}
found2: incr(j); l:=j;
while j<eqtb_size do
  begin if eqtb[j].int<>eqtb[j+1].int then goto done2;
  incr(j);
  end;
done2:dump_int(l-k);
while k<l do
  begin dump_wd(eqtb[k]); incr(k);
  end;
k:=j+1; dump_int(k-l);
until k>eqtb_size

@ @<Undump regions 1 to 6 of |eqtb|@>=
k:=active_base;
repeat undump_int(x);
if (x<1)or(k+x>eqtb_size+1) then goto bad_fmt;
for j:=k to k+x-1 do undump_wd(eqtb[j]);
k:=k+x;
undump_int(x);
if (x<0)or(k+x>eqtb_size+1) then goto bad_fmt;
for j:=k to k+x-1 do eqtb[j]:=eqtb[k-1];
k:=k+x;
until k>eqtb_size

@ A different scheme is used to compress the hash table, since its lower
region is usually sparse. When |text(p)<>0| for |p<=hash_used|, we output
two words, |p| and |hash[p]|. The hash table is, of course, densely packed
for |p>=hash_used|, so the remaining entries are output in a~block.

@<Dump the hash table@>=
for p:=0 to prim_size do dump_hh(prim[p]);
for p:=0 to prim_size do dump_wd(prim_eqtb[p]);
dump_int(hash_used); cs_count:=frozen_control_sequence-1-hash_used;
for p:=hash_base to hash_used do if text(p)<>0 then
  begin dump_int(p); dump_hh(hash[p]); incr(cs_count);
  end;
for p:=hash_used+1 to undefined_control_sequence-1 do dump_hh(hash[p]);
dump_int(cs_count);@/
print_ln; print_int(cs_count); print(" multiletter control sequences")

@ @<Undump the hash table@>=
for p:=0 to prim_size do undump_hh(prim[p]);
for p:=0 to prim_size do undump_wd(prim_eqtb[p]);
undump(hash_base)(frozen_control_sequence)(hash_used); p:=hash_base-1;
repeat undump(p+1)(hash_used)(p); undump_hh(hash[p]);
until p=hash_used;
for p:=hash_used+1 to undefined_control_sequence-1 do undump_hh(hash[p]);
undump_int(cs_count)

@ @<Dump the font information@>=
dump_int(max_font_id);
for k:=0 to max_font_id do
  @<Dump the array info for internal font number |k|@>;
print_ln; print_int(max_font_id); print(" preloaded font");
if max_font_id<>1 then print_char("s")

@ @<Undump the font information@>=
undump_int(x);
set_max_font_id(x);
for k:=0 to max_font_id do
  @<Undump the array info for internal font number |k|@>

@ @<Dump the array info for internal font number |k|@>=
begin dump_font(k);
print_nl("\font"); print_esc(font_id_text(k)); print_char("=");
print_file_name(tex_font_name(k),tex_font_area(k),"");
flush_string; flush_string;
if font_size(k)<>font_dsize(k) then
  begin print(" at "); print_scaled(font_size(k)); print("pt");
  end;
end

@ @<Undump the array info for internal font number |k|@>=
begin undump_font(k);@/
end

@ @<Dump the active ocp information@>=
dump_int(active_min_ptr);
dump_int(active_max_ptr);
for k:=0 to active_max_ptr-1 do dump_wd(active_info[k]);
if active_max_ptr>0 then begin
  print_ln; print_int(active_max_ptr); print(" words of active ocps");
  end;

@ @<Undump the active ocp information@>=
undump_size(0)(active_mem_size)('active start point')(active_min_ptr);
undump_size(0)(active_mem_size)('active mem size')(active_max_ptr);
for k:=0 to active_max_ptr-1 do undump_wd(active_info[k]);

@ @<Dump the ocp information@>=
dump_int(ocp_ptr);
for k:=null_ocp to ocp_ptr do
  @<Dump the array info for internal ocp number |k|@>;
if ocp_ptr-ocp_base>0 then begin
  print_ln; print_int(ocp_ptr-ocp_base); print(" preloaded ocp");
  if ocp_ptr<>ocp_base+1 then print_char("s");
  end

@ @<Undump the ocp information@>=
undump_size(ocp_base)(ocp_biggest)('ocp max')(ocp_ptr);
for k:=null_ocp to ocp_ptr do
  @<Undump the array info for internal ocp number |k|@>

@ @<Dump the array info for internal ocp number |k|@>=
begin dump_ocp_table(k);
if ocp_ptr-ocp_base>0 then begin
  print_nl("\ocp"); print_esc(ocp_id_text(k)); print_char("=");
  print_file_name(ocp_name(k),ocp_area(k),"");
  end;
end

@ @<Undump the array info for internal ocp number |k|@>=
begin undump_ocp_table(k);
end

@ @<Dump the ocp list information@>=
dump_int(ocp_listmem_ptr);
for k:=0 to ocp_listmem_ptr-1 do dump_wd(ocp_list_info[k]);
dump_int(ocp_list_ptr);
for k:=null_ocp_list to ocp_list_ptr do begin
  dump_int(ocp_list_list[k]);
  if null_ocp_list<>ocp_list_ptr then begin
    print_nl("\ocplist"); 
    print_esc(ocp_list_id_text(k)); 
    print_char("=");
    print_ocp_list(ocp_list_list[k]);
    end;
  end;
dump_int(ocp_lstackmem_ptr);
for k:=0 to ocp_lstackmem_ptr-1 do dump_wd(ocp_lstack_info[k])

@ @<Undump the ocp list information@>=
undump_size(1)(1000000)('ocp list mem size')(ocp_listmem_ptr);
for k:=0 to ocp_listmem_ptr-1 do undump_wd(ocp_list_info[k]);
undump_size(ocp_list_base)(ocp_list_biggest)('ocp list max')(ocp_list_ptr);
for k:=null_ocp_list to ocp_list_ptr do
  undump_int(ocp_list_list[k]);
undump_size(1)(1000000)('ocp lstack mem size')(ocp_lstackmem_ptr);
for k:=0 to ocp_lstackmem_ptr-1 do undump_wd(ocp_lstack_info[k])

@ This is done in C

@<Dump the hyphenation tables@>=
dump_language_data

@ @<Undump the hyphenation tables@>=
undump_language_data

@ This is also done in C

@<Dump the lua bytecodes@>=
dump_luac_registers;

@ @<Undump the lua bytecodes@>=
undump_luac_registers;

@ We have already printed a lot of statistics, so we set |tracing_stats:=0|
to prevent them from appearing again.

@<Dump a couple more things and the closing check word@>=
dump_int(interaction); dump_int(format_ident); dump_int(format_name); dump_int(69069);
tracing_stats:=0

@ @<Undump a couple more things and the closing check word@>=
undump(batch_mode)(error_stop_mode)(interaction);
undump(0)(str_ptr)(format_ident);
undump(0)(str_ptr)(format_name);
undump_int(x);
if (x<>69069)or eof(fmt_file) then goto bad_fmt

@ @<Create the |format_ident|...@>=
selector:=new_string;
print(" (preloaded format="); print(job_name); print_char(" ");
print_int(year); print_char(".");
print_int(month); print_char("."); print_int(day); print_char(")");
str_room(2);
format_ident:=make_string;
print(job_name);
format_name:=make_string;
if interaction=batch_mode then selector:=log_only
else selector:=term_and_log;
pack_job_name(format_extension);
while not w_open_out(fmt_file) do
  prompt_file_name("format file name",format_extension);
print_nl("Beginning to dump on file ");
@.Beginning to dump...@>
slow_print(w_make_name_string(fmt_file)); flush_string;
print_nl(""); slow_print(format_ident)

@ @<Close the format file@>=
w_close(fmt_file)

@* \[51] The main program.
This is it: the part of \TeX\ that executes all those procedures we have
written.

Well---almost. Let's leave space for a few more routines that we may
have forgotten.

@p @<Last-minute procedures@>

@ We have noted that there are two versions of \TeX82. One, called \.{INITEX},
@.INITEX@>
has to be run first; it initializes everything from scratch, without
reading a format file, and it has the capability of dumping a format file.
The other one is called `\.{VIRTEX}'; it is a ``virgin'' program that needs
@.VIRTEX@>
to input a format file in order to get started. \.{VIRTEX} typically has
more memory capacity than \.{INITEX}, because it does not need the space
consumed by the auxiliary hyphenation tables and the numerous calls on
|primitive|, etc.

The \.{VIRTEX} program cannot read a format file instantaneously, of course;
the best implementations therefore allow for production versions of \TeX\ that
not only avoid the loading routine for \PASCAL\ object code, they also have
a format file pre-loaded. This is impossible to do if we stick to standard
\PASCAL; but there is a simple way to fool many systems into avoiding the
initialization, as follows:\quad(1)~We declare a global integer variable
called |ready_already|. The probability is negligible that this
variable holds any particular value like 314159 when \.{VIRTEX} is first
loaded.\quad(2)~After we have read in a format file and initialized
everything, we set |ready_already:=314159|.\quad(3)~Soon \.{VIRTEX}
will print `\.*', waiting for more input; and at this point we
interrupt the program and save its core image in some form that the
operating system can reload speedily.\quad(4)~When that core image is
activated, the program starts again at the beginning; but now
|ready_already=314159| and all the other global variables have
their initial values too. The former chastity has vanished!

In other words, if we allow ourselves to test the condition
|ready_already=314159|, before |ready_already| has been
assigned a value, we can avoid the lengthy initialization. Dirty tricks
rarely pay off so handsomely.
@^dirty \PASCAL@>
@^system dependencies@>

On systems that allow such preloading, the standard program called \.{TeX}
should be the one that has \.{plain} format preloaded, since that agrees
with {\sl The \TeX book}. Other versions, e.g., \.{AmSTeX}, should also
@:TeXbook}{\sl The \TeX book@>
@.AmSTeX@>
@.plain@>
be provided for commonly used formats.

@<Glob...@>=
@!ready_already:integer; {a sacrifice of purity for economy}

@ Now this is really it: \TeX\ starts and ends here.

The initial test involving |ready_already| should be deleted if the
\PASCAL\ runtime system is smart enough to detect such a ``mistake.''
@^system dependencies@>

@p begin @!{|start_here|}
history:=fatal_error_stop; {in case we quit during initialization}
t_open_out; {open the terminal for output}
if ready_already=314159 then goto start_of_TEX;
@<Check the ``constant'' values...@>@;
if bad>0 then
  begin wterm_ln('Ouch---my internal constants have been clobbered!',
    '---case ',bad:1);
@.Ouch...clobbered@>
  goto final_end;
  end;
initialize; {set global variables to their starting values}
@!init if not get_strings_started then goto final_end;
init_prim; {call |primitive| for each primitive}
init_str_ptr:=str_ptr; init_pool_ptr:=pool_ptr; fix_date_and_time;
tini@/
ready_already:=314159;
start_of_TEX: @<Initialize the output routines@>;
@<Get the first line of input and prepare to start@>;
history:=spotless; {ready to go!}
main_control; {come to life}
final_cleanup; {prepare for death}
end_of_TEX: close_files_and_terminate;
final_end: ready_already:=0;
end.

@ Put this in a function because two extra variables are needed
for callback testing, and putting those inside the main body is
ugly

@<Basic print...@>=
procedure print_banner;
var res:boolean;
   callback_id:integer;
begin
callback_id:=callback_defined(start_run_callback);
if callback_id=0 then begin
  wterm(banner);
  if format_ident=0 then wterm_ln(' (no format preloaded)')
  else  begin slow_print(format_ident); print_ln;
    end;
  end
else
  res:= run_callback(callback_id,'->');
update_terminal;
end;
@#
procedure print_version_banner;
begin
wterm(banner);
end;


@ Here we do whatever is needed to complete \TeX's job gracefully on the
local operating system. The code here might come into play after a fatal
error; it must therefore consist entirely of ``safe'' operations that
cannot produce error messages. For example, it would be a mistake to call
|str_room| or |make_string| at this time, because a call on |overflow|
might lead to an infinite loop.
@^system dependencies@>

Actually there's one way to get error messages, via |prepare_mag|;
but that can't cause infinite recursion.
@^recursion@>

This program doesn't bother to close the input files that may still be open.

@<Last-minute...@>=
procedure close_files_and_terminate;
label done, done1;
var a, b, c, i, j, k, l: integer; {all-purpose index}
    is_root: boolean; {|pdf_last_pages| is root of Pages tree?}
    is_names: boolean; {flag for name tree output: is it Names or Kids?}
    root, outlines, threads, names_tree, dests: integer;
    xref_offset_width, names_head, names_tail: integer;
	callback_id:integer;
	res:boolean;
begin 
callback_id:=callback_defined(stop_run_callback);
@<Finish the extensions@>;
@!stat if tracing_stats>0 then
  if callback_id=0 then @<Output statistics about this job@>;@;@+tats@/
wake_up_terminal;
if not fixed_pdfoutput_set then
    fix_pdfoutput;
if fixed_pdfoutput > 0 then begin
    if history = fatal_error_stop then begin
        remove_pdffile;
        print_err(" ==> Fatal error occurred, no output PDF file produced!")
        end
    else begin
        @<Finish the PDF file@>;
	    if callback_id=0 then begin
        if log_opened then
            begin wlog_cr;
            wlog_ln('PDF statistics:');
            wlog_ln(' ',obj_ptr:1,' PDF objects out of ',obj_tab_size:1,
                ' (max. ',sup_obj_tab_size:1,')');
            if pdf_os_cntr > 0 then begin
                wlog(' ',((pdf_os_cntr - 1) * pdf_os_max_objs + pdf_os_objidx + 1):1,
                    ' compressed objects within ',pdf_os_cntr:1,' object stream');
                if pdf_os_cntr > 1 then
                    wlog('s');
                wlog_cr;
            end;
            wlog_ln(' ',pdf_dest_names_ptr:1,' named destinations out of ',dest_names_size:1,
                ' (max. ',sup_dest_names_size:1,')');
            wlog_ln(' ',pdf_mem_ptr:1,' words of extra memory for PDF output out of ',pdf_mem_size:1,
                ' (max. ',sup_pdf_mem_size:1,')');
        end;
        end;
    end;
end
else begin
    @<Finish the \.{DVI} file@>;
end;
if log_opened then
  begin wlog_cr; selector:=selector-2;
  if (selector=term_only)and(callback_id=0) then begin
     print_nl("Transcript written on ");
@.Transcript written...@>
     slow_print(log_name); print_char(".");
    end;
  lua_a_close_out(log_file);
  end;
end;

@ The present section goes directly to the log file instead of using
|print| commands, because there's no need for these strings to take
up |str_pool| memory when a non-{\bf stat} version of \TeX\ is being used.

@<Output statistics...@>=
if log_opened then
  begin wlog_ln(' ');
  wlog_ln('Here is how much of TeX''s memory',' you used:');
@.Here is how much...@>
  wlog(' ',str_ptr-init_str_ptr:1,' string');
  if str_ptr<>init_str_ptr+1 then wlog('s');
  wlog_ln(' out of ', max_strings-init_str_ptr+string_offset:1);@/
  wlog_ln(' ',pool_ptr-init_pool_ptr:1,' string characters out of ',
    pool_size-init_pool_ptr:1);@/
  wlog_ln(' ',var_mem_max:1,',',fix_mem_max:1,@|
    ' words of node,token memory allocated');@/
  print_node_mem_stats(tracing_stats, tracing_online);
  wlog_ln(' ',cs_count:1,' multiletter control sequences out of ',
    hash_size:1);@/
  wlog(' ',max_font_id,' font');
  if max_font_id<>1 then wlog('s');
  wlog_ln(' using ', font_bytes:1, ' bytes');
  wlog_ln(' ',max_in_stack:1,'i,',max_nest_stack:1,'n,',@|
    max_param_stack:1,'p,',@|
    max_buf_stack+1:1,'b,',@|
    max_save_stack+6:1,'s stack positions out of ',@|
    stack_size:1,'i,',
    nest_size:1,'n,',
    param_size:1,'p,',
    buf_size:1,'b,',
    save_size:1,'s');
  end

@ We get to the |final_cleanup| routine when \.{\\end} or \.{\\dump} has
been scanned and |its_all_over|\kern-2pt.

@<Last-minute...@>=
procedure final_cleanup;
label exit;
var c:small_number; {0 for \.{\\end}, 1 for \.{\\dump}}
i:halfword; { for looping marks }
begin c:=cur_chr;
if job_name=0 then open_log_file;
while input_ptr>0 do
  if state=token_list then end_token_list@+else end_file_reading;
while open_parens>0 do
  begin 
	if tracefilenames then print(" )"); 
	decr(open_parens);
  end;
if cur_level>level_one then
  begin print_nl("("); print_esc("end occurred ");
  print("inside a group at level ");
@:end_}{\.{(\\end occurred...)}@>
  print_int(cur_level-level_one); print_char(")");
  show_save_groups;
  end;
while cond_ptr<>null do
  begin print_nl("("); print_esc("end occurred ");
  print("when "); print_cmd_chr(if_test,cur_if);
  if if_line<>0 then
    begin print(" on line "); print_int(if_line);
    end;
  print(" was incomplete)");
  if_line:=if_line_field(cond_ptr);
  cur_if:=subtype(cond_ptr); temp_ptr:=cond_ptr;
  cond_ptr:=vlink(cond_ptr); flush_node(temp_ptr);
  end;
if not callback_defined(stop_run_callback) then 
  if history<>spotless then
    if ((history=warning_issued)or(interaction<error_stop_mode)) then
      if selector=term_and_log then
        begin selector:=term_only;
        print_nl("(see the transcript file for additional information)");
@.see the transcript file...@>
        selector:=term_and_log;
        end;
if c=1 then
  begin @!init for i:=0 to biggest_used_mark do begin
    delete_top_mark(i); delete_first_mark(i); delete_bot_mark(i);
    delete_split_first_mark(i); delete_split_bot_mark(i);
    end;
  for c:=last_box_code to vsplit_code do flush_node_list(disc_ptr[c]);
  @<Close the pseudo files@>;
  store_fmt_file; return;@+tini@/
  print_nl("(\dump is performed only by INITEX)"); return;
@:dump_}{\.{\\dump...only by INITEX}@>
  end;
exit:end;

@ @<Last-minute...@>=
@!init procedure init_prim; {initialize all the primitives}
begin no_new_control_sequence:=false;
first:=0;
@<Put each...@>;
no_new_control_sequence:=true;
end;
tini

@ When we begin the following code, \TeX's tables may still contain garbage;
the strings might not even be present. Thus we must proceed cautiously to get
bootstrapped in.

But when we finish this part of the program, \TeX\ is ready to call on the
|main_control| routine to do its work.

@<Get the first line...@>=
begin @<Initialize the input routines@>;
@<Enable \eTeX, if requested@>@;@/
if (format_ident=0)or(buffer[loc]="&") then
  begin if format_ident<>0 then initialize; {erase preloaded format}
  if not open_fmt_file then goto final_end;
  if not load_fmt_file then
    begin w_close(fmt_file); goto final_end;
    end;
  w_close(fmt_file);
  while (loc<limit)and(buffer[loc]=" ") do incr(loc);
  end;
if (pdf_output_option <> 0) then pdf_output := pdf_output_value;
if (pdf_draftmode_option <> 0) then pdf_draftmode := pdf_draftmode_value;
pdf_init_map_file('pdftex.map');
if false then wterm_ln('entering extended mode');
if end_line_char_inactive then decr(limit)
else  buffer[limit]:=end_line_char;
fix_date_and_time;@/
random_seed :=(microseconds*1000)+(epochseconds mod 1000000);@/
init_randoms(random_seed);@/
@<Compute the magic offset@>;
@<Initialize the print |selector|...@>;
if (loc<limit)and(get_cat_code(cat_code_table,buffer[loc])<>escape) then start_input;
  {\.{\\input} assumed}
@<DIR: Initialize |text_dir_ptr|@>;
end

@* \[52] Debugging.
Once \TeX\ is working, you should be able to diagnose most errors with
the \.{\\show} commands and other diagnostic features. But for the initial
stages of debugging, and for the revelation of really deep mysteries, you
can compile \TeX\ with a few more aids, including the \PASCAL\ runtime
checks and its debugger. An additional routine called |debug_help|
will also come into play when you type `\.D' after an error message;
|debug_help| also occurs just before a fatal error causes \TeX\ to succumb.
@^debugging@>
@^system dependencies@>

The interface to |debug_help| is primitive, but it is good enough when used
with a \PASCAL\ debugger that allows you to set breakpoints and to read
variables and change their values. After getting the prompt `\.{debug \#}', you
type either a negative number (this exits |debug_help|), or zero (this
goes to a location where you can set a breakpoint, thereby entering into
dialog with the \PASCAL\ debugger), or a positive number |m| followed by
an argument |n|. The meaning of |m| and |n| will be clear from the
program below. (If |m=13|, there is an additional argument, |l|.)
@.debug \#@>

@d breakpoint=888 {place where a breakpoint is desirable}

@<Last-minute...@>=
@!debug procedure debug_help; {routine to display various things}
label breakpoint,exit;
var k,@!l,@!m,@!n:integer;
begin loop begin wake_up_terminal;
  print_nl("debug # (-1 to exit):"); update_terminal;
@.debug \#@>
  read(term_in,m);
  if m<0 then return
  else if m=0 then
    begin goto breakpoint;@\ {go to every label at least once}
    breakpoint: m:=0; @{'BREAKPOINT'@}@\
    end
  else  begin read(term_in,n);
    case m of
    @t\4@>@<Numbered cases for |debug_help|@>@;
    othercases print("?")
    endcases;
    end;
  end;
exit:end;
gubed

@ @<Numbered cases...@>=
1: print_word(mem(n)); {display |mem[n]| in all forms}
2: print_int(info(n));
3: print_int(link(n));
4: print_word(eqtb[n]);
5: ;
6: print_word(save_stack[n]);
7: show_box(n);
  {show a box, abbreviated by |show_box_depth| and |show_box_breadth|}
8: begin breadth_max:=10000; depth_threshold:=pool_size-pool_ptr-10;
  show_node_list(n); {show a box in its entirety}
  end;
9: show_token_list(n,null,1000);
10: slow_print(n);
13: begin read(term_in,l); print_cmd_chr(n,l);
  end;
14: for k:=0 to n do print(buffer[k]);
15: begin font_in_short_display:=null_font; short_display(n);
  end;

@* \[53] Extensions.
The program above includes a bunch of ``hooks'' that allow further
capabilities to be added without upsetting \TeX's basic structure.
Most of these hooks are concerned with ``whatsit'' nodes, which are
intended to be used for special purposes; whenever a new extension to
\TeX\ involves a new kind of whatsit node, a corresponding change needs
to be made to the routines below that deal with such nodes,
but it will usually be unnecessary to make many changes to the
other parts of this program.

In order to demonstrate how extensions can be made, we shall treat
`\.{\\write}', `\.{\\openout}', `\.{\\closeout}', `\.{\\immediate}',
and `\.{\\special}' as if they were extensions.
These commands are actually primitives of \TeX, and they should
appear in all implementations of the system; but let's try to imagine
that they aren't. Then the program below illustrates how a person
could add them.

Sometimes, of course, an extension will require changes to \TeX\ itself;
no system of hooks could be complete enough for all conceivable extensions.
The features associated with `\.{\\write}' are almost all confined to the
following paragraphs, but there are small parts of the |print_ln| and
|print_char| procedures that were introduced specifically to \.{\\write}
characters. Furthermore one of the token lists recognized by the scanner
is a |write_text|; and there are a few other miscellaneous places where we
have already provided for some aspect of \.{\\write}.  The goal of a \TeX\
extender should be to minimize alterations to the standard parts of the
program, and to avoid them completely if possible. He or she should also
be quite sure that there's no easy way to accomplish the desired goals
with the standard features that \TeX\ already has. ``Think thrice before
extending,'' because that may save a lot of work, and it will also keep
incompatible extensions of \TeX\ from proliferating.
@^system dependencies@>
@^extensions to \TeX@>

@ First let's consider the format of whatsit nodes that are used to represent
the data associated with \.{\\write} and its relatives. Recall that a whatsit
has |type=whatsit_node|, and the |subtype| is supposed to distinguish
different kinds of whatsits. Each node occupies two or more words; the
exact number is immaterial, as long as it is readily determined from the
|subtype| or other data.

We shall introduce five |subtype| values here, corresponding to the
control sequences \.{\\openout}, \.{\\write}, \.{\\closeout}, and \.{\\special}. 
The second word of I/O whatsits has a |write_stream| field
that identifies the write-stream number (0 to 15, or 16 for out-of-range and
positive, or 17 for out-of-range and negative).
In the case of \.{\\write} and \.{\\special}, there is also a field that
points to the reference count of a token list that should be sent. In the
case of \.{\\openout}, we need three words and three auxiliary subfields
to hold the string numbers for name, area, and extension.

@d open_node=0 {|subtype| in whatsits that represent files to \.{\\openout}}
@d open_node_size==4 {number of words in an open/whatsit node}
@d write_node=1 {|subtype| in whatsits that represent things to \.{\\write}}
@d write_node_size==3 {number of words in a write/whatsit node}
@d close_node=2 {|subtype| in whatsits that represent streams to \.{\\closeout}}
@d close_node_size==3 {number of words in a write/whatsit node}
@d special_node=3 {|subtype| in whatsits that represent \.{\\special} things}
@d special_node_size==3 {number of words in a write/whatsit node}
@d dir_node_size=4 {number of words in change direction node}
@d dir_dir(#)==vinfo(#+2) {keep the direction to be taken}
@d dir_level(#)==vlink(#+2) {the save level at which the direction was defined}
@d dir_dvi_ptr(#)==vinfo(#+3) {for reflecting dvi output}
@d dir_dvi_h(#)==vlink(#+3) {for reflecting dvi output}
@d what_lang(#)==vlink(#+2) {language number, in the range |0..255|}
@d what_lhm(#)==type(#+2) {minimum left fragment, in the range |1..63|}
@d what_rhm(#)==subtype(#+2) {minimum right fragment, in the range |1..63|}
@d write_tokens(#) == vlink(#+2) {reference count of token list to write}
@d write_stream(#) == vinfo(#+2) {stream number (0 to 17)}
@d open_name(#) == vlink(#+2) {string number of file name to open}
@d open_area(#) == vinfo(#+3) {string number of file area for |open_name|}
@d open_ext(#) == vlink(#+3) {string number of file extension for |open_name|}

@ The sixteen possible \.{\\write} streams are represented by the |write_file|
array. The |j|th file is open if and only if |write_open[j]=true|. The last
two streams are special; |write_open[16]| represents a stream number
greater than 15, while |write_open[17]| represents a negative stream number,
and both of these variables are always |false|.

@<Glob...@>=
@!write_file:array[0..15] of alpha_file;
@!write_file_mode:array[0..15] of halfword;
@!write_file_translation:array[0..15] of halfword;
@!write_open:array[0..17] of boolean;
@!neg_wd:scaled;
@!pos_wd:scaled;
@!neg_ht:scaled;
@!dvi_direction:integer;
@!dir_primary:array[0..31] of 0..31;
@!dir_secondary:array[0..31] of 0..31;
@!dir_tertiary:array[0..31] of 0..31;
@!dir_rearrange:array[0..3] of 0..31;
@!dir_names:array[0..3] of str_number;
@!text_dir_ptr:pointer;
@!text_dir_tmp:pointer;

@ 
@<Set init...@>=
for k:=0 to 17 do write_open[k]:=false;
pack_direction:=-1;
for k:= 0 to 7 do begin
  dir_primary  [k   ]:=dir_T;
  dir_primary  [k+ 8]:=dir_L;
  dir_primary  [k+16]:=dir_B;
  dir_primary  [k+24]:=dir_R;
  end;
for k:= 0 to 3 do begin
  dir_secondary[k   ]:=dir_L;
  dir_secondary[k+ 4]:=dir_R;
  dir_secondary[k+ 8]:=dir_T;
  dir_secondary[k+12]:=dir_B;

  dir_secondary[k+16]:=dir_L;
  dir_secondary[k+20]:=dir_R;
  dir_secondary[k+24]:=dir_T;
  dir_secondary[k+28]:=dir_B;
  end;
for k:=0 to 7 do begin
  dir_tertiary[k*4  ]:=dir_T;
  dir_tertiary[k*4+1]:=dir_L;
  dir_tertiary[k*4+2]:=dir_B;
  dir_tertiary[k*4+3]:=dir_R;
  end;
dir_rearrange[0]:=0;
dir_rearrange[1]:=0;
dir_rearrange[2]:=1;
dir_rearrange[3]:=1;
dir_names[0]:="T";
dir_names[1]:="L";
dir_names[2]:="B";
dir_names[3]:="R";

@ Extensions might introduce new command codes; but it's best to use
|extension| with a modifier, whenever possible, so that |main_control|
stays the same.

@d immediate_code=4 {command modifier for \.{\\immediate}}
@d local_par_node==6 {|subtype| in whatsits for local paragraph node}
{|local_par_node| has to be a macro, not numeric }
@d dir_node=7 {|subtype| in whatsits for change direction node}
@d pdftex_first_extension_code = 8
@d pdf_literal_node            == pdftex_first_extension_code + 0
@d pdf_obj_code                == pdftex_first_extension_code + 1
@d pdf_refobj_node             == pdftex_first_extension_code + 2
@d pdf_xform_code              == pdftex_first_extension_code + 3
@d pdf_refxform_node           == pdftex_first_extension_code + 4
@d pdf_ximage_code             == pdftex_first_extension_code + 5
@d pdf_refximage_node          == pdftex_first_extension_code + 6
@d pdf_annot_node              == pdftex_first_extension_code + 7
@d pdf_start_link_node         == pdftex_first_extension_code + 8
@d pdf_end_link_node           == pdftex_first_extension_code + 9
@d pdf_end_link_node_size==3
@d pdf_outline_code            == pdftex_first_extension_code + 10
@d pdf_dest_node               == pdftex_first_extension_code + 11
@d pdf_thread_node             == pdftex_first_extension_code + 12
@d pdf_start_thread_node       == pdftex_first_extension_code + 13
@d pdf_end_thread_node         == pdftex_first_extension_code + 14
@d pdf_end_thread_node_size==3
@d pdf_save_pos_node           == pdftex_first_extension_code + 15
@d pdf_save_pos_node_size==3
@d pdf_info_code               == pdftex_first_extension_code + 16
@d pdf_thread_data_node        == pdftex_first_extension_code + 16
@d pdf_catalog_code            == pdftex_first_extension_code + 17
@d pdf_link_data_node          == pdftex_first_extension_code + 17
@d pdf_names_code              == pdftex_first_extension_code + 18
@d pdf_font_attr_code          == pdftex_first_extension_code + 19
@d pdf_include_chars_code      == pdftex_first_extension_code + 20
@d pdf_map_file_code           == pdftex_first_extension_code + 21
@d pdf_map_line_code           == pdftex_first_extension_code + 22
@d pdf_trailer_code            == pdftex_first_extension_code + 23
@d pdf_font_expand_code        == pdftex_first_extension_code + 24
@d set_random_seed_code        == pdftex_first_extension_code + 25
@d pdf_glyph_to_unicode_code   == pdftex_first_extension_code + 26
@d late_lua_node               == pdftex_first_extension_code + 27
@d close_lua_node              == pdftex_first_extension_code + 28
@d save_cat_code_table_code    == pdftex_first_extension_code + 29
@d init_cat_code_table_code    == pdftex_first_extension_code + 30
@d pdf_colorstack_node         == pdftex_first_extension_code + 31
@d pdf_setmatrix_node          == pdftex_first_extension_code + 32
@d pdf_save_node               == pdftex_first_extension_code + 33
@d pdf_restore_node            == pdftex_first_extension_code + 34
@d pdftex_last_extension_code  == pdftex_first_extension_code + 34

@<Put each...@>=
primitive("openout",extension,open_node);@/
@!@:open_out_}{\.{\\openout} primitive@>
primitive("write",extension,write_node); write_loc:=cur_val;@/
@!@:write_}{\.{\\write} primitive@>
primitive("closeout",extension,close_node);@/
@!@:close_out_}{\.{\\closeout} primitive@>
primitive("special",extension,special_node);@/
@!@:special_}{\.{\\special} primitive@>
primitive("immediate",extension,immediate_code);@/
@!@:immediate_}{\.{\\immediate} primitive@>
primitive("localinterlinepenalty",assign_int,local_inter_line_penalty_code);@/
primitive("localbrokenpenalty",assign_int,local_broken_penalty_code);@/
primitive("pagedir",assign_dir,dir_base+page_direction_code);@/
primitive("bodydir",assign_dir,dir_base+body_direction_code);@/
primitive("pardir",assign_dir,dir_base+par_direction_code);@/
primitive("textdir",assign_dir,dir_base+text_direction_code);@/
primitive("mathdir",assign_dir,dir_base+math_direction_code);@/
primitive("pagerightoffset",assign_dimen,dimen_base+page_right_offset_code);
primitive("pagebottomoffset",assign_dimen,dimen_base+page_bottom_offset_code);
primitive("pdfliteral",extension,pdf_literal_node);@/
@!@:pdf_literal_}{\.{\\pdfliteral} primitive@>
primitive("pdfcolorstack",extension,pdf_colorstack_node);@/
@!@:pdf_colorstack_}{\.{\\pdfcolorstack} primitive@>
primitive("pdfsetmatrix",extension,pdf_setmatrix_node);@/
@!@:pdf_setmatrix_}{\.{\\pdfsetmatrix} primitive@>
primitive("pdfsave",extension,pdf_save_node);@/
@!@:pdf_save_}{\.{\\pdfsave} primitive@>
primitive("pdfrestore",extension,pdf_restore_node);@/
@!@:pdf_restore_}{\.{\\pdfrestore} primitive@>
primitive("pdfobj",extension,pdf_obj_code);@/
@!@:pdf_obj_}{\.{\\pdfobj} primitive@>
primitive("pdfrefobj",extension,pdf_refobj_node);@/
@!@:pdf_refobj_}{\.{\\pdfrefobj} primitive@>
primitive("pdfxform",extension,pdf_xform_code);@/
@!@:pdf_xform_}{\.{\\pdfxform} primitive@>
primitive("pdfrefxform",extension,pdf_refxform_node);@/
@!@:pdf_refxform_}{\.{\\pdfrefxform} primitive@>
primitive("pdfximage",extension,pdf_ximage_code);@/
@!@:pdf_ximage_}{\.{\\pdfximage} primitive@>
primitive("pdfrefximage",extension,pdf_refximage_node);@/
@!@:pdf_refximage_}{\.{\\pdfrefximage} primitive@>
primitive("pdfannot",extension,pdf_annot_node);@/
@!@:pdf_annot_}{\.{\\pdfannot} primitive@>
primitive("pdfstartlink",extension,pdf_start_link_node);@/
@!@:pdf_start_link_}{\.{\\pdfstartlink} primitive@>
primitive("pdfendlink",extension,pdf_end_link_node);@/
@!@:pdf_end_link_}{\.{\\pdfendlink} primitive@>
primitive("pdfoutline",extension,pdf_outline_code);@/
@!@:pdf_outline_}{\.{\\pdfoutline} primitive@>
primitive("pdfdest",extension,pdf_dest_node);@/
@!@:pdf_dest_}{\.{\\pdfdest} primitive@>
primitive("pdfthread",extension,pdf_thread_node);@/
@!@:pdf_thread_}{\.{\\pdfthread} primitive@>
primitive("pdfstartthread",extension,pdf_start_thread_node);@/
@!@:pdf_start_thread_}{\.{\\pdfstartthread} primitive@>
primitive("pdfendthread",extension,pdf_end_thread_node);@/
@!@:pdf_end_thread_}{\.{\\pdfendthread} primitive@>
primitive("pdfsavepos",extension,pdf_save_pos_node);@/
@!@:pdf_save_pos_}{\.{\\pdfsavepos} primitive@>
primitive("pdfinfo",extension,pdf_info_code);@/
@!@:pdf_info_}{\.{\\pdfinfo} primitive@>
primitive("pdfcatalog",extension,pdf_catalog_code);@/
@!@:pdf_catalog_}{\.{\\pdfcatalog} primitive@>
primitive("pdfnames",extension,pdf_names_code);@/
@!@:pdf_names_}{\.{\\pdfnames} primitive@>
primitive("pdfincludechars",extension,pdf_include_chars_code);@/
@!@:pdf_include_chars_}{\.{\\pdfincludechars} primitive@>
primitive("pdffontattr",extension,pdf_font_attr_code);@/
@!@:pdf_font_attr_}{\.{\\pdffontattr} primitive@>
primitive("pdfmapfile",extension,pdf_map_file_code);@/
@!@:pdf_map_file_}{\.{\\pdfmapfile} primitive@>
primitive("pdfmapline",extension,pdf_map_line_code);@/
@!@:pdf_map_line_}{\.{\\pdfmapline} primitive@>
primitive("pdftrailer",extension,pdf_trailer_code);@/
@!@:pdf_trailer_}{\.{\\pdftrailer} primitive@>
primitive("savecatcodetable",extension,save_cat_code_table_code);@/
@!@:save_cat_code_table_}{\.{\\savecatcodetable} primitive@>
primitive("initcatcodetable",extension,init_cat_code_table_code);@/
@!@:init_cat_code_table_}{\.{\\initcatcodetable} primitive@>
primitive("pdfsetrandomseed",extension,set_random_seed_code);@/
@!@:set_random_seed_code}{\.{\\pdfsetrandomseed} primitive@>
primitive("latelua",extension,late_lua_node);@/
@!@:late_lua_node_}{\.{\\latelua} primitive@>
primitive("closelua",extension,close_lua_node);@/
@!@:close_lua_node_}{\.{\\closelua} primitive@>
primitive("pdffontexpand",extension,pdf_font_expand_code);@/
@!@:pdf_font_expand_}{\.{\\pdffontexpand} primitive@>
primitive("pdfglyphtounicode",extension,pdf_glyph_to_unicode_code);@/
@!@:pdf_glyph_to_unicode_}{\.{\\pdfglyphtounicode} primitive@>

@ The variable |write_loc| just introduced is used to provide an
appropriate error message in case of ``runaway'' write texts.

@<Glob...@>=
@!write_loc:pointer; {|eqtb| address of \.{\\write}}

@ @<Cases of |print_cmd_chr|...@>=
extension: case chr_code of
  open_node:print_esc("openout");
  write_node:print_esc("write");
  close_node:print_esc("closeout");
  special_node:print_esc("special");
  immediate_code:print_esc("immediate");
  pdf_annot_node: print_esc("pdfannot");
  pdf_catalog_code: print_esc("pdfcatalog");
  pdf_dest_node: print_esc("pdfdest");
  pdf_end_link_node: print_esc("pdfendlink");
  pdf_end_thread_node: print_esc("pdfendthread");
  pdf_font_attr_code: print_esc("pdffontattr");
  pdf_font_expand_code: print_esc("pdffontexpand");
  pdf_include_chars_code: print_esc("pdfincludechars");
  pdf_info_code: print_esc("pdfinfo");
  pdf_literal_node: print_esc("pdfliteral");
  pdf_colorstack_node: print_esc("pdfcolorstack");
  pdf_setmatrix_node: print_esc("pdfsetmatrix");
  pdf_save_node: print_esc("pdfsave");
  pdf_restore_node: print_esc("pdfrestore");
  pdf_map_file_code: print_esc("pdfmapfile");
  pdf_map_line_code: print_esc("pdfmapline");
  pdf_names_code: print_esc("pdfnames");
  pdf_obj_code: print_esc("pdfobj");
  pdf_outline_code: print_esc("pdfoutline");
  pdf_refobj_node: print_esc("pdfrefobj");
  pdf_refxform_node: print_esc("pdfrefxform");
  pdf_refximage_node: print_esc("pdfrefximage");
  pdf_save_pos_node: print_esc("pdfsavepos");
  pdf_start_link_node: print_esc("pdfstartlink");
  pdf_start_thread_node: print_esc("pdfstartthread");
  pdf_thread_node: print_esc("pdfthread");
  pdf_trailer_code: print_esc("pdftrailer");
  pdf_xform_code: print_esc("pdfxform");
  pdf_ximage_code: print_esc("pdfximage");
  save_cat_code_table_code: print_esc("savecatcodetable");
  init_cat_code_table_code: print_esc("initcatcodetable");
  set_random_seed_code: print_esc("pdfsetrandomseed");
  pdf_glyph_to_unicode_code: print_esc("pdfglyphtounicode");
  late_lua_node: print_esc("latelua");
  close_lua_node: print_esc("closelua");
  cancel_boundary_node: print_esc("noboundary");
  othercases print("[unknown extension!]")
  endcases;

@ When an |extension| command occurs in |main_control|, in any mode,
the |do_extension| routine is called.

@<Cases of |main_control| that are for extensions...@>=
any_mode(extension):do_extension;

@ @<Declare act...@>=
@t\4@>@<Declare procedures needed in |do_extension|@>@;
procedure do_extension;
var i,@!j,@!k:integer; {all-purpose integers}
@!p,@!q,@!r:pointer; {all-purpose pointers}
begin case cur_chr of
  open_node:@<Implement \.{\\openout}@>;
  write_node:@<Implement \.{\\write}@>;
  close_node:@<Implement \.{\\closeout}@>;
  special_node:@<Implement \.{\\special}@>;
  immediate_code:@<Implement \.{\\immediate}@>;
  pdf_annot_node: @<Implement \.{\\pdfannot}@>;
  pdf_catalog_code: @<Implement \.{\\pdfcatalog}@>;
  pdf_dest_node: @<Implement \.{\\pdfdest}@>;
  pdf_end_link_node: @<Implement \.{\\pdfendlink}@>;
  pdf_end_thread_node: @<Implement \.{\\pdfendthread}@>;
  pdf_font_attr_code: @<Implement \.{\\pdffontattr}@>;
  pdf_font_expand_code: @<Implement \.{\\pdffontexpand}@>;
  pdf_include_chars_code: @<Implement \.{\\pdfincludechars}@>;
  pdf_info_code: @<Implement \.{\\pdfinfo}@>;
  pdf_literal_node: @<Implement \.{\\pdfliteral}@>;
  pdf_colorstack_node: @<Implement \.{\\pdfcolorstack}@>;
  pdf_setmatrix_node: @<Implement \.{\\pdfsetmatrix}@>;
  pdf_save_node: @<Implement \.{\\pdfsave}@>;
  pdf_restore_node: @<Implement \.{\\pdfrestore}@>;
  pdf_map_file_code: @<Implement \.{\\pdfmapfile}@>;
  pdf_map_line_code: @<Implement \.{\\pdfmapline}@>;
  pdf_names_code: @<Implement \.{\\pdfnames}@>;
  pdf_obj_code: @<Implement \.{\\pdfobj}@>;
  pdf_outline_code: @<Implement \.{\\pdfoutline}@>;
  pdf_refobj_node: @<Implement \.{\\pdfrefobj}@>;
  pdf_refxform_node: @<Implement \.{\\pdfrefxform}@>;
  pdf_refximage_node: @<Implement \.{\\pdfrefximage}@>;
  pdf_save_pos_node: @<Implement \.{\\pdfsavepos}@>;
  pdf_start_link_node: @<Implement \.{\\pdfstartlink}@>;
  pdf_start_thread_node: @<Implement \.{\\pdfstartthread}@>;
  pdf_thread_node: @<Implement \.{\\pdfthread}@>;
  pdf_trailer_code: @<Implement \.{\\pdftrailer}@>;
  pdf_xform_code: @<Implement \.{\\pdfxform}@>;
  pdf_ximage_code: @<Implement \.{\\pdfximage}@>;
  save_cat_code_table_code: @<Implement \.{\\savecatcodetable}@>;
  init_cat_code_table_code: @<Implement \.{\\initcatcodetable}@>;
  set_random_seed_code: @<Implement \.{\\pdfsetrandomseed}@>;
  pdf_glyph_to_unicode_code: @<Implement \.{\\pdfglyphtounicode}@>;
  late_lua_node: @<Implement \.{\\latelua}@>;
  close_lua_node: @<Implement \.{\\closelua}@>;
othercases confusion("ext1")
@:this can't happen ext1}{\quad ext1@>
endcases;
end;

@ Here is a subroutine that creates a whatsit node having a given |subtype|
and a given number of words. It initializes only the first word of the whatsit,
and appends it to the current list.

@<Declare procedures needed in |do_extension|@>=
procedure new_whatsit(@!s:small_number);
var p:pointer; {the new node}
begin p:=new_node(whatsit_node,s);
vlink(tail):=p; tail:=p;
end;

@ The next subroutine uses |cur_chr| to decide what sort of whatsit is
involved, and also inserts a |write_stream| number.

@<Declare procedures needed in |do_ext...@>=
procedure new_write_whatsit(@!w:small_number);
begin new_whatsit(cur_chr);
if w<>write_node_size then scan_four_bit_int
else  begin scan_int;
  if cur_val<0 then cur_val:=17
  else if cur_val>15 then cur_val:=16;
  end;
write_stream(tail):=cur_val;
end;

@ @<Implement \.{\\openout}@>=
begin new_write_whatsit(open_node_size);
scan_optional_equals; scan_file_name;@/
open_name(tail):=cur_name; open_area(tail):=cur_area; open_ext(tail):=cur_ext;
end

@ When `\.{\\write 12\{...\}}' appears, we scan the token list `\.{\{...\}}'
without expanding its macros; the macros will be expanded later when this
token list is rescanned.

@<Implement \.{\\write}@>=
begin k:=cur_cs; new_write_whatsit(write_node_size);@/
cur_cs:=k; p:=scan_toks(false,false); write_tokens(tail):=def_ref;
end

@ @<Implement \.{\\closeout}@>=
begin new_write_whatsit(write_node_size); write_tokens(tail):=null;
end

@ When `\.{\\special\{...\}}' appears, we expand the macros in the token
list as in \.{\\xdef} and \.{\\mark}.

@<Implement \.{\\special}@>=
begin new_whatsit(special_node); write_stream(tail):=null;
p:=scan_toks(false,true); write_tokens(tail):=def_ref;
end

@ @<Implement \.{\\pdffontexpand}@>=
    read_expand_font

@ The following macros are needed for further manipulation with whatsit nodes
for \pdfTeX{} extensions (copying, destroying etc.)

@d add_action_ref(#) == incr(pdf_action_refcount(#)) {increase count of
references to this action}

@d delete_action_ref(#) == {decrease count of references to this
action; free it if there is no reference to this action}
begin
    if pdf_action_refcount(#) = null then begin
        if pdf_action_type(#) = pdf_action_user then
            delete_token_ref(pdf_action_tokens(#))
        else begin
            if pdf_action_file(#) <> null then
                delete_token_ref(pdf_action_file(#));
            if pdf_action_type(#) = pdf_action_page then
                delete_token_ref(pdf_action_tokens(#))
            else if pdf_action_named_id(#) > 0 then
                delete_token_ref(pdf_action_id(#));
        end;
        flush_node(#);
    end
    else
        decr(pdf_action_refcount(#));
end

@ We have to check whether \.{\\pdfoutput} is set for using \pdfTeX{}
  extensions.
@<Declare procedures needed in |do_ext...@>=
procedure check_pdfoutput(s: str_number; is_error : boolean);
begin
    if pdf_output <= 0 then
        begin
        if is_error then
            pdf_error(s, "not allowed in DVI mode (\pdfoutput <= 0)")
        else
            pdf_warning(s, "not allowed in DVI mode (\pdfoutput <= 0); ignoring it", true,true);
        end
end;

procedure scan_pdf_ext_toks;
begin
    call_func(scan_toks(false, true)); {like \.{\\special}}
end;

@ @<Implement \.{\\pdfliteral}@>=
begin
    check_pdfoutput("\pdfliteral", true);
    new_whatsit(pdf_literal_node);
    if scan_keyword("direct") then
        pdf_literal_mode(tail) := direct_always
    else if scan_keyword("page") then
        pdf_literal_mode(tail) := direct_page
    else
        pdf_literal_mode(tail) := set_origin;
    scan_pdf_ext_toks;
    pdf_literal_data(tail) := def_ref;
end

@ @<Implement \.{\\pdfcolorstack}@>=
begin
    check_pdfoutput("\pdfcolorstack", true);
    {Scan and check the stack number and store in |cur_val|}
    scan_int;
    if cur_val >= colorstackused then begin
        print_err("Unknown color stack number ");
        print_int(cur_val);
@.Unknown color stack@>
        help3("Allocate and initialize a color stack with \\pdfcolorstackinit.")@/
        ("I'll use default color stack 0 here.")@/
        ("Proceed, with fingers crossed.");
        error;
        cur_val := 0;
    end;
    if cur_val < 0 then begin
        print_err("Invalid negative color stack number");
@.Invalid negative color stack number@>
        help2("I'll use default color stack 0 here.")@/
        ("Proceed, with fingers corssed.");
        error;
        cur_val := 0;
    end;
    if scan_keyword("set") then begin
        i := colorstack_set;
    end
    else if scan_keyword("push") then begin
        i := colorstack_push;
    end
    else if scan_keyword("pop") then begin
        i := colorstack_pop;
    end
    else if scan_keyword("current") then begin
        i := colorstack_current;
    end
    else begin
        i := -1; {error}
    end;
    if i >= 0 then begin
        new_whatsit(pdf_colorstack_node);
        pdf_colorstack_stack(tail) := cur_val;
        pdf_colorstack_cmd(tail)   := i;
	    pdf_colorstack_data(tail)  := null;
        if i <= colorstack_data then begin
            scan_pdf_ext_toks;
            pdf_colorstack_data(tail) := def_ref;
        end;
    end
    else begin
        print_err("Color stack action is missing");
@.Color stack action is missing@>
        help3("The expected actions for \pdfcolorstack:")@/
        ("    set, push, pop, current")@/
        ("I'll ignore the color stack command.");
        error;
    end
end

@ @<Implement \.{\\pdfsetmatrix}@>=
begin
    check_pdfoutput("\pdfsetmatrix", true);
    new_whatsit(pdf_setmatrix_node);
    scan_pdf_ext_toks;
    pdf_setmatrix_data(tail) := def_ref;
end

@ @<Implement \.{\\pdfsave}@>=
begin
    check_pdfoutput("\pdfsave", true);
    new_whatsit(pdf_save_node);
end

@ @<Implement \.{\\pdfrestore}@>=
begin
    check_pdfoutput("\pdfrestore", true);
    new_whatsit(pdf_restore_node);
end


@ @<Implement \.{\\latelua}@>=
begin
    check_pdfoutput("\latelua", true);
    new_whatsit(late_lua_node);
    scan_register_num;
    late_lua_reg(tail) := cur_val;
    scan_pdf_ext_toks;
    late_lua_data(tail) := def_ref;
end

@ @<Implement \.{\\closelua}@>=
begin
    check_pdfoutput("\closelua", true);
    new_whatsit(close_lua_node);
	scan_register_num;
	late_lua_reg(tail) := cur_val;
end

@ The \.{\\pdfobj} primitive is used to create a ``raw'' object in the PDF
  output file. The object contents will be hold in memory and will be written
  out only when the object is referenced by \.{\\pdfrefobj}. When \.{\\pdfobj}
  is used with \.{\\immediate}, the object contents will be written out
  immediately. Objects referenced in the current page are appended into
  |pdf_obj_list|.

@<Glob...@>=
@!pdf_last_obj: integer;

@ @<Implement \.{\\pdfobj}@>=
begin
    check_pdfoutput("\pdfobj", true);
    if scan_keyword("reserveobjnum") then begin
        @<Scan an optional space@>;
        incr(pdf_obj_count);
        pdf_create_obj(obj_type_obj, pdf_obj_count);
        pdf_last_obj := obj_ptr;
    end
    else begin
        k := -1;
        if scan_keyword("useobjnum") then begin
            scan_int;
            k := cur_val;
            if (k <= 0) or (k > obj_ptr) or (obj_data_ptr(k) <> 0) then begin
                pdf_warning("\pdfobj", "invalid object number being ignored", true, true);
                pdf_retval := -1; {signal the problem}
                k := -1; {will be generated again}
            end;
        end;
        if k < 0 then begin
            incr(pdf_obj_count);
            pdf_create_obj(obj_type_obj, pdf_obj_count);
            k := obj_ptr;
        end;
        obj_data_ptr(k) := pdf_get_mem(pdfmem_obj_size);
        if scan_keyword("stream") then begin
            obj_obj_is_stream(k) := 1;
            if scan_keyword("attr") then begin
                scan_pdf_ext_toks;
                obj_obj_stream_attr(k) := def_ref;
            end
            else
                obj_obj_stream_attr(k) := null;
        end
        else
            obj_obj_is_stream(k) := 0;
        if scan_keyword("file") then
            obj_obj_is_file(k) := 1
        else
            obj_obj_is_file(k) := 0;
        scan_pdf_ext_toks;
        obj_obj_data(k) := def_ref;
        pdf_last_obj := k;
    end;
end

@ We need to check whether the referenced object exists.

@<Declare procedures that need to be declared forward for \pdfTeX@>=
function prev_rightmost(s, e: pointer): pointer;
{finds the node preceding the rightmost node |e|; |s| is some node
before |e|}
var p: pointer;
begin
    prev_rightmost := null;
    p := s;
    if p = null then
        return;
    while vlink(p) <> e do begin
        p := vlink(p);
        if p = null then
            return;
    end;
    prev_rightmost := p;
end;

procedure pdf_check_obj(t, n: integer);
var k: integer;
begin
    k := head_tab[t];
    while (k <> 0) and (k <> n) do
        k := obj_link(k);
    if k = 0 then
        pdf_error("ext1", "cannot find referenced object");
end;

@ @<Implement \.{\\pdfrefobj}@>=
begin
    check_pdfoutput("\pdfrefobj", true);
    scan_int;
    pdf_check_obj(obj_type_obj, cur_val);
    new_whatsit(pdf_refobj_node);
    pdf_obj_objnum(tail) := cur_val;
end

@ \.{\\pdfxform} and \.{\\pdfrefxform} are similiar to \.{\\pdfobj} and
  \.{\\pdfrefobj}

@<Glob...@>=
@!pdf_last_xform: integer;

@ @<Implement \.{\\pdfxform}@>=
begin
    check_pdfoutput("\pdfxform", true);
    incr(pdf_xform_count);
    pdf_create_obj(obj_type_xform, pdf_xform_count);
    k := obj_ptr;
    obj_data_ptr(k) := pdf_get_mem(pdfmem_xform_size);
    if scan_keyword("attr") then begin
        scan_pdf_ext_toks;
        obj_xform_attr(k) := def_ref;
    end
    else
        obj_xform_attr(k) := null;
    if scan_keyword("resources") then begin
        scan_pdf_ext_toks;
        obj_xform_resources(k) := def_ref;
    end
    else
        obj_xform_resources(k) := null;
    scan_int;
	p:=box(cur_val);
    if p = null then
        pdf_error("ext1", "\pdfxform cannot be used with a void box");
    obj_xform_width(k) := width(p);
    obj_xform_height(k) := height(p);
    obj_xform_depth(k) := depth(p);
    obj_xform_box(k) := p; {save pointer to the box}
	box(cur_val):=null;
    pdf_last_xform := k;
end

@ @<Implement \.{\\pdfrefxform}@>=
begin
    check_pdfoutput("\pdfrefxform", true);
    scan_int;
    pdf_check_obj(obj_type_xform, cur_val);
    new_whatsit(pdf_refxform_node);
    pdf_xform_objnum(tail) := cur_val;
    pdf_width(tail) := obj_xform_width(cur_val);
    pdf_height(tail) := obj_xform_height(cur_val);
    pdf_depth(tail) := obj_xform_depth(cur_val);
end

@ \.{\\pdfximage} and \.{\\pdfrefximage} are similiar to \.{\\pdfxform} and
  \.{\\pdfrefxform}. As we have to scan |<rule spec>| quite often, it is better
  have a |rule_node| that holds the most recently scanned |<rule spec>|.

@<Glob...@>=
@!pdf_last_ximage: integer;
@!pdf_last_ximage_pages: integer;
@!pdf_last_ximage_colordepth: integer;
@!alt_rule: pointer;
@!warn_pdfpagebox: boolean;

@ @<Set init...@>=
alt_rule := null;
warn_pdfpagebox := true;

@ @<Declare procedures needed in |do_ext...@>=

function scan_pdf_box_spec: integer; {scans PDF pagebox specification}
begin
    scan_pdf_box_spec := 0;
    if scan_keyword("mediabox") then
        scan_pdf_box_spec := pdf_box_spec_media
    else if scan_keyword("cropbox") then
        scan_pdf_box_spec := pdf_box_spec_crop
    else if scan_keyword("bleedbox") then
        scan_pdf_box_spec := pdf_box_spec_bleed
    else if scan_keyword("trimbox") then
        scan_pdf_box_spec := pdf_box_spec_trim
    else if scan_keyword("artbox") then
        scan_pdf_box_spec := pdf_box_spec_art
end;

procedure scan_alt_rule; {scans rule spec to |alt_rule|}
label reswitch;
begin
    if alt_rule = null then
        alt_rule := new_rule;
    width(alt_rule) := null_flag;
    height(alt_rule) := null_flag;
    depth(alt_rule) := null_flag;
reswitch:
    if scan_keyword("width") then begin
        scan_normal_dimen;
        width(alt_rule) := cur_val;
        goto reswitch;
    end;
    if scan_keyword("height") then begin
        scan_normal_dimen;
        height(alt_rule) := cur_val;
        goto reswitch;
    end;
    if scan_keyword("depth") then begin
        scan_normal_dimen;
        depth(alt_rule) := cur_val;
        goto reswitch;
    end;
end;

procedure scan_image;
label reswitch;
var i, k, img_wd, img_ht, img_dp, ref: integer;
    named, attr: str_number;
    s: str_number;
    page, pagebox, colorspace: integer;
begin
    incr(pdf_ximage_count);
    pdf_create_obj(obj_type_ximage, pdf_ximage_count);
    k := obj_ptr;
    scan_alt_rule; {scans |<rule spec>| to |alt_rule|}
    img_wd := width(alt_rule);
    img_ht := height(alt_rule);
    img_dp := depth(alt_rule);
    attr := 0;
    named := 0;
    page := 1;
    colorspace := 0;
    if scan_keyword("attr") then begin
        scan_pdf_ext_toks;
        attr := tokens_to_string(def_ref);
        delete_token_ref(def_ref);
    end;
    if scan_keyword("named") then begin
        scan_pdf_ext_toks;
        named := tokens_to_string(def_ref);
        delete_token_ref(def_ref);
        page := 0;
    end
    else if scan_keyword("page") then begin
        scan_int;
        page := cur_val;
    end;
    if scan_keyword("colorspace") then begin
        scan_int;
        colorspace := cur_val;
    end;
    pagebox := scan_pdf_box_spec;
    if pagebox = 0 then
        pagebox := pdf_pagebox;
    scan_pdf_ext_toks;
    s := tokens_to_string(def_ref);
    delete_token_ref(def_ref);
    if pdf_option_always_use_pdfpagebox <> 0 then begin
        pdf_warning("PDF inclusion", "Primitive \pdfoptionalwaysusepdfpagebox is obsolete; use \pdfpagebox instead.", true, true);
        pdf_force_pagebox := pdf_option_always_use_pdfpagebox;
        pdf_option_always_use_pdfpagebox := 0; {warn once}
        warn_pdfpagebox := false;
    end;
    if pdf_option_pdf_inclusion_errorlevel <> 0 then begin
        pdf_warning("PDF inclusion", "Primitive \pdfoptionpdfinclusionerrorlevel is obsolete; use \pdfinclusionerrorlevel instead.", true, true);
        pdf_inclusion_errorlevel := pdf_option_pdf_inclusion_errorlevel;
        pdf_option_pdf_inclusion_errorlevel := 0; {warn once}
    end;
    if pdf_force_pagebox > 0 then begin
        if warn_pdfpagebox then begin
            pdf_warning("PDF inclusion", "Primitive \pdfforcepagebox is obsolete; use \pdfpagebox instead.", true, true);
            warn_pdfpagebox := false;
        end;
        pagebox := pdf_force_pagebox;
    end;
    if pagebox = 0 then {no pagebox specification given}
        pagebox := pdf_box_spec_crop;
    ref := read_image(k, pdf_ximage_count, s, page, named, attr, colorspace, pagebox,
                      pdf_minor_version, pdf_inclusion_errorlevel);
    flush_str(s);
    obj_data_ptr(k) := ref;
    if named <> 0 then flush_str(named);
    set_image_dimensions(ref, img_wd, img_ht, img_dp);
    if attr <> 0 then flush_str(attr);
    scale_image(ref);
    pdf_last_ximage := k;
    pdf_last_ximage_pages := image_pages(ref);
    pdf_last_ximage_colordepth := image_colordepth(ref);
end;

@ @<Implement \.{\\pdfximage}@>=
begin
    check_pdfoutput("\pdfximage", true);
    check_pdfminorversion;
    scan_image;
end

@ @<Implement \.{\\pdfrefximage}@>=
begin
    check_pdfoutput("\pdfrefximage", true);
    scan_int;
    pdf_check_obj(obj_type_ximage, cur_val);
    new_whatsit(pdf_refximage_node);
    j := obj_data_ptr(cur_val);
    pdf_ximage_ref(tail) := j;
    pdf_width(tail) := image_width(j);
    pdf_height(tail) := image_height(j);
    pdf_depth(tail) := image_depth(j);
end

@ The following function finds object with identifier |i| and type |t|.
  |i < 0| indicates that |-i| should be treated as a string number. If no
  such object exists then it will be created. This function is used mainly to
  find destination for link annotations and outlines; however it is also used
  in |pdf_ship_out| (to check whether a Page object already exists) so we need
  to declare it together with subroutines needed in |pdf_hlist_out| and
  |pdf_vlist_out|.

@<Declare procedures that need to be declared forward for \pdfTeX@>=
function find_obj(t, i: integer; byname: boolean): integer;
begin
    find_obj := avl_find_obj(t, i, byname);
end;

procedure flush_str(s: str_number); {flush a string if possible}
begin
    if flushable(s) then
        flush_string;
end;

function get_obj(t, i: integer; byname: boolean): integer;
var r: integer;
    s: str_number;
begin
    if byname > 0 then begin
        s := tokens_to_string(i);
        r := find_obj(t, s, true);
    end
    else begin
        s := 0;
        r := find_obj(t, i, false);
    end;
    if r = 0 then begin
        if byname > 0 then begin
            pdf_create_obj(t, -s);
            s := 0;
        end
        else
            pdf_create_obj(t, i);
        r := obj_ptr;
        if t = obj_type_dest then
            obj_dest_ptr(r) := null;
    end;
    if s <> 0 then
        flush_str(s);
    get_obj := r;
end;

function get_microinterval:integer;
var s,@!m:integer; {seconds and microseconds}
begin
   seconds_and_micros(s,m);
   if (s-epochseconds)>32767 then
     get_microinterval := max_integer
   else if (microseconds>m)  then
     get_microinterval := ((s-1-epochseconds)*65536)+ (((m+1000000-microseconds)/100)*65536)/10000
   else
     get_microinterval := ((s-epochseconds)*65536)  + (((m-microseconds)/100)*65536)/10000;
end;


@ @<Declare procedures needed in |do_ext...@>=
function scan_action: pointer; {read an action specification}
var p: integer;
begin
    p := new_node(action_node,0);
    scan_action := p;
    if scan_keyword("user") then
        pdf_action_type(p) := pdf_action_user
    else if scan_keyword("goto") then
        pdf_action_type(p) := pdf_action_goto
    else if scan_keyword("thread") then
        pdf_action_type(p) := pdf_action_thread
    else
        pdf_error("ext1", "action type missing");
    if pdf_action_type(p) = pdf_action_user then begin
        scan_pdf_ext_toks;
        pdf_action_tokens(p) := def_ref;
        return;
    end;
    if scan_keyword("file") then begin
        scan_pdf_ext_toks;
        pdf_action_file(p) := def_ref;
    end;
    if scan_keyword("page") then begin
        if pdf_action_type(p) <> pdf_action_goto then
            pdf_error("ext1", "only GoTo action can be used with `page'");
        pdf_action_type(p) := pdf_action_page;
        scan_int;
        if cur_val <= 0 then
            pdf_error("ext1", "page number must be positive");
        pdf_action_id(p) := cur_val;
        pdf_action_named_id(p) := 0;
        scan_pdf_ext_toks;
        pdf_action_tokens(p) := def_ref;
    end
    else if scan_keyword("name") then begin
        scan_pdf_ext_toks;
        pdf_action_named_id(p) := 1;
        pdf_action_id(p) := def_ref;
    end
    else if scan_keyword("num") then begin
        if (pdf_action_type(p) = pdf_action_goto) and
            (pdf_action_file(p) <> null) then
            pdf_error("ext1",
                "`goto' option cannot be used with both `file' and `num'");
        scan_int;
        if cur_val <= 0 then
            pdf_error("ext1", "num identifier must be positive");
        pdf_action_named_id(p) := 0;
        pdf_action_id(p) := cur_val;
    end
    else
        pdf_error("ext1", "identifier type missing");
    if scan_keyword("newwindow") then begin
        pdf_action_new_window(p) := 1;
        @<Scan an optional space@>; end
    else if scan_keyword("nonewwindow") then begin
        pdf_action_new_window(p) := 2;
        @<Scan an optional space@>; end
    else
        pdf_action_new_window(p) := 0;
    if (pdf_action_new_window(p) > 0) and
        (((pdf_action_type(p) <> pdf_action_goto) and
          (pdf_action_type(p) <> pdf_action_page)) or
         (pdf_action_file(p) = null)) then
            pdf_error("ext1",
                "`newwindow'/`nonewwindow' must be used with `goto' and `file' option");
end;

procedure new_annot_whatsit(w: small_number); {create a new whatsit node for
annotation}
begin
    new_whatsit(w);
    scan_alt_rule; {scans |<rule spec>| to |alt_rule|}
    pdf_width(tail) := width(alt_rule);
    pdf_height(tail) := height(alt_rule);
    pdf_depth(tail) := depth(alt_rule);
    if (w = pdf_thread_node) or (w = pdf_start_thread_node) then begin
        if scan_keyword("attr") then begin
            scan_pdf_ext_toks;
            pdf_thread_attr(tail) := def_ref;
        end
        else
            pdf_thread_attr(tail) := null;
    end;
end;

@ @<Glob...@>=
@!pdf_last_annot: integer;

@ @<Implement \.{\\pdfannot}@>=
begin
    check_pdfoutput("\pdfannot", true);
    if scan_keyword("reserveobjnum") then begin
        pdf_last_annot := pdf_new_objnum;
        @<Scan an optional space@>; end
    else begin
        if scan_keyword("useobjnum") then begin
            scan_int;
            k := cur_val;
            if (k <= 0) or (k > obj_ptr) or (obj_annot_ptr(k) <> 0) then
                pdf_error("ext1", "invalid object number");
        end
        else
            k := pdf_new_objnum;
        new_annot_whatsit(pdf_annot_node);
        pdf_annot_objnum(tail) := k;
        scan_pdf_ext_toks;
        pdf_annot_data(tail) := def_ref;
        pdf_last_annot := k;
    end
end

@ pdflastlink needs an extra global variable
@<Glob...@>=
@!pdf_last_link: integer;

@ @<Implement \.{\\pdfstartlink}@>=
begin
    check_pdfoutput("\pdfstartlink", true);
    if abs(mode) = vmode then
        pdf_error("ext1", "\pdfstartlink cannot be used in vertical mode");
    k := pdf_new_objnum;
    new_annot_whatsit(pdf_start_link_node);
	    pdf_link_attr(tail) := null;
        if scan_keyword("attr") then begin
            scan_pdf_ext_toks;
            pdf_link_attr(tail) := def_ref;
        end;
    r := scan_action; pdf_link_action(tail) := r;
    pdf_link_objnum(tail) := k;
    pdf_last_link := k;
    {N.B.: although it is possible to set |obj_annot_ptr(k) := tail| here, it
     is not safe if nodes are later copied/destroyed/moved; a better place
     to do this is inside |do_link|, when the whatsit node is written out}
end

@ @<Implement \.{\\pdfendlink}@>=
begin
    check_pdfoutput("\pdfendlink", true);
    if abs(mode) = vmode then
        pdf_error("ext1", "\pdfendlink cannot be used in vertical mode");
    new_whatsit(pdf_end_link_node);
end

@ @<Declare procedures needed in |do_ext...@>=
function outline_list_count(p: pointer): integer; {return number of outline
entries in the same level with |p|}
var k: integer;
begin
    k := 1;
    while obj_outline_prev(p) <> 0 do begin
        incr(k);
        p := obj_outline_prev(p);
    end;
    outline_list_count := k;
end;

@ @<Implement \.{\\pdfoutline}@>=
begin
    check_pdfoutput("\pdfoutline", true);
    if scan_keyword("attr") then begin
        scan_pdf_ext_toks;
        r := def_ref;
    end
    else
        r := 0;
    p := scan_action;
    if scan_keyword("count") then begin
        scan_int;
        i := cur_val;
    end
    else
        i := 0;
    scan_pdf_ext_toks;
    q := def_ref;
    pdf_new_obj(obj_type_others, 0, 1);
    j := obj_ptr;
    write_action(p);
    pdf_end_obj;
    delete_action_ref(p);
    pdf_create_obj(obj_type_outline, 0);
    k := obj_ptr;
    obj_outline_ptr(k) := pdf_get_mem(pdfmem_outline_size);
    obj_outline_action_objnum(k) := j;
    obj_outline_count(k) := i;
    pdf_new_obj(obj_type_others, 0, 1);
    pdf_print_str_ln(tokens_to_string(q));
    flush_str(last_tokens_string);
    delete_token_ref(q);
    pdf_end_obj;
    obj_outline_title(k) := obj_ptr;
    obj_outline_prev(k) := 0;
    obj_outline_next(k) := 0;
    obj_outline_first(k) := 0;
    obj_outline_last(k) := 0;
    obj_outline_parent(k) := pdf_parent_outline;
    obj_outline_attr(k) := r;
    if pdf_first_outline = 0 then
        pdf_first_outline :=  k;
    if pdf_last_outline = 0 then begin
        if pdf_parent_outline <> 0 then
            obj_outline_first(pdf_parent_outline) := k;
    end
    else begin
        obj_outline_next(pdf_last_outline) := k;
        obj_outline_prev(k) := pdf_last_outline;
    end;
    pdf_last_outline := k;
    if obj_outline_count(k) <> 0 then begin
        pdf_parent_outline := k;
        pdf_last_outline := 0;
    end
    else if (pdf_parent_outline <> 0) and
    (outline_list_count(k) = abs(obj_outline_count(pdf_parent_outline))) then
    begin
        j := pdf_last_outline;
        repeat
            obj_outline_last(pdf_parent_outline) := j;
            j := pdf_parent_outline;
            pdf_parent_outline := obj_outline_parent(pdf_parent_outline);
        until (pdf_parent_outline = 0) or
        (outline_list_count(j) < abs(obj_outline_count(pdf_parent_outline)));
        if pdf_parent_outline = 0 then
            pdf_last_outline := pdf_first_outline
        else
            pdf_last_outline := obj_outline_first(pdf_parent_outline);
        while obj_outline_next(pdf_last_outline) <> 0 do
            pdf_last_outline := obj_outline_next(pdf_last_outline);
    end;
end

@ When a destination is created we need to check whether another destination
with the same identifier already exists and give a warning if needed.

@<Declare procedures needed in |pdf_hlist_out|, |pdf_vlist_out|@>=
procedure warn_dest_dup(id: integer; byname: small_number; s1, s2: str_number);
begin
    pdf_warning(s1, "destination with the same identifier (", false, false);
    if byname > 0 then begin
        print("name");
        print_mark(id);
    end
    else begin
        print("num");
        print_int(id);
    end;
    print(") ");
    print(s2);
    print_ln;
    show_context;
end;

@ Notice that |scan_keyword| doesn't care if two words have same prefix; so
we should be careful when scan keywords with same prefix. The main rule: if
there are two or more keywords with the same prefix, then always test in
order from the longest one to the shortest one.

@<Implement \.{\\pdfdest}@>=
begin
    check_pdfoutput("\pdfdest", true);
    q := tail;
    new_whatsit(pdf_dest_node);
    if scan_keyword("num") then begin
        scan_int;
        if cur_val <= 0 then
            pdf_error("ext1", "num identifier must be positive");
        if cur_val > max_halfword then
            pdf_error("ext1", "number too big");
        pdf_dest_id(tail) := cur_val;
        pdf_dest_named_id(tail) := 0;
    end
    else if scan_keyword("name") then begin
        scan_pdf_ext_toks;
        pdf_dest_id(tail) := def_ref;
        pdf_dest_named_id(tail) := 1;
    end
    else
        pdf_error("ext1", "identifier type missing");
    if scan_keyword("xyz") then begin
        pdf_dest_type(tail) := pdf_dest_xyz;
        if scan_keyword("zoom") then begin
            scan_int;
            if cur_val > max_halfword then
                pdf_error("ext1", "number too big");
            pdf_dest_xyz_zoom(tail) := cur_val;
        end
        else
            pdf_dest_xyz_zoom(tail) := null;
    end
    else if scan_keyword("fitbh") then
        pdf_dest_type(tail) := pdf_dest_fitbh
    else if scan_keyword("fitbv") then
        pdf_dest_type(tail) := pdf_dest_fitbv
    else if scan_keyword("fitb") then
        pdf_dest_type(tail) := pdf_dest_fitb
    else if scan_keyword("fith") then
        pdf_dest_type(tail) := pdf_dest_fith
    else if scan_keyword("fitv") then
        pdf_dest_type(tail) := pdf_dest_fitv
    else if scan_keyword("fitr") then
        pdf_dest_type(tail) := pdf_dest_fitr
    else if scan_keyword("fit") then
        pdf_dest_type(tail) := pdf_dest_fit
    else
        pdf_error("ext1", "destination type missing");
    @<Scan an optional space@>;
    if pdf_dest_type(tail) = pdf_dest_fitr then begin
        scan_alt_rule; {scans |<rule spec>| to |alt_rule|}
        pdf_width(tail) := width(alt_rule);
        pdf_height(tail) := height(alt_rule);
        pdf_depth(tail) := depth(alt_rule);
    end;
    if pdf_dest_named_id(tail) <> 0 then begin
        i := tokens_to_string(pdf_dest_id(tail));
        k := find_obj(obj_type_dest, i, true);
        flush_str(i);
    end
    else
        k := find_obj(obj_type_dest, pdf_dest_id(tail), false);
    if (k <> 0) and (obj_dest_ptr(k) <> null) then begin
        warn_dest_dup(pdf_dest_id(tail), pdf_dest_named_id(tail),
                      "ext4", "has been already used, duplicate ignored");
        flush_node_list(tail);
        tail := q;
        vlink(q) := null;
    end;
end

@ @<Declare procedures needed in |do_ext...@>=
procedure scan_thread_id;
begin
    if scan_keyword("num") then begin
        scan_int;
        if cur_val <= 0 then
            pdf_error("ext1", "num identifier must be positive");
        if cur_val > max_halfword then
            pdf_error("ext1", "number too big");
        pdf_thread_id(tail) := cur_val;
        pdf_thread_named_id(tail) := 0;
    end
    else if scan_keyword("name") then begin
        scan_pdf_ext_toks;
        pdf_thread_id(tail) := def_ref;
        pdf_thread_named_id(tail) := 1;
    end
    else
        pdf_error("ext1", "identifier type missing");
end;

@ @<Implement \.{\\pdfthread}@>=
begin
    check_pdfoutput("\pdfthread", true);
    new_annot_whatsit(pdf_thread_node);
    scan_thread_id;
end

@ @<Implement \.{\\pdfstartthread}@>=
begin
    check_pdfoutput("\pdfstartthread", true);
    new_annot_whatsit(pdf_start_thread_node);
    scan_thread_id;
end

@ @<Implement \.{\\pdfendthread}@>=
begin
    check_pdfoutput("\pdfendthread", true);
    new_whatsit(pdf_end_thread_node);
end

@ @<Glob...@>=
@!pdf_last_x_pos: integer;
@!pdf_last_y_pos: integer;

@ @<Implement \.{\\pdfsavepos}@>=
begin
    new_whatsit(pdf_save_pos_node);
end

@ To implement primitives as \.{\\pdfinfo}, \.{\\pdfcatalog} or
\.{\\pdfnames} we need to concatenate tokens lists.

@<Declare procedures needed in |do_ext...@>=
function concat_tokens(q, r: pointer): pointer; {concat |q| and |r| and
returns the result tokens list}
var p: pointer;
begin
    if q = null then begin
        concat_tokens := r;
        return;
    end;
    p := q;
    while link(p) <> null do
        p := link(p);
    link(p) := link(r);
    free_avail(r);
    concat_tokens := q;
end;

@ @<Implement \.{\\pdfinfo}@>=
begin
    check_pdfoutput("\pdfinfo", false);
    scan_pdf_ext_toks;
    if pdf_output > 0 then
        pdf_info_toks := concat_tokens(pdf_info_toks, def_ref);
end

@ @<Implement \.{\\pdfcatalog}@>=
begin
    check_pdfoutput("\pdfcatalog", false);
    scan_pdf_ext_toks;
    if pdf_output > 0 then
        pdf_catalog_toks := concat_tokens(pdf_catalog_toks, def_ref);
    if scan_keyword("openaction") then begin
        if pdf_catalog_openaction <> 0 then
            pdf_error("ext1", "duplicate of openaction")
        else begin
            p := scan_action;
            pdf_new_obj(obj_type_others, 0, 1);
            if pdf_output > 0 then
                pdf_catalog_openaction := obj_ptr;
            write_action(p);
            pdf_end_obj;
            delete_action_ref(p);
        end;
    end
end

@ @<Implement \.{\\pdfnames}@>=
begin
    check_pdfoutput("\pdfnames", true);
    scan_pdf_ext_toks;
    pdf_names_toks := concat_tokens(pdf_names_toks, def_ref);
end

@ @<Implement \.{\\pdftrailer}@>=
begin
    check_pdfoutput("\pdftrailer", false);
    scan_pdf_ext_toks;
    if pdf_output > 0 then
        pdf_trailer_toks := concat_tokens(pdf_trailer_toks, def_ref);
end

@ @<Glob...@>=
@!pdf_retval: integer; {global multi-purpose return value}

@ @<Set initial values of key variables@>=
  seconds_and_micros(epochseconds,microseconds);
  init_start_time;

@ Negative random seed values are silently converted to positive ones

@<Implement \.{\\pdfsetrandomseed}@>=
begin
  scan_int;
  if cur_val<0 then negate(cur_val);
  random_seed := cur_val;
  init_randoms(random_seed);
end

@ @<Implement \.{\\savecatcodetable}@>=
begin
  scan_int;
  if (cur_val<0)or(cur_val>@"FFFFFFF) then begin
	print_err("Invalid \catcode table");
	help1("All \catcode table ids must be between 0 and 0xFFFFFFF");
	error;
    end 
  else begin if cur_val=cat_code_table then begin
      print_err("Invalid \catcode table");
  	  help1("You cannot overwrite the current \catcode table");
      error;
      end
    else
      copy_cat_codes(cat_code_table,cur_val);
    end;
end

@ @<Implement \.{\\initcatcodetable}@>=
begin
  scan_int;
  if (cur_val<0)or(cur_val>@"FFFFFFF) then begin
	print_err("Invalid \catcode table");
	help1("All \catcode table ids must be between 0 and 0xFFFFFFF");
	error;
    end 
  else begin if cur_val=cat_code_table then begin
    print_err("Invalid \catcode table");
  	help1("You cannot overwrite the current \catcode table");
	error;
    end
  else
    initex_cat_codes(cur_val);
    end;
end

@ The following subroutines are about PDF-specific font issues.

@<Declare procedures needed in |do_ext...@>=
procedure pdf_include_chars;
var s: str_number;
    k: pool_pointer; {running indices}
    f: internal_font_number;
begin
    scan_font_ident;
    f := cur_val;
    if f = null_font then
        pdf_error("font", "invalid font identifier");
    pdf_check_vf_cur_val;
    if not font_used(f) then
        pdf_init_font(f);
    scan_pdf_ext_toks;
    s := tokens_to_string(def_ref);
    delete_token_ref(def_ref);
    k := str_start_macro(s);
    while k < str_start_macro(s + 1) do begin
       pdf_mark_char(f, str_pool[k]);
       incr(k);
    end;
    flush_str(s);
end;

procedure glyph_to_unicode;
var s1, s2: str_number;
begin
    scan_pdf_ext_toks;
    s1 := tokens_to_string(def_ref);
    delete_token_ref(def_ref);
    scan_pdf_ext_toks;
    s2 := tokens_to_string(def_ref);
    delete_token_ref(def_ref);
    def_tounicode(s1, s2);
    flush_str(s2);
    flush_str(s1);
end;

@ @<Implement \.{\\pdfincludechars}@>=
begin
    check_pdfoutput("\pdfincludechars", true);
    pdf_include_chars;
end

@ @<Implement \.{\\pdfglyphtounicode}@>=
begin
    glyph_to_unicode;
end

@ A change from \THANH's original code: the font attributes are simply
initialized to zero now, this is easier to deal with from C than an
empty \TeX{} string, and surely nobody will want to set
\.{\\pdffontattr} to a string containing a single zero, as that
would be nonsensical in the PDF output.

@<Implement \.{\\pdffontattr}@>=
begin
    check_pdfoutput("\pdffontattr", true);
    scan_font_ident;
    k := cur_val;
    if k = null_font then
        pdf_error("font", "invalid font identifier");
    scan_pdf_ext_toks;
    set_pdf_font_attr(k, tokens_to_string(def_ref));
    if length(pdf_font_attr(k)) = 0 then begin
      flush_string;
      set_pdf_font_attr(k,0);
      end;
end

@ @<Implement \.{\\pdfmapfile}@>=
begin
    check_pdfoutput("\pdfmapfile", true);
    scan_pdf_ext_toks;
    pdfmapfile(def_ref);
    delete_token_ref(def_ref);
end

@ @<Implement \.{\\pdfmapline}@>=
begin
    check_pdfoutput("\pdfmapline", true);
    scan_pdf_ext_toks;
    pdfmapline(def_ref);
    delete_token_ref(def_ref);
end

@ The following function are needed for outputing article thread.

@<Declare procedures needed in |do_ext...@>=
procedure thread_title(thread: integer);
begin
    pdf_print("/Title (");
    if obj_info(thread) < 0 then
        pdf_print(-obj_info(thread))
    else
        pdf_print_int(obj_info(thread));
    pdf_print_ln(")");
end;

procedure pdf_fix_thread(thread: integer);
var a: pointer;
begin
    pdf_warning("thread", "destination ", false, false);
    if obj_info(thread) < 0 then begin
        print("name{");
        print(-obj_info(thread));
        print("}");
    end
    else begin
        print("num");
        print_int(obj_info(thread));
    end;
    print(" has been referenced but does not exist, replaced by a fixed one");
    print_ln; print_ln;
    pdf_new_dict(obj_type_others, 0, 0);
    a := obj_ptr;
    pdf_indirect_ln("T", thread);
    pdf_indirect_ln("V", a);
    pdf_indirect_ln("N", a);
    pdf_indirect_ln("P", head_tab[obj_type_page]);
    pdf_print("/R [0 0 ");
    pdf_print_bp(page_width); pdf_out(" ");
    pdf_print_bp(page_height);
    pdf_print_ln("]");
    pdf_end_dict;
    pdf_begin_dict(thread, 1);
    pdf_print_ln("/I << ");
    thread_title(thread);
    pdf_print_ln(">>");
    pdf_indirect_ln("F", a);
    pdf_end_dict;
end;

procedure out_thread(thread: integer);
var a, b: pointer;
    last_attr: integer;
begin
    if obj_thread_first(thread) = 0 then begin
        pdf_fix_thread(thread);
        return;
    end;
    pdf_begin_dict(thread, 1);
    a := obj_thread_first(thread);
    b := a;
    last_attr := 0;
    repeat
        if obj_bead_attr(a) <> 0 then
            last_attr := obj_bead_attr(a);
        a := obj_bead_next(a);
    until a = b;
    if last_attr <> 0 then
        pdf_print_ln(last_attr)
    else begin
        pdf_print_ln("/I << ");
        thread_title(thread);
        pdf_print_ln(">>");
    end;
    pdf_indirect_ln("F", a);
    pdf_end_dict;
    repeat
        pdf_begin_dict(a, 1);
        if a = b then
            pdf_indirect_ln("T", thread);
        pdf_indirect_ln("V", obj_bead_prev(a));
        pdf_indirect_ln("N", obj_bead_next(a));
        pdf_indirect_ln("P", obj_bead_page(a));
        pdf_indirect_ln("R", obj_bead_rect(a));
        pdf_end_dict;
        a := obj_bead_next(a);
    until a = b;
end;

@ @<Display <rule spec> for whatsit node created by \pdfTeX@>=
print("(");
print_rule_dimen(pdf_height(p));
print_char("+");
print_rule_dimen(pdf_depth(p));
print(")x");
print_rule_dimen(pdf_width(p))

@ Each new type of node that appears in our data structure must be capable
of being displayed, copied, destroyed, and so on. The routines that we
need for write-oriented whatsits are somewhat like those for mark nodes;
other extensions might, of course, involve more subtlety here.

@<Basic printing...@>=
procedure print_write_whatsit(@!s:str_number;@!p:pointer);
begin print_esc(s);
if write_stream(p)<16 then print_int(write_stream(p))
else if write_stream(p)=16 then print_char("*")
@.*\relax@>
else print_char("-");
end;

@ Three extra node types carry information from |main_control|.

@ |cancel_boundary_nodes| indicate that the next left boundary be
ignored. These are created by the \.{\\noboundary} command in
horizontal mode.

@d cancel_boundary_node==pdf_restore_node+1
@d cancel_boundary_size==3

@<Append a |cancel_boundary_node| @>=
begin new_whatsit(cancel_boundary_node);
end

@ User defined whatsits can be inserted into node lists to pass data
along from one lua call to anotherb without interference from the
typesetting engine itself. Each has an id, a type, and a value. The
type of the value depends on the |user_node_type| field. 

@d user_defined_node==cancel_boundary_node+1
@d user_defined_node_size=4
@d user_node_id(#)==vlink(#+2)
@d user_node_type(#)==vinfo(#+2)
@d user_node_value(#)==vinfo(#+3)

@ @<Display the whatsit...@>=
case subtype(p) of
open_node:begin print_write_whatsit("openout",p);
  print_char("="); print_file_name(open_name(p),open_area(p),open_ext(p));
  end;
write_node:begin print_write_whatsit("write",p);
  print_mark(write_tokens(p));
  end;
close_node:print_write_whatsit("closeout",p);
special_node:begin print_esc("special");
  print_mark(write_tokens(p));
  end;
dir_node:
  if dir_dir(p)<0 then begin
    print_esc("enddir"); print(" "); print_dir(dir_dir(p)+64);
    end
  else begin
    print_esc("begindir"); print(" "); print_dir(dir_dir(p));
    end;
@<LOCAL: print out |local_paragraph| node@>;
pdf_literal_node: begin
    print_esc("pdfliteral");
    case pdf_literal_mode(p) of
    set_origin:
        do_nothing;
    direct_page:
        print(" page");
    direct_always:
        print(" direct");
    othercases confusion("literal2")
    endcases;
    print_mark(pdf_literal_data(p));
end;
pdf_colorstack_node: begin
    print_esc("pdfcolorstack ");
    print_int(pdf_colorstack_stack(p));
    case  pdf_colorstack_cmd(p) of
    colorstack_set:
        print(" set ");
    colorstack_push:
        print(" push ");
    colorstack_pop:
        print(" pop");
    colorstack_current:
        print(" current");
    othercases confusion("pdfcolorstack")
    endcases;
    if pdf_colorstack_cmd(p) <= colorstack_data then
        print_mark(pdf_colorstack_data(p));
end;
pdf_setmatrix_node: begin
    print_esc("pdfsetmatrix");
    print_mark(pdf_setmatrix_data(p));
end;
pdf_save_node: begin
    print_esc("pdfsave");
end;
pdf_restore_node: begin
    print_esc("pdfrestore");
end;
cancel_boundary_node: begin
    print_esc("noboundary");
end;
late_lua_node: begin
    print_esc("latelua");
    print_int(late_lua_reg(p));
    print_mark(late_lua_data(p));
end;
close_lua_node: begin
    print_esc("closelua");
	print_int(late_lua_reg(p));
end;
pdf_refobj_node: begin
    print_esc("pdfrefobj");
    if obj_obj_is_stream(pdf_obj_objnum(p)) > 0 then begin
        if obj_obj_stream_attr(pdf_obj_objnum(p)) <> null then begin
            print(" attr");
            print_mark(obj_obj_stream_attr(pdf_obj_objnum(p)));
        end;
        print(" stream");
    end;
    if obj_obj_is_file(pdf_obj_objnum(p)) > 0 then
        print(" file");
    print_mark(obj_obj_data(pdf_obj_objnum(p)));
end;
pdf_refxform_node: begin
    print_esc("pdfrefxform");
    print("(");
    print_scaled(obj_xform_height(pdf_xform_objnum(p)));
    print_char("+");
    print_scaled(obj_xform_depth(pdf_xform_objnum(p)));
    print(")x");
    print_scaled(obj_xform_width(pdf_xform_objnum(p)));
end;
pdf_refximage_node: begin
    print_esc("pdfrefximage");
    print("(");
    print_scaled(pdf_height(p));
    print_char("+");
    print_scaled(pdf_depth(p));
    print(")x");
    print_scaled(pdf_width(p));
end;
pdf_annot_node: begin
    print_esc("pdfannot");
    @<Display <rule spec> for whatsit node created by \pdfTeX@>;
    print_mark(pdf_annot_data(p));
end;
pdf_start_link_node: begin
    print_esc("pdflink");
    @<Display <rule spec> for whatsit node created by \pdfTeX@>;
    if pdf_link_attr(p) <> null then begin
        print(" attr");
        print_mark(pdf_link_attr(p));
    end;
    print(" action");
    if pdf_action_type(pdf_link_action(p)) = pdf_action_user then begin
        print(" user");
        print_mark(pdf_action_tokens(pdf_link_action(p)));
        return;
    end;
    if pdf_action_file(pdf_link_action(p)) <> null then begin
        print(" file");
        print_mark(pdf_action_file(pdf_link_action(p)));
    end;
    case pdf_action_type(pdf_link_action(p)) of
    pdf_action_goto: begin
        if pdf_action_named_id(pdf_link_action(p)) > 0 then begin
            print(" goto name");
            print_mark(pdf_action_id(pdf_link_action(p)));
        end
        else begin
            print(" goto num");
            print_int(pdf_action_id(pdf_link_action(p)))
        end;
    end;
    pdf_action_page: begin
        print(" page");
        print_int(pdf_action_id(pdf_link_action(p)));
        print_mark(pdf_action_tokens(pdf_link_action(p)));
    end;
    pdf_action_thread: begin
        if pdf_action_named_id(pdf_link_action(p)) > 0 then begin
            print(" thread name");
            print_mark(pdf_action_id(pdf_link_action(p)));
        end
        else begin
            print(" thread num");
            print_int(pdf_action_id(pdf_link_action(p)));
        end;
    end;
    othercases pdf_error("displaying", "unknown action type");
    endcases;
end;
pdf_end_link_node: print_esc("pdfendlink");
pdf_dest_node: begin
    print_esc("pdfdest");
    if pdf_dest_named_id(p) > 0 then begin
        print(" name");
        print_mark(pdf_dest_id(p));
    end
    else begin
        print(" num");
        print_int(pdf_dest_id(p));
    end;
    print(" ");
    case pdf_dest_type(p) of
    pdf_dest_xyz: begin
        print("xyz");
        if pdf_dest_xyz_zoom(p) <> null then begin
            print(" zoom");
            print_int(pdf_dest_xyz_zoom(p));
        end;
    end;
    pdf_dest_fitbh: print("fitbh");
    pdf_dest_fitbv: print("fitbv");
    pdf_dest_fitb: print("fitb");
    pdf_dest_fith: print("fith");
    pdf_dest_fitv: print("fitv");
    pdf_dest_fitr: begin
        print("fitr");
        @<Display <rule spec> for whatsit node created by \pdfTeX@>;
    end;
    pdf_dest_fit: print("fit");
    othercases print("unknown!");
    endcases;
end;
pdf_thread_node,
pdf_start_thread_node: begin
    if subtype(p) = pdf_thread_node then
        print_esc("pdfthread")
    else
        print_esc("pdfstartthread");
    print("("); print_rule_dimen(pdf_height(p)); print_char("+");
    print_rule_dimen(pdf_depth(p)); print(")x");
    print_rule_dimen(pdf_width(p));
    if pdf_thread_attr(p) <> null then begin
        print(" attr");
        print_mark(pdf_thread_attr(p));
    end;
    if pdf_thread_named_id(p) > 0 then begin
        print(" name");
        print_mark(pdf_thread_id(p));
    end
    else begin
        print(" num");
        print_int(pdf_thread_id(p));
    end;
end;
pdf_end_thread_node: print_esc("pdfendthread");
pdf_save_pos_node: print_esc("pdfsavepos");
user_defined_node: begin
    print_esc("whatsit");
	print_int(user_node_id(p));
    print_char("=");
    case user_node_type(p) of 
    "a": print("<>");
    "n": begin print("["); show_node_list(user_node_value(p)); print("]"); end;
    "s": begin print(""""); print(user_node_value(p)); print(""""); end;
    "t": print_mark(user_node_value(p));
    othercases  { only d }
      print_int(user_node_value(p));
    endcases;
	end;
othercases print("whatsit?")
endcases

@ @<Incorporate a whatsit node into a vbox@>=
if (subtype(p) = pdf_refxform_node) or (subtype(p) = pdf_refximage_node) then
begin x:=x+d+pdf_height(p); d:=pdf_depth(p);
s:=0;
if pdf_width(p)+s>w then w:=pdf_width(p)+s;
end

@ @<Incorporate a whatsit node into an hbox@>=
begin
if subtype(p)=dir_node then 
  begin
  @<DIR: Adjust the dir stack for the |hpack| routine@>;
  end 
else begin
if (subtype(p) = pdf_refxform_node) or (subtype(p) = pdf_refximage_node) then
begin x:=x+pdf_width(p);
s:=0;
if pdf_height(p)-s>h then h:=pdf_height(p)-s;
if pdf_depth(p)+s>d then d:=pdf_depth(p)+s;
end;
end;
end

@ @<Let |d| be the width of the whatsit |p|@>=
if (subtype(p) = pdf_refxform_node) or (subtype(p) = pdf_refximage_node) then
    d := pdf_width(p)
else
    d := 0

@ @<Prepare to move whatsit |p| to the current page, then |goto contribute|@>=
begin
  if (subtype(p) = pdf_refxform_node) or (subtype(p) = pdf_refximage_node) then
  begin page_total:=page_total+page_depth+pdf_height(p);
  page_depth:=pdf_depth(p);
  end;
  goto contribute;
end

@ @<Process whatsit |p| in |vert_break| loop, |goto not_found|@>=
begin
  if (subtype(p) = pdf_refxform_node) or (subtype(p) = pdf_refximage_node) then
  begin cur_height:=cur_height+prev_dp+pdf_height(p); prev_dp:=pdf_depth(p);
  end;
  goto not_found;
end

@ @<Output the whatsit node |p| in a vlist@>=
out_what(p)

@ @<Output the whatsit node |p| in an hlist@>=
if subtype(p)<>dir_node then out_what(p)
else @<Output a reflection instruction if the direction has changed@>

@ After all this preliminary shuffling, we come finally to the routines
that actually send out the requested data. Let's do \.{\\special} first
(it's easier).

@<Declare procedures needed in |hlist_out|, |vlist_out|@>=
procedure special_out(@!p:pointer);
var old_setting:0..max_selector; {holds print |selector|}
@!k:pool_pointer; {index into |str_pool|}
begin synch_h; synch_v;@/
old_setting:=selector; selector:=new_string;
show_token_list(link(write_tokens(p)),null,pool_size-pool_ptr);
selector:=old_setting;
str_room(1);
if cur_length<256 then
  begin dvi_out(xxx1); dvi_out(cur_length);
  end
else  begin dvi_out(xxx4); dvi_four(cur_length);
  end;
for k:=str_start_macro(str_ptr) to pool_ptr-1 do dvi_out(so(str_pool[k]));
pool_ptr:=str_start_macro(str_ptr); {erase the string}
end;

@ To write a token list, we must run it through \TeX's scanner, expanding
macros and \.{\\the} and \.{\\number}, etc. This might cause runaways,
if a delimited macro parameter isn't matched, and runaways would be
extremely confusing since we are calling on \TeX's scanner in the middle
of a \.{\\shipout} command. Therefore we will put a dummy control sequence as
a ``stopper,'' right after the token list. This control sequence is
artificially defined to be \.{\\outer}.
@:end_write_}{\.{\\endwrite}@>

@<Initialize table...@>=
text(end_write):="endwrite"; eq_level(end_write):=level_one;
eq_type(end_write):=outer_call; equiv(end_write):=null;

@ @<Declare procedures needed in |hlist_out|, |vlist_out|@>=
procedure write_out(@!p:pointer);
var old_setting:0..max_selector; {holds print |selector|}
@!old_mode:integer; {saved |mode|}
@!j:small_number; {write stream number}
@!q,@!r:pointer; {temporary variables for list manipulation}
begin @<Expand macros in the token list
  and make |link(def_ref)| point to the result@>;
old_setting:=selector; j:=write_stream(p);
if write_open[j] then selector:=j
else  begin {write to the terminal if file isn't open}
  if (j=17)and(selector=term_and_log) then selector:=log_only;
  print_nl("");
  end;
token_show(def_ref); print_ln;
flush_list(def_ref); selector:=old_setting;
end;

@ The final line of this routine is slightly subtle; at least, the author
didn't think about it until getting burnt! There is a used-up token list
@^Knuth, Donald Ervin@>
on the stack, namely the one that contained |end_write_token|. (We
insert this artificial `\.{\\endwrite}' to prevent runaways, as explained
above.) If it were not removed, and if there were numerous writes on a
single page, the stack would overflow.

@d end_write_token==cs_token_flag+end_write

@<Expand macros in the token list and...@>=
q:=get_avail; info(q):=right_brace_token+"}";@/
r:=get_avail; link(q):=r; info(r):=end_write_token; ins_list(q);@/
begin_token_list(write_tokens(p),write_text);@/
q:=get_avail; info(q):=left_brace_token+"{"; ins_list(q);
{now we're ready to scan
  `\.\{$\langle\,$token list$\,\rangle$\.{\} \\endwrite}'}
old_mode:=mode; mode:=0;
  {disable \.{\\prevdepth}, \.{\\spacefactor}, \.{\\lastskip}, \.{\\prevgraf}}
cur_cs:=write_loc; q:=scan_toks(false,true); {expand macros, etc.}
get_token;@+if cur_tok<>end_write_token then
  @<Recover from an unbalanced write command@>;
mode:=old_mode;
end_token_list {conserve stack space}

@ @<Recover from an unbalanced write command@>=
begin print_err("Unbalanced write command");
@.Unbalanced write...@>
help2("On this page there's a \write with fewer real {'s than }'s.")@/
("I can't handle that very well; good luck."); error;
repeat get_token;
until cur_tok=end_write_token;
end

@ The |out_what| procedure takes care of outputting whatsit nodes for
|vlist_out| and |hlist_out|\kern-.3pt.

@<Declare procedures needed in |hlist_out|, |vlist_out|@>=
procedure out_what(@!p:pointer);
var j:small_number; {write stream number}
begin case subtype(p) of
open_node,write_node,close_node:@<Do some work that has been queued up
  for \.{\\write}@>;
special_node:special_out(p);
pdf_save_pos_node:
  @<Save current position in DVI mode@>;
local_par_node:do_nothing;
cancel_boundary_node: do_nothing;
othercases  confusion("ext4") {TH: those will be pdf extension nodes in dvi mode, most likely}
@:this can't happen ext4}{\quad ext4@>
endcases;
end;

@ @<Save current position in DVI mode@>=
begin
    pdf_last_x_pos := cur_h + one_inch;
    pdf_last_y_pos := cur_page_height - cur_v - one_inch;
end

@ We don't implement \.{\\write} inside of leaders. (The reason is that
the number of times a leader box appears might be different in different
implementations, due to machine-dependent rounding in the glue calculations.)
@^leaders@>

@<Do some work that has been queued up...@>=
if not doing_leaders then
  begin j:=write_stream(p);
  if subtype(p)=write_node then write_out(p)
  else  begin if write_open[j] then lua_a_close_out(write_file[j]);
    if subtype(p)=close_node then write_open[j]:=false
    else if j<16 then
      begin cur_name:=open_name(p); cur_area:=open_area(p);
      cur_ext:=open_ext(p);
      if cur_ext="" then cur_ext:=".tex";
      pack_cur_name;
      while not lua_a_open_out(write_file[j],(j+1)) do
        prompt_file_name("output file name",".tex");
      write_file[j]:= name_file_pointer;
      write_open[j]:=true;
      end;
    end;
  end

@ The presence of `\.{\\immediate}' causes the |do_extension| procedure
to descend to one level of recursion. Nothing happens unless \.{\\immediate}
is followed by `\.{\\openout}', `\.{\\write}', or `\.{\\closeout}'.
@^recursion@>

@<Implement \.{\\immediate}@>=
begin get_x_token;
if cur_cmd=extension then begin
    if cur_chr<=close_node then
      begin p:=tail; do_extension; {append a whatsit node}
      out_what(tail); {do the action immediately}
      flush_node_list(tail); tail:=p; vlink(p):=null;
      end
    else case cur_chr of
      close_lua_node: begin
        scan_register_num;
	    closelua(cur_val);
      end;
        pdf_obj_code: begin
            do_extension; {scan object and set |pdf_last_obj|}
            if obj_data_ptr(pdf_last_obj) = 0 then {this object has not been initialized yet}
                pdf_error("ext1", "`\pdfobj reserveobjnum' cannot be used with \immediate");
            pdf_write_obj(pdf_last_obj);
        end;
        pdf_xform_code: begin
            do_extension; {scan form and set |pdf_last_xform|}
            pdf_cur_form := pdf_last_xform;
            pdf_ship_out(obj_xform_box(pdf_last_xform), false);
        end;
        pdf_ximage_code: begin
            do_extension; {scan image and set |pdf_last_ximage|}
            pdf_write_image(pdf_last_ximage);
        end;
        othercases back_input
    endcases;
end
else
    back_input;
end

@ @<Finish the extensions@>=
for k:=0 to 15 do if write_open[k] then lua_a_close_out(write_file[k])

@ 
@d local_pen_inter(#)==vinfo(#+2) {\.{\\localinterlinepenalty}}
@d local_pen_broken(#)==vlink(#+2) {\.{\\localbrokenpenalty}}
@d local_box_left(#)==vlink(#+3) {\.{\\localleftbox}}
@d local_box_left_width(#)==vinfo(#+3)
@d local_box_right(#)==vlink(#+4) {\.{\\localleftbox}}
@d local_box_right_width(#)==vinfo(#+4)
@d local_par_dir(#)==vinfo(#+5)
@d local_par_size==6

@<LOCAL: Declare |make_local_par_node|@>=
function make_local_par_node:pointer;
{This function creates a |local_paragraph| node}
var p,q:pointer;
begin
p:=new_node(whatsit_node,local_par_node);
local_pen_inter(p):=local_inter_line_penalty;
local_pen_broken(p):=local_broken_penalty;
if local_left_box<>null then begin
  q:=copy_node_list(local_left_box); local_box_left(p):=q;
  local_box_left_width(p):=width(local_left_box);
  end;
if local_right_box<>null then begin
  q:=copy_node_list(local_right_box); local_box_right(p):=q;
  local_box_right_width(p):=width(local_right_box);
  end;
local_par_dir(p):=par_direction;
make_local_par_node:=p;
end

@ @<LOCAL: print out |local_paragraph| node@>=
local_par_node: begin
  print_esc("whatsit");
  append_char(".");
  print_ln; print_current_string;
  print_esc("localinterlinepenalty"); print("=");
  print_int(local_pen_inter(p));
  print_ln; print_current_string;
  print_esc("localbrokenpenalty"); print("=");
  print_int(local_pen_broken(p));
  print_ln; print_current_string;
  print_esc("localleftbox");
  if local_box_left(p)=null then print("=null")
  else begin
    append_char(".");
    show_node_list(local_box_left(p));
    decr(pool_ptr);
    end;
  print_ln; print_current_string;
  print_esc("localrightbox");
  if local_box_right(p)=null then print("=null")
  else begin
    append_char(".");
    show_node_list(local_box_right(p));
    decr(pool_ptr);
    end;
  decr(pool_ptr);
  end

@ @<LOCAL: Add local paragraph node@>=
begin tail_append(make_local_par_node) end

@ @<DIR: Assign direction codes@>=
case cur_chr of
dir_base+page_direction_code: begin
  if its_all_over then begin
    scan_direction;
    eq_word_define(dir_base+page_direction_code,cur_val);
    end;
  end;
dir_base+body_direction_code: begin
  if its_all_over then begin
    scan_direction;
    eq_word_define(dir_base+body_direction_code,cur_val);
    end;
  end;
dir_base+par_direction_code: begin
  scan_direction;
  eq_word_define(dir_base+par_direction_code,cur_val);
  end;
dir_base+text_direction_code: begin scan_direction;
  if (no_local_dirs>0) and (abs(mode)=hmode) then begin
    @<DIR: Add local dir node@>;
    dir_dir(tail):=dir_dir(tail)-64;
    end;
  if dir_level(text_dir_ptr)=cur_level then
    @<DIR: Remove from |text_dir_ptr|@>;
  eq_word_define(dir_base+text_direction_code,cur_val);
  @<DIR: Add to |text_dir_ptr|@>;
  if abs(mode)=hmode then
    begin
    @<DIR: Add local dir node@>;
    dir_level(tail):=cur_level;
    end;
  eq_word_define(int_base+no_local_dirs_code,no_local_dirs+1);
  eq_word_define(int_base+level_local_dir_code,cur_level);
  end;
dir_base+math_direction_code: begin scan_direction;
  eq_word_define(dir_base+math_direction_code,cur_val);
  end;
end;

@
@d push_dir(#)==
begin dir_tmp:=new_dir(#);
vlink(dir_tmp):=dir_ptr;
dir_ptr:=dir_tmp;
end

@d push_dir_node(#)==
begin dir_tmp:=copy_node(#);
vlink(dir_tmp):=dir_ptr; 
dir_ptr:=dir_tmp;
end

@d pop_dir_node==
begin dir_tmp:=dir_ptr;
dir_ptr:=vlink(dir_tmp);
flush_node(dir_tmp);
end

@ @<DIR: Declare |new_dir|@>=
function new_dir(s:small_number): pointer;
var p:pointer; {the new node}
begin p:=new_node(whatsit_node,dir_node);
dir_dir(p):=s; dir_dvi_ptr(p):=-1;
dir_level(p):=cur_level; new_dir:=p;
end

@ @<Append a begin direction to the tail of the current list@>=
tail_append(new_dir(math_direction))

@ @<Append an end direction to the tail of the current list@>=
tail_append(new_dir(math_direction-64))

@ @<DIR: Add local dir node@>=
tail_append(new_dir(text_direction))

@ @<DIR: Adjust the dir stack for the |hpack| routine@>=
begin
if dir_dir(p)>=0 then begin
  hpack_dir:=dir_dir(p);
  push_dir_node(p);
  end
else begin
  pop_dir_node;
  if dir_ptr<>null then
    hpack_dir:=dir_dir(dir_ptr);
  end
end

@ @<DIR: Reset |dir_ptr|@>=
begin
 while dir_ptr<>null do
  pop_dir_node
end

@ @<DIR: |unsave| math@>=
begin
unsave;
decr(save_ptr);
flush_node_list(text_dir_ptr);
text_dir_ptr:=saved(0);
end

@ @<DIR: |new_save_level| math@>=
begin
saved(0):=text_dir_ptr;
text_dir_ptr:=new_dir(math_direction);
incr(save_ptr); 
new_save_level(c);
eq_word_define(dir_base+body_direction_code,math_direction);
eq_word_define(dir_base+par_direction_code,math_direction);
eq_word_define(dir_base+text_direction_code,math_direction);
eq_word_define(int_base+level_local_dir_code,cur_level);
end

@ @<DIR: Adjust |text_dir_ptr| for |scan_spec|@>=
begin
if spec_direction<>-1 then begin
  saved(4):=text_dir_ptr;
  text_dir_ptr:=new_dir(spec_direction);
  end
else saved(4):=null;
end

@ @<DIR: Adjust back |text_dir_ptr| for |scan_spec|@>=
begin
flush_node_list(text_dir_ptr);
text_dir_ptr:=saved(4);
end

@ @<DIR: Add to |text_dir_ptr|@>=
begin
text_dir_tmp:=new_dir(text_direction);
vlink(text_dir_tmp):=text_dir_ptr;
text_dir_ptr:=text_dir_tmp;
end

@ @<DIR: Remove from |text_dir_ptr|@>=
begin
text_dir_tmp:=vlink(text_dir_ptr);
flush_node(text_dir_ptr);
text_dir_ptr:=text_dir_tmp;
end

@ @<DIR: Initialize |text_dir_ptr|@>=
begin
text_dir_ptr:=new_dir(0);
end

@ @<DIR: Initialize |dir_ptr| for |ship_out|@>=
begin dir_ptr:=null; push_dir(dvi_direction);
dir_dvi_ptr(dir_ptr):=dvi_ptr;
end

@ @<Output a reflection instruction if the direction has changed@>=
begin
if dir_dir(p)>=0 then
  begin synch_h; synch_v;
  push_dir_node(p);
  if dir_opposite(dir_secondary[dir_dir(dir_ptr)])(dir_secondary[dvi_direction])
  then begin
    if (dir_secondary[dvi_direction]=0) or
       (dir_secondary[dvi_direction]=2) then
      dvi_out(down4)
    else
      dvi_out(right4);
    dir_dvi_ptr(dir_ptr):=dvi_ptr;
    dir_dvi_h(dir_ptr):=dvi_h;
    dvi_four(0);
    cur_h:=0; dvi_h:=0;
    end
  else begin
    dir_dvi_ptr(dir_ptr):=dvi_ptr;
    dir_dvi_h(dir_ptr):=dvi_h;
    end;
  dvi_direction:=dir_dir(dir_ptr);
  end
else begin
  dvi_dir_h:=dir_dvi_h(dir_ptr);
  dvi_dir_ptr:=dir_dvi_ptr(dir_ptr);
  pop_dir_node;
  synch_h; synch_v;
  if dir_ptr<>null then
	 dvi_direction:=dir_dir(dir_ptr)
  else
	dvi_direction:=0;
 if dir_opposite(dir_secondary[dir_dir(p)+64])(dir_secondary[dvi_direction])
  then begin
    dvi_temp_ptr:=dvi_ptr;
    dvi_ptr:=dvi_dir_ptr;
    if (dir_secondary[dvi_direction]=0) or
       (dir_secondary[dvi_direction]=1) then
      dvi_four(dvi_h)
    else
      dvi_four(-dvi_h);
    dvi_ptr:=dvi_temp_ptr;
    if (dir_secondary[dvi_direction]=0) or
       (dir_secondary[dvi_direction]=2) then
      dvi_out(down4)
    else
      dvi_out(right4);
    if (dir_secondary[dvi_direction]=0) or
       (dir_secondary[dvi_direction]=1) then
      dvi_four(dvi_h)
    else
      dvi_four(-dvi_h);
    end;
    cur_h:=dvi_dir_h+dvi_h; dvi_h:=cur_h;
  end
end

@ Many things regarding output work differently in pdf compared to dvi
output. The easiest way to deal with in-line direction changes in pdf
mode seems to be to move forward to find the needed width of the
reversed section, then skip forward (or backward, depending on your
viewpont) by that distance.

@<(PDF) Output a reflection instruction if the direction has changed@>=
begin
if dir_dir(p)>=0 then begin
  push_dir_node(p);
  if dir_opposite(dir_secondary[dir_dir(dir_ptr)])(dir_secondary[dvi_direction])
  then begin
	@<(PDF) Calculate the needed width to the matching |enddir|, and store it in |w|, as
      well as in the enddir's |dir_dvi_h|@>;
    case box_direction(dvi_direction) of
    dir_TL_,dir_BL_: pdf_dvicmd_right(w);
    dir_TR_,dir_BR_: pdf_dvicmd_left(w);
    end;
  end;
  dvi_direction:=dir_dir(dir_ptr);
  end
else begin
  pop_dir_node;
  if dir_ptr<>null then
    dvi_direction:=dir_dir(dir_ptr)
  else
    dvi_direction:=0;
  case box_direction(dvi_direction) of
    dir_TL_,dir_BL_: pdf_dvicmd_right(dir_dvi_h(p));
    dir_TR_,dir_BR_: pdf_dvicmd_left(dir_dvi_h(p));
  end;
  end
end

@ This code scans forward to the ending |dir_node| while keeping
track of the needed width in |w|. When it finds the node that will end
this segment, it stores the accumulated with in the |dir_dvi_h| field
of that end node, so that when that node is found later in the
processing, the correct glue correction can be applied.

@<(PDF) Calculate the needed width to the matching |enddir|...@>=
begin
  q:=p; w:=0; 
  save_cur_g:=cur_g;
  save_cur_glue:=cur_glue;
  { to me, it looks like the next is needed. but Aleph doesn't do that,
   so let us not do it either }
  {|w:=w-cur_g; cur_glue:=0;|}
  dir_nest:=1;
  while (q<>null) and (vlink(q)<>null) do begin
	q:=vlink(q);
    if is_char_node(q) then begin
      w:=w+glyph_width(q); {TODO no vertical support for now}
      end 
    else begin
      case type(q) of
      hlist_node,vlist_node,rule_node,
      margin_kern_node,kern_node:w:=w+width(q);
	  glue_node: begin 
        g:=glue_ptr(q);
        w:=w+width(g)-cur_g; 
        if g_sign<>normal then
          begin if g_sign=stretching then
            begin if stretch_order(g)=g_order then
              begin cur_glue:=cur_glue+stretch(g);
              vet_glue(float(glue_set(this_box))*cur_glue);
              cur_g:=round(glue_temp);
              end;
            end
          else if shrink_order(g)=g_order then
             begin cur_glue:=cur_glue-shrink(g);
             vet_glue(float(glue_set(this_box))*cur_glue);
             cur_g:=round(glue_temp);
             end;
          end;
        w:=w+cur_g; 
        end;
      math_node: w:=w+surround(q);
      whatsit_node: begin
        if subtype(q)=dir_node then begin 
          if dir_dir(q)>=0 then incr(dir_nest) else decr(dir_nest);
          if dir_nest=0 then begin
            dir_dvi_h(q) := w;
           q:=null;
            end;
          end 
        else if (subtype(q) = pdf_refxform_node) or 
                (subtype(q) = pdf_refximage_node) then
         w:=w+pdf_width(q);
      end;
      othercases do_nothing;
      endcases;
    end;
  end;
  cur_g:=save_cur_g;
  cur_glue:=save_cur_glue;
end


@ Shipping out PDF marks.

@<Types...@>=
dest_name_entry = record
    objname: str_number; {destination name}
    objnum: integer; {destination object number}
end;

@ @<Glob...@>=
@!cur_page_width: scaled; {width of page being shipped}
@!cur_page_height: scaled; {height of page being shipped}
@!cur_right_offset: scaled; {horizontal inverted offset of page being shipped}
@!cur_bottom_offset: scaled; {vertical inverted offset of page being shipped}
@!pdf_obj_list: pointer; {list of objects in the current page}
@!pdf_xform_list: pointer; {list of forms in the current page}
@!pdf_ximage_list: pointer; {list of images in the current page}
@!last_thread: pointer; {pointer to the last thread}
@!pdf_thread_ht, pdf_thread_dp, pdf_thread_wd: scaled; {dimensions of the last
thread}
@!pdf_last_thread_id: halfword; {identifier of the last thread}
@!pdf_last_thread_named_id: boolean; {is identifier of the last thread named}
@!pdf_thread_level: integer; {depth of nesting of box containing the last thread}
@!pdf_annot_list: pointer; {list of annotations in the current page}
@!pdf_link_list: pointer; {list of link annotations in the current page}
@!pdf_dest_list: pointer; {list of destinations in the current page}
@!pdf_bead_list: pointer; {list of thread beads in the current page}
@!pdf_obj_count: integer; {counter of objects}
@!pdf_xform_count: integer; {counter of forms}
@!pdf_ximage_count: integer; {counter of images}
@!pdf_cur_form: integer; {the form being output}
@!pdf_first_outline, pdf_last_outline, pdf_parent_outline: integer;
@!pdf_info_toks: pointer; {additional keys of Info dictionary}
@!pdf_catalog_toks: pointer; {additional keys of Catalog dictionary}
@!pdf_catalog_openaction: integer;
@!pdf_names_toks: pointer; {additional keys of Names dictionary}
@!pdf_dest_names_ptr: integer; {first unused position in |dest_names|}
@!dest_names_size: integer; {maximum number of names in name tree of PDF output file}
@!dest_names: ^dest_name_entry;
@!pk_dpi: integer; {PK pixel density value from \.{texmf.cnf}}
@!image_orig_x, image_orig_y: integer; {origin of cropped PDF images}
@!pdf_trailer_toks: pointer; {additional keys of Trailer dictionary}

@ @<Set init...@>=
pdf_first_outline:= 0;
pdf_last_outline:= 0;
pdf_parent_outline:= 0;
pdf_obj_count := 0;
pdf_xform_count := 0;
pdf_ximage_count := 0;
pdf_dest_names_ptr := 0;
pdf_info_toks := null;
pdf_catalog_toks := null;
pdf_names_toks := null;
pdf_catalog_openaction := 0;
pdf_trailer_toks := null;

@ The following procedures are needed for outputing whatsit nodes for
\pdfTeX{}.

@<Declare procedures needed in |pdf_hlist_out|, |pdf_vlist_out|@>=
procedure write_action(p: pointer); {write an action specification}
var s: str_number;
    d: integer;
begin d:=0;
    if pdf_action_type(p) = pdf_action_user then begin
        pdf_print_toks_ln(pdf_action_tokens(p));
        return;
    end;
    pdf_print("<< ");
    if pdf_action_file(p) <> null then begin
        pdf_print("/F ");
        s := tokens_to_string(pdf_action_file(p));
        if (str_pool[str_start_macro(s)] = 40) and
           (str_pool[str_start_macro(s) + length(s) - 1] = 41) then
            pdf_print(s)
        else begin
            pdf_print_str(s);
        end;
        flush_str(s);
        pdf_print(" ");
        if pdf_action_new_window(p) > 0 then begin
            pdf_print("/NewWindow ");
            if pdf_action_new_window(p) = 1 then
                pdf_print("true ")
            else
                pdf_print("false ");
        end;
    end;
    case pdf_action_type(p) of
    pdf_action_page: begin
        if pdf_action_file(p) = null then begin
            pdf_print("/S /GoTo /D [");
            pdf_print_int(get_obj(obj_type_page, pdf_action_id(p), false));
            pdf_print(" 0 R");
        end
        else begin
            pdf_print("/S /GoToR /D [");
            pdf_print_int(pdf_action_id(p) - 1);
        end;
        pdf_out(" ");
        pdf_print(tokens_to_string(pdf_action_tokens(p)));
        flush_str(last_tokens_string);
        pdf_out("]");
    end;
    pdf_action_goto: begin
        if pdf_action_file(p) = null then begin
            pdf_print("/S /GoTo ");
            d := get_obj(obj_type_dest, pdf_action_id(p),
                         pdf_action_named_id(p));
        end
        else
            pdf_print("/S /GoToR ");
        if pdf_action_named_id(p) > 0 then begin
            pdf_str_entry("D", tokens_to_string(pdf_action_id(p)));
            flush_str(last_tokens_string);
        end
        else if pdf_action_file(p) = null then
            pdf _indirect("D", d)
        else
            pdf_error("ext4", "`goto' option cannot be used with both `file' and `num'");
    end;
    pdf_action_thread: begin
        pdf_print("/S /Thread ");
        if pdf_action_file(p) = null then
            d := get_obj(obj_type_thread, pdf_action_id(p),
                         pdf_action_named_id(p));
        if pdf_action_named_id(p) > 0 then begin
            pdf_str_entry("D", tokens_to_string(pdf_action_id(p)));
            flush_str(last_tokens_string);
        end
        else if pdf_action_file(p) = null then
            pdf_indirect("D", d)
        else
            pdf_int_entry("D", pdf_action_id(p));
    end;
    endcases;
    pdf_print_ln(" >>");
end;

procedure set_rect_dimens(p, parent_box: pointer; x, y, w, h, d, margin: scaled);
begin
    pdf_left(p) := cur_h;
    if is_running(w) then
        pdf_right(p) := x + width(parent_box)
    else
        pdf_right(p) := cur_h + w;
    if is_running(h) then
        pdf_top(p) := y - height(parent_box)
    else
        pdf_top(p) := cur_v - h;
    if is_running(d) then
        pdf_bottom(p) := y  + depth(parent_box)
    else
        pdf_bottom(p) := cur_v + d;
    if is_shipping_page and matrixused then begin
        matrixtransformrect(pdf_left(p), cur_page_height - pdf_bottom(p),
                            pdf_right(p), cur_page_height - pdf_top(p));
        pdf_left(p)   := getllx;
        pdf_bottom(p) := cur_page_height - getlly;
        pdf_right(p)  := geturx;
        pdf_top(p)    := cur_page_height - getury;
    end;
    pdf_left(p)   := pdf_left(p)   - margin;
    pdf_top(p)    := pdf_top(p)    - margin;
    pdf_right(p)  := pdf_right(p)  + margin;
    pdf_bottom(p) := pdf_bottom(p) + margin;
end;

procedure do_annot(p, parent_box: pointer; x, y: scaled);
begin
    if not is_shipping_page then
        pdf_error("ext4", "annotations cannot be inside an XForm");
    if doing_leaders then
        return;
    set_rect_dimens(p, parent_box, x, y,
                    pdf_width(p), pdf_height(p), pdf_depth(p), 0);
    obj_annot_ptr(pdf_annot_objnum(p)) := p;
    pdf_append_list(pdf_annot_objnum(p))(pdf_annot_list);
end;

@ To implement nesting link annotations, we need a stack to hold copy of
|pdf_start_link_node|'s that are being written out, together with their box
nesting level.

@d pdf_link_stack_top == pdf_link_stack[pdf_link_stack_ptr]

@<Constants...@>=
@!pdf_max_link_level = 10; {maximum depth of link nesting}

@ @<Types...@>=
@!pdf_link_stack_record = record
    nesting_level: small_number;
    link_node: pointer; {holds a copy of the corresponding |pdf_start_link_node|}
    ref_link_node: pointer; {points to original |pdf_start_link_node|, or a
                             copy of |link_node| created by |append_link| in
                             case of multi-line link}
end;

@ @<Glob...@>=
@!pdf_link_stack: array[1..pdf_max_link_level] of pdf_link_stack_record;
@!pdf_link_stack_ptr: small_number;

@ @<Set init...@>=
pdf_link_stack_ptr := 0;

@ @<Declare procedures needed in |pdf_hlist_out|, |pdf_vlist_out|@>=
procedure push_link_level(p: pointer);
begin
    if pdf_link_stack_ptr >= pdf_max_link_level then
        overflow("pdf link stack size", pdf_max_link_level);
    pdfassert((type(p) = whatsit_node) and (subtype(p) = pdf_start_link_node));
    incr(pdf_link_stack_ptr);
    pdf_link_stack_top.nesting_level := cur_s;
    pdf_link_stack_top.link_node := copy_node_list(p);
    pdf_link_stack_top.ref_link_node := p;
end;

procedure pop_link_level;
begin
    pdfassert(pdf_link_stack_ptr > 0);
    flush_node_list(pdf_link_stack_top.link_node);
    decr(pdf_link_stack_ptr);
end;

procedure do_link(p, parent_box: pointer; x, y: scaled);
begin
    if not is_shipping_page then
        pdf_error("ext4", "link annotations cannot be inside an XForm");
    pdfassert(type(parent_box) = hlist_node);
    push_link_level(p);
    set_rect_dimens(p, parent_box, x, y,
                    pdf_width(p), pdf_height(p), pdf_depth(p),
                    pdf_link_margin);
    obj_annot_ptr(pdf_link_objnum(p)) := p; {the reference for the pdf annot object
                                             must be set here}
    pdf_append_list(pdf_link_objnum(p))(pdf_link_list);
end;

procedure end_link;
var p: pointer;
begin
    if pdf_link_stack_ptr < 1 then
        pdf_error("ext4", "pdf_link_stack empty, \pdfendlink used without \pdfstartlink?");
    if pdf_link_stack_top.nesting_level <> cur_s then
        pdf_error("ext4", "\pdfendlink ended up in different nesting level than \pdfstartlink");

    {N.B.: test for running link must be done on |link_node| and not |ref_link_node|,
     as |ref_link_node| can be set by |do_link| or |append_link| already}

    if is_running(pdf_width(pdf_link_stack_top.link_node)) then begin
        p := pdf_link_stack_top.ref_link_node;
        if is_shipping_page and matrixused then begin
            matrixrecalculate(cur_h + pdf_link_margin);
            pdf_left(p)   := getllx - pdf_link_margin;
            pdf_top(p)    := cur_page_height - getury - pdf_link_margin;
            pdf_right(p)  := geturx + pdf_link_margin;
            pdf_bottom(p) := cur_page_height - getlly + pdf_link_margin;
         end
         else
            pdf_right(p) := cur_h + pdf_link_margin;
    end;
    pop_link_level;
end;

@ For ``running'' annotations we must append a new node when the end of
annotation is in other box than its start. The new created node is identical to
corresponding whatsit node representing the start of annotation,  but its
|info| field is |max_halfword|. We set |info| field just before destroying the
node, in order to use |flush_node_list| to do the job.

@<Declare procedures needed in |pdf_hlist_out|, |pdf_vlist_out|@>=
procedure append_link(parent_box: pointer; x, y: scaled; i: small_number); {append a new
pdf annot to |pdf_link_list|}
var p: pointer;
begin
    pdfassert(type(parent_box) = hlist_node);
    p := copy_node(pdf_link_stack[i].link_node);
    pdf_link_stack[i].ref_link_node := p;
    subtype(p) := pdf_link_data_node; { this node is not a normal link node}
    set_rect_dimens(p, parent_box, x, y,
                    pdf_width(p), pdf_height(p), pdf_depth(p),
                    pdf_link_margin);
    pdf_create_obj(obj_type_others, 0);
    obj_annot_ptr(obj_ptr) := p;
    pdf_append_list(obj_ptr)(pdf_link_list);
end;

@ Threads are handled in similar way as link annotations.

@<Declare procedures needed in |pdf_hlist_out|, |pdf_vlist_out|@>=
procedure append_bead(p: pointer);
var a, b, c, t: integer;
begin
    if not is_shipping_page then
        pdf_error("ext4", "threads cannot be inside an XForm");
    t := get_obj(obj_type_thread, pdf_thread_id(p), pdf_thread_named_id(p));
    b := pdf_new_objnum;
    obj_bead_ptr(b) := pdf_get_mem(pdfmem_bead_size);
    obj_bead_page(b) := pdf_last_page;
    obj_bead_data(b) := p;
    if pdf_thread_attr(p) <> null then
        obj_bead_attr(b) := tokens_to_string(pdf_thread_attr(p))
    else
        obj_bead_attr(b) := 0;
    if obj_thread_first(t) = 0 then begin
        obj_thread_first(t) := b;
        obj_bead_next(b) := b;
        obj_bead_prev(b) := b;
    end
    else begin
        a := obj_thread_first(t);
        c := obj_bead_prev(a);
        obj_bead_prev(b) := c;
        obj_bead_next(b) := a;
        obj_bead_prev(a) := b;
        obj_bead_next(c) := b;
    end;
    pdf_append_list(b)(pdf_bead_list);
end;

procedure do_thread(p, parent_box: pointer; x, y: scaled);
begin
    if doing_leaders then
        return;
    if subtype(p) = pdf_start_thread_node then begin
        pdf_thread_wd := pdf_width(p);
        pdf_thread_ht := pdf_height(p);
        pdf_thread_dp := pdf_depth(p);
        pdf_last_thread_id := pdf_thread_id(p);
        pdf_last_thread_named_id := (pdf_thread_named_id(p) > 0);
        if pdf_last_thread_named_id then
            add_token_ref(pdf_thread_id(p));
        pdf_thread_level := cur_s;
    end;
    set_rect_dimens(p, parent_box, x, y,
                    pdf_width(p), pdf_height(p), pdf_depth(p),
                    pdf_thread_margin);
    append_bead(p);
    last_thread := p;
end;

procedure append_thread(parent_box: pointer; x, y: scaled);
var p: pointer;
begin
    p := new_node(whatsit_node,pdf_thread_data_node);
    pdf_width(p) := pdf_thread_wd;
    pdf_height(p) := pdf_thread_ht;
    pdf_depth(p) := pdf_thread_dp;
    pdf_thread_attr(p) := null;
    pdf_thread_id(p) := pdf_last_thread_id;
    if pdf_last_thread_named_id then begin
        add_token_ref(pdf_thread_id(p));
        pdf_thread_named_id(p) := 1;
    end
    else
        pdf_thread_named_id(p) := 0;
    set_rect_dimens(p, parent_box, x, y,
                    pdf_width(p), pdf_height(p), pdf_depth(p),
                    pdf_thread_margin);
    append_bead(p);
    last_thread := p;
end;

procedure end_thread;
begin
    if pdf_thread_level <> cur_s then
        pdf_error("ext4", "\pdfendthread ended up in different nesting level than \pdfstartthread");
    if is_running(pdf_thread_dp) and (last_thread <> null) then
        pdf_bottom(last_thread) := cur_v + pdf_thread_margin;
    if pdf_last_thread_named_id then
        delete_token_ref(pdf_last_thread_id);
    last_thread := null;
end;

function open_subentries(p: pointer): integer;
var k, c: integer;
    l, r: integer;
begin
    k := 0;
    if obj_outline_first(p) <> 0 then begin
        l := obj_outline_first(p);
        repeat
            incr(k);
            c := open_subentries(l);
            if obj_outline_count(l) > 0 then
                k := k + c;
            obj_outline_parent(l) := p;
            r := obj_outline_next(l);
            if r = 0 then
                obj_outline_last(p) := l;
            l := r;
        until l = 0;
    end;
    if obj_outline_count(p) > 0 then
        obj_outline_count(p) := k
    else
        obj_outline_count(p) := -k;
    open_subentries := k;
end;

procedure do_dest(p, parent_box: pointer; x, y: scaled);
var k: integer;
begin
    if not is_shipping_page then
        pdf_error("ext4", "destinations cannot be inside an XForm");
    if doing_leaders then
        return;
    k := get_obj(obj_type_dest, pdf_dest_id(p), pdf_dest_named_id(p));
    if obj_dest_ptr(k) <> null then begin
        warn_dest_dup(pdf_dest_id(p), pdf_dest_named_id(p),
                      "ext4", "has been already used, duplicate ignored");
        return;
    end;
    obj_dest_ptr(k) := p;
    pdf_append_list(k)(pdf_dest_list);
    case pdf_dest_type(p) of
    pdf_dest_xyz:
        if matrixused then
            set_rect_dimens(p, parent_box, x, y,
                            pdf_width(p), pdf_height(p), pdf_depth(p),
                            pdf_dest_margin)
        else begin
        pdf_left(p) := cur_h;
        pdf_top(p) := cur_v;
    end;
    pdf_dest_fith,
    pdf_dest_fitbh:
        if matrixused then
            set_rect_dimens(p, parent_box, x, y,
                            pdf_width(p), pdf_height(p), pdf_depth(p),
                            pdf_dest_margin)
        else
        pdf_top(p) := cur_v;
    pdf_dest_fitv,
    pdf_dest_fitbv:
       if matrixused then
            set_rect_dimens(p, parent_box, x, y,
                            pdf_width(p), pdf_height(p), pdf_depth(p),
                            pdf_dest_margin)
       else
       pdf_left(p) := cur_h;
    pdf_dest_fit,
    pdf_dest_fitb:
        do_nothing;
    pdf_dest_fitr:
        set_rect_dimens(p, parent_box, x, y,
                        pdf_width(p), pdf_height(p), pdf_depth(p),
                        pdf_dest_margin);
    endcases;
end;

procedure out_form(p: pointer);
var v: scaled;
begin
    pdf_end_text;
    pdf_print_ln("q");
    if pdf_lookup_list(pdf_xform_list, pdf_xform_objnum(p)) = null then
        pdf_append_list(pdf_xform_objnum(p))(pdf_xform_list);
    v := cur_v + obj_xform_depth(pdf_xform_objnum(p));
    pdf_set_origin_temp(cur_h, v);
    pdf_print("/Fm");
    pdf_print_int(obj_info(pdf_xform_objnum(p)));
    pdf_print_resname_prefix;
    pdf_print_ln(" Do");
    pdf_print_ln("Q");
end;

@ @<Output the whatsit node |p| in |pdf_vlist_out|@>=
case subtype(p) of
pdf_literal_node:
    pdf_out_literal(p);
pdf_colorstack_node:
    pdf_out_colorstack(p);
pdf_setmatrix_node:
    pdf_out_setmatrix(p);
pdf_save_node:
    pdf_out_save;
pdf_restore_node:
    pdf_out_restore;
late_lua_node:
    do_late_lua(p);
close_lua_node:
    closelua(late_lua_reg(p));
pdf_refobj_node:
    pdf_append_list(pdf_obj_objnum(p))(pdf_obj_list);
pdf_refxform_node:
    @<Output a Form node in a vlist@>;
pdf_refximage_node:
    @<Output a Image node in a vlist@>;
pdf_annot_node:
    do_annot(p, this_box, left_edge, top_edge + height(this_box));
pdf_start_link_node:
    pdf_error("ext4", "\pdfstartlink ended up in vlist");
pdf_end_link_node:
    pdf_error("ext4", "\pdfendlink ended up in vlist");
pdf_dest_node:
    do_dest(p, this_box, left_edge, top_edge + height(this_box));
pdf_thread_node,
pdf_start_thread_node:
    do_thread(p, this_box, left_edge, top_edge + height(this_box));
pdf_end_thread_node:
    end_thread;
pdf_save_pos_node:
    @<Save current position to |pdf_last_x_pos|, |pdf_last_y_pos|@>;
special_node:
    pdf_special(p);
othercases out_what(p);
endcases

@ @<Glob...@>=
@!is_shipping_page: boolean; {set to |shipping_page| when |pdf_ship_out| starts}

@ @<Save current position to |pdf_last_x_pos|, |pdf_last_y_pos|@>=
begin
    pdf_last_x_pos := cur_h;
    pdf_last_y_pos := cur_page_height - cur_v
end

@ @<Output a Image node in a vlist@>=
begin cur_v:=cur_v+pdf_height(p)+pdf_depth(p);
  cur_h:=left_edge;
  out_image(pdf_ximage_ref(p), cur_h-pdf_origin_h, pdf_origin_v-cur_v);
  if pdf_lookup_list(pdf_ximage_list, image_objnum(pdf_ximage_ref(p))) = null then
      pdf_append_list(image_objnum(pdf_ximage_ref(p)))(pdf_ximage_list);
end

@ @<Output a Form node in a vlist@>=
begin cur_v:=cur_v+pdf_height(p);
  cur_h:=left_edge;
  out_form(p);
  cur_v:=cur_v+pdf_depth(p);
end

@ @<Output the whatsit node |p| in |pdf_hlist_out|@>=
case subtype(p) of
pdf_literal_node:
    pdf_out_literal(p);
pdf_colorstack_node:
    pdf_out_colorstack(p);
pdf_setmatrix_node:
    pdf_out_setmatrix(p);
pdf_save_node:
    pdf_out_save;
pdf_restore_node:
    pdf_out_restore;
late_lua_node:
    do_late_lua(p);
close_lua_node:
	closelua(late_lua_reg(p));
pdf_refobj_node:
    pdf_append_list(pdf_obj_objnum(p))(pdf_obj_list);
pdf_refxform_node:
    @<Output a Form node in a hlist@>;
pdf_refximage_node:
    @<Output a Image node in a hlist@>;
pdf_annot_node:
    do_annot(p, this_box, left_edge, base_line);
pdf_start_link_node:
    do_link(p, this_box, left_edge, base_line);
pdf_end_link_node:
    end_link;
pdf_dest_node:
    do_dest(p, this_box, left_edge, base_line);
pdf_thread_node:
    do_thread(p, this_box, left_edge, base_line);
pdf_start_thread_node:
    pdf_error("ext4", "\pdfstartthread ended up in hlist");
pdf_end_thread_node:
    pdf_error("ext4", "\pdfendthread ended up in hlist");
pdf_save_pos_node:
    @<Save current position to |pdf_last_x_pos|, |pdf_last_y_pos|@>;
special_node:
    pdf_special(p);
othercases if subtype(p)<>dir_node then out_what(p)
else @<(PDF) Output a reflection instruction if the direction has changed@>;
endcases

@ @<Output a Image node in a hlist@>=
begin
  cur_v:=base_line+pdf_depth(p);
  out_image(pdf_ximage_ref(p), cur_h-pdf_origin_h, pdf_origin_v-cur_v);
  if pdf_lookup_list(pdf_ximage_list, image_objnum(pdf_ximage_ref(p))) = null then
      pdf_append_list(image_objnum(pdf_ximage_ref(p)))(pdf_ximage_list);
  edge:=cur_h+pdf_width(p); cur_h:=edge; cur_v:=base_line;
end

@ @<Output a Form node in a hlist@>=
begin
  cur_v:=base_line;
  out_form(p);
  edge:=cur_h+pdf_width(p); cur_h:=edge;
end

@* \[53a] The extended features of \eTeX.
The program has two modes of operation:  (1)~In \TeX\ compatibility mode
it fully deserves the name \TeX\ and there are neither extended features
nor additional primitive commands.  There are, however, a few
modifications that would be legitimate in any implementation of \TeX\
such as, e.g., preventing inadequate results of the glue to \.{DVI}
unit conversion during |ship_out|.  (2)~In extended mode there are
additional primitive commands and the extended features of \eTeX\ are
available.

The distinction between these two modes of operation initially takes
place when a `virgin' \.{eINITEX} starts without reading a format file.
Later on the values of all \eTeX\ state variables are inherited when
\.{eVIRTEX} (or \.{eINITEX}) reads a format file.

The code below is designed to work for cases where `$|init|\ldots|tini|$'
is a run-time switch.

@<Enable \eTeX, if requested@>=
@!init if format_ident=" (INITEX)" then
  begin no_new_control_sequence:=false;
  @<Generate all \eTeX\ primitives@>@;
  if buffer[loc]="*" then incr(loc); 
  end;
tini@;@/
if not no_new_control_sequence then {just entered extended mode ?}
  no_new_control_sequence:=true@+else

@ The \eTeX\ features available in extended mode are grouped into two
categories:  (1)~Some of them are permanently enabled and have no
semantic effect as long as none of the additional primitives are
executed.  (2)~The remaining \eTeX\ features are optional and can be
individually enabled and disabled.  For each optional feature there is
an \eTeX\ state variable named \.{\\...state}; the feature is enabled,
resp.\ disabled by assigning a positive, resp.\ non-positive value to
that integer.


@d Aleph_version_code=Aleph_int {code for \.{\\Alephversion}}
@d Omega_version_code=Aleph_int+1 {code for \.{\\Omegaversion}}
@d Aleph_minor_version_code=Aleph_int+2 {code for \.{\\Alephminorversion}}
@d Omega_minor_version_code=Aleph_int+3 {code for \.{\\Omegaminorversion}}
@d eTeX_minor_version_code=Aleph_int+4 {code for \.{\\eTeXminorversion}}
@d eTeX_version_code=eTeX_int {code for \.{\\eTeXversion}}
@d Aleph_revision_code=job_name_code+1 {command code for \.{\\Alephrevision}}
@d Omega_revision_code=job_name_code+2 {command code for \.{\\Omegarevision}}
@d eTeX_revision_code=job_name_code+3 {command code for \.{\\eTeXrevision}}

@<Generate all \eTeX...@>=
primitive("lastnodetype",last_item,last_node_type_code);
@!@:last_node_type_}{\.{\\lastnodetype} primitive@>
primitive("Alephversion",last_item,Aleph_version_code);
@!@:eTeX_version_}{\.{\\Alephversion} primitive@>
primitive("Omegaversion",last_item,Omega_version_code);
@!@:eTeX_version_}{\.{\\Omegaversion} primitive@>
primitive("eTeXversion",last_item,eTeX_version_code);
@!@:eTeX_version_}{\.{\\eTeXversion} primitive@>
primitive("Alephminorversion",last_item,Aleph_minor_version_code);
@!@:eTeX_minor_version_}{\.{\\Alephminorversion} primitive@>
primitive("Omegaminorversion",last_item,Omega_minor_version_code);
@!@:eTeX_minor_version_}{\.{\\Omegaminorversion} primitive@>
primitive("eTeXminorversion",last_item,eTeX_minor_version_code);
@!@:eTeX_minor_version_}{\.{\\eTeXminorversion} primitive@>
primitive("Alephrevision",convert,Aleph_revision_code);@/
@!@:eTeX_revision_}{\.{\\Alephrevision} primitive@>
primitive("Omegarevision",convert,Omega_revision_code);@/
@!@:eTeX_revision_}{\.{\\Omegarevision} primitive@>
primitive("eTeXrevision",convert,eTeX_revision_code);@/
@!@:eTeX_revision_}{\.{\\eTeXrevision} primitive@>

@ @<Cases of |last_item| for |print_cmd_chr|@>=
last_node_type_code: print_esc("lastnodetype");
Aleph_version_code: print_esc("Alephversion");
Omega_version_code: print_esc("Omegaversion");
eTeX_version_code: print_esc("eTeXversion");
Aleph_minor_version_code: print_esc("Alephminorversion");
Omega_minor_version_code: print_esc("Omegaminorversion");
eTeX_minor_version_code: print_esc("eTeXminorversion");


@ @<Cases for fetching an integer value@>=
Aleph_version_code: cur_val:=Aleph_version;
Omega_version_code: cur_val:=Omega_version;
eTeX_version_code: cur_val:=eTeX_version;
Aleph_minor_version_code: cur_val:=Aleph_minor_version;
Omega_minor_version_code: cur_val:=Omega_minor_version;
eTeX_minor_version_code: cur_val:=eTeX_minor_version;

@ @<Cases of |convert| for |print_cmd_chr|@>=
Aleph_revision_code: print_esc("Alephrevision");
Omega_revision_code: print_esc("Omegarevision");
eTeX_revision_code: print_esc("eTeXrevision");

@ @<Cases of `Scan the argument for command |c|'@>=
Aleph_revision_code: do_nothing;
Omega_revision_code: do_nothing;
eTeX_revision_code: do_nothing;

@ @<Cases of `Print the result of command |c|'@>=
Aleph_revision_code: print(Aleph_revision);
Omega_revision_code: print(Omega_revision);
eTeX_revision_code: print(eTeX_revision);

@ First we implement the additional \eTeX\ parameters in the table of
equivalents.

@<Generate all \eTeX...@>=
primitive("everyeof",assign_toks,every_eof_loc);
@!@:every_eof_}{\.{\\everyeof} primitive@>
primitive("tracingassigns",assign_int,int_base+tracing_assigns_code);@/
@!@:tracing_assigns_}{\.{\\tracingassigns} primitive@>
primitive("tracinggroups",assign_int,int_base+tracing_groups_code);@/
@!@:tracing_groups_}{\.{\\tracinggroups} primitive@>
primitive("tracingifs",assign_int,int_base+tracing_ifs_code);@/
@!@:tracing_ifs_}{\.{\\tracingifs} primitive@>
primitive("tracingscantokens",assign_int,int_base+tracing_scan_tokens_code);@/
@!@:tracing_scan_tokens_}{\.{\\tracingscantokens} primitive@>
primitive("tracingnesting",assign_int,int_base+tracing_nesting_code);@/
@!@:tracing_nesting_}{\.{\\tracingnesting} primitive@>
primitive("predisplaydirection",
  assign_int,int_base+pre_display_direction_code);@/
@!@:pre_display_direction_}{\.{\\predisplaydirection} primitive@>
primitive("lastlinefit",assign_int,int_base+last_line_fit_code);@/
@!@:last_line_fit_}{\.{\\lastlinefit} primitive@>
primitive("savingvdiscards",assign_int,int_base+saving_vdiscards_code);@/
@!@:saving_vdiscards_}{\.{\\savingvdiscards} primitive@>
primitive("savinghyphcodes",assign_int,int_base+saving_hyph_codes_code);@/
@!@:saving_hyph_codes_}{\.{\\savinghyphcodes} primitive@>
primitive("suppressfontnotfounderror",assign_int,int_base+suppress_fontnotfound_error_code);@/
@!@:suppress_fontnotfound_error_codes_}{\.{\\suppressfontnotfounderror} primitive@>

@ @d every_eof==equiv(every_eof_loc)

@<Cases of |assign_toks| for |print_cmd_chr|@>=
every_eof_loc: print_esc("everyeof");

@ @<Cases for |print_param|@>=
tracing_assigns_code:print_esc("tracingassigns");
tracing_groups_code:print_esc("tracinggroups");
tracing_ifs_code:print_esc("tracingifs");
tracing_scan_tokens_code:print_esc("tracingscantokens");
tracing_nesting_code:print_esc("tracingnesting");
pre_display_direction_code:print_esc("predisplaydirection");
last_line_fit_code:print_esc("lastlinefit");
saving_vdiscards_code:print_esc("savingvdiscards");
saving_hyph_codes_code:print_esc("savinghyphcodes");
suppress_fontnotfound_error_code:print_esc("suppressfontnotfounderror");

@ In order to handle \.{\\everyeof} we need an array |eof_seen| of
boolean variables.

@<Glob...@>=
@!eof_seen : array[1..max_in_open] of boolean; {has eof been seen?}

@ The |print_group| procedure prints the current level of grouping and
the name corresponding to |cur_group|.

@<Declare \eTeX\ procedures for tr...@>=
procedure print_group(@!e:boolean);
label exit;
begin case cur_group of
  bottom_level: begin print("bottom level"); return;
    end;
  simple_group,semi_simple_group:
    begin if cur_group=semi_simple_group then print("semi ");
    print("simple");
    end;
  hbox_group,adjusted_hbox_group:
    begin if cur_group=adjusted_hbox_group then print("adjusted ");
    print("hbox");
    end;
  vbox_group: print("vbox");
  vtop_group: print("vtop");
  align_group,no_align_group:
    begin if cur_group=no_align_group then print("no ");
    print("align");
    end;
  output_group: print("output");
  disc_group: print("disc");
  insert_group: print("insert");
  vcenter_group: print("vcenter");
  math_group,math_choice_group,math_shift_group,math_left_group:
    begin print("math");
    if cur_group=math_choice_group then print(" choice")
    else if cur_group=math_shift_group then print(" shift")
    else if cur_group=math_left_group then print(" left");
    end;
  end; {there are no other cases}
print(" group (level "); print_int(qo(cur_level)); print_char(")");
if saved(-1)<>0 then
  begin if e then print(" entered at line ") else print(" at line ");
  print_int(saved(-1));
  end;
exit:end;

@ The |group_trace| procedure is called when a new level of grouping
begins (|e=false|) or ends (|e=true|) with |saved(-1)| containing the
line number.

@<Declare \eTeX\ procedures for tr...@>=
@!stat procedure group_trace(@!e:boolean);
begin begin_diagnostic; print_char("{");
if e then print("leaving ") else print("entering ");
print_group(e); print_char("}"); end_diagnostic(false);
end;
tats

@ The \.{\\currentgrouplevel} and \.{\\currentgrouptype} commands return
the current level of grouping and the type of the current group
respectively.

@d current_group_level_code=eTeX_int+1 {code for \.{\\currentgrouplevel}}
@d current_group_type_code=eTeX_int+2 {code for \.{\\currentgrouptype}}

@<Generate all \eTeX...@>=
primitive("currentgrouplevel",last_item,current_group_level_code);
@!@:current_group_level_}{\.{\\currentgrouplevel} primitive@>
primitive("currentgrouptype",last_item,current_group_type_code);
@!@:current_group_type_}{\.{\\currentgrouptype} primitive@>

@ @<Cases of |last_item| for |print_cmd_chr|@>=
current_group_level_code: print_esc("currentgrouplevel");
current_group_type_code: print_esc("currentgrouptype");

@ @<Cases for fetching an integer value@>=
current_group_level_code: cur_val:=cur_level-level_one;
current_group_type_code: cur_val:=cur_group;

@ The \.{\\currentiflevel}, \.{\\currentiftype}, and
\.{\\currentifbranch} commands return the current level of conditionals
and the type and branch of the current conditional.

@d current_if_level_code=eTeX_int+3 {code for \.{\\currentiflevel}}
@d current_if_type_code=eTeX_int+4 {code for \.{\\currentiftype}}
@d current_if_branch_code=eTeX_int+5 {code for \.{\\currentifbranch}}

@<Generate all \eTeX...@>=
primitive("currentiflevel",last_item,current_if_level_code);
@!@:current_if_level_}{\.{\\currentiflevel} primitive@>
primitive("currentiftype",last_item,current_if_type_code);
@!@:current_if_type_}{\.{\\currentiftype} primitive@>
primitive("currentifbranch",last_item,current_if_branch_code);
@!@:current_if_branch_}{\.{\\currentifbranch} primitive@>

@ @<Cases of |last_item| for |print_cmd_chr|@>=
current_if_level_code: print_esc("currentiflevel");
current_if_type_code: print_esc("currentiftype");
current_if_branch_code: print_esc("currentifbranch");

@ @<Cases for fetching an integer value@>=
current_if_level_code: begin q:=cond_ptr; cur_val:=0;
  while q<>null do
    begin incr(cur_val); q:=vlink(q);
    end;
  end;
current_if_type_code: if cond_ptr=null then cur_val:=0
  else if cur_if<unless_code then cur_val:=cur_if+1
  else cur_val:=-(cur_if-unless_code+1);
current_if_branch_code:
  if (if_limit=or_code)or(if_limit=else_code) then cur_val:=1
  else if if_limit=fi_code then cur_val:=-1
  else cur_val:=0;

@ The \.{\\fontcharwd}, \.{\\fontcharht}, \.{\\fontchardp}, and
\.{\\fontcharic} commands return information about a character in a
font.

@d font_char_wd_code=eTeX_dim {code for \.{\\fontcharwd}}
@d font_char_ht_code=eTeX_dim+1 {code for \.{\\fontcharht}}
@d font_char_dp_code=eTeX_dim+2 {code for \.{\\fontchardp}}
@d font_char_ic_code=eTeX_dim+3 {code for \.{\\fontcharic}}

@<Generate all \eTeX...@>=
primitive("charwd",last_item,font_char_wd_code);
primitive("fontcharwd",last_item,font_char_wd_code);
@!@:font_char_wd_}{\.{\\fontcharwd} primitive@>
primitive("charht",last_item,font_char_ht_code);
primitive("fontcharht",last_item,font_char_ht_code);
@!@:font_char_ht_}{\.{\\fontcharht} primitive@>
primitive("chardp",last_item,font_char_dp_code);
primitive("fontchardp",last_item,font_char_dp_code);
@!@:font_char_dp_}{\.{\\fontchardp} primitive@>
primitive("charic",last_item,font_char_ic_code);
primitive("fontcharic",last_item,font_char_ic_code);
@!@:font_char_ic_}{\.{\\fontcharic} primitive@>

@ @<Cases of |last_item| for |print_cmd_chr|@>=
font_char_wd_code: print_esc("fontcharwd");
font_char_ht_code: print_esc("fontcharht");
font_char_dp_code: print_esc("fontchardp");
font_char_ic_code: print_esc("fontcharic");

@ @<Cases for fetching a dimension value@>=
font_char_wd_code,
font_char_ht_code,
font_char_dp_code,
font_char_ic_code: begin scan_font_ident; q:=cur_val; scan_char_num;
  if char_exists(q,cur_val) then
    begin
    case m of
    font_char_wd_code: cur_val:=char_width(q,cur_val);
    font_char_ht_code: cur_val:=char_height(q,cur_val);
    font_char_dp_code: cur_val:=char_depth(q,cur_val);
    font_char_ic_code: cur_val:=char_italic(q,cur_val);
    end; {there are no other cases}
    end
  else cur_val:=0;
  end;

@ The \.{\\parshapedimen}, \.{\\parshapeindent}, and \.{\\parshapelength}
commands return the indent and length parameters of the current
\.{\\parshape} specification.

@d par_shape_length_code=eTeX_dim+4 {code for \.{\\parshapelength}}
@d par_shape_indent_code=eTeX_dim+5 {code for \.{\\parshapeindent}}
@d par_shape_dimen_code=eTeX_dim+6 {code for \.{\\parshapedimen}}

@<Generate all \eTeX...@>=
primitive("parshapelength",last_item,par_shape_length_code);
@!@:par_shape_length_}{\.{\\parshapelength} primitive@>
primitive("parshapeindent",last_item,par_shape_indent_code);
@!@:par_shape_indent_}{\.{\\parshapeindent} primitive@>
primitive("parshapedimen",last_item,par_shape_dimen_code);
@!@:par_shape_dimen_}{\.{\\parshapedimen} primitive@>

@ @<Cases of |last_item| for |print_cmd_chr|@>=
par_shape_length_code: print_esc("parshapelength");
par_shape_indent_code: print_esc("parshapeindent");
par_shape_dimen_code: print_esc("parshapedimen");

@ @<Cases for fetching a dimension value@>=
par_shape_length_code,
par_shape_indent_code,
par_shape_dimen_code: begin q:=cur_chr-par_shape_length_code; scan_int;
  if (par_shape_ptr=null)or(cur_val<=0) then cur_val:=0
  else  begin if q=2 then
      begin q:=cur_val mod 2; cur_val:=(cur_val+q)div 2;
      end;
    if cur_val>vinfo(par_shape_ptr) then cur_val:=vinfo(par_shape_ptr);
    cur_val:=vmem(par_shape_ptr+2*cur_val-q).sc;
    end;
  cur_val_level:=dimen_val;
  end;

@ The \.{\\showgroups} command displays all currently active grouping
levels.

@d show_groups=4 { \.{\\showgroups} }

@<Generate all \eTeX...@>=
primitive("showgroups",xray,show_groups);
@!@:show_groups_}{\.{\\showgroups} primitive@>

@ @<Cases of |xray| for |print_cmd_chr|@>=
show_groups:print_esc("showgroups");

@ @<Cases for |show_whatever|@>=
show_groups: begin begin_diagnostic; show_save_groups;
  end;

@ @<Types...@>=
@!save_pointer=0..save_size; {index into |save_stack|}

@ The modifications of \TeX\ required for the display produced by the
|show_save_groups| procedure were first discussed by Donald~E. Knuth in
{\sl TUGboat\/} {\bf 11}, 165--170 and 499--511, 1990.
@^Knuth, Donald Ervin@>

In order to understand a group type we also have to know its mode.
Since unrestricted horizontal modes are not associated with grouping,
they are skipped when traversing the semantic nest.

@<Declare \eTeX\ procedures for use...@>=
procedure show_save_groups;
label found1,found2,found,done;
var p:0..nest_size; {index into |nest|}
@!m:-mmode..mmode; {mode}
@!v:save_pointer; {saved value of |save_ptr|}
@!l:quarterword; {saved value of |cur_level|}
@!c:group_code; {saved value of |cur_group|}
@!a:-1..1; {to keep track of alignments}
@!i:integer;
@!j:quarterword;
@!s:str_number;
begin p:=nest_ptr; nest[p]:=cur_list; {put the top level into the array}
v:=save_ptr; l:=cur_level; c:=cur_group;
save_ptr:=cur_boundary; decr(cur_level);@/
a:=1; s:="";
print_nl(""); print_ln;
loop@+begin print_nl("### "); print_group(true);
  if cur_group=bottom_level then goto done;
  repeat m:=nest[p].mode_field;
  if p>0 then decr(p) else m:=vmode;
  until m<>hmode;
  print(" (");
  case cur_group of
    simple_group: begin incr(p); goto found2;
      end;
    hbox_group,adjusted_hbox_group: s:="hbox";
    vbox_group: s:="vbox";
    vtop_group: s:="vtop";
    align_group: if a=0 then
        begin if m=-vmode then s:="halign" else s:="valign";
        a:=1; goto found1;
        end
      else  begin if a=1 then print("align entry") else print_esc("cr");
        if p>=a then p:=p-a;
        a:=0; goto found;
        end;
    no_align_group:
      begin incr(p); a:=-1; print_esc("noalign"); goto found2;
      end;
    output_group:
      begin print_esc("output"); goto found;
      end;
    math_group: goto found2;
    disc_group,math_choice_group:
      begin if cur_group=disc_group then print_esc("discretionary")
      else print_esc("mathchoice");
      for i:=1 to 3 do if i<=saved(-2) then print("{}");
      goto found2;
      end;
    insert_group:
      begin if saved(-2)=255 then print_esc("vadjust")
      else  begin print_esc("insert"); print_int(saved(-2));
        end;
      goto found2;
      end;
    vcenter_group: begin s:="vcenter"; goto found1;
      end;
    semi_simple_group: begin incr(p); print_esc("begingroup"); goto found;
      end;
    math_shift_group:
      begin if m=mmode then print_char("$")
      else if nest[p].mode_field=mmode then
        begin print_cmd_chr(eq_no,saved(-2)); goto found;
        end;
      print_char("$"); goto found;
      end;
    math_left_group:
      begin if type(nest[p+1].eTeX_aux_field)=left_noad then print_esc("left")
      else print_esc("middle");
      goto found;
      end;
    end; {there are no other cases}
  @<Show the box context@>;
  found1: print_esc(s); @<Show the box packaging info@>;
  found2: print_char("{");
  found: print_char(")"); decr(cur_level);
  cur_group:=save_level(save_ptr); save_ptr:=save_index(save_ptr)
  end;
done: save_ptr:=v; cur_level:=l; cur_group:=c;
end;

@ @<Show the box packaging info@>=
if saved(-2)<>0 then
  begin print_char(" ");
  if saved(-3)=exactly then print("to") else print("spread");
  print_scaled(saved(-2)); print("pt");
  end

@ @<Show the box context@>=
i:=saved(-4);
if i<>0 then
  if i<box_flag then
    begin if abs(nest[p].mode_field)=vmode then j:=hmove else j:=vmove;
    if i>0 then print_cmd_chr(j,0) else print_cmd_chr(j,1);
    print_scaled(abs(i)); print("pt");
    end
  else if i<ship_out_flag then
    begin if i>=global_box_flag then
      begin print_esc("global"); i:=i-(global_box_flag-box_flag);
      end;
    print_esc("setbox"); print_int(i-box_flag); print_char("=");
    end
  else print_cmd_chr(leader_ship,i-(leader_flag-a_leaders))

@ The |scan_general_text| procedure is much like |scan_toks(false,false)|,
but will be invoked via |expand|, i.e., recursively.
@^recursion@>

@<Declare \eTeX\ procedures for sc...@>=
procedure@?scan_general_text; forward;@t\2@>

@ The token list (balanced text) created by |scan_general_text| begins
at |link(temp_token_head)| and ends at |cur_val|.  (If |cur_val=temp_token_head|,
the list is empty.)

@<Declare \eTeX\ procedures for tok...@>=
procedure scan_general_text;
label found;
var s:normal..absorbing; {to save |scanner_status|}
@!w:pointer; {to save |warning_index|}
@!d:pointer; {to save |def_ref|}
@!p:pointer; {tail of the token list being built}
@!q:pointer; {new node being added to the token list via |store_new_token|}
@!unbalance:halfword; {number of unmatched left braces}
begin s:=scanner_status; w:=warning_index; d:=def_ref;
scanner_status:=absorbing; warning_index:=cur_cs;
p:=get_avail; def_ref:=p; token_ref_count(def_ref):=0; p:=def_ref;
scan_left_brace; {remove the compulsory left brace}
unbalance:=1;
loop@+  begin get_token;
  if cur_tok<right_brace_limit then
    if cur_cmd<right_brace then incr(unbalance)
    else  begin decr(unbalance);
      if unbalance=0 then goto found;
      end;
  store_new_token(cur_tok);
  end;
found: q:=link(def_ref); free_avail(def_ref); {discard reference count}
if q=null then cur_val:=temp_token_head @+ else cur_val:=p;
link(temp_token_head):=q;
scanner_status:=s; warning_index:=w; def_ref:=d;
end;

@ The \.{\\showtokens} command displays a token list.

@d show_tokens=5 { \.{\\showtokens} , must be odd! }

@<Generate all \eTeX...@>=
primitive("showtokens",xray,show_tokens);
@!@:show_tokens_}{\.{\\showtokens} primitive@>

@ @<Cases of |xray| for |print_cmd_chr|@>=
show_tokens:print_esc("showtokens");

@ The \.{\\unexpanded} primitive prevents expansion of tokens much as
the result from \.{\\the} applied to a token variable.  The
\.{\\detokenize} primitive converts a token list into a list of
character tokens much as if the token list were written to a file.  We
use the fact that the command modifiers for \.{\\unexpanded} and
\.{\\detokenize} are odd whereas those for \.{\\the} and \.{\\showthe}
are even.

@<Generate all \eTeX...@>=
primitive("unexpanded",the,1);@/
@!@:unexpanded_}{\.{\\unexpanded} primitive@>
primitive("detokenize",the,show_tokens);@/
@!@:detokenize_}{\.{\\detokenize} primitive@>

@ @<Cases of |the| for |print_cmd_chr|@>=
else if chr_code=1 then print_esc("unexpanded")
else print_esc("detokenize")

@ @<Handle \.{\\unexpanded} or \.{\\detokenize} and |return|@>=
if odd(cur_chr) then
  begin c:=cur_chr; scan_general_text;
  if c=1 then the_toks:=cur_val
  else begin old_setting:=selector; selector:=new_string; b:=pool_ptr;
    p:=get_avail; link(p):=link(temp_token_head);
    token_show(p); flush_list(p);
    selector:=old_setting; the_toks:=str_toks(b);
    end;
  return;
  end

@ The \.{\\showifs} command displays all currently active conditionals.

@d show_ifs=6 { \.{\\showifs} }

@<Generate all \eTeX...@>=
primitive("showifs",xray,show_ifs);
@!@:show_ifs_}{\.{\\showifs} primitive@>

@ @<Cases of |xray| for |print_cmd_chr|@>=
show_ifs:print_esc("showifs");

@
@d print_if_line(#)==if #<>0 then
  begin print(" entered on line "); print_int(#);
  end

@<Cases for |show_whatever|@>=
show_ifs: begin begin_diagnostic; print_nl(""); print_ln;
  if cond_ptr=null then
    begin print_nl("### "); print("no active conditionals");
    end
  else  begin p:=cond_ptr; n:=0;
    repeat incr(n); p:=vlink(p);@+until p=null;
    p:=cond_ptr; t:=cur_if; l:=if_line; m:=if_limit;
    repeat print_nl("### level "); print_int(n); print(": ");
    print_cmd_chr(if_test,t);
    if m=fi_code then print_esc("else");
    print_if_line(l);
    decr(n); t:=if_limit_subtype(p); l:=if_line_field(p); m:=if_limit_type(p); p:=vlink(p);
    until p=null;
    end;
  end;

@ The \.{\\interactionmode} primitive allows to query and set the
interaction mode.

@<Generate all \eTeX...@>=
primitive("interactionmode",set_page_int,2);
@!@:interaction_mode_}{\.{\\interactionmode} primitive@>

@ @<Cases of |set_page_int| for |print_cmd_chr|@>=
else if chr_code=2 then print_esc("interactionmode")

@ @<Cases for `Fetch the |dead_cycles| or the |insert_penalties|'@>=
else if m=2 then cur_val:=interaction

@ @<Declare \eTeX\ procedures for use...@>=
procedure@?new_interaction; forward;@t\2@>

@ @<Cases for |alter_integer|@>=
else if c=2 then
  begin if (cur_val<batch_mode)or(cur_val>error_stop_mode) then
    begin print_err("Bad interaction mode");
@.Bad interaction mode@>
    help2("Modes are 0=batch, 1=nonstop, 2=scroll, and")@/
    ("3=errorstop. Proceed, and I'll ignore this case.");
    int_error(cur_val);
    end
  else  begin cur_chr:=cur_val; new_interaction;
    end;
  end

@ The |middle| feature of \eTeX\ allows one ore several \.{\\middle}
delimiters to appear between \.{\\left} and \.{\\right}.

@<Generate all \eTeX...@>=
primitive("middle",left_right,middle_noad);
@!@:middle_}{\.{\\middle} primitive@>

@ @<Cases of |left_right| for |print_cmd_chr|@>=
else if chr_code=middle_noad then print_esc("middle")

@ The |scan_tokens| feature of \eTeX\ defines the \.{\\scantokens}
primitive.

@<Generate all \eTeX...@>=
primitive("scantokens",input,2);
@!@:scan_tokens_}{\.{\\scantokens} primitive@>
primitive("scantextokens",input,3);
@!@:scan_tex_tokens_}{\.{\\scantextokens} primitive@>

@ @<Cases of |input| for |print_cmd_chr|@>=
else if chr_code=2 then print_esc("scantokens")
else if chr_code=3 then print_esc("scantextokens")

@ @<Cases for |input|@>=
else if cur_chr=2 then pseudo_start
else if cur_chr=3 then begin pseudo_start; name := 19; end

@ The global variable |pseudo_files| is used to maintain a stack of
pseudo files.  The |pseudo_lines| field of each pseudo file points to
a linked list of variable size nodes representing lines not yet
processed: the |subtype| field contains the size of this node, 
all the following words contain ASCII codes.

@<Glob...@>=
@!pseudo_files:pointer; {stack of pseudo files}

@ @<Set init...@>=
pseudo_files:=null;

@ The |pseudo_start| procedure initiates reading from a pseudo file.

@<Declare \eTeX\ procedures for ex...@>=
procedure@?pseudo_start; forward;@t\2@>

@ @<Declare \eTeX\ procedures for tok...@>=
procedure pseudo_start;
var old_setting:0..max_selector; {holds |selector| setting}
@!s:str_number; {string to be converted into a pseudo file}
@!p:pointer; {for list construction}
begin scan_general_text;
old_setting:=selector; selector:=new_string;
token_show(temp_token_head); selector:=old_setting;
flush_list(link(temp_token_head));
str_room(1); s:=make_string;
@<Convert string |s| into a new pseudo file@>;
flush_string;
@<Initiate input from new pseudo file@>;
end;

procedure pseudo_from_string;
var @!s:str_number; {string to be converted into a pseudo file}
@!p:pointer; {for list construction}
begin 
s:=make_string;
@<Convert string |s| into a new pseudo file@>;
flush_string;
@<Initiate input from new pseudo file@>;
end;

procedure lua_string_start;
begin 
begin_file_reading; {set up |cur_file| and new level of input}
line:=0; limit:=start; loc:=limit+1; {force line read}
name:=21; luacstring_start(index);
end;

@ @<Convert string |s| into a new pseudo file@>=
str_pool[pool_ptr]:=si(" ");
p:=string_to_pseudo(str_start_macro(s),pool_ptr,new_line_char);
vlink(p):=pseudo_files; pseudo_files:=p

@ @<Initiate input from new pseudo file@>=
begin_file_reading; {set up |cur_file| and new level of input}
line:=0; limit:=start; loc:=limit+1; {force line read}
if tracing_scan_tokens>0 then
  begin if term_offset>max_print_line-3 then print_ln
  else if (term_offset>0)or(file_offset>0) then print_char(" ");
  name:=20; print("( "); incr(open_parens); update_terminal;
  end
else name:=18

@ Here we read a line from the current pseudo file into |buffer|.

@d pseudo_lines(#)==vlink(#+1)

@<Declare \eTeX\ procedures for tr...@>=
function pseudo_input: boolean; {inputs the next line or returns |false|}
var p:pointer; {current line from pseudo file}
@!sz:integer; {size of node |p|}
@!w:four_quarters; {four ASCII codes}
@!r:pointer; {loop index}
begin last:=first; {cf.\ Matthew 19\thinspace:\thinspace30}
p:=pseudo_lines(pseudo_files);
if p=null then begin pseudo_input:=false; end
else  begin pseudo_lines(pseudo_files):=vlink(p); sz:=subtype(p);
  if 4*sz-3>=buf_size-last then
     check_buffer_overflow(last+4*sz);
  last:=first;
  for r:=p+1 to p+sz-1 do
    begin w:=vmem(r).qqqq;
    buffer[last]:=w.b0; buffer[last+1]:=w.b1;
    buffer[last+2]:=w.b2; buffer[last+3]:=w.b3;
    last:=last+4;
    end;
  if last>=max_buf_stack then max_buf_stack:=last+1;
  while (last>first)and(buffer[last-1]=" ") do decr(last);
  flush_node(p);
  pseudo_input:=true;
  end;
end;

@ When we are done with a pseudo file we `close' it.

@<Declare \eTeX\ procedures for tr...@>=
procedure pseudo_close; {close the top level pseudo file}
var p,@!q: pointer;
begin p:=vlink(pseudo_files);
flush_node(pseudo_files); 
pseudo_files:=p;
end;

@ @<Close the pseudo files@>=
while pseudo_files<>null do pseudo_close; {flush pseudo files}

@ @<Generate all \eTeX...@>=
primitive("readline",read_to_cs,1);@/
@!@:read_line_}{\.{\\readline} primitive@>

@ @<Cases of |read| for |print_cmd_chr|@>=
else print_esc("readline")

@ @<Handle \.{\\readline} and |goto done|@>=
if j=1 then
  begin while loc<=limit do {current line not yet finished}
    begin cur_chr:=buffer[loc]; incr(loc);
    if cur_chr=" " then cur_tok:=space_token
    @+else cur_tok:=cur_chr+other_token;
    store_new_token(cur_tok);
    end;
  goto done;
  end

@ Here we define the additional conditionals of \eTeX\ as well as the
\.{\\unless} prefix.

@d if_def_code=17 { `\.{\\ifdefined}' }
@d if_cs_code=18 { `\.{\\ifcsname}' }
@d if_font_char_code=19 { `\.{\\iffontchar}' }
@d if_in_csname_code=20 { `\.{\\ifincsname}' }
@d if_abs_num_code=22 { `\.{\\ifabsnum}' } { 21 = |if_primitive|}
@d if_abs_dim_code=23 { `\.{\\ifabsdim}' }

@<Generate all \eTeX...@>=
primitive("unless",expand_after,1);@/
@!@:unless_}{\.{\\unless} primitive@>
primitive("ifdefined",if_test,if_def_code);
@!@:if_defined_}{\.{\\ifdefined} primitive@>
primitive("ifcsname",if_test,if_cs_code);
@!@:if_cs_name_}{\.{\\ifcsname} primitive@>
primitive("iffontchar",if_test,if_font_char_code);
@!@:if_font_char_}{\.{\\iffontchar} primitive@>
primitive("ifincsname",if_test,if_in_csname_code);
@!@:if_in_csname_}{\.{\\ifincsname} primitive@>
primitive("ifabsnum",if_test,if_abs_num_code);
@!@:if_abs_num_}{\.{\\ifabsnum} primitive@>
primitive("ifabsdim",if_test,if_abs_dim_code);
@!@:if_abs_dim_}{\.{\\ifabsdim} primitive@>
primitive("ifpdfabsnum",if_test,if_abs_num_code);
@!@:if_abs_num_}{\.{\\ifpdfabsnum} primitive@>
primitive("ifpdfabsdim",if_test,if_abs_dim_code);
@!@:if_abs_dim_}{\.{\\ifpdfabsdim} primitive@>

@ @<Cases of |expandafter| for |print_cmd_chr|@>=
else print_esc("unless")

@ @<Cases of |if_test| for |print_cmd_chr|@>=
if_def_code:print_esc("ifdefined");
if_cs_code:print_esc("ifcsname");
if_font_char_code:print_esc("iffontchar");
if_in_csname_code:print_esc("ifincsname");
if_abs_num_code:print_esc("ifabsnum");
if_abs_dim_code:print_esc("ifabsdim");

@ The result of a boolean condition is reversed when the conditional is
preceded by \.{\\unless}.

@<Negate a boolean conditional and |goto reswitch|@>=
begin get_token;
if (cur_cmd=if_test)and(cur_chr<>if_case_code) then
  begin cur_chr:=cur_chr+unless_code; goto reswitch;
  end;
print_err("You can't use `"); print_esc("unless"); print("' before `");
@.You can't use \\unless...@>
print_cmd_chr(cur_cmd,cur_chr); print_char("'");
help1("Continue, and I'll forget that it ever happened.");
back_error;
end

@ The conditional \.{\\ifdefined} tests if a control sequence is
defined.

We need to reset |scanner_status|, since \.{\\outer} control sequences
are allowed, but we might be scanning a macro definition or preamble.

@<Cases for |conditional|@>=
if_def_code:begin save_scanner_status:=scanner_status;
  scanner_status:=normal;
  get_filtered_next; b:=(cur_cmd<>undefined_cs);
  scanner_status:=save_scanner_status;
  end;

@ The conditional \.{\\ifcsname} is equivalent to \.{\{\\expandafter}
\.{\}\\expandafter} \.{\\ifdefined} \.{\\csname}, except that no new
control sequence will be entered into the hash table (once all tokens
preceding the mandatory \.{\\endcsname} have been expanded).

@<Cases for |conditional|@>=
if_cs_code:begin n:=get_avail; p:=n; {head of the list of characters}
  b:=false;
  repeat get_x_token;
  if cur_cs=0 then store_new_token(cur_tok);
  until cur_cs<>0;
  if cur_cmd<>end_cs_name then @<Complain about missing \.{\\endcsname}@>;
  @<Look up the characters of list |n| in the hash table, and set |cur_cs|@>;
  flush_list(n);
  b:=(eq_type(cur_cs)<>undefined_cs);
  end;

@ @<Look up the characters of list |n| in the hash table...@>=
m:=first; p:=link(n);
while p<>null do
  begin if m>=max_buf_stack then
    begin max_buf_stack:=m+4;
    if max_buf_stack=buf_size then
      check_buffer_overflow(max_buf_stack);
@:TeX capacity exceeded buffer size}{\quad buffer size@>
    end;
  s := info(p) mod string_offset;
  if s <= @"7F then begin
    buffer[m]:=s; incr(m);
    end
  else if s<=@"7FF then begin
    buffer[m]:=@"C0 + s div @"40; incr(m);
    buffer[m]:=@"80 + s mod @"40; incr(m);
    end
  else if s<=@"FFFF then begin
    buffer[m]:=@"E0 + s div @"1000; incr(m);
    buffer[m]:=@"80 + (s mod @"1000) div @"40; incr(m);
    buffer[m]:=@"80 + (s mod @"1000) mod @"40; incr(m);
    end 
  else begin
    buffer[m]:=@"F0 + s div @"40000;  incr(m);
    buffer[m]:=@"80 + (s mod @"40000) div @"1000;  incr(m);
    buffer[m]:=@"80 + ((s mod @"40000) mod @"1000) div @"40;  incr(m);
    buffer[m]:=@"80 + ((s mod @"40000) mod @"1000) mod @"40;  incr(m);
    end;
  p:=link(p); 
  end;
if m>first then
  cur_cs:=id_lookup(first,m-first) {|no_new_control_sequence| is |true|}
else if m=first then cur_cs:=null_cs {the list is empty}

@ The conditional \.{\\iffontchar} tests the existence of a character in
a font.

@<Cases for |conditional|@>=
if_in_csname_code: b := is_in_csname;
if_abs_dim_code, if_abs_num_code: begin
  if this_if=if_abs_num_code then scan_int@+else scan_normal_dimen;
  n:=cur_val;
  if n < 0 then negate(n);
  @<Get the next non-blank non-call...@>;
  if (cur_tok>=other_token+"<")and(cur_tok<=other_token+">") then
    r:=cur_tok-other_token
  else  begin print_err("Missing = inserted for ");
  @.Missing = inserted@>
    print_cmd_chr(if_test,this_if);
    help1("I was expecting to see `<', `=', or `>'. Didn't.");
    back_error; r:="=";
    end;
  if this_if=if_abs_num_code then scan_int@+else scan_normal_dimen;
  if cur_val < 0 then negate(cur_val);
  case r of
  "<": b:=(n<cur_val);
  "=": b:=(n=cur_val);
  ">": b:=(n>cur_val);
  end;
  end;
if_font_char_code:begin scan_font_ident; n:=cur_val; scan_char_num;
  b:=char_exists(n,cur_val);
  end;

@ The |protected| feature of \eTeX\ defines the \.{\\protected} prefix
command for macro definitions.  Such macros are protected against
expansions when lists of expanded tokens are built, e.g., for \.{\\edef}
or during \.{\\write}.

@<Generate all \eTeX...@>=
primitive("protected",prefix,8);
@!@:protected_}{\.{\\protected} primitive@>

@ @<Cases of |prefix| for |print_cmd_chr|@>=
else if chr_code=8 then print_esc("protected")

@ The |get_x_or_protected| procedure is like |get_x_token| except that
protected macros are not expanded.

@<Declare \eTeX\ procedures for sc...@>=
procedure get_x_or_protected; {sets |cur_cmd|, |cur_chr|, |cur_tok|,
  and expands non-protected macros}
label exit;
begin loop@+begin get_token;
  if cur_cmd<=max_command then return;
  if (cur_cmd>=call)and(cur_cmd<end_template) then
    if info(link(cur_chr))=protected_token then return;
  expand;
  end;
exit:end;

@ A group entered (or a conditional started) in one file may end in a
different file.  Such slight anomalies, although perfectly legitimate,
may cause errors that are difficult to locate.  In order to be able to
give a warning message when such anomalies occur, \eTeX\ uses the
|grp_stack| and |if_stack| arrays to record the initial |cur_boundary|
and |cond_ptr| values for each input file.

@<Glob...@>=
@!grp_stack : array[0..max_in_open] of save_pointer; {initial |cur_boundary|}
@!if_stack : array[0..max_in_open] of pointer; {initial |cond_ptr|}

@ When a group ends that was apparently entered in a different input
file, the |group_warning| procedure is invoked in order to update the
|grp_stack|.  If moreover \.{\\tracingnesting} is positive we want to
give a warning message.  The situation is, however, somewhat complicated
by two facts:  (1)~There may be |grp_stack| elements without a
corresponding \.{\\input} file or \.{\\scantokens} pseudo file (e.g.,
error insertions from the terminal); and (2)~the relevant information is
recorded in the |name_field| of the |input_stack| only loosely
synchronized with the |in_open| variable indexing |grp_stack|.

@<Declare \eTeX\ procedures for tr...@>=
procedure group_warning;
var i:0..max_in_open; {index into |grp_stack|}
@!w:boolean; {do we need a warning?}
begin base_ptr:=input_ptr; input_stack[base_ptr]:=cur_input;
  {store current state}
i:=in_open; w:=false;
while (grp_stack[i]=cur_boundary)and(i>0) do
  begin @<Set variable |w| to indicate if this case should be reported@>;
  grp_stack[i]:=save_index(save_ptr); decr(i);
  end;
if w then
  begin print_nl("Warning: end of "); print_group(true);
@.Warning: end of...@>
  print(" of a different file"); print_ln;
  if tracing_nesting>1 then show_context;
  if history=spotless then history:=warning_issued;
  end;
end;

@ This code scans the input stack in order to determine the type of the
current input file.

@<Set variable |w| to...@>=
if tracing_nesting>0 then
  begin while (input_stack[base_ptr].state_field=token_list)or@|
    (input_stack[base_ptr].index_field>i) do decr(base_ptr);
  if input_stack[base_ptr].name_field>17 then w:=true;
  end

@ When a conditional ends that was apparently started in a different
input file, the |if_warning| procedure is invoked in order to update the
|if_stack|.  If moreover \.{\\tracingnesting} is positive we want to
give a warning message (with the same complications as above).

@<Declare \eTeX\ procedures for tr...@>=
procedure if_warning;
var i:0..max_in_open; {index into |if_stack|}
@!w:boolean; {do we need a warning?}
begin base_ptr:=input_ptr; input_stack[base_ptr]:=cur_input;
  {store current state}
i:=in_open; w:=false;
while if_stack[i]=cond_ptr do
  begin @<Set variable |w| to...@>;
  if_stack[i]:=vlink(cond_ptr); decr(i);
  end;
if w then
  begin print_nl("Warning: end of "); print_cmd_chr(if_test,cur_if);
@.Warning: end of...@>
  print_if_line(if_line); print(" of a different file"); print_ln;
  if tracing_nesting>1 then show_context;
  if history=spotless then history:=warning_issued;
  end;
end;

@ Conversely, the |file_warning| procedure is invoked when a file ends
and some groups entered or conditionals started while reading from that
file are still incomplete.

@<Declare \eTeX\ procedures for tr...@>=
procedure file_warning;
var p:pointer; {saved value of |save_ptr| or |cond_ptr|}
@!l:quarterword; {saved value of |cur_level| or |if_limit|}
@!c:quarterword; {saved value of |cur_group| or |cur_if|}
@!i:integer; {saved value of |if_line|}
begin 
p:=save_ptr; l:=cur_level; c:=cur_group; save_ptr:=cur_boundary;
while grp_stack[in_open]<>save_ptr do
  begin decr(cur_level);
  print_nl("Warning: end of file when ");
@.Warning: end of file when...@>
  print_group(true); print(" is incomplete");@/
  cur_group:=save_level(save_ptr); save_ptr:=save_index(save_ptr)
  end;
save_ptr:=p; cur_level:=l; cur_group:=c; {restore old values}
p:=cond_ptr; l:=if_limit; c:=cur_if; i:=if_line;
while if_stack[in_open]<>cond_ptr do
  begin print_nl("Warning: end of file when ");
@.Warning: end of file when...@>
  print_cmd_chr(if_test,cur_if);
  if if_limit=fi_code then print_esc("else");
  print_if_line(if_line); print(" is incomplete");@/
  if_line:=if_line_field(cond_ptr); cur_if:=if_limit_subtype(cond_ptr);
  if_limit:=if_limit_type(cond_ptr); cond_ptr:=vlink(cond_ptr);
  end;
cond_ptr:=p; if_limit:=l; cur_if:=c; if_line:=i; {restore old values}
print_ln;
if tracing_nesting>1 then show_context;
if history=spotless then history:=warning_issued;
end;

@ Here are the additional \eTeX\ primitives for expressions.

@<Generate all \eTeX...@>=
primitive("numexpr",last_item,eTeX_expr-int_val+int_val);
@!@:num_expr_}{\.{\\numexpr} primitive@>
primitive("dimexpr",last_item,eTeX_expr-int_val+dimen_val);
@!@:dim_expr_}{\.{\\dimexpr} primitive@>
primitive("glueexpr",last_item,eTeX_expr-int_val+glue_val);
@!@:glue_expr_}{\.{\\glueexpr} primitive@>
primitive("muexpr",last_item,eTeX_expr-int_val+mu_val);
@!@:mu_expr_}{\.{\\muexpr} primitive@>

@ @<Cases of |last_item| for |print_cmd_chr|@>=
eTeX_expr-int_val+int_val: print_esc("numexpr");
eTeX_expr-int_val+dimen_val: print_esc("dimexpr");
eTeX_expr-int_val+glue_val: print_esc("glueexpr");
eTeX_expr-int_val+mu_val: print_esc("muexpr");

@ This code for reducing |cur_val_level| and\slash or negating the
result is similar to the one for all the other cases of
|scan_something_internal|, with the difference that |scan_expr| has
already increased the reference count of a glue specification.

@<Process an expression and |return|@>=
begin if m<eTeX_mu then
  begin case m of
  @/@<Cases for fetching a glue value@>@/
  end; {there are no other cases}
  cur_val_level:=glue_val;
  end
else if m<eTeX_expr then
  begin case m of
  @/@<Cases for fetching a mu value@>@/
  end; {there are no other cases}
  cur_val_level:=mu_val;
  end
else  begin cur_val_level:=m-eTeX_expr+int_val; scan_expr;
  end;
while cur_val_level>level do
  begin if cur_val_level=glue_val then
    begin m:=cur_val; cur_val:=width(m); delete_glue_ref(m);
    end
  else if cur_val_level=mu_val then mu_error;
  decr(cur_val_level);
  end;
if negative then
  if cur_val_level>=glue_val then
    begin m:=cur_val; cur_val:=new_spec(m); delete_glue_ref(m);
    @<Negate all three glue components of |cur_val|@>;
    end
  else negate(cur_val);
return;
end

@ @<Declare \eTeX\ procedures for sc...@>=
procedure@?scan_expr; forward;@t\2@>

@ The |scan_expr| procedure scans and evaluates an expression.

@<Declare procedures needed for expressions@>=
@t\4@>@<Declare subprocedures for |scan_expr|@>
procedure scan_expr; {scans and evaluates an expression}
label restart, continue, found;
var a,@!b:boolean; {saved values of |arith_error|}
@!l:small_number; {type of expression}
@!r:small_number; {state of expression so far}
@!s:small_number; {state of term so far}
@!o:small_number; {next operation or type of next factor}
@!e:integer; {expression so far}
@!t:integer; {term so far}
@!f:integer; {current factor}
@!n:integer; {numerator of combined multiplication and division}
@!p:pointer; {top of expression stack}
@!q:pointer; {for stack manipulations}
begin l:=cur_val_level; a:=arith_error; b:=false; p:=null;
@<Scan and evaluate an expression |e| of type |l|@>;
if b then
  begin print_err("Arithmetic overflow");
@.Arithmetic overflow@>
  help2("I can't evaluate this expression,")@/
    ("since the result is out of range.");
  error;
  if l>=glue_val then
    begin delete_glue_ref(e); e:=zero_glue; add_glue_ref(e);
    end
  else e:=0;
  end;
arith_error:=a; cur_val:=e; cur_val_level:=l;
end;

@ Evaluating an expression is a recursive process:  When the left
parenthesis of a subexpression is scanned we descend to the next level
of recursion; the previous level is resumed with the matching right
parenthesis.

@d expr_none=0 {\.( seen, or \.( $\langle\it expr\rangle$ \.) seen}
@d expr_add=1 {\.( $\langle\it expr\rangle$ \.+ seen}
@d expr_sub=2 {\.( $\langle\it expr\rangle$ \.- seen}
@d expr_mult=3 {$\langle\it term\rangle$ \.* seen}
@d expr_div=4 {$\langle\it term\rangle$ \./ seen}
@d expr_scale=5 {$\langle\it term\rangle$ \.*
  $\langle\it factor\rangle$ \./ seen}

@<Scan and eval...@>=
restart: r:=expr_none; e:=0; s:=expr_none; t:=0; n:=0;
continue: if s=expr_none then o:=l@+else o:=int_val;
@<Scan a factor |f| of type |o| or start a subexpression@>;
found: @<Scan the next operator and set |o|@>;
arith_error:=b;
@<Make sure that |f| is in the proper range@>;
case s of @<Cases for evaluation of the current term@>@;
end; {there are no other cases}
if o>expr_sub then s:=o@+else @<Evaluate the current expression@>;
b:=arith_error;
if o<>expr_none then goto continue;
if p<>null then @<Pop the expression stack and |goto found|@>

@ @<Scan the next op...@>=
@<Get the next non-blank non-call token@>;
if cur_tok=other_token+"+" then o:=expr_add
else if cur_tok=other_token+"-" then o:=expr_sub
else if cur_tok=other_token+"*" then o:=expr_mult
else if cur_tok=other_token+"/" then o:=expr_div
else  begin o:=expr_none;
  if p=null then
    begin if cur_cmd<>relax then back_input;
    end
  else if cur_tok<>other_token+")" then
    begin print_err("Missing ) inserted for expression");
@.Missing ) inserted@>
    help1("I was expecting to see `+', `-', `*', `/', or `)'. Didn't.");
    back_error;
    end;
  end

@ @<Scan a factor...@>=
@<Get the next non-blank non-call token@>;
if cur_tok=other_token+"(" then
  @<Push the expression stack and |goto restart|@>;
back_input;
if (o=int_val)or(o=attr_val) then scan_int
else if o=dimen_val then scan_normal_dimen
else if o=glue_val then scan_normal_glue
else scan_mu_glue;
f:=cur_val

@ @<Declare \eTeX\ procedures for sc...@>=
procedure@?scan_normal_glue; forward;@t\2@>@/
procedure@?scan_mu_glue; forward;@t\2@>

@ Here we declare to trivial procedures in order to avoid mutually
recursive procedures with parameters.

@<Declare procedures needed for expressions@>=
procedure scan_normal_glue;
begin scan_glue(glue_val);
end;
@#
procedure scan_mu_glue;
begin scan_glue(mu_val);
end;

@ Parenthesized subexpressions can be inside expressions, and this
nesting has a stack.  Seven local variables represent the top of the
expression stack:  |p| points to pushed-down entries, if any; |l|
specifies the type of expression currently beeing evaluated; |e| is the
expression so far and |r| is the state of its evaluation; |t| is the
term so far and |s| is the state of its evaluation; finally |n| is the
numerator for a combined multiplication and division, if any.

@d expr_node=39 { stack entry for subexpressions}
@d expr_type(#)==type(#+1)
@d expr_state(#)==subtype(#+1)
@d expr_e_field(#)==vlink(#+1) {saved expression so far}
@d expr_t_field(#)==vlink(#+2) {saved term so far}
@d expr_n_field(#)==vinfo(#+2) {saved numerator}

@<Push the expression...@>=
begin q:=new_node(expr_node,0); vlink(q):=p; 
expr_type(q):=l; expr_state(q):=4*s+r;
expr_e_field(q):=e; expr_t_field(q):=t; expr_n_field(q):=n;
p:=q; l:=o; goto restart;
end

@ @<Pop the expression...@>=
begin f:=e; q:=p;
e:=expr_e_field(q); t:=expr_t_field(q); n:=expr_n_field(q);
s:=expr_state(q) div 4; r:=expr_state(q) mod 4;
l:=expr_type(q); p:=vlink(q); flush_node(q);
goto found;
end

@ We want to make sure that each term and (intermediate) result is in
the proper range.  Integer values must not exceed |infinity|
($2^{31}-1$) in absolute value, dimensions must not exceed |max_dimen|
($2^{30}-1$).  We avoid the absolute value of an integer, because this
might fail for the value $-2^{31}$ using 32-bit arithmetic.

@d num_error(#)== {clear a number or dimension and set |arith_error|}
  begin arith_error:=true; #:=0;
  end
@d glue_error(#)== {clear a glue spec and set |arith_error|}
  begin arith_error:=true; delete_glue_ref(#); #:=new_spec(zero_glue);
  end

@<Make sure that |f|...@>=
if ((l=int_val)or(l=attr_val))or(s>expr_sub) then
  begin if (f>infinity)or(f<-infinity) then num_error(f);
  end
else if l=dimen_val then
  begin if abs(f)>max_dimen then num_error(f);
  end
else  begin if (abs(width(f))>max_dimen)or@|
   (abs(stretch(f))>max_dimen)or@|
   (abs(shrink(f))>max_dimen) then glue_error(f);
  end

@ Applying the factor |f| to the partial term |t| (with the operator
|s|) is delayed until the next operator |o| has been scanned.  Here we
handle the first factor of a partial term.  A glue spec has to be copied
unless the next operator is a right parenthesis; this allows us later on
to simply modify the glue components.

@d normalize_glue(#)==
  if stretch(#)=0 then stretch_order(#):=normal;
  if shrink(#)=0 then shrink_order(#):=normal

@<Cases for evaluation of the current term@>=
expr_none: if (l>=glue_val)and(o<>expr_none) then
    begin t:=new_spec(f); delete_glue_ref(f); normalize_glue(t);
    end
  else t:=f;

@ When a term |t| has been completed it is copied to, added to, or
subtracted from the expression |e|.

@d expr_add_sub(#)==add_or_sub(#,r=expr_sub)
@d expr_a(#)==expr_add_sub(#,max_dimen)

@<Evaluate the current expression@>=
begin s:=expr_none;
if r=expr_none then e:=t
else if (l=int_val)or(l=attr_val) then e:=expr_add_sub(e,t,infinity)
else if l=dimen_val then e:=expr_a(e,t)
else @<Compute the sum or difference of two glue specs@>;
r:=o;
end

@ The function |add_or_sub(x,y,max_answer,negative)| computes the sum
(for |negative=false|) or difference (for |negative=true|) of |x| and
|y|, provided the absolute value of the result does not exceed
|max_answer|.

@<Declare subprocedures for |scan_expr|@>=
function add_or_sub(@!x,@!y,@!max_answer:integer;@!negative:boolean):integer;
var a:integer; {the answer}
begin if negative then negate(y);
if x>=0 then
  if y<=max_answer-x then a:=x+y@+else num_error(a)
else if y>=-max_answer-x then a:=x+y@+else num_error(a);
add_or_sub:=a;
end;

@ We know that |stretch_order(e)>normal| implies |stretch(e)<>0| and
|shrink_order(e)>normal| implies |shrink(e)<>0|.

@<Compute the sum or diff...@>=
begin width(e):=expr_a(width(e),width(t));
if stretch_order(e)=stretch_order(t) then
  stretch(e):=expr_a(stretch(e),stretch(t))
else if (stretch_order(e)<stretch_order(t))and(stretch(t)<>0) then
  begin stretch(e):=stretch(t); stretch_order(e):=stretch_order(t);
  end;
if shrink_order(e)=shrink_order(t) then
  shrink(e):=expr_a(shrink(e),shrink(t))
else if (shrink_order(e)<shrink_order(t))and(shrink(t)<>0) then
  begin shrink(e):=shrink(t); shrink_order(e):=shrink_order(t);
  end;
delete_glue_ref(t); normalize_glue(e);
end

@ If a multiplication is followed by a division, the two operations are
combined into a `scaling' operation.  Otherwise the term |t| is
multiplied by the factor |f|.

@d expr_m(#)==#:=nx_plus_y(#,f,0)

@<Cases for evaluation of the current term@>=
expr_mult: if o=expr_div then
    begin n:=f; o:=expr_scale;
    end
  else if (l=int_val)or(l=attr_val) then t:=mult_integers(t,f)
  else if l=dimen_val then expr_m(t)
  else  begin expr_m(width(t)); expr_m(stretch(t)); expr_m(shrink(t));
    end;

@ Here we divide the term |t| by the factor |f|.

@d expr_d(#)==#:=quotient(#,f)

@<Cases for evaluation of the current term@>=
expr_div: if l<glue_val then expr_d(t)
  else  begin expr_d(width(t)); expr_d(stretch(t)); expr_d(shrink(t));
    end;

@ The function |quotient(n,d)| computes the rounded quotient
$q=\lfloor n/d+{1\over2}\rfloor$, when $n$ and $d$ are positive.

@<Declare subprocedures for |scan_expr|@>=
function quotient(@!n,@!d:integer):integer;
var negative:boolean; {should the answer be negated?}
@!a:integer; {the answer}
begin if d=0 then num_error(a)
else  begin if d>0 then negative:=false
  else  begin negate(d); negative:=true;
    end;
  if n<0 then
    begin negate(n); negative:=not negative;
    end;
  a:=n div d; n:=n-a*d; d:=n-d; {avoid certain compiler optimizations!}
  if d+n>=0 then incr(a);
  if negative then negate(a);
  end;
quotient:=a;
end;

@ Here the term |t| is multiplied by the quotient $n/f$.

@d expr_s(#)==#:=fract(#,n,f,max_dimen)

@<Cases for evaluation of the current term@>=
expr_scale: if (l=int_val)or(l=attr_val) then t:=fract(t,n,f,infinity)
  else if l=dimen_val then expr_s(t)
  else  begin expr_s(width(t)); expr_s(stretch(t)); expr_s(shrink(t));
    end;

@ Finally, the function |fract(x,n,d,max_answer)| computes the integer
$q=\lfloor xn/d+{1\over2}\rfloor$, when $x$, $n$, and $d$ are positive
and the result does not exceed |max_answer|.  We can't use floating
point arithmetic since the routine must produce identical results in all
cases; and it would be too dangerous to multiply by~|n| and then divide
by~|d|, in separate operations, since overflow might well occur.  Hence
this subroutine simulates double precision arithmetic, somewhat
analogous to \MF's |make_fraction| and |take_fraction| routines.

@d too_big=88 {go here when the result is too big}

@<Declare subprocedures for |scan_expr|@>=
function fract(@!x,@!n,@!d,@!max_answer:integer):integer;
label found, found1, too_big, done;
var negative:boolean; {should the answer be negated?}
@!a:integer; {the answer}
@!f:integer; {a proper fraction}
@!h:integer; {smallest integer such that |2*h>=d|}
@!r:integer; {intermediate remainder}
@!t:integer; {temp variable}
begin if d=0 then goto too_big;
a:=0;
if d>0 then negative:=false
else  begin negate(d); negative:=true;
  end;
if x<0 then
  begin negate(x); negative:=not negative;
  end
else if x=0 then goto done;
if n<0 then
  begin negate(n); negative:=not negative;
  end;
t:=n div d;
if t>max_answer div x then goto too_big;
a:=t*x; n:=n-t*d;
if n=0 then goto found;
t:=x div d;
if t>(max_answer-a) div n then goto too_big;
a:=a+t*n; x:=x-t*d;
if x=0 then goto found;
if x<n then
  begin t:=x; x:=n; n:=t;
  end; {now |0<n<=x<d|}
@<Compute \(f)$f=\lfloor xn/d+{1\over2}\rfloor$@>@;
if f>(max_answer-a) then goto too_big;
a:=a+f;
found: if negative then negate(a);
goto done;
too_big: num_error(a);
done: fract:=a;
end;

@ The loop here preserves the following invariant relations
between |f|, |x|, |n|, and~|r|:
(i)~$f+\lfloor(xn+(r+d))/d\rfloor=\lfloor x_0n_0/d+{1\over2}\rfloor$;
(ii)~|-d<=r<0<n<=x<d|, where $x_0$, $n_0$ are the original values of~$x$
and $n$.

Notice that the computation specifies |(x-d)+x| instead of |(x+x)-d|,
because the latter could overflow.

@<Compute \(f)$f=\lfloor xn/d+{1\over2}\rfloor$@>=
f:=0; r:=(d div 2)-d; h:=-r;
loop@+begin if odd(n) then
    begin r:=r+x;
    if r>=0 then
      begin r:=r-d; incr(f);
      end;
    end;
  n:=n div 2;
  if n=0 then goto found1;
  if x<h then x:=x+x
  else  begin t:=x-d; x:=t+x; f:=f+n;
      if x<n then
        begin if x=0 then goto found1;
        t:=x; x:=n; n:=t;
        end;
    end;
  end;
found1:

@ The \.{\\gluestretch}, \.{\\glueshrink}, \.{\\gluestretchorder}, and
\.{\\glueshrinkorder} commands return the stretch and shrink components
and their orders of ``infinity'' of a glue specification.

@d glue_stretch_order_code=eTeX_int+6 {code for \.{\\gluestretchorder}}
@d glue_shrink_order_code=eTeX_int+7 {code for \.{\\glueshrinkorder}}
@d glue_stretch_code=eTeX_dim+7 {code for \.{\\gluestretch}}
@d glue_shrink_code=eTeX_dim+8 {code for \.{\\glueshrink}}

@<Generate all \eTeX...@>=
primitive("gluestretchorder",last_item,glue_stretch_order_code);
@!@:glue_stretch_order_}{\.{\\gluestretchorder} primitive@>
primitive("glueshrinkorder",last_item,glue_shrink_order_code);
@!@:glue_shrink_order_}{\.{\\glueshrinkorder} primitive@>
primitive("gluestretch",last_item,glue_stretch_code);
@!@:glue_stretch_}{\.{\\gluestretch} primitive@>
primitive("glueshrink",last_item,glue_shrink_code);
@!@:glue_shrink_}{\.{\\glueshrink} primitive@>

@ @<Cases of |last_item| for |print_cmd_chr|@>=
glue_stretch_order_code: print_esc("gluestretchorder");
glue_shrink_order_code: print_esc("glueshrinkorder");
glue_stretch_code: print_esc("gluestretch");
glue_shrink_code: print_esc("glueshrink");

@ @<Cases for fetching an integer value@>=
glue_stretch_order_code, glue_shrink_order_code:
  begin scan_normal_glue; q:=cur_val;
  if m=glue_stretch_order_code then cur_val:=stretch_order(q)
  else cur_val:=shrink_order(q);
  delete_glue_ref(q);
  end;

@ @<Cases for fetching a dimension value@>=
glue_stretch_code, glue_shrink_code:
  begin scan_normal_glue; q:=cur_val;
  if m=glue_stretch_code then cur_val:=stretch(q)
  else cur_val:=shrink(q);
  delete_glue_ref(q);
  end;

@ The \.{\\mutoglue} and \.{\\gluetomu} commands convert ``math'' glue
into normal glue and vice versa; they allow to manipulate math glue with
\.{\\gluestretch} etc.

@d mu_to_glue_code=eTeX_glue {code for \.{\\mutoglue}}
@d glue_to_mu_code=eTeX_mu {code for \.{\\gluetomu}}

@<Generate all \eTeX...@>=
primitive("mutoglue",last_item,mu_to_glue_code);
@!@:mu_to_glue_}{\.{\\mutoglue} primitive@>
primitive("gluetomu",last_item,glue_to_mu_code);
@!@:glue_to_mu_}{\.{\\gluetomu} primitive@>

@ @<Cases of |last_item| for |print_cmd_chr|@>=
mu_to_glue_code: print_esc("mutoglue");
glue_to_mu_code: print_esc("gluetomu");

@ @<Cases for fetching a glue value@>=
mu_to_glue_code: scan_mu_glue;

@ @<Cases for fetching a mu value@>=
glue_to_mu_code: scan_normal_glue;

@ @<Glob...@>=
@!last_line_fill:pointer; {the |par_fill_skip| glue node of the new paragraph}

@ When |saving_vdiscards| is positive then the glue, kern, and penalty
nodes removed by the page builder or by \.{\\vsplit} from the top of a
vertical list are saved in special lists instead of being discarded.

@d tail_page_disc==disc_ptr[copy_code] {last item removed by page builder}
@d page_disc==disc_ptr[last_box_code] {first item removed by page builder}
@d split_disc==disc_ptr[vsplit_code] {first item removed by \.{\\vsplit}}

@<Glob...@>=
@!disc_ptr:array[copy_code..vsplit_code] of pointer; {list pointers}

@ @<Set init...@>=
page_disc:=null; split_disc:=null;

@ The \.{\\pagediscards} and \.{\\splitdiscards} commands share the
command code |un_vbox| with \.{\\unvbox} and \.{\\unvcopy}, they are
distinguished by their |chr_code| values |last_box_code| and
|vsplit_code|.  These |chr_code| values are larger than |box_code| and
|copy_code|.

@<Generate all \eTeX...@>=
primitive("pagediscards",un_vbox,last_box_code);@/
@!@:page_discards_}{\.{\\pagediscards} primitive@>
primitive("splitdiscards",un_vbox,vsplit_code);@/
@!@:split_discards_}{\.{\\splitdiscards} primitive@>

@ @<Cases of |un_vbox| for |print_cmd_chr|@>=
else if chr_code=last_box_code then print_esc("pagediscards")
else if chr_code=vsplit_code then print_esc("splitdiscards")

@ @<Handle saved items and |goto done|@>=
begin vlink(tail):=disc_ptr[cur_chr]; disc_ptr[cur_chr]:=null;
goto done;
end

@ The \.{\\interlinepenalties}, \.{\\clubpenalties}, \.{\\widowpenalties},
and \.{\\displaywidowpenalties} commands allow to define arrays of
penalty values to be used instead of the corresponding single values.

@d inter_line_penalties_ptr==equiv(inter_line_penalties_loc)
@d club_penalties_ptr==equiv(club_penalties_loc)
@d widow_penalties_ptr==equiv(widow_penalties_loc)
@d display_widow_penalties_ptr==equiv(display_widow_penalties_loc)

@<Generate all \eTeX...@>=
primitive("interlinepenalties",set_shape,inter_line_penalties_loc);@/
@!@:inter_line_penalties_}{\.{\\interlinepenalties} primitive@>
primitive("clubpenalties",set_shape,club_penalties_loc);@/
@!@:club_penalties_}{\.{\\clubpenalties} primitive@>
primitive("widowpenalties",set_shape,widow_penalties_loc);@/
@!@:widow_penalties_}{\.{\\widowpenalties} primitive@>
primitive("displaywidowpenalties",set_shape,display_widow_penalties_loc);@/
@!@:display_widow_penalties_}{\.{\\displaywidowpenalties} primitive@>

@ @<Cases of |set_shape| for |print_cmd_chr|@>=
inter_line_penalties_loc: print_esc("interlinepenalties");
club_penalties_loc: print_esc("clubpenalties");
widow_penalties_loc: print_esc("widowpenalties");
display_widow_penalties_loc: print_esc("displaywidowpenalties");

@ @<Fetch a penalties array element@>=
begin scan_int;
if (equiv(m)=null)or(cur_val<0) then cur_val:=0
else  begin if cur_val>penalty(equiv(m)) then cur_val:=penalty(equiv(m));
  cur_val:=penalty(equiv(m)+cur_val);
  end;
end

@ This is needed to get the relative order of the marks code correct

@<Show the meaning of a mark node@>=
if (cur_cmd=top_bot_mark)and(cur_chr<marks_code) then
  begin print_char(":"); print_ln;
  case cur_chr of
    first_mark_code:       token_show(first_mark(0));
    bot_mark_code:         token_show(bot_mark(0));
    split_first_mark_code: token_show(split_first_mark(0));
    split_bot_mark_code:   token_show(split_bot_mark(0));
    othercases             token_show(top_mark(0));
  endcases;
end


@ The lua interface needs some extra pascal functions. The functions
themselves are quite boring, but they are handy because otherwise this
internal stuff has to be accessed from C directly, where lots of the
pascal defines are not available.

@p function get_tex_dimen_register (j:integer):scaled;
begin
  get_tex_dimen_register := dimen(j);
end;

function set_tex_dimen_register (j:integer;v:scaled):integer;
var a:small_number;
begin  {return non-nil for error}
a:=0;
word_define(j+scaled_base,v);
set_tex_dimen_register := 0;
end;

function get_tex_count_register (j:integer):scaled;
begin
  get_tex_count_register := count(j);
end;

function set_tex_count_register (j:integer;v:scaled):integer;
var a:small_number;
begin  {return non-nil for error}
a:=0;
word_define(j+count_base,v);
set_tex_count_register := 0;
end;

function get_tex_attribute_register (j:integer):scaled;
begin
  get_tex_attribute_register := attribute(j);
end;

function set_tex_attribute_register (j:integer;v:scaled):integer;
var a:small_number;
begin  {return non-nil for error}
a:=0;
word_define(j+attribute_base,v);
set_tex_attribute_register := 0;
end;

function get_tex_toks_register (j:integer):str_number;
var s:str_number;
begin
  s:="";
  if toks(j) <> min_halfword then begin
	s := tokens_to_string(toks(j));
  end;
  get_tex_toks_register := s;
end;

function set_tex_toks_register (j:integer;s:str_number):integer;
var s_pool_ptr:pool_pointer;
  ref:pointer;
  a:small_number;
  junk:pointer;
begin
  set_tex_toks_register := 0;
  s_pool_ptr := pool_ptr;
  pool_ptr := str_start_macro(s+1);
  ref := get_avail;
  junk := str_toks(str_start_macro(s));
  pool_ptr := s_pool_ptr;
  token_ref_count(ref) := 0;
  link(ref) := link(temp_token_head);
  a:=0;
  define(j+toks_base,call,ref);
  flush_str(s);
end;

function get_tex_box_register (j:integer):integer;
begin
  get_tex_box_register := box(j);
end;

function set_tex_box_register (j:integer;v:scaled):integer;
var a:small_number;
begin  {return non-nil for error}
a:=0;
eq_define(j+box_base,box_ref,v);
set_tex_box_register := 0;
end;


function get_tex_box_width (j:integer):scaled;
var q:pointer;
begin
 q := box(j);
 get_tex_box_width := 0;
 if q <> null then
    get_tex_box_width := width(q);
end;

function set_tex_box_width (j:integer;v:scaled):integer;
var q:pointer;
begin
  q := box(j);
  set_tex_box_width := 0;
  if q <> null then
    width(q) := v
  else
    set_tex_box_width := 1;
end;

function get_tex_box_height (j:integer):scaled;
var q:pointer;
begin
 q := box(j);
 get_tex_box_height := 0;
 if q <> null then
    get_tex_box_height := height(q);
end;

function set_tex_box_height (j:integer;v:scaled):integer;
var q:pointer;
begin
  q := box(j);
  set_tex_box_height := 0;
  if q <> null then
    height(q) := v
  else
    set_tex_box_height := 1;
end;

function get_tex_box_depth (j:integer):scaled;
var q:pointer;
begin
 q := box(j);
 get_tex_box_depth := 0;
 if q <> null then
    get_tex_box_depth := depth(q);
end;

function set_tex_box_depth (j:integer;v:scaled):integer;
var q:pointer;
begin
  q := box(j);
  set_tex_box_depth := 0;
  if q <> null then
    depth(q) := v
  else
    set_tex_box_depth := 1;
end;

function get_cur_v: integer;
begin
    get_cur_v := cur_page_height - cur_v;
end;

function get_cur_h: integer;
begin
    get_cur_h := cur_h;
end;

@* \[54] $\Omega$ changes.

@ Here we do the main work required for reading and interpreting
  $\Omega$ Compiled Translation Processes.

@ Here are all the instructions in our mini-assembler.
@d otp_right_output=1
@d otp_right_num=2
@d otp_right_char=3
@d otp_right_lchar=4
@d otp_right_some=5

@d otp_pback_output=6
@d otp_pback_num=7
@d otp_pback_char=8
@d otp_pback_lchar=9
@d otp_pback_some=10

@d otp_add=11
@d otp_sub=12
@d otp_mult=13
@d otp_div=14
@d otp_mod=15
@d otp_lookup=16
@d otp_push_num=17
@d otp_push_char=18
@d otp_push_lchar=19

@d otp_state_change=20
@d otp_state_push=21
@d otp_state_pop=22

@d otp_left_start=23
@d otp_left_return=24
@d otp_left_backup=25

@d otp_goto=26
@d otp_goto_ne=27
@d otp_goto_eq=28
@d otp_goto_lt=29
@d otp_goto_le=30
@d otp_goto_gt=31
@d otp_goto_ge=32
@d otp_goto_no_advance=33
@d otp_goto_beg=34
@d otp_goto_end=35

@d otp_stop=36

@
@<Glob...@>=
@!otp_init_input_start:halfword;
@!otp_init_input_last:halfword;
@!otp_init_input_end:halfword;
@!otp_i:halfword;
@!otp_init_input_buf:array[0..20000] of quarterword;

@!otp_input_start:halfword;
@!otp_input_last:halfword;
@!otp_input_end:halfword;
@!otp_input_buf:array[0..20000] of quarterword;

@!otp_output_end:halfword;
@!otp_output_buf:array[0..20000] of quarterword;

@!otp_stack_used:halfword;
@!otp_stack_last:halfword;
@!otp_stack_new:halfword;
@!otp_stack_buf:array[0..1000] of quarterword;

@!otp_pc:halfword;

@!otp_calc_ptr:halfword;
@!otp_calcs:array[0..1000] of halfword;
@!otp_state_ptr:halfword;
@!otp_states:array[0..1000] of halfword;

@!otp_input_char:halfword;
@!otp_calculated_char:halfword;
@!otp_no_input_chars:halfword;

@!otp_instruction:halfword;
@!otp_instr:halfword;
@!otp_arg:halfword;
@!otp_first_arg:halfword;
@!otp_second_arg:halfword;

@!otp_input_ocp:halfword;
@!otp_counter:halfword;

@!otp_finished:boolean;
@!otp_ext_str:integer;
@!otp_ext_str_arg:integer;
@!otp_ext_i:integer;

@
@<Initialize table...@>=

@
@<Create a buffer with character |cur_chr| and the following
  characters (if~any) and then apply the current active OCP filter
  to this buffer@>=
begin
@<Read in the buffer for treatment@>;
@<Apply the OCP to the input buffer@>;
@<Place the output buffer back on the stream@>;
goto big_switch;
end;

@ The OTP input buffer is an array of 16-bit values. 
In the future, the range |@"D800| \dots |@"DFFF| will be used for 
surrogate pairs, so it cannot be used for simple 16-bit values
like it is in Omega, so a future incompatibility with Aleph is 
unavoidable.

@<Read in the buffer for treatment@>=
begin
otp_init_input_end:=0;
while (cur_cmd=letter) or (cur_cmd=other_char) or
      (cur_cmd=char_given) or (cur_cmd=spacer) do begin
  incr(otp_init_input_end);
  if otp_init_input_end >ocp_buf_size then
    overflow_ocp_buf_size;
  { |cur_chr| can cover the full range |0..0x10FFFF| }
  if cur_chr<@"10000 then
    otp_init_input_buf[otp_init_input_end]:=cur_chr
  else begin
    otp_init_input_buf[otp_init_input_end]:=((cur_chr - @"10000) div @"400) + @"D800;
    incr(otp_init_input_end);
    if otp_init_input_end >ocp_buf_size then
      overflow_ocp_buf_size;
    otp_init_input_buf[otp_init_input_end]:=((cur_chr - @"10000) mod @"400) + @"DC00;
    end;
  get_token;
  if (cur_cmd<>letter) and (cur_cmd<>other_char) and
     (cur_cmd<>char_given) then begin
    x_token;
    if (cur_cmd=char_num) then begin
      scan_char_num; cur_cmd:=other_char; cur_chr:=cur_val;
      end;
    end;
  end;
back_input;
otp_input_end:=otp_init_input_end;
for otp_i:=0 to otp_init_input_end do begin
  otp_input_buf[otp_i]:=otp_init_input_buf[otp_i];
  end;
end

@
@<Apply the OCP to the input buffer@>=
begin
otp_input_ocp:=active_ocp(active_real);
if otp_input_ocp=0 then begin
  print_err("Null ocp being used: all input lost");
  error;
  otp_output_end:=0;
  end
else if ocp_external(otp_input_ocp)=0 then begin
  otp_input_start:=0;
  otp_input_last:=0;
  otp_stack_used:=0;
  otp_stack_last:=0;
  otp_stack_new:=0;
  otp_output_end:=0;
  otp_pc:=0;
  otp_finished:=false;
  otp_calc_ptr:=0;
  otp_calcs[otp_calc_ptr]:=0;
  otp_state_ptr:=0;
  otp_states[otp_state_ptr]:=0;
  while not otp_finished do
    @<Run the OTP program@>;
  end
else begin
  k:=0;
  if nameoffile then libcfree (nameoffile);
  otp_ext_str:=ocp_external(otp_input_ocp);
  otp_ext_str_arg:=ocp_external_arg(otp_input_ocp);
  nameoffile := xmalloc (4 + length(otp_ext_str) + length(otp_ext_str_arg));
  for otp_ext_i:=str_start_macro(otp_ext_str) to
         str_start_macro(otp_ext_str)+length(otp_ext_str)-1 do
    append_to_name(str_pool[otp_ext_i]);
  append_to_name(" ");
  for otp_ext_i:=str_start_macro(otp_ext_str_arg) to
         str_start_macro(otp_ext_str_arg)+length(otp_ext_str_arg)-1 do
    append_to_name(str_pool[otp_ext_i]);
  nameoffile[length(otp_ext_str)+length(otp_ext_str_arg)+2]:=0;
  run_external_ocp(nameoffile);
  end
end

@ The OTP output buffer is an array of 16-bit values. To convert back
to the |buffer| it has to be re-encoded into UTF-8. An incompatibility
with Aleph is unavoidable here: The range |@"D800| \dots |@"DFFF| is
used for surrogate pairs, not for simple 16-bit values.

@<Place the output buffer back on the stream@>=
begin
if (first+otp_output_end)>=ocp_buf_size then
  overflow_ocp_buf_size;
push_input; 
current_ocp_lstack:=active_lstack_no(active_real);
current_ocp_no:=active_counter(active_real);
state:=mid_line;
start:=first;
last:=start;
loc:=start;
for otp_counter:=1 to otp_output_end do begin
    { convert back to utf-8 }
	t := otp_output_buf[otp_counter];
	if otp_counter < otp_output_end then
       if ((t>=@"D800) and (t<@"DC00)) then 
	     if (otp_output_buf[otp_counter+1]>=@"DC00)
          and (otp_output_buf[otp_counter+1]<@"E000) then begin
             incr(otp_counter);
	         t := (t-@"D800) * @"400 + (otp_output_buf[otp_counter]-@"DC00) + @"10000;
           end
       else if ((t>=@"DC00) and (t<@"E000)) then 
	     if (otp_output_buf[otp_counter+1]>=@"D800)
           and (otp_output_buf[otp_counter+1]<@"DC00) then begin
             incr(otp_counter);
	         t := (otp_output_buf[otp_counter]-@"D800) * @"400 + (t-@"DC00) + @"10000;
           end;
    if t <= @"7F then
      buffer[last]:= t
    else if t<=@"7FF then begin
      buffer[last]:=@"C0 + t div @"40;
      incr(last); 
      if last=buf_size-2 then
        @<Report overflow of the input buffer, and abort@>;
      buffer[last]:=@"80 + t mod @"40;
      end
    else if t<=@"FFFF then	begin
      buffer[last]:=@"E0 + t div @"1000;
      incr(last);
      if last=buf_size-2 then
        @<Report overflow of the input buffer, and abort@>;
      buffer[last]:=@"80 + (t mod @"1000) div @"40;
      incr(last);
      if last=buf_size-2 then
        @<Report overflow of the input buffer, and abort@>;
      buffer[last]:=@"80 + (t mod @"1000) mod @"40;
      end
    else begin
      buffer[last]:=@"F0 + t div @"40000;
      incr(last);
      if last=buf_size-2 then
        @<Report overflow of the input buffer, and abort@>;
      buffer[last]:=@"80 + (t mod @"40000) div @"1000;
      incr(last);
      if last=buf_size-2 then
        @<Report overflow of the input buffer, and abort@>;
      buffer[last]:=@"80 + ((t mod @"40000) mod @"1000) div @"40;
      incr(last);
      if last=buf_size-2 then
        @<Report overflow of the input buffer, and abort@>;
      buffer[last]:=@"80 + ((t mod @"40000) mod @"1000) mod @"40;
      end;
    incr(last);
    if last=buf_size-2 then
      @<Report overflow of the input buffer, and abort@>;
  end;
limit:=last-1;
if (t>@"FFFF) then decr(limit);
if (t>@"7FF)  then decr(limit);
if (t>@"7F)   then decr(limit);
first:=last;
end

@
@d otp_cur_state==otp_states[otp_state_ptr]
@d otp_set_instruction==begin
if otp_pc>=ocp_state_no(otp_input_ocp)(otp_cur_state) then begin
  print_err("bad OCP program -- PC not valid");
  succumb;
  end;
otp_instruction:=ocp_state_entry(otp_input_ocp)(otp_cur_state)(otp_pc);
otp_instr:=otp_instruction div @"1000000;
otp_arg:=otp_instruction mod @"1000000;
end

@<Run the OTP program@>=
begin
otp_set_instruction;
case otp_instr of
  @<Run the |otp_right| instructions@>;
  @<Run the |otp_pback| instructions@>;
  @<Run the arithmetic instructions@>;
  @<Run the |otp_state| instructions@>;
  @<Run the |otp_left| instructions@>;
  @<Run the |otp_goto| instructions@>;
  @<Run the |otp_stop| instruction@>;
  othercases begin
    print_err("bad OCP program -- unknown instruction");
    succumb;
    end
  endcases;
end

@

@d otp_check_char(#)==
if (1>#) or (#>otp_no_input_chars) then begin
  print_err("right hand side of OCP expression is bad");
  succumb;
  end

@d otp_get_char(#)==begin
otp_check_char(#);
if #>otp_stack_last then begin
  otp_calculated_char:=otp_input_buf[otp_input_start+#-otp_stack_last];
  end
else begin
  otp_calculated_char:=otp_stack_buf[#];
  end;
end

@<Run the |otp_right| instructions@>=
  otp_right_output: begin
    incr(otp_output_end);
    if otp_output_end >ocp_buf_size then
      overflow_ocp_buf_size;
    otp_output_buf[otp_output_end]:=otp_calcs[otp_calc_ptr];
    decr(otp_calc_ptr);
    incr(otp_pc);
    end;
  otp_right_num: begin
    incr(otp_output_end);
    if otp_output_end >ocp_buf_size then
      overflow_ocp_buf_size;
    otp_output_buf[otp_output_end]:=otp_arg;
    incr(otp_pc);
    end;
  otp_right_char: begin
    otp_get_char(otp_arg);
    incr(otp_output_end);
    if otp_output_end >ocp_buf_size then
      overflow_ocp_buf_size;
    otp_output_buf[otp_output_end]:=otp_calculated_char;
    incr(otp_pc);
    end;
  otp_right_lchar: begin
    otp_get_char(otp_no_input_chars-otp_arg);
    incr(otp_output_end);
    if otp_output_end >ocp_buf_size then
      overflow_ocp_buf_size;
    otp_output_buf[otp_output_end]:=otp_calculated_char;
    incr(otp_pc);
    end;
  otp_right_some: begin
    otp_first_arg:=otp_arg+1;
    incr(otp_pc);
    otp_set_instruction;
    otp_second_arg:=otp_no_input_chars-otp_arg;
    for otp_counter:=otp_first_arg to otp_second_arg do begin
      otp_get_char(otp_counter);
      incr(otp_output_end);
      if otp_output_end >ocp_buf_size then
        overflow_ocp_buf_size;
      otp_output_buf[otp_output_end]:=otp_calculated_char;
      end;
    incr(otp_pc);
    end

@
@<Run the |otp_pback| instructions@>=
  otp_pback_output: begin
    incr(otp_stack_new);
    if otp_stack_new >= ocp_stack_size then
      overflow_ocp_stack_size;
    otp_stack_buf[otp_stack_new]:=otp_calcs[otp_calc_ptr];
    decr(otp_calc_ptr);
    incr(otp_pc);
    end;
  otp_pback_num: begin
    incr(otp_stack_new);
    if otp_stack_new >= ocp_stack_size then
      overflow_ocp_stack_size;
    otp_stack_buf[otp_stack_new]:=otp_arg;
    incr(otp_pc);
    end;
  otp_pback_char: begin
    otp_get_char(otp_arg);
    incr(otp_stack_new);
    if otp_stack_new >= ocp_stack_size then
      overflow_ocp_stack_size;
    otp_stack_buf[otp_stack_new]:=otp_calculated_char;
    incr(otp_pc);
    end;
  otp_pback_lchar: begin
    otp_get_char(otp_no_input_chars-otp_arg);
    incr(otp_stack_new);
    if otp_stack_new >= ocp_stack_size then
      overflow_ocp_stack_size;
    otp_stack_buf[otp_stack_new]:=otp_calculated_char;
    incr(otp_pc);
    end;
  otp_pback_some: begin
    otp_first_arg:=otp_arg+1;
    incr(otp_pc);
    otp_set_instruction;
    otp_second_arg:=otp_no_input_chars-otp_arg;
    for otp_counter:=otp_first_arg to otp_second_arg do begin
      otp_get_char(otp_counter);
      incr(otp_stack_new);
      if otp_stack_new >= ocp_stack_size then
        overflow_ocp_stack_size;
      otp_stack_buf[otp_stack_new]:=otp_calculated_char;
      end;
    incr(otp_pc);
    end
   
@
@<Run the arithmetic instructions@>=
  otp_add: begin
    otp_calcs[otp_calc_ptr-1] :=
      otp_calcs[otp_calc_ptr-1] + otp_calcs[otp_calc_ptr];
    incr(otp_pc);
    decr(otp_calc_ptr);
    end;
  otp_sub: begin
    otp_calcs[otp_calc_ptr-1] :=
      otp_calcs[otp_calc_ptr-1] - otp_calcs[otp_calc_ptr];
    incr(otp_pc);
    decr(otp_calc_ptr);
    end;
  otp_mult: begin
    otp_calcs[otp_calc_ptr-1] :=
      otp_calcs[otp_calc_ptr-1] * otp_calcs[otp_calc_ptr];
    incr(otp_pc);
    decr(otp_calc_ptr);
    end;
  otp_div: begin
    otp_calcs[otp_calc_ptr-1] :=
      otp_calcs[otp_calc_ptr-1] div otp_calcs[otp_calc_ptr];
    incr(otp_pc);
    decr(otp_calc_ptr);
    end;
  otp_mod: begin
    otp_calcs[otp_calc_ptr-1] :=
      otp_calcs[otp_calc_ptr-1] mod otp_calcs[otp_calc_ptr];
    incr(otp_pc);
    decr(otp_calc_ptr);
    end;
  otp_lookup: begin
    if otp_calcs[otp_calc_ptr]>=
       ocp_table_no(otp_input_ocp)(otp_calcs[otp_calc_ptr-1]) then begin
      print_err("bad OCP program -- table index not valid");
      succumb;
      end;
    otp_calcs[otp_calc_ptr-1]:=
    ocp_table_entry(otp_input_ocp)(otp_calcs[otp_calc_ptr-1])
                   (otp_calcs[otp_calc_ptr]);
    incr(otp_pc);
    decr(otp_calc_ptr);
    end;
  otp_push_num: begin
    incr(otp_calc_ptr);
    if otp_calc_ptr >= ocp_stack_size then
      overflow_ocp_stack_size;
    otp_calcs[otp_calc_ptr]:=otp_arg;
    incr(otp_pc);
    end;
  otp_push_char: begin
    otp_get_char(otp_arg);
    incr(otp_calc_ptr);
    if otp_calc_ptr >= ocp_stack_size then
      overflow_ocp_stack_size;
    otp_calcs[otp_calc_ptr]:=otp_calculated_char;
    incr(otp_pc);
    end;
  otp_push_lchar: begin
    otp_get_char(otp_no_input_chars-otp_arg);
    incr(otp_calc_ptr);
    if otp_calc_ptr >= ocp_stack_size then
      overflow_ocp_stack_size;
    otp_calcs[otp_calc_ptr]:=otp_calculated_char;
    incr(otp_pc);
    end
   
@
@<Run the |otp_state| instructions@>=
  otp_state_change: begin
    otp_input_start:=otp_input_last;
    for otp_counter:=1 to (otp_stack_new-otp_stack_used) do begin
      otp_stack_buf[otp_counter] := 
        otp_stack_buf[otp_counter+otp_stack_used];
      end;
    otp_stack_new:=otp_stack_new-otp_stack_used;
    otp_stack_last:=otp_stack_new;
    otp_stack_used:=0;
    otp_states[otp_state_ptr]:=otp_arg;
    otp_pc:=0;
    end;
  otp_state_push: begin
    otp_input_start:=otp_input_last;
    for otp_counter:=1 to (otp_stack_new-otp_stack_used) do begin
      otp_stack_buf[otp_counter] := 
        otp_stack_buf[otp_counter+otp_stack_used];
      end;
    otp_stack_new:=otp_stack_new-otp_stack_used;
    otp_stack_last:=otp_stack_new;
    otp_stack_used:=0;
    incr(otp_state_ptr);
    if otp_state_ptr >= ocp_stack_size then
      overflow_ocp_stack_size;
    otp_states[otp_state_ptr]:=otp_arg;
    otp_pc:=0;
    end;
  otp_state_pop: begin
    otp_input_start:=otp_input_last;
    for otp_counter:=1 to (otp_stack_new-otp_stack_used) do begin
      otp_stack_buf[otp_counter] := 
        otp_stack_buf[otp_counter+otp_stack_used];
      end;
    otp_stack_new:=otp_stack_new-otp_stack_used;
    otp_stack_last:=otp_stack_new;
    otp_stack_used:=0;
    if otp_state_ptr>0 then decr(otp_state_ptr);
    otp_pc:=0;
    end
   
@
@<Run the |otp_left| instructions@>=
  otp_left_start: begin
    otp_input_start:=otp_input_last;
    otp_input_last:=otp_input_start;
    otp_stack_used:=0;
    if (otp_stack_last=0) and (otp_input_last>=otp_input_end) then
      otp_finished:=true
    else if (otp_stack_used < otp_stack_last) then begin
      incr(otp_stack_used); {no overflow problem}
      otp_input_char:=otp_stack_buf[otp_stack_used];
      otp_no_input_chars:=1;
      incr(otp_pc);
      end
    else begin
      incr(otp_input_last); {no overflow problem}
      otp_input_char:=otp_input_buf[otp_input_last];
      otp_no_input_chars:=1;
      incr(otp_pc);
      end;
    end;
  otp_left_return: begin
    otp_input_last:=otp_input_start;
    otp_stack_used:=0;
    if (otp_stack_used < otp_stack_last) then begin
      incr(otp_stack_used); {no overflow problem}
      otp_input_char:=otp_stack_buf[otp_stack_used];
      otp_no_input_chars:=1;
      incr(otp_pc);
      end
    else begin
      incr(otp_input_last); {no overflow problem}
      otp_input_char:=otp_input_buf[otp_input_last];
      otp_no_input_chars:=1;
      incr(otp_pc);
      end;
    end;
  otp_left_backup: begin
    if otp_input_start < otp_input_last then begin
      decr(otp_input_last); otp_input_char:=otp_input_buf[otp_input_last];
      end
    else begin
      decr(otp_stack_used); otp_input_char:=otp_stack_buf[otp_stack_used];
      end;
    decr(otp_no_input_chars);
    incr(otp_pc);
    end
   
@
@<Run the |otp_goto| instructions@>=
  otp_goto: begin
    otp_pc:=otp_arg;
    end;
  otp_goto_ne: begin
    otp_first_arg:=otp_arg;
    incr(otp_pc);
    otp_set_instruction;
    if otp_input_char <> otp_first_arg then begin
      otp_pc:=otp_arg;
      end
    else begin
      incr(otp_pc);
      end;
    end;
  otp_goto_eq: begin
    otp_first_arg:=otp_arg;
    incr(otp_pc);
    otp_set_instruction;
    if otp_input_char = otp_first_arg then begin
      otp_pc:=otp_arg;
      end
    else begin
      incr(otp_pc);
      end;
    end;
  otp_goto_lt: begin
    otp_first_arg:=otp_arg;
    incr(otp_pc);
    otp_set_instruction;
    if otp_input_char < otp_first_arg then begin
      otp_pc:=otp_arg;
      end
    else begin
      incr(otp_pc);
      end;
   end;
  otp_goto_le: begin
    otp_first_arg:=otp_arg;
    incr(otp_pc);
    otp_set_instruction;
    if otp_input_char <= otp_first_arg then begin
      otp_pc:=otp_arg;
      end
    else begin
      incr(otp_pc);
      end;
    end;
  otp_goto_gt: begin
    otp_first_arg:=otp_arg;
    incr(otp_pc);
    otp_set_instruction;
    if otp_input_char > otp_first_arg then begin
      otp_pc:=otp_arg;
      end
    else begin
      incr(otp_pc);
      end;
    end;
  otp_goto_ge: begin
    otp_first_arg:=otp_arg;
    incr(otp_pc);
    otp_set_instruction;
    if otp_input_char >= otp_first_arg then begin
      otp_pc:=otp_arg;
      end
    else begin
      incr(otp_pc);
      end;
    end;
  otp_goto_no_advance: begin
    if (otp_stack_used < otp_stack_last) then begin
      incr(otp_stack_used); {no overflow problem}
      otp_input_char:=otp_stack_buf[otp_stack_used];
      incr(otp_no_input_chars); {no overflow problem}
      incr(otp_pc);
      end
    else if otp_input_last>=otp_input_end then begin
      otp_pc:=otp_arg;
      end
    else begin
      incr(otp_input_last); {no overflow problem}
      otp_input_char:=otp_input_buf[otp_input_last];
      incr(otp_no_input_chars); {no overflow problem}
      incr(otp_pc);
      end;
    end;
  otp_goto_beg: begin
    if otp_input_last=0 then begin
      otp_pc:=otp_arg;
      end
    else begin
      incr(otp_pc);
      end;
    end;
  otp_goto_end: begin
    if otp_input_last>=otp_input_end then begin
      otp_pc:=otp_arg;
      end
    else begin
      incr(otp_pc);
      end;
    end
   
@
@<Run the |otp_stop| instruction@>=
  otp_stop: begin
    otp_input_start:=otp_input_last;
    for otp_counter:=1 to (otp_stack_new-otp_stack_used) do begin
      otp_stack_buf[otp_counter] := 
        otp_stack_buf[otp_counter+otp_stack_used];
      end;
    otp_stack_new:=otp_stack_new-otp_stack_used;
    otp_stack_last:=otp_stack_new;
    otp_stack_used:=0;
    otp_pc:=0;
    end
   
@ @<Put each...@>=
primitive("ocp", def_ocp, 0);
primitive("externalocp", def_ocp, 1);
primitive("ocplist", def_ocp_list, 0);
primitive("pushocplist", push_ocp_list, 0);
primitive("popocplist", pop_ocp_list, 0);
primitive("clearocplists", clear_ocp_lists, 0);
primitive("addbeforeocplist", ocp_list_op, add_before_op);
primitive("addafterocplist", ocp_list_op, add_after_op);
primitive("removebeforeocplist", ocp_list_op, remove_before_op);
primitive("removeafterocplist", ocp_list_op, remove_after_op);
primitive("ocptracelevel", ocp_trace_level, 0);
equiv(ocp_trace_level_base):=0;

@ @<Cases of |print_cmd_chr|...@>=
set_ocp: begin
  print("select ocp "); 
  slow_print(ocp_name(chr_code)); 
  end;
def_ocp: if cur_chr=0 then print_esc("ocp")
  else print_esc("externalocp");
set_ocp_list: print("select ocp list "); 
def_ocp_list:  print_esc("ocplist");
push_ocp_list: print_esc("pushocplist");
pop_ocp_list:  print_esc("popocplist");
clear_ocp_lists: print_esc("clearocplists");
ocp_list_op:
  if chr_code=add_before_op then print_esc("addbeforeocplist")
  else if chr_code=add_after_op then print_esc("addafterocplist")
  else if chr_code=remove_before_op then print_esc("removebeforeocplist")
  else {|chr_code|=|remove_after_op|} print_esc("removeafterocplist");
ocp_trace_level: print_esc("ocptracelevel");

@ @<Assignments@>=
set_ocp: begin
  print_err("To use ocps, use the "); print_esc("pushocplist"); 
  print(" primitive");print_ln
  end;
def_ocp: new_ocp(a);
set_ocp_list: begin
  print_err("To use ocp lists, use the "); 
  print_esc("pushocplist"); print(" primitive");print_ln
  end;
def_ocp_list: new_ocp_list(a);
push_ocp_list: do_push_ocp_list(a);
pop_ocp_list: do_pop_ocp_list(a);
clear_ocp_lists: do_clear_ocp_lists(a);
ocp_list_op: begin
  print_err("To build ocp lists, use the ");
  print_esc("ocplist"); print(" primitive"); print_ln
  end;
ocp_trace_level: begin scan_optional_equals; scan_int;
  if cur_val<>0 then cur_val:=1;
  define(ocp_trace_level_base, data, cur_val);
  end;

@ @<Declare subprocedures for |prefixed_command|@>=
procedure new_ocp(@!a:small_number);
label common_ending;
var u:pointer; {user's ocp identifier}
@!f:internal_ocp_number; {runs through existing ocps}
@!t:str_number; {name for the frozen ocp identifier}
@!old_setting:0..max_selector; {holds |selector| setting}
@!flushable_string:str_number; {string not yet referenced}
@!external_ocp:boolean; {external binary file}
begin if job_name=0 then open_log_file;
  {avoid confusing \.{texput} with the ocp name}
@.texput@>
if cur_chr=1 then external_ocp:=true
else external_ocp:=false;
get_r_token; u:=cur_cs;
if u>=hash_base then t:=text(u)
else if u=null_cs then t:="OCP"
else  begin old_setting:=selector; selector:=new_string;
  print("OCP"); print(u-active_base); selector:=old_setting;
@.OCPx@>
  str_room(1); t:=make_string;
  end;
define(u,set_ocp,null_ocp); scan_optional_equals; scan_file_name;
@<If this ocp has already been loaded, set |f| to the internal
  ocp number and |goto common_ending|@>;
f:=read_ocp_info(u,cur_name,cur_area,cur_ext,external_ocp);
common_ending: 
equiv(u):=f; eqtb[ocp_id_base+f] := eqtb[u];
text(ocp_id_base+f) := t;
if equiv(ocp_trace_level_base)=1 then begin
  print_nl(""); print_esc("ocp"); print_esc(t); print("="); print(cur_name);
  end;
end;

@ When the user gives a new identifier to a ocp that was previously loaded,
the new name becomes the ocp identifier of record. OCP names `\.{xyz}' and
`\.{XYZ}' are considered to be different.

@<If this ocp has already been loaded...@>=
flushable_string:=str_ptr-1;
for f:=ocp_base+1 to ocp_ptr do
  if str_eq_str(ocp_name(f),cur_name)and str_eq_str(ocp_area(f),cur_area) then
    begin
    if cur_name=flushable_string then begin
      flush_string; cur_name:=ocp_name(f);
      end;
    goto common_ending
    end

@ @<Declare subprocedures for |prefixed_command|@>=
procedure new_ocp_list(@!a:small_number);
var u:pointer; {user's ocp list identifier}
@!f:internal_ocp_list_number; {runs through existing ocp lists}
@!t:str_number; {name for the frozen ocp list identifier}
@!old_setting:0..max_selector; {holds |selector| setting}
begin if job_name=0 then open_log_file;
  {avoid confusing \.{texput} with the ocp list name}
@.texput@>
get_r_token; u:=cur_cs;
if u>=hash_base then t:=text(u)
else if u=null_cs then t:="OCPLIST"
else  begin old_setting:=selector; selector:=new_string;
  print("OCPLIST"); print(u-active_base); selector:=old_setting;
@.OCPx@>
  str_room(1); t:=make_string;
  end;
define(u,set_ocp_list,null_ocp_list); scan_optional_equals; 
f:=read_ocp_list;
    equiv(u) := f; eqtb[ocp_list_id_base+f] := eqtb[u];
    text(ocp_list_id_base+f) := t;
if equiv(ocp_trace_level_base)=1 then begin
  print_nl(""); print_esc("ocplist"); print_esc(t); print("=");
  print_ocp_list(ocp_list_list[f]);
  end;
end;

@ @<Declare subprocedures for |prefixed_command|@>=
procedure do_push_ocp_list(@!a:small_number);
var ocp_list_no:halfword;
    old_number:halfword;
    i:integer;
begin
scan_ocp_list_ident; ocp_list_no:=cur_val;
old_number:=equiv(ocp_active_number_base);
define(ocp_active_base+old_number, data, ocp_list_no);
define(ocp_active_number_base, data, (old_number+1));

if equiv(ocp_trace_level_base)=1 then begin
  print_nl("New active ocp list: {");
  for i:=old_number downto 0 do begin
    print_esc(ocp_list_id_text(equiv(ocp_active_base+i)));
    print("="); print_ocp_list(ocp_list_list[equiv(ocp_active_base+i)]);
    if i<>0 then print(",");
    end;
  print("}");
  end;

active_compile;
define(ocp_active_min_ptr_base, data, active_min_ptr);
define(ocp_active_max_ptr_base, data, active_max_ptr);
end;

@ @<Declare subprocedures for |prefixed_command|@>=
procedure do_pop_ocp_list(@!a:small_number);
var old_number:halfword;
    i:integer;
begin
old_number:=equiv(ocp_active_number_base);
if old_number=0 then begin
  print_err("No active ocp lists to be popped");
  end
else
  define(ocp_active_number_base, data, (old_number-1));

if equiv(ocp_trace_level_base)=1 then begin
  print_nl("New active ocp list: {");
  for i:=(old_number-2) downto 0 do begin
    print_esc(ocp_list_id_text(equiv(ocp_active_base+i)));
    print("="); print_ocp_list(ocp_list_list[equiv(ocp_active_base+i)]);
    if i<>0 then print(",");
    end;
  print("}");
  end;

active_compile;
define(ocp_active_min_ptr_base, data, active_min_ptr);
define(ocp_active_max_ptr_base, data, active_max_ptr);
end;

@ @<Declare subprocedures for |prefixed_command|@>=
procedure do_clear_ocp_lists(@!a:small_number);
begin
define(ocp_active_number_base, data, 0);
active_compile;
define(ocp_active_min_ptr_base, data, active_min_ptr);
define(ocp_active_max_ptr_base, data, active_max_ptr);
end;


@* \[54] System-dependent changes.
This section should be replaced, if necessary, by any special
modifications of the program
that are necessary to make \TeX\ work at a particular installation.
It is usually best to design your change file so that all changes to
previous sections preserve the section numbering; then everybody's version
will be consistent with the published program. More extensive changes,
which introduce new sections, can be inserted here; then only the index
itself will get a new section number.
@^system dependencies@>

@* \[55] Index.
Here is where you can find all uses of each identifier in the program,
with underlined entries pointing to where the identifier was defined.
If the identifier is only one letter long, however, you get to see only
the underlined entries. {\sl All references are to section numbers instead of
page numbers.}

This index also lists error messages and other aspects of the program
that you might want to look up some day. For example, the entry
for ``system dependencies'' lists all sections that should receive
special attention from people who are installing \TeX\ in a new
operating environment. A list of various things that can't happen appears
under ``this can't happen''. Approximately 40 sections are listed under
``inner loop''; these account for about 60\pct! of \TeX's running time,
exclusive of input and output.