From ad547a6b5986815fda458221149728d9d9ab1d87 Mon Sep 17 00:00:00 2001 From: Karl Berry Date: Thu, 25 Feb 2021 19:22:25 +0000 Subject: restore Build,TODO from r57911 git-svn-id: svn://tug.org/texlive/trunk@57915 c570f23f-e606-0410-a88d-b1316a301751 --- Build/source/texk/web2c/pdftexdir/pdftex.web | 39995 +++++++++++++++++++++++++ 1 file changed, 39995 insertions(+) create mode 100644 Build/source/texk/web2c/pdftexdir/pdftex.web (limited to 'Build/source/texk/web2c/pdftexdir/pdftex.web') diff --git a/Build/source/texk/web2c/pdftexdir/pdftex.web b/Build/source/texk/web2c/pdftexdir/pdftex.web new file mode 100644 index 00000000000..4ae1f20716f --- /dev/null +++ b/Build/source/texk/web2c/pdftexdir/pdftex.web @@ -0,0 +1,39995 @@ +% Copyright 1996-2021 Han Th\^e\llap{\raise 0.5ex\hbox{\'{}}} Th\`anh, +% + +% This file is part of pdfTeX. + +% pdfTeX 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. + +% pdfTeX 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 +% this program. If not, see . + +% e-TeX is copyright (C) 1999-2015 by P. Breitenlohner (1994,98 by the NTS +% team); all rights are reserved. Copying of this file is authorized only if +% (1) you are P. Breitenlohner, or if (2) you make absolutely no changes to +% your copy. (Programs such as TIE allow the application of several change +% files to tex.web; the master files tex.web and etex.ch should stay intact.) + +% See etex_gen.tex for hints on how to install this program. +% And see etripman.tex for details about how to validate it. + +% 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). +% Version 3.1415926 was a general cleanup with minor fixes (February 2008). +% Version 3.14159265 was similar (January 2014). +% Version 3.141592653 was similar but more extensive (January 2021). + +% A preliminary version of TeX--XeT was released in April 1992. +% TeX--XeT version 1.0 was released in June 1992, +% version 1.1 prevented arith overflow in glue computation (Oct 1992). +% A preliminary e-TeX version 0.95 was operational in March 1994. +% Version 1.0beta was released in May 1995. +% Version 1.01beta fixed bugs in just_copy and every_eof (December 1995). +% Version 1.02beta allowed 256 mark classes (March 1996). +% Version 1.1 changed \group{type,level} -> \currentgroup{type,level}, +% first public release (October 1996). +% Version 2.0 development was started in March 1997; +% fixed a ligature-\beginR bug in January 1998; +% was released in March 1998. +% Version 2.1 fixed a \marks bug (when min_halfword<>0) (January 1999). +% Version 2.2 development was started in Feb 2003; released in Oct 2004. +% fixed a bug in sparse array handling (0=>null), Jun 2002; +% fixed a bug in \lastnodetype (cur_val=>cur_val_level) +% reported by Hartmut Henkel , +% fix by Fabrice Popineau , +% Jan 2004; +% another bug in sparse array handling (cur_ptr=>cur_chr) +% reported by Taco Hoekwater , Jul 2004; +% fixed a sparse array reference count bug (\let,\futurelet), +% fix by Bernd Raichle , Aug 2004; +% reorganized handling of banner, additional token list and +% integer parameters, and similar in order to reduce the +% interference between eTeX, pdfTeX, and web2c change files. +% adapted to tex.web 3.141592, revised glue rounding for mixed +% direction typesetting; +% fixed a bug in the revised glue rounding code, detected by +% Tigran Aivazian , Oct 2004. +% Version 2.3 development was started in Feb 2008; released in Apr 2011. +% fixed a bug in hyph_code handling (\savinghyphcodes) +% reported by Vladimir Volovich , Feb 2008. +% fixed the error messages for improper use of \protected, +% reported by Heiko Oberdiek +% , May 2010. +% some rearrangements to reduce interferences between +% e-TeX and pTeX, in part suggested by Hironori Kitagawa +% , Mar 2011. +% Version 2.4 fixed an uninitialized line number bug, released in May 2012. +% Version 2.5 development was started in Aug 2012; released in Feb 2013. +% better tracing of font definitions, reported by +% Bruno Le Floch , Jul 2012. +% Version 2.6 development was started in Mar 2013; released in ??? 201?. +% enable hyphenation of text between \beginL and \endL or +% between \beginR and \endR, problem reported by +% Vafa Khalighi , Nov 2013. +% better handling of right-to-left text -- to be done. + +% Although considerable effort has been expended to make the e-TeX program +% correct and reliable, no warranty is implied; the author disclaims 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 author hopes 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\eTeX{$\varepsilon$-\TeX} +\font\revrm=xbmc10 % for right-to-left text +% to generate xbmc10 (i.e., reflected cmbx10) use a file +% xbmc10.mf containing: +%+++++++++++++++++++++++++++++++++++++++++++++++++ +% if unknown cmbase: input cmbase fi +% extra_endchar := extra_endchar & +% "currentpicture:=currentpicture " & +% "reflectedabout((.5[l,r],0),(.5[l,r],1));"; +% input cmbx10 +%+++++++++++++++++++++++++++++++++++++++++++++++++ +\ifx\beginL\undefined % this is TeX + \def\XeT{X\kern-.125em\lower.5ex\hbox{E}\kern-.1667emT} + \def\TeXeT{\TeX-\hbox{\revrm \XeT}} % for TeX-XeT + \def\TeXXeT{\TeX-\hbox{\revrm -\XeT}} % for TeX--XeT +\else + \ifx\eTeXversion\undefined % this is \TeXeT + \def\TeXeT{\TeX-{\revrm\beginR\TeX\endR}} % for TeX-XeT + \def\TeXXeT{\TeX-{\revrm\beginR\TeX-\endR}} % for TeX--XeT + \else % this is \eTeX + \def\TeXeT{\TeX-{\TeXXeTstate=1\revrm\beginR\TeX\endR}} % for TeX-XeT + \def\TeXXeT{\TeX-{\TeXXeTstate=1\revrm\beginR\TeX-\endR}} % for TeX--XeT + \fi +\fi +\def\PASCAL{Pascal} +\def\pdfTeX{pdf\TeX} +\def\pdfeTeX{pdf\eTeX} +\def\PDF{PDF} +\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{\pdfTeX} +% system dependent redefinitions of \title should come later +% and should use: +% \toks0=\expandafter{\title} +% \edef\title{...\the\toks0...} +\let\maybe=\iftrue % 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 "" +\def\gglob{20, 26} % this should be the next two sections of "" + +@* \[1] Introduction. +This is \eTeX, a program derived from and extending the capabilities of +\TeX, a document compiler intended to produce typesetting of high +quality. +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 +@^Trabb Pardo, Luis Isidoro@> +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=2 { \.{\\eTeXversion} } +@d eTeX_revision==".6" { \.{\\eTeXrevision} } +@d eTeX_version_string=='-2.6' {current \eTeX\ version} +@# +@d eTeX_banner=='This is e-TeX, Version 3.141592653',eTeX_version_string + {printed when \eTeX\ starts} +@# +@d pdftex_version==140 { \.{\\pdftexversion} } +@d pdftex_revision=="22" { \.{\\pdftexrevision} } +@d pdftex_version_string=='-1.40.22' {current \pdfTeX\ version} +@# +@d pdfTeX_banner=='This is pdfTeX, Version 3.141592653',eTeX_version_string,pdftex_version_string + {printed when \pdfTeX\ starts} +@# +@d TeX_banner=='This is TeX, Version 3.141592653' {printed when \TeX\ starts} +@# +@d banner==pdfTeX_banner +@# +@d TEX==PDFTEX {change program name into |PDFTEX|} +@# +@d TeXXeT_code=0 {the \TeXXeT\ feature is optional} +@# +@d eTeX_states=1 {number of \eTeX\ state variables in |eqtb|} + +@ 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 and 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. +@:PASCAL H}{\ph@> +@^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@>@@/ +program TEX; {all file names are defined dynamically} +label @@/ +const @@/ +mtype @@/ +var @@/ +@# +procedure initialize; {this procedure gets things started properly} + var @@/ + begin @@; + end;@# +@t\4@>@@/ +@t\4@>@@/ + +@ 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} + +@= +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}, +\.{\\tracingpages}, and \.{\\tracingrestores}. +@^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 + +@= +@@/ +@!init @@;@+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. +@:PASCAL H}{\ph@> +@^system dependencies@> +@^overflow in arithmetic@> + +@= +@{@&$C-,A+,D-@} {no range check, catch arithmetic overflow, no debug overhead} +@!debug @{@&$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!) +@:PASCAL H}{\ph@> + +@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@> + +@= +@!mem_max=30000; {greatest index in \TeX's internal |mem| array; + must be strictly less than |max_halfword|; + must be equal to |mem_top| in \.{INITEX}, otherwise |>=mem_top|} +@!mem_min=0; {smallest index in \TeX's internal |mem| array; + must be |min_halfword| or more; + must be equal to |mem_bot| in \.{INITEX}, otherwise |<=mem_bot|} +@!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} +@!font_max=75; {maximum internal font number; must not exceed |max_quarterword| + and must be at most |font_base+256|} +@!font_mem_size=20000; {number of words of |font_info| for all fonts} +@!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|} +@!trie_size=8000; {space for hyphenation patterns; should be larger for + \.{INITEX} than it is in production versions of \TeX} +@!trie_op_size=500; {space for ``opcodes'' in the hyphenation patterns} +@!dvi_buf_size=800; {size of the output buffer; must be a multiple of 8} +@!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@> + +@ 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 mem_bot=0 {smallest index in the |mem| array dumped by \.{INITEX}; + must not be less than |mem_min|} +@d mem_top==30000 {largest index in the |mem| array dumped by \.{INITEX}; + must be substantially larger than |mem_bot| + and not greater than |mem_max|} +@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 |(mem_max-mem_min)/10|} +@d hash_prime=1777 {a prime number equal to about 85\pct! of |hash_size|} +@d hyph_size=307 {another prime; the number of \.{\\hyphenation} exceptions} +@^system dependencies@> + +@ 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. + +@= +@!bad:integer; {is some ``constant'' wrong?} + +@ Later on we will say `\ignorespaces|if mem_max>=max_halfword then bad:=14|', +or something similar. (We can't do that until |max_halfword| has been defined.) + +@= +bad:=0; +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 mem_bot+1100>mem_top then bad:=4; +if hash_prime>hash_size then bad:=5; +if max_in_open>=128 then bad:=6; +if mem_top<256+11 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 == {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 eight-bit +code that includes standard 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. + +@= +@!ASCII_code=0..255; {eight-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|} + +@= +@!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. + +@= +@!xord: array [text_char] of ASCII_code; + {specifies conversion of input characters} +@!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@> + +@= +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@> + +@= +for i:=0 to @'37 do xchr[i]:=' '; +for i:=@'177 to @'377 do xchr[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= +for i:=first_text_char to last_text_char do xord[chr(i)]:=invalid_code; +for i:=@'200 to @'377 do xord[xchr[i]]:=i; +for i:=0 to @'176 do xord[xchr[i]]:=i; + +@* \[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. + +@= +@!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 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 |name_of_file| 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 +|name_of_file|. +@^system dependencies@> + +@= +@!name_of_file:packed array[1..file_name_size] of char;@;@/ + {on some systems this may be a \&{record} variable} +@!name_length:0..file_name_size;@/{this many characters are actually + relevant in |name_of_file| (the rest are blank)} + +@ 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 +|name_of_file| 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,name_of_file,'/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,name_of_file,'/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,name_of_file,'/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,name_of_file,'/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,name_of_file,'/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,name_of_file,'/O'); w_open_out:=rewrite_OK(f); +end; + +@ Files can be closed with the \ph\ routine `|close(f)|', which +@:PASCAL H}{\ph@> +@^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; + +@ 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 +|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. + +@= +@!buffer:array[0..buf_size] of 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 |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 |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 |input_ln|, the condition +|first + +@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 + @; + end; + buffer[last]:=xord[f^]; get(f); incr(last); + if buffer[last-1]<>" " then last_nonblank:=last; + end; + last:=last_nonblank; input_ln:=true; + 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@> + +@= +@!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|. +@:PASCAL H}{\ph@> +@^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: +@:PASCAL H}{\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.) + +@= +if format_ident=0 then + begin write_ln(term_out,'Buffer size exceeded!'); goto final_end; +@.Buffer size exceeded@> + end +else begin cur_input.loc_field:=first; cur_input.limit_field:=last-1; + overflow("buffer size",buf_size); +@:TeX capacity exceeded buffer size}{\quad buffer size@> + end + +@ 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 + +@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 write_ln(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 +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~255. String number 46 will presumably be the +single character `\..'; but some ASCII codes have no standard visible +representation, and \TeX\ sometimes needs to be able to print an arbitrary +ASCII character, so the first 256 strings are used to specify exactly what +should be printed for each of the 256 possibilities. + +Elements of the |str_pool| array must be ASCII codes that can actually +be printed; i.e., they must have an |xchr| equivalent in the local +character set. (This restriction applies only to preloaded strings, +not to those generated dynamically by the user.) + +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. +@^system dependencies@> + +@d si(#) == # {convert from |ASCII_code| to |packed_ASCII_code|} +@d so(#) == # {convert from |packed_ASCII_code| to |ASCII_code|} + +@= +@!pool_pointer = 0..pool_size; {for variables that point into |str_pool|} +@!str_number = 0..max_strings; {for variables that point into |str_start|} +@!packed_ASCII_code = 0..255; {elements of |str_pool| array} + +@ @= +@!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[#+1]-str_start[#]) {the number of characters + in string number \#} + +@ The length of the current string is called |cur_length|: + +@d cur_length == (pool_ptr - str_start[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(#) == {make sure that the pool hasn't overflowed} + begin if pool_ptr+# > pool_size then + overflow("pool size",pool_size-init_pool_ptr); +@:TeX capacity exceeded pool size}{\quad pool size@> + 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 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[str_ptr]:=pool_ptr; +make_string:=str_ptr-1; +end; + +@ To destroy the most recently made string, we say |flush_string|. + +@d flush_string==begin decr(str_ptr); pool_ptr:=str_start[str_ptr]; + 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} +@!result: boolean; {result of comparison} +begin j:=str_start[s]; +while jbuffer[k] then + begin result:=false; goto not_found; + end; + incr(j); incr(k); + 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 not_found; {loop exit} +var j,@!k: pool_pointer; {running indices} +@!result: boolean; {result of comparison} +begin result:=false; +if length(s)<>length(t) then goto not_found; +j:=str_start[s]; k:=str_start[t]; +while jstr_pool[k] then goto not_found; + incr(j); incr(k); + end; +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@> + +@p @!init function get_strings_started:boolean; {initializes the string pool, + but returns |false| if something goes wrong} +label done,exit; +var k,@!l:0..255; {small indices or counters} +@!m,@!n:text_char; {characters input from |pool_file|} +@!g:str_number; {garbage} +@!a:integer; {accumulator for check sum} +@!c:boolean; {check sum has been checked} +begin pool_ptr:=0; str_ptr:=0; str_start[0]:=0; +@; +@; +exit:end; +tini + +@ @d app_lc_hex(#)==l:=#; + if l<10 then append_char(l+"0")@+else append_char(l-10+"a") + +@= +for k:=0 to 255 do + begin if (@) then + begin append_char("^"); append_char("^"); + if k<@'100 then append_char(k+@'100) + else if k<@'200 then append_char(k-@'100) + else begin app_lc_hex(k div 16); app_lc_hex(k mod 16); + end; + end + else append_char(k); + g:=make_string; + end + +@ 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}. + +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, @'136, @'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@> + +@= + (k<" ")or(k>"~") + +@ When the \.{WEB} system program called \.{TANGLE} processes the \.{TEX.WEB} +description that you are now reading, it outputs the \PASCAL\ program +\.{TEX.PAS} and also a string pool file called \.{TEX.POOL}. The \.{INITEX} +@.WEB@>@.INITEX@> +program reads the latter file, where each string appears as a two-digit decimal +length followed by the string itself, and the information is recorded in +\TeX's string memory. + +@= +@!init @!pool_file:alpha_file; {the string-pool file output by \.{TANGLE}} +tini + +@ @d bad_pool(#)==begin wake_up_terminal; write_ln(term_out,#); + a_close(pool_file); get_strings_started:=false; return; + end +@= +name_of_file:=pool_name; {we needn't set |name_length|} +if a_open_in(pool_file) then + begin c:=false; + repeat @; + until c; + a_close(pool_file); get_strings_started:=true; + end +else bad_pool('! I can''t read TEX.POOL.') +@.I can't read TEX.POOL@> + +@ @= +begin if eof(pool_file) then bad_pool('! TEX.POOL has no check sum.'); +@.TEX.POOL has no check sum@> +read(pool_file,m,n); {read two digits of string length} +if m='*' then @ +else begin if (xord[m]<"0")or(xord[m]>"9")or@| + (xord[n]<"0")or(xord[n]>"9") then + bad_pool('! TEX.POOL line doesn''t begin with two digits.'); +@.TEX.POOL line doesn't...@> + l:=xord[m]*10+xord[n]-"0"*11; {compute the length} + if pool_ptr+l+string_vacancies>pool_size then + bad_pool('! You have to increase POOLSIZE.'); +@.You have to increase POOLSIZE@> + for k:=1 to l do + begin if eoln(pool_file) then m:=' '@+else read(pool_file,m); + append_char(xord[m]); + end; + read_ln(pool_file); g:=make_string; + end; +end + +@ The \.{WEB} operation \.{@@\$} denotes the value that should be at the +end of this \.{TEX.POOL} file; any other value means that the wrong pool +file has been loaded. +@^check sum@> + +@= +begin a:=0; k:=1; +loop@+ begin if (xord[n]<"0")or(xord[n]>"9") then + bad_pool('! TEX.POOL check sum doesn''t have nine digits.'); +@.TEX.POOL check sum...@> + a:=10*a+xord[n]-"0"; + if k=9 then goto done; + incr(k); read(pool_file,n); + end; +done: if a<>@$ then bad_pool('! TEX.POOL doesn''t match; TANGLE me again.'); +@.TEX.POOL doesn't match@> +c:=true; +end + +@* \[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} + +@= +@!log_file : alpha_file; {transcript of \TeX\ session} +@!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 ASCII_code; {circular buffer for + pseudoprinting} +@!trick_count: integer; {threshold for pseudoprinting, explained later} +@!first_count: integer; {another variable for pseudoprinting} + +@ @= +selector:=term_only; tally:=0; term_offset:=0; file_offset:=0; + +@ 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(#)==write_ln(term_out,#) +@d wterm_cr==write_ln(term_out) +@d wlog(#)==write(log_file,#) +@d wlog_ln(#)==write_ln(log_file,#) +@d wlog_cr==write_ln(log_file) + +@ To end a line of text output, we call |print_ln|. + +@= +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 write_ln(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 +|input_ln|. All printing comes through |print_ln| or |print_char|. + +@= +procedure print_char(@!s:ASCII_code); {prints a single character} +label exit; +begin if @ then + if selector + +@= +procedure print(@!s:integer); {prints string |s|} +label exit; +var j:pool_pointer; {current character code position} +@!nl:integer; {new-line character to restore} +begin if s>=str_ptr then s:="???" {this can't happen} +@.???@> +else if s<256 then + if s<0 then s:="???" {can't happen} + else begin if selector>pseudo then + begin print_char(s); return; {internal strings are not expanded} + end; + if (@) then + if selector= +procedure slow_print(@!s:integer); {prints string |s|} +var j:pool_pointer; {current character code position} +begin if (s>=str_ptr) or (s<256) then print(s) +else begin j:=str_start[s]; + while j + +@= +wterm(banner); +if format_ident=0 then wterm_ln(' (no format preloaded)') +else begin slow_print(format_ident); print_ln; + end; +update_terminal; + +@ The procedure |print_nl| is like |print|, but it makes sure that the +string appears at the beginning of a new line. + +@= +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; + +@ The procedure |print_esc| prints a string that is preceded by +the user's escape character (which is usually a backslash). + +@= +procedure print_esc(@!s:str_number); {prints escape character, then |s|} +var c:integer; {the escape character code} +begin @; +if c>=0 then if c<256 then print(c); +slow_print(s); +end; + +@ An array of digits in the range |0..15| is printed by |print_the_digs|. + +@= +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. + +@= +procedure print_int(@!n:longinteger); {prints an integer in decimal form} +var k:0..23; {index to current digit; we assume that $\vert n\vert<10^{23}$} +@!m:longinteger; {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 + +@ 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["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[str_ptr]; +while j +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(#); + end + +@= +@!interaction:batch_mode..error_stop_mode; {current level of interaction} + +@ @=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). + +@= +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} + +@= +@!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. + +@= +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. + +@= +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} + +@= +@!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?} + +@ @= +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. + +@= +procedure jump_out; +begin goto end_of_TEX; +end; + +@ Here now is the general |error| routine. + +@= +procedure error; {completes the job of error reporting} +label continue,exit; +var c:ASCII_code; {what the user types} +@!s1,@!s2,@!s3,@!s4:integer; + {used to save global variables when deleting tokens} +begin if history; +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; +@; +exit:end; + +@ @= +loop@+begin continue: if interaction<>error_stop_mode then return; + 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} + @; + 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@> + +@= +case c of +"0","1","2","3","4","5","6","7","8","9": if deletions_allowed then + @; +@t\4\4@>@;@+@!debug "D": begin debug_help; goto continue;@+end;@+gubed@/ +"E": if base_ptr>0 then if input_stack[base_ptr].name_field>=256 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": @; +"I":@; +"Q","R","S":@; +"X":begin interaction:=scroll_mode; jump_out; + end; +othercases do_nothing +endcases;@/ +@ + +@ @= +begin print("Type to proceed, S to scroll future error messages,");@/ +@.Type to proceed...@> +print_nl("R to run without stopping, Q to run quietly,");@/ +print_nl("I to insert something, "); +if base_ptr>0 then if input_stack[base_ptr].name_field>=256 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@> + +@= +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. + +@= +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. + +@= +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 + +@ @= +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 + +@ @= +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 + +@= +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. + +@= +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; + +@ 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@> + +@= +procedure confusion(@!s:str_number); + {consistency check violated; |s| tells where} +begin normalize_selector; +if history + 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@> + +@d check_interrupt==begin if interrupt<>0 then pause_for_instructions; + end + +@= +@!interrupt:integer; {should \TeX\ pause for instructions?} +@!OK_to_interrupt:boolean; {should interrupts be observed?} + +@ @= +interrupt:=0; OK_to_interrupt:=true; + +@ 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 an instruction 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} + +@= +@!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}funity 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. + +@= +@!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|} + +@= +@!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 \MP. 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. + +@= +@!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 \MF\ 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; + @; + 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 + +@= +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 @=0| and |q>0|@>; +if f; +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; + +@ @=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@> + +@= +p:=fraction_half; {that's $2^{27}$; the invariants hold now with $k=28$} +if q= +@!two_to_the:array[0..30] of integer; {powers of two} +@!spec_log:array[1..28] of integer; {special logarithms} + + +@ @= +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 @ +else begin y:=1302456956+4-100; {$14\times2^{27}\ln2\approx1302456956.421063$} + z:=27595+6553600; {and $2^{16}\times .421063\approx 27595$} + while xfraction_four+4 do + @; + m_log:=y div 8; + end; +end; + +@ @= +begin z:=((x-1) div two_to_the[k])+1; {$z=\lceil x/2^k\rceil$} +while x= +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 @=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; + +@ @= +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=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)=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. + +Since we are assuming 32-bit integers, a halfword must contain at least +16 bits, and a quarterword must contain at least 8 bits. +@^system dependencies@> +But it doesn't hurt to have more bits; for example, with enough 36-bit +words you might be able to have |mem_max| as large as 262142, which is +eight times as much memory as anybody had during the first four years of +\TeX's existence. + +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. + +@d min_quarterword=0 {smallest allowable value in a |quarterword|} +@d max_quarterword=255 {largest allowable value in a |quarterword|} +@d min_halfword==0 {smallest allowable value in a |halfword|} +@d max_halfword==65535 {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): + +@= +init if (mem_min<>mem_bot)or(mem_max<>mem_top) then bad:=10;@+tini@;@/ +if (mem_min>mem_bot)or(mem_max0)or(max_quarterword<127) then bad:=11; +if (min_halfword>0)or(max_halfword<32767) then bad:=12; +if (min_quarterwordmax_halfword) then bad:=13; +if (mem_min=max_halfword)or@| + (mem_bot-mem_min>max_halfword+1) then bad:=14; +if (font_basemax_quarterword) then bad:=15; +if font_max>font_base+256 then bad:=16; +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<255 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|} + +@= +@!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 a large array |mem| 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==min_halfword {the null pointer} + +@= +@!temp_ptr:pointer; {a pointer variable for occasional emergency use} + +@ The |mem| array is divided into two regions that are allocated separately, +but the dividing line between these two regions is not fixed; they grow +together until finding their ``natural'' size in a particular job. +Locations less than or equal to |lo_mem_max| 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 greater than or equal to +|hi_mem_min| are used for storing one-word records; a conventional +\.{AVAIL} stack is used for allocation in this region. + +Locations of |mem| between |mem_bot| and |mem_top| may be dumped as part +of preloaded format files, by the \.{INITEX} preprocessor. +@.INITEX@> +Production versions of \TeX\ may extend the memory at both ends in order to +provide more space; locations between |mem_min| and |mem_bot| are always +used for variable-size nodes, and locations between |mem_top| and |mem_max| +are always used for single-word nodes. + +The key pointers that govern |mem| allocation have a prescribed order: +$$\advance\thickmuskip-2mu +\hbox{|null<=mem_min<=mem_bot= +@!mem : array[mem_min..mem_max] of memory_word; {the big dynamic storage area} +@!lo_mem_max : pointer; {the largest location of variable-size memory in use} +@!hi_mem_min : pointer; {the smallest location of one-word memory in use} + +@ In order to study the memory requirements of particular applications, it +is possible to prepare a version of \TeX\ that keeps track of current and +maximum memory usage. When code between the delimiters |@!stat| $\ldots$ +|tats| is not ``commented out,'' \TeX\ will run a bit slower but it will +report these statistics when |tracing_stats| is sufficiently large. + +@= +@!var_used, @!dyn_used : integer; {how much memory is in use} + +@ Let's consider the one-word memory region first, since it's the +simplest. The pointer variable |mem_end| holds the highest-numbered location +of |mem| that has ever been used. The free locations of |mem| that +occur between |hi_mem_min| and |mem_end|, inclusive, are of type +|two_halves|, and we write |info(p)| and |link(p)| for the |lh| +and |rh| fields of |mem[p]| when it is of this type. The single-word +free locations form a linked list +$$|avail|,\;\hbox{|link(avail)|},\;\hbox{|link(link(avail))|},\;\ldots$$ +terminated by |null|. + +@d link(#) == mem[#].hh.rh {the |link| field of a memory word} +@d info(#) == mem[#].hh.lh {the |info| field of a memory word} + +@= +@!avail : pointer; {head of the list of available one-word nodes} +@!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 @@/ +@ + +@ 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 |mem_end|. If that cannot be done, i.e., if +|mem_end=mem_max|, we try to decrease |hi_mem_min|. If that cannot be +done, i.e., if |hi_mem_min=lo_mem_max+1|, we have to quit. + +@p function get_avail : pointer; {single-word node allocation} +var p:pointer; {the new node being got} +begin p:=avail; {get top location in the |avail| stack} +if p<>null then avail:=link(avail) {and pop it off} +else if mem_end + 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|. + +Each empty node has size 2 or more; the first word contains the special +value |max_halfword| in its |link| field and the size in its |info| field; +the second word contains the two pointers for double linking. + +Each nonempty node also has size 2 or more. Its first word is of type +|two_halves|\kern-1pt, and its |link| field is never equal to |max_halfword|. +Otherwise there is complete flexibility with respect to the contents +of its other fields and its other words. + +(We require |mem_max= +@!rover : pointer; {points to some node in the list of empties} + +@ A call to |get_node| with argument |s| returns a pointer to a new node +of size~|s|, which must be 2~or more. The |link| field of the first word +of this new node is set to null. An overflow stop occurs if no suitable +space exists. + +If |get_node| is called with $s=2^{30}$, it simply merges adjacent free +areas and returns the value |max_halfword|. + +@p function get_node(@!s:integer):pointer; {variable-size node allocation} +label found,exit,restart; +var p:pointer; {the node currently under inspection} +@!q:pointer; {the node physically after node |p|} +@!r:integer; {the newly allocated node, or a candidate for this honor} +@!t:integer; {temporary register} +begin restart: p:=rover; {start at some free node in the ring} +repeat @; +@^inner loop@> +p:=rlink(p); {move to the next node in the ring} +until p=rover; {repeat until the whole list has been traversed} +if s=@'10000000000 then + begin get_node:=max_halfword; return; + end; +if lo_mem_max+2; +overflow("main memory size",mem_max+1-mem_min); + {sorry, nothing satisfactory is left} +@:TeX capacity exceeded main memory size}{\quad main memory size@> +found: link(r):=null; {this node is now nonempty} +@!stat var_used:=var_used+s; {maintain usage statistics} +tats@;@/ +get_node:=r; +exit:end; + +@ The lower part of |mem| grows by 1000 words at a time, unless +we are very close to going under. When it grows, we simply link +a new node into the available-space list. This method of controlled +growth helps to keep the |mem| usage consecutive when \TeX\ is +implemented on ``virtual memory'' systems. +@^virtual memory@> + +@= +begin if hi_mem_min-lo_mem_max>=1998 then t:=lo_mem_max+1000 +else t:=lo_mem_max+1+(hi_mem_min-lo_mem_max) div 2; + {|lo_mem_max+2<=tmem_bot+max_halfword then t:=mem_bot+max_halfword; +rlink(q):=rover; llink(q):=p; link(q):=empty_flag; node_size(q):=t-lo_mem_max;@/ +lo_mem_max:=t; link(lo_mem_max):=null; info(lo_mem_max):=null; +rover:=q; goto restart; +end + +@ Empirical tests show that the routine in this section performs a +node-merging operation about 0.75 times per allocation, on the average, +after which it finds that |r>p+1| about 95\pct! of the time. + +@= +q:=p+node_size(p); {find the physical successor} +@^inner loop@> +while is_empty(q) do {merge node |p| with node |q|} + begin t:=rlink(q); + if q=rover then rover:=t; + llink(t):=llink(q); rlink(llink(q)):=t;@/ + q:=q+node_size(q); + end; +r:=q-s; +if r>p+1 then @; +if r=p then if rlink(p)<>p then + @; +node_size(p):=q-p {reset the size in case it grew} + +@ @= +begin node_size(p):=r-p; {store the remaining size} +@^inner loop@> +rover:=p; {start searching here next time} +goto found; +end + +@ Here we delete node |p| from the ring, and let |rover| rove around. + +@= +begin rover:=rlink(p); t:=llink(p); +llink(rover):=t; rlink(t):=rover; +goto found; +end + +@ Conversely, when some variable-size node |p| of size |s| is no longer needed, +the operation |free_node(p,s)| will make its words available, by inserting +|p| as a new empty node just before where |rover| now points. +@^inner loop@> + +@p procedure free_node(@!p:pointer; @!s:halfword); {variable-size node + liberation} +var q:pointer; {|llink(rover)|} +begin node_size(p):=s; link(p):=empty_flag; +q:=llink(rover); llink(p):=q; rlink(p):=rover; {set both links} +llink(rover):=p; rlink(q):=p; {insert |p| into the ring} +@!stat var_used:=var_used-s;@+tats@;{maintain statistics} +end; + +@ Just before \.{INITEX} writes out the memory, it sorts the doubly linked +available space list. The list is probably very short at such times, so a +simple insertion sort is used. The smallest available location will be +pointed to by |rover|, the next-smallest by |rlink(rover)|, etc. + +@p @!init procedure sort_avail; {sorts the available variable-size nodes + by location} +var p,@!q,@!r: pointer; {indices into |mem|} +@!old_rover:pointer; {initial |rover| setting} +begin p:=get_node(@'10000000000); {merge adjacent free areas} +p:=rlink(rover); rlink(rover):=max_halfword; old_rover:=rover; +while p<>old_rover do @; +p:=rover; +while rlink(p)<>max_halfword do + begin llink(rlink(p)):=p; p:=rlink(p); + end; +rlink(p):=rover; llink(rover):=p; +end; +tini + +@ The following |while| loop is guaranteed to +terminate, since the list that starts at +|rover| ends with |max_halfword| during the sorting procedure. + +@= +if p@^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. + +@d is_char_node(#) == (#>=hi_mem_min) + {does the argument point to a |char_node|?} +@d font == type {the font code in a |char_node|} +@d character == subtype {the character code in a |char_node|} + +@ 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|, +|fil|, |fill|, or |filll|). The |subtype| field is not used in \TeX. +In \eTeX\ the |subtype| field records the box direction mode |box_lr|. + +@d hlist_node=0 {|type| of hlist nodes} +@d box_node_size=7 {number of words to allocate for a box node} +@d width_offset=1 {position of |width| field in a box node} +@d depth_offset=2 {position of |depth| field in a box node} +@d height_offset=3 {position of |height| field in a box node} +@d width(#) == mem[#+width_offset].sc {width of the box, in sp} +@d depth(#) == mem[#+depth_offset].sc {depth of the box, in sp} +@d height(#) == mem[#+height_offset].sc {height of the box, in sp} +@d shift_amount(#) == mem[#+4].sc {repositioning distance, in sp} +@d list_offset=5 {position of |list_ptr| field in a box node} +@d list_ptr(#) == link(#+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 = 6 {position of |glue_set| in a box node} +@d glue_set(#) == mem[#+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|, for historic reasons +that are no longer relevant.) + +@p function new_null_box:pointer; {creates a new box node} +var p:pointer; {the new node} +begin p:=get_node(box_node_size); type(p):=hlist_node; +subtype(p):=min_quarterword; +width(p):=0; depth(p):=0; height(p):=0; shift_amount(p):=0; list_ptr(p):=null; +glue_sign(p):=normal; glue_order(p):=normal; set_glue_ratio_zero(glue_set(p)); +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=4 {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} + +@ 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:=get_node(rule_node_size); type(p):=rule_node; +subtype(p):=0; {the |subtype| is not used} +width(p):=null_flag; depth(p):=null_flag; height(p):=null_flag; +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=5 {number of words to allocate for an insertion} +@d float_cost(#)==mem[#+1].int {the |floating_penalty| to be used} +@d ins_ptr(#)==info(#+4) {the vertical list to be inserted} +@d split_top_ptr(#)==link(#+4) {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 small_node_size=2 {number of words to allocate for most node types} +@d mark_ptr(#)==link(#+1) {head of the token list for a mark} +@d mark_class(#)==info(#+1) {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_pre == subtype {<>0 => pre-adjustment} +@#{|append_list| is used to append a list to |tail|} +@d append_list(#) == begin link(tail) := link(#); append_list_end +@d append_list_end(#) == tail := #; end + +@d adjust_ptr(#)==mem[#+1].int + {vertical list to be moved out of horizontal list} + +@ A |ligature_node|, which occurs only in horizontal lists, specifies +a character that was fabricated from the interaction of two or more +actual characters. The second word of the node, which is called the +|lig_char| word, contains |font| and |character| fields just as in a +|char_node|. The characters that generated the ligature have not been +forgotten, since they are needed for diagnostic messages and for +hyphenation; 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 is 0, plus 2 and/or 1 if the original source of the +ligature included implicit left and/or right boundaries. + +@d ligature_node=6 {|type| of a ligature node} +@d lig_char(#)==#+1 {the word where the ligature is to be found} +@d lig_ptr(#)==link(lig_char(#)) {the list of characters} + +@ The |new_ligature| function creates a ligature node having given +contents of the |font|, |character|, and |lig_ptr| fields. We also have +a |new_lig_item| function, which returns a two-word node having a given +|character| field. Such nodes are used for temporary processing as ligatures +are being created. + +@p function new_ligature(@!f,@!c:quarterword; @!q:pointer):pointer; +var p:pointer; {the new node} +begin p:=get_node(small_node_size); type(p):=ligature_node; +font(lig_char(p)):=f; character(lig_char(p)):=c; lig_ptr(p):=q; +subtype(p):=0; new_ligature:=p; +end; +@# +function new_lig_item(@!c:quarterword):pointer; +var p:pointer; {the new node} +begin p:=get_node(small_node_size); character(p):=c; lig_ptr(p):=null; +new_lig_item:=p; +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 the next +|replace_count(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 |replace_count=0|. All three of the discretionary texts must be +lists that consist entirely of character, kern, box, rule, and ligature nodes. + +If |pre_break(p)=null|, 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 replace_count==subtype {how many subsequent nodes to replace} +@d pre_break==llink {text that precedes a discretionary break} +@d post_break==rlink {text that follows a discretionary break} + +@p function new_disc:pointer; {creates an empty |disc_node|} +var p:pointer; {the new node} +begin p:=get_node(small_node_size); type(p):=disc_node; +replace_count(p):=0; pre_break(p):=null; post_break(p):=null; +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 |width| field, which represents +the amount of surrounding space inserted by \.{\\mathsurround}. + +In addition a |math_node| with |subtype>after| and |width=0| will be +(ab)used to record a regular |math_node| reinserted after being +discarded at a line break or one of the text direction primitives ( +\.{\\beginL}, \.{\\endL}, \.{\\beginR}, and \.{\\endR} ). + +@d math_node=9 {|type| of a math node} +@d before=0 {|subtype| for math node that introduces a formula} +@d after=1 {|subtype| for math node that winds up a formula} +@# +@d M_code=2 +@d begin_M_code=M_code+before {|subtype| for \.{\\beginM} node} +@d end_M_code=M_code+after {|subtype| for \.{\\endM} node} +@d L_code=4 +@d begin_L_code=L_code+begin_M_code {|subtype| for \.{\\beginL} node} +@d end_L_code=L_code+end_M_code {|subtype| for \.{\\endL} node} +@d R_code=L_code+L_code +@d begin_R_code=R_code+begin_M_code {|subtype| for \.{\\beginR} node} +@d end_R_code=R_code+end_M_code {|subtype| for \.{\\endR} node} +@# +@d end_LR(#)==odd(subtype(#)) +@d end_LR_type(#)==(L_code*(subtype(#) div L_code)+end_M_code) +@d begin_LR_type(#)==(#-after+before) + +@p function new_math(@!w:scaled;@!s:small_number):pointer; +var p:pointer; {the new node} +begin p:=get_node(small_node_size); type(p):=math_node; +subtype(p):=s; width(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|, |ligature_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(#) +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|, |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_ref_count(#) == link(#) {reference count of a glue specification} +@d stretch(#) == mem[#+2].sc {the stretchability of this glob of glue} +@d shrink(#) == mem[#+3].sc {the shrinkability of this glob of glue} +@d stretch_order == type {order of infinity for stretching} +@d shrink_order == subtype {order of infinity for shrinking} +@d fil=1 {first-order infinity} +@d fill=2 {second-order infinity} +@d filll=3 {third-order infinity} + +@= +@!glue_ord=normal..filll; {infinity to the 0, 1, 2, or 3 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:=get_node(glue_spec_size);@/ +mem[q]:=mem[p]; glue_ref_count(q):=null;@/ +width(q):=width(p); stretch(q):=stretch(p); shrink(q):=shrink(p); +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:=get_node(small_node_size); type(p):=glue_node; subtype(p):=n+1; +leader_ptr(p):=null;@/ +q:=@@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:=get_node(small_node_size); type(p):=glue_node; subtype(p):=normal; +leader_ptr(p):=null; 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(@); +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 explicit=1 {|subtype| of kern nodes from \.{\\kern} and \.{\\/}} +@d acc_kern=2 {|subtype| of kern nodes from accents} +@d auto_kern=3 {|subtype| of kern nodes created by |get_auto_kern|} + +@# {memory structure for marginal kerns} +@d margin_kern_node = 40 +@d margin_kern_node_size = 3 +@d margin_char(#) == info(# + 2) + +@# {|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 kn_bs_code_base == 7 +@d st_bs_code_base == 8 +@d sh_bs_code_base == 9 +@d kn_bc_code_base == 10 +@d kn_ac_code_base == 11 + + +@d no_lig_code == 6 + +@d max_hlist_stack = 512 {maximum fill level for |hlist_stack|} +{maybe good if larger than |2 * max_quarterword|, so that box nesting level would overflow first} + +@ 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:=get_node(small_node_size); type(p):=kern_node; +subtype(p):=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 inf_penalty=inf_bad {``infinite'' penalty value} +@d eject_penalty=-inf_penalty {``negatively infinite'' penalty value} +@d penalty(#) == mem[#+1].int {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:=get_node(small_node_size); type(p):=penalty_node; +subtype(p):=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(#)==mem[#+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, locations |mem_bot| to |mem_bot+3| are always used to store the +specification 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. Static variable-size nodes appear +in locations |mem_bot| through |lo_mem_stat_max|, and static single-word nodes +appear in locations |hi_mem_stat_min| through |mem_top|, inclusive. It is +harmless to let |lig_trick| and |garbage| share the same location of |mem|. + +@d zero_glue==mem_bot {specification for \.{0pt plus 0pt minus 0pt}} +@d fil_glue==zero_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 lo_mem_stat_max==fil_neg_glue+glue_spec_size-1 {largest statically + allocated word in the variable-size |mem|} +@# +@d page_ins_head==mem_top {list of insertion data for current page} +@d contrib_head==mem_top-1 {vlist of items not yet on current page} +@d page_head==mem_top-2 {vlist for current page} +@d temp_head==mem_top-3 {head of a temporary list of some kind} +@d hold_head==mem_top-4 {head of a temporary list of another kind} +@d adjust_head==mem_top-5 {head of adjustment list returned by |hpack|} +@d active==mem_top-7 {head of active list in |line_break|, needs two words} +@d align_head==mem_top-8 {head of preamble list for alignments} +@d end_span==mem_top-9 {tail of spanned-width lists} +@d omit_template==mem_top-10 {a constant token list} +@d null_list==mem_top-11 {permanently empty list} +@d lig_trick==mem_top-12 {a ligature masquerading as a |char_node|} +@d garbage==mem_top-12 {used for scrap information} +@d backup_head==mem_top-13 {head of token list built by |scan_keyword|} +@d pre_adjust_head==mem_top-14 {head of pre-adjustment list returned by |hpack|} +@d hi_mem_stat_min==mem_top-14 {smallest statically allocated word in + the one-word |mem|} +@d hi_mem_stat_usage=15 {the number of one-word nodes always present} + +@ The following code gets |mem| off to a good start, when \TeX\ is +initializing itself the slow~way. + +@= +@!k:integer; {index into |mem|, |eqtb|, etc.} + +@ @= +for k:=mem_bot+1 to lo_mem_stat_max do mem[k].sc:=0; + {all glue dimensions are zeroed} +@^data structure assumptions@> +k:=mem_bot;@+while k<=lo_mem_stat_max do + {set first words of glue specifications} + begin glue_ref_count(k):=null+1; + stretch_order(k):=normal; shrink_order(k):=normal; + k:=k+glue_spec_size; + end; +stretch(fil_glue):=unity; stretch_order(fil_glue):=fil;@/ +stretch(fill_glue):=unity; stretch_order(fill_glue):=fill;@/ +stretch(ss_glue):=unity; stretch_order(ss_glue):=fil;@/ +shrink(ss_glue):=unity; shrink_order(ss_glue):=fil;@/ +stretch(fil_neg_glue):=-unity; stretch_order(fil_neg_glue):=fil;@/ +rover:=lo_mem_stat_max+1; +link(rover):=empty_flag; {now initialize the dynamic memory} +node_size(rover):=1000; {which is a 1000-word available node} +llink(rover):=rover; rlink(rover):=rover;@/ +lo_mem_max:=rover+1000; link(lo_mem_max):=null; info(lo_mem_max):=null;@/ +for k:=hi_mem_stat_min to mem_top do + mem[k]:=mem[lo_mem_max]; {clear list heads} +@; +avail:=null; mem_end:=mem_top; +hi_mem_min:=hi_mem_stat_min; {initialize the one-word memory} +var_used:=lo_mem_stat_max+1-mem_bot; dyn_used:=hi_mem_stat_usage; + {initialize statistics} + +@ If \TeX\ is extended improperly, the |mem| array might get screwed up. +For example, some pointers might be wrong, or some ``dead'' nodes might not +have been freed when the last reference to them disappeared. Procedures +|check_mem| and |search_mem| are available to help diagnose such +problems. These procedures make use of two arrays called |free| and +|was_free| that are present only if \TeX's debugging routines have +been included. (You may want to decrease the size of |mem| while you +@^debugging@> +are debugging.) + +@= +@!debug @!free: packed array [mem_min..mem_max] of boolean; {free cells} +@t\hskip10pt@>@!was_free: packed array [mem_min..mem_max] of boolean; + {previously free cells} +@t\hskip10pt@>@!was_mem_end,@!was_lo_max,@!was_hi_min: pointer; + {previous |mem_end|, |lo_mem_max|, and |hi_mem_min|} +@t\hskip10pt@>@!panicking:boolean; {do we want to check memory constantly?} +gubed + +@ @= +@!debug was_mem_end:=mem_min; {indicate that everything was previously free} +was_lo_max:=mem_min; was_hi_min:=mem_max; +panicking:=false; +gubed + +@ Procedure |check_mem| makes sure that the available space lists of +|mem| are well formed, and it optionally prints out all locations +that are reserved now but were free the last time this procedure was called. + +@p @!debug procedure check_mem(@!print_locs : boolean); +label done1,done2; {loop exits} +var p,@!q:pointer; {current locations of interest in |mem|} +@!clobbered:boolean; {is something amiss?} +begin for p:=mem_min to lo_mem_max do free[p]:=false; {you can probably + do this faster} +for p:=hi_mem_min to mem_end do free[p]:=false; {ditto} +@; +@; +@; +if print_locs then @; +for p:=mem_min to lo_mem_max do was_free[p]:=free[p]; +for p:=hi_mem_min to mem_end do was_free[p]:=free[p]; + {|was_free:=free| might be faster} +was_mem_end:=mem_end; was_lo_max:=lo_mem_max; was_hi_min:=hi_mem_min; +end; +gubed + +@ @= +p:=avail; q:=null; clobbered:=false; +while p<>null do + begin if (p>mem_end)or(p + print_int(q); goto done1; + end; + free[p]:=true; q:=p; p:=link(q); + end; +done1: + +@ @= +p:=rover; q:=null; clobbered:=false; +repeat if (p>=lo_mem_max)or(p=lo_mem_max)or(rlink(p)lo_mem_max)or@| (llink(rlink(p))<>p) then clobbered:=true; + if clobbered then + begin print_nl("Double-AVAIL list clobbered at "); + print_int(q); goto done2; + end; +for q:=p to p+node_size(p)-1 do {mark all locations free} + begin if free[q] then + begin print_nl("Doubly free location at "); +@.Doubly free location...@> + print_int(q); goto done2; + end; + free[q]:=true; + end; +q:=p; p:=rlink(p); +until p=rover; +done2: + +@ @= +p:=mem_min; +while p<=lo_mem_max do {node |p| should not be empty} + begin if is_empty(p) then + begin print_nl("Bad flag at "); print_int(p); +@.Bad flag...@> + end; + while (p<=lo_mem_max) and not free[p] do incr(p); + while (p<=lo_mem_max) and free[p] do incr(p); + end + +@ @= +begin print_nl("New busy locs:"); +for p:=mem_min to lo_mem_max do + if not free[p] and ((p>was_lo_max) or was_free[p]) then + begin print_char(" "); print_int(p); + end; +for p:=hi_mem_min to mem_end do + if not free[p] and + ((pwas_mem_end) or was_free[p]) then + begin print_char(" "); print_int(p); + end; +end + +@ The |search_mem| procedure attempts to answer the question ``Who points +to node~|p|?'' In doing so, it fetches |link| and |info| fields of |mem| +that might not be of type |two_halves|. Strictly speaking, this is +@^dirty \PASCAL@> +undefined in \PASCAL, and it can lead to ``false drops'' (words that seem to +point to |p| purely by coincidence). But for debugging purposes, we want +to rule out the places that do {\sl not\/} point to |p|, so a few false +drops are tolerable. + +@p @!debug procedure search_mem(@!p:pointer); {look for pointers to |p|} +var q:integer; {current position being searched} +begin for q:=mem_min to lo_mem_max do + begin if link(q)=p then + begin print_nl("LINK("); print_int(q); print_char(")"); + end; + if info(q)=p then + begin print_nl("INFO("); print_int(q); print_char(")"); + end; + end; +for q:=hi_mem_min to mem_end do + begin if link(q)=p then + begin print_nl("LINK("); print_int(q); print_char(")"); + end; + if info(q)=p then + begin print_nl("INFO("); print_int(q); print_char(")"); + end; + end; +@; +@; +@; +end; +gubed + +@@; + +@* \[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. + +@= +@!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|} +var n:integer; {for replacement counts} +begin while p>mem_min do + begin if is_char_node(p) then + begin if p<=mem_end then + begin if font(p)<>font_in_short_display then + begin if (font(p)font_max) then + print_char("*") +@.*\relax@> + else print_font_identifier(font(p)); + print_char(" "); font_in_short_display:=font(p); + end; + print_ASCII(qo(character(p))); + end; + end + else @; + p:=link(p); + end; +end; + +@ @= +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: if subtype(p)>=L_code then print("[]") + else print_char("$"); +ligature_node: short_display(lig_ptr(p)); +disc_node: begin short_display(pre_break(p)); + short_display(post_break(p));@/ + n:=replace_count(p); + while n>0 do + begin if link(p)<>null then p:=link(p); + decr(n); + end; + 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 p>mem_end then print_esc("CLOBBERED.") +else begin if (font(p)font_max) then print_char("*") +@.*\relax@> + else print_font_identifier(font(p)); + print_char(" "); print_ASCII(qo(character(p))); + end; +end; +@# +procedure print_mark(@!p:integer); {prints token list data in braces} +begin print_char("{"); +if (pmem_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; + +@ 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 (orderfilll) then print("foul") +else if order>normal then + begin print("fil"); + while order>fil 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=lo_mem_max) 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 @@; +@ + +@ 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. + +@= +@!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>mem_min do + begin print_ln; print_current_string; {display the nesting history} + if p>mem_end then {pointer out of range} + begin print("Bad link, display aborted."); return; +@.Bad link...@> + end; + incr(n); if n>breadth_max then {time to stop} + begin print("etc."); return; +@.etc@> + end; + @; + p:=link(p); + end; +exit: +end; + +@ @= +if is_char_node(p) then print_font_and_char(p) +else case type(p) of + hlist_node,vlist_node,unset_node: @; + rule_node: @; + ins_node: @; + whatsit_node: @; + glue_node: @; + 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: @; + math_node: @; + ligature_node: @; + penalty_node: @; + disc_node: @; + mark_node: @; + adjust_node: @; + @t\4@>@@; + othercases print("Unknown node type!") + endcases + +@ @= +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 + @ +else begin @; + if shift_amount(p)<>0 then + begin print(", shifted "); print_scaled(shift_amount(p)); + end; + if eTeX_ex then @; + end; +node_list_display(list_ptr(p)); {recursive call} +end + +@ @= +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@> + +@= +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(mem[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 + +@ @= +begin print_esc("rule("); print_rule_dimen(height(p)); print_char("+"); +print_rule_dimen(depth(p)); print(")x"); print_rule_dimen(width(p)); +end + +@ @= +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 + +@ @= +if subtype(p)>=a_leaders then @ +else begin print_esc("glue"); + if subtype(p)<>normal then + begin print_char("("); + if subtype(p)cond_math_glue then + begin print_char(" "); + if subtype(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. + +@= +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@> + if subtype(p)=auto_kern then print(" (for \pdfprependkern/\pdfappendkern)"); + end +else begin print_esc("mkern"); print_scaled(width(p)); print("mu"); + end + +@ @= +if subtype(p)>after then + begin if end_LR(p) then print_esc("end") + else print_esc("begin"); + if subtype(p)>R_code then print_char("R") + else if subtype(p)>L_code then print_char("L") + else print_char("M"); + end else +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 + +@ @= +begin print_font_and_char(lig_char(p)); print(" (ligature "); +if subtype(p)>1 then print_char("|"); +font_in_short_display:=font(lig_char(p)); short_display(lig_ptr(p)); +if odd(subtype(p)) then print_char("|"); +print_char(")"); +end + +@ @= +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. + +@= +begin print_esc("discretionary"); +if replace_count(p)>0 then + begin print(" replacing "); print_int(replace_count(p)); + end; +node_list_display(pre_break(p)); {recursive call} +append_char("|"); show_node_list(post_break(p)); flush_char; {recursive call} +end + +@ @= +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 + +@ @= +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 @; +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 if token_ref_count(p)=null 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 free_node(#,glue_spec_size) + else decr(glue_ref_count(#)); + end + +@p procedure delete_glue_ref(@!p:pointer); {|p| points to a glue specification} +fast_delete_glue_ref(p); + +@ 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@> + +@p procedure flush_node_list(@!p:pointer); {erase list of nodes starting at |p|} +label done; {go here when node |p| has been freed} +var q:pointer; {successor to node |p|} +begin while p<>null do +@^inner loop@> + begin q:=link(p); + if is_char_node(p) then free_avail(p) + else begin case type(p) of + hlist_node,vlist_node,unset_node: begin flush_node_list(list_ptr(p)); + free_node(p,box_node_size); goto done; + end; + rule_node: begin free_node(p,rule_node_size); goto done; + end; + ins_node: begin flush_node_list(ins_ptr(p)); + delete_glue_ref(split_top_ptr(p)); + free_node(p,ins_node_size); goto done; + end; + whatsit_node: @; + glue_node: begin fast_delete_glue_ref(glue_ptr(p)); + if leader_ptr(p)<>null then flush_node_list(leader_ptr(p)); + end; + kern_node,math_node,penalty_node: do_nothing; + margin_kern_node: begin + free_avail(margin_char(p)); + free_node(p, margin_kern_node_size); + goto done; + end; + ligature_node: flush_node_list(lig_ptr(p)); + mark_node: delete_token_ref(mark_ptr(p)); + disc_node: begin flush_node_list(pre_break(p)); + flush_node_list(post_break(p)); + end; + adjust_node: flush_node_list(adjust_ptr(p)); + @t\4@>@@; + othercases confusion("flushing") +@:this can't happen flushing}{\quad flushing@> + endcases;@/ + free_node(p,small_node_size); + done:end; + p:=q; + end; +end; + +@* \[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} + +@ The copying procedure copies words en masse without bothering +to look at their individual fields. If the node format changes---for +example, if the size is altered, or if some link field is moved to another +relative position---then this code may need to be changed too. +@^data structure assumptions@> + +@p function copy_node_list(@!p:pointer):pointer; {makes a duplicate of the + node list that starts at |p| and returns a pointer to the new list} +var h:pointer; {temporary head of copied list} +@!q:pointer; {previous position in new list} +@!r:pointer; {current node being fabricated for new list} +@!words:0..5; {number of words remaining to be copied} +begin h:=get_avail; q:=h; +while p<>null do + begin @; + link(q):=r; q:=r; p:=link(p); + end; +link(q):=null; q:=link(h); free_avail(h); +copy_node_list:=q; +end; + +@ @= +words:=1; {this setting occurs in more branches than any other} +if is_char_node(p) then r:=get_avail +else @; +while words>0 do + begin decr(words); mem[r+words]:=mem[p+words]; + end + +@ @= +case type(p) of +hlist_node,vlist_node,unset_node: begin r:=get_node(box_node_size); + mem[r+6]:=mem[p+6]; mem[r+5]:=mem[p+5]; {copy the last two words} + list_ptr(r):=copy_node_list(list_ptr(p)); {this affects |mem[r+5]|} + words:=5; + end; +rule_node: begin r:=get_node(rule_node_size); words:=rule_node_size; + end; +ins_node: begin r:=get_node(ins_node_size); mem[r+4]:=mem[p+4]; + add_glue_ref(split_top_ptr(p)); + ins_ptr(r):=copy_node_list(ins_ptr(p)); {this affects |mem[r+4]|} + words:=ins_node_size-1; + end; +whatsit_node:@; +glue_node: begin r:=get_node(small_node_size); add_glue_ref(glue_ptr(p)); + glue_ptr(r):=glue_ptr(p); leader_ptr(r):=copy_node_list(leader_ptr(p)); + end; +kern_node,math_node,penalty_node: begin r:=get_node(small_node_size); + words:=small_node_size; + end; +margin_kern_node: begin + r := get_node(margin_kern_node_size); + fast_get_avail(margin_char(r)); + font(margin_char(r)) := font(margin_char(p)); + character(margin_char(r)) := character(margin_char(p)); + words := small_node_size; + end; +ligature_node: begin r:=get_node(small_node_size); + mem[lig_char(r)]:=mem[lig_char(p)]; {copy |font| and |character|} + lig_ptr(r):=copy_node_list(lig_ptr(p)); + end; +disc_node: begin r:=get_node(small_node_size); + pre_break(r):=copy_node_list(pre_break(p)); + post_break(r):=copy_node_list(post_break(p)); + end; +mark_node: begin r:=get_node(small_node_size); add_token_ref(mark_ptr(p)); + words:=small_node_size; + end; +adjust_node: begin r:=get_node(small_node_size); + adjust_ptr(r):=copy_node_list(adjust_ptr(p)); + end; {|words=1=small_node_size-1|} +othercases confusion("copying") +@:this can't happen copying}{\quad copying@> +endcases + +@* \[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 \ 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} )} + {or text direction directives ( \.{\\beginL}, etc.~)} +@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 min_internal=68 {the smallest code that can follow \.{\\the}} +@d char_given=68 {character code defined by \.{\\chardef}} +@d math_given=69 {math code defined by \.{\\mathchardef}} +@d last_item=70 {most recent item ( \.{\\lastpenalty}, + \.{\\lastkern}, \.{\\lastskip} )} +@d max_non_prefixed_command=70 {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}'. + +@d toks_register=71 {token list register ( \.{\\toks} )} +@d assign_toks=72 {special token list ( \.{\\output}, \.{\\everypar}, etc.~)} +@d assign_int=73 {user-defined integer ( \.{\\tolerance}, \.{\\day}, etc.~)} +@d assign_dimen=74 {user-defined length ( \.{\\hsize}, etc.~)} +@d assign_glue=75 {user-defined glue ( \.{\\baselineskip}, etc.~)} +@d assign_mu_glue=76 {user-defined muglue ( \.{\\thinmuskip}, etc.~)} +@d assign_font_dimen=77 {user-defined font dimension ( \.{\\fontdimen} )} +@d assign_font_int=78 {user-defined font integer ( \.{\\hyphenchar}, + \.{\\skewchar} )} +@d set_aux=79 {specify state info ( \.{\\spacefactor}, \.{\\prevdepth} )} +@d set_prev_graf=80 {specify state info ( \.{\\prevgraf} )} +@d set_page_dimen=81 {specify state info ( \.{\\pagegoal}, etc.~)} +@d set_page_int=82 {specify state info ( \.{\\deadcycles}, + \.{\\insertpenalties} )} + {( or \.{\\interactionmode} )} +@d set_box_dimen=83 {change dimension of box ( \.{\\wd}, \.{\\ht}, \.{\\dp} )} +@d set_shape=84 {specify fancy paragraph shape ( \.{\\parshape} )} + {(or \.{\\interlinepenalties}, etc.~)} +@d def_code=85 {define a character code ( \.{\\catcode}, etc.~)} +@d def_family=86 {declare math fonts ( \.{\\textfont}, etc.~)} +@d set_font=87 {set current font ( font identifiers )} +@d def_font=88 {define a font file ( \.{\\font} )} +@d register=89 {internal register ( \.{\\count}, \.{\\dimen}, etc.~)} +@d max_internal=89 {the largest code that can follow \.{\\the}} +@d advance=90 {advance a register or parameter ( \.{\\advance} )} +@d multiply=91 {multiply a register or parameter ( \.{\\multiply} )} +@d divide=92 {divide a register or parameter ( \.{\\divide} )} +@d prefix=93 {qualify a definition ( \.{\\global}, \.{\\long}, \.{\\outer} )} + {( or \.{\\protected} )} +@d let=94 {assign a command code ( \.{\\let}, \.{\\futurelet} )} +@d shorthand_def=95 {code definition ( \.{\\chardef}, \.{\\countdef}, etc.~)} +@d read_to_cs=96 {read into a control sequence ( \.{\\read} )} + {( or \.{\\readline} )} +@d def=97 {macro definition ( \.{\\def}, \.{\\gdef}, \.{\\xdef}, \.{\\edef} )} +@d set_box=98 {set a box ( \.{\\setbox} )} +@d hyph_data=99 {hyphenation data ( \.{\\hyphenation}, \.{\\patterns} )} +@d set_interaction=100 {define level of interaction ( \.{\\batchmode}, etc.~)} +@d letterspace_font=101 {letterspace a font ( \.{\\letterspacefont} )} +@d pdf_copy_font=102 {create a new font instance ( \.{\\pdfcopyfont} )} +@d max_command=102 {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} )} +@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. + +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; + +@ 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| and |clang|; it holds the current space factor used in +spacing calculations, and the current language used for hyphenation. +(The value of |clang| is undefined in restricted horizontal mode.) +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 vertical modes it is known as |LR_save| and holds the LR stack when a +paragraph is interrupted by a displayed formula. In display math mode +it is known as |LR_box| and holds a pointer to a prototype box for the +display. 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 {magic dimension value to mean `ignore me'} + +@= +@!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; + 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 LR_save==eTeX_aux {LR stack when a paragraph is interrupted} +@d LR_box==eTeX_aux {prototype box for display} +@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 clang==aux.hh.rh {the other 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} + +@= +@!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: + +@d tail_append(#)==begin link(tail):=#; tail:=link(tail); + 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. + +@= +nest_ptr:=0; max_nest_stack:=0; +mode:=vmode; head:=contrib_head; tail:=contrib_head; +eTeX_aux:=null; save_tail:=null; +prev_depth:=ignore_depth; mode_line:=0; +prev_graf:=0; shown_mode:=0; +@; + +@ 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:=get_avail; tail:=head; prev_graf:=0; mode_line:=line; +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 free_avail(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 @; + if link(contrib_head)<>null then + print_nl("### recent contributions:"); + end; + show_box(link(nest[p].head_field)); + @; + end; +end; + +@ @= +case abs(m) div (max_command+1) of +0: begin print_nl("prevdepth "); + if a.sc<=pdf_ignored_dimen 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 begin 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 256 equivalents for ``active characters'' that +act as control sequences, followed by 256 equivalents for single-character +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 single_base=active_base+256 {equivalents of one-character control sequences} +@d null_cs=single_base+256 {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 prim_size=2100 {maximum number of primitives } +@d frozen_null_font=frozen_control_sequence+10 + {permanent `\.{\\nullfont}'} +@d frozen_primitive=frozen_control_sequence+11 + {permanent `\.{\\pdfprimitive}'} +@d prim_eqtb_base=frozen_primitive+1 +@d font_id_base=frozen_null_font-font_base + {begins table of 257 permanent font identifiers} +@d undefined_control_sequence=frozen_null_font+257 {dummy location} +@d glue_base=undefined_control_sequence+1 {beginning of region 3} + +@= +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.) + +@= +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 256 \.{\\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 256 ``skip'' registers} +@d mu_skip_base=skip_base+256 {table of 256 ``muskip'' registers} +@d local_base=mu_skip_base+256 {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) + +@=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. + +@= +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. + +@= +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@> + +@ @= +assign_glue,assign_mu_glue: if chr_code= +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; + +@ @= +if n= +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@> + +@ @= +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"); + @/@@/ + 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 var_code==@'70000 {math code meaning ``use the current family''} + +@= +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+255 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+255 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;@/ +for k:=cat_code_base+1 to int_base-1 do eqtb[k]:=eqtb[cat_code_base]; +for k:=0 to 255 do + begin cat_code(k):=other_char; math_code(k):=hi(k); sf_code(k):=1000; + end; +cat_code(carriage_return):=car_ret; cat_code(" "):=spacer; +cat_code("\"):=escape; cat_code("%"):=comment; +cat_code(invalid_code):=invalid_char; cat_code(null_code):=ignore; +for k:="0" to "9" do math_code(k):=hi(k+var_code); +for k:="A" to "Z" do + begin cat_code(k):=letter; cat_code(k+"a"-"A"):=letter;@/ + math_code(k):=hi(k+var_code+@"100); + math_code(k+"a"-"A"):=hi(k+"a"-"A"+var_code+@"100);@/ + lc_code(k):=k+"a"-"A"; lc_code(k+"a"-"A"):=k+"a"-"A";@/ + uc_code(k):=k; uc_code(k+"a"-"A"):=k;@/ + sf_code(k):=999; + end; + +@ @= +if (n=par_shape_loc) or ((n>=etex_pen_base) and (npar_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(info(par_shape_ptr)); + end +else if n +else @ + +@ @= +begin if n=cur_font_loc then print("current font") +else if n@/ +othercases print("[unknown integer parameter!]") +endcases; +end; + +@ The integer parameter names must be entered into the hash table. + +@= +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("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("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("pdfmajorversion",assign_int,int_base+pdf_major_version_code);@/ +@!@:pdf_major_version_}{\.{\\pdfmajorversion} 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("pdfadjustinterwordglue",assign_int,int_base+pdf_adjust_interword_glue_code);@/ +@!@:pdf_adjust_interword_glue_}{\.{\\pdfadjustinterwordglue} primitive@> +primitive("pdfprependkern",assign_int,int_base+pdf_prepend_kern_code);@/ +@!@:pdf_prepend_kern_}{\.{\\pdfprependkern} primitive@> +primitive("pdfappendkern",assign_int,int_base+pdf_append_kern_code);@/ +@!@:pdf_append_kern_}{\.{\\pdfappendkern} 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("pdfinclusioncopyfonts",assign_int,int_base+pdf_inclusion_copy_font_code);@/ +@!@:pdf_inclusion_copy_font_}{\.{\\pdfinclusioncopyfonts} primitive@> + +primitive("pdfsuppresswarningdupdest",assign_int,int_base+pdf_suppress_warning_dup_dest_code);@/ +@!@:pdf_suppress_warning_dup_dest_}{\.{\\pdfsuppresswarningdupdest} primitive@> + +primitive("pdfsuppresswarningdupmap",assign_int,int_base+pdf_suppress_warning_dup_map_code);@/ +@!@:pdf_suppress_warning_dup_map_}{\.{\\pdfsuppresswarningdupmap} primitive@> + +primitive("pdfsuppresswarningpagegroup",assign_int,int_base+pdf_suppress_warning_page_group_code);@/ +@!@:pdf_suppress_warning_page_group_}{\.{\\pdfsuppresswarningpagegroup} primitive@> + +primitive("pdfinfoomitdate",assign_int,int_base+pdf_info_omit_date_code);@/ +@!@:pdf_info_omit_date_}{\.{\\pdfinfoomitdate} primitive@> + +primitive("pdfsuppressptexinfo",assign_int,int_base+pdf_suppress_ptex_info_code);@/ +@!@:pdf_suppress_ptex_info_}{\.{\\pdfsuppressptexinfo} primitive@> + +primitive("pdfomitcharset",assign_int,int_base+pdf_omit_charset_code);@/ +@!@:pdf_omit_charset}{\.{\\pdfomitcharset} primitive@> + +@ @= +assign_int: if chr_code + +@= +for k:=int_base to del_code_base-1 do eqtb[k].int:=0; +mag:=1000; tolerance:=10000; hang_after:=1; max_dead_cycles:=25; +escape_char:="\"; end_line_char:=carriage_return; +for k:=0 to 255 do del_code(k):=-1; +del_code("."):=0; {this null delimiter is used in error recovery} + +@ 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 assumes that suitable values appear in +the global variables \\{sys\_time}, \\{sys\_day}, \\{sys\_month}, and +\\{sys\_year} (which are initialized to noon on 4 July 1776, +in case the implementor is careless). + +@p procedure fix_date_and_time; +begin sys_time:=12*60; +sys_day:=4; sys_month:=7; sys_year:=1776; {self-evident truths} +time:=sys_time; {minutes since midnight} +day:=sys_day; {day of the month} +month:=sys_month; {month of the year} +year:=sys_year; {Anno Domini} +end; + +@ @= +begin if n= +@!old_setting:0..max_selector; +@!sys_time,@!sys_day,@!sys_month,@!sys_year:integer; + {date and time supplied by external system} + +@ The final region of |eqtb| contains the dimension parameters defined +here, and the 256 \.{\\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 pdftex_first_dimen_code = 21 {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 pdf_page_width_code = pdftex_first_dimen_code + 2 {page width of the PDF output} +@d pdf_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_ignored_dimen_code = pdftex_first_dimen_code + 11 +@d pdf_px_dimen_code = pdftex_first_dimen_code + 12 +@d pdftex_last_dimen_code = pdftex_first_dimen_code + 12 {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 256 user-defined \.{\\dimen} registers} +@d eqtb_size=scaled_base+255 {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 pdf_h_origin == dimen_par(pdf_h_origin_code) +@d pdf_v_origin == dimen_par(pdf_v_origin_code) +@d pdf_page_width == dimen_par(pdf_page_width_code) +@d pdf_page_height == dimen_par(pdf_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_ignored_dimen == dimen_par(pdf_ignored_dimen_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"); +pdf_h_origin_code: print_esc("pdfhorigin"); +pdf_v_origin_code: print_esc("pdfvorigin"); +pdf_page_width_code: print_esc("pdfpagewidth"); +pdf_page_height_code: print_esc("pdfpageheight"); +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_ignored_dimen_code: print_esc("pdfignoreddimen"); +pdf_px_dimen_code: print_esc("pdfpxdimen"); +othercases print("[unknown dimen parameter!]") +endcases; +end; + +@ @= +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("pdfpagewidth",assign_dimen,dimen_base+pdf_page_width_code);@/ +@!@:pdf_page_width_}{\.{\\pdfpagewidth} primitive@> +primitive("pdfpageheight",assign_dimen,dimen_base+pdf_page_height_code);@/ +@!@:pdf_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("pdfignoreddimen",assign_dimen,dimen_base+pdf_ignored_dimen_code);@/ +@!@:pdf_ignored_dimen_}{\.{\\pdfignoreddimen} primitive@> +primitive("pdfpxdimen",assign_dimen,dimen_base+pdf_px_dimen_code);@/ +@!@:pdf_px_dimen_}{\.{\\pdfpxdimen} primitive@> + +@ @= +assign_dimen: if chr_code= +for k:=dimen_base to eqtb_size do eqtb[k].sc:=0; + +@ @= +begin if n@@;@/ +@!stat procedure show_eqtb(@!n:pointer); +begin if n +else if n +else if n +else if n +else if n<=eqtb_size then @ +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|. + +@= +@!eqtb:array[active_base..eqtb_size] of memory_word; +@!xeq_level:array[int_base..eqtb_size] of quarterword; + +@ @= +for k:=int_base to eqtb_size do xeq_level[k]:=level_one; + +@ When the debugging routine |search_mem| is looking for pointers having a +given value, it is interested only in regions 1 to~3 of~|eqtb|, and in the +first part of region~4. + +@= +for q:=active_base to box_base+255 do + begin if equiv(q)=p then + begin print_nl("EQUIV("); print_int(q); print_char(")"); + end; + end + +@* \[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} + +@= +@!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_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, plus one} +@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(eqtb[prim_eqtb_base+#]) {level of definition} +@d prim_eq_type(#)==prim_eq_type_field(eqtb[prim_eqtb_base+#]) {command code for equivalent} +@d prim_equiv(#)==prim_equiv_field(eqtb[prim_eqtb_base+#]) {equivalent value} +@d undefined_primitive=0 +@d biggest_char=255 { 65535 in XeTeX } + +@= +@!prim: array [0..prim_size] of two_halves; {the primitives table} +@!prim_used:pointer; {allocation pointer for |prim|} + +@ @= +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]; +next(hash_base):=0; text(hash_base):=0; +for k:=hash_base+1 to undefined_control_sequence-1 do hash[k]:=hash[hash_base]; + +@ @= +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):="pdfprimitive"; +@ 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 @; +p:=h+hash_base; {we start searching here; note that |0<=h0 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 @; + goto found; + end; + p:=next(p); + end; +found: id_lookup:=p; +end; + +@ @= +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[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@> + +@= +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} +@!j,@!l:integer; +begin +if s<=biggest_char then begin + if s<0 then begin p:=undefined_primitive; goto found; end + else p:=(s mod prim_prime)+prim_base; {we start searching here} + end +else begin + j:=str_start[s]; + if s = str_ptr then l := cur_length else l := length(s); + @; + p:=h+prim_base; {we start searching here; note that |0<=h1+biggest_char then { |p| points a multi-letter primitive } + begin if length(prim_text(p)-1)=l then + if str_eq_str(prim_text(p)-1,s) then goto found; + end + else if prim_text(p)=1+s then goto found; { |p| points a single-letter primitive } + if prim_next(p)=0 then + begin if no_new_control_sequence then + p:=undefined_primitive + else @; + goto found; + end; + p:=prim_next(p); + end; +found: prim_lookup:=p; +end; + +@ @= +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+1; +end + +@ The value of |prim_prime| should be roughly 85\pct! of +|prim_size|, and it should be a prime number. + +@= +h:=str_pool[j]; +for k:=j+1 to j+l-1 do + begin h:=h+h+str_pool[k]; + while h>=prim_prime do h:=h-prim_prime; + end + + +@ Single-character control sequences do not need to be looked up in a hash +table, since we can use the character code itself as a direct address. +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. + +@= +procedure print_cs(@!p:integer); {prints a purported control sequence} +begin if p=single_base then + if p=null_cs then + begin print_esc("csname"); print_esc("endcsname"); print_char(" "); + end + else begin print_esc(p-single_base); + if cat_code(p-single_base)=letter then print_char(" "); + end + else if p + 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 + if (p>=prim_eqtb_base)and(p= +procedure sprint_cs(@!p:pointer); {prints a control sequence} +begin if p=prim_eqtb_base)and(p=cs_token_flag|, $t$ points to an |eqtb| location +|t - cs_token_flag|. + +\textindent{--} If |tbuf_size+1 then + overflow("buffer size",buf_size); +@: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); + end; +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: + +@= +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("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("pdfcopyfont",pdf_copy_font,0);@/ +@!@:pdf_copy_font_}{\.{\\pdfcopyfont} 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("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("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("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("read",read_to_cs,0);@/ +@!@:read_}{\.{\\read} primitive@> +primitive("relax",relax,256); {cf.\ |scan_file_name|} +@!@:relax_}{\.{\\relax} primitive@> +text(frozen_relax):="relax"; eqtb[frozen_relax]:=eqtb[cur_val];@/ +primitive("setbox",set_box,0);@/ +@!@:set_box_}{\.{\\setbox} primitive@> +primitive("the",the,0);@/ +@!@:the_}{\.{\\the} primitive@> +primitive("toks",toks_register,mem_bot);@/ +@!@: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. + +@= +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"); +cs_name: print_esc("csname"); +def_font: print_esc("font"); +letterspace_font: print_esc("letterspacefont"); +pdf_copy_font: print_esc("pdfcopyfont"); +delim_num: print_esc("delimiter"); +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") + @; +halign: print_esc("halign"); +hrule: print_esc("hrule"); +ignore_spaces: if chr_code=0 then print_esc("ignorespaces") else print_esc("pdfprimitive"); +insert: print_esc("insert"); +ital_corr: print_esc("/"); +mark: begin print_esc("mark"); + if chr_code>0 then print_char("s"); + end; +math_accent: print_esc("mathaccent"); +math_char_num: print_esc("mathchar"); +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("pdfprimitive"); +non_script: print_esc("nonscript"); +omit: print_esc("omit"); +radical: print_esc("radical"); +read_to_cs: if chr_code=0 then print_esc("read") + @; +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"); + @@;@/ + end; {there are no other cases} +the: if chr_code=0 then print_esc("the") + @; +toks_register: @; +vadjust: print_esc("vadjust"); +valign: if chr_code=0 then 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@> + +Meanwhile, this is a convenient place to catch up on something we were unable +to do before the hash table was defined: + +@* \[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 five 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 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. + +\yskip\hang 5) If |save_type(p)=restore_sa|, then |sa_chain| points to a +chain of sparse array entries to be restored at the end of the current +group. Furthermore |save_index(p)| and |save_level(p)| should replace +the values of |sa_chain| and |sa_level| respectively. + +@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 token 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} +@d restore_sa=4 {|save_type| when sparse array entries should be restored} + +@p@t\4@>@ + +@ 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 max_group_code=16 + +@= +@!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|. + +@ @= +@!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|. + +@= +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 seven 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-7 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 five 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; +if eTeX_ex then + begin saved(0):=line; incr(save_ptr); + end; +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 free_node(q,info(q)+info(q)+1); + end; {such a block is |2n+1| words long, where |n=info(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 eTeX_ex and(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 eTeX_ex and(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; +if cur_level>level_one then + begin decr(cur_level); + @; + end +else confusion("curlevel"); {|unsave| is not used when |cur_group=bottom_level|} +@:this can't happen curlevel}{\quad curlevel@> +end; + +@ @= +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 + @ + else if save_type(save_ptr)=restore_sa then + begin sa_restore; sa_chain:=p; sa_level:=save_level(save_ptr); + end + 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]; + @; + 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); +if eTeX_ex then 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. + +@= +if p0 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 + +@ @= +@!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 + +@ When looking for possible pointers to a memory location, it is helpful +to look for references from |eqtb| that might be waiting on the +save stack. Of course, we might find spurious pointers too; but this +routine is merely an aid when debugging, and at such times we are +grateful for any scraps of information, even if they prove to be irrelevant. +@^dirty \PASCAL@> + +@= +if save_ptr>0 then for q:=0 to save_ptr-1 do + begin if equiv_field(save_stack[q])=p then + begin print_nl("SAVE("); print_int(q); print_char(")"); + end; + end + +@ 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. + +@= +@!mag_set:integer; {if nonzero, this magnification should be used henceforth} + +@ @= +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 $2^8m+c$; 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$2^{12}-1$@>| is larger than +$2^8m+c$, 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= +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 an output routine +will be enclosed in braces. + +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\ }'. + +@= +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; + @; + p:=link(p); + end; +if p<>null then print_esc("ETC."); +@.ETC@> +exit: +end; + +@ @= +if (pmem_end) then + begin print_esc("CLOBBERED."); return; +@.CLOBBERED@> + end; +if info(p)>=cs_token_flag then print_cs(info(p)-cs_token_flag) +else begin m:=info(p) div @'400; c:=info(p) mod @'400; + if info(p)<0 then print_esc("BAD.") +@.BAD@> + else @; + 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. + +@= +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 if (cur_cmd=top_bot_mark)and(cur_chr= +@!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_ASCII(chr_code); + end + +@= +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@>@@/ +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:=link(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: + +@= +@!in_state_record = record + @!state_field, @!index_field: quarterword; + @!start_field,@!loc_field, @!limit_field, @!name_field: halfword; + end; + +@ @= +@!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 name==cur_input.name_field {name of the current file} + +@ 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<=19| indicates that we are reading a pseudo file +created by the \.{\\scantokens} 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} + +@= +@!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} + +@= +@!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: + +@= +procedure runaway; +var p:pointer; {head of runaway list} +begin 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_head; + end; + aligning: begin print("preamble"); p:=hold_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 \ part of an alignment +template is being scanned; + +\hang|v_template|, if the \ 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 \ template} +@d v_template=2 {|token_type| code for \ 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=toks_base-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. + +@= +@!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 +\ 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 \ template, after which it is set to zero; the +\ template begins when a tab mark or \.{\\cr} occurs at a time that +|align_state=0|. + +@= +@!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. + +@= +@!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?} +@@/ +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>19) or (base_ptr=0) then bottom_line:=true; + if (base_ptr=input_ptr)or bottom_line or(nn + 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; + +@ @= +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 state<>token_list then + begin @; + @; + end + else begin @; + @; + end; + selector:=old_setting; {stop pseudoprinting} + @; + 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@> + +@= +if name<=17 then + if terminal_input then + if base_ptr=0 then print_nl("<*>") else print_nl(" ") + else begin print_nl(" + 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(" ") + +@ @= +case token_type of +parameter: print_nl(" "); +u_template,v_template: print_nl("