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diff --git a/Build/source/texk/web2c/tex.web b/Build/source/texk/web2c/tex.web new file mode 100644 index 00000000000..0eaf4dbd078 --- /dev/null +++ b/Build/source/texk/web2c/tex.web @@ -0,0 +1,24970 @@ +% This program is copyright (C) 1982 by D. E. Knuth; all rights are reserved. +% Copying of this file is authorized only if (1) you are D. E. Knuth, or if +% (2) you make absolutely no changes to your copy. (The WEB system provides +% for alterations via an auxiliary file; the master file should stay intact.) +% See Appendix H of the WEB manual for hints on how to install this program. +% And see Appendix A of the TRIP manual for details about how to validate it. + +% TeX is a trademark of the American Mathematical Society. +% METAFONT is a trademark of Addison-Wesley Publishing Company. + +% 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). + +% A reward of $327.68 will be paid to the first finder of any remaining bug. + +% Although considerable effort has been expended to make the TeX program +% correct and reliable, no warranty is implied; the author disclaims any +% obligation or liability for damages, including but not limited to +% special, indirect, or consequential damages arising out of or in +% connection with the use or performance of this software. This work has +% been a ``labor of love'' and the author hopes that users enjoy it. + +% Here is TeX material that gets inserted after \input webmac +\def\hang{\hangindent 3em\noindent\ignorespaces} +\def\hangg#1 {\hang\hbox{#1 }} +\def\textindent#1{\hangindent2.5em\noindent\hbox to2.5em{\hss#1 }\ignorespaces} +\font\ninerm=cmr9 +\let\mc=\ninerm % medium caps for names like SAIL +\def\PASCAL{Pascal} +\def\ph{\hbox{Pascal-H}} +\def\pct!{{\char`\%}} % percent sign in ordinary text +\font\logo=logo10 % font used for the METAFONT logo +\def\MF{{\logo META}\-{\logo FONT}} +\def\<#1>{$\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{\TeX82} +\def\topofcontents{\hsize 5.5in + \vglue 0pt plus 1fil minus 1.5in + \def\?##1]{\hbox to 1in{\hfil##1.\ }} + } +\def\botofcontents{\vskip 0pt plus 1fil minus 1.5in} +\pageno=3 +\def\glob{13} % this should be the section number of "<Global...>" +\def\gglob{20, 26} % this should be the next two sections of "<Global...>" + +@* \[1] Introduction. +This is \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 +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@> + +If this program is changed, the resulting system should not be called +`\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]. + +@d banner=='This is TeX, Version 3.141592' {printed when \TeX\ starts} + +@ Different \PASCAL s have slightly different conventions, and the present +@!@:PASCAL H}{\ph@> +program expresses \TeX\ in terms of the \PASCAL\ that was +available to the author in 1982. Constructions that apply to +this particular compiler, which we shall call \ph, should help the +reader see how to make an appropriate interface for other systems +if necessary. (\ph\ is Charles Hedrick's modification of a compiler +@^Hedrick, Charles Locke@> +for the DECsystem-10 that was originally developed at the University of +Hamburg; cf.\ {\sl SOFTWARE---Practice \AM\ Experience \bf6} (1976), +29--42. The \TeX\ program below is intended to be adaptable, without +extensive changes, to most other versions of \PASCAL, so it does not fully +use the admirable features of \ph. Indeed, a conscious effort has been +made here to avoid using several idiosyncratic features of standard +\PASCAL\ itself, so that most of the code can be translated mechanically +into other high-level languages. For example, the `\&{with}' and `\\{new}' +features are not used, nor are pointer types, set types, or enumerated +scalar types; there are no `\&{var}' parameters, except in the case of files; +there are no tag fields on variant records; there are no assignments +|real:=integer|; no procedures are declared local to other procedures.) + +The portions of this program that involve system-dependent code, where +changes might be necessary because of differences between \PASCAL\ compilers +and/or differences between +operating systems, can be identified by looking at the sections whose +numbers are listed under `system dependencies' in the index. Furthermore, +the index entries for `dirty \PASCAL' list all places where the restrictions +of \PASCAL\ have not been followed perfectly, for one reason or another. +@!@^system dependencies@> +@!@^dirty \PASCAL@> + +Incidentally, \PASCAL's standard |round| function can be problematical, +because it disagrees with the IEEE floating-point standard. +Many implementors have +therefore chosen to substitute their own home-grown rounding procedure. + +@ The program begins with a normal \PASCAL\ program heading, whose +components will be filled in later, using the conventions of \.{WEB}. +@.WEB@> +For example, the portion of the program called `\X\glob:Global +variables\X' below will be replaced by a sequence of variable declarations +that starts in $\section\glob$ of this documentation. In this way, we are able +to define each individual global variable when we are prepared to +understand what it means; we do not have to define all of the globals at +once. Cross references in $\section\glob$, where it says ``See also +sections \gglob, \dots,'' also make it possible to look at the set of +all global variables, if desired. Similar remarks apply to the other +portions of the program heading. + +Actually the heading shown here is not quite normal: The |program| line +does not mention any |output| file, because \ph\ would ask the \TeX\ user +to specify a file name if |output| were specified here. +@^system dependencies@> + +@d mtype==t@&y@&p@&e {this is a \.{WEB} coding trick:} +@f mtype==type {`\&{mtype}' will be equivalent to `\&{type}'} +@f type==true {but `|type|' will not be treated as a reserved word} + +@p @t\4@>@<Compiler directives@>@/ +program TEX; {all file names are defined dynamically} +label @<Labels in the outer block@>@/ +const @<Constants in the outer block@>@/ +mtype @<Types in the outer block@>@/ +var @<Global variables@>@/ +@# +procedure initialize; {this procedure gets things started properly} + var @<Local variables for initialization@>@/ + begin @<Initialize whatever \TeX\ might access@>@; + end;@# +@t\4@>@<Basic printing procedures@>@/ +@t\4@>@<Error handling procedures@>@/ + +@ The overall \TeX\ program begins with the heading just shown, after which +comes a bunch of procedure declarations and function declarations. +Finally we will get to the main program, which begins with the +comment `|start_here|'. If you want to skip down to the +main program now, you can look up `|start_here|' in the index. +But the author suggests that the best way to understand this program +is to follow pretty much the order of \TeX's components as they appear in the +\.{WEB} description you are now reading, since the present ordering is +intended to combine the advantages of the ``bottom up'' and ``top down'' +approaches to the problem of understanding a somewhat complicated system. + +@ Three labels must be declared in the main program, so we give them +symbolic names. + +@d start_of_TEX=1 {go here when \TeX's variables are initialized} +@d end_of_TEX=9998 {go here to close files and terminate gracefully} +@d final_end=9999 {this label marks the ending of the program} + +@<Labels in the out...@>= +start_of_TEX@t\hskip-2pt@>, end_of_TEX@t\hskip-2pt@>,@,final_end; + {key control points} + +@ Some of the code below is intended to be used only when diagnosing the +strange behavior that sometimes occurs when \TeX\ is being installed or +when system wizards are fooling around with \TeX\ without quite knowing +what they are doing. Such code will not normally be compiled; it is +delimited by the codewords `$|debug|\ldots|gubed|$', with apologies +to people who wish to preserve the purity of English. + +Similarly, there is some conditional code delimited by +`$|stat|\ldots|tats|$' that is intended for use when statistics are to be +kept about \TeX's memory usage. The |stat| $\ldots$ |tats| code also +implements diagnostic information for \.{\\tracingparagraphs} and +\.{\\tracingpages}. +@^debugging@> + +@d debug==@{ {change this to `$\\{debug}\equiv\null$' when debugging} +@d gubed==@t@>@} {change this to `$\\{gubed}\equiv\null$' when debugging} +@f debug==begin +@f gubed==end +@# +@d stat==@{ {change this to `$\\{stat}\equiv\null$' when gathering + usage statistics} +@d tats==@t@>@} {change this to `$\\{tats}\equiv\null$' when gathering + usage statistics} +@f stat==begin +@f tats==end + +@ This program has two important variations: (1) There is a long and slow +version called \.{INITEX}, which does the extra calculations needed to +@.INITEX@> +initialize \TeX's internal tables; and (2)~there is a shorter and faster +production version, which cuts the initialization to a bare minimum. +Parts of the program that are needed in (1) but not in (2) are delimited by +the codewords `$|init|\ldots|tini|$'. + +@d init== {change this to `$\\{init}\equiv\.{@@\{}$' in the production version} +@d tini== {change this to `$\\{tini}\equiv\.{@@\}}$' in the production version} +@f init==begin +@f tini==end + +@<Initialize whatever...@>= +@<Set initial values of key variables@>@/ +@!init @<Initialize table entries (done by \.{INITEX} only)@>@;@+tini + +@ If the first character of a \PASCAL\ comment is a dollar sign, +\ph\ treats the comment as a list of ``compiler directives'' that will +affect the translation of this program into machine language. The +directives shown below specify full checking and inclusion of the \PASCAL\ +debugger when \TeX\ is being debugged, but they cause range checking and other +redundant code to be eliminated when the production system is being generated. +Arithmetic overflow will be detected in all cases. +@^system dependencies@> +@^Overflow in arithmetic@> + +@<Compiler directives@>= +@{@&$C-,A+,D-@} {no range check, catch arithmetic overflow, no debug overhead} +@!debug @{@&$C+,D+@}@+ gubed {but turn everything on when debugging} + +@ This \TeX\ implementation conforms to the rules of the {\sl Pascal User +@:PASCAL}{\PASCAL@> +@^system dependencies@> +Manual} published by Jensen and Wirth in 1975, except where system-dependent +@^Wirth, Niklaus@> +@^Jensen, Kathleen@> +code is necessary to make a useful system program, and except in another +respect where such conformity would unnecessarily obscure the meaning +and clutter up the code: We assume that |case| statements may include a +default case that applies if no matching label is found. Thus, we shall use +constructions like +$$\vbox{\halign{\ignorespaces#\hfil\cr +|case x of|\cr +1: $\langle\,$code for $x=1\,\rangle$;\cr +3: $\langle\,$code for $x=3\,\rangle$;\cr +|othercases| $\langle\,$code for |x<>1| and |x<>3|$\,\rangle$\cr +|endcases|\cr}}$$ +since most \PASCAL\ compilers have plugged this hole in the language by +incorporating some sort of default mechanism. For example, the \ph\ +compiler allows `|others|:' as a default label, and other \PASCAL s allow +syntaxes like `\&{else}' or `\&{otherwise}' or `\\{otherwise}:', etc. The +definitions of |othercases| and |endcases| should be changed to agree with +local conventions. Note that no semicolon appears before |endcases| in +this program, so the definition of |endcases| should include a semicolon +if the compiler wants one. (Of course, if no default mechanism is +available, the |case| statements of \TeX\ will have to be laboriously +extended by listing all remaining cases. People who are stuck with such +\PASCAL s have, in fact, done this, successfully but not happily!) + +@d othercases == others: {default for cases not listed explicitly} +@d endcases == @+end {follows the default case in an extended |case| statement} +@f othercases == else +@f endcases == end + +@ The following parameters can be changed at compile time to extend or +reduce \TeX's capacity. They may have different values in \.{INITEX} and +in production versions of \TeX. +@.INITEX@> +@^system dependencies@> + +@<Constants...@>= +@!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. + +@<Glob...@>= +@!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.) + +@<Check the ``constant'' values for consistency@>= +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 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. + +@<Types...@>= +@!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|} + +@<Local variables for init...@>= +@!i:integer; + +@ The \TeX\ processor converts between ASCII code and +the user's external character set by means of arrays |xord| and |xchr| +that are analogous to \PASCAL's |ord| and |chr| functions. + +@<Glob...@>= +@!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@> + +@<Set init...@>= +xchr[@'40]:=' '; +xchr[@'41]:='!'; +xchr[@'42]:='"'; +xchr[@'43]:='#'; +xchr[@'44]:='$'; +xchr[@'45]:='%'; +xchr[@'46]:='&'; +xchr[@'47]:='''';@/ +xchr[@'50]:='('; +xchr[@'51]:=')'; +xchr[@'52]:='*'; +xchr[@'53]:='+'; +xchr[@'54]:=','; +xchr[@'55]:='-'; +xchr[@'56]:='.'; +xchr[@'57]:='/';@/ +xchr[@'60]:='0'; +xchr[@'61]:='1'; +xchr[@'62]:='2'; +xchr[@'63]:='3'; +xchr[@'64]:='4'; +xchr[@'65]:='5'; +xchr[@'66]:='6'; +xchr[@'67]:='7';@/ +xchr[@'70]:='8'; +xchr[@'71]:='9'; +xchr[@'72]:=':'; +xchr[@'73]:=';'; +xchr[@'74]:='<'; +xchr[@'75]:='='; +xchr[@'76]:='>'; +xchr[@'77]:='?';@/ +xchr[@'100]:='@@'; +xchr[@'101]:='A'; +xchr[@'102]:='B'; +xchr[@'103]:='C'; +xchr[@'104]:='D'; +xchr[@'105]:='E'; +xchr[@'106]:='F'; +xchr[@'107]:='G';@/ +xchr[@'110]:='H'; +xchr[@'111]:='I'; +xchr[@'112]:='J'; +xchr[@'113]:='K'; +xchr[@'114]:='L'; +xchr[@'115]:='M'; +xchr[@'116]:='N'; +xchr[@'117]:='O';@/ +xchr[@'120]:='P'; +xchr[@'121]:='Q'; +xchr[@'122]:='R'; +xchr[@'123]:='S'; +xchr[@'124]:='T'; +xchr[@'125]:='U'; +xchr[@'126]:='V'; +xchr[@'127]:='W';@/ +xchr[@'130]:='X'; +xchr[@'131]:='Y'; +xchr[@'132]:='Z'; +xchr[@'133]:='['; +xchr[@'134]:='\'; +xchr[@'135]:=']'; +xchr[@'136]:='^'; +xchr[@'137]:='_';@/ +xchr[@'140]:='`'; +xchr[@'141]:='a'; +xchr[@'142]:='b'; +xchr[@'143]:='c'; +xchr[@'144]:='d'; +xchr[@'145]:='e'; +xchr[@'146]:='f'; +xchr[@'147]:='g';@/ +xchr[@'150]:='h'; +xchr[@'151]:='i'; +xchr[@'152]:='j'; +xchr[@'153]:='k'; +xchr[@'154]:='l'; +xchr[@'155]:='m'; +xchr[@'156]:='n'; +xchr[@'157]:='o';@/ +xchr[@'160]:='p'; +xchr[@'161]:='q'; +xchr[@'162]:='r'; +xchr[@'163]:='s'; +xchr[@'164]:='t'; +xchr[@'165]:='u'; +xchr[@'166]:='v'; +xchr[@'167]:='w';@/ +xchr[@'170]:='x'; +xchr[@'171]:='y'; +xchr[@'172]:='z'; +xchr[@'173]:='{'; +xchr[@'174]:='|'; +xchr[@'175]:='}'; +xchr[@'176]:='~';@/ + +@ Some of the ASCII codes without visible characters have been given symbolic +names in this program because they are used with a special meaning. + +@d null_code=@'0 {ASCII code that might disappear} +@d carriage_return=@'15 {ASCII code used at end of line} +@d invalid_code=@'177 {ASCII code that many systems prohibit in text files} + +@ The ASCII code is ``standard'' only to a certain extent, since many +computer installations have found it advantageous to have ready access +to more than 94 printing characters. Appendix~C of {\sl The \TeX book\/} +gives a complete specification of the intended correspondence between +characters and \TeX's internal representation. +@:TeXbook}{\sl The \TeX book@> + +If \TeX\ is being used +on a garden-variety \PASCAL\ for which only standard ASCII +codes will appear in the input and output files, it doesn't really matter +what codes are specified in |xchr[0..@'37]|, but the safest policy is to +blank everything out by using the code shown below. + +However, other settings of |xchr| will make \TeX\ more friendly on +computers that have an extended character set, so that users can type things +like `\.^^Z' instead of `\.{\\ne}'. People with extended character sets can +assign codes arbitrarily, giving an |xchr| equivalent to whatever +characters the users of \TeX\ are allowed to have in their input files. +It is best to make the codes correspond to the intended interpretations as +shown in Appendix~C whenever possible; but this is not necessary. For +example, in countries with an alphabet of more than 26 letters, it is +usually best to map the additional letters into codes less than~@'40. +To get the most ``permissive'' character set, change |' '| on the +right of these assignment statements to |chr(i)|. +@^character set dependencies@> +@^system dependencies@> + +@<Set init...@>= +for i:=0 to @'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<j<@'177|, the value of |xord[xchr[i]]| will turn out to be +|j| or more; hence, standard ASCII code numbers will be used instead of +codes below @'40 in case there is a coincidence. + +@<Set init...@>= +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. + +@<Types...@>= +@!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@> + +@<Glob...@>= +@!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 +@^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. + +@<Glob...@>= +@!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<buf_size| will always hold, so that there is always room for an +``empty'' line. + +The variable |max_buf_stack|, which is used to keep track of how large +the |buf_size| parameter must be to accommodate the present job, is +also kept up to date by |input_ln|. + +If the |bypass_eoln| parameter is |true|, |input_ln| will do a |get| +before looking at the first character of the line; this skips over +an |eoln| that was in |f^|. The procedure does not do a |get| when it +reaches the end of the line; therefore it can be used to acquire input +from the user's terminal as well as from ordinary text files. + +Standard \PASCAL\ says that a file should have |eoln| immediately +before |eof|, but \TeX\ needs only a weaker restriction: If |eof| +occurs in the middle of a line, the system function |eoln| should return +a |true| result (even though |f^| will be undefined). + +Since the inner loop of |input_ln| is part of \TeX's ``inner loop''---each +character of input comes in at this place---it is wise to reduce system +overhead by making use of special routines that read in an entire array +of characters at once, if such routines are available. The following +code uses standard \PASCAL\ to illustrate what needs to be done, but +finer tuning is often possible at well-developed \PASCAL\ sites. +@^inner loop@> + +@p function input_ln(var f:alpha_file;@!bypass_eoln:boolean):boolean; + {inputs the next line or returns |false|} +var last_nonblank:0..buf_size; {|last| with trailing blanks removed} +begin if bypass_eoln then if not eof(f) then get(f); + {input the first character of the line into |f^|} +last:=first; {cf.\ Matthew 19\thinspace:\thinspace30} +if eof(f) then input_ln:=false +else begin last_nonblank:=first; + while not eoln(f) do + begin if last>=max_buf_stack then + begin max_buf_stack:=last+1; + if max_buf_stack=buf_size then + @<Report overflow of the input buffer, and abort@>; + end; + buffer[last]:=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@> + +@<Glob...@>= +@!term_in:alpha_file; {the terminal as an input file} +@!term_out:alpha_file; {the terminal as an output file} + +@ Here is how to open the terminal files +in \ph. The `\.{/I}' switch suppresses the first |get|. +@^system dependencies@> + +@d t_open_in==reset(term_in,'TTY:','/O/I') {open the terminal for text input} +@d t_open_out==rewrite(term_out,'TTY:','/O') {open the terminal for text output} + +@ Sometimes it is necessary to synchronize the input/output mixture that +happens on the user's terminal, and three system-dependent +procedures are used for this +purpose. The first of these, |update_terminal|, is called when we want +to make sure that everything we have output to the terminal so far has +actually left the computer's internal buffers and been sent. +The second, |clear_terminal|, is called when we wish to cancel any +input that the user may have typed ahead (since we are about to +issue an unexpected error message). The third, |wake_up_terminal|, +is supposed to revive the terminal if the user has disabled it by +some instruction to the operating system. The following macros show how +these operations can be specified in \ph: +@^system dependencies@> + +@d update_terminal == break(term_out) {empty the terminal output buffer} +@d clear_terminal == break_in(term_in,true) {clear the terminal input buffer} +@d wake_up_terminal == do_nothing {cancel the user's cancellation of output} + +@ We need a special routine to read the first line of \TeX\ input from +the user's terminal. This line is different because it is read before we +have opened the transcript file; there is sort of a ``chicken and +egg'' problem here. If the user types `\.{\\input paper}' on the first +line, or if some macro invoked by that line does such an \.{\\input}, +the transcript file will be named `\.{paper.log}'; but if no \.{\\input} +commands are performed during the first line of terminal input, the transcript +file will acquire its default name `\.{texput.log}'. (The transcript file +will not contain error messages generated by the first line before the +first \.{\\input} command.) +@.texput@> + +The first line is even more special if we are lucky enough to have an operating +system that treats \TeX\ differently from a run-of-the-mill \PASCAL\ object +program. It's nice to let the user start running a \TeX\ job by typing +a command line like `\.{tex paper}'; in such a case, \TeX\ will operate +as if the first line of input were `\.{paper}', i.e., the first line will +consist of the remainder of the command line, after the part that invoked +\TeX. + +The first line is special also because it may be read before \TeX\ has +input a format file. In such cases, normal error messages cannot yet +be given. The following code uses concepts that will be explained later. +(If the \PASCAL\ compiler does not support non-local |@!goto|\unskip, the +@^system dependencies@> +statement `|goto final_end|' should be replaced by something that +quietly terminates the program.) + +@<Report overflow of the input buffer, and abort@>= +if format_ident=0 then + begin 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<last|. + +\yskip\noindent(It may be necessary to prompt the user several times +before a non-blank line comes in. The prompt is `\.{**}' instead of the +later `\.*' because the meaning is slightly different: `\.{\\input}' need +not be typed immediately after~`\.{**}'.) + +@d loc==cur_input.loc_field {location of first unread character in |buffer|} + +@ The following program does the required initialization +without retrieving a possible command line. +It should be clear how to modify this routine to deal with command lines, +if the system permits them. +@^system dependencies@> + +@p function init_terminal:boolean; {gets the terminal input started} +label exit; +begin t_open_in; +loop@+begin wake_up_terminal; write(term_out,'**'); update_terminal; +@.**@> + if not input_ln(term_in,true) then {this shouldn't happen} + begin 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<last)and(buffer[loc]=" ") do incr(loc); + if loc<last then + begin init_terminal:=true; + return; {return unless the line was all blank} + end; + write_ln(term_out,'Please type the name of your input file.'); + end; +exit:end; + +@* \[4] String handling. +Control sequence names and diagnostic messages are variable-length strings +of eight-bit characters. Since \PASCAL\ does not have a well-developed string +mechanism, \TeX\ does all of its string processing by homegrown methods. + +Elaborate facilities for dynamic strings are not needed, so all of the +necessary operations can be handled with a simple data structure. +The array |str_pool| contains all of the (eight-bit) ASCII codes in all +of the strings, and the array |str_start| contains indices of the starting +points of each string. Strings are referred to by integer numbers, so that +string number |s| comprises the characters |str_pool[j]| for +|str_start[s]<=j<str_start[s+1]|. Additional integer variables +|pool_ptr| and |str_ptr| indicate the number of entries used so far +in |str_pool| and |str_start|, respectively; locations +|str_pool[pool_ptr]| and |str_start[str_ptr]| are +ready for the next string to be allocated. + +String numbers 0 to 255 are reserved for strings that correspond to single +ASCII characters. This is in accordance with the conventions of \.{WEB}, +@.WEB@> +which converts single-character strings into the ASCII code number of the +single character involved, while it converts other strings into integers +and builds a string pool file. Thus, when the string constant \.{"."} appears +in the program below, \.{WEB} converts it into the integer 46, which is the +ASCII code for a period, while \.{WEB} will convert a string like \.{"hello"} +into some integer greater than~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. + +@d si(#) == # {convert from |ASCII_code| to |packed_ASCII_code|} +@d so(#) == # {convert from |packed_ASCII_code| to |ASCII_code|} + +@<Types...@>= +@!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} + +@ @<Glob...@>= +@!str_pool:packed array[pool_pointer] of packed_ASCII_code; {the characters} +@!str_start : array[str_number] of pool_pointer; {the starting pointers} +@!pool_ptr : pool_pointer; {first unused position in |str_pool|} +@!str_ptr : str_number; {number of the current string being created} +@!init_pool_ptr : pool_pointer; {the starting value of |pool_ptr|} +@!init_str_ptr : str_number; {the starting value of |str_ptr|} + +@ Several of the elementary string operations are performed using \.{WEB} +macros instead of \PASCAL\ procedures, because many of the +operations are done quite frequently and we want to avoid the +overhead of procedure calls. For example, here is +a simple macro that computes the length of a string. +@.WEB@> + +@d length(#)==(str_start[#+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 j<str_start[s+1] do + begin if so(str_pool[j])<>buffer[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 j<str_start[s+1] do + begin if str_pool[j]<>str_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; +@<Make the first 256 strings@>; +@<Read the other strings from the \.{TEX.POOL} file and return |true|, + or give an error message and return |false|@>; +exit:end; +tini + +@ @d app_lc_hex(#)==l:=#; + if l<10 then append_char(l+"0")@+else append_char(l-10+"a") + +@<Make the first 256...@>= +for k:=0 to 255 do + begin if (@<Character |k| cannot be printed@>) 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, @'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@> + +@<Character |k| cannot be printed@>= + (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. + +@<Glob...@>= +@!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 +@<Read the other strings...@>= +name_of_file:=pool_name; {we needn't set |name_length|} +if a_open_in(pool_file) then + begin c:=false; + repeat @<Read one string, but return |false| if the + string memory space is getting too tight for comfort@>; + 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@> + +@ @<Read one string...@>= +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 @<Check the pool check sum@> +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@> + +@<Check the pool 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} + +@<Glob...@>= +@!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} + +@ @<Initialize the output routines@>= +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|. + +@<Basic print...@>= +procedure print_ln; {prints an end-of-line} +begin case selector of +term_and_log: begin wterm_cr; wlog_cr; + term_offset:=0; file_offset:=0; + end; +log_only: begin wlog_cr; file_offset:=0; + end; +term_only: begin wterm_cr; term_offset:=0; + end; +no_print,pseudo,new_string: do_nothing; +othercases 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|. + +@<Basic printing...@>= +procedure print_char(@!s:ASCII_code); {prints a single character} +label exit; +begin if @<Character |s| is the current new-line character@> then + if selector<pseudo then + begin print_ln; return; + end; +case selector of +term_and_log: begin wterm(xchr[s]); wlog(xchr[s]); + incr(term_offset); incr(file_offset); + if term_offset=max_print_line then + begin wterm_cr; term_offset:=0; + end; + if file_offset=max_print_line then + begin wlog_cr; file_offset:=0; + end; + end; +log_only: begin wlog(xchr[s]); incr(file_offset); + if file_offset=max_print_line then print_ln; + end; +term_only: begin wterm(xchr[s]); incr(term_offset); + if term_offset=max_print_line then print_ln; + end; +no_print: do_nothing; +pseudo: if tally<trick_count then trick_buf[tally mod error_line]:=s; +new_string: begin if pool_ptr<pool_size then append_char(s); + end; {we drop characters if the string space is full} +othercases write(write_file[selector],xchr[s]) +endcases;@/ +incr(tally); +exit:end; + +@ An entire string is output by calling |print|. Note that if we are outputting +the single standard ASCII character \.c, we could call |print("c")|, since +|"c"=99| is the number of a single-character string, as explained above. But +|print_char("c")| is quicker, so \TeX\ goes directly to the |print_char| +routine when it knows that this is safe. (The present implementation +assumes that it is always safe to print a visible ASCII character.) +@^system dependencies@> + +@<Basic print...@>= +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 (@<Character |s| is the current new-line character@>) then + if selector<pseudo then + begin print_ln; return; + end; + nl:=new_line_char; new_line_char:=-1; + {temporarily disable new-line character} + j:=str_start[s]; + while j<str_start[s+1] do + begin print_char(so(str_pool[j])); incr(j); + end; + new_line_char:=nl; return; + end; +j:=str_start[s]; +while j<str_start[s+1] do + begin print_char(so(str_pool[j])); incr(j); + end; +exit:end; + +@ Control sequence names, file names, and strings constructed with +\.{\\string} might contain |ASCII_code| values that can't +be printed using |print_char|. Therefore we use |slow_print| for them: + +@<Basic print...@>= +procedure slow_print(@!s:integer); {prints string |s|} +var j:pool_pointer; {current character code position} +begin if (s>=str_ptr) or (s<256) then print(s) +else begin j:=str_start[s]; + while j<str_start[s+1] do + begin print(so(str_pool[j])); incr(j); + end; + end; +end; + +@ Here is the very first thing that \TeX\ prints: a headline that identifies +the version number and format package. The |term_offset| variable is temporarily +incorrect, but the discrepancy is not serious since we assume that the banner +and format identifier together will occupy at most |max_print_line| +character positions. + +@<Initialize the output...@>= +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. + +@<Basic print...@>= +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). + +@<Basic print...@>= +procedure print_esc(@!s:str_number); {prints escape character, then |s|} +var c:integer; {the escape character code} +begin @<Set variable |c| to the current escape character@>; +if c>=0 then if c<256 then print(c); +slow_print(s); +end; + +@ An array of digits in the range |0..15| is printed by |print_the_digs|. + +@<Basic print...@>= +procedure print_the_digs(@!k:eight_bits); + {prints |dig[k-1]|$\,\ldots\,$|dig[0]|} +begin while k>0 do + begin decr(k); + if dig[k]<10 then print_char("0"+dig[k]) + else print_char("A"-10+dig[k]); + end; +end; + +@ The following procedure, which prints out the decimal representation of a +given integer |n|, has been written carefully so that it works properly +if |n=0| or if |(-n)| would cause overflow. It does not apply |mod| or |div| +to negative arguments, since such operations are not implemented consistently +by all \PASCAL\ compilers. + +@<Basic print...@>= +procedure print_int(@!n:integer); {prints an integer in decimal form} +var k:0..23; {index to current digit; we assume that $|n|<10^{23}$} +@!m:integer; {used to negate |n| in possibly dangerous cases} +begin k:=0; +if n<0 then + begin print_char("-"); + if n>-100000000 then negate(n) + else begin m:=-1-n; n:=m div 10; m:=(m mod 10)+1; k:=1; + if m<10 then dig[0]:=m + else begin dig[0]:=0; incr(n); + end; + end; + end; +repeat dig[k]:=n mod 10; n:=n div 10; incr(k); +until n=0; +print_the_digs(k); +end; + +@ Here is a trivial procedure to print two digits; it is usually called with +a parameter in the range |0<=n<=99|. + +@p procedure print_two(@!n:integer); {prints two least significant digits} +begin n:=abs(n) mod 100; print_char("0"+(n div 10)); +print_char("0"+(n mod 10)); +end; + +@ Hexadecimal printing of nonnegative integers is accomplished by |print_hex|. + +@p procedure print_hex(@!n:integer); + {prints a positive integer in hexadecimal form} +var k:0..22; {index to current digit; we assume that $0\L n<16^{22}$} +begin k:=0; print_char(""""); +repeat dig[k]:=n mod 16; n:=n div 16; incr(k); +until n=0; +print_the_digs(k); +end; + +@ Old versions of \TeX\ needed a procedure called |print_ASCII| whose function +is now subsumed by |print|. We retain the old name here as a possible aid to +future software arch\ae ologists. + +@d print_ASCII == print + +@ 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<pool_ptr do + begin print_char(so(str_pool[j])); incr(j); + end; +end; + +@ Here is a procedure that asks the user to type a line of input, +assuming that the |selector| setting is either |term_only| or |term_and_log|. +The input is placed into locations |first| through |last-1| of the +|buffer| array, and echoed on the transcript file if appropriate. + +This procedure is never called when |interaction<scroll_mode|. + +@d prompt_input(#)==begin wake_up_terminal; print(#); term_input; + end {prints a string and gets a line of input} + +@p procedure term_input; {gets a line from the terminal} +var k:0..buf_size; {index into |buffer|} +begin update_terminal; {now the user sees the prompt for sure} +if not input_ln(term_in,true) then fatal_error("End of file on the terminal!"); +@.End of file on the terminal@> +term_offset:=0; {the user's line ended with \<\rm return>} +decr(selector); {prepare to echo the input} +if last<>first then for k:=first to last-1 do print(buffer[k]); +print_ln; incr(selector); {restore previous status} +end; + +@* \[6] Reporting errors. +When something anomalous is detected, \TeX\ typically does something like this: +$$\vbox{\halign{#\hfil\cr +|print_err("Something anomalous has been detected");|\cr +|help3("This is the first line of my offer to help.")|\cr +|("This is the second line. I'm trying to")|\cr +|("explain the best way for you to proceed.");|\cr +|error;|\cr}}$$ +A two-line help message would be given using |help2|, etc.; these informal +helps should use simple vocabulary that complements the words used in the +official error message that was printed. (Outside the U.S.A., the help +messages should preferably be translated into the local vernacular. Each +line of help is at most 60 characters long, in the present implementation, +so that |max_print_line| will not be exceeded.) + +The |print_err| procedure supplies a `\.!' before the official message, +and makes sure that the terminal is awake if a stop is going to occur. +The |error| procedure supplies a `\..' after the official message, then it +shows the location of the error; and if |interaction=error_stop_mode|, +it also enters into a dialog with the user, during which time the help +message may be printed. +@^system dependencies@> + +@ The global variable |interaction| has four settings, representing increasing +amounts of user interaction: + +@d batch_mode=0 {omits all stops and omits terminal output} +@d nonstop_mode=1 {omits all stops} +@d scroll_mode=2 {omits error stops} +@d error_stop_mode=3 {stops at every opportunity to interact} +@d print_err(#)==begin if interaction=error_stop_mode then wake_up_terminal; + print_nl("! "); print(#); + end + +@<Glob...@>= +@!interaction:batch_mode..error_stop_mode; {current level of interaction} + +@ @<Set init...@>=interaction:=error_stop_mode; + +@ \TeX\ is careful not to call |error| when the print |selector| setting +might be unusual. The only possible values of |selector| at the time of +error messages are + +\yskip\hang|no_print| (when |interaction=batch_mode| + and |log_file| not yet open); + +\hang|term_only| (when |interaction>batch_mode| and |log_file| not yet open); + +\hang|log_only| (when |interaction=batch_mode| and |log_file| is open); + +\hang|term_and_log| (when |interaction>batch_mode| and |log_file| is open). + +@<Initialize the print |selector| based on |interaction|@>= +if interaction=batch_mode then selector:=no_print@+else selector:=term_only + +@ A global variable |deletions_allowed| is set |false| if the |get_next| +routine is active when |error| is called; this ensures that |get_next| +and related routines like |get_token| will never be called recursively. +A similar interlock is provided by |set_box_allowed|. +@^recursion@> + +The global variable |history| records the worst level of error that +has been detected. It has four possible values: |spotless|, |warning_issued|, +|error_message_issued|, and |fatal_error_stop|. + +Another global variable, |error_count|, is increased by one when an +|error| occurs without an interactive dialog, and it is reset to zero at +the end of every paragraph. If |error_count| reaches 100, \TeX\ decides +that there is no point in continuing further. + +@d spotless=0 {|history| value when nothing has been amiss yet} +@d warning_issued=1 {|history| value when |begin_diagnostic| has been called} +@d error_message_issued=2 {|history| value when |error| has been called} +@d fatal_error_stop=3 {|history| value when termination was premature} + +@<Glob...@>= +@!deletions_allowed:boolean; {is it safe for |error| to call |get_token|?} +@!set_box_allowed:boolean; {is it safe to do a \.{\\setbox} assignment?} +@!history:spotless..fatal_error_stop; {has the source input been clean so far?} +@!error_count:-1..100; {the number of scrolled errors since the + last paragraph ended} + +@ The value of |history| is initially |fatal_error_stop|, but it will +be changed to |spotless| if \TeX\ survives the initialization process. + +@<Set init...@>= +deletions_allowed:=true; set_box_allowed:=true; +error_count:=0; {|history| is initialized elsewhere} + +@ Since errors can be detected almost anywhere in \TeX, we want to declare the +error procedures near the beginning of the program. But the error procedures +in turn use some other procedures, which need to be declared |forward| +before we get to |error| itself. + +It is possible for |error| to be called recursively if some error arises +when |get_token| is being used to delete a token, and/or if some fatal error +occurs while \TeX\ is trying to fix a non-fatal one. But such recursion +@^recursion@> +is never more than two levels deep. + +@<Error handling...@>= +procedure@?normalize_selector; forward;@t\2@>@/ +procedure@?get_token; forward;@t\2@>@/ +procedure@?term_input; forward;@t\2@>@/ +procedure@?show_context; forward;@t\2@>@/ +procedure@?begin_file_reading; forward;@t\2@>@/ +procedure@?open_log_file; forward;@t\2@>@/ +procedure@?close_files_and_terminate; forward;@t\2@>@/ +procedure@?clear_for_error_prompt; forward;@t\2@>@/ +procedure@?give_err_help; forward;@t\2@>@/ +@t\4\hskip-\fontdimen2\font@>@;@+@!debug@+procedure@?debug_help; + forward;@;@+gubed + +@ Individual lines of help are recorded in the array |help_line|, which +contains entries in positions |0..(help_ptr-1)|. They should be printed +in reverse order, i.e., with |help_line[0]| appearing last. + +@d hlp1(#)==help_line[0]:=#;@+end +@d hlp2(#)==help_line[1]:=#; hlp1 +@d hlp3(#)==help_line[2]:=#; hlp2 +@d hlp4(#)==help_line[3]:=#; hlp3 +@d hlp5(#)==help_line[4]:=#; hlp4 +@d hlp6(#)==help_line[5]:=#; hlp5 +@d help0==help_ptr:=0 {sometimes there might be no help} +@d help1==@+begin help_ptr:=1; hlp1 {use this with one help line} +@d help2==@+begin help_ptr:=2; hlp2 {use this with two help lines} +@d help3==@+begin help_ptr:=3; hlp3 {use this with three help lines} +@d help4==@+begin help_ptr:=4; hlp4 {use this with four help lines} +@d help5==@+begin help_ptr:=5; hlp5 {use this with five help lines} +@d help6==@+begin help_ptr:=6; hlp6 {use this with six help lines} + +@<Glob...@>= +@!help_line:array[0..5] of str_number; {helps for the next |error|} +@!help_ptr:0..6; {the number of help lines present} +@!use_err_help:boolean; {should the |err_help| list be shown?} + +@ @<Set init...@>= +help_ptr:=0; use_err_help:=false; + +@ The |jump_out| procedure just cuts across all active procedure levels and +goes to |end_of_TEX|. This is the only nontrivial |@!goto| statement in the +whole program. It is used when there is no recovery from a particular error. + +Some \PASCAL\ compilers do not implement non-local |goto| statements. +@^system dependencies@> +In such cases the body of |jump_out| should simply be +`|close_files_and_terminate|;\thinspace' followed by a call on some system +procedure that quietly terminates the program. + +@<Error hand...@>= +procedure jump_out; +begin goto end_of_TEX; +end; + +@ Here now is the general |error| routine. + +@<Error hand...@>= +procedure error; {completes the job of error reporting} +label continue,exit; +var c:ASCII_code; {what the user types} +@!s1,@!s2,@!s3,@!s4:integer; + {used to save global variables when deleting tokens} +begin if history<error_message_issued then history:=error_message_issued; +print_char("."); show_context; +if interaction=error_stop_mode then @<Get user's advice and |return|@>; +incr(error_count); +if error_count=100 then + begin print_nl("(That makes 100 errors; please try again.)"); +@.That makes 100 errors...@> + history:=fatal_error_stop; jump_out; + end; +@<Put help message on the transcript file@>; +exit:end; + +@ @<Get user's advice...@>= +loop@+begin continue: clear_for_error_prompt; prompt_input("? "); +@.?\relax@> + if last=first then return; + c:=buffer[first]; + if c>="a" then c:=c+"A"-"a"; {convert to uppercase} + @<Interpret code |c| and |return| if done@>; + end + +@ It is desirable to provide an `\.E' option here that gives the user +an easy way to return from \TeX\ to the system editor, with the offending +line ready to be edited. But such an extension requires some system +wizardry, so the present implementation simply types out the name of the +file that should be +edited and the relevant line number. +@^system dependencies@> + +There is a secret `\.D' option available when the debugging routines haven't +been commented~out. +@^debugging@> + +@<Interpret code |c| and |return| if done@>= +case c of +"0","1","2","3","4","5","6","7","8","9": if deletions_allowed then + @<Delete \(c)|c-"0"| tokens and |goto continue|@>; +@t\4\4@>@;@+@!debug "D": begin debug_help; goto continue;@+end;@+gubed@/ +"E": if base_ptr>0 then + begin print_nl("You want to edit file "); +@.You want to edit file x@> + slow_print(input_stack[base_ptr].name_field); + print(" at line "); print_int(line); + interaction:=scroll_mode; jump_out; + end; +"H": @<Print the help information and |goto continue|@>; +"I":@<Introduce new material from the terminal and |return|@>; +"Q","R","S":@<Change the interaction level and |return|@>; +"X":begin interaction:=scroll_mode; jump_out; + end; +othercases do_nothing +endcases;@/ +@<Print the menu of available options@> + +@ @<Print the menu...@>= +begin print("Type <return> to proceed, S to scroll future error messages,");@/ +@.Type <return> to proceed...@> +print_nl("R to run without stopping, Q to run quietly,");@/ +print_nl("I to insert something, "); +if base_ptr>0 then print("E to edit your file,"); +if deletions_allowed then + print_nl("1 or ... or 9 to ignore the next 1 to 9 tokens of input,"); +print_nl("H for help, X to quit."); +end + +@ Here the author of \TeX\ apologizes for making use of the numerical +relation between |"Q"|, |"R"|, |"S"|, and the desired interaction settings +|batch_mode|, |nonstop_mode|, |scroll_mode|. +@^Knuth, Donald Ervin@> + +@<Change the interaction...@>= +begin error_count:=0; interaction:=batch_mode+c-"Q"; +print("OK, entering "); +case c of +"Q":begin print_esc("batchmode"); decr(selector); + end; +"R":print_esc("nonstopmode"); +"S":print_esc("scrollmode"); +end; {there are no other cases} +print("..."); print_ln; update_terminal; return; +end + +@ When the following code is executed, |buffer[(first+1)..(last-1)]| may +contain the material inserted by the user; otherwise another prompt will +be given. In order to understand this part of the program fully, you need +to be familiar with \TeX's input stacks. + +@<Introduce new material...@>= +begin begin_file_reading; {enter a new syntactic level for terminal input} +{now |state=mid_line|, so an initial blank space will count as a blank} +if last>first+1 then + begin loc:=first+1; buffer[first]:=" "; + end +else begin prompt_input("insert>"); loc:=first; +@.insert>@> + end; +first:=last; +cur_input.limit_field:=last-1; {no |end_line_char| ends this line} +return; +end + +@ We allow deletion of up to 99 tokens at a time. + +@<Delete \(c)|c-"0"| tokens...@>= +begin s1:=cur_tok; s2:=cur_cmd; s3:=cur_chr; s4:=align_state; +align_state:=1000000; OK_to_interrupt:=false; +if (last>first+1) and (buffer[first+1]>="0")and(buffer[first+1]<="9") then + c:=c*10+buffer[first+1]-"0"*11 +else c:=c-"0"; +while c>0 do + begin get_token; {one-level recursive call of |error| is possible} + decr(c); + end; +cur_tok:=s1; cur_cmd:=s2; cur_chr:=s3; align_state:=s4; OK_to_interrupt:=true; +help2("I have just deleted some text, as you asked.")@/ +("You can now delete more, or insert, or whatever."); +show_context; goto continue; +end + +@ @<Print the help info...@>= +begin if use_err_help then + begin give_err_help; use_err_help:=false; + end +else begin if help_ptr=0 then + help2("Sorry, I don't know how to help in this situation.")@/ + @t\kern1em@>("Maybe you should try asking a human?"); + repeat decr(help_ptr); print(help_line[help_ptr]); print_ln; + until help_ptr=0; + end; +help4("Sorry, I already gave what help I could...")@/ + ("Maybe you should try asking a human?")@/ + ("An error might have occurred before I noticed any problems.")@/ + ("``If all else fails, read the instructions.''");@/ +goto continue; +end + +@ @<Put help message on the transcript file@>= +if interaction>batch_mode then decr(selector); {avoid terminal output} +if use_err_help then + begin print_ln; give_err_help; + end +else while help_ptr>0 do + begin decr(help_ptr); print_nl(help_line[help_ptr]); + end; +print_ln; +if interaction>batch_mode then incr(selector); {re-enable terminal output} +print_ln + +@ A dozen or so error messages end with a parenthesized integer, so we +save a teeny bit of program space by declaring the following procedure: + +@p procedure int_error(@!n:integer); +begin print(" ("); print_int(n); print_char(")"); error; +end; + +@ In anomalous cases, the print selector might be in an unknown state; +the following subroutine is called to fix things just enough to keep +running a bit longer. + +@p procedure normalize_selector; +begin if log_opened then selector:=term_and_log +else selector:=term_only; +if job_name=0 then open_log_file; +if interaction=batch_mode then decr(selector); +end; + +@ The following procedure prints \TeX's last words before dying. + +@d succumb==begin if interaction=error_stop_mode then + interaction:=scroll_mode; {no more interaction} + if log_opened then error; + @!debug if interaction>batch_mode then debug_help;@+gubed@;@/ + history:=fatal_error_stop; jump_out; {irrecoverable error} + end + +@<Error hand...@>= +procedure fatal_error(@!s:str_number); {prints |s|, and that's it} +begin normalize_selector;@/ +print_err("Emergency stop"); help1(s); succumb; +@.Emergency stop@> +end; + +@ Here is the most dreaded error message. + +@<Error hand...@>= +procedure 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@> + +@<Error hand...@>= +procedure confusion(@!s:str_number); + {consistency check violated; |s| tells where} +begin normalize_selector; +if history<error_message_issued then + begin print_err("This can't happen ("); print(s); print_char(")"); +@.This can't happen@> + help1("I'm broken. Please show this to someone who can fix can fix"); + end +else begin print_err("I can't go on meeting you like this"); +@.I can't go on...@> + help2("One of your faux pas seems to have wounded me deeply...")@/ + ("in fact, I'm barely conscious. Please fix it and try again."); + end; +succumb; +end; + +@ Users occasionally want to interrupt \TeX\ while it's running. +If the \PASCAL\ runtime system allows this, one can implement +a routine that sets the global variable |interrupt| to some nonzero value +when such an interrupt is signalled. Otherwise there is probably at least +a way to make |interrupt| nonzero using the \PASCAL\ debugger. +@^system dependencies@> +@^debugging@> + +@d check_interrupt==begin if interrupt<>0 then pause_for_instructions; + end + +@<Global...@>= +@!interrupt:integer; {should \TeX\ pause for instructions?} +@!OK_to_interrupt:boolean; {should interrupts be observed?} + +@ @<Set init...@>= +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 some instructions for me (e.g.,`I\showlists'),")@/ + ("unless you just want to quit by typing `X'."); + deletions_allowed:=false; error; deletions_allowed:=true; + interrupt:=0; + end; +end; + +@* \[7] Arithmetic with scaled dimensions. +The principal computations performed by \TeX\ are done entirely in terms of +integers less than $2^{31}$ in magnitude; and divisions are done only when both +dividend and divisor are nonnegative. Thus, the arithmetic specified in this +program can be carried out in exactly the same way on a wide variety of +computers, including some small ones. Why? Because the arithmetic +calculations need to be spelled out precisely in order to guarantee that +\TeX\ will produce identical output on different machines. If some +quantities were rounded differently in different implementations, we would +find that line breaks and even page breaks might occur in different places. +Hence the arithmetic of \TeX\ has been designed with care, and systems that +claim to be implementations of \TeX82 should follow precisely the +@:TeX82}{\TeX82@> +calculations as they appear in the present program. + +(Actually there are three places where \TeX\ uses |div| with a possibly negative +numerator. These are harmless; see |div| in the index. Also if the user +sets the \.{\\time} or the \.{\\year} to a negative value, some diagnostic +information will involve negative-numerator division. The same remarks +apply for |mod| as well as for |div|.) + +@ Here is a routine that calculates half of an integer, using an +unambiguous convention with respect to signed odd numbers. + +@p function half(@!x:integer):integer; +begin if odd(x) then half:=(x+1) div 2 +else half:=x @!div 2; +end; + +@ Fixed-point arithmetic is done on {\sl scaled integers\/} that are multiples +of $2^{-16}$. In other words, a binary point is assumed to be sixteen bit +positions from the right end of a binary computer word. + +@d unity == @'200000 {$2^{16}$, represents 1.00000} +@d two == @'400000 {$2^{17}$, represents 2.00000} + +@<Types...@>= +@!scaled = integer; {this type is used for scaled integers} +@!nonnegative_integer=0..@'17777777777; {$0\L x<2^{31}$} +@!small_number=0..63; {this type is self-explanatory} + +@ The following function is used to create a scaled integer from a given decimal +fraction $(.d_0d_1\ldots d_{k-1})$, where |0<=k<=17|. The digit $d_i$ is +given in |dig[i]|, and the calculation produces a correctly rounded result. + +@p function round_decimals(@!k:small_number) : scaled; + {converts a decimal fraction} +var a:integer; {the accumulator} +begin a:=0; +while k>0 do + begin decr(k); a:=(a+dig[k]*two) div 10; + end; +round_decimals:=(a+1) div 2; +end; + +@ Conversely, here is a procedure analogous to |print_int|. If the output +of this procedure is subsequently read by \TeX\ and converted by the +|round_decimals| routine above, it turns out that the original value will +be reproduced exactly; the ``simplest'' such decimal number is output, +but there is always at least one digit following the decimal point. + +The invariant relation in the \&{repeat} loop is that a sequence of +decimal digits yet to be printed will yield the original number if and only if +they form a fraction~$f$ in the range $s-\delta\L10\cdot2^{16}f<s$. +We can stop if and only if $f=0$ satisfies this condition; the loop will +terminate before $s$ can possibly become zero. + +@p procedure print_scaled(@!s:scaled); {prints scaled real, rounded to five + digits} +var delta:scaled; {amount of allowable inaccuracy} +begin if s<0 then + begin print_char("-"); negate(s); {print the sign, if negative} + end; +print_int(s div unity); {print the integer part} +print_char("."); +s:=10*(s mod unity)+5; delta:=10; +repeat if delta>unity then s:=s+@'100000-50000; {round the last digit} +print_char("0"+(s div unity)); s:=10*(s mod unity); delta:=delta*10; +until s<=delta; +end; + +@ Physical sizes that a \TeX\ user specifies for portions of documents are +represented internally as scaled points. Thus, if we define an `sp' (scaled +@^sp@> +point) as a unit equal to $2^{-16}$ printer's points, every dimension +inside of \TeX\ is an integer number of sp. There are exactly +4,736,286.72 sp per inch. Users are not allowed to specify dimensions +larger than $2^{30}-1$ sp, which is a distance of about 18.892 feet (5.7583 +meters); two such quantities can be added without overflow on a 32-bit +computer. + +The present implementation of \TeX\ does not check for overflow when +@^Overflow in arithmetic@> +dimensions are added or subtracted. This could be done by inserting a +few dozen tests of the form `\ignorespaces|if x>=@'10000000000 then +@t\\{report\_overflow}@>|', but the chance of overflow is so remote that +such tests do not seem worthwhile. + +\TeX\ needs to do only a few arithmetic operations on scaled quantities, +other than addition and subtraction, and the following subroutines do most of +the work. A single computation might use several subroutine calls, and it is +desirable to avoid producing multiple error messages in case of arithmetic +overflow; so the routines set the global variable |arith_error| to |true| +instead of reporting errors directly to the user. Another global variable, +|remainder|, holds the remainder after a division. + +@<Glob...@>= +@!arith_error:boolean; {has arithmetic overflow occurred recently?} +@!remainder:scaled; {amount subtracted to get an exact division} + +@ The first arithmetical subroutine we need computes $nx+y$, where |x| +and~|y| are |scaled| and |n| is an integer. We will also use it to +multiply integers. + +@d nx_plus_y(#)==mult_and_add(#,@'7777777777) +@d mult_integers(#)==mult_and_add(#,0,@'17777777777) + +@p function mult_and_add(@!n:integer;@!x,@!y,@!max_answer:scaled):scaled; +begin if n<0 then + begin negate(x); negate(n); + end; +if n=0 then mult_and_add:=y +else if ((x<=(max_answer-y) div n)and(-x<=(max_answer+y) div n)) then + mult_and_add:=n*x+y +else begin arith_error:=true; mult_and_add:=0; + end; +end; + +@ We also need to divide scaled dimensions by integers. + +@p function x_over_n(@!x:scaled;@!n:integer):scaled; +var negative:boolean; {should |remainder| be negated?} +begin negative:=false; +if n=0 then + begin arith_error:=true; x_over_n:=0; remainder:=x; + end +else begin if n<0 then + begin negate(x); negate(n); negative:=true; + end; + if x>=0 then + begin x_over_n:=x div n; remainder:=x mod n; + end + else begin x_over_n:=-((-x) div n); remainder:=-((-x) mod n); + end; + end; +if negative then negate(remainder); +end; + +@ Then comes the multiplication of a scaled number by a fraction |n/d|, +where |n| and |d| are nonnegative integers |<=@t$2^{16}$@>| and |d| is +positive. It would be too dangerous to multiply by~|n| and then divide +by~|d|, in separate operations, since overflow might well occur; and it +would be too inaccurate to divide by |d| and then multiply by |n|. Hence +this subroutine simulates 1.5-precision arithmetic. + +@p function xn_over_d(@!x:scaled; @!n,@!d:integer):scaled; +var positive:boolean; {was |x>=0|?} +@!t,@!u,@!v:nonnegative_integer; {intermediate quantities} +begin if x>=0 then positive:=true +else begin negate(x); positive:=false; + end; +t:=(x mod @'100000)*n; +u:=(x div @'100000)*n+(t div @'100000); +v:=(u mod d)*@'100000 + (t mod @'100000); +if u div d>=@'100000 then arith_error:=true +else u:=@'100000*(u div d) + (v div d); +if positive then + begin xn_over_d:=u; remainder:=v mod d; + end +else begin xn_over_d:=-u; remainder:=-(v mod d); + end; +end; + +@ The next subroutine is used to compute the ``badness'' of glue, when a +total~|t| is supposed to be made from amounts that sum to~|s|. According +to {\sl The \TeX book}, the badness of this situation is $100(t/s)^3$; +however, badness is simply a heuristic, so we need not squeeze out the +last drop of accuracy when computing it. All we really want is an +approximation that has similar properties. +@:TeXbook}{\sl The \TeX book@> + +The actual method used to compute the badness is easier to read from the +program than to describe in words. It produces an integer value that is a +reasonably close approximation to $100(t/s)^3$, and all implementations +of \TeX\ should use precisely this method. Any badness of $2^{13}$ or more is +treated as infinitely bad, and represented by 10000. + +It is not difficult to prove that $$\hbox{|badness(t+1,s)>=badness(t,s) +>=badness(t,s+1)|}.$$ The badness function defined here is capable of +computing at most 1095 distinct values, but that is plenty. + +@d inf_bad = 10000 {infinitely bad value} + +@p function badness(@!t,@!s:scaled):halfword; {compute badness, given |t>=0|} +var r:integer; {approximation to $\alpha t/s$, where $\alpha^3\approx + 100\cdot2^{18}$} +begin if t=0 then badness:=0 +else if s<=0 then badness:=inf_bad +else begin if t<=7230584 then r:=(t*297) div s {$297^3=99.94\times2^{18}$} + else if s>=1663497 then r:=t div (s div 297) + else r:=t; + if r>1290 then badness:=inf_bad {$1290^3<2^{31}<1291^3$} + else badness:=(r*r*r+@'400000) div @'1000000; + end; {that was $r^3/2^{18}$, rounded to the nearest integer} +end; + +@ When \TeX\ ``packages'' a list into a box, it needs to calculate the +proportionality ratio by which the glue inside the box should stretch +or shrink. This calculation does not affect \TeX's decision making, +so the precise details of rounding, etc., in the glue calculation are not +of critical importance for the consistency of results on different computers. + +We shall use the type |glue_ratio| for such proportionality ratios. +A glue ratio should take the same amount of memory as an +|integer| (usually 32 bits) if it is to blend smoothly with \TeX's +other data structures. Thus |glue_ratio| should be equivalent to +|short_real| in some implementations of \PASCAL. Alternatively, +it is possible to deal with glue ratios using nothing but fixed-point +arithmetic; see {\sl TUGboat \bf3},1 (March 1982), 10--27. (But the +routines cited there must be modified to allow negative glue ratios.) +@^system dependencies@> + +@d set_glue_ratio_zero(#) == #:=0.0 {store the representation of zero ratio} +@d set_glue_ratio_one(#) == #:=1.0 {store the representation of unit ratio} +@d float(#) == # {convert from |glue_ratio| to type |real|} +@d unfloat(#) == # {convert from |real| to type |glue_ratio|} +@d float_constant(#) == #.0 {convert |integer| constant to |real|} + +@<Types...@>= +@!glue_ratio=real; {one-word representation of a glue expansion factor} + +@* \[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): + +@<Check the ``constant''...@>= +init if (mem_min<>mem_bot)or(mem_max<>mem_top) then bad:=10;@+tini@;@/ +if (mem_min>mem_bot)or(mem_max<mem_top) then bad:=10; +if (min_quarterword>0)or(max_quarterword<127) then bad:=11; +if (min_halfword>0)or(max_halfword<32767) then bad:=12; +if (min_quarterword<min_halfword)or@| + (max_quarterword>max_halfword) then bad:=13; +if (mem_min<min_halfword)or(mem_max>=max_halfword)or@| + (mem_bot-mem_min>max_halfword+1) then bad:=14; +if (font_base<min_quarterword)or(font_max>max_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|} + +@<Types...@>= +@!quarterword = min_quarterword..max_quarterword; {1/4 of a word} +@!halfword=min_halfword..max_halfword; {1/2 of a word} +@!two_choices = 1..2; {used when there are two variants in a record} +@!four_choices = 1..4; {used when there are four variants in a record} +@!two_halves = packed record@;@/ + @!rh:halfword; + case two_choices of + 1: (@!lh:halfword); + 2: (@!b0:quarterword; @!b1:quarterword); + end; +@!four_quarters = packed record@;@/ + @!b0:quarterword; + @!b1:quarterword; + @!b2:quarterword; + @!b3:quarterword; + end; +@!memory_word = record@;@/ + case four_choices of + 1: (@!int:integer); + 2: (@!gr:glue_ratio); + 3: (@!hh:two_halves); + 4: (@!qqqq:four_quarters); + end; +@!word_file = file of memory_word; + +@ When debugging, we may want to print a |memory_word| without knowing +what type it is; so we print it in all modes. +@^dirty \PASCAL@>@^debugging@> + +@p @!debug procedure print_word(@!w:memory_word); + {prints |w| in all ways} +begin print_int(w.int); print_char(" ");@/ +print_scaled(w.sc); print_char(" ");@/ +print_scaled(round(unity*float(w.gr))); print_ln;@/ +@^real multiplication@> +print_int(w.hh.lh); print_char("="); print_int(w.hh.b0); print_char(":"); +print_int(w.hh.b1); print_char(";"); print_int(w.hh.rh); print_char(" ");@/ +print_int(w.qqqq.b0); print_char(":"); print_int(w.qqqq.b1); print_char(":"); +print_int(w.qqqq.b2); print_char(":"); print_int(w.qqqq.b3); +end; +gubed + +@* \[9] Dynamic memory allocation. +The \TeX\ system does nearly all of its own memory allocation, so that it +can readily be transported into environments that do not have automatic +facilities for strings, garbage collection, etc., and so that it can be in +control of what error messages the user receives. The dynamic storage +requirements of \TeX\ are handled by providing 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} + +@<Glob...@>= +@!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: +$$\advance\thickmuskip-2mu +\hbox{|null<=mem_min<=mem_bot<lo_mem_max< + hi_mem_min<mem_top<=mem_end<=mem_max|.}$$ + +Empirical tests show that the present implementation of \TeX\ tends to +spend about 9\pct! of its running time allocating nodes, and about 6\pct! +deallocating them after their use. + +@<Glob...@>= +@!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. + +@<Glob...@>= +@!var_used, @!dyn_used : integer; {how much memory is in use} + +@ Let's consider the one-word memory region first, since it's the +simplest. The pointer variable |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} + +@<Glob...@>= +@!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 @<Declare the procedure called |show_token_list|@>@/ +@<Declare the procedure called |runaway|@> + +@ The function |get_avail| returns a pointer to a new one-word node whose +|link| field is null. However, \TeX\ will halt if there is no more room left. +@^inner loop@> + +If the available-space list is empty, i.e., if |avail=null|, +we try first to increase |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<mem_max then {or go into virgin territory} + begin incr(mem_end); p:=mem_end; + end +else begin decr(hi_mem_min); p:=hi_mem_min; + if hi_mem_min<=lo_mem_max then + begin runaway; {if memory is exhausted, display possible runaway text} + overflow("main memory size",mem_max+1-mem_min); + {quit; all one-word nodes are busy} +@:TeX capacity exceeded main memory size}{\quad main memory size@> + 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<max_halfword| because terrible things can happen +when |max_halfword| appears in the |link| field of a nonempty node.) + +@d empty_flag == max_halfword {the |link| of an empty variable-size node} +@d is_empty(#) == (link(#)=empty_flag) {tests for empty node} +@d node_size == info {the size field in empty variable-size nodes} +@d llink(#) == info(#+1) {left link in doubly-linked list of empty nodes} +@d rlink(#) == link(#+1) {right link in doubly-linked list of empty nodes} + +@<Glob...@>= +@!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 @<Try to allocate within node |p| and its physical successors, + and |goto found| if allocation was possible@>; +@^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<hi_mem_min then if lo_mem_max+2<=mem_bot+max_halfword then + @<Grow more variable-size memory and |goto restart|@>; +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@> + +@<Grow more variable-size memory and |goto restart|@>= +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<=t<hi_mem_min|} +p:=llink(rover); q:=lo_mem_max; rlink(p):=q; llink(rover):=q;@/ +if t>mem_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. + +@<Try to allocate...@>= +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 @<Allocate from the top of node |p| and |goto found|@>; +if r=p then if rlink(p)<>p then + @<Allocate entire node |p| and |goto found|@>; +node_size(p):=q-p {reset the size in case it grew} + +@ @<Allocate from the top...@>= +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. + +@<Allocate entire...@>= +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 @<Sort \(p)|p| into the list starting at |rover| + and advance |p| to |rlink(p)|@>; +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. + +@<Sort \(p)|p|...@>= +if p<rover then + begin q:=p; p:=rlink(q); rlink(q):=rover; rover:=q; + end +else begin q:=rover; + while rlink(q)<p do q:=rlink(q); + r:=rlink(p); rlink(p):=rlink(q); rlink(q):=p; p:=r; + end + +@* \[10] Data structures for boxes and their friends. +From the computer's standpoint, \TeX's chief mission is to create +horizontal and vertical lists. We shall now investigate how the elements +of these lists are represented internally as nodes in the dynamic memory. + +A horizontal or vertical list is linked together by |link| fields in +the first word of each node. Individual nodes represent boxes, glue, +penalties, or special things like discretionary hyphens; because of this +variety, some nodes are longer than others, and we must distinguish different +kinds of nodes. We do this by putting a `|type|' field in the first word, +together with the link and an optional `|subtype|'. + +@d type(#) == mem[#].hh.b0 {identifies what kind of node this is} +@d subtype(#) == mem[#].hh.b1 {secondary identification in some cases} + +@ A |@!char_node|, which represents a single character, is the most important +kind of node because it accounts for the vast majority of all boxes. +Special precautions are therefore taken to ensure that a |char_node| does +not take up much memory space. Every such node is one word long, and in fact +it is identifiable by this property, since other kinds of nodes have at least +two words, and they appear in |mem| locations less than |hi_mem_min|. +This makes it possible to omit the |type| field in a |char_node|, leaving +us room for two bytes that identify a |font| and a |character| within +that font. + +Note that the format of a |char_node| allows for up to 256 different +fonts and up to 256 characters per font; but most implementations will +probably limit the total number of fonts to fewer than 75 per job, +and most fonts will stick to characters whose codes are +less than 128 (since higher codes +are more difficult to access on most keyboards). + +Extensions of \TeX\ intended for oriental languages will need even more +than $256\times256$ possible characters, when we consider different sizes +@^oriental characters@>@^Chinese characters@>@^Japanese characters@> +and styles of type. It is suggested that Chinese and Japanese fonts be +handled by representing such characters in two consecutive |char_node| +entries: The first of these has |font=font_base|, and its |link| points +to the second; +the second identifies the font and the character dimensions. +The saving feature about oriental characters is that most of them have +the same box dimensions. The |character| field of the first |char_node| +is a ``\\{charext}'' that distinguishes between graphic symbols whose +dimensions are identical for typesetting purposes. (See the \MF\ manual.) +Such an extension of \TeX\ would not be difficult; further details are +left to the reader. + +In order to make sure that the |character| code fits in a quarterword, +\TeX\ adds the quantity |min_quarterword| to the actual code. + +Character nodes appear only in horizontal lists, never in vertical lists. + +@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. + +@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|, since that's the desired +|span_count| value if this |hlist_node| is changed to an |unset_node|. + +@p function new_null_box:pointer; {creates a new box node} +var p:pointer; {the new node} +begin p:=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. +This field occupies a full word instead of a halfword, because +there's nothing to put in the other halfword; it is easier in \PASCAL\ to +use the full word than to risk leaving garbage in the unused half. + +@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(#)==mem[#+1].int {head of the token list for a mark} + +@ 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_ptr==mark_ptr {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}. + +@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} + +@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(#)<math_node) +@d non_discardable(#)==(type(#)<math_node) + +@ A |glue_node| represents glue in a list. However, it is really only +a pointer to a separate glue specification, since \TeX\ makes use of the +fact that many essentially identical nodes of glue are usually present. +If |p| points to a |glue_node|, |glue_ptr(p)| points to +another packet of words that specify the stretch and shrink components, etc. + +Glue nodes also serve to represent leaders; the |subtype| is used to +distinguish between ordinary glue (which is called |normal|) and the three +kinds of leaders (which are called |a_leaders|, |c_leaders|, and |x_leaders|). +The |leader_ptr| field points to a rule node or to a box node containing the +leaders; it is set to |null| in ordinary glue nodes. + +Many kinds of glue are computed from \TeX's ``skip'' parameters, and +it is helpful to know which parameter has led to a particular glue node. +Therefore the |subtype| is set to indicate the source of glue, whenever +it originated as a parameter. We will be defining symbolic names for the +parameter numbers later (e.g., |line_skip_code=0|, |baseline_skip_code=1|, +etc.); it suffices for now to say that the |subtype| of parametric glue +will be the same as the parameter number, plus~one. + +In math formulas there are two more possibilities for the |subtype| in a +glue node: |mu_glue| denotes an \.{\\mskip} (where the units are scaled \.{mu} +instead of scaled \.{pt}); and |cond_math_glue| denotes the `\.{\\nonscript}' +feature that cancels the glue node immediately following if it appears +in a subscript. + +@d glue_node=10 {|type| of node that points to a glue specification} +@d cond_math_glue=98 {special |subtype| to suppress glue in the next node} +@d mu_glue=99 {|subtype| for math glue} +@d a_leaders=100 {|subtype| for aligned leaders} +@d c_leaders=101 {|subtype| for centered leaders} +@d x_leaders=102 {|subtype| for expanded leaders} +@d glue_ptr==llink {pointer to a glue specification} +@d leader_ptr==rlink {pointer to box or rule node for leaders} + +@ A glue specification has a halfword reference count in its first word, +@^reference counts@> +representing |null| plus the number of glue nodes that point to it (less one). +Note that the reference count appears in the same position as +the |link| field in list nodes; this is the field that is initialized +to |null| when a node is allocated, and it is also the field that is flagged +by |empty_flag| in empty nodes. + +Glue specifications also contain three |scaled| fields, for the |width|, +|stretch|, and |shrink| dimensions. Finally, there are two one-byte +fields called |stretch_order| and |shrink_order|; these contain the +orders of infinity (|normal|, |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} + +@<Types...@>= +@!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:=@<Current |mem| equivalent of glue parameter number |n|@>@t@>; +glue_ptr(p):=q; incr(glue_ref_count(q)); +new_param_glue:=p; +end; + +@ Glue nodes that are more or less anonymous are created by |new_glue|, +whose argument points to a glue specification. + +@p function new_glue(@!q:pointer):pointer; +var p:pointer; {the new node} +begin p:=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(@<Current |mem| equivalent of glue parameter...@>); +p:=new_glue(temp_ptr); glue_ref_count(temp_ptr):=null; subtype(p):=n+1; +new_skip_param:=p; +end; + +@ A |kern_node| has a |width| field to specify a (normally negative) +amount of spacing. This spacing correction appears in horizontal lists +between letters like A and V when the font designer said that it looks +better to move them closer together or further apart. A kern node can +also appear in a vertical list, when its `|width|' denotes additional +spacing in the vertical direction. The |subtype| is either |normal| (for +kerns inserted from font information or math mode calculations) or |explicit| +(for kerns inserted from \.{\\kern} and \.{\\/} commands) or |acc_kern| +(for kerns inserted from non-math accents) or |mu_glue| (for kerns +inserted from \.{\\mkern} specifications in math formulas). + +@d kern_node=11 {|type| of a kern node} +@d explicit=1 {|subtype| of kern nodes from \.{\\kern} and \.{\\/}} +@d acc_kern=2 {|subtype| of kern nodes from accents} + +@ 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 hi_mem_stat_min==mem_top-13 {smallest statically allocated word in + the one-word |mem|} +@d hi_mem_stat_usage=14 {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. + +@<Local variables for init...@>= +@!k:integer; {index into |mem|, |eqtb|, etc.} + +@ @<Initialize table entries...@>= +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} +@<Initialize the special list heads and constant nodes@>; +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.) + +@<Glob...@>= +@!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 + +@ @<Set initial...@>= +@!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} +@<Check single-word |avail| list@>; +@<Check variable-size |avail| list@>; +@<Check flags of unavailable nodes@>; +if print_locs then @<Print newly busy locations@>; +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 + +@ @<Check single-word...@>= +p:=avail; q:=null; clobbered:=false; +while p<>null do + begin if (p>mem_end)or(p<hi_mem_min) then clobbered:=true + else if free[p] then clobbered:=true; + if clobbered then + begin print_nl("AVAIL list clobbered at "); +@.AVAIL list clobbered...@> + print_int(q); goto done1; + end; + free[p]:=true; q:=p; p:=link(q); + end; +done1: + +@ @<Check variable-size...@>= +p:=rover; q:=null; clobbered:=false; +repeat if (p>=lo_mem_max)or(p<mem_min) then clobbered:=true + else if (rlink(p)>=lo_mem_max)or(rlink(p)<mem_min) then clobbered:=true + else if not(is_empty(p))or(node_size(p)<2)or@| + (p+node_size(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: + +@ @<Check flags...@>= +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 + +@ @<Print newly busy...@>= +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 + ((p<was_hi_min) or (p>was_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; +@<Search |eqtb| for equivalents equal to |p|@>; +@<Search |save_stack| for equivalents that point to |p|@>; +@<Search |hyph_list| for pointers to |p|@>; +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. + +@<Glob...@>= +@!font_in_short_display:integer; {an internal font number} + +@ Boxes, rules, inserts, whatsits, marks, and things in general that are +sort of ``complicated'' are indicated only by printing `\.{[]}'. + +@p procedure 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_base)or(font(p)>font_max) then + print_char("*") +@.*\relax@> + else @<Print the font identifier for |font(p)|@>; + print_char(" "); font_in_short_display:=font(p); + end; + print_ASCII(qo(character(p))); + end; + end + else @<Print a short indication of the contents of node |p|@>; + p:=link(p); + end; +end; + +@ @<Print a short indication of the contents of node |p|@>= +case type(p) of +hlist_node,vlist_node,ins_node,whatsit_node,mark_node,adjust_node, + unset_node: print("[]"); +rule_node: print_char("|"); +glue_node: if glue_ptr(p)<>zero_glue then print_char(" "); +math_node: print_char("$"); +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_base)or(font(p)>font_max) then print_char("*") +@.*\relax@> + else @<Print the font identifier for |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 (p<hi_mem_min)or(p>mem_end) then print_esc("CLOBBERED.") +else show_token_list(link(p),null,max_print_line-10); +print_char("}"); +end; +@# +procedure print_rule_dimen(@!d:scaled); {prints dimension in rule node} +begin if is_running(d) then print_char("*") else print_scaled(d); +@.*\relax@> +end; + +@ Then there is a subroutine that prints glue stretch and shrink, possibly +followed by the name of finite units: + +@p procedure print_glue(@!d:scaled;@!order:integer;@!s:str_number); + {prints a glue component} +begin print_scaled(d); +if (order<normal)or(order>filll) then print("foul") +else if order>normal then + begin print("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<mem_min)or(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 @<Declare procedures needed for displaying the elements of mlists@>@; +@<Declare the procedure called |print_skip_param|@> + +@ Since boxes can be inside of boxes, |show_node_list| is inherently recursive, +@^recursion@> +up to a given maximum number of levels. The history of nesting is indicated +by the current string, which will be printed at the beginning of each line; +the length of this string, namely |cur_length|, is the depth of nesting. + +Recursive calls on |show_node_list| therefore use the following pattern: + +@d node_list_display(#)== + begin append_char("."); show_node_list(#); flush_char; + end {|str_room| need not be checked; see |show_box| below} + +@ A global variable called |depth_threshold| is used to record the maximum +depth of nesting for which |show_node_list| will show information. If we +have |depth_threshold=0|, for example, only the top level information will +be given and no sublists will be traversed. Another global variable, called +|breadth_max|, tells the maximum number of items to show at each level; +|breadth_max| had better be positive, or you won't see anything. + +@<Glob...@>= +@!depth_threshold : integer; {maximum nesting depth in box displays} +@!breadth_max : integer; {maximum number of items shown at the same list level} + +@ Now we are ready for |show_node_list| itself. This procedure has been +written to be ``extra robust'' in the sense that it should not crash or get +into a loop even if the data structures have been messed up by bugs in +the rest of the program. You can safely call its parent routine +|show_box(p)| for arbitrary values of |p| when you are debugging \TeX. +However, in the presence of bad data, the procedure may +@^dirty \PASCAL@>@^debugging@> +fetch a |memory_word| whose variant is different from the way it was stored; +for example, it might try to read |mem[p].hh| when |mem[p]| +contains a scaled integer, if |p| is a pointer that has been +clobbered or chosen at random. + +@p procedure show_node_list(@!p:integer); {prints a node list symbolically} +label exit; +var n:integer; {the number of items already printed at this level} +@!g:real; {a glue ratio, as a floating point number} +begin if cur_length>depth_threshold then + begin if p>null then print(" []"); + {indicate that there's been some truncation} + return; + end; +n:=0; +while p>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; + @<Display node |p|@>; + p:=link(p); + end; +exit: +end; + +@ @<Display node |p|@>= +if is_char_node(p) then print_font_and_char(p) +else case type(p) of + hlist_node,vlist_node,unset_node: @<Display box |p|@>; + rule_node: @<Display rule |p|@>; + ins_node: @<Display insertion |p|@>; + whatsit_node: @<Display the whatsit node |p|@>; + glue_node: @<Display glue |p|@>; + kern_node: @<Display kern |p|@>; + math_node: @<Display math node |p|@>; + ligature_node: @<Display ligature |p|@>; + penalty_node: @<Display penalty |p|@>; + disc_node: @<Display discretionary |p|@>; + mark_node: @<Display mark |p|@>; + adjust_node: @<Display adjustment |p|@>; + @t\4@>@<Cases of |show_node_list| that arise in mlists only@>@; + othercases print("Unknown node type!") + endcases + +@ @<Display box |p|@>= +begin if type(p)=hlist_node then print_esc("h") +else if type(p)=vlist_node then print_esc("v") +else print_esc("unset"); +print("box("); print_scaled(height(p)); print_char("+"); +print_scaled(depth(p)); print(")x"); print_scaled(width(p)); +if type(p)=unset_node then + @<Display special fields of the unset node |p|@> +else begin @<Display the value of |glue_set(p)|@>; + if shift_amount(p)<>0 then + begin print(", shifted "); print_scaled(shift_amount(p)); + end; + end; +node_list_display(list_ptr(p)); {recursive call} +end + +@ @<Display special fields of the unset node |p|@>= +begin if span_count(p)<>min_quarterword then + begin print(" ("); print_int(qo(span_count(p))+1); + print(" columns)"); + end; +if glue_stretch(p)<>0 then + begin print(", stretch "); print_glue(glue_stretch(p),glue_order(p),0); + end; +if glue_shrink(p)<>0 then + begin print(", shrink "); print_glue(glue_shrink(p),glue_sign(p),0); + end; +end + +@ The code will have to change in this place if |glue_ratio| is +a structured type instead of an ordinary |real|. Note that this routine +should avoid arithmetic errors even if the |glue_set| field holds an +arbitrary random value. The following code assumes that a properly +formed nonzero |real| number has absolute value $2^{20}$ or more when +it is regarded as an integer; this precaution was adequate to prevent +floating point underflow on the author's computer. +@^system dependencies@> +@^dirty \PASCAL@> + +@<Display the value of |glue_set(p)|@>= +g:=float(glue_set(p)); +if (g<>float_constant(0))and(glue_sign(p)<>normal) then + begin print(", glue set "); + if glue_sign(p)=shrinking then print("- "); + if abs(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 + +@ @<Display rule |p|@>= +begin print_esc("rule("); print_rule_dimen(height(p)); print_char("+"); +print_rule_dimen(depth(p)); print(")x"); print_rule_dimen(width(p)); +end + +@ @<Display insertion |p|@>= +begin print_esc("insert"); print_int(qo(subtype(p))); +print(", natural size "); print_scaled(height(p)); +print("; split("); print_spec(split_top_ptr(p),0); +print_char(","); print_scaled(depth(p)); +print("); float cost "); print_int(float_cost(p)); +node_list_display(ins_ptr(p)); {recursive call} +end + +@ @<Display glue |p|@>= +if subtype(p)>=a_leaders then @<Display leaders |p|@> +else begin print_esc("glue"); + if subtype(p)<>normal then + begin print_char("("); + if subtype(p)<cond_math_glue then + print_skip_param(subtype(p)-1) + else if subtype(p)=cond_math_glue then print_esc("nonscript") + else print_esc("mskip"); + print_char(")"); + end; + if subtype(p)<>cond_math_glue then + begin print_char(" "); + if subtype(p)<cond_math_glue then print_spec(glue_ptr(p),0) + else print_spec(glue_ptr(p),"mu"); + end; + end + +@ @<Display leaders |p|@>= +begin print_esc(""); +if subtype(p)=c_leaders then print_char("c") +else if subtype(p)=x_leaders then print_char("x"); +print("leaders "); print_spec(glue_ptr(p),0); +node_list_display(leader_ptr(p)); {recursive call} +end + +@ An ``explicit'' kern value is indicated implicitly by an explicit space. + +@<Display kern |p|@>= +if subtype(p)<>mu_glue then + begin print_esc("kern"); + if subtype(p)<>normal then print_char(" "); + print_scaled(width(p)); + if subtype(p)=acc_kern then print(" (for accent)"); +@.for accent@> + end +else begin print_esc("mkern"); print_scaled(width(p)); print("mu"); + end + +@ @<Display math node |p|@>= +begin print_esc("math"); +if subtype(p)=before then print("on") +else print("off"); +if width(p)<>0 then + begin print(", surrounded "); print_scaled(width(p)); + end; +end + +@ @<Display ligature |p|@>= +begin print_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 + +@ @<Display penalty |p|@>= +begin print_esc("penalty "); print_int(penalty(p)); +end + +@ The |post_break| list of a discretionary node is indicated by a prefixed +`\.{\char'174}' instead of the `\..' before the |pre_break| list. + +@<Display discretionary |p|@>= +begin print_esc("discretionary"); +if 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 + +@ @<Display mark |p|@>= +begin print_esc("mark"); print_mark(mark_ptr(p)); +end + +@ @<Display adjustment |p|@>= +begin print_esc("vadjust"); node_list_display(adjust_ptr(p)); {recursive call} +end + +@ The recursive machinery is started by calling |show_box|. +@^recursion@> + +@p procedure show_box(@!p:pointer); +begin @<Assign the values |depth_threshold:=show_box_depth| and + |breadth_max:=show_box_breadth|@>; +if breadth_max<=0 then breadth_max:=5; +if pool_ptr+depth_threshold>=pool_size then + depth_threshold:=pool_size-pool_ptr-1; + {now there's enough room for prefix string} +show_node_list(p); {the show starts at |p|} +print_ln; +end; + +@* \[13] Destroying boxes. +When we are done with a node list, we are obliged to return it to free +storage, including all of its sublists. The recursive procedure +|flush_node_list| does this for us. + +@ First, however, we shall consider two non-recursive procedures that do +simpler tasks. The first of these, |delete_token_ref|, is called when +a pointer to a token list's reference count is being removed. This means +that the token list should disappear if the reference count was |null|, +otherwise the count should be decreased by one. +@^reference counts@> + +@d token_ref_count(#) == info(#) {reference count preceding a token list} + +@p procedure delete_token_ref(@!p:pointer); {|p| points to the reference count + of a token list that is losing one reference} +begin 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: @<Wipe out the whatsit node |p| and |goto done|@>; + 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; + 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@>@<Cases of |flush_node_list| that arise in mlists only@>@; + 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 @<Make a copy of node |p| in node |r|@>; + link(q):=r; q:=r; p:=link(p); + end; +link(q):=null; q:=link(h); free_avail(h); +copy_node_list:=q; +end; + +@ @<Make a copy of node |p|...@>= +words:=1; {this setting occurs in more branches than any other} +if is_char_node(p) then r:=get_avail +else @<Case statement to copy different types and set |words| to the number + of initial words not yet copied@>; +while words>0 do + begin decr(words); mem[r+words]:=mem[p+words]; + end + +@ @<Case statement to copy...@>= +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:@<Make a partial copy of the whatsit node |p| and make |r| + point to it; set |words| to the number of initial words not yet copied@>; +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; +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 \<v_j> list in alignment template} +@d spacer=10 {characters equivalent to blank space ( \.{\ } )} +@d letter=11 {characters regarded as letters ( \.{A..Z}, \.{a..z} )} +@d other_char=12 {none of the special character types} +@d active_char=13 {characters that invoke macros ( \.{\char`\~} )} +@d par_end=13 {end of paragraph ( \.{\\par} )} +@d match=13 {match a macro parameter} +@d comment=14 {characters that introduce comments ( \.\% )} +@d end_match=14 {end of parameters to macro} +@d stop=14 {end of job ( \.{\\end}, \.{\\dump} )} +@d invalid_char=15 {characters that shouldn't appear ( \.{\^\^?} )} +@d delim_num=15 {specify delimiter numerically ( \.{\\delimiter} )} +@d max_char_code=15 {largest catcode for individual characters} + +@ Next are the ordinary run-of-the-mill command codes. Codes that are +|min_internal| or more represent internal quantities that might be +expanded by `\.{\\the}'. + +@d char_num=16 {character specified numerically ( \.{\\char} )} +@d math_char_num=17 {explicit math code ( \.{\\mathchar} )} +@d mark=18 {mark definition ( \.{\\mark} )} +@d xray=19 {peek inside of \TeX\ ( \.{\\show}, \.{\\showbox}, etc.~)} +@d make_box=20 {make a box ( \.{\\box}, \.{\\copy}, \.{\\hbox}, etc.~)} +@d hmove=21 {horizontal motion ( \.{\\moveleft}, \.{\\moveright} )} +@d vmove=22 {vertical motion ( \.{\\raise}, \.{\\lower} )} +@d un_hbox=23 {unglue a box ( \.{\\unhbox}, \.{\\unhcopy} )} +@d un_vbox=24 {unglue a box ( \.{\\unvbox}, \.{\\unvcopy} )} +@d remove_item=25 {nullify last item ( \.{\\unpenalty}, + \.{\\unkern}, \.{\\unskip} )} +@d hskip=26 {horizontal glue ( \.{\\hskip}, \.{\\hfil}, etc.~)} +@d vskip=27 {vertical glue ( \.{\\vskip}, \.{\\vfil}, etc.~)} +@d mskip=28 {math glue ( \.{\\mskip} )} +@d kern=29 {fixed space ( \.{\\kern})} +@d mkern=30 {math kern ( \.{\\mkern} )} +@d leader_ship=31 {use a box ( \.{\\shipout}, \.{\\leaders}, etc.~)} +@d halign=32 {horizontal table alignment ( \.{\\halign} )} +@d valign=33 {vertical table alignment ( \.{\\valign} )} +@d no_align=34 {temporary escape from alignment ( \.{\\noalign} )} +@d vrule=35 {vertical rule ( \.{\\vrule} )} +@d hrule=36 {horizontal rule ( \.{\\hrule} )} +@d insert=37 {vlist inserted in box ( \.{\\insert} )} +@d vadjust=38 {vlist inserted in enclosing paragraph ( \.{\\vadjust} )} +@d ignore_spaces=39 {gobble |spacer| tokens ( \.{\\ignorespaces} )} +@d after_assignment=40 {save till assignment is done ( \.{\\afterassignment} )} +@d after_group=41 {save till group is done ( \.{\\aftergroup} )} +@d break_penalty=42 {additional badness ( \.{\\penalty} )} +@d start_par=43 {begin paragraph ( \.{\\indent}, \.{\\noindent} )} +@d ital_corr=44 {italic correction ( \.{\\/} )} +@d accent=45 {attach accent in text ( \.{\\accent} )} +@d math_accent=46 {attach accent in math ( \.{\\mathaccent} )} +@d discretionary=47 {discretionary texts ( \.{\\-}, \.{\\discretionary} )} +@d eq_no=48 {equation number ( \.{\\eqno}, \.{\\leqno} )} +@d left_right=49 {variable delimiter ( \.{\\left}, \.{\\right} )} +@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} )} +@d set_box_dimen=83 {change dimension of box ( \.{\\wd}, \.{\\ht}, \.{\\dp} )} +@d set_shape=84 {specify fancy paragraph shape ( \.{\\parshape} )} +@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} )} +@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} )} +@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 max_command=100 {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} )} +@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} )} +@d top_bot_mark=max_command+10 {inserted mark ( \.{\\topmark}, etc.~)} +@d call=max_command+11 {non-long, non-outer control sequence} +@d long_call=max_command+12 {long, non-outer control sequence} +@d outer_call=max_command+13 {non-long, outer control sequence} +@d long_outer_call=max_command+14 {long, outer control sequence} +@d end_template=max_command+15 {end of an alignment template} +@d dont_expand=max_command+16 {the following token was marked by \.{\\noexpand}} +@d glue_ref=max_command+17 {the equivalent points to a glue specification} +@d shape_ref=max_command+18 {the equivalent points to a parshape specification} +@d box_ref=max_command+19 {the equivalent points to a box node, or is |null|} +@d data=max_command+20 {the equivalent is simply a halfword number} + +@* \[16] The semantic nest. +\TeX\ is typically in the midst of building many lists at once. For example, +when a math formula is being processed, \TeX\ is in math mode and +working on an mlist; this formula has temporarily interrupted \TeX\ from +being in horizontal mode and building the hlist of a paragraph; and this +paragraph has temporarily interrupted \TeX\ from being in vertical mode +and building the vlist for the next page of a document. Similarly, when a +\.{\\vbox} occurs inside of an \.{\\hbox}, \TeX\ is temporarily +interrupted from working in restricted horizontal mode, and it enters +internal vertical mode. The ``semantic nest'' is a stack that +keeps track of what lists and modes are currently suspended. + +At each level of processing we are in one of six modes: + +\yskip\hang|vmode| stands for vertical mode (the page builder); + +\hang|hmode| stands for horizontal mode (the paragraph builder); + +\hang|mmode| stands for displayed formula mode; + +\hang|-vmode| stands for internal vertical mode (e.g., in a \.{\\vbox}); + +\hang|-hmode| stands for restricted horizontal mode (e.g., in an \.{\\hbox}); + +\hang|-mmode| stands for math formula mode (not displayed). + +\yskip\noindent The mode is temporarily set to zero while processing \.{\\write} +texts in the |ship_out| routine. + +Numeric values are assigned to |vmode|, |hmode|, and |mmode| so that +\TeX's ``big semantic switch'' can select the appropriate thing to +do by computing the value |abs(mode)+cur_cmd|, where |mode| is the current +mode and |cur_cmd| is the current command code. + +@d vmode=1 {vertical mode} +@d hmode=vmode+max_command+1 {horizontal mode} +@d mmode=hmode+max_command+1 {math mode} + +@p procedure print_mode(@!m:integer); {prints the mode represented by |m|} +begin if m>0 then + case m div (max_command+1) of + 0:print("vertical"); + 1:print("horizontal"); + 2:print("display math"); + end +else if m=0 then print("no") +else case (-m) div (max_command+1) of + 0:print("internal vertical"); + 1:print("restricted horizontal"); + 2:print("math"); + end; +print(" mode"); +end; + +@ 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. + +In horizontal mode, the |prev_graf| field is used for initial language data. + +The semantic nest is an array called |nest| that holds the |mode|, |head|, +|tail|, |prev_graf|, |aux|, and |mode_line| values for all semantic levels +below the currently active one. Information about the currently active +level is kept in the global quantities |mode|, |head|, |tail|, |prev_graf|, +|aux|, and |mode_line|, which live in a \PASCAL\ record that is ready to +be pushed onto |nest| if necessary. + +@d ignore_depth==-65536000 {|prev_depth| value that is ignored} + +@<Types...@>= +@!list_state_record=record@!mode_field:-mmode..mmode;@+ + @!head_field,@!tail_field: pointer; + @!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 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} + +@<Glob...@>= +@!nest:array[0..nest_size] of list_state_record; +@!nest_ptr:0..nest_size; {first unused location of |nest|} +@!max_nest_stack:0..nest_size; {maximum of |nest_ptr| when pushing} +@!cur_list:list_state_record; {the ``top'' semantic state} +@!shown_mode:-mmode..mmode; {most recent mode shown by \.{\\tracingcommands}} + +@ 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. + +@<Set init...@>= +nest_ptr:=0; max_nest_stack:=0; +mode:=vmode; head:=contrib_head; tail:=contrib_head; +prev_depth:=ignore_depth; mode_line:=0; +prev_graf:=0; shown_mode:=0; +@<Start a new current page@>; + +@ 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; +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 @<Show the status of the current page@>; + if link(contrib_head)<>null then + print_nl("### recent contributions:"); + end; + show_box(link(nest[p].head_field)); + @<Show the auxiliary field, |a|@>; + end; +end; + +@ @<Show the auxiliary...@>= +case abs(m) div (max_command+1) of +0: begin print_nl("prevdepth "); + if a.sc<=ignore_depth then print("ignored") + else print_scaled(a.sc); + if nest[p].pg_field<>0 then + begin print(", prevgraf "); + print_int(nest[p].pg_field); print(" line"); + if nest[p].pg_field<>1 then print_char("s"); + end; + end; +1: begin print_nl("spacefactor "); print_int(a.hh.lh); + if m>0 then@+ if a.hh.rh>0 then + begin print(", current language "); print_int(a.hh.rh);@+ + end; + end; +2: if a.int<>null then + begin print("this will be denominator of:"); show_box(a.int);@+ + end; +end {there are no other cases} + +@* \[17] The table of equivalents. +Now that we have studied the data structures for \TeX's semantic routines, +we ought to consider the data structures used by its syntactic routines. In +other words, our next concern will be +the tables that \TeX\ looks at when it is scanning +what the user has written. + +The biggest and most important such table is called |eqtb|. It holds the +current ``equivalents'' of things; i.e., it explains what things mean +or what their current values are, for all quantities that are subject to +the nesting structure provided by \TeX's grouping mechanism. There are six +parts to |eqtb|: + +\yskip\hangg 1) |eqtb[active_base..(hash_base-1)]| holds the current +equivalents of single-character control sequences. + +\yskip\hangg 2) |eqtb[hash_base..(glue_base-1)]| holds the current +equivalents of multiletter control sequences. + +\yskip\hangg 3) |eqtb[glue_base..(local_base-1)]| holds the current +equivalents of glue parameters like the current baselineskip. + +\yskip\hangg 4) |eqtb[local_base..(int_base-1)]| holds the current +equivalents of local halfword quantities like the current box registers, +the current ``catcodes,'' the current font, and a pointer to the current +paragraph shape. + +\yskip\hangg 5) |eqtb[int_base..(dimen_base-1)]| holds the current +equivalents of fullword integer parameters like the current hyphenation +penalty. + +\yskip\hangg 6) |eqtb[dimen_base..eqtb_size]| holds the current equivalents +of fullword dimension parameters like the current hsize or amount of +hanging indentation. + +\yskip\noindent Note that, for example, the current amount of +baselineskip glue is determined by the setting of a particular location +in region~3 of |eqtb|, while the current meaning of the control sequence +`\.{\\baselineskip}' (which might have been changed by \.{\\def} or +\.{\\let}) appears in region~2. + +@ Each entry in |eqtb| is a |memory_word|. Most of these words are of type +|two_halves|, and subdivided into three fields: + +\yskip\hangg 1) The |eq_level| (a quarterword) is the level of grouping at +which this equivalent was defined. If the level is |level_zero|, the +equivalent has never been defined; |level_one| refers to the outer level +(outside of all groups), and this level is also used for global +definitions that never go away. Higher levels are for equivalents that +will disappear at the end of their group. @^global definitions@> + +\yskip\hangg 2) The |eq_type| (another quarterword) specifies what kind of +entry this is. There are many types, since each \TeX\ primitive like +\.{\\hbox}, \.{\\def}, etc., has its own special code. The list of +command codes above includes all possible settings of the |eq_type| field. + +\yskip\hangg 3) The |equiv| (a halfword) is the current equivalent value. +This may be a font number, a pointer into |mem|, or a variety of other +things. + +@d eq_level_field(#)==#.hh.b1 +@d eq_type_field(#)==#.hh.b0 +@d equiv_field(#)==#.hh.rh +@d eq_level(#)==eq_level_field(eqtb[#]) {level of definition} +@d eq_type(#)==eq_type_field(eqtb[#]) {command code for equivalent} +@d equiv(#)==equiv_field(eqtb[#]) {equivalent value} +@d level_zero=min_quarterword {level for undefined quantities} +@d level_one=level_zero+1 {outermost level for defined quantities} + +@ Many locations in |eqtb| have symbolic names. The purpose of the next +paragraphs is to define these names, and to set up the initial values of the +equivalents. + +In the first region we have 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 frozen_null_font=frozen_control_sequence+10 + {permanent `\.{\\nullfont}'} +@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} + +@<Initialize table entries...@>= +eq_type(undefined_control_sequence):=undefined_cs; +equiv(undefined_control_sequence):=null; +eq_level(undefined_control_sequence):=level_zero; +for k:=active_base to undefined_control_sequence-1 do + eqtb[k]:=eqtb[undefined_control_sequence]; + +@ Here is a routine that displays the current meaning of an |eqtb| entry +in region 1 or~2. (Similar routines for the other regions will appear +below.) + +@<Show equivalent |n|, in region 1 or 2@>= +begin sprint_cs(n); print_char("="); print_cmd_chr(eq_type(n),equiv(n)); +if eq_type(n)>=call then + begin print_char(":"); show_token_list(link(equiv(n)),null,32); + end; +end + +@ Region 3 of |eqtb| contains the 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) + +@<Current |mem| equivalent of glue parameter number |n|@>=glue_par(n) + +@ Sometimes we need to convert \TeX's internal code numbers into symbolic +form. The |print_skip_param| routine gives the symbolic name of a glue +parameter. + +@<Declare the procedure called |print_skip_param|@>= +procedure print_skip_param(@!n:integer); +begin case n of +line_skip_code: print_esc("lineskip"); +baseline_skip_code: print_esc("baselineskip"); +par_skip_code: print_esc("parskip"); +above_display_skip_code: print_esc("abovedisplayskip"); +below_display_skip_code: print_esc("belowdisplayskip"); +above_display_short_skip_code: print_esc("abovedisplayshortskip"); +below_display_short_skip_code: print_esc("belowdisplayshortskip"); +left_skip_code: print_esc("leftskip"); +right_skip_code: print_esc("rightskip"); +top_skip_code: print_esc("topskip"); +split_top_skip_code: print_esc("splittopskip"); +tab_skip_code: print_esc("tabskip"); +space_skip_code: print_esc("spaceskip"); +xspace_skip_code: print_esc("xspaceskip"); +par_fill_skip_code: print_esc("parfillskip"); +thin_mu_skip_code: print_esc("thinmuskip"); +med_mu_skip_code: print_esc("medmuskip"); +thick_mu_skip_code: print_esc("thickmuskip"); +othercases print("[unknown glue parameter!]") +endcases; +end; + +@ The symbolic names for glue parameters are put into \TeX's hash table +by using the routine called |primitive|, defined below. Let us enter them +now, so that we don't have to list all those parameter names anywhere else. + +@<Put each of \TeX's primitives into the hash table@>= +primitive("lineskip",assign_glue,glue_base+line_skip_code);@/ +@!@:line_skip_}{\.{\\lineskip} primitive@> +primitive("baselineskip",assign_glue,glue_base+baseline_skip_code);@/ +@!@:baseline_skip_}{\.{\\baselineskip} primitive@> +primitive("parskip",assign_glue,glue_base+par_skip_code);@/ +@!@:par_skip_}{\.{\\parskip} primitive@> +primitive("abovedisplayskip",assign_glue,glue_base+above_display_skip_code);@/ +@!@:above_display_skip_}{\.{\\abovedisplayskip} primitive@> +primitive("belowdisplayskip",assign_glue,glue_base+below_display_skip_code);@/ +@!@:below_display_skip_}{\.{\\belowdisplayskip} primitive@> +primitive("abovedisplayshortskip", + assign_glue,glue_base+above_display_short_skip_code);@/ +@!@:above_display_short_skip_}{\.{\\abovedisplayshortskip} primitive@> +primitive("belowdisplayshortskip", + assign_glue,glue_base+below_display_short_skip_code);@/ +@!@:below_display_short_skip_}{\.{\\belowdisplayshortskip} primitive@> +primitive("leftskip",assign_glue,glue_base+left_skip_code);@/ +@!@:left_skip_}{\.{\\leftskip} primitive@> +primitive("rightskip",assign_glue,glue_base+right_skip_code);@/ +@!@:right_skip_}{\.{\\rightskip} primitive@> +primitive("topskip",assign_glue,glue_base+top_skip_code);@/ +@!@:top_skip_}{\.{\\topskip} primitive@> +primitive("splittopskip",assign_glue,glue_base+split_top_skip_code);@/ +@!@:split_top_skip_}{\.{\\splittopskip} primitive@> +primitive("tabskip",assign_glue,glue_base+tab_skip_code);@/ +@!@:tab_skip_}{\.{\\tabskip} primitive@> +primitive("spaceskip",assign_glue,glue_base+space_skip_code);@/ +@!@:space_skip_}{\.{\\spaceskip} primitive@> +primitive("xspaceskip",assign_glue,glue_base+xspace_skip_code);@/ +@!@:xspace_skip_}{\.{\\xspaceskip} primitive@> +primitive("parfillskip",assign_glue,glue_base+par_fill_skip_code);@/ +@!@:par_fill_skip_}{\.{\\parfillskip} primitive@> +primitive("thinmuskip",assign_mu_glue,glue_base+thin_mu_skip_code);@/ +@!@:thin_mu_skip_}{\.{\\thinmuskip} primitive@> +primitive("medmuskip",assign_mu_glue,glue_base+med_mu_skip_code);@/ +@!@:med_mu_skip_}{\.{\\medmuskip} primitive@> +primitive("thickmuskip",assign_mu_glue,glue_base+thick_mu_skip_code);@/ +@!@:thick_mu_skip_}{\.{\\thickmuskip} primitive@> + +@ @<Cases of |print_cmd_chr| for symbolic printing of primitives@>= +assign_glue,assign_mu_glue: if chr_code<skip_base then + print_skip_param(chr_code-glue_base) + else if chr_code<mu_skip_base then + begin print_esc("skip"); print_int(chr_code-skip_base); + end + else begin print_esc("muskip"); print_int(chr_code-mu_skip_base); + end; + +@ All glue parameters and registers are initially `\.{0pt plus0pt minus0pt}'. + +@<Initialize table entries...@>= +equiv(glue_base):=zero_glue; eq_level(glue_base):=level_one; +eq_type(glue_base):=glue_ref; +for k:=glue_base+1 to local_base-1 do eqtb[k]:=eqtb[glue_base]; +glue_ref_count(zero_glue):=glue_ref_count(zero_glue)+local_base-glue_base; + +@ @<Show equivalent |n|, in region 3@>= +if n<skip_base then + begin print_skip_param(n-glue_base); print_char("="); + if n<glue_base+thin_mu_skip_code then print_spec(equiv(n),"pt") + else print_spec(equiv(n),"mu"); + end +else if n<mu_skip_base then + begin print_esc("skip"); print_int(n-skip_base); print_char("="); + print_spec(equiv(n),"pt"); + end +else begin print_esc("muskip"); print_int(n-mu_skip_base); print_char("="); + print_spec(equiv(n),"mu"); + end + +@ Region 4 of |eqtb| contains the local quantities defined here. The +bulk of this region is taken up by five tables that are indexed by eight-bit +characters; these tables are important to both the syntactic and semantic +portions of \TeX. There are also a bunch of special things like font and +token parameters, as well as the tables of \.{\\toks} and \.{\\box} +registers. + +@d par_shape_loc=local_base {specifies paragraph shape} +@d output_routine_loc=local_base+1 {points to token list for \.{\\output}} +@d every_par_loc=local_base+2 {points to token list for \.{\\everypar}} +@d every_math_loc=local_base+3 {points to token list for \.{\\everymath}} +@d every_display_loc=local_base+4 {points to token list for \.{\\everydisplay}} +@d every_hbox_loc=local_base+5 {points to token list for \.{\\everyhbox}} +@d every_vbox_loc=local_base+6 {points to token list for \.{\\everyvbox}} +@d every_job_loc=local_base+7 {points to token list for \.{\\everyjob}} +@d every_cr_loc=local_base+8 {points to token list for \.{\\everycr}} +@d err_help_loc=local_base+9 {points to token list for \.{\\errhelp}} +@d toks_base=local_base+10 {table of 256 token list registers} +@d box_base=toks_base+256 {table of 256 box registers} +@d cur_font_loc=box_base+256 {internal font number outside math mode} +@d math_font_base=cur_font_loc+1 {table of 48 math font numbers} +@d cat_code_base=math_font_base+48 + {table of 256 command codes (the ``catcodes'')} +@d lc_code_base=cat_code_base+256 {table of 256 lowercase mappings} +@d uc_code_base=lc_code_base+256 {table of 256 uppercase mappings} +@d sf_code_base=uc_code_base+256 {table of 256 spacefactor mappings} +@d math_code_base=sf_code_base+256 {table of 256 math mode mappings} +@d int_base=math_code_base+256 {beginning of region 5} +@# +@d par_shape_ptr==equiv(par_shape_loc) +@d output_routine==equiv(output_routine_loc) +@d every_par==equiv(every_par_loc) +@d every_math==equiv(every_math_loc) +@d every_display==equiv(every_display_loc) +@d every_hbox==equiv(every_hbox_loc) +@d every_vbox==equiv(every_vbox_loc) +@d every_job==equiv(every_job_loc) +@d every_cr==equiv(every_cr_loc) +@d err_help==equiv(err_help_loc) +@d toks(#)==equiv(toks_base+#) +@d box(#)==equiv(box_base+#) +@d cur_font==equiv(cur_font_loc) +@d fam_fnt(#)==equiv(math_font_base+#) +@d cat_code(#)==equiv(cat_code_base+#) +@d lc_code(#)==equiv(lc_code_base+#) +@d uc_code(#)==equiv(uc_code_base+#) +@d sf_code(#)==equiv(sf_code_base+#) +@d math_code(#)==equiv(math_code_base+#) + {Note: |math_code(c)| is the true math code plus |min_halfword|} + +@<Put each...@>= +primitive("output",assign_toks,output_routine_loc); +@!@:output_}{\.{\\output} primitive@> +primitive("everypar",assign_toks,every_par_loc); +@!@:every_par_}{\.{\\everypar} primitive@> +primitive("everymath",assign_toks,every_math_loc); +@!@:every_math_}{\.{\\everymath} primitive@> +primitive("everydisplay",assign_toks,every_display_loc); +@!@:every_display_}{\.{\\everydisplay} primitive@> +primitive("everyhbox",assign_toks,every_hbox_loc); +@!@:every_hbox_}{\.{\\everyhbox} primitive@> +primitive("everyvbox",assign_toks,every_vbox_loc); +@!@:every_vbox_}{\.{\\everyvbox} primitive@> +primitive("everyjob",assign_toks,every_job_loc); +@!@:every_job_}{\.{\\everyjob} primitive@> +primitive("everycr",assign_toks,every_cr_loc); +@!@:every_cr_}{\.{\\everycr} primitive@> +primitive("errhelp",assign_toks,err_help_loc); +@!@:err_help_}{\.{\\errhelp} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +assign_toks: if chr_code>=toks_base then + begin print_esc("toks"); print_int(chr_code-toks_base); + end +else case chr_code of + output_routine_loc: print_esc("output"); + every_par_loc: print_esc("everypar"); + every_math_loc: print_esc("everymath"); + every_display_loc: print_esc("everydisplay"); + every_hbox_loc: print_esc("everyhbox"); + every_vbox_loc: print_esc("everyvbox"); + every_job_loc: print_esc("everyjob"); + every_cr_loc: print_esc("everycr"); + 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''} + +@<Initialize table entries...@>= +par_shape_ptr:=null; eq_type(par_shape_loc):=shape_ref; +eq_level(par_shape_loc):=level_one;@/ +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; + +@ @<Show equivalent |n|, in region 4@>= +if n=par_shape_loc then + begin print_esc("parshape"); print_char("="); + if par_shape_ptr=null then print_char("0") + else print_int(info(par_shape_ptr)); + end +else if n<toks_base then + begin print_cmd_chr(assign_toks,n); print_char("="); + if equiv(n)<>null then show_token_list(link(equiv(n)),null,32); + end +else if n<box_base then + begin print_esc("toks"); print_int(n-toks_base); print_char("="); + if equiv(n)<>null then show_token_list(link(equiv(n)),null,32); + end +else if n<cur_font_loc then + begin print_esc("box"); print_int(n-box_base); print_char("="); + if equiv(n)=null then print("void") + else begin depth_threshold:=0; breadth_max:=1; show_node_list(equiv(n)); + end; + end +else if n<cat_code_base then @<Show the font identifier in |eqtb[n]|@> +else @<Show the halfword code in |eqtb[n]|@> + +@ @<Show the font identifier in |eqtb[n]|@>= +begin if n=cur_font_loc then print("current font") +else if n<math_font_base+16 then + begin print_esc("textfont"); print_int(n-math_font_base); + end +else if n<math_font_base+32 then + begin print_esc("scriptfont"); print_int(n-math_font_base-16); + end +else begin print_esc("scriptscriptfont"); print_int(n-math_font_base-32); + end; +print_char("=");@/ +print_esc(hash[font_id_base+equiv(n)].rh); + {that's |font_id_text(equiv(n))|} +end + +@ @<Show the halfword code in |eqtb[n]|@>= +if n<math_code_base then + begin if n<lc_code_base then + begin print_esc("catcode"); print_int(n-cat_code_base); + end + else if n<uc_code_base then + begin print_esc("lccode"); print_int(n-lc_code_base); + end + else if n<sf_code_base then + begin print_esc("uccode"); print_int(n-uc_code_base); + end + else begin print_esc("sfcode"); print_int(n-sf_code_base); + end; + print_char("="); print_int(equiv(n)); + end +else begin print_esc("mathcode"); print_int(n-math_code_base); + print_char("="); print_int(ho(equiv(n))); + end + +@ Region 5 of |eqtb| contains the integer parameters and registers defined +here, as well as the |del_code| table. The latter table differs from the +|cat_code..math_code| tables that precede it, since delimiter codes are +fullword integers while the other kinds of codes occupy at most a +halfword. This is what makes region~5 different from region~4. We will +store the |eq_level| information in an auxiliary array of quarterwords +that will be defined later. + +@d pretolerance_code=0 {badness tolerance before hyphenation} +@d tolerance_code=1 {badness tolerance after hyphenation} +@d line_penalty_code=2 {added to the badness of every line} +@d hyphen_penalty_code=3 {penalty for break after discretionary hyphen} +@d ex_hyphen_penalty_code=4 {penalty for break after explicit hyphen} +@d club_penalty_code=5 {penalty for creating a club line} +@d widow_penalty_code=6 {penalty for creating a widow line} +@d display_widow_penalty_code=7 {ditto, just before a display} +@d broken_penalty_code=8 {penalty for breaking a page at a broken line} +@d bin_op_penalty_code=9 {penalty for breaking after a binary operation} +@d rel_penalty_code=10 {penalty for breaking after a relation} +@d pre_display_penalty_code=11 + {penalty for breaking just before a displayed formula} +@d post_display_penalty_code=12 + {penalty for breaking just after a displayed formula} +@d inter_line_penalty_code=13 {additional penalty between lines} +@d double_hyphen_demerits_code=14 {demerits for double hyphen break} +@d final_hyphen_demerits_code=15 {demerits for final hyphen break} +@d adj_demerits_code=16 {demerits for adjacent incompatible lines} +@d mag_code=17 {magnification ratio} +@d delimiter_factor_code=18 {ratio for variable-size delimiters} +@d looseness_code=19 {change in number of lines for a paragraph} +@d time_code=20 {current time of day} +@d day_code=21 {current day of the month} +@d month_code=22 {current month of the year} +@d year_code=23 {current year of our Lord} +@d show_box_breadth_code=24 {nodes per level in |show_box|} +@d show_box_depth_code=25 {maximum level in |show_box|} +@d hbadness_code=26 {hboxes exceeding this badness will be shown by |hpack|} +@d vbadness_code=27 {vboxes exceeding this badness will be shown by |vpack|} +@d pausing_code=28 {pause after each line is read from a file} +@d tracing_online_code=29 {show diagnostic output on terminal} +@d tracing_macros_code=30 {show macros as they are being expanded} +@d tracing_stats_code=31 {show memory usage if \TeX\ knows it} +@d tracing_paragraphs_code=32 {show line-break calculations} +@d tracing_pages_code=33 {show page-break calculations} +@d tracing_output_code=34 {show boxes when they are shipped out} +@d tracing_lost_chars_code=35 {show characters that aren't in the font} +@d tracing_commands_code=36 {show command codes at |big_switch|} +@d tracing_restores_code=37 {show equivalents when they are restored} +@d uc_hyph_code=38 {hyphenate words beginning with a capital letter} +@d output_penalty_code=39 {penalty found at current page break} +@d max_dead_cycles_code=40 {bound on consecutive dead cycles of output} +@d hang_after_code=41 {hanging indentation changes after this many lines} +@d floating_penalty_code=42 {penalty for insertions heldover after a split} +@d global_defs_code=43 {override \.{\\global} specifications} +@d cur_fam_code=44 {current family} +@d escape_char_code=45 {escape character for token output} +@d default_hyphen_char_code=46 {value of \.{\\hyphenchar} when a font is loaded} +@d default_skew_char_code=47 {value of \.{\\skewchar} when a font is loaded} +@d end_line_char_code=48 {character placed at the right end of the buffer} +@d new_line_char_code=49 {character that prints as |print_ln|} +@d language_code=50 {current hyphenation table} +@d left_hyphen_min_code=51 {minimum left hyphenation fragment size} +@d right_hyphen_min_code=52 {minimum right hyphenation fragment size} +@d holding_inserts_code=53 {do not remove insertion nodes from \.{\\box255}} +@d error_context_lines_code=54 {maximum intermediate line pairs shown} +@d int_pars=55 {total number of integer parameters} +@d count_base=int_base+int_pars {256 user \.{\\count} registers} +@d del_code_base=count_base+256 {256 delimiter code mappings} +@d dimen_base=del_code_base+256 {beginning of region 6} +@# +@d del_code(#)==eqtb[del_code_base+#].int +@d count(#)==eqtb[count_base+#].int +@d int_par(#)==eqtb[int_base+#].int {an integer parameter} +@d pretolerance==int_par(pretolerance_code) +@d tolerance==int_par(tolerance_code) +@d line_penalty==int_par(line_penalty_code) +@d hyphen_penalty==int_par(hyphen_penalty_code) +@d ex_hyphen_penalty==int_par(ex_hyphen_penalty_code) +@d club_penalty==int_par(club_penalty_code) +@d widow_penalty==int_par(widow_penalty_code) +@d display_widow_penalty==int_par(display_widow_penalty_code) +@d broken_penalty==int_par(broken_penalty_code) +@d bin_op_penalty==int_par(bin_op_penalty_code) +@d rel_penalty==int_par(rel_penalty_code) +@d pre_display_penalty==int_par(pre_display_penalty_code) +@d post_display_penalty==int_par(post_display_penalty_code) +@d inter_line_penalty==int_par(inter_line_penalty_code) +@d double_hyphen_demerits==int_par(double_hyphen_demerits_code) +@d final_hyphen_demerits==int_par(final_hyphen_demerits_code) +@d adj_demerits==int_par(adj_demerits_code) +@d mag==int_par(mag_code) +@d delimiter_factor==int_par(delimiter_factor_code) +@d looseness==int_par(looseness_code) +@d time==int_par(time_code) +@d day==int_par(day_code) +@d month==int_par(month_code) +@d year==int_par(year_code) +@d show_box_breadth==int_par(show_box_breadth_code) +@d show_box_depth==int_par(show_box_depth_code) +@d hbadness==int_par(hbadness_code) +@d vbadness==int_par(vbadness_code) +@d pausing==int_par(pausing_code) +@d tracing_online==int_par(tracing_online_code) +@d tracing_macros==int_par(tracing_macros_code) +@d tracing_stats==int_par(tracing_stats_code) +@d tracing_paragraphs==int_par(tracing_paragraphs_code) +@d tracing_pages==int_par(tracing_pages_code) +@d tracing_output==int_par(tracing_output_code) +@d tracing_lost_chars==int_par(tracing_lost_chars_code) +@d tracing_commands==int_par(tracing_commands_code) +@d tracing_restores==int_par(tracing_restores_code) +@d uc_hyph==int_par(uc_hyph_code) +@d output_penalty==int_par(output_penalty_code) +@d max_dead_cycles==int_par(max_dead_cycles_code) +@d hang_after==int_par(hang_after_code) +@d floating_penalty==int_par(floating_penalty_code) +@d global_defs==int_par(global_defs_code) +@d cur_fam==int_par(cur_fam_code) +@d escape_char==int_par(escape_char_code) +@d default_hyphen_char==int_par(default_hyphen_char_code) +@d default_skew_char==int_par(default_skew_char_code) +@d end_line_char==int_par(end_line_char_code) +@d new_line_char==int_par(new_line_char_code) +@d language==int_par(language_code) +@d left_hyphen_min==int_par(left_hyphen_min_code) +@d right_hyphen_min==int_par(right_hyphen_min_code) +@d holding_inserts==int_par(holding_inserts_code) +@d error_context_lines==int_par(error_context_lines_code) + +@<Assign the values |depth_threshold:=show_box_depth|...@>= +depth_threshold:=show_box_depth; +breadth_max:=show_box_breadth + +@ We can print the symbolic name of an integer parameter as follows. + +@p procedure print_param(@!n:integer); +begin case n of +pretolerance_code:print_esc("pretolerance"); +tolerance_code:print_esc("tolerance"); +line_penalty_code:print_esc("linepenalty"); +hyphen_penalty_code:print_esc("hyphenpenalty"); +ex_hyphen_penalty_code:print_esc("exhyphenpenalty"); +club_penalty_code:print_esc("clubpenalty"); +widow_penalty_code:print_esc("widowpenalty"); +display_widow_penalty_code:print_esc("displaywidowpenalty"); +broken_penalty_code:print_esc("brokenpenalty"); +bin_op_penalty_code:print_esc("binoppenalty"); +rel_penalty_code:print_esc("relpenalty"); +pre_display_penalty_code:print_esc("predisplaypenalty"); +post_display_penalty_code:print_esc("postdisplaypenalty"); +inter_line_penalty_code:print_esc("interlinepenalty"); +double_hyphen_demerits_code:print_esc("doublehyphendemerits"); +final_hyphen_demerits_code:print_esc("finalhyphendemerits"); +adj_demerits_code:print_esc("adjdemerits"); +mag_code:print_esc("mag"); +delimiter_factor_code:print_esc("delimiterfactor"); +looseness_code:print_esc("looseness"); +time_code:print_esc("time"); +day_code:print_esc("day"); +month_code:print_esc("month"); +year_code:print_esc("year"); +show_box_breadth_code:print_esc("showboxbreadth"); +show_box_depth_code:print_esc("showboxdepth"); +hbadness_code:print_esc("hbadness"); +vbadness_code:print_esc("vbadness"); +pausing_code:print_esc("pausing"); +tracing_online_code:print_esc("tracingonline"); +tracing_macros_code:print_esc("tracingmacros"); +tracing_stats_code:print_esc("tracingstats"); +tracing_paragraphs_code:print_esc("tracingparagraphs"); +tracing_pages_code:print_esc("tracingpages"); +tracing_output_code:print_esc("tracingoutput"); +tracing_lost_chars_code:print_esc("tracinglostchars"); +tracing_commands_code:print_esc("tracingcommands"); +tracing_restores_code:print_esc("tracingrestores"); +uc_hyph_code:print_esc("uchyph"); +output_penalty_code:print_esc("outputpenalty"); +max_dead_cycles_code:print_esc("maxdeadcycles"); +hang_after_code:print_esc("hangafter"); +floating_penalty_code:print_esc("floatingpenalty"); +global_defs_code:print_esc("globaldefs"); +cur_fam_code:print_esc("fam"); +escape_char_code:print_esc("escapechar"); +default_hyphen_char_code:print_esc("defaulthyphenchar"); +default_skew_char_code:print_esc("defaultskewchar"); +end_line_char_code:print_esc("endlinechar"); +new_line_char_code:print_esc("newlinechar"); +language_code:print_esc("language"); +left_hyphen_min_code:print_esc("lefthyphenmin"); +right_hyphen_min_code:print_esc("righthyphenmin"); +holding_inserts_code:print_esc("holdinginserts"); +error_context_lines_code:print_esc("errorcontextlines"); +othercases print("[unknown integer parameter!]") +endcases; +end; + +@ The integer parameter names must be entered into the hash table. + +@<Put each...@>= +primitive("pretolerance",assign_int,int_base+pretolerance_code);@/ +@!@:pretolerance_}{\.{\\pretolerance} primitive@> +primitive("tolerance",assign_int,int_base+tolerance_code);@/ +@!@:tolerance_}{\.{\\tolerance} primitive@> +primitive("linepenalty",assign_int,int_base+line_penalty_code);@/ +@!@:line_penalty_}{\.{\\linepenalty} primitive@> +primitive("hyphenpenalty",assign_int,int_base+hyphen_penalty_code);@/ +@!@:hyphen_penalty_}{\.{\\hyphenpenalty} primitive@> +primitive("exhyphenpenalty",assign_int,int_base+ex_hyphen_penalty_code);@/ +@!@:ex_hyphen_penalty_}{\.{\\exhyphenpenalty} primitive@> +primitive("clubpenalty",assign_int,int_base+club_penalty_code);@/ +@!@:club_penalty_}{\.{\\clubpenalty} primitive@> +primitive("widowpenalty",assign_int,int_base+widow_penalty_code);@/ +@!@:widow_penalty_}{\.{\\widowpenalty} primitive@> +primitive("displaywidowpenalty", + assign_int,int_base+display_widow_penalty_code);@/ +@!@:display_widow_penalty_}{\.{\\displaywidowpenalty} primitive@> +primitive("brokenpenalty",assign_int,int_base+broken_penalty_code);@/ +@!@:broken_penalty_}{\.{\\brokenpenalty} primitive@> +primitive("binoppenalty",assign_int,int_base+bin_op_penalty_code);@/ +@!@:bin_op_penalty_}{\.{\\binoppenalty} primitive@> +primitive("relpenalty",assign_int,int_base+rel_penalty_code);@/ +@!@:rel_penalty_}{\.{\\relpenalty} primitive@> +primitive("predisplaypenalty",assign_int,int_base+pre_display_penalty_code);@/ +@!@:pre_display_penalty_}{\.{\\predisplaypenalty} primitive@> +primitive("postdisplaypenalty",assign_int,int_base+post_display_penalty_code);@/ +@!@:post_display_penalty_}{\.{\\postdisplaypenalty} primitive@> +primitive("interlinepenalty",assign_int,int_base+inter_line_penalty_code);@/ +@!@:inter_line_penalty_}{\.{\\interlinepenalty} primitive@> +primitive("doublehyphendemerits", + assign_int,int_base+double_hyphen_demerits_code);@/ +@!@:double_hyphen_demerits_}{\.{\\doublehyphendemerits} primitive@> +primitive("finalhyphendemerits", + assign_int,int_base+final_hyphen_demerits_code);@/ +@!@:final_hyphen_demerits_}{\.{\\finalhyphendemerits} primitive@> +primitive("adjdemerits",assign_int,int_base+adj_demerits_code);@/ +@!@:adj_demerits_}{\.{\\adjdemerits} primitive@> +primitive("mag",assign_int,int_base+mag_code);@/ +@!@:mag_}{\.{\\mag} primitive@> +primitive("delimiterfactor",assign_int,int_base+delimiter_factor_code);@/ +@!@:delimiter_factor_}{\.{\\delimiterfactor} primitive@> +primitive("looseness",assign_int,int_base+looseness_code);@/ +@!@:looseness_}{\.{\\looseness} primitive@> +primitive("time",assign_int,int_base+time_code);@/ +@!@:time_}{\.{\\time} primitive@> +primitive("day",assign_int,int_base+day_code);@/ +@!@:day_}{\.{\\day} primitive@> +primitive("month",assign_int,int_base+month_code);@/ +@!@:month_}{\.{\\month} primitive@> +primitive("year",assign_int,int_base+year_code);@/ +@!@:year_}{\.{\\year} primitive@> +primitive("showboxbreadth",assign_int,int_base+show_box_breadth_code);@/ +@!@:show_box_breadth_}{\.{\\showboxbreadth} primitive@> +primitive("showboxdepth",assign_int,int_base+show_box_depth_code);@/ +@!@:show_box_depth_}{\.{\\showboxdepth} primitive@> +primitive("hbadness",assign_int,int_base+hbadness_code);@/ +@!@:hbadness_}{\.{\\hbadness} primitive@> +primitive("vbadness",assign_int,int_base+vbadness_code);@/ +@!@:vbadness_}{\.{\\vbadness} primitive@> +primitive("pausing",assign_int,int_base+pausing_code);@/ +@!@:pausing_}{\.{\\pausing} primitive@> +primitive("tracingonline",assign_int,int_base+tracing_online_code);@/ +@!@:tracing_online_}{\.{\\tracingonline} primitive@> +primitive("tracingmacros",assign_int,int_base+tracing_macros_code);@/ +@!@:tracing_macros_}{\.{\\tracingmacros} primitive@> +primitive("tracingstats",assign_int,int_base+tracing_stats_code);@/ +@!@:tracing_stats_}{\.{\\tracingstats} primitive@> +primitive("tracingparagraphs",assign_int,int_base+tracing_paragraphs_code);@/ +@!@:tracing_paragraphs_}{\.{\\tracingparagraphs} primitive@> +primitive("tracingpages",assign_int,int_base+tracing_pages_code);@/ +@!@:tracing_pages_}{\.{\\tracingpages} primitive@> +primitive("tracingoutput",assign_int,int_base+tracing_output_code);@/ +@!@:tracing_output_}{\.{\\tracingoutput} primitive@> +primitive("tracinglostchars",assign_int,int_base+tracing_lost_chars_code);@/ +@!@:tracing_lost_chars_}{\.{\\tracinglostchars} primitive@> +primitive("tracingcommands",assign_int,int_base+tracing_commands_code);@/ +@!@:tracing_commands_}{\.{\\tracingcommands} primitive@> +primitive("tracingrestores",assign_int,int_base+tracing_restores_code);@/ +@!@:tracing_restores_}{\.{\\tracingrestores} primitive@> +primitive("uchyph",assign_int,int_base+uc_hyph_code);@/ +@!@:uc_hyph_}{\.{\\uchyph} primitive@> +primitive("outputpenalty",assign_int,int_base+output_penalty_code);@/ +@!@:output_penalty_}{\.{\\outputpenalty} primitive@> +primitive("maxdeadcycles",assign_int,int_base+max_dead_cycles_code);@/ +@!@:max_dead_cycles_}{\.{\\maxdeadcycles} primitive@> +primitive("hangafter",assign_int,int_base+hang_after_code);@/ +@!@:hang_after_}{\.{\\hangafter} primitive@> +primitive("floatingpenalty",assign_int,int_base+floating_penalty_code);@/ +@!@:floating_penalty_}{\.{\\floatingpenalty} primitive@> +primitive("globaldefs",assign_int,int_base+global_defs_code);@/ +@!@:global_defs_}{\.{\\globaldefs} primitive@> +primitive("fam",assign_int,int_base+cur_fam_code);@/ +@!@:fam_}{\.{\\fam} primitive@> +primitive("escapechar",assign_int,int_base+escape_char_code);@/ +@!@:escape_char_}{\.{\\escapechar} primitive@> +primitive("defaulthyphenchar",assign_int,int_base+default_hyphen_char_code);@/ +@!@:default_hyphen_char_}{\.{\\defaulthyphenchar} primitive@> +primitive("defaultskewchar",assign_int,int_base+default_skew_char_code);@/ +@!@:default_skew_char_}{\.{\\defaultskewchar} primitive@> +primitive("endlinechar",assign_int,int_base+end_line_char_code);@/ +@!@:end_line_char_}{\.{\\endlinechar} primitive@> +primitive("newlinechar",assign_int,int_base+new_line_char_code);@/ +@!@:new_line_char_}{\.{\\newlinechar} primitive@> +primitive("language",assign_int,int_base+language_code);@/ +@!@:language_}{\.{\\language} primitive@> +primitive("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@> + +@ @<Cases of |print_cmd_chr|...@>= +assign_int: if chr_code<count_base then print_param(chr_code-int_base) + else begin print_esc("count"); print_int(chr_code-count_base); + end; + +@ The integer parameters should really be initialized by a macro package; +the following initialization does the minimum to keep \TeX\ from +complete failure. +@^null delimiter@> + +@<Initialize table entries...@>= +for k:=int_base to 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 specifies July 4, 1776, at noon; but +users probably want a better approximation to the truth. + +@p procedure fix_date_and_time; +begin time:=12*60; {minutes since midnight} +day:=4; {fourth day of the month} +month:=7; {seventh month of the year} +year:=1776; {Anno Domini} +end; + +@ @<Show equivalent |n|, in region 5@>= +begin if n<count_base then print_param(n-int_base) +else if n<del_code_base then + begin print_esc("count"); print_int(n-count_base); + end +else begin print_esc("delcode"); print_int(n-del_code_base); + end; +print_char("="); print_int(eqtb[n].int); +end + +@ @<Set variable |c| to the current escape character@>=c:=escape_char + +@ @<Character |s| is the current new-line character@>=s=new_line_char + +@ \TeX\ is occasionally supposed to print diagnostic information that +goes only into the transcript file, unless |tracing_online| is positive. +Here are two routines that adjust the destination of print commands: + +@p procedure begin_diagnostic; {prepare to do some tracing} +begin old_setting:=selector; +if (tracing_online<=0)and(selector=term_and_log) then + begin decr(selector); + if history=spotless then history:=warning_issued; + end; +end; +@# +procedure end_diagnostic(@!blank_line:boolean); + {restore proper conditions after tracing} +begin print_nl(""); +if blank_line then print_ln; +selector:=old_setting; +end; + +@ Of course we had better declare another global variable, if the previous +routines are going to work. + +@<Glob...@>= +@!old_setting:0..max_selector; + +@ 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 dimen_pars=21 {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) + +@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"); +othercases print("[unknown dimen parameter!]") +endcases; +end; + +@ @<Put each...@>= +primitive("parindent",assign_dimen,dimen_base+par_indent_code);@/ +@!@:par_indent_}{\.{\\parindent} primitive@> +primitive("mathsurround",assign_dimen,dimen_base+math_surround_code);@/ +@!@:math_surround_}{\.{\\mathsurround} primitive@> +primitive("lineskiplimit",assign_dimen,dimen_base+line_skip_limit_code);@/ +@!@:line_skip_limit_}{\.{\\lineskiplimit} primitive@> +primitive("hsize",assign_dimen,dimen_base+hsize_code);@/ +@!@:hsize_}{\.{\\hsize} primitive@> +primitive("vsize",assign_dimen,dimen_base+vsize_code);@/ +@!@:vsize_}{\.{\\vsize} primitive@> +primitive("maxdepth",assign_dimen,dimen_base+max_depth_code);@/ +@!@:max_depth_}{\.{\\maxdepth} primitive@> +primitive("splitmaxdepth",assign_dimen,dimen_base+split_max_depth_code);@/ +@!@:split_max_depth_}{\.{\\splitmaxdepth} primitive@> +primitive("boxmaxdepth",assign_dimen,dimen_base+box_max_depth_code);@/ +@!@:box_max_depth_}{\.{\\boxmaxdepth} primitive@> +primitive("hfuzz",assign_dimen,dimen_base+hfuzz_code);@/ +@!@:hfuzz_}{\.{\\hfuzz} primitive@> +primitive("vfuzz",assign_dimen,dimen_base+vfuzz_code);@/ +@!@:vfuzz_}{\.{\\vfuzz} primitive@> +primitive("delimitershortfall", + assign_dimen,dimen_base+delimiter_shortfall_code);@/ +@!@:delimiter_shortfall_}{\.{\\delimitershortfall} primitive@> +primitive("nulldelimiterspace", + assign_dimen,dimen_base+null_delimiter_space_code);@/ +@!@:null_delimiter_space_}{\.{\\nulldelimiterspace} primitive@> +primitive("scriptspace",assign_dimen,dimen_base+script_space_code);@/ +@!@:script_space_}{\.{\\scriptspace} primitive@> +primitive("predisplaysize",assign_dimen,dimen_base+pre_display_size_code);@/ +@!@:pre_display_size_}{\.{\\predisplaysize} primitive@> +primitive("displaywidth",assign_dimen,dimen_base+display_width_code);@/ +@!@:display_width_}{\.{\\displaywidth} primitive@> +primitive("displayindent",assign_dimen,dimen_base+display_indent_code);@/ +@!@:display_indent_}{\.{\\displayindent} primitive@> +primitive("overfullrule",assign_dimen,dimen_base+overfull_rule_code);@/ +@!@:overfull_rule_}{\.{\\overfullrule} primitive@> +primitive("hangindent",assign_dimen,dimen_base+hang_indent_code);@/ +@!@:hang_indent_}{\.{\\hangindent} primitive@> +primitive("hoffset",assign_dimen,dimen_base+h_offset_code);@/ +@!@:h_offset_}{\.{\\hoffset} primitive@> +primitive("voffset",assign_dimen,dimen_base+v_offset_code);@/ +@!@:v_offset_}{\.{\\voffset} primitive@> +primitive("emergencystretch",assign_dimen,dimen_base+emergency_stretch_code);@/ +@!@:emergency_stretch_}{\.{\\emergencystretch} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +assign_dimen: if chr_code<scaled_base then + print_length_param(chr_code-dimen_base) + else begin print_esc("dimen"); print_int(chr_code-scaled_base); + end; + +@ @<Initialize table entries...@>= +for k:=dimen_base to eqtb_size do eqtb[k].sc:=0; + +@ @<Show equivalent |n|, in region 6@>= +begin if n<scaled_base then print_length_param(n-dimen_base) +else begin print_esc("dimen"); print_int(n-scaled_base); + end; +print_char("="); print_scaled(eqtb[n].sc); print("pt"); +end + +@ Here is a procedure that displays the contents of |eqtb[n]| +symbolically. + +@p@t\4@>@<Declare the procedure called |print_cmd_chr|@>@;@/ +@!stat procedure show_eqtb(@!n:pointer); +begin if n<active_base then print_char("?") {this can't happen} +else if n<glue_base then @<Show equivalent |n|, in region 1 or 2@> +else if n<local_base then @<Show equivalent |n|, in region 3@> +else if n<int_base then @<Show equivalent |n|, in region 4@> +else if n<dimen_base then @<Show equivalent |n|, in region 5@> +else if n<=eqtb_size then @<Show equivalent |n|, in region 6@> +else print_char("?"); {this can't happen either} +end; +tats + +@ The last two regions of |eqtb| have fullword values instead of the +three fields |eq_level|, |eq_type|, and |equiv|. An |eq_type| is unnecessary, +but \TeX\ needs to store the |eq_level| information in another array +called |xeq_level|. + +@<Glob...@>= +@!eqtb:array[active_base..eqtb_size] of memory_word; +@!xeq_level:array[int_base..eqtb_size] of quarterword; + +@ @<Set init...@>= +for k:=int_base to eqtb_size do xeq_level[k]:=level_one; + +@ 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. + +@<Search |eqtb| for equivalents equal to |p|@>= +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} + +@<Glob...@>= +@!hash: array[hash_base..undefined_control_sequence-1] of two_halves; + {the hash table} +@!hash_used:pointer; {allocation pointer for |hash|} +@!no_new_control_sequence:boolean; {are new identifiers legal?} +@!cs_count:integer; {total number of known identifiers} + +@ @<Set init...@>= +no_new_control_sequence:=true; {new identifiers are usually forbidden} +next(hash_base):=0; text(hash_base):=0; +for k:=hash_base+1 to undefined_control_sequence-1 do hash[k]:=hash[hash_base]; + +@ @<Initialize table entries...@>= +hash_used:=frozen_control_sequence; {nothing is used} +cs_count:=0; +eq_type(frozen_dont_expand):=dont_expand; +text(frozen_dont_expand):="notexpanded:"; +@.notexpanded:@> + +@ Here is the subroutine that searches the hash table for an identifier +that matches a given string of length |l>1| appearing in |buffer[j.. +(j+l-1)]|. If the identifier is found, the corresponding hash table address +is returned. Otherwise, if the global variable |no_new_control_sequence| +is |true|, the dummy address |undefined_control_sequence| is returned. +Otherwise the identifier is inserted into the hash table and its location +is returned. + +@p function id_lookup(@!j,@!l:integer):pointer; {search the hash table} +label found; {go here if you found it} +var h:integer; {hash code} +@!d:integer; {number of characters in incomplete current string} +@!p:pointer; {index in |hash| array} +@!k:pointer; {index in |buffer| array} +begin @<Compute the hash code |h|@>; +p:=h+hash_base; {we start searching here; note that |0<=h<hash_prime|} +loop@+begin if text(p)>0 then if length(text(p))=l then + if str_eq_buf(text(p),j) then goto found; + if next(p)=0 then + begin if no_new_control_sequence then + p:=undefined_control_sequence + else @<Insert a new control sequence after |p|, then make + |p| point to it@>; + goto found; + end; + p:=next(p); + end; +found: id_lookup:=p; +end; + +@ @<Insert a new control...@>= +begin if text(p)>0 then + begin repeat if hash_is_full then overflow("hash size",hash_size); +@:TeX capacity exceeded hash size}{\quad hash size@> + decr(hash_used); + until text(hash_used)=0; {search for an empty location in |hash|} + next(p):=hash_used; p:=hash_used; + end; +str_room(l); d:=cur_length; +while pool_ptr>str_start[str_ptr] do + begin decr(pool_ptr); str_pool[pool_ptr+l]:=str_pool[pool_ptr]; + end; {move current string up to make room for another} +for k:=j to j+l-1 do append_char(buffer[k]); +text(p):=make_string; pool_ptr:=pool_ptr+d; +@!stat incr(cs_count);@+tats@;@/ +end + +@ The value of |hash_prime| should be roughly 85\pct! of |hash_size|, and it +should be a prime number. The theory of hashing tells us to expect fewer +than two table probes, on the average, when the search is successful. +[See J.~S. Vitter, {\sl Journal of the ACM\/ \bf30} (1983), 231--258.] +@^Vitter, Jeffrey Scott@> + +@<Compute the hash code |h|@>= +h:=buffer[j]; +for k:=j+1 to j+l-1 do + begin h:=h+h+buffer[k]; + while h>=hash_prime do h:=h-hash_prime; + end + +@ 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. + +@<Basic printing...@>= +procedure print_cs(@!p:integer); {prints a purported control sequence} +begin if p<hash_base then {single character} + if p>=single_base then + if p=null_cs then + begin print_esc("csname"); print_esc("endcsname"); + end + else begin print_esc(p-single_base); + if cat_code(p-single_base)=letter then print_char(" "); + end + else if p<active_base then print_esc("IMPOSSIBLE.") +@.IMPOSSIBLE@> + else print(p-active_base) +else if p>=undefined_control_sequence then print_esc("IMPOSSIBLE.") +else if (text(p)<0)or(text(p)>=str_ptr) then print_esc("NONEXISTENT.") +@.NONEXISTENT@> +else begin print_esc(text(p)); + print_char(" "); + end; +end; + +@ Here is a similar procedure; it avoids the error checks, and it never +prints a space after the control sequence. + +@<Basic printing procedures@>= +procedure sprint_cs(@!p:pointer); {prints a control sequence} +begin if p<hash_base then + if p<single_base then print(p-active_base) + else if p<null_cs then print_esc(p-single_base) + else begin print_esc("csname"); print_esc("endcsname"); + end +else print_esc(text(p)); +end; + +@ We need to put \TeX's ``primitive'' control sequences into the hash +table, together with their command code (which will be the |eq_type|) +and an operand (which will be the |equiv|). The |primitive| procedure +does this, in a way that no \TeX\ user can. The global value |cur_val| +contains the new |eqtb| pointer after |primitive| has acted. + +@p @!init procedure primitive(@!s:str_number;@!c:quarterword;@!o:halfword); +var k:pool_pointer; {index into |str_pool|} +@!j:small_number; {index into |buffer|} +@!l:small_number; {length of the string} +begin if s<256 then cur_val:=s+single_base +else begin k:=str_start[s]; l:=str_start[s+1]-k; + {we will move |s| into the (empty) |buffer|} + for j:=0 to l-1 do buffer[j]:=so(str_pool[k+j]); + cur_val:=id_lookup(0,l); {|no_new_control_sequence| is |false|} + flush_string; text(cur_val):=s; {we don't want to have the string twice} + end; +eq_level(cur_val):=level_one; eq_type(cur_val):=c; equiv(cur_val):=o; +end; +tini + +@ Many of \TeX's primitives need no |equiv|, since they are identifiable +by their |eq_type| alone. These primitives are loaded into the hash table +as follows: + +@<Put each of \TeX's primitives into the hash table@>= +primitive(" ",ex_space,0);@/ +@!@:Single-character primitives /}{\quad\.{\\\ }@> +primitive("/",ital_corr,0);@/ +@!@:Single-character primitives /}{\quad\.{\\/}@> +primitive("accent",accent,0);@/ +@!@:accent_}{\.{\\accent} primitive@> +primitive("advance",advance,0);@/ +@!@:advance_}{\.{\\advance} primitive@> +primitive("afterassignment",after_assignment,0);@/ +@!@:after_assignment_}{\.{\\afterassignment} primitive@> +primitive("aftergroup",after_group,0);@/ +@!@:after_group_}{\.{\\aftergroup} primitive@> +primitive("begingroup",begin_group,0);@/ +@!@:begin_group_}{\.{\\begingroup} primitive@> +primitive("char",char_num,0);@/ +@!@:char_}{\.{\\char} primitive@> +primitive("csname",cs_name,0);@/ +@!@:cs_name_}{\.{\\csname} primitive@> +primitive("delimiter",delim_num,0);@/ +@!@:delimiter_}{\.{\\delimiter} primitive@> +primitive("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("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("nonscript",non_script,0);@/ +@!@:non_script_}{\.{\\nonscript} primitive@> +primitive("omit",omit,0);@/ +@!@:omit_}{\.{\\omit} primitive@> +primitive("parshape",set_shape,0);@/ +@!@: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,0);@/ +@!@:toks_}{\.{\\toks} primitive@> +primitive("vadjust",vadjust,0);@/ +@!@:vadjust_}{\.{\\vadjust} primitive@> +primitive("valign",valign,0);@/ +@!@:valign_}{\.{\\valign} primitive@> +primitive("vcenter",vcenter,0);@/ +@!@:vcenter_}{\.{\\vcenter} primitive@> +primitive("vrule",vrule,0);@/ +@!@:vrule_}{\.{\\vrule} primitive@> + +@ Each primitive has a corresponding inverse, so that it is possible to +display the cryptic numeric contents of |eqtb| in symbolic form. +Every call of |primitive| in this program is therefore accompanied by some +straightforward code that forms part of the |print_cmd_chr| routine +below. + +@<Cases of |print_cmd_chr|...@>= +accent: print_esc("accent"); +advance: print_esc("advance"); +after_assignment: print_esc("afterassignment"); +after_group: print_esc("aftergroup"); +assign_font_dimen: print_esc("fontdimen"); +begin_group: print_esc("begingroup"); +break_penalty: print_esc("penalty"); +char_num: print_esc("char"); +cs_name: print_esc("csname"); +def_font: print_esc("font"); +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: print_esc("expandafter"); +halign: print_esc("halign"); +hrule: print_esc("hrule"); +ignore_spaces: print_esc("ignorespaces"); +insert: print_esc("insert"); +ital_corr: print_esc("/"); +mark: print_esc("mark"); +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: print_esc("noexpand"); +non_script: print_esc("nonscript"); +omit: print_esc("omit"); +radical: print_esc("radical"); +read_to_cs: print_esc("read"); +relax: print_esc("relax"); +set_box: print_esc("setbox"); +set_prev_graf: print_esc("prevgraf"); +set_shape: print_esc("parshape"); +the: print_esc("the"); +toks_register: print_esc("toks"); +vadjust: print_esc("vadjust"); +valign: print_esc("valign"); +vcenter: print_esc("vcenter"); +vrule: print_esc("vrule"); + +@ We will deal with the other primitives later, at some point in the program +where their |eq_type| and |equiv| values are more meaningful. For example, +the primitives for math mode will be loaded when we consider the routines +that deal with formulas. It is easy to find where each particular +primitive was treated by looking in the index at the end; for example, the +section where |"radical"| entered |eqtb| is listed under `\.{\\radical} +primitive'. (Primitives consisting of a single nonalphabetic character, +@!like `\.{\\/}', are listed under `Single-character primitives'.) +@!@^Single-character primitives@> + +Meanwhile, this is a convenient place to catch up on something we were unable +to do before the hash table was defined: + +@<Print the font identifier for |font(p)|@>= +print_esc(font_id_text(font(p))) + +@* \[19] Saving and restoring equivalents. +The nested structure provided by `$\.{\char'173}\ldots\.{\char'175}$' groups +in \TeX\ means that |eqtb| entries valid in outer groups should be saved +and restored later if they are overridden inside the braces. When a new |eqtb| +value is being assigned, the program therefore checks to see if the previous +entry belongs to an outer level. In such a case, the old value is placed +on the |save_stack| just before the new value enters |eqtb|. At the +end of a grouping level, i.e., when the right brace is sensed, the +|save_stack| is used to restore the outer values, and the inner ones are +destroyed. + +Entries on the |save_stack| are of type |memory_word|. The top item on +this stack is |save_stack[p]|, where |p=save_ptr-1|; it contains three +fields called |save_type|, |save_level|, and |save_index|, and it is +interpreted in one of four ways: + +\yskip\hangg 1) If |save_type(p)=restore_old_value|, then +|save_index(p)| is a location in |eqtb| whose current value should +be destroyed at the end of the current group and replaced by |save_stack[p-1]|. +Furthermore if |save_index(p)>=int_base|, then |save_level(p)| +should replace the corresponding entry in |xeq_level|. + +\yskip\hangg 2) If |save_type(p)=restore_zero|, then |save_index(p)| +is a location in |eqtb| whose current value should be destroyed at the end +of the current group, when it should be +replaced by the current value of |eqtb[undefined_control_sequence]|. + +\yskip\hangg 3) If |save_type(p)=insert_token|, then |save_index(p)| +is a token that should be inserted into \TeX's input when the current +group ends. + +\yskip\hangg 4) If |save_type(p)=level_boundary|, then |save_level(p)| +is a code explaining what kind of group we were previously in, and +|save_index(p)| points to the level boundary word at the bottom of +the entries for that group. + +@d save_type(#)==save_stack[#].hh.b0 {classifies a |save_stack| entry} +@d save_level(#)==save_stack[#].hh.b1 + {saved level for regions 5 and 6, or group code} +@d save_index(#)==save_stack[#].hh.rh + {|eqtb| location or |save_stack| location} +@d restore_old_value=0 {|save_type| when a value should be restored later} +@d restore_zero=1 {|save_type| when an undefined entry should be restored} +@d insert_token=2 {|save_type| when a token is being saved for later use} +@d level_boundary=3 {|save_type| corresponding to beginning of group} + +@ 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 + +@<Types...@>= +@!group_code=0..max_group_code; {|save_level| for a level boundary} + +@ The global variable |cur_group| keeps track of what sort of group we are +currently in. Another global variable, |cur_boundary|, points to the +topmost |level_boundary| word. And |cur_level| is the current depth of +nesting. The routines are designed to preserve the condition that no entry +in the |save_stack| or in |eqtb| ever has a level greater than |cur_level|. + +@ @<Glob...@>= +@!save_stack : array[0..save_size] of memory_word; +@!save_ptr : 0..save_size; {first unused entry on |save_stack|} +@!max_save_stack:0..save_size; {maximum usage of save stack} +@!cur_level: quarterword; {current nesting level for groups} +@!cur_group: group_code; {current group type} +@!cur_boundary: 0..save_size; {where the current level begins} + +@ At this time it might be a good idea for the reader to review the introduction +to |eqtb| that was given above just before the long lists of parameter names. +Recall that the ``outer level'' of the program is |level_one|, since +undefined control sequences are assumed to be ``defined'' at |level_zero|. + +@<Set init...@>= +save_ptr:=0; cur_level:=level_one; cur_group:=bottom_level; cur_boundary:=0; +max_save_stack:=0; + +@ The following macro is used to test if there is room for up to six 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-6 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; +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; incr(cur_level); incr(save_ptr); cur_group:=c; +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. + +@p procedure eq_define(@!p:pointer;@!t:quarterword;@!e:halfword); + {new data for |eqtb|} +begin 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; +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); +begin if xeq_level[p]<>cur_level then + begin eq_save(p,xeq_level[p]); xeq_level[p]:=cur_level; + end; +eqtb[p].int:=w; +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 eq_destroy(eqtb[p]); +eq_level(p):=level_one; eq_type(p):=t; equiv(p):=e; +end; +@# +procedure geq_word_define(@!p:pointer;@!w:integer); {global |eq_word_define|} +begin eqtb[p].int:=w; xeq_level[p]:=level_one; +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@t\4@>@<Declare the procedure called |restore_trace|@>@;@/ +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|} +begin if cur_level>level_one then + begin decr(cur_level); + @<Clear off top level from |save_stack|@>; + end +else confusion("curlevel"); {|unsave| is not used when |cur_group=bottom_level|} +@:this can't happen curlevel}{\quad curlevel@> +end; + +@ @<Clear off...@>= +loop@+begin decr(save_ptr); + if save_type(save_ptr)=level_boundary then goto done; + p:=save_index(save_ptr); + if save_type(save_ptr)=insert_token then + @<Insert token |p| into \TeX's input@> + else begin if save_type(save_ptr)=restore_old_value then + begin l:=save_level(save_ptr); decr(save_ptr); + end + else save_stack[save_ptr]:=eqtb[undefined_control_sequence]; + @<Store \(s)|save_stack[save_ptr]| in |eqtb[p]|, unless + |eqtb[p]| holds a global value@>; + end; + end; +done: cur_group:=save_level(save_ptr); cur_boundary:=save_index(save_ptr) + +@ A global definition, which sets the level to |level_one|, +@^global definitions@> +will not be undone by |unsave|. If at least one global definition of +|eqtb[p]| has been carried out within the group that just ended, the +last such definition will therefore survive. + +@<Store \(s)|save...@>= +if p<int_base then + if eq_level(p)=level_one then + begin eq_destroy(save_stack[save_ptr]); {destroy the saved value} + @!stat if tracing_restores>0 then restore_trace(p,"retaining");@+tats@;@/ + end + else begin eq_destroy(eqtb[p]); {destroy the current value} + eqtb[p]:=save_stack[save_ptr]; {restore the saved value} + @!stat if tracing_restores>0 then restore_trace(p,"restoring");@+tats@;@/ + end +else if xeq_level[p]<>level_one then + begin eqtb[p]:=save_stack[save_ptr]; xeq_level[p]:=l; + @!stat if tracing_restores>0 then restore_trace(p,"restoring");@+tats@;@/ + end +else begin + @!stat if tracing_restores>0 then restore_trace(p,"retaining");@+tats@;@/ + end + +@ @<Declare the procedure called |restore_trace|@>= +@!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@> + +@<Search |save_stack| for equivalents that point to |p|@>= +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. + +@<Glob...@>= +@!mag_set:integer; {if nonzero, this magnification should be used henceforth} + +@ @<Set init...@>= +mag_set:=0; + +@ The |prepare_mag| subroutine is called whenever \TeX\ wants to use |mag| +for magnification. + +@p procedure prepare_mag; +begin if (mag_set>0)and(mag<>mag_set) then + begin print_err("Incompatible magnification ("); print_int(mag); +@.Incompatible magnification@> + print(");"); print_nl(" the previous value will be retained"); + help2("I can handle only one magnification ratio per job. So I've")@/ + ("reverted to the magnification you used earlier on this run.");@/ + int_error(mag_set); + geq_word_define(int_base+mag_code,mag_set); {|mag:=mag_set|} + end; +if (mag<=0)or(mag>32768) then + begin print_err("Illegal magnification has been changed to 1000");@/ +@.Illegal magnification...@> + help1("The magnification ratio must be between 1 and 32768."); + int_error(mag); geq_word_define(int_base+mag_code,1000); + end; +mag_set:=mag; +end; + +@* \[20] Token lists. +A \TeX\ token is either a character or a control sequence, and it is +@^token@> +represented internally in one of two ways: (1)~A character whose ASCII +code number is |c| and whose command code is |m| is represented as the +number $2^8m+c$; 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<left_brace_limit|; it represents a |right_brace| command if and only if +we have |left_brace_limit<=t<right_brace_limit|; and it represents a |match| or +|end_match| command if and only if |match_token<=t<=end_match_token|. +The following definitions take care of these token-oriented constants +and a few others. + +@d cs_token_flag==@'7777 {amount added to the |eqtb| location in a + token that stands for a control sequence; is a multiple of~256, less~1} +@d left_brace_token=@'0400 {$2^8\cdot|left_brace|$} +@d left_brace_limit=@'1000 {$2^8\cdot(|left_brace|+1)$} +@d right_brace_token=@'1000 {$2^8\cdot|right_brace|$} +@d right_brace_limit=@'1400 {$2^8\cdot(|right_brace|+1)$} +@d math_shift_token=@'1400 {$2^8\cdot|math_shift|$} +@d tab_token=@'2000 {$2^8\cdot|tab_mark|$} +@d out_param_token=@'2400 {$2^8\cdot|out_param|$} +@d space_token=@'5040 {$2^8\cdot|spacer|+|" "|$} +@d letter_token=@'5400 {$2^8\cdot|letter|$} +@d other_token=@'6000 {$2^8\cdot|other_char|$} +@d match_token=@'6400 {$2^8\cdot|match|$} +@d end_match_token=@'7000 {$2^8\cdot|end_match|$} + +@ @<Check the ``constant''...@>= +if cs_token_flag+undefined_control_sequence>max_halfword then bad:=21; + +@ A token list is a singly linked list of one-word nodes in |mem|, where +each word contains a token and a link. Macro definitions, output-routine +definitions, marks, \.{\\write} texts, and a few other things +are remembered by \TeX\ in the form +of token lists, usually preceded by a node with a reference count in its +|token_ref_count| field. The token stored in location |p| is called +|info(p)|. + +Three special commands appear in the token lists of macro definitions. +When |m=match|, it means that \TeX\ should scan a parameter +for the current macro; when |m=end_match|, it means that parameter +matching should end and \TeX\ should start reading the macro text; and +when |m=out_param|, it means that \TeX\ should insert parameter +number |c| into the text at this point. + +The enclosing \.{\char'173} and \.{\char'175} characters of a macro +definition are omitted, but the final right brace of an output routine +is included at the end of its token list. + +Here is an example macro definition that illustrates these conventions. +After \TeX\ processes the text +$$\.{\\def\\mac a\#1\#2 \\b \{\#1\\-a \#\#1\#2 \#2\}}$$ +the definition of \.{\\mac} is represented as a token list containing +$$\def\,{\hskip2pt} +\vbox{\halign{\hfil#\hfil\cr +(reference count), |letter|\,\.a, |match|\,\#, |match|\,\#, |spacer|\,\.\ , +\.{\\b}, |end_match|,\cr +|out_param|\,1, \.{\\-}, |letter|\,\.a, |spacer|\,\.\ , |mac_param|\,\#, +|other_char|\,\.1,\cr +|out_param|\,2, |spacer|\,\.\ , |out_param|\,2.\cr}}$$ +The procedure |scan_toks| builds such token lists, and |macro_call| +does the parameter matching. +@^reference counts@> + +Examples such as +$$\.{\\def\\m\{\\def\\m\{a\}\ b\}}$$ +explain why reference counts would be needed even if \TeX\ had no \.{\\let} +operation: When the token list for \.{\\m} is being read, the redefinition of +\.{\\m} changes the |eqtb| entry before the token list has been fully +consumed, so we dare not simply destroy a token list when its +control sequence is being redefined. + +If the parameter-matching part of a definition ends with `\.{\#\{}', +the corresponding token list will have `\.\{' just before the `|end_match|' +and also at the very end. The first `\.\{' is used to delimit the parameter; the +second one keeps the first from disappearing. + +@ The procedure |show_token_list|, which prints a symbolic form of +the token list that starts at a given node |p|, illustrates these +conventions. The token list being displayed should not begin with a reference +count. However, the procedure is intended to be robust, so that if the +memory links are awry or if |p| is not really a pointer to a token list, +nothing catastrophic will happen. + +An additional parameter |q| is also given; this parameter is either null +or it points to a node in the token list where a certain magic computation +takes place that will be explained later. (Basically, |q| is non-null when +we are printing the two-line context information at the time of an error +message; |q| marks the place corresponding to where the second line +should begin.) + +For example, if |p| points to the node containing the first \.a in the +token list above, then |show_token_list| will print the string +$$\hbox{`\.{a\#1\#2\ \\b\ ->\#1\\-a\ \#\#1\#2\ \#2}';}$$ +and if |q| points to the node containing the second \.a, +the magic computation will be performed just before the second \.a is printed. + +The generation will stop, and `\.{\\ETC.}' will be printed, if the length +of printing exceeds a given limit~|l|. Anomalous entries are printed in the +form of control sequences that are not followed by a blank space, e.g., +`\.{\\BAD.}'; this cannot be confused with actual control sequences because +a real control sequence named \.{BAD} would come out `\.{\\BAD\ }'. + +@<Declare the procedure called |show_token_list|@>= +procedure show_token_list(@!p,@!q:integer;@!l:integer); +label exit; +var m,@!c:integer; {pieces of a token} +@!match_chr:ASCII_code; {character used in a `|match|'} +@!n:ASCII_code; {the highest parameter number, as an ASCII digit} +begin match_chr:="#"; n:="0"; tally:=0; +while (p<>null) and (tally<l) do + begin if p=q then @<Do magic computation@>; + @<Display token |p|, and |return| if there are problems@>; + p:=link(p); + end; +if p<>null then print_esc("ETC."); +@.ETC@> +exit: +end; + +@ @<Display token |p|...@>= +if (p<hi_mem_min) or (p>mem_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 @<Display the token $(|m|,|c|)$@>; + end + +@ The procedure usually ``learns'' the character code used for macro +parameters by seeing one in a |match| command before it runs into any +|out_param| commands. + +@<Display the token ...@>= +case m of +left_brace,right_brace,math_shift,tab_mark,sup_mark,sub_mark,spacer, + letter,other_char: print(c); +mac_param: begin print(c); print(c); + end; +out_param: begin print(match_chr); + if c<=9 then print_char(c+"0") + else begin print_char("!"); return; + end; + end; +match: begin match_chr:=c; print(c); incr(n); print_char(n); + if n>"9" then return; + end; +end_match: 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 then + begin print_char(":"); print_ln; + token_show(cur_mark[cur_chr]); + end; +end; + +@* \[21] Introduction to the syntactic routines. +Let's pause a moment now and try to look at the Big Picture. +The \TeX\ program consists of three main parts: syntactic routines, +semantic routines, and output routines. The chief purpose of the +syntactic routines is to deliver the user's input to the semantic routines, +one token at a time. The semantic routines act as an interpreter +responding to these tokens, which may be regarded as commands. And the +output routines are periodically called on to convert box-and-glue +lists into a compact set of instructions that will be sent +to a typesetter. We have discussed the basic data structures and utility +routines of \TeX, so we are good and ready to plunge into the real activity by +considering the syntactic routines. + +Our current goal is to come to grips with the |get_next| procedure, +which is the keystone of \TeX's input mechanism. Each call of |get_next| +sets the value of three variables |cur_cmd|, |cur_chr|, and |cur_cs|, +representing the next input token. +$$\vbox{\halign{#\hfil\cr + \hbox{|cur_cmd| denotes a command code from the long list of codes + given above;}\cr + \hbox{|cur_chr| denotes a character code or other modifier of the command + code;}\cr + \hbox{|cur_cs| is the |eqtb| location of the current control sequence,}\cr + \hbox{\qquad if the current token was a control sequence, + otherwise it's zero.}\cr}}$$ +Underlying this external behavior of |get_next| is all the machinery +necessary to convert from character files to tokens. At a given time we +may be only partially finished with the reading of several files (for +which \.{\\input} was specified), and partially finished with the expansion +of some user-defined macros and/or some macro parameters, and partially +finished with the generation of some text in a template for \.{\\halign}, +and so on. When reading a character file, special characters must be +classified as math delimiters, etc.; comments and extra blank spaces must +be removed, paragraphs must be recognized, and control sequences must be +found in the hash table. Furthermore there are occasions in which the +scanning routines have looked ahead for a word like `\.{plus}' but only +part of that word was found, hence a few characters must be put back +into the input and scanned again. + +To handle these situations, which might all be present simultaneously, +\TeX\ uses various stacks that hold information about the incomplete +activities, and there is a finite state control for each level of the +input mechanism. These stacks record the current state of an implicitly +recursive process, but the |get_next| procedure is not recursive. +Therefore it will not be difficult to translate these algorithms into +low-level languages that do not support recursion. + +@<Glob...@>= +@!cur_cmd: eight_bits; {current command set by |get_next|} +@!cur_chr: halfword; {operand of current command} +@!cur_cs: pointer; {control sequence found here, zero if none found} +@!cur_tok: halfword; {packed representative of |cur_cmd| and |cur_chr|} + +@ The |print_cmd_chr| routine prints a symbolic interpretation of a +command code and its modifier. This is used in certain `\.{You can\'t}' +error messages, and in the implementation of diagnostic routines like +\.{\\show}. + +The body of |print_cmd_chr| is a rather tedious listing of print +commands, and most of it is essentially an inverse to the |primitive| +routine that enters a \TeX\ primitive into |eqtb|. Therefore much of +this procedure appears elsewhere in the program, +together with the corresponding |primitive| calls. + +@d chr_cmd(#)==begin print(#); print_ASCII(chr_code); + end + +@<Declare the procedure called |print_cmd_chr|@>= +procedure print_cmd_chr(@!cmd:quarterword;@!chr_code:halfword); +begin case cmd of +left_brace: chr_cmd("begin-group character "); +right_brace: chr_cmd("end-group character "); +math_shift: chr_cmd("math shift character "); +mac_param: chr_cmd("macro parameter character "); +sup_mark: chr_cmd("superscript character "); +sub_mark: chr_cmd("subscript character "); +endv: print("end of alignment template"); +spacer: chr_cmd("blank space "); +letter: chr_cmd("the letter "); +other_char: chr_cmd("the character "); +@t\4@>@<Cases of |print_cmd_chr| for symbolic printing of primitives@>@/ +othercases print("[unknown command code!]") +endcases; +end; + +@ Here is a procedure that displays the current command. + +@p procedure show_cur_cmd_chr; +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); print_char("}"); +end_diagnostic(false); +end; + +@* \[22] Input stacks and states. +This implementation of +\TeX\ uses two different conventions for representing sequential stacks. +@^stack conventions@>@^conventions for representing stacks@> + +\yskip\hangg 1) If there is frequent access to the top entry, and if the +stack is essentially never empty, then the top entry is kept in a global +variable (even better would be a machine register), and the other entries +appear in the array $\\{stack}[0\to(\\{ptr}-1)]$. For example, the +semantic stack described above is handled this way, and so is the input +stack that we are about to study. + +\yskip\hangg 2) If there is infrequent top access, the entire stack contents +are in the array $\\{stack}[0\to(\\{ptr}-1)]$. For example, the |save_stack| +is treated this way, as we have seen. + +\yskip\noindent +The state of \TeX's input mechanism appears in the input stack, whose +entries are records with six fields, called |state|, |index|, |start|, |loc|, +|limit|, and |name|. This stack is maintained with +convention~(1), so it is declared in the following way: + +@<Types...@>= +@!in_state_record = record + @!state_field, @!index_field: quarterword; + @!start_field,@!loc_field, @!limit_field, @!name_field: halfword; + end; + +@ @<Glob...@>= +@!input_stack : array[0..stack_size] of in_state_record; +@!input_ptr : 0..stack_size; {first unused location of |input_stack|} +@!max_in_stack: 0..stack_size; {largest value of |input_ptr| when pushing} +@!cur_input : in_state_record; + {the ``top'' input state, according to convention (1)} + +@ We've already defined the special variable |loc==cur_input.loc_field| +in our discussion of basic input-output routines. The other components of +|cur_input| are defined in the same way: + +@d state==cur_input.state_field {current scanner state} +@d index==cur_input.index_field {reference for buffer information} +@d start==cur_input.start_field {starting position in |buffer|} +@d limit==cur_input.limit_field {end of current line in |buffer|} +@d 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|.) + +The |state| variable has one of three values, when we are scanning such +files: +$$\baselineskip 15pt\vbox{\halign{#\hfil\cr +1) |state=mid_line| is the normal state.\cr +2) |state=skip_blanks| is like |mid_line|, but blanks are ignored.\cr +3) |state=new_line| is the state at the beginning of a line.\cr}}$$ +These state values are assigned numeric codes so that if we add the state +code to the next character's command code, we get distinct values. For +example, `|mid_line+spacer|' stands for the case that a blank +space character occurs in the middle of a line when it is not being +ignored; after this case is processed, the next value of |state| will +be |skip_blanks|. + +@d mid_line=1 {|state| code when scanning a line of characters} +@d skip_blanks=2+max_char_code {|state| code when ignoring blanks} +@d new_line=3+max_char_code+max_char_code {|state| code at start of line} + +@ Additional information about the current line is available via the +|index| variable, which counts how many lines of characters are present +in the buffer below the current level. We have |index=0| when reading +from the terminal and prompting the user for each line; then if the user types, +e.g., `\.{\\input paper}', we will have |index=1| while reading +the file \.{paper.tex}. However, it does not follow that |index| is the +same as the input stack pointer, since many of the levels on the input +stack may come from token lists. For example, the instruction `\.{\\input +paper}' might occur in a token list. + +The global variable |in_open| is equal to the |index| +value of the highest non-token-list level. Thus, the number of partially read +lines in the buffer is |in_open+1|, and we have |in_open=index| +when we are not reading a token list. + +If we are not currently reading from the terminal, or from an input +stream, we are reading from the file variable |input_file[index]|. We use +the notation |terminal_input| as a convenient abbreviation for |name=0|, +and |cur_file| as an abbreviation for |input_file[index]|. + +The global variable |line| contains the line number in the topmost +open file, for use in error messages. If we are not reading from +the terminal, |line_stack[index]| holds the line number for the +enclosing level, so that |line| can be restored when the current +file has been read. Line numbers should never be negative, since the +negative of the current line number is used to identify the user's output +routine in the |mode_line| field of the semantic nest entries. + +If more information about the input state is needed, it can be +included in small arrays like those shown here. For example, +the current page or segment number in the input file might be +put into a variable |@!page|, maintained for enclosing levels in +`\ignorespaces|@!page_stack:array[1..max_in_open] of integer|\unskip' +by analogy with |line_stack|. +@^system dependencies@> + +@d terminal_input==(name=0) {are we reading from the terminal?} +@d cur_file==input_file[index] {the current |alpha_file| variable} + +@<Glob...@>= +@!in_open : 0..max_in_open; {the number of lines in the buffer, less one} +@!open_parens : 0..max_in_open; {the number of open text files} +@!input_file : array[1..max_in_open] of alpha_file; +@!line : integer; {current line number in the current source file} +@!line_stack : array[1..max_in_open] of integer; + +@ Users of \TeX\ sometimes forget to balance left and right braces properly, +and one of the ways \TeX\ tries to spot such errors is by considering an +input file as broken into subfiles by control sequences that +are declared to be \.{\\outer}. + +A variable called |scanner_status| tells \TeX\ whether or not to complain +when a subfile ends. This variable has six possible values: + +\yskip\hang|normal|, means that a subfile can safely end here without incident. + +\yskip\hang|skipping|, means that a subfile can safely end here, but not a file, +because we're reading past some conditional text that was not selected. + +\yskip\hang|defining|, means that a subfile shouldn't end now because a +macro is being defined. + +\yskip\hang|matching|, means that a subfile shouldn't end now because a +macro is being used and we are searching for the end of its arguments. + +\yskip\hang|aligning|, means that a subfile shouldn't end now because we are +not finished with the preamble of an \.{\\halign} or \.{\\valign}. + +\yskip\hang|absorbing|, means that a subfile shouldn't end now because we are +reading a balanced token list for \.{\\message}, \.{\\write}, etc. + +\yskip\noindent +If the |scanner_status| is not |normal|, the variable |warning_index| points +to the |eqtb| location for the relevant control sequence name to print +in an error message. + +@d skipping=1 {|scanner_status| when passing conditional text} +@d defining=2 {|scanner_status| when reading a macro definition} +@d matching=3 {|scanner_status| when reading macro arguments} +@d aligning=4 {|scanner_status| when reading an alignment preamble} +@d absorbing=5 {|scanner_status| when reading a balanced text} + +@<Glob...@>= +@!scanner_status : normal..absorbing; {can a subfile end now?} +@!warning_index : pointer; {identifier relevant to non-|normal| scanner status} +@!def_ref : pointer; {reference count of token list being defined} + +@ Here is a procedure that uses |scanner_status| to print a warning message +when a subfile has ended, and at certain other crucial times: + +@<Declare the procedure called |runaway|@>= +procedure runaway; +var p:pointer; {head of runaway list} +begin 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 \<u_j> part of an alignment +template is being scanned; + +\hang|v_template|, if the \<v_j> part of an alignment +template is being scanned; + +\hang|backed_up|, if the token list being scanned has been inserted as +`to be read again'. + +\hang|inserted|, if the token list being scanned has been inserted as +the text expansion of a \.{\\count} or similar variable; + +\hang|macro|, if a user-defined control sequence is being scanned; + +\hang|output_text|, if an \.{\\output} routine is being scanned; + +\hang|every_par_text|, if the text of \.{\\everypar} is being scanned; + +\hang|every_math_text|, if the text of \.{\\everymath} is being scanned; + +\hang|every_display_text|, if the text of \.{\\everydisplay} is being scanned; + +\hang|every_hbox_text|, if the text of \.{\\everyhbox} is being scanned; + +\hang|every_vbox_text|, if the text of \.{\\everyvbox} is being scanned; + +\hang|every_job_text|, if the text of \.{\\everyjob} is being scanned; + +\hang|every_cr_text|, if the text of \.{\\everycr} is being scanned; + +\hang|mark_text|, if the text of a \.{\\mark} is being scanned; + +\hang|write_text|, if the text of a \.{\\write} is being scanned. + +\yskip\noindent +The codes for |output_text|, |every_par_text|, etc., are equal to a constant +plus the corresponding codes for token list parameters |output_routine_loc|, +|every_par_loc|, etc. The token list begins with a reference count if and +only if |token_type>=macro|. +@^reference counts@> + +@d token_list=0 {|state| code when scanning a token list} +@d token_type==index {type of current token list} +@d param_start==limit {base of macro parameters in |param_stack|} +@d parameter=0 {|token_type| code for parameter} +@d u_template=1 {|token_type| code for \<u_j> template} +@d v_template=2 {|token_type| code for \<v_j> template} +@d backed_up=3 {|token_type| code for text to be reread} +@d inserted=4 {|token_type| code for inserted texts} +@d macro=5 {|token_type| code for defined control sequences} +@d output_text=6 {|token_type| code for output routines} +@d every_par_text=7 {|token_type| code for \.{\\everypar}} +@d every_math_text=8 {|token_type| code for \.{\\everymath}} +@d every_display_text=9 {|token_type| code for \.{\\everydisplay}} +@d every_hbox_text=10 {|token_type| code for \.{\\everyhbox}} +@d every_vbox_text=11 {|token_type| code for \.{\\everyvbox}} +@d every_job_text=12 {|token_type| code for \.{\\everyjob}} +@d every_cr_text=13 {|token_type| code for \.{\\everycr}} +@d mark_text=14 {|token_type| code for \.{\\topmark}, etc.} +@d write_text=15 {|token_type| code for \.{\\write}} + +@ The |param_stack| is an auxiliary array used to hold pointers to the token +lists for parameters at the current level and subsidiary levels of input. +This stack is maintained with convention (2), and it grows at a different +rate from the others. + +@<Glob...@>= +@!param_stack:array [0..param_size] of pointer; + {token list pointers for parameters} +@!param_ptr:0..param_size; {first unused entry in |param_stack|} +@!max_param_stack:integer; + {largest value of |param_ptr|, will be |<=param_size+9|} + +@ The input routines must also interact with the processing of +\.{\\halign} and \.{\\valign}, since the appearance of tab marks and +\.{\\cr} in certain places is supposed to trigger the beginning of special +\<v_j> template text in the scanner. This magic is accomplished by an +|align_state| variable that is increased by~1 when a `\.{\char'173}' is +scanned and decreased by~1 when a `\.{\char'175}' is scanned. The |align_state| +is nonzero during the \<u_j> template, after which it is set to zero; the +\<v_j> template begins when a tab mark or \.{\\cr} occurs at a time that +|align_state=0|. + +@<Glob...@>= +@!align_state:integer; {group level with respect to current alignment} + +@ Thus, the ``current input state'' can be very complicated indeed; there +can be many levels and each level can arise in a variety of ways. The +|show_context| procedure, which is used by \TeX's error-reporting routine to +print out the current input state on all levels down to the most recent +line of characters from an input file, illustrates most of these conventions. +The global variable |base_ptr| contains the lowest level that was +displayed by this procedure. + +@<Glob...@>= +@!base_ptr:0..stack_size; {shallowest level shown by |show_context|} + +@ The status at each level is indicated by printing two lines, where the first +line indicates what was read so far and the second line shows what remains +to be read. The context is cropped, if necessary, so that the first line +contains at most |half_error_line| characters, and the second contains +at most |error_line|. Non-current input levels whose |token_type| is +`|backed_up|' are shown only if they have not been fully read. + +@p procedure show_context; {prints where the scanner is} +label done; +var old_setting:0..max_selector; {saved |selector| setting} +@!nn:integer; {number of contexts shown so far, less one} +@!bottom_line:boolean; {have we reached the final context to be shown?} +@<Local variables for formatting calculations@>@/ +begin base_ptr:=input_ptr; input_stack[base_ptr]:=cur_input; + {store current state} +nn:=-1; bottom_line:=false; +loop@+begin cur_input:=input_stack[base_ptr]; {enter into the context} + if (state<>token_list) then + if (name>17) or (base_ptr=0) then bottom_line:=true; + if (base_ptr=input_ptr)or bottom_line or(nn<error_context_lines) then + @<Display the current context@> + else if nn=error_context_lines then + begin print_nl("..."); incr(nn); {omitted if |error_context_lines<0|} + end; + if bottom_line then goto done; + decr(base_ptr); + end; +done: cur_input:=input_stack[input_ptr]; {restore original state} +end; + +@ @<Display the current context@>= +begin if (base_ptr=input_ptr) or (state<>token_list) or + (token_type<>backed_up) or (loc<>null) then + {we omit backed-up token lists that have already been read} + begin tally:=0; {get ready to count characters} + old_setting:=selector; + if state<>token_list then + begin @<Print location of current line@>; + @<Pseudoprint the line@>; + end + else begin @<Print type of token list@>; + @<Pseudoprint the token list@>; + end; + selector:=old_setting; {stop pseudoprinting} + @<Print two lines using the tricky pseudoprinted information@>; + incr(nn); + end; +end + +@ This routine should be changed, if necessary, to give the best possible +indication of where the current line resides in the input file. +For example, on some systems it is best to print both a page and line number. +@^system dependencies@> + +@<Print location of current line@>= +if name<=17 then + if terminal_input then + if base_ptr=0 then print_nl("<*>") else print_nl("<insert> ") + else begin print_nl("<read "); + if name=17 then print_char("*")@+else print_int(name-1); +@.*\relax@> + print_char(">"); + end +else begin print_nl("l."); print_int(line); + end; +print_char(" ") + +@ @<Print type of token list@>= +case token_type of +parameter: print_nl("<argument> "); +u_template,v_template: print_nl("<template> "); +backed_up: if loc=null then print_nl("<recently read> ") + else print_nl("<to be read again> "); +inserted: print_nl("<inserted text> "); +macro: begin print_ln; print_cs(name); + end; +output_text: print_nl("<output> "); +every_par_text: print_nl("<everypar> "); +every_math_text: print_nl("<everymath> "); +every_display_text: print_nl("<everydisplay> "); +every_hbox_text: print_nl("<everyhbox> "); +every_vbox_text: print_nl("<everyvbox> "); +every_job_text: print_nl("<everyjob> "); +every_cr_text: print_nl("<everycr> "); +mark_text: print_nl("<mark> "); +write_text: print_nl("<write> "); +othercases print_nl("?") {this should never happen} +endcases + +@ Here it is necessary to explain a little trick. We don't want to store a long +string that corresponds to a token list, because that string might take up +lots of memory; and we are printing during a time when an error message is +being given, so we dare not do anything that might overflow one of \TeX's +tables. So `pseudoprinting' is the answer: We enter a mode of printing +that stores characters into a buffer of length |error_line|, where character +$k+1$ is placed into \hbox{|trick_buf[k mod error_line]|} if +|k<trick_count|, otherwise character |k| is dropped. Initially we set +|tally:=0| and |trick_count:=1000000|; then when we reach the +point where transition from line 1 to line 2 should occur, we +set |first_count:=tally| and |trick_count:=@tmax@>(error_line, +tally+1+error_line-half_error_line)|. At the end of the +pseudoprinting, the values of |first_count|, |tally|, and +|trick_count| give us all the information we need to print the two lines, +and all of the necessary text is in |trick_buf|. + +Namely, let |l| be the length of the descriptive information that appears +on the first line. The length of the context information gathered for that +line is |k=first_count|, and the length of the context information +gathered for line~2 is $m=\min(|tally|, |trick_count|)-k$. If |l+k<=h|, +where |h=half_error_line|, we print |trick_buf[0..k-1]| after the +descriptive information on line~1, and set |n:=l+k|; here |n| is the +length of line~1. If $l+k>h$, some cropping is necessary, so we set |n:=h| +and print `\.{...}' followed by +$$\hbox{|trick_buf[(l+k-h+3)..k-1]|,}$$ +where subscripts of |trick_buf| are circular modulo |error_line|. The +second line consists of |n|~spaces followed by |trick_buf[k..(k+m-1)]|, +unless |n+m>error_line|; in the latter case, further cropping is done. +This is easier to program than to explain. + +@<Local variables for formatting...@>= +@!i:0..buf_size; {index into |buffer|} +@!j:0..buf_size; {end of current line in |buffer|} +@!l:0..half_error_line; {length of descriptive information on line 1} +@!m:integer; {context information gathered for line 2} +@!n:0..error_line; {length of line 1} +@!p: integer; {starting or ending place in |trick_buf|} +@!q: integer; {temporary index} + +@ The following code sets up the print routines so that they will gather +the desired information. + +@d begin_pseudoprint== + begin l:=tally; tally:=0; selector:=pseudo; + trick_count:=1000000; + end +@d set_trick_count== + begin first_count:=tally; + trick_count:=tally+1+error_line-half_error_line; + if trick_count<error_line then trick_count:=error_line; + end + +@ And the following code uses the information after it has been gathered. + +@<Print two lines using the tricky pseudoprinted information@>= +if trick_count=1000000 then set_trick_count; + {|set_trick_count| must be performed} +if tally<trick_count then m:=tally-first_count +else m:=trick_count-first_count; {context on line 2} +if l+first_count<=half_error_line then + begin p:=0; n:=l+first_count; + end +else begin print("..."); p:=l+first_count-half_error_line+3; + n:=half_error_line; + end; +for q:=p to first_count-1 do print_char(trick_buf[q mod error_line]); +print_ln; +for q:=1 to n do print_char(" "); {print |n| spaces to begin line~2} +if m+n<=error_line then p:=first_count+m else p:=first_count+(error_line-n-3); +for q:=first_count to p-1 do print_char(trick_buf[q mod error_line]); +if m+n>error_line then print("...") + +@ But the trick is distracting us from our current goal, which is to +understand the input state. So let's concentrate on the data structures that +are being pseudoprinted as we finish up the |show_context| procedure. + +@<Pseudoprint the line@>= +begin_pseudoprint; +if buffer[limit]=end_line_char then j:=limit +else j:=limit+1; {determine the effective end of the line} +if j>0 then for i:=start to j-1 do + begin if i=loc then set_trick_count; + print(buffer[i]); + end + +@ @<Pseudoprint the token list@>= +begin_pseudoprint; +if token_type<macro then show_token_list(start,loc,100000) +else show_token_list(link(start),loc,100000) {avoid reference count} + +@ Here is the missing piece of |show_token_list| that is activated when the +token beginning line~2 is about to be shown: + +@<Do magic computation@>=set_trick_count + +@* \[23] Maintaining the input stacks. +The following subroutines change the input status in commonly needed ways. + +First comes |push_input|, which stores the current state and creates a +new level (having, initially, the same properties as the old). + +@d push_input==@t@> {enter a new input level, save the old} + begin if input_ptr>max_in_stack then + begin max_in_stack:=input_ptr; + if input_ptr=stack_size then overflow("input stack size",stack_size); +@:TeX capacity exceeded input stack size}{\quad input stack size@> + end; + input_stack[input_ptr]:=cur_input; {stack the record} + incr(input_ptr); + end + +@ And of course what goes up must come down. + +@d pop_input==@t@> {leave an input level, re-enter the old} + begin decr(input_ptr); cur_input:=input_stack[input_ptr]; + end + +@ Here is a procedure that starts a new level of token-list input, given +a token list |p| and its type |t|. If |t=macro|, the calling routine should +set |name| and |loc|. + +@d back_list(#)==begin_token_list(#,backed_up) {backs up a simple token list} +@d ins_list(#)==begin_token_list(#,inserted) {inserts a simple token list} + +@p procedure begin_token_list(@!p:pointer;@!t:quarterword); +begin push_input; state:=token_list; start:=p; token_type:=t; +if t>=macro then {the token list starts with a reference count} + begin add_token_ref(p); + if t=macro then param_start:=param_ptr + else begin loc:=link(p); + if tracing_macros>1 then + begin begin_diagnostic; print_nl(""); + case t of + mark_text:print_esc("mark"); + write_text:print_esc("write"); + othercases print_cmd_chr(assign_toks,t-output_text+output_routine_loc) + endcases;@/ + print("->"); token_show(p); end_diagnostic(false); + end; + end; + end +else loc:=p; +end; + +@ When a token list has been fully scanned, the following computations +should be done as we leave that level of input. The |token_type| tends +to be equal to either |backed_up| or |inserted| about 2/3 of the time. +@^inner loop@> + +@p procedure end_token_list; {leave a token-list input level} +begin if token_type>=backed_up then {token list to be deleted} + begin if token_type<=inserted then flush_list(start) + else begin delete_token_ref(start); {update reference count} + if token_type=macro then {parameters must be flushed} + while param_ptr>param_start do + begin decr(param_ptr); + flush_list(param_stack[param_ptr]); + end; + end; + end +else if token_type=u_template then + if align_state>500000 then align_state:=0 + else fatal_error("(interwoven alignment preambles are not allowed)"); +@.interwoven alignment preambles...@> +pop_input; +check_interrupt; +end; + +@ Sometimes \TeX\ has read too far and wants to ``unscan'' what it has +seen. The |back_input| procedure takes care of this by putting the token +just scanned back into the input stream, ready to be read again. This +procedure can be used only if |cur_tok| represents the token to be +replaced. Some applications of \TeX\ use this procedure a lot, +so it has been slightly optimized for speed. +@^inner loop@> + +@p procedure back_input; {undoes one token of input} +var p:pointer; {a token list of length one} +begin while (state=token_list)and(loc=null)and(token_type<>v_template) do + end_token_list; {conserve stack space} +p:=get_avail; info(p):=cur_tok; +if cur_tok<right_brace_limit then + if cur_tok<left_brace_limit then decr(align_state) + else incr(align_state); +push_input; state:=token_list; start:=p; token_type:=backed_up; +loc:=p; {that was |back_list(p)|, without procedure overhead} +end; + +@ @<Insert token |p| into \TeX's input@>= +begin t:=cur_tok; cur_tok:=p; back_input; cur_tok:=t; +end + +@ The |back_error| routine is used when we want to replace an offending token +just before issuing an error message. This routine, like |back_input|, +requires that |cur_tok| has been set. We disable interrupts during the +call of |back_input| so that the help message won't be lost. + +@p procedure back_error; {back up one token and call |error|} +begin OK_to_interrupt:=false; back_input; OK_to_interrupt:=true; error; +end; +@# +procedure ins_error; {back up one inserted token and call |error|} +begin OK_to_interrupt:=false; back_input; token_type:=inserted; +OK_to_interrupt:=true; error; +end; + +@ The |begin_file_reading| procedure starts a new level of input for lines +of characters to be read from a file, or as an insertion from the +terminal. It does not take care of opening the file, nor does it set |loc| +or |limit| or |line|. +@^system dependencies@> + +@p procedure begin_file_reading; +begin if in_open=max_in_open then overflow("text input levels",max_in_open); +@:TeX capacity exceeded text input levels}{\quad text input levels@> +if first=buf_size then overflow("buffer size",buf_size); +@:TeX capacity exceeded buffer size}{\quad buffer size@> +incr(in_open); push_input; index:=in_open; +line_stack[index]:=line; start:=first; state:=mid_line; +name:=0; {|terminal_input| is now |true|} +end; + +@ Conversely, the variables must be downdated when such a level of input +is finished: + +@p procedure end_file_reading; +begin first:=start; line:=line_stack[index]; +if name>17 then a_close(cur_file); {forget it} +pop_input; decr(in_open); +end; + +@ In order to keep the stack from overflowing during a long sequence of +inserted `\.{\\show}' commands, the following routine removes completed +error-inserted lines from memory. + +@p procedure clear_for_error_prompt; +begin while (state<>token_list)and terminal_input and@| + (input_ptr>0)and(loc>limit) do end_file_reading; +print_ln; clear_terminal; +end; + +@ To get \TeX's whole input mechanism going, we perform the following +actions. + +@<Initialize the input routines@>= +begin input_ptr:=0; max_in_stack:=0; +in_open:=0; open_parens:=0; max_buf_stack:=0; +param_ptr:=0; max_param_stack:=0; +first:=buf_size; repeat buffer[first]:=0; decr(first); until first=0; +scanner_status:=normal; warning_index:=null; first:=1; +state:=new_line; start:=1; index:=0; line:=0; name:=0; +force_eof:=false; +align_state:=1000000;@/ +if not init_terminal then goto final_end; +limit:=last; first:=last+1; {|init_terminal| has set |loc| and |last|} +end + +@* \[24] Getting the next token. +The heart of \TeX's input mechanism is the |get_next| procedure, which +we shall develop in the next few sections of the program. Perhaps we +shouldn't actually call it the ``heart,'' however, because it really acts +as \TeX's eyes and mouth, reading the source files and gobbling them up. +And it also helps \TeX\ to regurgitate stored token lists that are to be +processed again. +@^eyes and mouth@> + +The main duty of |get_next| is to input one token and to set |cur_cmd| +and |cur_chr| to that token's command code and modifier. Furthermore, if +the input token is a control sequence, the |eqtb| location of that control +sequence is stored in |cur_cs|; otherwise |cur_cs| is set to zero. + +Underlying this simple description is a certain amount of complexity +because of all the cases that need to be handled. +However, the inner loop of |get_next| is reasonably short and fast. + +When |get_next| is asked to get the next token of a \.{\\read} line, +it sets |cur_cmd=cur_chr=cur_cs=0| in the case that no more tokens +appear on that line. (There might not be any tokens at all, if the +|end_line_char| has |ignore| as its catcode.) + +@ The value of |par_loc| is the |eqtb| address of `\.{\\par}'. This quantity +is needed because a blank line of input is supposed to be exactly equivalent +to the appearance of \.{\\par}; we must set |cur_cs:=par_loc| +when detecting a blank line. + +@<Glob...@>= +@!par_loc:pointer; {location of `\.{\\par}' in |eqtb|} +@!par_token:halfword; {token representing `\.{\\par}'} + +@ @<Put each...@>= +primitive("par",par_end,256); {cf. |scan_file_name|} +@!@:par_}{\.{\\par} primitive@> +par_loc:=cur_val; par_token:=cs_token_flag+par_loc; + +@ @<Cases of |print_cmd_chr|...@>= +par_end:print_esc("par"); + +@ Before getting into |get_next|, let's consider the subroutine that +is called when an `\.{\\outer}' control sequence has been scanned or +when the end of a file has been reached. These two cases are distinguished +by |cur_cs|, which is zero at the end of a file. + +@p procedure check_outer_validity; +var p:pointer; {points to inserted token list} +@!q:pointer; {auxiliary pointer} +begin if scanner_status<>normal then + begin deletions_allowed:=false; + @<Back up an outer control sequence so that it can be reread@>; + if scanner_status>skipping then + @<Tell the user what has run away and try to recover@> + else begin print_err("Incomplete "); print_cmd_chr(if_test,cur_if); +@.Incomplete \\if...@> + print("; all text was ignored after line "); print_int(skip_line); + help3("A forbidden control sequence occurred in skipped text.")@/ + ("This kind of error happens when you say `\if...' and forget")@/ + ("the matching `\fi'. I've inserted a `\fi'; this might work."); + if cur_cs<>0 then cur_cs:=0 + else help_line[2]:=@| + "The file ended while I was skipping conditional text."; + cur_tok:=cs_token_flag+frozen_fi; ins_error; + end; + deletions_allowed:=true; + end; +end; + +@ An outer control sequence that occurs in a \.{\\read} will not be reread, +since the error recovery for \.{\\read} is not very powerful. + +@<Back up an outer control sequence so that it can be reread@>= +if cur_cs<>0 then + begin if (state=token_list)or(name<1)or(name>17) then + begin p:=get_avail; info(p):=cs_token_flag+cur_cs; + back_list(p); {prepare to read the control sequence again} + end; + cur_cmd:=spacer; cur_chr:=" "; {replace it by a space} + end + +@ @<Tell the user what has run away...@>= +begin runaway; {print a definition, argument, or preamble} +if cur_cs=0 then print_err("File ended") +@.File ended while scanning...@> +else begin cur_cs:=0; print_err("Forbidden control sequence found"); +@.Forbidden control sequence...@> + end; +print(" while scanning "); +@<Print either `\.{definition}' or `\.{use}' or `\.{preamble}' or `\.{text}', + and insert tokens that should lead to recovery@>; +print(" of "); sprint_cs(warning_index); +help4("I suspect you have forgotten a `}', causing me")@/ +("to read past where you wanted me to stop.")@/ +("I'll try to recover; but if the error is serious,")@/ +("you'd better type `E' or `X' now and fix your file.");@/ +error; +end + +@ The recovery procedure can't be fully understood without knowing more +about the \TeX\ routines that should be aborted, but we can sketch the +ideas here: For a runaway definition we will insert a right brace; for a +runaway preamble, we will insert a special \.{\\cr} token and a right +brace; and for a runaway argument, we will set |long_state| to +|outer_call| and insert \.{\\par}. + +@<Print either `\.{definition}' or ...@>= +p:=get_avail; +case scanner_status of +defining:begin print("definition"); info(p):=right_brace_token+"}"; + end; +matching:begin print("use"); info(p):=par_token; long_state:=outer_call; + end; +aligning:begin print("preamble"); info(p):=right_brace_token+"}"; q:=p; + p:=get_avail; link(p):=q; info(p):=cs_token_flag+frozen_cr; + align_state:=-1000000; + end; +absorbing:begin print("text"); info(p):=right_brace_token+"}"; + end; +end; {there are no other cases} +ins_list(p) + +@ We need to mention a procedure here that may be called by |get_next|. + +@p procedure@?firm_up_the_line; forward; + +@ Now we're ready to take the plunge into |get_next| itself. Parts of +this routine are executed more often than any other instructions of \TeX. +@^mastication@>@^inner loop@> + +@d switch=25 {a label in |get_next|} +@d start_cs=26 {another} + +@p procedure get_next; {sets |cur_cmd|, |cur_chr|, |cur_cs| to next token} +label restart, {go here to get the next input token} + switch, {go here to eat the next character from a file} + reswitch, {go here to digest it again} + start_cs, {go here to start looking for a control sequence} + found, {go here when a control sequence has been found} + exit; {go here when the next input token has been got} +var k:0..buf_size; {an index into |buffer|} +@!t:halfword; {a token} +@!cat:0..15; {|cat_code(cur_chr)|, usually} +@!c,@!cc:ASCII_code; {constituents of a possible expanded code} +@!d:2..3; {number of excess characters in an expanded code} +begin restart: cur_cs:=0; +if state<>token_list then +@<Input from external file, |goto restart| if no input found@> +else @<Input from token list, |goto restart| if end of list or + if a parameter needs to be expanded@>; +@<If an alignment entry has just ended, take appropriate action@>; +exit:end; + +@ An alignment entry ends when a tab or \.{\\cr} occurs, provided that the +current level of braces is the same as the level that was present at the +beginning of that alignment entry; i.e., provided that |align_state| has +returned to the value it had after the \<u_j> template for that entry. +@^inner loop@> + +@<If an alignment entry has just ended, take appropriate action@>= +if cur_cmd<=car_ret then if cur_cmd>=tab_mark then if align_state=0 then + @<Insert the \(v)\<v_j> template and |goto restart|@> + +@ @<Input from external file, |goto restart| if no input found@>= +@^inner loop@> +begin switch: if loc<=limit then {current line not yet finished} + begin cur_chr:=buffer[loc]; incr(loc); + reswitch: cur_cmd:=cat_code(cur_chr); + @<Change state if necessary, and |goto switch| if the + current character should be ignored, + or |goto reswitch| if the current character + changes to another@>; + end +else begin state:=new_line;@/ + @<Move to next line of file, + or |goto restart| if there is no next line, + or |return| if a \.{\\read} line has finished@>; + check_interrupt; + goto switch; + end; +end + +@ The following 48-way switch accomplishes the scanning quickly, assuming +that a decent \PASCAL\ compiler has translated the code. Note that the numeric +values for |mid_line|, |skip_blanks|, and |new_line| are spaced +apart from each other by |max_char_code+1|, so we can add a character's +command code to the state to get a single number that characterizes both. + +@d any_state_plus(#) == mid_line+#,skip_blanks+#,new_line+# + +@<Change state if necessary...@>= +case state+cur_cmd of +@<Cases where character is ignored@>: goto switch; +any_state_plus(escape): @<Scan a control sequence + and set |state:=skip_blanks| or |mid_line|@>; +any_state_plus(active_char): @<Process an active-character control sequence + and set |state:=mid_line|@>; +any_state_plus(sup_mark): @<If this |sup_mark| starts an expanded character + like~\.{\^\^A} or~\.{\^\^df}, then |goto reswitch|, + otherwise set |state:=mid_line|@>; +any_state_plus(invalid_char): @<Decry the invalid character and + |goto restart|@>; +@t\4@>@<Handle situations involving spaces, braces, changes of state@>@; +othercases do_nothing +endcases + +@ @<Cases where character is ignored@>= +any_state_plus(ignore),skip_blanks+spacer,new_line+spacer + +@ We go to |restart| instead of to |switch|, because |state| might equal +|token_list| after the error has been dealt with +(cf.\ |clear_for_error_prompt|). + +@<Decry the invalid...@>= +begin print_err("Text line contains an invalid character"); +@.Text line contains...@> +help2("A funny symbol that I can't read has just been input.")@/ +("Continue, and I'll forget that it ever happened.");@/ +deletions_allowed:=false; error; deletions_allowed:=true; +goto restart; +end + +@ @d add_delims_to(#)==#+math_shift,#+tab_mark,#+mac_param, + #+sub_mark,#+letter,#+other_char + +@<Handle situations involving spaces, braces, changes of state@>= +mid_line+spacer:@<Enter |skip_blanks| state, emit a space@>; +mid_line+car_ret:@<Finish line, emit a space@>; +skip_blanks+car_ret,any_state_plus(comment): + @<Finish line, |goto switch|@>; +new_line+car_ret:@<Finish line, emit a \.{\\par}@>; +mid_line+left_brace: incr(align_state); +skip_blanks+left_brace,new_line+left_brace: begin + state:=mid_line; incr(align_state); + end; +mid_line+right_brace: decr(align_state); +skip_blanks+right_brace,new_line+right_brace: begin + state:=mid_line; decr(align_state); + end; +add_delims_to(skip_blanks),add_delims_to(new_line): state:=mid_line; + +@ When a character of type |spacer| gets through, its character code is +changed to $\.{"\ "}=@'40$. This means that the ASCII codes for tab and space, +and for the space inserted at the end of a line, will +be treated alike when macro parameters are being matched. We do this +since such characters are indistinguishable on most computer terminal displays. + +@<Finish line, emit a space@>= +begin loc:=limit+1; cur_cmd:=spacer; cur_chr:=" "; +end + +@ The following code is performed only when |cur_cmd=spacer|. + +@<Enter |skip_blanks| state, emit a space@>= +begin state:=skip_blanks; cur_chr:=" "; +end + +@ @<Finish line, |goto switch|@>= +begin loc:=limit+1; goto switch; +end + +@ @<Finish line, emit a \.{\\par}@>= +begin loc:=limit+1; cur_cs:=par_loc; cur_cmd:=eq_type(cur_cs); +cur_chr:=equiv(cur_cs); +if cur_cmd>=outer_call then check_outer_validity; +end + +@ Notice that a code like \.{\^\^8} becomes \.x if not followed by a hex digit. + +@d is_hex(#)==(((#>="0")and(#<="9"))or((#>="a")and(#<="f"))) +@d hex_to_cur_chr== + if c<="9" then cur_chr:=c-"0" @+else cur_chr:=c-"a"+10; + if cc<="9" then cur_chr:=16*cur_chr+cc-"0" + else cur_chr:=16*cur_chr+cc-"a"+10 + +@<If this |sup_mark| starts an expanded character...@>= +begin if cur_chr=buffer[loc] then if loc<limit then + begin c:=buffer[loc+1]; @+if c<@'200 then {yes we have an expanded char} + begin loc:=loc+2; + if is_hex(c) then if loc<=limit then + begin cc:=buffer[loc]; @+if is_hex(cc) then + begin incr(loc); hex_to_cur_chr; goto reswitch; + end; + end; + if c<@'100 then cur_chr:=c+@'100 @+else cur_chr:=c-@'100; + goto reswitch; + end; + end; +state:=mid_line; +end + +@ @<Process an active-character...@>= +begin cur_cs:=cur_chr+active_base; +cur_cmd:=eq_type(cur_cs); cur_chr:=equiv(cur_cs); state:=mid_line; +if cur_cmd>=outer_call then check_outer_validity; +end + +@ Control sequence names are scanned only when they appear in some line of +a file; once they have been scanned the first time, their |eqtb| location +serves as a unique identification, so \TeX\ doesn't need to refer to the +original name any more except when it prints the equivalent in symbolic form. + +The program that scans a control sequence has been written carefully +in order to avoid the blowups that might otherwise occur if a malicious +user tried something like `\.{\\catcode\'15=0}'. The algorithm might +look at |buffer[limit+1]|, but it never looks at |buffer[limit+2]|. + +If expanded characters like `\.{\^\^A}' or `\.{\^\^df}' +appear in or just following +a control sequence name, they are converted to single characters in the +buffer and the process is repeated, slowly but surely. + +@<Scan a control...@>= +begin if loc>limit then cur_cs:=null_cs {|state| is irrelevant in this case} +else begin start_cs: k:=loc; cur_chr:=buffer[k]; cat:=cat_code(cur_chr); + incr(k); + if cat=letter then state:=skip_blanks + else if cat=spacer then state:=skip_blanks + else state:=mid_line; + if (cat=letter)and(k<=limit) then + @<Scan ahead in the buffer until finding a nonletter; + if an expanded code is encountered, reduce it + and |goto start_cs|; otherwise if a multiletter control + sequence is found, adjust |cur_cs| and |loc|, and + |goto found|@> + else @<If an expanded code is present, reduce it and |goto start_cs|@>; + cur_cs:=single_base+buffer[loc]; incr(loc); + end; +found: cur_cmd:=eq_type(cur_cs); cur_chr:=equiv(cur_cs); +if cur_cmd>=outer_call then check_outer_validity; +end + +@ Whenever we reach the following piece of code, we will have +|cur_chr=buffer[k-1]| and |k<=limit+1| and |cat=cat_code(cur_chr)|. If an +expanded code like \.{\^\^A} or \.{\^\^df} appears in |buffer[(k-1)..(k+1)]| +or |buffer[(k-1)..(k+2)]|, we +will store the corresponding code in |buffer[k-1]| and shift the rest of +the buffer left two or three places. + +@<If an expanded...@>= +begin if buffer[k]=cur_chr then @+if cat=sup_mark then @+if k<limit then + begin c:=buffer[k+1]; @+if c<@'200 then {yes, one is indeed present} + begin d:=2; + if is_hex(c) then @+if k+2<=limit then + begin cc:=buffer[k+2]; @+if is_hex(cc) then incr(d); + end; + if d>2 then + begin hex_to_cur_chr; buffer[k-1]:=cur_chr; + end + else if c<@'100 then buffer[k-1]:=c+@'100 + else buffer[k-1]:=c-@'100; + limit:=limit-d; first:=first-d; + while k<=limit do + begin buffer[k]:=buffer[k+d]; incr(k); + end; + goto start_cs; + end; + end; +end + +@ @<Scan ahead in the buffer...@>= +begin repeat cur_chr:=buffer[k]; cat:=cat_code(cur_chr); incr(k); +until (cat<>letter)or(k>limit); +@<If an expanded...@>; +if cat<>letter then decr(k); + {now |k| points to first nonletter} +if k>loc+1 then {multiletter control sequence has been scanned} + begin cur_cs:=id_lookup(loc,k-loc); loc:=k; goto found; + end; +end + +@ Let's consider now what happens when |get_next| is looking at a token list. + +@<Input from token list, |goto restart| if end of list or + if a parameter needs to be expanded@>= +if loc<>null then {list not exhausted} +@^inner loop@> + begin t:=info(loc); loc:=link(loc); {move to next} + if t>=cs_token_flag then {a control sequence token} + begin cur_cs:=t-cs_token_flag; + cur_cmd:=eq_type(cur_cs); cur_chr:=equiv(cur_cs); + if cur_cmd>=outer_call then + if cur_cmd=dont_expand then + @<Get the next token, suppressing expansion@> + else check_outer_validity; + end + else begin cur_cmd:=t div @'400; cur_chr:=t mod @'400; + case cur_cmd of + left_brace: incr(align_state); + right_brace: decr(align_state); + out_param: @<Insert macro parameter and |goto restart|@>; + othercases do_nothing + endcases; + end; + end +else begin {we are done with this token list} + end_token_list; goto restart; {resume previous level} + end + +@ The present point in the program is reached only when the |expand| +routine has inserted a special marker into the input. In this special +case, |info(loc)| is known to be a control sequence token, and |link(loc)=null|. + +@d no_expand_flag=257 {this characterizes a special variant of |relax|} + +@<Get the next token, suppressing expansion@>= +begin cur_cs:=info(loc)-cs_token_flag; loc:=null;@/ +cur_cmd:=eq_type(cur_cs); cur_chr:=equiv(cur_cs); +if cur_cmd>max_command then + begin cur_cmd:=relax; cur_chr:=no_expand_flag; + end; +end + +@ @<Insert macro parameter...@>= +begin begin_token_list(param_stack[param_start+cur_chr-1],parameter); +goto restart; +end + +@ All of the easy branches of |get_next| have now been taken care of. +There is one more branch. + +@d end_line_char_inactive == (end_line_char<0)or(end_line_char>255) + +@<Move to next line of file, or |goto restart|...@>= +if name>17 then @<Read next line of file into |buffer|, or + |goto restart| if the file has ended@> +else begin if not terminal_input then {\.{\\read} line has ended} + begin cur_cmd:=0; cur_chr:=0; return; + end; + if input_ptr>0 then {text was inserted during error recovery} + begin end_file_reading; goto restart; {resume previous level} + end; + if selector<log_only then open_log_file; + if interaction>nonstop_mode then + begin if end_line_char_inactive then incr(limit); + if limit=start then {previous line was empty} + print_nl("(Please type a command or say `\end')"); +@.Please type...@> + print_ln; first:=start; + prompt_input("*"); {input on-line into |buffer|} +@.*\relax@> + limit:=last; + if end_line_char_inactive then decr(limit) + else buffer[limit]:=end_line_char; + first:=limit+1; + loc:=start; + end + else fatal_error("*** (job aborted, no legal \end found)"); +@.job aborted@> + {nonstop mode, which is intended for overnight batch processing, + never waits for on-line input} + end + +@ The global variable |force_eof| is normally |false|; it is set |true| +by an \.{\\endinput} command. + +@<Glob...@>= +@!force_eof:boolean; {should the next \.{\\input} be aborted early?} + +@ @<Read next line of file into |buffer|, or + |goto restart| if the file has ended@>= +begin incr(line); first:=start; +if not force_eof then + begin if input_ln(cur_file,true) then {not end of file} + firm_up_the_line {this sets |limit|} + else force_eof:=true; + end; +if force_eof then + begin print_char(")"); decr(open_parens); + update_terminal; {show user that file has been read} + force_eof:=false; + end_file_reading; {resume previous level} + check_outer_validity; goto restart; + end; +if end_line_char_inactive then decr(limit) +else buffer[limit]:=end_line_char; +first:=limit+1; loc:=start; {ready to read} +end + +@ If the user has set the |pausing| parameter to some positive value, +and if nonstop mode has not been selected, each line of input is displayed +on the terminal and the transcript file, followed by `\.{=>}'. +\TeX\ waits for a response. If the response is simply |carriage_return|, the +line is accepted as it stands, otherwise the line typed is +used instead of the line in the file. + +@p procedure firm_up_the_line; +var k:0..buf_size; {an index into |buffer|} +begin limit:=last; +if pausing>0 then if interaction>nonstop_mode then + begin wake_up_terminal; print_ln; + if start<limit then for k:=start to limit-1 do print(buffer[k]); + first:=limit; prompt_input("=>"); {wait for user response} +@.=>@> + if last>first then + begin for k:=first to last-1 do {move line down in buffer} + buffer[k+start-first]:=buffer[k]; + limit:=start+last-first; + end; + end; +end; + +@ Since |get_next| is used so frequently in \TeX, it is convenient +to define three related procedures that do a little more: + +\yskip\hang|get_token| not only sets |cur_cmd| and |cur_chr|, it +also sets |cur_tok|, a packed halfword version of the current token. + +\yskip\hang|get_x_token|, meaning ``get an expanded token,'' is like +|get_token|, but if the current token turns out to be a user-defined +control sequence (i.e., a macro call), or a conditional, +or something like \.{\\topmark} or \.{\\expandafter} or \.{\\csname}, +it is eliminated from the input by beginning the expansion of the macro +or the evaluation of the conditional. + +\yskip\hang|x_token| is like |get_x_token| except that it assumes that +|get_next| has already been called. + +\yskip\noindent +In fact, these three procedures account for {\sl all\/} uses of |get_next|, +except for two places in the ``inner loop'' when |cur_tok| need not be set, +and except when the arguments to \.{\\ifx} are being scanned. + +@ No new control sequences will be defined except during a call of +|get_token|, or when \.{\\csname} compresses a token list, because +|no_new_control_sequence| is always |true| at other times. + +@p procedure get_token; {sets |cur_cmd|, |cur_chr|, |cur_tok|} +begin no_new_control_sequence:=false; get_next; no_new_control_sequence:=true; +@^inner loop@> +if cur_cs=0 then cur_tok:=(cur_cmd*@'400)+cur_chr +else cur_tok:=cs_token_flag+cur_cs; +end; + +@* \[25] Expanding the next token. +Only a dozen or so command codes |>max_command| can possibly be returned by +|get_next|; in increasing order, they are |undefined_cs|, |expand_after|, +|no_expand|, |input|, |if_test|, |fi_or_else|, |cs_name|, |convert|, |the|, +|top_bot_mark|, |call|, |long_call|, |outer_call|, |long_outer_call|, and +|end_template|.{\emergencystretch=40pt\par} + +The |expand| subroutine is used when |cur_cmd>max_command|. It removes a +``call'' or a conditional or one of the other special operations just +listed. It follows that |expand| might invoke itself recursively. In all +cases, |expand| destroys the current token, but it sets things up so that +the next |get_next| will deliver the appropriate next token. The value of +|cur_tok| need not be known when |expand| is called. + +Since several of the basic scanning routines communicate via global variables, +their values are saved as local variables of |expand| so that +recursive calls don't invalidate them. +@^recursion@> + +@p@t\4@>@<Declare the procedure called |macro_call|@>@;@/ +@t\4@>@<Declare the procedure called |insert_relax|@>@;@/ +procedure@?pass_text; forward;@t\2@> +procedure@?start_input; forward;@t\2@> +procedure@?conditional; forward;@t\2@> +procedure@?get_x_token; forward;@t\2@> +procedure@?conv_toks; forward;@t\2@> +procedure@?ins_the_toks; forward;@t\2@> +procedure expand; +var t:halfword; {token that is being ``expanded after''} +@!p,@!q,@!r:pointer; {for list manipulation} +@!j:0..buf_size; {index into |buffer|} +@!cv_backup:integer; {to save the global quantity |cur_val|} +@!cvl_backup,@!radix_backup,@!co_backup:small_number; + {to save |cur_val_level|, etc.} +@!backup_backup:pointer; {to save |link(backup_head)|} +@!save_scanner_status:small_number; {temporary storage of |scanner_status|} +begin cv_backup:=cur_val; cvl_backup:=cur_val_level; radix_backup:=radix; +co_backup:=cur_order; backup_backup:=link(backup_head); +if cur_cmd<call then @<Expand a nonmacro@> +else if cur_cmd<end_template then macro_call +else @<Insert a token containing |frozen_endv|@>; +cur_val:=cv_backup; cur_val_level:=cvl_backup; radix:=radix_backup; +cur_order:=co_backup; link(backup_head):=backup_backup; +end; + +@ @<Expand a nonmacro@>= +begin if tracing_commands>1 then show_cur_cmd_chr; +case cur_cmd of +top_bot_mark:@<Insert the \(a)appropriate mark text into the scanner@>; +expand_after:@<Expand the token after the next token@>; +no_expand:@<Suppress expansion of the next token@>; +cs_name:@<Manufacture a control sequence name@>; +convert:conv_toks; {this procedure is discussed in Part 27 below} +the:ins_the_toks; {this procedure is discussed in Part 27 below} +if_test:conditional; {this procedure is discussed in Part 28 below} +fi_or_else:@<Terminate the current conditional and skip to \.{\\fi}@>; +input:@<Initiate or terminate input from a file@>; +othercases @<Complain about an undefined macro@> +endcases; +end + +@ It takes only a little shuffling to do what \TeX\ calls \.{\\expandafter}. + +@<Expand the token after...@>= +begin get_token; t:=cur_tok; get_token; +if cur_cmd>max_command then expand@+else back_input; +cur_tok:=t; back_input; +end + +@ The implementation of \.{\\noexpand} is a bit trickier, because it is +necessary to insert a special `|dont_expand|' marker into \TeX's reading +mechanism. This special marker is processed by |get_next|, but it does +not slow down the inner loop. + +Since \.{\\outer} macros might arise here, we must also +clear the |scanner_status| temporarily. + +@<Suppress expansion...@>= +begin save_scanner_status:=scanner_status; scanner_status:=normal; +get_token; scanner_status:=save_scanner_status; t:=cur_tok; +back_input; {now |start| and |loc| point to the backed-up token |t|} +if t>=cs_token_flag then + begin p:=get_avail; info(p):=cs_token_flag+frozen_dont_expand; + link(p):=loc; start:=p; loc:=p; + end; +end + +@ @<Complain about an undefined macro@>= +begin print_err("Undefined control sequence"); +@.Undefined control sequence@> +help5("The control sequence at the end of the top line")@/ +("of your error message was never \def'ed. If you have")@/ +("misspelled it (e.g., `\hobx'), type `I' and the correct")@/ +("spelling (e.g., `I\hbox'). Otherwise just continue,")@/ +("and I'll forget about whatever was undefined."); +error; +end + +@ The |expand| procedure and some other routines that construct token +lists find it convenient to use the following macros, which are valid only if +the variables |p| and |q| are reserved for token-list building. + +@d store_new_token(#)==begin q:=get_avail; link(p):=q; info(q):=#; + p:=q; {|link(p)| is |null|} + end +@d fast_store_new_token(#)==begin fast_get_avail(q); link(p):=q; info(q):=#; + p:=q; {|link(p)| is |null|} + end + +@ @<Manufacture a control...@>= +begin r:=get_avail; p:=r; {head of the list of characters} +repeat get_x_token; +if cur_cs=0 then store_new_token(cur_tok); +until cur_cs<>0; +if cur_cmd<>end_cs_name then @<Complain about missing \.{\\endcsname}@>; +@<Look up the characters of list |r| in the hash table, and set |cur_cs|@>; +flush_list(r); +if eq_type(cur_cs)=undefined_cs then + begin eq_define(cur_cs,relax,256); {N.B.: The |save_stack| might change} + end; {the control sequence will now match `\.{\\relax}'} +cur_tok:=cur_cs+cs_token_flag; back_input; +end + +@ @<Complain about missing \.{\\endcsname}@>= +begin print_err("Missing "); print_esc("endcsname"); print(" inserted"); +@.Missing \\endcsname...@> +help2("The control sequence marked <to be read again> should")@/ + ("not appear between \csname and \endcsname."); +back_error; +end + +@ @<Look up the characters of list |r| in the hash table...@>= +j:=first; p:=link(r); +while p<>null do + begin if j>=max_buf_stack then + begin max_buf_stack:=j+1; + if max_buf_stack=buf_size then + overflow("buffer size",buf_size); +@:TeX capacity exceeded buffer size}{\quad buffer size@> + end; + buffer[j]:=info(p) mod @'400; incr(j); p:=link(p); + end; +if j>first+1 then + begin no_new_control_sequence:=false; cur_cs:=id_lookup(first,j-first); + no_new_control_sequence:=true; + end +else if j=first then cur_cs:=null_cs {the list is empty} +else cur_cs:=single_base+buffer[first] {the list has length one} + +@ An |end_template| command is effectively changed to an |endv| command +by the following code. (The reason for this is discussed below; the +|frozen_end_template| at the end of the template has passed the +|check_outer_validity| test, so its mission of error detection has been +accomplished.) + +@<Insert a token containing |frozen_endv|@>= +begin cur_tok:=cs_token_flag+frozen_endv; back_input; +end + +@ The processing of \.{\\input} involves the |start_input| subroutine, +which will be declared later; the processing of \.{\\endinput} is trivial. + +@<Put each...@>= +primitive("input",input,0);@/ +@!@:input_}{\.{\\input} primitive@> +primitive("endinput",input,1);@/ +@!@:end_input_}{\.{\\endinput} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +input: if chr_code=0 then print_esc("input")@+else print_esc("endinput"); + +@ @<Initiate or terminate input...@>= +if cur_chr>0 then force_eof:=true +else if name_in_progress then insert_relax +else start_input + +@ Sometimes the expansion looks too far ahead, so we want to insert +a harmless \.{\\relax} into the user's input. + +@<Declare the procedure called |insert_relax|@>= +procedure insert_relax; +begin cur_tok:=cs_token_flag+cur_cs; back_input; +cur_tok:=cs_token_flag+frozen_relax; back_input; token_type:=inserted; +end; + +@ Here is a recursive procedure that is \TeX's usual way to get the +next token of input. It has been slightly optimized to take account of +common cases. + +@p procedure get_x_token; {sets |cur_cmd|, |cur_chr|, |cur_tok|, + and expands macros} +label restart,done; +begin restart: get_next; +@^inner loop@> +if cur_cmd<=max_command then goto done; +if cur_cmd>=call then + if cur_cmd<end_template then macro_call + else begin cur_cs:=frozen_endv; cur_cmd:=endv; + goto done; {|cur_chr=null_list|} + end +else expand; +goto restart; +done: if cur_cs=0 then cur_tok:=(cur_cmd*@'400)+cur_chr +else cur_tok:=cs_token_flag+cur_cs; +end; + +@ The |get_x_token| procedure is equivalent to two consecutive +procedure calls: |get_next; x_token|. + +@p procedure x_token; {|get_x_token| without the initial |get_next|} +begin while cur_cmd>max_command do + begin expand; + get_next; + end; +if cur_cs=0 then cur_tok:=(cur_cmd*@'400)+cur_chr +else cur_tok:=cs_token_flag+cur_cs; +end; + +@ A control sequence that has been \.{\\def}'ed by the user is expanded by +\TeX's |macro_call| procedure. + +Before we get into the details of |macro_call|, however, let's consider the +treatment of primitives like \.{\\topmark}, since they are essentially +macros without parameters. The token lists for such marks are kept in a +global array of five pointers; we refer to the individual entries of this +array by symbolic names |top_mark|, etc. The value of |top_mark| is either +|null| or a pointer to the reference count of a token list. + +@d top_mark_code=0 {the mark in effect at the previous page break} +@d first_mark_code=1 {the first mark between |top_mark| and |bot_mark|} +@d bot_mark_code=2 {the mark in effect at the current page break} +@d split_first_mark_code=3 {the first mark found by \.{\\vsplit}} +@d split_bot_mark_code=4 {the last mark found by \.{\\vsplit}} +@d top_mark==cur_mark[top_mark_code] +@d first_mark==cur_mark[first_mark_code] +@d bot_mark==cur_mark[bot_mark_code] +@d split_first_mark==cur_mark[split_first_mark_code] +@d split_bot_mark==cur_mark[split_bot_mark_code] + +@<Glob...@>= +@!cur_mark:array[top_mark_code..split_bot_mark_code] of pointer; + {token lists for marks} + +@ @<Set init...@>= +top_mark:=null; first_mark:=null; bot_mark:=null; +split_first_mark:=null; split_bot_mark:=null; + +@ @<Put each...@>= +primitive("topmark",top_bot_mark,top_mark_code); +@!@:top_mark_}{\.{\\topmark} primitive@> +primitive("firstmark",top_bot_mark,first_mark_code); +@!@:first_mark_}{\.{\\firstmark} primitive@> +primitive("botmark",top_bot_mark,bot_mark_code); +@!@:bot_mark_}{\.{\\botmark} primitive@> +primitive("splitfirstmark",top_bot_mark,split_first_mark_code); +@!@:split_first_mark_}{\.{\\splitfirstmark} primitive@> +primitive("splitbotmark",top_bot_mark,split_bot_mark_code); +@!@:split_bot_mark_}{\.{\\splitbotmark} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +top_bot_mark: case chr_code of + first_mark_code: print_esc("firstmark"); + bot_mark_code: print_esc("botmark"); + split_first_mark_code: print_esc("splitfirstmark"); + split_bot_mark_code: print_esc("splitbotmark"); + othercases print_esc("topmark") + endcases; + +@ The following code is activated when |cur_cmd=top_bot_mark| and +when |cur_chr| is a code like |top_mark_code|. + +@<Insert the \(a)appropriate mark text into the scanner@>= +begin if cur_mark[cur_chr]<>null then + begin_token_list(cur_mark[cur_chr],mark_text); +end + +@ Now let's consider |macro_call| itself, which is invoked when \TeX\ is +scanning a control sequence whose |cur_cmd| is either |call|, |long_call|, +|outer_call|, or |long_outer_call|. The control sequence definition +appears in the token list whose reference count is in location |cur_chr| +of |mem|. + +The global variable |long_state| will be set to |call| or to |long_call|, +depending on whether or not the control sequence disallows \.{\\par} +in its parameters. The |get_next| routine will set |long_state| to +|outer_call| and emit \.{\\par}, if a file ends or if an \.{\\outer} +control sequence occurs in the midst of an argument. + +@<Glob...@>= +@!long_state:call..long_outer_call; {governs the acceptance of \.{\\par}} + +@ The parameters, if any, must be scanned before the macro is expanded. +Parameters are token lists without reference counts. They are placed on +an auxiliary stack called |pstack| while they are being scanned, since +the |param_stack| may be losing entries during the matching process. +(Note that |param_stack| can't be gaining entries, since |macro_call| is +the only routine that puts anything onto |param_stack|, and it +is not recursive.) + +@<Glob...@>= +@!pstack:array[0..8] of pointer; {arguments supplied to a macro} + +@ After parameter scanning is complete, the parameters are moved to the +|param_stack|. Then the macro body is fed to the scanner; in other words, +|macro_call| places the defined text of the control sequence at the +top of\/ \TeX's input stack, so that |get_next| will proceed to read it +next. + +The global variable |cur_cs| contains the |eqtb| address of the control sequence +being expanded, when |macro_call| begins. If this control sequence has not been +declared \.{\\long}, i.e., if its command code in the |eq_type| field is +not |long_call| or |long_outer_call|, its parameters are not allowed to contain +the control sequence \.{\\par}. If an illegal \.{\\par} appears, the macro +call is aborted, and the \.{\\par} will be rescanned. + +@<Declare the procedure called |macro_call|@>= +procedure macro_call; {invokes a user-defined control sequence} +label exit, continue, done, done1, found; +var r:pointer; {current node in the macro's token list} +@!p:pointer; {current node in parameter token list being built} +@!q:pointer; {new node being put into the token list} +@!s:pointer; {backup pointer for parameter matching} +@!t:pointer; {cycle pointer for backup recovery} +@!u,@!v:pointer; {auxiliary pointers for backup recovery} +@!rbrace_ptr:pointer; {one step before the last |right_brace| token} +@!n:small_number; {the number of parameters scanned} +@!unbalance:halfword; {unmatched left braces in current parameter} +@!m:halfword; {the number of tokens or groups (usually)} +@!ref_count:pointer; {start of the token list} +@!save_scanner_status:small_number; {|scanner_status| upon entry} +@!save_warning_index:pointer; {|warning_index| upon entry} +@!match_chr:ASCII_code; {character used in parameter} +begin save_scanner_status:=scanner_status; save_warning_index:=warning_index; +warning_index:=cur_cs; ref_count:=cur_chr; r:=link(ref_count); n:=0; +if tracing_macros>0 then @<Show the text of the macro being expanded@>; +if info(r)<>end_match_token then + @<Scan the parameters and make |link(r)| point to the macro body; but + |return| if an illegal \.{\\par} is detected@>; +@<Feed the macro body and its parameters to the scanner@>; +exit:scanner_status:=save_scanner_status; warning_index:=save_warning_index; +end; + +@ Before we put a new token list on the input stack, it is wise to clean off +all token lists that have recently been depleted. Then a user macro that ends +with a call to itself will not require unbounded stack space. + +@<Feed the macro body and its parameters to the scanner@>= +while (state=token_list)and(loc=null)and(token_type<>v_template) do + end_token_list; {conserve stack space} +begin_token_list(ref_count,macro); name:=warning_index; loc:=link(r); +if n>0 then + begin if param_ptr+n>max_param_stack then + begin max_param_stack:=param_ptr+n; + if max_param_stack>param_size then + overflow("parameter stack size",param_size); +@:TeX capacity exceeded parameter stack size}{\quad parameter stack size@> + end; + for m:=0 to n-1 do param_stack[param_ptr+m]:=pstack[m]; + param_ptr:=param_ptr+n; + end + +@ At this point, the reader will find it advisable to review the explanation +of token list format that was presented earlier, since many aspects of that +format are of importance chiefly in the |macro_call| routine. + +The token list might begin with a string of compulsory tokens before the +first |match| or |end_match|. In that case the macro name is supposed to be +followed by those tokens; the following program will set |s=null| to +represent this restriction. Otherwise |s| will be set to the first token of +a string that will delimit the next parameter. + +@<Scan the parameters and make |link(r)| point to the macro body...@>= +begin scanner_status:=matching; unbalance:=0; +long_state:=eq_type(cur_cs); +if long_state>=outer_call then long_state:=long_state-2; +repeat link(temp_head):=null; +if (info(r)>match_token+255)or(info(r)<match_token) then s:=null +else begin match_chr:=info(r)-match_token; s:=link(r); r:=s; + p:=temp_head; m:=0; + end; +@<Scan a parameter until its delimiter string has been found; or, if |s=null|, + simply scan the delimiter string@>;@/ +{now |info(r)| is a token whose command code is either |match| or |end_match|} +until info(r)=end_match_token; +end + +@ If |info(r)| is a |match| or |end_match| command, it cannot be equal to +any token found by |get_token|. Therefore an undelimited parameter---i.e., +a |match| that is immediately followed by |match| or |end_match|---will +always fail the test `|cur_tok=info(r)|' in the following algorithm. + +@<Scan a parameter until its delimiter string has been found; or, ...@>= +continue: get_token; {set |cur_tok| to the next token of input} +if cur_tok=info(r) then + @<Advance \(r)|r|; |goto found| if the parameter delimiter has been + fully matched, otherwise |goto continue|@>; +@<Contribute the recently matched tokens to the current parameter, and + |goto continue| if a partial match is still in effect; + but abort if |s=null|@>; +if cur_tok=par_token then if long_state<>long_call then + @<Report a runaway argument and abort@>; +if cur_tok<right_brace_limit then + if cur_tok<left_brace_limit then + @<Contribute an entire group to the current parameter@> + else @<Report an extra right brace and |goto continue|@> +else @<Store the current token, but |goto continue| if it is + a blank space that would become an undelimited parameter@>; +incr(m); +if info(r)>end_match_token then goto continue; +if info(r)<match_token then goto continue; +found: if s<>null then @<Tidy up the parameter just scanned, and tuck it away@> + +@ @<Store the current token, but |goto continue| if it is...@>= +begin if cur_tok=space_token then + if info(r)<=end_match_token then + if info(r)>=match_token then goto continue; +store_new_token(cur_tok); +end + +@ A slightly subtle point arises here: When the parameter delimiter ends +with `\.{\#\{}', the token list will have a left brace both before and +after the |end_match|\kern-.4pt. Only one of these should affect the +|align_state|, but both will be scanned, so we must make a correction. + +@<Advance \(r)|r|; |goto found| if the parameter delimiter has been fully...@>= +begin r:=link(r); +if (info(r)>=match_token)and(info(r)<=end_match_token) then + begin if cur_tok<left_brace_limit then decr(align_state); + goto found; + end +else goto continue; +end + +@ @<Report an extra right brace and |goto continue|@>= +begin back_input; print_err("Argument of "); sprint_cs(warning_index); +@.Argument of \\x has...@> +print(" has an extra }"); +help6("I've run across a `}' that doesn't seem to match anything.")@/ + ("For example, `\def\a#1{...}' and `\a}' would produce")@/ + ("this error. If you simply proceed now, the `\par' that")@/ + ("I've just inserted will cause me to report a runaway")@/ + ("argument that might be the root of the problem. But if")@/ + ("your `}' was spurious, just type `2' and it will go away."); +incr(align_state); long_state:=call; cur_tok:=par_token; ins_error; +end {a white lie; the \.{\\par} won't always trigger a runaway} + +@ If |long_state=outer_call|, a runaway argument has already been reported. + +@<Report a runaway argument and abort@>= +begin if long_state=call then + begin runaway; print_err("Paragraph ended before "); +@.Paragraph ended before...@> + sprint_cs(warning_index); print(" was complete"); + help3("I suspect you've forgotten a `}', causing me to apply this")@/ + ("control sequence to too much text. How can we recover?")@/ + ("My plan is to forget the whole thing and hope for the best."); + back_error; + end; +pstack[n]:=link(temp_head); align_state:=align_state-unbalance; +for m:=0 to n do flush_list(pstack[m]); +return; +end + +@ When the following code becomes active, we have matched tokens from |s| to +the predecessor of |r|, and we have found that |cur_tok<>info(r)|. An +interesting situation now presents itself: If the parameter is to be +delimited by a string such as `\.{ab}', and if we have scanned `\.{aa}', +we want to contribute one `\.a' to the current parameter and resume +looking for a `\.b'. The program must account for such partial matches and +for others that can be quite complex. But most of the time we have |s=r| +and nothing needs to be done. + +Incidentally, it is possible for \.{\\par} tokens to sneak in to certain +parameters of non-\.{\\long} macros. For example, consider a case like +`\.{\\def\\a\#1\\par!\{...\}}' where the first \.{\\par} is not followed +by an exclamation point. In such situations it does not seem appropriate +to prohibit the \.{\\par}, so \TeX\ keeps quiet about this bending of +the rules. + +@<Contribute the recently matched tokens to the current parameter...@>= +if s<>r then + if s=null then @<Report an improper use of the macro and abort@> + else begin t:=s; + repeat store_new_token(info(t)); incr(m); u:=link(t); v:=s; + loop@+ begin if u=r then + if cur_tok<>info(v) then goto done + else begin r:=link(v); goto continue; + end; + if info(u)<>info(v) then goto done; + u:=link(u); v:=link(v); + end; + done: t:=link(t); + until t=r; + r:=s; {at this point, no tokens are recently matched} + end + +@ @<Report an improper use...@>= +begin print_err("Use of "); sprint_cs(warning_index); +@.Use of x doesn't match...@> +print(" doesn't match its definition"); +help4("If you say, e.g., `\def\a1{...}', then you must always")@/ + ("put `1' after `\a', since control sequence names are")@/ + ("made up of letters only. The macro here has not been")@/ + ("followed by the required stuff, so I'm ignoring it."); +error; return; +end + +@ @<Contribute an entire group to the current parameter@>= +begin unbalance:=1; +@^inner loop@> +loop@+ begin fast_store_new_token(cur_tok); get_token; + if cur_tok=par_token then if long_state<>long_call then + @<Report a runaway argument and abort@>; + if cur_tok<right_brace_limit then + if cur_tok<left_brace_limit then incr(unbalance) + else begin decr(unbalance); + if unbalance=0 then goto done1; + end; + end; +done1: rbrace_ptr:=p; store_new_token(cur_tok); +end + +@ If the parameter consists of a single group enclosed in braces, we must +strip off the enclosing braces. That's why |rbrace_ptr| was introduced. + +@<Tidy up the parameter just scanned, and tuck it away@>= +begin if (m=1)and(info(p)<right_brace_limit)and(p<>temp_head) then + begin link(rbrace_ptr):=null; free_avail(p); + p:=link(temp_head); pstack[n]:=link(p); free_avail(p); + end +else pstack[n]:=link(temp_head); +incr(n); +if tracing_macros>0 then + begin begin_diagnostic; print_nl(match_chr); print_int(n); + print("<-"); show_token_list(pstack[n-1],null,1000); + end_diagnostic(false); + end; +end + +@ @<Show the text of the macro being expanded@>= +begin begin_diagnostic; print_ln; print_cs(warning_index); +token_show(ref_count); end_diagnostic(false); +end + +@* \[26] Basic scanning subroutines. +Let's turn now to some procedures that \TeX\ calls upon frequently to digest +certain kinds of patterns in the input. Most of these are quite simple; +some are quite elaborate. Almost all of the routines call |get_x_token|, +which can cause them to be invoked recursively. +@^stomach@> +@^recursion@> + +@ The |scan_left_brace| routine is called when a left brace is supposed to be +the next non-blank token. (The term ``left brace'' means, more precisely, +a character whose catcode is |left_brace|.) \TeX\ allows \.{\\relax} to +appear before the |left_brace|. + +@p procedure scan_left_brace; {reads a mandatory |left_brace|} +begin @<Get the next non-blank non-relax non-call token@>; +if cur_cmd<>left_brace then + begin print_err("Missing { inserted"); +@.Missing \{ inserted@> + help4("A left brace was mandatory here, so I've put one in.")@/ + ("You might want to delete and/or insert some corrections")@/ + ("so that I will find a matching right brace soon.")@/ + ("(If you're confused by all this, try typing `I}' now.)"); + back_error; cur_tok:=left_brace_token+"{"; cur_cmd:=left_brace; + cur_chr:="{"; incr(align_state); + end; +end; + +@ @<Get the next non-blank non-relax non-call token@>= +repeat get_x_token; +until (cur_cmd<>spacer)and(cur_cmd<>relax) + +@ The |scan_optional_equals| routine looks for an optional `\.=' sign preceded +by optional spaces; `\.{\\relax}' is not ignored here. + +@p procedure scan_optional_equals; +begin @<Get the next non-blank non-call token@>; +if cur_tok<>other_token+"=" then back_input; +end; + +@ @<Get the next non-blank non-call token@>= +repeat get_x_token; +until cur_cmd<>spacer + +@ In case you are getting bored, here is a slightly less trivial routine: +Given a string of lowercase letters, like `\.{pt}' or `\.{plus}' or +`\.{width}', the |scan_keyword| routine checks to see whether the next +tokens of input match this string. The match must be exact, except that +uppercase letters will match their lowercase counterparts; uppercase +equivalents are determined by subtracting |"a"-"A"|, rather than using the +|uc_code| table, since \TeX\ uses this routine only for its own limited +set of keywords. + +If a match is found, the characters are effectively removed from the input +and |true| is returned. Otherwise |false| is returned, and the input +is left essentially unchanged (except for the fact that some macros +may have been expanded, etc.). +@^inner loop@> + +@p function scan_keyword(@!s:str_number):boolean; {look for a given string} +label exit; +var p:pointer; {tail of the backup list} +@!q:pointer; {new node being added to the token list via |store_new_token|} +@!k:pool_pointer; {index into |str_pool|} +begin p:=backup_head; link(p):=null; k:=str_start[s]; +while k<str_start[s+1] do + begin get_x_token; {recursion is possible here} +@^recursion@> + if (cur_cs=0)and@| + ((cur_chr=so(str_pool[k]))or(cur_chr=so(str_pool[k])-"a"+"A")) then + begin store_new_token(cur_tok); incr(k); + end + else if (cur_cmd<>spacer)or(p<>backup_head) then + begin back_input; + if p<>backup_head then back_list(link(backup_head)); + scan_keyword:=false; return; + end; + end; +flush_list(link(backup_head)); scan_keyword:=true; +exit:end; + +@ Here is a procedure that sounds an alarm when mu and non-mu units +are being switched. + +@p procedure mu_error; +begin print_err("Incompatible glue units"); +@.Incompatible glue units@> +help1("I'm going to assume that 1mu=1pt when they're mixed."); +error; +end; + +@ The next routine `|scan_something_internal|' is used to fetch internal +numeric quantities like `\.{\\hsize}', and also to handle the `\.{\\the}' +when expanding constructions like `\.{\\the\\toks0}' and +`\.{\\the\\baselineskip}'. Soon we will be considering the |scan_int| +procedure, which calls |scan_something_internal|; on the other hand, +|scan_something_internal| also calls |scan_int|, for constructions like +`\.{\\catcode\`\\\$}' or `\.{\\fontdimen} \.3 \.{\\ff}'. So we +have to declare |scan_int| as a |forward| procedure. A few other +procedures are also declared at this point. + +@p procedure@?scan_int; forward; {scans an integer value} +@t\4\4@>@<Declare procedures that scan restricted classes of integers@>@; +@t\4\4@>@<Declare procedures that scan font-related stuff@> + +@ \TeX\ doesn't know exactly what to expect when |scan_something_internal| +begins. For example, an integer or dimension or glue value could occur +immediately after `\.{\\hskip}'; and one can even say \.{\\the} with +respect to token lists in constructions like +`\.{\\xdef\\o\{\\the\\output\}}'. On the other hand, only integers are +allowed after a construction like `\.{\\count}'. To handle the various +possibilities, |scan_something_internal| has a |level| parameter, which +tells the ``highest'' kind of quantity that |scan_something_internal| is +allowed to produce. Six levels are distinguished, namely |int_val|, +|dimen_val|, |glue_val|, |mu_val|, |ident_val|, and |tok_val|. + +The output of |scan_something_internal| (and of the other routines +|scan_int|, |scan_dimen|, and |scan_glue| below) is put into the global +variable |cur_val|, and its level is put into |cur_val_level|. The highest +values of |cur_val_level| are special: |mu_val| is used only when +|cur_val| points to something in a ``muskip'' register, or to one of the +three parameters \.{\\thinmuskip}, \.{\\medmuskip}, \.{\\thickmuskip}; +|ident_val| is used only when |cur_val| points to a font identifier; +|tok_val| is used only when |cur_val| points to |null| or to the reference +count of a token list. The last two cases are allowed only when +|scan_something_internal| is called with |level=tok_val|. + +If the output is glue, |cur_val| will point to a glue specification, and +the reference count of that glue will have been updated to reflect this +reference; if the output is a nonempty token list, |cur_val| will point to +its reference count, but in this case the count will not have been updated. +Otherwise |cur_val| will contain the integer or scaled value in question. + +@d int_val=0 {integer values} +@d dimen_val=1 {dimension values} +@d glue_val=2 {glue specifications} +@d mu_val=3 {math glue specifications} +@d ident_val=4 {font identifier} +@d tok_val=5 {token lists} + +@<Glob...@>= +@!cur_val:integer; {value returned by numeric scanners} +@!cur_val_level:int_val..tok_val; {the ``level'' of this value} + +@ The hash table is initialized with `\.{\\count}', `\.{\\dimen}', `\.{\\skip}', +and `\.{\\muskip}' all having |register| as their command code; they are +distinguished by the |chr_code|, which is either |int_val|, |dimen_val|, +|glue_val|, or |mu_val|. + +@<Put each...@>= +primitive("count",register,int_val); +@!@:count_}{\.{\\count} primitive@> +primitive("dimen",register,dimen_val); +@!@:dimen_}{\.{\\dimen} primitive@> +primitive("skip",register,glue_val); +@!@:skip_}{\.{\\skip} primitive@> +primitive("muskip",register,mu_val); +@!@:mu_skip_}{\.{\\muskip} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +register: if chr_code=int_val then print_esc("count") + else if chr_code=dimen_val then print_esc("dimen") + else if chr_code=glue_val then print_esc("skip") + else print_esc("muskip"); + +@ OK, we're ready for |scan_something_internal| itself. A second parameter, +|negative|, is set |true| if the value that is found should be negated. +It is assumed that |cur_cmd| and |cur_chr| represent the first token of +the internal quantity to be scanned; an error will be signalled if +|cur_cmd<min_internal| or |cur_cmd>max_internal|. + +@d scanned_result_end(#)==cur_val_level:=#;@+end +@d scanned_result(#)==@+begin cur_val:=#;scanned_result_end + +@p procedure scan_something_internal(@!level:small_number;@!negative:boolean); + {fetch an internal parameter} +var m:halfword; {|chr_code| part of the operand token} +@!p:0..nest_size; {index into |nest|} +begin m:=cur_chr; +case cur_cmd of +def_code: @<Fetch a character code from some table@>; +toks_register,assign_toks,def_family,set_font,def_font: @<Fetch a token list or + font identifier, provided that |level=tok_val|@>; +assign_int: scanned_result(eqtb[m].int)(int_val); +assign_dimen: scanned_result(eqtb[m].sc)(dimen_val); +assign_glue: scanned_result(equiv(m))(glue_val); +assign_mu_glue: scanned_result(equiv(m))(mu_val); +set_aux: @<Fetch the |space_factor| or the |prev_depth|@>; +set_prev_graf: @<Fetch the |prev_graf|@>; +set_page_int:@<Fetch the |dead_cycles| or the |insert_penalties|@>; +set_page_dimen: @<Fetch something on the |page_so_far|@>; +set_shape: @<Fetch the |par_shape| size@>; +set_box_dimen: @<Fetch a box dimension@>; +char_given,math_given: scanned_result(cur_chr)(int_val); +assign_font_dimen: @<Fetch a font dimension@>; +assign_font_int: @<Fetch a font integer@>; +register: @<Fetch a register@>; +last_item: @<Fetch an item in the current node, if appropriate@>; +othercases @<Complain that \.{\\the} can't do this; give zero result@> +endcases;@/ +while cur_val_level>level do @<Convert \(c)|cur_val| to a lower level@>; +@<Fix the reference count, if any, and negate |cur_val| if |negative|@>; +end; + +@ @<Fetch a character code from some table@>= +begin scan_char_num; +if m=math_code_base then scanned_result(ho(math_code(cur_val)))(int_val) +else if m<math_code_base then scanned_result(equiv(m+cur_val))(int_val) +else scanned_result(eqtb[m+cur_val].int)(int_val); +end + +@ @<Fetch a token list...@>= +if level<>tok_val then + begin print_err("Missing number, treated as zero"); +@.Missing number...@> + help3("A number should have been here; I inserted `0'.")@/ + ("(If you can't figure out why I needed to see a number,")@/ + ("look up `weird error' in the index to The TeXbook.)"); +@:TeXbook}{\sl The \TeX book@> + back_error; scanned_result(0)(dimen_val); + end +else if cur_cmd<=assign_toks then + begin if cur_cmd<assign_toks then {|cur_cmd=toks_register|} + begin scan_eight_bit_int; m:=toks_base+cur_val; + end; + scanned_result(equiv(m))(tok_val); + end +else begin back_input; scan_font_ident; + scanned_result(font_id_base+cur_val)(ident_val); + end + +@ Users refer to `\.{\\the\\spacefactor}' only in horizontal +mode, and to `\.{\\the\\prevdepth}' only in vertical mode; so we put the +associated mode in the modifier part of the |set_aux| command. +The |set_page_int| command has modifier 0 or 1, for `\.{\\deadcycles}' and +`\.{\\insertpenalties}', respectively. The |set_box_dimen| command is +modified by either |width_offset|, |height_offset|, or |depth_offset|. +And the |last_item| command is modified by either |int_val|, |dimen_val|, +|glue_val|, |input_line_no_code|, or |badness_code|. + +@d input_line_no_code=glue_val+1 {code for \.{\\inputlineno}} +@d badness_code=glue_val+2 {code for \.{\\badness}} + +@<Put each...@>= +primitive("spacefactor",set_aux,hmode); +@!@:space_factor_}{\.{\\spacefactor} primitive@> +primitive("prevdepth",set_aux,vmode);@/ +@!@:prev_depth_}{\.{\\prevdepth} primitive@> +primitive("deadcycles",set_page_int,0); +@!@:dead_cycles_}{\.{\\deadcycles} primitive@> +primitive("insertpenalties",set_page_int,1); +@!@:insert_penalties_}{\.{\\insertpenalties} primitive@> +primitive("wd",set_box_dimen,width_offset); +@!@:wd_}{\.{\\wd} primitive@> +primitive("ht",set_box_dimen,height_offset); +@!@:ht_}{\.{\\ht} primitive@> +primitive("dp",set_box_dimen,depth_offset); +@!@:dp_}{\.{\\dp} primitive@> +primitive("lastpenalty",last_item,int_val); +@!@:last_penalty_}{\.{\\lastpenalty} primitive@> +primitive("lastkern",last_item,dimen_val); +@!@:last_kern_}{\.{\\lastkern} primitive@> +primitive("lastskip",last_item,glue_val); +@!@:last_skip_}{\.{\\lastskip} primitive@> +primitive("inputlineno",last_item,input_line_no_code); +@!@:input_line_no_}{\.{\\inputlineno} primitive@> +primitive("badness",last_item,badness_code); +@!@:badness_}{\.{\\badness} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +set_aux: if chr_code=vmode then print_esc("prevdepth") +@+else print_esc("spacefactor"); +set_page_int: if chr_code=0 then print_esc("deadcycles") +@+else print_esc("insertpenalties"); +set_box_dimen: if chr_code=width_offset then print_esc("wd") +else if chr_code=height_offset then print_esc("ht") +else print_esc("dp"); +last_item: case chr_code of + int_val: print_esc("lastpenalty"); + dimen_val: print_esc("lastkern"); + glue_val: print_esc("lastskip"); + input_line_no_code: print_esc("inputlineno"); + othercases print_esc("badness") + endcases; + +@ @<Fetch the |space_factor| or the |prev_depth|@>= +if abs(mode)<>m then + begin print_err("Improper "); print_cmd_chr(set_aux,m); +@.Improper \\spacefactor@> +@.Improper \\prevdepth@> + help4("You can refer to \spacefactor only in horizontal mode;")@/ + ("you can refer to \prevdepth only in vertical mode; and")@/ + ("neither of these is meaningful inside \write. So")@/ + ("I'm forgetting what you said and using zero instead."); + error; + if level<>tok_val then scanned_result(0)(dimen_val) + else scanned_result(0)(int_val); + end +else if m=vmode then + begin cur_val:=prev_depth; cur_val_level:=dimen_val; + end +else begin cur_val:=space_factor; cur_val_level:=int_val; + end + +@ @<Fetch the |dead_cycles| or the |insert_penalties|@>= +begin if m=0 then cur_val:=dead_cycles@+else cur_val:=insert_penalties; +cur_val_level:=int_val; +end + +@ @<Fetch a box dimension@>= +begin scan_eight_bit_int; +if box(cur_val)=null then cur_val:=0 @+else cur_val:=mem[box(cur_val)+m].sc; +cur_val_level:=dimen_val; +end + +@ Inside an \.{\\output} routine, a user may wish to look at the page totals +that were present at the moment when output was triggered. + +@d max_dimen==@'7777777777 {$2^{30}-1$} + +@<Fetch something on the |page_so_far|@>= +begin if (page_contents=empty) and (not output_active) then + if m=0 then cur_val:=max_dimen@+else cur_val:=0 +else cur_val:=page_so_far[m]; +cur_val_level:=dimen_val; +end + +@ @<Fetch the |prev_graf|@>= +if mode=0 then scanned_result(0)(int_val) {|prev_graf=0| within \.{\\write}} +else begin nest[nest_ptr]:=cur_list; p:=nest_ptr; + while abs(nest[p].mode_field)<>vmode do decr(p); + scanned_result(nest[p].pg_field)(int_val); + end + +@ @<Fetch the |par_shape| size@>= +begin if par_shape_ptr=null then cur_val:=0 +else cur_val:=info(par_shape_ptr); +cur_val_level:=int_val; +end + +@ Here is where \.{\\lastpenalty}, \.{\\lastkern}, and \.{\\lastskip} are +implemented. The reference count for \.{\\lastskip} will be updated later. + +We also handle \.{\\inputlineno} and \.{\\badness} here, because they are +legal in similar contexts. + +@<Fetch an item in the current node...@>= +if cur_chr>glue_val then + begin if cur_chr=input_line_no_code then cur_val:=line + else cur_val:=last_badness; {|cur_chr=badness_code|} + cur_val_level:=int_val; + end +else begin if cur_chr=glue_val then cur_val:=zero_glue@+else cur_val:=0; + cur_val_level:=cur_chr; + if not is_char_node(tail)and(mode<>0) then + case cur_chr of + int_val: if type(tail)=penalty_node then cur_val:=penalty(tail); + dimen_val: if type(tail)=kern_node then cur_val:=width(tail); + glue_val: if type(tail)=glue_node then + begin cur_val:=glue_ptr(tail); + if subtype(tail)=mu_glue then cur_val_level:=mu_val; + end; + end {there are no other cases} + else if (mode=vmode)and(tail=head) then + case cur_chr of + int_val: cur_val:=last_penalty; + dimen_val: cur_val:=last_kern; + glue_val: if last_glue<>max_halfword then cur_val:=last_glue; + end; {there are no other cases} + end + +@ @<Fetch a font dimension@>= +begin find_font_dimen(false); font_info[fmem_ptr].sc:=0; +scanned_result(font_info[cur_val].sc)(dimen_val); +end + +@ @<Fetch a font integer@>= +begin scan_font_ident; +if m=0 then scanned_result(hyphen_char[cur_val])(int_val) +else scanned_result(skew_char[cur_val])(int_val); +end + +@ @<Fetch a register@>= +begin scan_eight_bit_int; +case m of +int_val:cur_val:=count(cur_val); +dimen_val:cur_val:=dimen(cur_val); +glue_val: cur_val:=skip(cur_val); +mu_val: cur_val:=mu_skip(cur_val); +end; {there are no other cases} +cur_val_level:=m; +end + +@ @<Complain that \.{\\the} can't do this; give zero result@>= +begin print_err("You can't use `"); print_cmd_chr(cur_cmd,cur_chr); +@.You can't use x after ...@> +print("' after "); print_esc("the"); +help1("I'm forgetting what you said and using zero instead."); +error; +if level<>tok_val then scanned_result(0)(dimen_val) +else scanned_result(0)(int_val); +end + +@ When a |glue_val| changes to a |dimen_val|, we use the width component +of the glue; there is no need to decrease the reference count, since it +has not yet been increased. When a |dimen_val| changes to an |int_val|, +we use scaled points so that the value doesn't actually change. And when a +|mu_val| changes to a |glue_val|, the value doesn't change either. + +@<Convert \(c)|cur_val| to a lower level@>= +begin if cur_val_level=glue_val then cur_val:=width(cur_val) +else if cur_val_level=mu_val then mu_error; +decr(cur_val_level); +end + +@ If |cur_val| points to a glue specification at this point, the reference +count for the glue does not yet include the reference by |cur_val|. +If |negative| is |true|, |cur_val_level| is known to be |<=mu_val|. + +@<Fix the reference count, if any, ...@>= +if negative then + if cur_val_level>=glue_val then + begin cur_val:=new_spec(cur_val); + @<Negate all three glue components of |cur_val|@>; + end + else negate(cur_val) +else if (cur_val_level>=glue_val)and(cur_val_level<=mu_val) then + add_glue_ref(cur_val) + +@ @<Negate all three...@>= +begin negate(width(cur_val)); +negate(stretch(cur_val)); +negate(shrink(cur_val)); +end + +@ Our next goal is to write the |scan_int| procedure, which scans anything that +\TeX\ treats as an integer. But first we might as well look at some simple +applications of |scan_int| that have already been made inside of +|scan_something_internal|. + +@ @<Declare procedures that scan restricted classes of integers@>= +procedure scan_eight_bit_int; +begin scan_int; +if (cur_val<0)or(cur_val>255) then + begin print_err("Bad register code"); +@.Bad register code@> + help2("A register number must be between 0 and 255.")@/ + ("I changed this one to zero."); int_error(cur_val); cur_val:=0; + end; +end; + +@ @<Declare procedures that scan restricted classes of integers@>= +procedure scan_char_num; +begin scan_int; +if (cur_val<0)or(cur_val>255) then + begin print_err("Bad character code"); +@.Bad character code@> + help2("A character number must be between 0 and 255.")@/ + ("I changed this one to zero."); int_error(cur_val); cur_val:=0; + end; +end; + +@ While we're at it, we might as well deal with similar routines that +will be needed later. + +@<Declare procedures that scan restricted classes of integers@>= +procedure scan_four_bit_int; +begin scan_int; +if (cur_val<0)or(cur_val>15) then + begin print_err("Bad number"); +@.Bad number@> + help2("Since I expected to read a number between 0 and 15,")@/ + ("I changed this one to zero."); int_error(cur_val); cur_val:=0; + end; +end; + +@ @<Declare procedures that scan restricted classes of integers@>= +procedure scan_fifteen_bit_int; +begin scan_int; +if (cur_val<0)or(cur_val>@'77777) then + begin print_err("Bad mathchar"); +@.Bad mathchar@> + help2("A mathchar number must be between 0 and 32767.")@/ + ("I changed this one to zero."); int_error(cur_val); cur_val:=0; + end; +end; + +@ @<Declare procedures that scan restricted classes of integers@>= +procedure scan_twenty_seven_bit_int; +begin scan_int; +if (cur_val<0)or(cur_val>@'777777777) then + begin print_err("Bad delimiter code"); +@.Bad delimiter code@> + help2("A numeric delimiter code must be between 0 and 2^{27}-1.")@/ + ("I changed this one to zero."); int_error(cur_val); cur_val:=0; + end; +end; + +@ An integer number can be preceded by any number of spaces and `\.+' or +`\.-' signs. Then comes either a decimal constant (i.e., radix 10), an +octal constant (i.e., radix 8, preceded by~\.\'), a hexadecimal constant +(radix 16, preceded by~\."), an alphabetic constant (preceded by~\.\`), or +an internal variable. After scanning is complete, +|cur_val| will contain the answer, which must be at most +$2^{31}-1=2147483647$ in absolute value. The value of |radix| is set to +10, 8, or 16 in the cases of decimal, octal, or hexadecimal constants, +otherwise |radix| is set to zero. An optional space follows a constant. + +@d octal_token=other_token+"'" {apostrophe, indicates an octal constant} +@d hex_token=other_token+"""" {double quote, indicates a hex constant} +@d alpha_token=other_token+"`" {reverse apostrophe, precedes alpha constants} +@d point_token=other_token+"." {decimal point} +@d continental_point_token=other_token+"," {decimal point, Eurostyle} + +@<Glob...@>= +@!radix:small_number; {|scan_int| sets this to 8, 10, 16, or zero} + +@ We initialize the following global variables just in case |expand| +comes into action before any of the basic scanning routines has assigned +them a value. + +@<Set init...@>= +cur_val:=0; cur_val_level:=int_val; radix:=0; cur_order:=0; + +@ The |scan_int| routine is used also to scan the integer part of a +fraction; for example, the `\.3' in `\.{3.14159}' will be found by +|scan_int|. The |scan_dimen| routine assumes that |cur_tok=point_token| +after the integer part of such a fraction has been scanned by |scan_int|, +and that the decimal point has been backed up to be scanned again. + +@p procedure scan_int; {sets |cur_val| to an integer} +label done; +var negative:boolean; {should the answer be negated?} +@!m:integer; {|@t$2^{31}$@> div radix|, the threshold of danger} +@!d:small_number; {the digit just scanned} +@!vacuous:boolean; {have no digits appeared?} +@!OK_so_far:boolean; {has an error message been issued?} +begin radix:=0; OK_so_far:=true;@/ +@<Get the next non-blank non-sign token; set |negative| appropriately@>; +if cur_tok=alpha_token then @<Scan an alphabetic character code into |cur_val|@> +else if (cur_cmd>=min_internal)and(cur_cmd<=max_internal) then + scan_something_internal(int_val,false) +else @<Scan a numeric constant@>; +if negative then negate(cur_val); +end; + +@ @<Get the next non-blank non-sign token...@>= +negative:=false; +repeat @<Get the next non-blank non-call token@>; +if cur_tok=other_token+"-" then + begin negative := not negative; cur_tok:=other_token+"+"; + end; +until cur_tok<>other_token+"+" + +@ A space is ignored after an alphabetic character constant, so that +such constants behave like numeric ones. + +@<Scan an alphabetic character code into |cur_val|@>= +begin get_token; {suppress macro expansion} +if cur_tok<cs_token_flag then + begin cur_val:=cur_chr; + if cur_cmd<=right_brace then + if cur_cmd=right_brace then incr(align_state) + else decr(align_state); + end +else if cur_tok<cs_token_flag+single_base then + cur_val:=cur_tok-cs_token_flag-active_base +else cur_val:=cur_tok-cs_token_flag-single_base; +if cur_val>255 then + begin print_err("Improper alphabetic constant"); +@.Improper alphabetic constant@> + help2("A one-character control sequence belongs after a ` mark.")@/ + ("So I'm essentially inserting \0 here."); + cur_val:="0"; back_error; + end +else @<Scan an optional space@>; +end + +@ @<Scan an optional space@>= +begin get_x_token; if cur_cmd<>spacer then back_input; +end + +@ @<Scan a numeric constant@>= +begin radix:=10; m:=214748364; +if cur_tok=octal_token then + begin radix:=8; m:=@'2000000000; get_x_token; + end +else if cur_tok=hex_token then + begin radix:=16; m:=@'1000000000; get_x_token; + end; +vacuous:=true; cur_val:=0;@/ +@<Accumulate the constant until |cur_tok| is not a suitable digit@>; +if vacuous then @<Express astonishment that no number was here@> +else if cur_cmd<>spacer then back_input; +end + +@ @d infinity==@'17777777777 {the largest positive value that \TeX\ knows} +@d zero_token=other_token+"0" {zero, the smallest digit} +@d A_token=letter_token+"A" {the smallest special hex digit} +@d other_A_token=other_token+"A" {special hex digit of type |other_char|} + +@<Accumulate the constant...@>= +loop@+ begin if (cur_tok<zero_token+radix)and(cur_tok>=zero_token)and + (cur_tok<=zero_token+9) then d:=cur_tok-zero_token + else if radix=16 then + if (cur_tok<=A_token+5)and(cur_tok>=A_token) then d:=cur_tok-A_token+10 + else if (cur_tok<=other_A_token+5)and(cur_tok>=other_A_token) then + d:=cur_tok-other_A_token+10 + else goto done + else goto done; + vacuous:=false; + if (cur_val>=m)and((cur_val>m)or(d>7)or(radix<>10)) then + begin if OK_so_far then + begin print_err("Number too big"); +@.Number too big@> + help2("I can only go up to 2147483647='17777777777=""7FFFFFFF,")@/ + ("so I'm using that number instead of yours."); + error; cur_val:=infinity; OK_so_far:=false; + end; + end + else cur_val:=cur_val*radix+d; + get_x_token; + end; +done: + +@ @<Express astonishment...@>= +begin print_err("Missing number, treated as zero"); +@.Missing number...@> +help3("A number should have been here; I inserted `0'.")@/ + ("(If you can't figure out why I needed to see a number,")@/ + ("look up `weird error' in the index to The TeXbook.)"); +@:TeXbook}{\sl The \TeX book@> +back_error; +end + +@ The |scan_dimen| routine is similar to |scan_int|, but it sets |cur_val| to +a |scaled| value, i.e., an integral number of sp. One of its main tasks +is therefore to interpret the abbreviations for various kinds of units and +to convert measurements to scaled points. + +There are three parameters: |mu| is |true| if the finite units must be +`\.{mu}', while |mu| is |false| if `\.{mu}' units are disallowed; +|inf| is |true| if the infinite units `\.{fil}', `\.{fill}', `\.{filll}' +are permitted; and |shortcut| is |true| if |cur_val| already contains +an integer and only the units need to be considered. + +The order of infinity that was found in the case of infinite glue is returned +in the global variable |cur_order|. + +@<Glob...@>= +@!cur_order:glue_ord; {order of infinity found by |scan_dimen|} + +@ Constructions like `\.{-\'77 pt}' are legal dimensions, so |scan_dimen| +may begin with |scan_int|. This explains why it is convenient to use +|scan_int| also for the integer part of a decimal fraction. + +Several branches of |scan_dimen| work with |cur_val| as an integer and +with an auxiliary fraction |f|, so that the actual quantity of interest is +$|cur_val|+|f|/2^{16}$. At the end of the routine, this ``unpacked'' +representation is put into the single word |cur_val|, which suddenly +switches significance from |integer| to |scaled|. + +@d attach_fraction=88 {go here to pack |cur_val| and |f| into |cur_val|} +@d attach_sign=89 {go here when |cur_val| is correct except perhaps for sign} +@d scan_normal_dimen==scan_dimen(false,false,false) + +@p procedure scan_dimen(@!mu,@!inf,@!shortcut:boolean); + {sets |cur_val| to a dimension} +label done, done1, done2, found, not_found, attach_fraction, attach_sign; +var negative:boolean; {should the answer be negated?} +@!f:integer; {numerator of a fraction whose denominator is $2^{16}$} +@<Local variables for dimension calculations@>@; +begin f:=0; arith_error:=false; cur_order:=normal; negative:=false; +if not shortcut then + begin @<Get the next non-blank non-sign...@>; + if (cur_cmd>=min_internal)and(cur_cmd<=max_internal) then + @<Fetch an internal dimension and |goto attach_sign|, + or fetch an internal integer@> + else begin back_input; + if cur_tok=continental_point_token then cur_tok:=point_token; + if cur_tok<>point_token then scan_int + else begin radix:=10; cur_val:=0; + end; + if cur_tok=continental_point_token then cur_tok:=point_token; + if (radix=10)and(cur_tok=point_token) then @<Scan decimal fraction@>; + end; + end; +if cur_val<0 then {in this case |f=0|} + begin negative := not negative; negate(cur_val); + end; +@<Scan units and set |cur_val| to $x\cdot(|cur_val|+f/2^{16})$, where there + are |x| sp per unit; |goto attach_sign| if the units are internal@>; +@<Scan an optional space@>; +attach_sign: if arith_error or(abs(cur_val)>=@'10000000000) then + @<Report that this dimension is out of range@>; +if negative then negate(cur_val); +end; + +@ @<Fetch an internal dimension and |goto attach_sign|...@>= +if mu then + begin scan_something_internal(mu_val,false); + @<Coerce glue to a dimension@>; + if cur_val_level=mu_val then goto attach_sign; + if cur_val_level<>int_val then mu_error; + end +else begin scan_something_internal(dimen_val,false); + if cur_val_level=dimen_val then goto attach_sign; + end + +@ @<Local variables for dimension calculations@>= +@!num,@!denom:1..65536; {conversion ratio for the scanned units} +@!k,@!kk:small_number; {number of digits in a decimal fraction} +@!p,@!q:pointer; {top of decimal digit stack} +@!v:scaled; {an internal dimension} +@!save_cur_val:integer; {temporary storage of |cur_val|} + +@ The following code is executed when |scan_something_internal| was +called asking for |mu_val|, when we really wanted a ``mudimen'' instead +of ``muglue.'' + +@<Coerce glue to a dimension@>= +if cur_val_level>=glue_val then + begin v:=width(cur_val); delete_glue_ref(cur_val); cur_val:=v; + end + +@ When the following code is executed, we have |cur_tok=point_token|, but this +token has been backed up using |back_input|; we must first discard it. + +It turns out that a decimal point all by itself is equivalent to `\.{0.0}'. +Let's hope people don't use that fact. + +@<Scan decimal fraction@>= +begin k:=0; p:=null; get_token; {|point_token| is being re-scanned} +loop@+ begin get_x_token; + if (cur_tok>zero_token+9)or(cur_tok<zero_token) then goto done1; + if k<17 then {digits for |k>=17| cannot affect the result} + begin q:=get_avail; link(q):=p; info(q):=cur_tok-zero_token; + p:=q; incr(k); + end; + end; +done1: for kk:=k downto 1 do + begin dig[kk-1]:=info(p); q:=p; p:=link(p); free_avail(q); + end; +f:=round_decimals(k); +if cur_cmd<>spacer then back_input; +end + +@ Now comes the harder part: At this point in the program, |cur_val| is a +nonnegative integer and $f/2^{16}$ is a nonnegative fraction less than 1; +we want to multiply the sum of these two quantities by the appropriate +factor, based on the specified units, in order to produce a |scaled| +result, and we want to do the calculation with fixed point arithmetic that +does not overflow. + +@<Scan units and set |cur_val| to $x\cdot(|cur_val|+f/2^{16})$...@>= +if inf then @<Scan for \(f)\.{fil} units; |goto attach_fraction| if found@>; +@<Scan for \(u)units that are internal dimensions; + |goto attach_sign| with |cur_val| set if found@>; +if mu then @<Scan for \(m)\.{mu} units and |goto attach_fraction|@>; +if scan_keyword("true") then @<Adjust \(f)for the magnification ratio@>; +@.true@> +if scan_keyword("pt") then goto attach_fraction; {the easy case} +@.pt@> +@<Scan for \(a)all other units and adjust |cur_val| and |f| accordingly; + |goto done| in the case of scaled points@>; +attach_fraction: if cur_val>=@'40000 then arith_error:=true +else cur_val:=cur_val*unity+f; +done: + +@ A specification like `\.{filllll}' or `\.{fill L L L}' will lead to two +error messages (one for each additional keyword \.{"l"}). + +@<Scan for \(f)\.{fil} units...@>= +if scan_keyword("fil") then +@.fil@> + begin cur_order:=fil; + while scan_keyword("l") do + begin if cur_order=filll then + begin print_err("Illegal unit of measure ("); +@.Illegal unit of measure@> + print("replaced by filll)"); + help1("I dddon't go any higher than filll."); error; + end + else incr(cur_order); + end; + goto attach_fraction; + end + +@ @<Scan for \(u)units that are internal dimensions...@>= +save_cur_val:=cur_val; +@<Get the next non-blank non-call...@>; +if (cur_cmd<min_internal)or(cur_cmd>max_internal) then back_input +else begin if mu then + begin scan_something_internal(mu_val,false); @<Coerce glue...@>; + if cur_val_level<>mu_val then mu_error; + end + else scan_something_internal(dimen_val,false); + v:=cur_val; goto found; + end; +if mu then goto not_found; +if scan_keyword("em") then v:=(@<The em width for |cur_font|@>) +@.em@> +else if scan_keyword("ex") then v:=(@<The x-height for |cur_font|@>) +@.ex@> +else goto not_found; +@<Scan an optional space@>; +found:cur_val:=nx_plus_y(save_cur_val,v,xn_over_d(v,f,@'200000)); +goto attach_sign; +not_found: + +@ @<Scan for \(m)\.{mu} units and |goto attach_fraction|@>= +if scan_keyword("mu") then goto attach_fraction +@.mu@> +else begin print_err("Illegal unit of measure ("); print("mu inserted)"); +@.Illegal unit of measure@> + help4("The unit of measurement in math glue must be mu.")@/ + ("To recover gracefully from this error, it's best to")@/ + ("delete the erroneous units; e.g., type `2' to delete")@/ + ("two letters. (See Chapter 27 of The TeXbook.)"); +@:TeXbook}{\sl The \TeX book@> + error; goto attach_fraction; + end + +@ @<Adjust \(f)for the magnification ratio@>= +begin prepare_mag; +if mag<>1000 then + begin cur_val:=xn_over_d(cur_val,1000,mag); + f:=(1000*f+@'200000*remainder) div mag; + cur_val:=cur_val+(f div @'200000); f:=f mod @'200000; + end; +end + +@ The necessary conversion factors can all be specified exactly as +fractions whose numerator and denominator are 32768 or less. +According to the definitions here, $\rm2660\,dd\approx1000.33297\,mm$; +this agrees well with the value $\rm1000.333\,mm$ cited by Bosshard +@^Bosshard, Hans Rudolf@> +in {\sl Technische Grundlagen zur Satzherstellung\/} (Bern, 1980). + +@d set_conversion_end(#)== denom:=#; end +@d set_conversion(#)==@+begin num:=#; set_conversion_end + +@<Scan for \(a)all other units and adjust |cur_val| and |f|...@>= +if scan_keyword("in") then set_conversion(7227)(100) +@.in@> +else if scan_keyword("pc") then set_conversion(12)(1) +@.pc@> +else if scan_keyword("cm") then set_conversion(7227)(254) +@.cm@> +else if scan_keyword("mm") then set_conversion(7227)(2540) +@.mm@> +else if scan_keyword("bp") then set_conversion(7227)(7200) +@.bp@> +else if scan_keyword("dd") then set_conversion(1238)(1157) +@.dd@> +else if scan_keyword("cc") then set_conversion(14856)(1157) +@.cc@> +else if scan_keyword("sp") then goto done +@.sp@> +else @<Complain about unknown unit and |goto done2|@>; +cur_val:=xn_over_d(cur_val,num,denom); +f:=(num*f+@'200000*remainder) div denom;@/ +cur_val:=cur_val+(f div @'200000); f:=f mod @'200000; +done2: + +@ @<Complain about unknown unit...@>= +begin print_err("Illegal unit of measure ("); print("pt inserted)"); +@.Illegal unit of measure@> +help6("Dimensions can be in units of em, ex, in, pt, pc,")@/ + ("cm, mm, dd, cc, bp, or sp; but yours is a new one!")@/ + ("I'll assume that you meant to say pt, for printer's points.")@/ + ("To recover gracefully from this error, it's best to")@/ + ("delete the erroneous units; e.g., type `2' to delete")@/ + ("two letters. (See Chapter 27 of The TeXbook.)"); +@:TeXbook}{\sl The \TeX book@> +error; goto done2; +end + + +@ @<Report that this dimension is out of range@>= +begin print_err("Dimension too large"); +@.Dimension too large@> +help2("I can't work with sizes bigger than about 19 feet.")@/ + ("Continue and I'll use the largest value I can.");@/ +error; cur_val:=max_dimen; arith_error:=false; +end + +@ The final member of \TeX's value-scanning trio is |scan_glue|, which +makes |cur_val| point to a glue specification. The reference count of that +glue spec will take account of the fact that |cur_val| is pointing to~it. + +The |level| parameter should be either |glue_val| or |mu_val|. + +Since |scan_dimen| was so much more complex than |scan_int|, we might expect +|scan_glue| to be even worse. But fortunately, it is very simple, since +most of the work has already been done. + +@p procedure scan_glue(@!level:small_number); + {sets |cur_val| to a glue spec pointer} +label exit; +var negative:boolean; {should the answer be negated?} +@!q:pointer; {new glue specification} +@!mu:boolean; {does |level=mu_val|?} +begin mu:=(level=mu_val); @<Get the next non-blank non-sign...@>; +if (cur_cmd>=min_internal)and(cur_cmd<=max_internal) then + begin scan_something_internal(level,negative); + if cur_val_level>=glue_val then + begin if cur_val_level<>level then mu_error; + return; + end; + if cur_val_level=int_val then scan_dimen(mu,false,true) + else if level=mu_val then mu_error; + end +else begin back_input; scan_dimen(mu,false,false); + if negative then negate(cur_val); + end; +@<Create a new glue specification whose width is |cur_val|; scan for its + stretch and shrink components@>; +exit:end; + +@ @<Create a new glue specification whose width is |cur_val|...@>= +q:=new_spec(zero_glue); width(q):=cur_val; +if scan_keyword("plus") then +@.plus@> + begin scan_dimen(mu,true,false); + stretch(q):=cur_val; stretch_order(q):=cur_order; + end; +if scan_keyword("minus") then +@.minus@> + begin scan_dimen(mu,true,false); + shrink(q):=cur_val; shrink_order(q):=cur_order; + end; +cur_val:=q + +@ Here's a similar procedure that returns a pointer to a rule node. This +routine is called just after \TeX\ has seen \.{\\hrule} or \.{\\vrule}; +therefore |cur_cmd| will be either |hrule| or |vrule|. The idea is to store +the default rule dimensions in the node, then to override them if +`\.{height}' or `\.{width}' or `\.{depth}' specifications are +found (in any order). + +@d default_rule=26214 {0.4\thinspace pt} + +@p function scan_rule_spec:pointer; +label reswitch; +var q:pointer; {the rule node being created} +begin q:=new_rule; {|width|, |depth|, and |height| all equal |null_flag| now} +if cur_cmd=vrule then width(q):=default_rule +else begin height(q):=default_rule; depth(q):=0; + end; +reswitch: if scan_keyword("width") then +@.width@> + begin scan_normal_dimen; width(q):=cur_val; goto reswitch; + end; +if scan_keyword("height") then +@.height@> + begin scan_normal_dimen; height(q):=cur_val; goto reswitch; + end; +if scan_keyword("depth") then +@.depth@> + begin scan_normal_dimen; depth(q):=cur_val; goto reswitch; + end; +scan_rule_spec:=q; +end; + +@* \[27] Building token lists. +The token lists for macros and for other things like \.{\\mark} and \.{\\output} +and \.{\\write} are produced by a procedure called |scan_toks|. + +Before we get into the details of |scan_toks|, let's consider a much +simpler task, that of converting the current string into a token list. +The |str_toks| function does this; it classifies spaces as type |spacer| +and everything else as type |other_char|. + +The token list created by |str_toks| begins at |link(temp_head)| and ends +at the value |p| that is returned. (If |p=temp_head|, the list is empty.) + +@p function str_toks(@!b:pool_pointer):pointer; + {changes the string |str_pool[b..pool_ptr]| to a token list} +var p:pointer; {tail of the token list} +@!q:pointer; {new node being added to the token list via |store_new_token|} +@!t:halfword; {token being appended} +@!k:pool_pointer; {index into |str_pool|} +begin str_room(1); +p:=temp_head; link(p):=null; k:=b; +while k<pool_ptr do + begin t:=so(str_pool[k]); + if t=" " then t:=space_token + else t:=other_token+t; + fast_store_new_token(t); + incr(k); + end; +pool_ptr:=b; str_toks:=p; +end; + +@ The main reason for wanting |str_toks| is the next function, +|the_toks|, which has similar input/output characteristics. + +This procedure is supposed to scan something like `\.{\\skip\\count12}', +i.e., whatever can follow `\.{\\the}', and it constructs a token list +containing something like `\.{-3.0pt minus 0.5fill}'. + +@p function the_toks:pointer; +var old_setting:0..max_selector; {holds |selector| setting} +@!p,@!q,@!r:pointer; {used for copying a token list} +@!b:pool_pointer; {base of temporary string} +begin get_x_token; scan_something_internal(tok_val,false); +if cur_val_level>=ident_val then @<Copy the token list@> +else begin old_setting:=selector; selector:=new_string; b:=pool_ptr; + case cur_val_level of + int_val:print_int(cur_val); + dimen_val:begin print_scaled(cur_val); print("pt"); + end; + glue_val: begin print_spec(cur_val,"pt"); delete_glue_ref(cur_val); + end; + mu_val: begin print_spec(cur_val,"mu"); delete_glue_ref(cur_val); + end; + end; {there are no other cases} + selector:=old_setting; the_toks:=str_toks(b); + end; +end; + +@ @<Copy the token list@>= +begin p:=temp_head; link(p):=null; +if cur_val_level=ident_val then store_new_token(cs_token_flag+cur_val) +else if cur_val<>null then + begin r:=link(cur_val); {do not copy the reference count} + while r<>null do + begin fast_store_new_token(info(r)); r:=link(r); + end; + end; +the_toks:=p; +end + +@ Here's part of the |expand| subroutine that we are now ready to complete: + +@p procedure ins_the_toks; +begin link(garbage):=the_toks; ins_list(link(temp_head)); +end; + +@ The primitives \.{\\number}, \.{\\romannumeral}, \.{\\string}, \.{\\meaning}, +\.{\\fontname}, and \.{\\jobname} are defined as follows. + +@d number_code=0 {command code for \.{\\number}} +@d roman_numeral_code=1 {command code for \.{\\romannumeral}} +@d string_code=2 {command code for \.{\\string}} +@d meaning_code=3 {command code for \.{\\meaning}} +@d font_name_code=4 {command code for \.{\\fontname}} +@d job_name_code=5 {command code for \.{\\jobname}} + +@<Put each...@>= +primitive("number",convert,number_code);@/ +@!@:number_}{\.{\\number} primitive@> +primitive("romannumeral",convert,roman_numeral_code);@/ +@!@:roman_numeral_}{\.{\\romannumeral} primitive@> +primitive("string",convert,string_code);@/ +@!@:string_}{\.{\\string} primitive@> +primitive("meaning",convert,meaning_code);@/ +@!@:meaning_}{\.{\\meaning} primitive@> +primitive("fontname",convert,font_name_code);@/ +@!@:font_name_}{\.{\\fontname} primitive@> +primitive("jobname",convert,job_name_code);@/ +@!@:job_name_}{\.{\\jobname} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +convert: case chr_code of + number_code: print_esc("number"); + roman_numeral_code: print_esc("romannumeral"); + string_code: print_esc("string"); + meaning_code: print_esc("meaning"); + font_name_code: print_esc("fontname"); + othercases print_esc("jobname") + endcases; + +@ The procedure |conv_toks| uses |str_toks| to insert the token list +for |convert| functions into the scanner; `\.{\\outer}' control sequences +are allowed to follow `\.{\\string}' and `\.{\\meaning}'. + +@p procedure conv_toks; +var old_setting:0..max_selector; {holds |selector| setting} +@!c:number_code..job_name_code; {desired type of conversion} +@!save_scanner_status:small_number; {|scanner_status| upon entry} +@!b:pool_pointer; {base of temporary string} +begin c:=cur_chr; @<Scan the argument for command |c|@>; +old_setting:=selector; selector:=new_string; b:=pool_ptr; +@<Print the result of command |c|@>; +selector:=old_setting; link(garbage):=str_toks(b); ins_list(link(temp_head)); +end; + +@ @<Scan the argument for command |c|@>= +case c of +number_code,roman_numeral_code: scan_int; +string_code, meaning_code: begin save_scanner_status:=scanner_status; + scanner_status:=normal; get_token; scanner_status:=save_scanner_status; + end; +font_name_code: scan_font_ident; +job_name_code: if job_name=0 then open_log_file; +end {there are no other cases} + +@ @<Print the result of command |c|@>= +case c of +number_code: print_int(cur_val); +roman_numeral_code: print_roman_int(cur_val); +string_code:if cur_cs<>0 then sprint_cs(cur_cs) + else print_char(cur_chr); +meaning_code: print_meaning; +font_name_code: begin print(font_name[cur_val]); + if font_size[cur_val]<>font_dsize[cur_val] then + begin print(" at "); print_scaled(font_size[cur_val]); + print("pt"); + end; + end; +job_name_code: print(job_name); +end {there are no other cases} + +@ Now we can't postpone the difficulties any longer; we must bravely tackle +|scan_toks|. This function returns a pointer to the tail of a new token +list, and it also makes |def_ref| point to the reference count at the +head of that list. + +There are two boolean parameters, |macro_def| and |xpand|. If |macro_def| +is true, the goal is to create the token list for a macro definition; +otherwise the goal is to create the token list for some other \TeX\ +primitive: \.{\\mark}, \.{\\output}, \.{\\everypar}, \.{\\lowercase}, +\.{\\uppercase}, \.{\\message}, \.{\\errmessage}, \.{\\write}, or +\.{\\special}. In the latter cases a left brace must be scanned next; this +left brace will not be part of the token list, nor will the matching right +brace that comes at the end. If |xpand| is false, the token list will +simply be copied from the input using |get_token|. Otherwise all expandable +tokens will be expanded until unexpandable tokens are left, except that +the results of expanding `\.{\\the}' are not expanded further. +If both |macro_def| and |xpand| are true, the expansion applies +only to the macro body (i.e., to the material following the first +|left_brace| character). + +The value of |cur_cs| when |scan_toks| begins should be the |eqtb| +address of the control sequence to display in ``runaway'' error +messages. + +@p function scan_toks(@!macro_def,@!xpand:boolean):pointer; +label found,done,done1,done2; +var t:halfword; {token representing the highest parameter number} +@!s:halfword; {saved token} +@!p:pointer; {tail of the token list being built} +@!q:pointer; {new node being added to the token list via |store_new_token|} +@!unbalance:halfword; {number of unmatched left braces} +@!hash_brace:halfword; {possible `\.{\#\{}' token} +begin if macro_def then scanner_status:=defining +@+else scanner_status:=absorbing; +warning_index:=cur_cs; def_ref:=get_avail; token_ref_count(def_ref):=null; +p:=def_ref; hash_brace:=0; t:=zero_token; +if macro_def then @<Scan and build the parameter part of the macro definition@> +else scan_left_brace; {remove the compulsory left brace} +@<Scan and build the body of the token list; |goto found| when finished@>; +found: scanner_status:=normal; +if hash_brace<>0 then store_new_token(hash_brace); +scan_toks:=p; +end; + +@ @<Scan and build the parameter part...@>= +begin loop begin get_token; {set |cur_cmd|, |cur_chr|, |cur_tok|} + if cur_tok<right_brace_limit then goto done1; + if cur_cmd=mac_param then + @<If the next character is a parameter number, make |cur_tok| + a |match| token; but if it is a left brace, store + `|left_brace|, |end_match|', set |hash_brace|, and |goto done|@>; + store_new_token(cur_tok); + end; +done1: store_new_token(end_match_token); +if cur_cmd=right_brace then + @<Express shock at the missing left brace; |goto found|@>; +done: end + +@ @<Express shock...@>= +begin print_err("Missing { inserted"); incr(align_state); +@.Missing \{ inserted@> +help2("Where was the left brace? You said something like `\def\a}',")@/ + ("which I'm going to interpret as `\def\a{}'."); error; goto found; +end + +@ @<If the next character is a parameter number...@>= +begin s:=match_token+cur_chr; get_token; +if cur_cmd=left_brace then + begin hash_brace:=cur_tok; + store_new_token(cur_tok); store_new_token(end_match_token); + goto done; + end; +if t=zero_token+9 then + begin print_err("You already have nine parameters"); +@.You already have nine...@> + help1("I'm going to ignore the # sign you just used."); error; + end +else begin incr(t); + if cur_tok<>t then + begin print_err("Parameters must be numbered consecutively"); +@.Parameters...consecutively@> + help2("I've inserted the digit you should have used after the #.")@/ + ("Type `1' to delete what you did use."); back_error; + end; + cur_tok:=s; + end; +end + +@ @<Scan and build the body of the token list; |goto found| when finished@>= +unbalance:=1; +loop@+ begin if xpand then @<Expand the next part of the input@> + else get_token; + if cur_tok<right_brace_limit then + if cur_cmd<right_brace then incr(unbalance) + else begin decr(unbalance); + if unbalance=0 then goto found; + end + else if cur_cmd=mac_param then + if macro_def then @<Look for parameter number or \.{\#\#}@>; + store_new_token(cur_tok); + end + +@ Here we insert an entire token list created by |the_toks| without +expanding it further. + +@<Expand the next part of the input@>= +begin loop begin get_next; + if cur_cmd<=max_command then goto done2; + if cur_cmd<>the then expand + else begin q:=the_toks; + if link(temp_head)<>null then + begin link(p):=link(temp_head); p:=q; + end; + end; + end; +done2: x_token +end + +@ @<Look for parameter number...@>= +begin s:=cur_tok; +if xpand then get_x_token else get_token; +if cur_cmd<>mac_param then + if (cur_tok<=zero_token)or(cur_tok>t) then + begin print_err("Illegal parameter number in definition of "); +@.Illegal parameter number...@> + sprint_cs(warning_index); + help3("You meant to type ## instead of #, right?")@/ + ("Or maybe a } was forgotten somewhere earlier, and things")@/ + ("are all screwed up? I'm going to assume that you meant ##."); + back_error; cur_tok:=s; + end + else cur_tok:=out_param_token-"0"+cur_chr; +end + +@ Another way to create a token list is via the \.{\\read} command. The +sixteen files potentially usable for reading appear in the following +global variables. The value of |read_open[n]| will be |closed| if +stream number |n| has not been opened or if it has been fully read; +|just_open| if an \.{\\openin} but not a \.{\\read} has been done; +and |normal| if it is open and ready to read the next line. + +@d closed=2 {not open, or at end of file} +@d just_open=1 {newly opened, first line not yet read} + +@<Glob...@>= +@!read_file:array[0..15] of alpha_file; {used for \.{\\read}} +@!read_open:array[0..16] of normal..closed; {state of |read_file[n]|} + +@ @<Set init...@>= +for k:=0 to 16 do read_open[k]:=closed; + +@ The |read_toks| procedure constructs a token list like that for any +macro definition, and makes |cur_val| point to it. Parameter |r| points +to the control sequence that will receive this token list. + +@p procedure read_toks(@!n:integer;@!r:pointer); +label done; +var p:pointer; {tail of the token list} +@!q:pointer; {new node being added to the token list via |store_new_token|} +@!s:integer; {saved value of |align_state|} +@!m:small_number; {stream number} +begin scanner_status:=defining; warning_index:=r; +def_ref:=get_avail; token_ref_count(def_ref):=null; +p:=def_ref; {the reference count} +store_new_token(end_match_token); +if (n<0)or(n>15) then m:=16@+else m:=n; +s:=align_state; align_state:=1000000; {disable tab marks, etc.} +repeat @<Input and store tokens from the next line of the file@>; +until align_state=1000000; +cur_val:=def_ref; scanner_status:=normal; align_state:=s; +end; + +@ @<Input and store tokens from the next line of the file@>= +begin_file_reading; name:=m+1; +if read_open[m]=closed then @<Input for \.{\\read} from the terminal@> +else if read_open[m]=just_open then @<Input the first line of |read_file[m]|@> +else @<Input the next line of |read_file[m]|@>; +limit:=last; +if end_line_char_inactive then decr(limit) +else buffer[limit]:=end_line_char; +first:=limit+1; loc:=start; state:=new_line;@/ +loop@+ begin get_token; + if cur_tok=0 then goto done; + {|cur_cmd=cur_chr=0| will occur at the end of the line} + if align_state<1000000 then {unmatched `\.\}' aborts the line} + begin repeat get_token; until cur_tok=0; + align_state:=1000000; goto done; + end; + store_new_token(cur_tok); + end; +done: end_file_reading + +@ Here we input on-line into the |buffer| array, prompting the user explicitly +if |n>=0|. The value of |n| is set negative so that additional prompts +will not be given in the case of multi-line input. + +@<Input for \.{\\read} from the terminal@>= +if interaction>nonstop_mode then + if n<0 then prompt_input("") + else begin wake_up_terminal; + print_ln; sprint_cs(r); prompt_input("="); n:=-1; + end +else fatal_error("*** (cannot \read from terminal in nonstop modes)") +@.cannot \\read@> + +@ The first line of a file must be treated specially, since |input_ln| +must be told not to start with |get|. +@^system dependencies@> + +@<Input the first line of |read_file[m]|@>= +if input_ln(read_file[m],false) then read_open[m]:=normal +else begin a_close(read_file[m]); read_open[m]:=closed; + end + +@ An empty line is appended at the end of a |read_file|. +@^empty line at end of file@> + +@<Input the next line of |read_file[m]|@>= +begin if not input_ln(read_file[m],true) then + begin a_close(read_file[m]); read_open[m]:=closed; + if align_state<>1000000 then + begin runaway; + print_err("File ended within "); print_esc("read"); +@.File ended within \\read@> + help1("This \read has unbalanced braces."); + align_state:=1000000; error; + end; + end; +end + +@* \[28] Conditional processing. +We consider now the way \TeX\ handles various kinds of \.{\\if} commands. + +@d if_char_code=0 { `\.{\\if}' } +@d if_cat_code=1 { `\.{\\ifcat}' } +@d if_int_code=2 { `\.{\\ifnum}' } +@d if_dim_code=3 { `\.{\\ifdim}' } +@d if_odd_code=4 { `\.{\\ifodd}' } +@d if_vmode_code=5 { `\.{\\ifvmode}' } +@d if_hmode_code=6 { `\.{\\ifhmode}' } +@d if_mmode_code=7 { `\.{\\ifmmode}' } +@d if_inner_code=8 { `\.{\\ifinner}' } +@d if_void_code=9 { `\.{\\ifvoid}' } +@d if_hbox_code=10 { `\.{\\ifhbox}' } +@d if_vbox_code=11 { `\.{\\ifvbox}' } +@d ifx_code=12 { `\.{\\ifx}' } +@d if_eof_code=13 { `\.{\\ifeof}' } +@d if_true_code=14 { `\.{\\iftrue}' } +@d if_false_code=15 { `\.{\\iffalse}' } +@d if_case_code=16 { `\.{\\ifcase}' } + +@<Put each...@>= +primitive("if",if_test,if_char_code); +@!@:if_char_}{\.{\\if} primitive@> +primitive("ifcat",if_test,if_cat_code); +@!@:if_cat_code_}{\.{\\ifcat} primitive@> +primitive("ifnum",if_test,if_int_code); +@!@:if_int_}{\.{\\ifnum} primitive@> +primitive("ifdim",if_test,if_dim_code); +@!@:if_dim_}{\.{\\ifdim} primitive@> +primitive("ifodd",if_test,if_odd_code); +@!@:if_odd_}{\.{\\ifodd} primitive@> +primitive("ifvmode",if_test,if_vmode_code); +@!@:if_vmode_}{\.{\\ifvmode} primitive@> +primitive("ifhmode",if_test,if_hmode_code); +@!@:if_hmode_}{\.{\\ifhmode} primitive@> +primitive("ifmmode",if_test,if_mmode_code); +@!@:if_mmode_}{\.{\\ifmmode} primitive@> +primitive("ifinner",if_test,if_inner_code); +@!@:if_inner_}{\.{\\ifinner} primitive@> +primitive("ifvoid",if_test,if_void_code); +@!@:if_void_}{\.{\\ifvoid} primitive@> +primitive("ifhbox",if_test,if_hbox_code); +@!@:if_hbox_}{\.{\\ifhbox} primitive@> +primitive("ifvbox",if_test,if_vbox_code); +@!@:if_vbox_}{\.{\\ifvbox} primitive@> +primitive("ifx",if_test,ifx_code); +@!@:ifx_}{\.{\\ifx} primitive@> +primitive("ifeof",if_test,if_eof_code); +@!@:if_eof_}{\.{\\ifeof} primitive@> +primitive("iftrue",if_test,if_true_code); +@!@:if_true_}{\.{\\iftrue} primitive@> +primitive("iffalse",if_test,if_false_code); +@!@:if_false_}{\.{\\iffalse} primitive@> +primitive("ifcase",if_test,if_case_code); +@!@:if_case_}{\.{\\ifcase} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +if_test: case chr_code of + if_cat_code:print_esc("ifcat"); + if_int_code:print_esc("ifnum"); + if_dim_code:print_esc("ifdim"); + if_odd_code:print_esc("ifodd"); + if_vmode_code:print_esc("ifvmode"); + if_hmode_code:print_esc("ifhmode"); + if_mmode_code:print_esc("ifmmode"); + if_inner_code:print_esc("ifinner"); + if_void_code:print_esc("ifvoid"); + if_hbox_code:print_esc("ifhbox"); + if_vbox_code:print_esc("ifvbox"); + ifx_code:print_esc("ifx"); + if_eof_code:print_esc("ifeof"); + if_true_code:print_esc("iftrue"); + if_false_code:print_esc("iffalse"); + if_case_code:print_esc("ifcase"); + othercases print_esc("if") + endcases; + +@ Conditions can be inside conditions, and this nesting has a stack +that is independent of the |save_stack|. + +Four global variables represent the top of the condition stack: +|cond_ptr| points to pushed-down entries, if any; |if_limit| specifies +the largest code of a |fi_or_else| command that is syntactically legal; +|cur_if| is the name of the current type of conditional; and |if_line| +is the line number at which it began. + +If no conditions are currently in progress, the condition stack has the +special state |cond_ptr=null|, |if_limit=normal|, |cur_if=0|, |if_line=0|. +Otherwise |cond_ptr| points to a two-word node; the |type|, |subtype|, and +|link| fields of the first word contain |if_limit|, |cur_if|, and +|cond_ptr| at the next level, and the second word contains the +corresponding |if_line|. + +@d if_node_size=2 {number of words in stack entry for conditionals} +@d if_line_field(#)==mem[#+1].int +@d if_code=1 {code for \.{\\if...} being evaluated} +@d fi_code=2 {code for \.{\\fi}} +@d else_code=3 {code for \.{\\else}} +@d or_code=4 {code for \.{\\or}} + +@<Glob...@>= +@!cond_ptr:pointer; {top of the condition stack} +@!if_limit:normal..or_code; {upper bound on |fi_or_else| codes} +@!cur_if:small_number; {type of conditional being worked on} +@!if_line:integer; {line where that conditional began} + +@ @<Set init...@>= +cond_ptr:=null; if_limit:=normal; cur_if:=0; if_line:=0; + +@ @<Put each...@>= +primitive("fi",fi_or_else,fi_code); +@!@:fi_}{\.{\\fi} primitive@> +text(frozen_fi):="fi"; eqtb[frozen_fi]:=eqtb[cur_val]; +primitive("or",fi_or_else,or_code); +@!@:or_}{\.{\\or} primitive@> +primitive("else",fi_or_else,else_code); +@!@:else_}{\.{\\else} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +fi_or_else: if chr_code=fi_code then print_esc("fi") + else if chr_code=or_code then print_esc("or") + else print_esc("else"); + +@ When we skip conditional text, we keep track of the line number +where skipping began, for use in error messages. + +@<Glob...@>= +@!skip_line:integer; {skipping began here} + +@ Here is a procedure that ignores text until coming to an \.{\\or}, +\.{\\else}, or \.{\\fi} at level zero of $\.{\\if}\ldots\.{\\fi}$ +nesting. After it has acted, |cur_chr| will indicate the token that +was found, but |cur_tok| will not be set (because this makes the +procedure run faster). + +@p procedure pass_text; +label done; +var l:integer; {level of $\.{\\if}\ldots\.{\\fi}$ nesting} +@!save_scanner_status:small_number; {|scanner_status| upon entry} +begin save_scanner_status:=scanner_status; scanner_status:=skipping; l:=0; +skip_line:=line; +loop@+ begin get_next; + if cur_cmd=fi_or_else then + begin if l=0 then goto done; + if cur_chr=fi_code then decr(l); + end + else if cur_cmd=if_test then incr(l); + end; +done: scanner_status:=save_scanner_status; +end; + +@ When we begin to process a new \.{\\if}, we set |if_limit:=if_code|; then +if\/ \.{\\or} or \.{\\else} or \.{\\fi} occurs before the current \.{\\if} +condition has been evaluated, \.{\\relax} will be inserted. +For example, a sequence of commands like `\.{\\ifvoid1\\else...\\fi}' +would otherwise require something after the `\.1'. + +@<Push the condition stack@>= +begin p:=get_node(if_node_size); link(p):=cond_ptr; type(p):=if_limit; +subtype(p):=cur_if; if_line_field(p):=if_line; +cond_ptr:=p; cur_if:=cur_chr; if_limit:=if_code; if_line:=line; +end + +@ @<Pop the condition stack@>= +begin p:=cond_ptr; if_line:=if_line_field(p); +cur_if:=subtype(p); if_limit:=type(p); cond_ptr:=link(p); +free_node(p,if_node_size); +end + +@ Here's a procedure that changes the |if_limit| code corresponding to +a given value of |cond_ptr|. + +@p procedure change_if_limit(@!l:small_number;@!p:pointer); +label exit; +var q:pointer; +begin if p=cond_ptr then if_limit:=l {that's the easy case} +else begin q:=cond_ptr; + loop@+ begin if q=null then confusion("if"); +@:this can't happen if}{\quad if@> + if link(q)=p then + begin type(q):=l; return; + end; + q:=link(q); + end; + end; +exit:end; + +@ A condition is started when the |expand| procedure encounters +an |if_test| command; in that case |expand| reduces to |conditional|, +which is a recursive procedure. +@^recursion@> + +@p procedure conditional; +label exit,common_ending; +var b:boolean; {is the condition true?} +@!r:"<"..">"; {relation to be evaluated} +@!m,@!n:integer; {to be tested against the second operand} +@!p,@!q:pointer; {for traversing token lists in \.{\\ifx} tests} +@!save_scanner_status:small_number; {|scanner_status| upon entry} +@!save_cond_ptr:pointer; {|cond_ptr| corresponding to this conditional} +@!this_if:small_number; {type of this conditional} +begin @<Push the condition stack@>;@+save_cond_ptr:=cond_ptr;this_if:=cur_chr;@/ +@<Either process \.{\\ifcase} or set |b| to the value of a boolean condition@>; +if tracing_commands>1 then @<Display the value of |b|@>; +if b then + begin change_if_limit(else_code,save_cond_ptr); + return; {wait for \.{\\else} or \.{\\fi}} + end; +@<Skip to \.{\\else} or \.{\\fi}, then |goto common_ending|@>; +common_ending: if cur_chr=fi_code then @<Pop the condition stack@> +else if_limit:=fi_code; {wait for \.{\\fi}} +exit:end; + +@ In a construction like `\.{\\if\\iftrue abc\\else d\\fi}', the first +\.{\\else} that we come to after learning that the \.{\\if} is false is +not the \.{\\else} we're looking for. Hence the following curious +logic is needed. + +@ @<Skip to \.{\\else} or \.{\\fi}...@>= +loop@+ begin pass_text; + if cond_ptr=save_cond_ptr then + begin if cur_chr<>or_code then goto common_ending; + print_err("Extra "); print_esc("or"); +@.Extra \\or@> + help1("I'm ignoring this; it doesn't match any \if."); + error; + end + else if cur_chr=fi_code then @<Pop the condition stack@>; + end + +@ @<Either process \.{\\ifcase} or set |b|...@>= +case this_if of +if_char_code, if_cat_code: @<Test if two characters match@>; +if_int_code, if_dim_code: @<Test relation between integers or dimensions@>; +if_odd_code: @<Test if an integer is odd@>; +if_vmode_code: b:=(abs(mode)=vmode); +if_hmode_code: b:=(abs(mode)=hmode); +if_mmode_code: b:=(abs(mode)=mmode); +if_inner_code: b:=(mode<0); +if_void_code, if_hbox_code, if_vbox_code: @<Test box register status@>; +ifx_code: @<Test if two tokens match@>; +if_eof_code: begin scan_four_bit_int; b:=(read_open[cur_val]=closed); + end; +if_true_code: b:=true; +if_false_code: b:=false; +if_case_code: @<Select the appropriate case + and |return| or |goto common_ending|@>; +end {there are no other cases} + +@ @<Display the value of |b|@>= +begin begin_diagnostic; +if b then print("{true}")@+else print("{false}"); +end_diagnostic(false); +end + +@ Here we use the fact that |"<"|, |"="|, and |">"| are consecutive ASCII +codes. +@^ASCII code@> + +@<Test relation between integers or dimensions@>= +begin if this_if=if_int_code then scan_int@+else scan_normal_dimen; +n:=cur_val; @<Get the next non-blank non-call...@>; +if (cur_tok>=other_token+"<")and(cur_tok<=other_token+">") then + r:=cur_tok-other_token +else begin print_err("Missing = inserted for "); +@.Missing = inserted@> + print_cmd_chr(if_test,this_if); + help1("I was expecting to see `<', `=', or `>'. Didn't."); + back_error; r:="="; + end; +if this_if=if_int_code then scan_int@+else scan_normal_dimen; +case r of +"<": b:=(n<cur_val); +"=": b:=(n=cur_val); +">": b:=(n>cur_val); +end; +end + +@ @<Test if an integer is odd@>= +begin scan_int; b:=odd(cur_val); +end + +@ @<Test box register status@>= +begin scan_eight_bit_int; p:=box(cur_val); +if this_if=if_void_code then b:=(p=null) +else if p=null then b:=false +else if this_if=if_hbox_code then b:=(type(p)=hlist_node) +else b:=(type(p)=vlist_node); +end + +@ An active character will be treated as category 13 following +\.{\\if\\noexpand} or following \.{\\ifcat\\noexpand}. We use the fact that +active characters have the smallest tokens, among all control sequences. + +@d get_x_token_or_active_char==@t@>@; + begin get_x_token; + if cur_cmd=relax then if cur_chr=no_expand_flag then + begin cur_cmd:=active_char; + cur_chr:=cur_tok-cs_token_flag-active_base; + end; + end + +@<Test if two characters match@>= +begin get_x_token_or_active_char; +if (cur_cmd>active_char)or(cur_chr>255) then {not a character} + begin m:=relax; n:=256; + end +else begin m:=cur_cmd; n:=cur_chr; + end; +get_x_token_or_active_char; +if (cur_cmd>active_char)or(cur_chr>255) then + begin cur_cmd:=relax; cur_chr:=256; + end; +if this_if=if_char_code then b:=(n=cur_chr)@+else b:=(m=cur_cmd); +end + +@ Note that `\.{\\ifx}' will declare two macros different if one is \\{long} +or \\{outer} and the other isn't, even though the texts of the macros are +the same. + +We need to reset |scanner_status|, since \.{\\outer} control sequences +are allowed, but we might be scanning a macro definition or preamble. + +@<Test if two tokens match@>= +begin save_scanner_status:=scanner_status; scanner_status:=normal; +get_next; n:=cur_cs; p:=cur_cmd; q:=cur_chr; +get_next; if cur_cmd<>p then b:=false +else if cur_cmd<call then b:=(cur_chr=q) +else @<Test if two macro texts match@>; +scanner_status:=save_scanner_status; +end + +@ Note also that `\.{\\ifx}' decides that macros \.{\\a} and \.{\\b} are +different in examples like this: +$$\vbox{\halign{\.{#}\hfil&\qquad\.{#}\hfil\cr + {}\\def\\a\{\\c\}& + {}\\def\\c\{\}\cr + {}\\def\\b\{\\d\}& + {}\\def\\d\{\}\cr}}$$ + +@<Test if two macro texts match@>= +begin p:=link(cur_chr); q:=link(equiv(n)); {omit reference counts} +if p=q then b:=true +else begin while (p<>null)and(q<>null) do + if info(p)<>info(q) then p:=null + else begin p:=link(p); q:=link(q); + end; + b:=((p=null)and(q=null)); + end; +end + +@ @<Select the appropriate case and |return| or |goto common_ending|@>= +begin scan_int; n:=cur_val; {|n| is the number of cases to pass} +if tracing_commands>1 then + begin begin_diagnostic; print("{case "); print_int(n); print_char("}"); + end_diagnostic(false); + end; +while n<>0 do + begin pass_text; + if cond_ptr=save_cond_ptr then + if cur_chr=or_code then decr(n) + else goto common_ending + else if cur_chr=fi_code then @<Pop the condition stack@>; + end; +change_if_limit(or_code,save_cond_ptr); +return; {wait for \.{\\or}, \.{\\else}, or \.{\\fi}} +end + +@ The processing of conditionals is complete except for the following +code, which is actually part of |expand|. It comes into play when +\.{\\or}, \.{\\else}, or \.{\\fi} is scanned. + +@<Terminate the current conditional and skip to \.{\\fi}@>= +if cur_chr>if_limit then + if if_limit=if_code then insert_relax {condition not yet evaluated} + else begin print_err("Extra "); print_cmd_chr(fi_or_else,cur_chr); +@.Extra \\or@> +@.Extra \\else@> +@.Extra \\fi@> + help1("I'm ignoring this; it doesn't match any \if."); + error; + end +else begin while cur_chr<>fi_code do pass_text; {skip to \.{\\fi}} + @<Pop the condition stack@>; + end + +@* \[29] File names. +It's time now to fret about file names. Besides the fact that different +operating systems treat files in different ways, we must cope with the +fact that completely different naming conventions are used by different +groups of people. The following programs show what is required for one +particular operating system; similar routines for other systems are not +difficult to devise. +@^fingers@> +@^system dependencies@> + +\TeX\ assumes that a file name has three parts: the name proper; its +``extension''; and a ``file area'' where it is found in an external file +system. The extension of an input file or a write file is assumed to be +`\.{.tex}' unless otherwise specified; it is `\.{.log}' on the +transcript file that records each run of \TeX; it is `\.{.tfm}' on the font +metric files that describe characters in the fonts \TeX\ uses; it is +`\.{.dvi}' on the output files that specify typesetting information; and it +is `\.{.fmt}' on the format files written by \.{INITEX} to initialize \TeX. +The file area can be arbitrary on input files, but files are usually +output to the user's current area. If an input file cannot be +found on the specified area, \TeX\ will look for it on a special system +area; this special area is intended for commonly used input files like +\.{webmac.tex}. + +Simple uses of \TeX\ refer only to file names that have no explicit +extension or area. For example, a person usually says `\.{\\input} \.{paper}' +or `\.{\\font\\tenrm} \.= \.{helvetica}' instead of `\.{\\input} +\.{paper.new}' or `\.{\\font\\tenrm} \.= \.{<csd.knuth>test}'. Simple file +names are best, because they make the \TeX\ source files portable; +whenever a file name consists entirely of letters and digits, it should be +treated in the same way by all implementations of \TeX. However, users +need the ability to refer to other files in their environment, especially +when responding to error messages concerning unopenable files; therefore +we want to let them use the syntax that appears in their favorite +operating system. + +The following procedures don't allow spaces to be part of +file names; but some users seem to like names that are spaced-out. +System-dependent changes to allow such things should probably +be made with reluctance, and only when an entire file name that +includes spaces is ``quoted'' somehow. + +@ In order to isolate the system-dependent aspects of file names, the +@^system dependencies@> +system-independent parts of \TeX\ are expressed in terms +of three system-dependent +procedures called |begin_name|, |more_name|, and |end_name|. In +essence, if the user-specified characters of the file name are $c_1\ldots c_n$, +the system-independent driver program does the operations +$$|begin_name|;\,|more_name|(c_1);\,\ldots\,;|more_name|(c_n); +\,|end_name|.$$ +These three procedures communicate with each other via global variables. +Afterwards the file name will appear in the string pool as three strings +called |cur_name|\penalty10000\hskip-.05em, +|cur_area|, and |cur_ext|; the latter two are null (i.e., +|""|), unless they were explicitly specified by the user. + +Actually the situation is slightly more complicated, because \TeX\ needs +to know when the file name ends. The |more_name| routine is a function +(with side effects) that returns |true| on the calls |more_name|$(c_1)$, +\dots, |more_name|$(c_{n-1})$. The final call |more_name|$(c_n)$ +returns |false|; or, it returns |true| and the token following $c_n$ is +something like `\.{\\hbox}' (i.e., not a character). In other words, +|more_name| is supposed to return |true| unless it is sure that the +file name has been completely scanned; and |end_name| is supposed to be able +to finish the assembly of |cur_name|, |cur_area|, and |cur_ext| regardless of +whether $|more_name|(c_n)$ returned |true| or |false|. + +@<Glob...@>= +@!cur_name:str_number; {name of file just scanned} +@!cur_area:str_number; {file area just scanned, or \.{""}} +@!cur_ext:str_number; {file extension just scanned, or \.{""}} + +@ The file names we shall deal with for illustrative purposes have the +following structure: If the name contains `\.>' or `\.:', the file area +consists of all characters up to and including the final such character; +otherwise the file area is null. If the remaining file name contains +`\..', the file extension consists of all such characters from the first +remaining `\..' to the end, otherwise the file extension is null. +@^system dependencies@> + +We can scan such file names easily by using two global variables that keep track +of the occurrences of area and extension delimiters: + +@<Glob...@>= +@!area_delimiter:pool_pointer; {the most recent `\.>' or `\.:', if any} +@!ext_delimiter:pool_pointer; {the relevant `\..', if any} + +@ Input files that can't be found in the user's area may appear in a standard +system area called |TEX_area|. Font metric files whose areas are not given +explicitly are assumed to appear in a standard system area called +|TEX_font_area|. These system area names will, of course, vary from place +to place. +@^system dependencies@> + +@d TEX_area=="TeXinputs:" +@.TeXinputs@> +@d TEX_font_area=="TeXfonts:" +@.TeXfonts@> + +@ Here now is the first of the system-dependent routines for file name scanning. +@^system dependencies@> + +@p procedure begin_name; +begin area_delimiter:=0; ext_delimiter:=0; +end; + +@ And here's the second. The string pool might change as the file name is +being scanned, since a new \.{\\csname} might be entered; therefore we keep +|area_delimiter| and |ext_delimiter| relative to the beginning of the current +string, instead of assigning an absolute address like |pool_ptr| to them. +@^system dependencies@> + +@p function more_name(@!c:ASCII_code):boolean; +begin if c=" " then more_name:=false +else begin str_room(1); append_char(c); {contribute |c| to the current string} + if (c=">")or(c=":") then + begin area_delimiter:=cur_length; ext_delimiter:=0; + end + else if (c=".")and(ext_delimiter=0) then ext_delimiter:=cur_length; + more_name:=true; + end; +end; + +@ The third. +@^system dependencies@> + +@p procedure end_name; +begin if str_ptr+3>max_strings then + overflow("number of strings",max_strings-init_str_ptr); +@:TeX capacity exceeded number of strings}{\quad number of strings@> +if area_delimiter=0 then cur_area:="" +else begin cur_area:=str_ptr; + str_start[str_ptr+1]:=str_start[str_ptr]+area_delimiter; incr(str_ptr); + end; +if ext_delimiter=0 then + begin cur_ext:=""; cur_name:=make_string; + end +else begin cur_name:=str_ptr; + str_start[str_ptr+1]:=str_start[str_ptr]+ext_delimiter-area_delimiter-1; + incr(str_ptr); cur_ext:=make_string; + end; +end; + +@ Conversely, here is a routine that takes three strings and prints a file +name that might have produced them. (The routine is system dependent, because +some operating systems put the file area last instead of first.) +@^system dependencies@> + +@<Basic printing...@>= +procedure print_file_name(@!n,@!a,@!e:integer); +begin slow_print(a); slow_print(n); slow_print(e); +end; + +@ Another system-dependent routine is needed to convert three internal +\TeX\ strings +into the |name_of_file| value that is used to open files. The present code +allows both lowercase and uppercase letters in the file name. +@^system dependencies@> + +@d append_to_name(#)==begin c:=#; incr(k); + if k<=file_name_size then name_of_file[k]:=xchr[c]; + end + +@p procedure pack_file_name(@!n,@!a,@!e:str_number); +var k:integer; {number of positions filled in |name_of_file|} +@!c: ASCII_code; {character being packed} +@!j:pool_pointer; {index into |str_pool|} +begin k:=0; +for j:=str_start[a] to str_start[a+1]-1 do append_to_name(so(str_pool[j])); +for j:=str_start[n] to str_start[n+1]-1 do append_to_name(so(str_pool[j])); +for j:=str_start[e] to str_start[e+1]-1 do append_to_name(so(str_pool[j])); +if k<=file_name_size then name_length:=k@+else name_length:=file_name_size; +for k:=name_length+1 to file_name_size do name_of_file[k]:=' '; +end; + +@ A messier routine is also needed, since format file names must be scanned +before \TeX's string mechanism has been initialized. We shall use the +global variable |TEX_format_default| to supply the text for default system areas +and extensions related to format files. +@^system dependencies@> + +@d format_default_length=20 {length of the |TEX_format_default| string} +@d format_area_length=11 {length of its area part} +@d format_ext_length=4 {length of its `\.{.fmt}' part} +@d format_extension=".fmt" {the extension, as a \.{WEB} constant} + +@<Glob...@>= +@!TEX_format_default:packed array[1..format_default_length] of char; + +@ @<Set init...@>= +TEX_format_default:='TeXformats:plain.fmt'; +@.TeXformats@> +@.plain@> +@^system dependencies@> + +@ @<Check the ``constant'' values for consistency@>= +if format_default_length>file_name_size then bad:=31; + +@ Here is the messy routine that was just mentioned. It sets |name_of_file| +from the first |n| characters of |TEX_format_default|, followed by +|buffer[a..b]|, followed by the last |format_ext_length| characters of +|TEX_format_default|. + +We dare not give error messages here, since \TeX\ calls this routine before +the |error| routine is ready to roll. Instead, we simply drop excess characters, +since the error will be detected in another way when a strange file name +isn't found. +@^system dependencies@> + +@p procedure pack_buffered_name(@!n:small_number;@!a,@!b:integer); +var k:integer; {number of positions filled in |name_of_file|} +@!c: ASCII_code; {character being packed} +@!j:integer; {index into |buffer| or |TEX_format_default|} +begin if n+b-a+1+format_ext_length>file_name_size then + b:=a+file_name_size-n-1-format_ext_length; +k:=0; +for j:=1 to n do append_to_name(xord[TEX_format_default[j]]); +for j:=a to b do append_to_name(buffer[j]); +for j:=format_default_length-format_ext_length+1 to format_default_length do + append_to_name(xord[TEX_format_default[j]]); +if k<=file_name_size then name_length:=k@+else name_length:=file_name_size; +for k:=name_length+1 to file_name_size do name_of_file[k]:=' '; +end; + +@ Here is the only place we use |pack_buffered_name|. This part of the program +becomes active when a ``virgin'' \TeX\ is trying to get going, just after +the preliminary initialization, or when the user is substituting another +format file by typing `\.\&' after the initial `\.{**}' prompt. The buffer +contains the first line of input in |buffer[loc..(last-1)]|, where +|loc<last| and |buffer[loc]<>" "|. + +@<Declare the function called |open_fmt_file|@>= +function open_fmt_file:boolean; +label found,exit; +var j:0..buf_size; {the first space after the format file name} +begin j:=loc; +if buffer[loc]="&" then + begin incr(loc); j:=loc; buffer[last]:=" "; + while buffer[j]<>" " do incr(j); + pack_buffered_name(0,loc,j-1); {try first without the system file area} + if w_open_in(fmt_file) then goto found; + pack_buffered_name(format_area_length,loc,j-1); + {now try the system format file area} + if w_open_in(fmt_file) then goto found; + wake_up_terminal; + wterm_ln('Sorry, I can''t find that format;',' will try PLAIN.'); +@.Sorry, I can't find...@> + update_terminal; + end; + {now pull out all the stops: try for the system \.{plain} file} +pack_buffered_name(format_default_length-format_ext_length,1,0); +if not w_open_in(fmt_file) then + begin wake_up_terminal; + wterm_ln('I can''t find the PLAIN format file!'); +@.I can't find PLAIN...@> +@.plain@> + open_fmt_file:=false; return; + end; +found:loc:=j; open_fmt_file:=true; +exit:end; + +@ Operating systems often make it possible to determine the exact name (and +possible version number) of a file that has been opened. The following routine, +which simply makes a \TeX\ string from the value of |name_of_file|, should +ideally be changed to deduce the full name of file~|f|, which is the file +most recently opened, if it is possible to do this in a \PASCAL\ program. +@^system dependencies@> + +This routine might be called after string memory has overflowed, hence +we dare not use `|str_room|'. + +@p function make_name_string:str_number; +var k:1..file_name_size; {index into |name_of_file|} +begin if (pool_ptr+name_length>pool_size)or(str_ptr=max_strings)or + (cur_length>0) then + make_name_string:="?" +else begin for k:=1 to name_length do append_char(xord[name_of_file[k]]); + make_name_string:=make_string; + end; +end; +function a_make_name_string(var f:alpha_file):str_number; +begin a_make_name_string:=make_name_string; +end; +function b_make_name_string(var f:byte_file):str_number; +begin b_make_name_string:=make_name_string; +end; +function w_make_name_string(var f:word_file):str_number; +begin w_make_name_string:=make_name_string; +end; + +@ Now let's consider the ``driver'' +routines by which \TeX\ deals with file names +in a system-independent manner. First comes a procedure that looks for a +file name in the input by calling |get_x_token| for the information. + +@p procedure scan_file_name; +label done; +begin name_in_progress:=true; begin_name; +@<Get the next non-blank non-call...@>; +loop@+begin if (cur_cmd>other_char)or(cur_chr>255) then {not a character} + begin back_input; goto done; + end; + if not more_name(cur_chr) then goto done; + get_x_token; + end; +done: end_name; name_in_progress:=false; +end; + +@ The global variable |name_in_progress| is used to prevent recursive +use of |scan_file_name|, since the |begin_name| and other procedures +communicate via global variables. Recursion would arise only by +devious tricks like `\.{\\input\\input f}'; such attempts at sabotage +must be thwarted. Furthermore, |name_in_progress| prevents \.{\\input} +@^recursion@> +from being initiated when a font size specification is being scanned. + +Another global variable, |job_name|, contains the file name that was first +\.{\\input} by the user. This name is extended by `\.{.log}' and `\.{.dvi}' +and `\.{.fmt}' in the names of \TeX's output files. + +@<Glob...@>= +@!name_in_progress:boolean; {is a file name being scanned?} +@!job_name:str_number; {principal file name} +@!log_opened:boolean; {has the transcript file been opened?} + +@ Initially |job_name=0|; it becomes nonzero as soon as the true name is known. +We have |job_name=0| if and only if the `\.{log}' file has not been opened, +except of course for a short time just after |job_name| has become nonzero. + +@<Initialize the output...@>= +job_name:=0; name_in_progress:=false; log_opened:=false; + +@ Here is a routine that manufactures the output file names, assuming that +|job_name<>0|. It ignores and changes the current settings of |cur_area| +and |cur_ext|. + +@d pack_cur_name==pack_file_name(cur_name,cur_area,cur_ext) + +@p procedure pack_job_name(@!s:str_number); {|s = ".log"|, |".dvi"|, or + |format_extension|} +begin cur_area:=""; cur_ext:=s; +cur_name:=job_name; pack_cur_name; +end; + +@ If some trouble arises when \TeX\ tries to open a file, the following +routine calls upon the user to supply another file name. Parameter~|s| +is used in the error message to identify the type of file; parameter~|e| +is the default extension if none is given. Upon exit from the routine, +variables |cur_name|, |cur_area|, |cur_ext|, and |name_of_file| are +ready for another attempt at file opening. + +@p procedure prompt_file_name(@!s,@!e:str_number); +label done; +var k:0..buf_size; {index into |buffer|} +begin if interaction=scroll_mode then wake_up_terminal; +if s="input file name" then print_err("I can't find file `") +@.I can't find file x@> +else print_err("I can't write on file `"); +@.I can't write on file x@> +print_file_name(cur_name,cur_area,cur_ext); print("'."); +if e=".tex" then show_context; +print_nl("Please type another "); print(s); +@.Please type...@> +if interaction<scroll_mode then + fatal_error("*** (job aborted, file error in nonstop mode)"); +@.job aborted, file error...@> +clear_terminal; prompt_input(": "); @<Scan file name in the buffer@>; +if cur_ext="" then cur_ext:=e; +pack_cur_name; +end; + +@ @<Scan file name in the buffer@>= +begin begin_name; k:=first; +while (buffer[k]=" ")and(k<last) do incr(k); +loop@+ begin if k=last then goto done; + if not more_name(buffer[k]) then goto done; + incr(k); + end; +done:end_name; +end + +@ Here's an example of how these conventions are used. Whenever it is time to +ship out a box of stuff, we shall use the macro |ensure_dvi_open|. + +@d ensure_dvi_open==if output_file_name=0 then + begin if job_name=0 then open_log_file; + pack_job_name(".dvi"); + while not b_open_out(dvi_file) do + prompt_file_name("file name for output",".dvi"); + output_file_name:=b_make_name_string(dvi_file); + end + +@<Glob...@>= +@!dvi_file: byte_file; {the device-independent output goes here} +@!output_file_name: str_number; {full name of the output file} +@!log_name:str_number; {full name of the log file} + +@ @<Initialize the output...@>=output_file_name:=0; + +@ The |open_log_file| routine is used to open the transcript file and to help +it catch up to what has previously been printed on the terminal. + +@p procedure open_log_file; +var old_setting:0..max_selector; {previous |selector| setting} +@!k:0..buf_size; {index into |months| and |buffer|} +@!l:0..buf_size; {end of first input line} +@!months:packed array [1..36] of char; {abbreviations of month names} +begin old_setting:=selector; +if job_name=0 then job_name:="texput"; +@.texput@> +pack_job_name(".log"); +while not a_open_out(log_file) do @<Try to get a different log file name@>; +log_name:=a_make_name_string(log_file); +selector:=log_only; log_opened:=true; +@<Print the banner line, including the date and time@>; +input_stack[input_ptr]:=cur_input; {make sure bottom level is in memory} +print_nl("**"); +@.**@> +l:=input_stack[0].limit_field; {last position of first line} +if buffer[l]=end_line_char then decr(l); +for k:=1 to l do print(buffer[k]); +print_ln; {now the transcript file contains the first line of input} +selector:=old_setting+2; {|log_only| or |term_and_log|} +end; + +@ Sometimes |open_log_file| is called at awkward moments when \TeX\ is +unable to print error messages or even to |show_context|. +The |prompt_file_name| routine can result in a |fatal_error|, but the |error| +routine will not be invoked because |log_opened| will be false. + +The normal idea of |batch_mode| is that nothing at all should be written +on the terminal. However, in the unusual case that +no log file could be opened, we make an exception and allow +an explanatory message to be seen. + +Incidentally, the program always refers to the log file as a `\.{transcript +file}', because some systems cannot use the extension `\.{.log}' for +this file. + +@<Try to get a different log file name@>= +begin selector:=term_only; +prompt_file_name("transcript file name",".log"); +end + +@ @<Print the banner...@>= +begin wlog(banner); +slow_print(format_ident); print(" "); +print_int(day); print_char(" "); +months:='JANFEBMARAPRMAYJUNJULAUGSEPOCTNOVDEC'; +for k:=3*month-2 to 3*month do wlog(months[k]); +print_char(" "); print_int(year); print_char(" "); +print_two(time div 60); print_char(":"); print_two(time mod 60); +end + +@ Let's turn now to the procedure that is used to initiate file reading +when an `\.{\\input}' command is being processed. + +@p procedure start_input; {\TeX\ will \.{\\input} something} +label done; +begin scan_file_name; {set |cur_name| to desired file name} +if cur_ext="" then cur_ext:=".tex"; +pack_cur_name; +loop@+ begin begin_file_reading; {set up |cur_file| and new level of input} + if a_open_in(cur_file) then goto done; + if cur_area="" then + begin pack_file_name(cur_name,TEX_area,cur_ext); + if a_open_in(cur_file) then goto done; + end; + end_file_reading; {remove the level that didn't work} + prompt_file_name("input file name",".tex"); + end; +done: name:=a_make_name_string(cur_file); +if job_name=0 then + begin job_name:=cur_name; open_log_file; + end; {|open_log_file| doesn't |show_context|, so |limit| + and |loc| needn't be set to meaningful values yet} +if term_offset+length(name)>max_print_line-2 then print_ln +else if (term_offset>0)or(file_offset>0) then print_char(" "); +print_char("("); incr(open_parens); slow_print(name); update_terminal; +state:=new_line; +if name=str_ptr-1 then {we can conserve string pool space now} + begin flush_string; name:=cur_name; + end; +@<Read the first line of the new file@>; +end; + +@ Here we have to remember to tell the |input_ln| routine not to +start with a |get|. If the file is empty, it is considered to +contain a single blank line. +@^system dependencies@> +@^empty line at end of file@> + +@<Read the first line...@>= +begin line:=1; +if input_ln(cur_file,false) then do_nothing; +firm_up_the_line; +if end_line_char_inactive then decr(limit) +else buffer[limit]:=end_line_char; +first:=limit+1; loc:=start; +end + +@* \[30] Font metric data. +\TeX\ gets its knowledge about fonts from font metric files, also called +\.{TFM} files; the `\.T' in `\.{TFM}' stands for \TeX, +but other programs know about them too. +@:TFM files}{\.{TFM} files@> +@^font metric files@> + +The information in a \.{TFM} file appears in a sequence of 8-bit bytes. +Since the number of bytes is always a multiple of 4, we could +also regard the file as a sequence of 32-bit words, but \TeX\ uses the +byte interpretation. The format of \.{TFM} files was designed by +Lyle Ramshaw in 1980. The intent is to convey a lot of different kinds +@^Ramshaw, Lyle Harold@> +of information in a compact but useful form. + +@<Glob...@>= +@!tfm_file:byte_file; + +@ The first 24 bytes (6 words) of a \.{TFM} file contain twelve 16-bit +integers that give the lengths of the various subsequent portions +of the file. These twelve integers are, in order: +$$\vbox{\halign{\hfil#&$\null=\null$#\hfil\cr +|lf|&length of the entire file, in words;\cr +|lh|&length of the header data, in words;\cr +|bc|&smallest character code in the font;\cr +|ec|&largest character code in the font;\cr +|nw|&number of words in the width table;\cr +|nh|&number of words in the height table;\cr +|nd|&number of words in the depth table;\cr +|ni|&number of words in the italic correction table;\cr +|nl|&number of words in the lig/kern table;\cr +|nk|&number of words in the kern table;\cr +|ne|&number of words in the extensible character table;\cr +|np|&number of font parameter words.\cr}}$$ +They are all nonnegative and less than $2^{15}$. We must have |bc-1<=ec<=255|, +and +$$\hbox{|lf=6+lh+(ec-bc+1)+nw+nh+nd+ni+nl+nk+ne+np|.}$$ +Note that a font may contain as many as 256 characters (if |bc=0| and |ec=255|), +and as few as 0 characters (if |bc=ec+1|). + +Incidentally, when two or more 8-bit bytes are combined to form an integer of +16 or more bits, the most significant bytes appear first in the file. +This is called BigEndian order. +@!@^BigEndian order@> + +@ The rest of the \.{TFM} file may be regarded as a sequence of ten data +arrays having the informal specification +$$\def\arr$[#1]#2${\&{array} $[#1]$ \&{of} #2} +\vbox{\halign{\hfil\\{#}&$\,:\,$\arr#\hfil\cr +header&|[0..lh-1]@t\\{stuff}@>|\cr +char\_info&|[bc..ec]char_info_word|\cr +width&|[0..nw-1]fix_word|\cr +height&|[0..nh-1]fix_word|\cr +depth&|[0..nd-1]fix_word|\cr +italic&|[0..ni-1]fix_word|\cr +lig\_kern&|[0..nl-1]lig_kern_command|\cr +kern&|[0..nk-1]fix_word|\cr +exten&|[0..ne-1]extensible_recipe|\cr +param&|[1..np]fix_word|\cr}}$$ +The most important data type used here is a |@!fix_word|, which is +a 32-bit representation of a binary fraction. A |fix_word| is a signed +quantity, with the two's complement of the entire word used to represent +negation. Of the 32 bits in a |fix_word|, exactly 12 are to the left of the +binary point; thus, the largest |fix_word| value is $2048-2^{-20}$, and +the smallest is $-2048$. We will see below, however, that all but two of +the |fix_word| values must lie between $-16$ and $+16$. + +@ The first data array is a block of header information, which contains +general facts about the font. The header must contain at least two words, +|header[0]| and |header[1]|, whose meaning is explained below. +Additional header information of use to other software routines might +also be included, but \TeX82 does not need to know about such details. +For example, 16 more words of header information are in use at the Xerox +Palo Alto Research Center; the first ten specify the character coding +scheme used (e.g., `\.{XEROX text}' or `\.{TeX math symbols}'), the next five +give the font identifier (e.g., `\.{HELVETICA}' or `\.{CMSY}'), and the +last gives the ``face byte.'' The program that converts \.{DVI} files +to Xerox printing format gets this information by looking at the \.{TFM} +file, which it needs to read anyway because of other information that +is not explicitly repeated in \.{DVI}~format. + +\yskip\hang|header[0]| is a 32-bit check sum that \TeX\ will copy into +the \.{DVI} output file. Later on when the \.{DVI} file is printed, +possibly on another computer, the actual font that gets used is supposed +to have a check sum that agrees with the one in the \.{TFM} file used by +\TeX. In this way, users will be warned about potential incompatibilities. +(However, if the check sum is zero in either the font file or the \.{TFM} +file, no check is made.) The actual relation between this check sum and +the rest of the \.{TFM} file is not important; the check sum is simply an +identification number with the property that incompatible fonts almost +always have distinct check sums. +@^check sum@> + +\yskip\hang|header[1]| is a |fix_word| containing the design size of +the font, in units of \TeX\ points. This number must be at least 1.0; it is +fairly arbitrary, but usually the design size is 10.0 for a ``10 point'' +font, i.e., a font that was designed to look best at a 10-point size, +whatever that really means. When a \TeX\ user asks for a font +`\.{at} $\delta$ \.{pt}', the effect is to override the design size +and replace it by $\delta$, and to multiply the $x$ and~$y$ coordinates +of the points in the font image by a factor of $\delta$ divided by the +design size. {\sl All other dimensions in the\/ \.{TFM} file are +|fix_word|\kern-1pt\ numbers in design-size units}, with the exception of +|param[1]| (which denotes the slant ratio). Thus, for example, the value +of |param[6]|, which defines the \.{em} unit, is often the |fix_word| value +$2^{20}=1.0$, since many fonts have a design size equal to one em. +The other dimensions must be less than 16 design-size units in absolute +value; thus, |header[1]| and |param[1]| are the only |fix_word| +entries in the whole \.{TFM} file whose first byte might be something +besides 0 or 255. + +@ Next comes the |char_info| array, which contains one |@!char_info_word| +per character. Each word in this part of the file contains six fields +packed into four bytes as follows. + +\yskip\hang first byte: |@!width_index| (8 bits)\par +\hang second byte: |@!height_index| (4 bits) times 16, plus |@!depth_index| + (4~bits)\par +\hang third byte: |@!italic_index| (6 bits) times 4, plus |@!tag| + (2~bits)\par +\hang fourth byte: |@!remainder| (8 bits)\par +\yskip\noindent +The actual width of a character is \\{width}|[width_index]|, in design-size +units; this is a device for compressing information, since many characters +have the same width. Since it is quite common for many characters +to have the same height, depth, or italic correction, the \.{TFM} format +imposes a limit of 16 different heights, 16 different depths, and +64 different italic corrections. + +@!@^italic correction@> +The italic correction of a character has two different uses. +(a)~In ordinary text, the italic correction is added to the width only if +the \TeX\ user specifies `\.{\\/}' after the character. +(b)~In math formulas, the italic correction is always added to the width, +except with respect to the positioning of subscripts. + +Incidentally, the relation $\\{width}[0]=\\{height}[0]=\\{depth}[0]= +\\{italic}[0]=0$ should always hold, so that an index of zero implies a +value of zero. The |width_index| should never be zero unless the +character does not exist in the font, since a character is valid if and +only if it lies between |bc| and |ec| and has a nonzero |width_index|. + +@ The |tag| field in a |char_info_word| has four values that explain how to +interpret the |remainder| field. + +\yskip\hangg|tag=0| (|no_tag|) means that |remainder| is unused.\par +\hangg|tag=1| (|lig_tag|) means that this character has a ligature/kerning +program starting at position |remainder| in the |lig_kern| array.\par +\hangg|tag=2| (|list_tag|) means that this character is part of a chain of +characters of ascending sizes, and not the largest in the chain. The +|remainder| field gives the character code of the next larger character.\par +\hangg|tag=3| (|ext_tag|) means that this character code represents an +extensible character, i.e., a character that is built up of smaller pieces +so that it can be made arbitrarily large. The pieces are specified in +|@!exten[remainder]|.\par +\yskip\noindent +Characters with |tag=2| and |tag=3| are treated as characters with |tag=0| +unless they are used in special circumstances in math formulas. For example, +the \.{\\sum} operation looks for a |list_tag|, and the \.{\\left} +operation looks for both |list_tag| and |ext_tag|. + +@d no_tag=0 {vanilla character} +@d lig_tag=1 {character has a ligature/kerning program} +@d list_tag=2 {character has a successor in a charlist} +@d ext_tag=3 {character is extensible} + +@ The |lig_kern| array contains instructions in a simple programming language +that explains what to do for special letter pairs. Each word in this array is a +|@!lig_kern_command| of four bytes. + +\yskip\hang first byte: |skip_byte|, indicates that this is the final program + step if the byte is 128 or more, otherwise the next step is obtained by + skipping this number of intervening steps.\par +\hang second byte: |next_char|, ``if |next_char| follows the current character, + then perform the operation and stop, otherwise continue.''\par +\hang third byte: |op_byte|, indicates a ligature step if less than~128, + a kern step otherwise.\par +\hang fourth byte: |remainder|.\par +\yskip\noindent +In a kern step, an +additional space equal to |kern[256*(op_byte-128)+remainder]| is inserted +between the current character and |next_char|. This amount is +often negative, so that the characters are brought closer together +by kerning; but it might be positive. + +There are eight kinds of ligature steps, having |op_byte| codes $4a+2b+c$ where +$0\le a\le b+c$ and $0\le b,c\le1$. The character whose code is +|remainder| is inserted between the current character and |next_char|; +then the current character is deleted if $b=0$, and |next_char| is +deleted if $c=0$; then we pass over $a$~characters to reach the next +current character (which may have a ligature/kerning program of its own). + +If the very first instruction of the |lig_kern| array has |skip_byte=255|, +the |next_char| byte is the so-called right boundary character of this font; +the value of |next_char| need not lie between |bc| and~|ec|. +If the very last instruction of the |lig_kern| array has |skip_byte=255|, +there is a special ligature/kerning program for a left boundary character, +beginning at location |256*op_byte+remainder|. +The interpretation is that \TeX\ puts implicit boundary characters +before and after each consecutive string of characters from the same font. +These implicit characters do not appear in the output, but they can affect +ligatures and kerning. + +If the very first instruction of a character's |lig_kern| program has +|skip_byte>128|, the program actually begins in location +|256*op_byte+remainder|. This feature allows access to large |lig_kern| +arrays, because the first instruction must otherwise +appear in a location |<=255|. + +Any instruction with |skip_byte>128| in the |lig_kern| array must satisfy +the condition +$$\hbox{|256*op_byte+remainder<nl|.}$$ +If such an instruction is encountered during +normal program execution, it denotes an unconditional halt; no ligature +or kerning command is performed. + +@d stop_flag==qi(128) {value indicating `\.{STOP}' in a lig/kern program} +@d kern_flag==qi(128) {op code for a kern step} +@d skip_byte(#)==#.b0 +@d next_char(#)==#.b1 +@d op_byte(#)==#.b2 +@d rem_byte(#)==#.b3 + +@ Extensible characters are specified by an |@!extensible_recipe|, which +consists of four bytes called |@!top|, |@!mid|, |@!bot|, and |@!rep| (in this +order). These bytes are the character codes of individual pieces used to +build up a large symbol. If |top|, |mid|, or |bot| are zero, they are not +present in the built-up result. For example, an extensible vertical line is +like an extensible bracket, except that the top and bottom pieces are missing. + +Let $T$, $M$, $B$, and $R$ denote the respective pieces, or an empty box +if the piece isn't present. Then the extensible characters have the form +$TR^kMR^kB$ from top to bottom, for some |k>=0|, unless $M$ is absent; +in the latter case we can have $TR^kB$ for both even and odd values of~|k|. +The width of the extensible character is the width of $R$; and the +height-plus-depth is the sum of the individual height-plus-depths of the +components used, since the pieces are butted together in a vertical list. + +@d ext_top(#)==#.b0 {|top| piece in a recipe} +@d ext_mid(#)==#.b1 {|mid| piece in a recipe} +@d ext_bot(#)==#.b2 {|bot| piece in a recipe} +@d ext_rep(#)==#.b3 {|rep| piece in a recipe} + +@ The final portion of a \.{TFM} file is the |param| array, which is another +sequence of |fix_word| values. + +\yskip\hang|param[1]=slant| is the amount of italic slant, which is used +to help position accents. For example, |slant=.25| means that when you go +up one unit, you also go .25 units to the right. The |slant| is a pure +number; it's the only |fix_word| other than the design size itself that is +not scaled by the design size. + +\hang|param[2]=space| is the normal spacing between words in text. +Note that character |" "| in the font need not have anything to do with +blank spaces. + +\hang|param[3]=space_stretch| is the amount of glue stretching between words. + +\hang|param[4]=space_shrink| is the amount of glue shrinking between words. + +\hang|param[5]=x_height| is the size of one ex in the font; it is also +the height of letters for which accents don't have to be raised or lowered. + +\hang|param[6]=quad| is the size of one em in the font. + +\hang|param[7]=extra_space| is the amount added to |param[2]| at the +ends of sentences. + +\yskip\noindent +If fewer than seven parameters are present, \TeX\ sets the missing parameters +to zero. Fonts used for math symbols are required to have +additional parameter information, which is explained later. + +@d slant_code=1 +@d space_code=2 +@d space_stretch_code=3 +@d space_shrink_code=4 +@d x_height_code=5 +@d quad_code=6 +@d extra_space_code=7 + +@ So that is what \.{TFM} files hold. Since \TeX\ has to absorb such information +about lots of fonts, it stores most of the data in a large array called +|font_info|. Each item of |font_info| is a |memory_word|; the |fix_word| +data gets converted into |scaled| entries, while everything else goes into +words of type |four_quarters|. + +When the user defines \.{\\font\\f}, say, \TeX\ assigns an internal number +to the user's font~\.{\\f}. Adding this number to |font_id_base| gives the +|eqtb| location of a ``frozen'' control sequence that will always select +the font. + +@<Types...@>= +@!internal_font_number=font_base..font_max; {|font| in a |char_node|} +@!font_index=0..font_mem_size; {index into |font_info|} + +@ Here now is the (rather formidable) array of font arrays. + +@d non_char==qi(256) {a |halfword| code that can't match a real character} +@d non_address=0 {a spurious |bchar_label|} + +@<Glob...@>= +@!font_info:array[font_index] of memory_word; + {the big collection of font data} +@!fmem_ptr:font_index; {first unused word of |font_info|} +@!font_ptr:internal_font_number; {largest internal font number in use} +@!font_check:array[internal_font_number] of four_quarters; {check sum} +@!font_size:array[internal_font_number] of scaled; {``at'' size} +@!font_dsize:array[internal_font_number] of scaled; {``design'' size} +@!font_params:array[internal_font_number] of font_index; {how many font + parameters are present} +@!font_name:array[internal_font_number] of str_number; {name of the font} +@!font_area:array[internal_font_number] of str_number; {area of the font} +@!font_bc:array[internal_font_number] of eight_bits; + {beginning (smallest) character code} +@!font_ec:array[internal_font_number] of eight_bits; + {ending (largest) character code} +@!font_glue:array[internal_font_number] of pointer; + {glue specification for interword space, |null| if not allocated} +@!font_used:array[internal_font_number] of boolean; + {has a character from this font actually appeared in the output?} +@!hyphen_char:array[internal_font_number] of integer; + {current \.{\\hyphenchar} values} +@!skew_char:array[internal_font_number] of integer; + {current \.{\\skewchar} values} +@!bchar_label:array[internal_font_number] of font_index; + {start of |lig_kern| program for left boundary character, + |non_address| if there is none} +@!font_bchar:array[internal_font_number] of min_quarterword..non_char; + {right boundary character, |non_char| if there is none} +@!font_false_bchar:array[internal_font_number] of min_quarterword..non_char; + {|font_bchar| if it doesn't exist in the font, otherwise |non_char|} + +@ Besides the arrays just enumerated, we have directory arrays that make it +easy to get at the individual entries in |font_info|. For example, the +|char_info| data for character |c| in font |f| will be in +|font_info[char_base[f]+c].qqqq|; and if |w| is the |width_index| +part of this word (the |b0| field), the width of the character is +|font_info[width_base[f]+w].sc|. (These formulas assume that +|min_quarterword| has already been added to |c| and to |w|, since \TeX\ +stores its quarterwords that way.) + +@<Glob...@>= +@!char_base:array[internal_font_number] of integer; + {base addresses for |char_info|} +@!width_base:array[internal_font_number] of integer; + {base addresses for widths} +@!height_base:array[internal_font_number] of integer; + {base addresses for heights} +@!depth_base:array[internal_font_number] of integer; + {base addresses for depths} +@!italic_base:array[internal_font_number] of integer; + {base addresses for italic corrections} +@!lig_kern_base:array[internal_font_number] of integer; + {base addresses for ligature/kerning programs} +@!kern_base:array[internal_font_number] of integer; + {base addresses for kerns} +@!exten_base:array[internal_font_number] of integer; + {base addresses for extensible recipes} +@!param_base:array[internal_font_number] of integer; + {base addresses for font parameters} + +@ @<Set init...@>= +for k:=font_base to font_max do font_used[k]:=false; + +@ \TeX\ always knows at least one font, namely the null font. It has no +characters, and its seven parameters are all equal to zero. + +@<Initialize table...@>= +font_ptr:=null_font; fmem_ptr:=7; +font_name[null_font]:="nullfont"; font_area[null_font]:=""; +hyphen_char[null_font]:="-"; skew_char[null_font]:=-1; +bchar_label[null_font]:=non_address; +font_bchar[null_font]:=non_char; font_false_bchar[null_font]:=non_char; +font_bc[null_font]:=1; font_ec[null_font]:=0; +font_size[null_font]:=0; font_dsize[null_font]:=0; +char_base[null_font]:=0; width_base[null_font]:=0; +height_base[null_font]:=0; depth_base[null_font]:=0; +italic_base[null_font]:=0; lig_kern_base[null_font]:=0; +kern_base[null_font]:=0; exten_base[null_font]:=0; +font_glue[null_font]:=null; font_params[null_font]:=7; +param_base[null_font]:=-1; +for k:=0 to 6 do font_info[k].sc:=0; + +@ @<Put each...@>= +primitive("nullfont",set_font,null_font); +@!@:null_font_}{\.{\\nullfont} primitive@> +text(frozen_null_font):="nullfont"; eqtb[frozen_null_font]:=eqtb[cur_val]; + +@ Of course we want to define macros that suppress the detail of how font +information is actually packed, so that we don't have to write things like +$$\hbox{|font_info[width_base[f]+font_info[char_base[f]+c].qqqq.b0].sc|}$$ +too often. The \.{WEB} definitions here make |char_info(f)(c)| the +|four_quarters| word of font information corresponding to character +|c| of font |f|. If |q| is such a word, |char_width(f)(q)| will be +the character's width; hence the long formula above is at least +abbreviated to +$$\hbox{|char_width(f)(char_info(f)(c))|.}$$ +Usually, of course, we will fetch |q| first and look at several of its +fields at the same time. + +The italic correction of a character will be denoted by +|char_italic(f)(q)|, so it is analogous to |char_width|. But we will get +at the height and depth in a slightly different way, since we usually want +to compute both height and depth if we want either one. The value of +|height_depth(q)| will be the 8-bit quantity +$$b=|height_index|\times16+|depth_index|,$$ and if |b| is such a byte we +will write |char_height(f)(b)| and |char_depth(f)(b)| for the height and +depth of the character |c| for which |q=char_info(f)(c)|. Got that? + +The tag field will be called |char_tag(q)|; the remainder byte will be +called |rem_byte(q)|, using a macro that we have already defined above. + +Access to a character's |width|, |height|, |depth|, and |tag| fields is +part of \TeX's inner loop, so we want these macros to produce code that is +as fast as possible under the circumstances. +@^inner loop@> + +@d char_info_end(#)==#].qqqq +@d char_info(#)==font_info[char_base[#]+char_info_end +@d char_width_end(#)==#.b0].sc +@d char_width(#)==font_info[width_base[#]+char_width_end +@d char_exists(#)==(#.b0>min_quarterword) +@d char_italic_end(#)==(qo(#.b2)) div 4].sc +@d char_italic(#)==font_info[italic_base[#]+char_italic_end +@d height_depth(#)==qo(#.b1) +@d char_height_end(#)==(#) div 16].sc +@d char_height(#)==font_info[height_base[#]+char_height_end +@d char_depth_end(#)==(#) mod 16].sc +@d char_depth(#)==font_info[depth_base[#]+char_depth_end +@d char_tag(#)==((qo(#.b2)) mod 4) + +@ The global variable |null_character| is set up to be a word of +|char_info| for a character that doesn't exist. Such a word provides a +convenient way to deal with erroneous situations. + +@<Glob...@>= +@!null_character:four_quarters; {nonexistent character information} + +@ @<Set init...@>= +null_character.b0:=min_quarterword; null_character.b1:=min_quarterword; +null_character.b2:=min_quarterword; null_character.b3:=min_quarterword; + +@ Here are some macros that help process ligatures and kerns. +We write |char_kern(f)(j)| to find the amount of kerning specified by +kerning command~|j| in font~|f|. If |j| is the |char_info| for a character +with a ligature/kern program, the first instruction of that program is either +|i=font_info[lig_kern_start(f)(j)]| or |font_info[lig_kern_restart(f)(i)]|, +depending on whether or not |skip_byte(i)<=stop_flag|. + +The constant |kern_base_offset| should be simplified, for \PASCAL\ compilers +that do not do local optimization. +@^system dependencies@> + +@d char_kern_end(#)==256*op_byte(#)+rem_byte(#)].sc +@d char_kern(#)==font_info[kern_base[#]+char_kern_end +@d kern_base_offset==256*(128+min_quarterword) +@d lig_kern_start(#)==lig_kern_base[#]+rem_byte {beginning of lig/kern program} +@d lig_kern_restart_end(#)==256*op_byte(#)+rem_byte(#)+32768-kern_base_offset +@d lig_kern_restart(#)==lig_kern_base[#]+lig_kern_restart_end + +@ Font parameters are referred to as |slant(f)|, |space(f)|, etc. + +@d param_end(#)==param_base[#]].sc +@d param(#)==font_info[#+param_end +@d slant==param(slant_code) {slant to the right, per unit distance upward} +@d space==param(space_code) {normal space between words} +@d space_stretch==param(space_stretch_code) {stretch between words} +@d space_shrink==param(space_shrink_code) {shrink between words} +@d x_height==param(x_height_code) {one ex} +@d quad==param(quad_code) {one em} +@d extra_space==param(extra_space_code) {additional space at end of sentence} + +@<The em width for |cur_font|@>=quad(cur_font) + +@ @<The x-height for |cur_font|@>=x_height(cur_font) + +@ \TeX\ checks the information of a \.{TFM} file for validity as the +file is being read in, so that no further checks will be needed when +typesetting is going on. The somewhat tedious subroutine that does this +is called |read_font_info|. It has four parameters: the user font +identifier~|u|, the file name and area strings |nom| and |aire|, and the +``at'' size~|s|. If |s|~is negative, it's the negative of a scale factor +to be applied to the design size; |s=-1000| is the normal case. +Otherwise |s| will be substituted for the design size; in this +case, |s| must be positive and less than $2048\rm\,pt$ +(i.e., it must be less than $2^{27}$ when considered as an integer). + +The subroutine opens and closes a global file variable called |tfm_file|. +It returns the value of the internal font number that was just loaded. +If an error is detected, an error message is issued and no font +information is stored; |null_font| is returned in this case. + +@d bad_tfm=11 {label for |read_font_info|} +@d abort==goto bad_tfm {do this when the \.{TFM} data is wrong} + +@p function read_font_info(@!u:pointer;@!nom,@!aire:str_number; + @!s:scaled):internal_font_number; {input a \.{TFM} file} +label done,bad_tfm,not_found; +var k:font_index; {index into |font_info|} +@!file_opened:boolean; {was |tfm_file| successfully opened?} +@!lf,@!lh,@!bc,@!ec,@!nw,@!nh,@!nd,@!ni,@!nl,@!nk,@!ne,@!np:halfword; + {sizes of subfiles} +@!f:internal_font_number; {the new font's number} +@!g:internal_font_number; {the number to return} +@!a,@!b,@!c,@!d:eight_bits; {byte variables} +@!qw:four_quarters;@!sw:scaled; {accumulators} +@!bch_label:integer; {left boundary start location, or infinity} +@!bchar:0..256; {right boundary character, or 256} +@!z:scaled; {the design size or the ``at'' size} +@!alpha:integer;@!beta:1..16; + {auxiliary quantities used in fixed-point multiplication} +begin g:=null_font;@/ +@<Read and check the font data; |abort| if the \.{TFM} file is + malformed; if there's no room for this font, say so and |goto + done|; otherwise |incr(font_ptr)| and |goto done|@>; +bad_tfm: @<Report that the font won't be loaded@>; +done: if file_opened then b_close(tfm_file); +read_font_info:=g; +end; + +@ There are programs called \.{TFtoPL} and \.{PLtoTF} that convert +between the \.{TFM} format and a symbolic property-list format +that can be easily edited. These programs contain extensive +diagnostic information, so \TeX\ does not have to bother giving +precise details about why it rejects a particular \.{TFM} file. +@.TFtoPL@> @.PLtoTF@> + +@d start_font_error_message==print_err("Font "); sprint_cs(u); + print_char("="); print_file_name(nom,aire,""); + if s>=0 then + begin print(" at "); print_scaled(s); print("pt"); + end + else if s<>-1000 then + begin print(" scaled "); print_int(-s); + end + +@<Report that the font won't be loaded@>= +start_font_error_message; +@.Font x=xx not loadable...@> +if file_opened then print(" not loadable: Bad metric (TFM) file") +else print(" not loadable: Metric (TFM) file not found"); +help5("I wasn't able to read the size data for this font,")@/ +("so I will ignore the font specification.")@/ +("[Wizards can fix TFM files using TFtoPL/PLtoTF.]")@/ +("You might try inserting a different font spec;")@/ +("e.g., type `I\font<same font id>=<substitute font name>'."); +error + +@ @<Read and check...@>= +@<Open |tfm_file| for input@>; +@<Read the {\.{TFM}} size fields@>; +@<Use size fields to allocate font information@>; +@<Read the {\.{TFM}} header@>; +@<Read character data@>; +@<Read box dimensions@>; +@<Read ligature/kern program@>; +@<Read extensible character recipes@>; +@<Read font parameters@>; +@<Make final adjustments and |goto done|@> + +@ @<Open |tfm_file| for input@>= +file_opened:=false; +if aire="" then pack_file_name(nom,TEX_font_area,".tfm") +else pack_file_name(nom,aire,".tfm"); +if not b_open_in(tfm_file) then abort; +file_opened:=true + +@ Note: A malformed \.{TFM} file might be shorter than it claims to be; +thus |eof(tfm_file)| might be true when |read_font_info| refers to +|tfm_file^| or when it says |get(tfm_file)|. If such circumstances +cause system error messages, you will have to defeat them somehow, +for example by defining |fget| to be `\ignorespaces|begin get(tfm_file);| +|if eof(tfm_file) then abort; end|\unskip'. +@^system dependencies@> + +@d fget==get(tfm_file) +@d fbyte==tfm_file^ +@d read_sixteen(#)==begin #:=fbyte; + if #>127 then abort; + fget; #:=#*@'400+fbyte; + end +@d store_four_quarters(#)==begin fget; a:=fbyte; qw.b0:=qi(a); + fget; b:=fbyte; qw.b1:=qi(b); + fget; c:=fbyte; qw.b2:=qi(c); + fget; d:=fbyte; qw.b3:=qi(d); + #:=qw; + end + +@ @<Read the {\.{TFM}} size fields@>= +begin read_sixteen(lf); +fget; read_sixteen(lh); +fget; read_sixteen(bc); +fget; read_sixteen(ec); +if (bc>ec+1)or(ec>255) then abort; +if bc>255 then {|bc=256| and |ec=255|} + begin bc:=1; ec:=0; + end; +fget; read_sixteen(nw); +fget; read_sixteen(nh); +fget; read_sixteen(nd); +fget; read_sixteen(ni); +fget; read_sixteen(nl); +fget; read_sixteen(nk); +fget; read_sixteen(ne); +fget; read_sixteen(np); +if lf<>6+lh+(ec-bc+1)+nw+nh+nd+ni+nl+nk+ne+np then abort; +end + +@ The preliminary settings of the index-offset variables |char_base|, +|width_base|, |lig_kern_base|, |kern_base|, and |exten_base| will be +corrected later by subtracting |min_quarterword| from them; and we will +subtract 1 from |param_base| too. It's best to forget about such anomalies +until later. + +@<Use size fields to allocate font information@>= +lf:=lf-6-lh; {|lf| words should be loaded into |font_info|} +if np<7 then lf:=lf+7-np; {at least seven parameters will appear} +if (font_ptr=font_max)or(fmem_ptr+lf>font_mem_size) then + @<Apologize for not loading the font, |goto done|@>; +f:=font_ptr+1; +char_base[f]:=fmem_ptr-bc; +width_base[f]:=char_base[f]+ec+1; +height_base[f]:=width_base[f]+nw; +depth_base[f]:=height_base[f]+nh; +italic_base[f]:=depth_base[f]+nd; +lig_kern_base[f]:=italic_base[f]+ni; +kern_base[f]:=lig_kern_base[f]+nl-kern_base_offset; +exten_base[f]:=kern_base[f]+kern_base_offset+nk; +param_base[f]:=exten_base[f]+ne + +@ @<Apologize for not loading...@>= +begin start_font_error_message; +print(" not loaded: Not enough room left"); +@.Font x=xx not loaded...@> +help4("I'm afraid I won't be able to make use of this font,")@/ +("because my memory for character-size data is too small.")@/ +("If you're really stuck, ask a wizard to enlarge me.")@/ +("Or maybe try `I\font<same font id>=<name of loaded font>'."); +error; goto done; +end + +@ Only the first two words of the header are needed by \TeX82. + +@<Read the {\.{TFM}} header@>= +begin if lh<2 then abort; +store_four_quarters(font_check[f]); +fget; read_sixteen(z); {this rejects a negative design size} +fget; z:=z*@'400+fbyte; fget; z:=(z*@'20)+(fbyte div@'20); +if z<unity then abort; +while lh>2 do + begin fget;fget;fget;fget;decr(lh); {ignore the rest of the header} + end; +font_dsize[f]:=z; +if s<>-1000 then + if s>=0 then z:=s + else z:=xn_over_d(z,-s,1000); +font_size[f]:=z; +end + +@ @<Read character data@>= +for k:=fmem_ptr to width_base[f]-1 do + begin store_four_quarters(font_info[k].qqqq); + if (a>=nw)or(b div @'20>=nh)or(b mod @'20>=nd)or + (c div 4>=ni) then abort; + case c mod 4 of + lig_tag: if d>=nl then abort; + ext_tag: if d>=ne then abort; + list_tag: @<Check for charlist cycle@>; + othercases do_nothing {|no_tag|} + endcases; + end + +@ We want to make sure that there is no cycle of characters linked together +by |list_tag| entries, since such a cycle would get \TeX\ into an endless +loop. If such a cycle exists, the routine here detects it when processing +the largest character code in the cycle. + +@d check_byte_range(#)==begin if (#<bc)or(#>ec) then abort@+end +@d current_character_being_worked_on==k+bc-fmem_ptr + +@<Check for charlist cycle@>= +begin check_byte_range(d); +while d<current_character_being_worked_on do + begin qw:=char_info(f)(d); + {N.B.: not |qi(d)|, since |char_base[f]| hasn't been adjusted yet} + if char_tag(qw)<>list_tag then goto not_found; + d:=qo(rem_byte(qw)); {next character on the list} + end; +if d=current_character_being_worked_on then abort; {yes, there's a cycle} +not_found:end + +@ A |fix_word| whose four bytes are $(a,b,c,d)$ from left to right represents +the number +$$x=\left\{\vcenter{\halign{$#$,\hfil\qquad&if $#$\hfil\cr +b\cdot2^{-4}+c\cdot2^{-12}+d\cdot2^{-20}&a=0;\cr +-16+b\cdot2^{-4}+c\cdot2^{-12}+d\cdot2^{-20}&a=255.\cr}}\right.$$ +(No other choices of |a| are allowed, since the magnitude of a number in +design-size units must be less than 16.) We want to multiply this +quantity by the integer~|z|, which is known to be less than $2^{27}$. +If $|z|<2^{23}$, the individual multiplications $b\cdot z$, +$c\cdot z$, $d\cdot z$ cannot overflow; otherwise we will divide |z| by 2, +4, 8, or 16, to obtain a multiplier less than $2^{23}$, and we can +compensate for this later. If |z| has thereby been replaced by +$|z|^\prime=|z|/2^e$, let $\beta=2^{4-e}$; we shall compute +$$\lfloor(b+c\cdot2^{-8}+d\cdot2^{-16})\,z^\prime/\beta\rfloor$$ +if $a=0$, or the same quantity minus $\alpha=2^{4+e}z^\prime$ if $a=255$. +This calculation must be done exactly, in order to guarantee portability +of \TeX\ between computers. + +@d store_scaled(#)==begin fget; a:=fbyte; fget; b:=fbyte; + fget; c:=fbyte; fget; d:=fbyte;@/ + sw:=(((((d*z)div@'400)+(c*z))div@'400)+(b*z))div beta; + if a=0 then #:=sw@+else if a=255 then #:=sw-alpha@+else abort; + end + +@<Read box dimensions@>= +begin @<Replace |z| by $|z|^\prime$ and compute $\alpha,\beta$@>; +for k:=width_base[f] to lig_kern_base[f]-1 do + store_scaled(font_info[k].sc); +if font_info[width_base[f]].sc<>0 then abort; {\\{width}[0] must be zero} +if font_info[height_base[f]].sc<>0 then abort; {\\{height}[0] must be zero} +if font_info[depth_base[f]].sc<>0 then abort; {\\{depth}[0] must be zero} +if font_info[italic_base[f]].sc<>0 then abort; {\\{italic}[0] must be zero} +end + +@ @<Replace |z|...@>= +begin alpha:=16; +while z>=@'40000000 do + begin z:=z div 2; alpha:=alpha+alpha; + end; +beta:=256 div alpha; alpha:=alpha*z; +end + +@ @d check_existence(#)==@t@>@;@/ + begin check_byte_range(#); + qw:=char_info(f)(#); {N.B.: not |qi(#)|} + if not char_exists(qw) then abort; + end + +@<Read ligature/kern program@>= +bch_label:=@'77777; bchar:=256; +if nl>0 then + begin for k:=lig_kern_base[f] to kern_base[f]+kern_base_offset-1 do + begin store_four_quarters(font_info[k].qqqq); + if a>128 then + begin if 256*c+d>=nl then abort; + if a=255 then if k=lig_kern_base[f] then bchar:=b; + end + else begin if b<>bchar then check_existence(b); + if c<128 then check_existence(d) {check ligature} + else if 256*(c-128)+d>=nk then abort; {check kern} + if a<128 then if k-lig_kern_base[f]+a+1>=nl then abort; + end; + end; + if a=255 then bch_label:=256*c+d; + end; +for k:=kern_base[f]+kern_base_offset to exten_base[f]-1 do + store_scaled(font_info[k].sc); + +@ @<Read extensible character recipes@>= +for k:=exten_base[f] to param_base[f]-1 do + begin store_four_quarters(font_info[k].qqqq); + if a<>0 then check_existence(a); + if b<>0 then check_existence(b); + if c<>0 then check_existence(c); + check_existence(d); + end + +@ We check to see that the \.{TFM} file doesn't end prematurely; but +no error message is given for files having more than |lf| words. + +@<Read font parameters@>= +begin for k:=1 to np do + if k=1 then {the |slant| parameter is a pure number} + begin fget; sw:=fbyte; if sw>127 then sw:=sw-256; + fget; sw:=sw*@'400+fbyte; fget; sw:=sw*@'400+fbyte; + fget; font_info[param_base[f]].sc:= + (sw*@'20)+(fbyte div@'20); + end + else store_scaled(font_info[param_base[f]+k-1].sc); +if eof(tfm_file) then abort; +for k:=np+1 to 7 do font_info[param_base[f]+k-1].sc:=0; +end + +@ Now to wrap it up, we have checked all the necessary things about the \.{TFM} +file, and all we need to do is put the finishing touches on the data for +the new font. + +@d adjust(#)==#[f]:=qo(#[f]) + {correct for the excess |min_quarterword| that was added} + +@<Make final adjustments...@>= +if np>=7 then font_params[f]:=np@+else font_params[f]:=7; +hyphen_char[f]:=default_hyphen_char; skew_char[f]:=default_skew_char; +if bch_label<nl then bchar_label[f]:=bch_label+lig_kern_base[f] +else bchar_label[f]:=non_address; +font_bchar[f]:=qi(bchar); +font_false_bchar[f]:=qi(bchar); +if bchar<=ec then if bchar>=bc then + begin qw:=char_info(f)(bchar); {N.B.: not |qi(bchar)|} + if char_exists(qw) then font_false_bchar[f]:=non_char; + end; +font_name[f]:=nom; +font_area[f]:=aire; +font_bc[f]:=bc; font_ec[f]:=ec; font_glue[f]:=null; +adjust(char_base); adjust(width_base); adjust(lig_kern_base); +adjust(kern_base); adjust(exten_base); +decr(param_base[f]); +fmem_ptr:=fmem_ptr+lf; font_ptr:=f; g:=f; goto done + +@ Before we forget about the format of these tables, let's deal with two +of \TeX's basic scanning routines related to font information. + +@<Declare procedures that scan font-related stuff@>= +procedure scan_font_ident; +var f:internal_font_number; +@!m:halfword; +begin @<Get the next non-blank non-call...@>; +if cur_cmd=def_font then f:=cur_font +else if cur_cmd=set_font then f:=cur_chr +else if cur_cmd=def_family then + begin m:=cur_chr; scan_four_bit_int; f:=equiv(m+cur_val); + end +else begin print_err("Missing font identifier"); +@.Missing font identifier@> + help2("I was looking for a control sequence whose")@/ + ("current meaning has been defined by \font."); + back_error; f:=null_font; + end; +cur_val:=f; +end; + +@ The following routine is used to implement `\.{\\fontdimen} |n| |f|'. +The boolean parameter |writing| is set |true| if the calling program +intends to change the parameter value. + +@<Declare procedures that scan font-related stuff@>= +procedure find_font_dimen(@!writing:boolean); + {sets |cur_val| to |font_info| location} +var f:internal_font_number; +@!n:integer; {the parameter number} +begin scan_int; n:=cur_val; scan_font_ident; f:=cur_val; +if n<=0 then cur_val:=fmem_ptr +else begin if writing and(n<=space_shrink_code)and@| + (n>=space_code)and(font_glue[f]<>null) then + begin delete_glue_ref(font_glue[f]); + font_glue[f]:=null; + end; + if n>font_params[f] then + if f<font_ptr then cur_val:=fmem_ptr + else @<Increase the number of parameters in the last font@> + else cur_val:=n+param_base[f]; + end; +@<Issue an error message if |cur_val=fmem_ptr|@>; +end; + +@ @<Issue an error message if |cur_val=fmem_ptr|@>= +if cur_val=fmem_ptr then + begin print_err("Font "); print_esc(font_id_text(f)); + print(" has only "); print_int(font_params[f]); + print(" fontdimen parameters"); +@.Font x has only...@> + help2("To increase the number of font parameters, you must")@/ + ("use \fontdimen immediately after the \font is loaded."); + error; + end + +@ @<Increase the number of parameters...@>= +begin repeat if fmem_ptr=font_mem_size then + overflow("font memory",font_mem_size); +@:TeX capacity exceeded font memory}{\quad font memory@> +font_info[fmem_ptr].sc:=0; incr(fmem_ptr); incr(font_params[f]); +until n=font_params[f]; +cur_val:=fmem_ptr-1; {this equals |param_base[f]+font_params[f]|} +end + +@ When \TeX\ wants to typeset a character that doesn't exist, the +character node is not created; thus the output routine can assume +that characters exist when it sees them. The following procedure +prints a warning message unless the user has suppressed it. + +@p procedure char_warning(@!f:internal_font_number;@!c:eight_bits); +begin if tracing_lost_chars>0 then + begin begin_diagnostic; + print_nl("Missing character: There is no "); +@.Missing character@> + print_ASCII(c); print(" in font "); + slow_print(font_name[f]); print_char("!"); end_diagnostic(false); + end; +end; + +@ Here is a function that returns a pointer to a character node for a +given character in a given font. If that character doesn't exist, +|null| is returned instead. + +@p function new_character(@!f:internal_font_number;@!c:eight_bits):pointer; +label exit; +var p:pointer; {newly allocated node} +begin if font_bc[f]<=c then if font_ec[f]>=c then + if char_exists(char_info(f)(qi(c))) then + begin p:=get_avail; font(p):=f; character(p):=qi(c); + new_character:=p; return; + end; +char_warning(f,c); +new_character:=null; +exit:end; + +@* \[31] Device-independent file format. +The most important output produced by a run of \TeX\ is the ``device +independent'' (\.{DVI}) file that specifies where characters and rules +are to appear on printed pages. The form of these files was designed by +David R. Fuchs in 1979. Almost any reasonable typesetting device can be +@^Fuchs, David Raymond@> +@:DVI_files}{\.{DVI} files@> +driven by a program that takes \.{DVI} files as input, and dozens of such +\.{DVI}-to-whatever programs have been written. Thus, it is possible to +print the output of \TeX\ on many different kinds of equipment, using \TeX\ +as a device-independent ``front end.'' + +A \.{DVI} file is a stream of 8-bit bytes, which may be regarded as a +series of commands in a machine-like language. The first byte of each command +is the operation code, and this code is followed by zero or more bytes +that provide parameters to the command. The parameters themselves may consist +of several consecutive bytes; for example, the `|set_rule|' command has two +parameters, each of which is four bytes long. Parameters are usually +regarded as nonnegative integers; but four-byte-long parameters, +and shorter parameters that denote distances, can be +either positive or negative. Such parameters are given in two's complement +notation. For example, a two-byte-long distance parameter has a value between +$-2^{15}$ and $2^{15}-1$. As in \.{TFM} files, numbers that occupy +more than one byte position appear in BigEndian order. + +A \.{DVI} file consists of a ``preamble,'' followed by a sequence of one +or more ``pages,'' followed by a ``postamble.'' The preamble is simply a +|pre| command, with its parameters that define the dimensions used in the +file; this must come first. Each ``page'' consists of a |bop| command, +followed by any number of other commands that tell where characters are to +be placed on a physical page, followed by an |eop| command. The pages +appear in the order that \TeX\ generated them. If we ignore |nop| commands +and \\{fnt\_def} commands (which are allowed between any two commands in +the file), each |eop| command is immediately followed by a |bop| command, +or by a |post| command; in the latter case, there are no more pages in the +file, and the remaining bytes form the postamble. Further details about +the postamble will be explained later. + +Some parameters in \.{DVI} commands are ``pointers.'' These are four-byte +quantities that give the location number of some other byte in the file; +the first byte is number~0, then comes number~1, and so on. For example, +one of the parameters of a |bop| command points to the previous |bop|; +this makes it feasible to read the pages in backwards order, in case the +results are being directed to a device that stacks its output face up. +Suppose the preamble of a \.{DVI} file occupies bytes 0 to 99. Now if the +first page occupies bytes 100 to 999, say, and if the second +page occupies bytes 1000 to 1999, then the |bop| that starts in byte 1000 +points to 100 and the |bop| that starts in byte 2000 points to 1000. (The +very first |bop|, i.e., the one starting in byte 100, has a pointer of~$-1$.) + +@ The \.{DVI} format is intended to be both compact and easily interpreted +by a machine. Compactness is achieved by making most of the information +implicit instead of explicit. When a \.{DVI}-reading program reads the +commands for a page, it keeps track of several quantities: (a)~The current +font |f| is an integer; this value is changed only +by \\{fnt} and \\{fnt\_num} commands. (b)~The current position on the page +is given by two numbers called the horizontal and vertical coordinates, +|h| and |v|. Both coordinates are zero at the upper left corner of the page; +moving to the right corresponds to increasing the horizontal coordinate, and +moving down corresponds to increasing the vertical coordinate. Thus, the +coordinates are essentially Cartesian, except that vertical directions are +flipped; the Cartesian version of |(h,v)| would be |(h,-v)|. (c)~The +current spacing amounts are given by four numbers |w|, |x|, |y|, and |z|, +where |w| and~|x| are used for horizontal spacing and where |y| and~|z| +are used for vertical spacing. (d)~There is a stack containing +|(h,v,w,x,y,z)| values; the \.{DVI} commands |push| and |pop| are used to +change the current level of operation. Note that the current font~|f| is +not pushed and popped; the stack contains only information about +positioning. + +The values of |h|, |v|, |w|, |x|, |y|, and |z| are signed integers having up +to 32 bits, including the sign. Since they represent physical distances, +there is a small unit of measurement such that increasing |h| by~1 means +moving a certain tiny distance to the right. The actual unit of +measurement is variable, as explained below; \TeX\ sets things up so that +its \.{DVI} output is in sp units, i.e., scaled points, in agreement with +all the |scaled| dimensions in \TeX's data structures. + +@ Here is a list of all the commands that may appear in a \.{DVI} file. Each +command is specified by its symbolic name (e.g., |bop|), its opcode byte +(e.g., 139), and its parameters (if any). The parameters are followed +by a bracketed number telling how many bytes they occupy; for example, +`|p[4]|' means that parameter |p| is four bytes long. + +\yskip\hang|set_char_0| 0. Typeset character number~0 from font~|f| +such that the reference point of the character is at |(h,v)|. Then +increase |h| by the width of that character. Note that a character may +have zero or negative width, so one cannot be sure that |h| will advance +after this command; but |h| usually does increase. + +\yskip\hang\\{set\_char\_1} through \\{set\_char\_127} (opcodes 1 to 127). +Do the operations of |set_char_0|; but use the character whose number +matches the opcode, instead of character~0. + +\yskip\hang|set1| 128 |c[1]|. Same as |set_char_0|, except that character +number~|c| is typeset. \TeX82 uses this command for characters in the +range |128<=c<256|. + +\yskip\hang|@!set2| 129 |c[2]|. Same as |set1|, except that |c|~is two +bytes long, so it is in the range |0<=c<65536|. \TeX82 never uses this +command, but it should come in handy for extensions of \TeX\ that deal +with oriental languages. +@^oriental characters@>@^Chinese characters@>@^Japanese characters@> + +\yskip\hang|@!set3| 130 |c[3]|. Same as |set1|, except that |c|~is three +bytes long, so it can be as large as $2^{24}-1$. Not even the Chinese +language has this many characters, but this command might prove useful +in some yet unforeseen extension. + +\yskip\hang|@!set4| 131 |c[4]|. Same as |set1|, except that |c|~is four +bytes long. Imagine that. + +\yskip\hang|set_rule| 132 |a[4]| |b[4]|. Typeset a solid black rectangle +of height~|a| and width~|b|, with its bottom left corner at |(h,v)|. Then +set |h:=h+b|. If either |a<=0| or |b<=0|, nothing should be typeset. Note +that if |b<0|, the value of |h| will decrease even though nothing else happens. +See below for details about how to typeset rules so that consistency with +\MF\ is guaranteed. + +\yskip\hang|@!put1| 133 |c[1]|. Typeset character number~|c| from font~|f| +such that the reference point of the character is at |(h,v)|. (The `put' +commands are exactly like the `set' commands, except that they simply put out a +character or a rule without moving the reference point afterwards.) + +\yskip\hang|@!put2| 134 |c[2]|. Same as |set2|, except that |h| is not changed. + +\yskip\hang|@!put3| 135 |c[3]|. Same as |set3|, except that |h| is not changed. + +\yskip\hang|@!put4| 136 |c[4]|. Same as |set4|, except that |h| is not changed. + +\yskip\hang|put_rule| 137 |a[4]| |b[4]|. Same as |set_rule|, except that +|h| is not changed. + +\yskip\hang|nop| 138. No operation, do nothing. Any number of |nop|'s +may occur between \.{DVI} commands, but a |nop| cannot be inserted between +a command and its parameters or between two parameters. + +\yskip\hang|bop| 139 $c_0[4]$ $c_1[4]$ $\ldots$ $c_9[4]$ $p[4]$. Beginning +of a page: Set |(h,v,w,x,y,z):=(0,0,0,0,0,0)| and set the stack empty. Set +the current font |f| to an undefined value. The ten $c_i$ parameters hold +the values of \.{\\count0} $\ldots$ \.{\\count9} in \TeX\ at the time +\.{\\shipout} was invoked for this page; they can be used to identify +pages, if a user wants to print only part of a \.{DVI} file. The parameter +|p| points to the previous |bop| in the file; the first +|bop| has $p=-1$. + +\yskip\hang|eop| 140. End of page: Print what you have read since the +previous |bop|. At this point the stack should be empty. (The \.{DVI}-reading +programs that drive most output devices will have kept a buffer of the +material that appears on the page that has just ended. This material is +largely, but not entirely, in order by |v| coordinate and (for fixed |v|) by +|h|~coordinate; so it usually needs to be sorted into some order that is +appropriate for the device in question.) + +\yskip\hang|push| 141. Push the current values of |(h,v,w,x,y,z)| onto the +top of the stack; do not change any of these values. Note that |f| is +not pushed. + +\yskip\hang|pop| 142. Pop the top six values off of the stack and assign +them respectively to |(h,v,w,x,y,z)|. The number of pops should never +exceed the number of pushes, since it would be highly embarrassing if the +stack were empty at the time of a |pop| command. + +\yskip\hang|right1| 143 |b[1]|. Set |h:=h+b|, i.e., move right |b| units. +The parameter is a signed number in two's complement notation, |-128<=b<128|; +if |b<0|, the reference point moves left. + +\yskip\hang|right2| 144 |b[2]|. Same as |right1|, except that |b| is a +two-byte quantity in the range |-32768<=b<32768|. + +\yskip\hang|right3| 145 |b[3]|. Same as |right1|, except that |b| is a +three-byte quantity in the range |@t$-2^{23}$@><=b<@t$2^{23}$@>|. + +\yskip\hang|right4| 146 |b[4]|. Same as |right1|, except that |b| is a +four-byte quantity in the range |@t$-2^{31}$@><=b<@t$2^{31}$@>|. + +\yskip\hang|w0| 147. Set |h:=h+w|; i.e., move right |w| units. With luck, +this parameterless command will usually suffice, because the same kind of motion +will occur several times in succession; the following commands explain how +|w| gets particular values. + +\yskip\hang|w1| 148 |b[1]|. Set |w:=b| and |h:=h+b|. The value of |b| is a +signed quantity in two's complement notation, |-128<=b<128|. This command +changes the current |w|~spacing and moves right by |b|. + +\yskip\hang|@!w2| 149 |b[2]|. Same as |w1|, but |b| is two bytes long, +|-32768<=b<32768|. + +\yskip\hang|@!w3| 150 |b[3]|. Same as |w1|, but |b| is three bytes long, +|@t$-2^{23}$@><=b<@t$2^{23}$@>|. + +\yskip\hang|@!w4| 151 |b[4]|. Same as |w1|, but |b| is four bytes long, +|@t$-2^{31}$@><=b<@t$2^{31}$@>|. + +\yskip\hang|x0| 152. Set |h:=h+x|; i.e., move right |x| units. The `|x|' +commands are like the `|w|' commands except that they involve |x| instead +of |w|. + +\yskip\hang|x1| 153 |b[1]|. Set |x:=b| and |h:=h+b|. The value of |b| is a +signed quantity in two's complement notation, |-128<=b<128|. This command +changes the current |x|~spacing and moves right by |b|. + +\yskip\hang|@!x2| 154 |b[2]|. Same as |x1|, but |b| is two bytes long, +|-32768<=b<32768|. + +\yskip\hang|@!x3| 155 |b[3]|. Same as |x1|, but |b| is three bytes long, +|@t$-2^{23}$@><=b<@t$2^{23}$@>|. + +\yskip\hang|@!x4| 156 |b[4]|. Same as |x1|, but |b| is four bytes long, +|@t$-2^{31}$@><=b<@t$2^{31}$@>|. + +\yskip\hang|down1| 157 |a[1]|. Set |v:=v+a|, i.e., move down |a| units. +The parameter is a signed number in two's complement notation, |-128<=a<128|; +if |a<0|, the reference point moves up. + +\yskip\hang|@!down2| 158 |a[2]|. Same as |down1|, except that |a| is a +two-byte quantity in the range |-32768<=a<32768|. + +\yskip\hang|@!down3| 159 |a[3]|. Same as |down1|, except that |a| is a +three-byte quantity in the range |@t$-2^{23}$@><=a<@t$2^{23}$@>|. + +\yskip\hang|@!down4| 160 |a[4]|. Same as |down1|, except that |a| is a +four-byte quantity in the range |@t$-2^{31}$@><=a<@t$2^{31}$@>|. + +\yskip\hang|y0| 161. Set |v:=v+y|; i.e., move down |y| units. With luck, +this parameterless command will usually suffice, because the same kind of motion +will occur several times in succession; the following commands explain how +|y| gets particular values. + +\yskip\hang|y1| 162 |a[1]|. Set |y:=a| and |v:=v+a|. The value of |a| is a +signed quantity in two's complement notation, |-128<=a<128|. This command +changes the current |y|~spacing and moves down by |a|. + +\yskip\hang|@!y2| 163 |a[2]|. Same as |y1|, but |a| is two bytes long, +|-32768<=a<32768|. + +\yskip\hang|@!y3| 164 |a[3]|. Same as |y1|, but |a| is three bytes long, +|@t$-2^{23}$@><=a<@t$2^{23}$@>|. + +\yskip\hang|@!y4| 165 |a[4]|. Same as |y1|, but |a| is four bytes long, +|@t$-2^{31}$@><=a<@t$2^{31}$@>|. + +\yskip\hang|z0| 166. Set |v:=v+z|; i.e., move down |z| units. The `|z|' commands +are like the `|y|' commands except that they involve |z| instead of |y|. + +\yskip\hang|z1| 167 |a[1]|. Set |z:=a| and |v:=v+a|. The value of |a| is a +signed quantity in two's complement notation, |-128<=a<128|. This command +changes the current |z|~spacing and moves down by |a|. + +\yskip\hang|@!z2| 168 |a[2]|. Same as |z1|, but |a| is two bytes long, +|-32768<=a<32768|. + +\yskip\hang|@!z3| 169 |a[3]|. Same as |z1|, but |a| is three bytes long, +|@t$-2^{23}$@><=a<@t$2^{23}$@>|. + +\yskip\hang|@!z4| 170 |a[4]|. Same as |z1|, but |a| is four bytes long, +|@t$-2^{31}$@><=a<@t$2^{31}$@>|. + +\yskip\hang|fnt_num_0| 171. Set |f:=0|. Font 0 must previously have been +defined by a \\{fnt\_def} instruction, as explained below. + +\yskip\hang\\{fnt\_num\_1} through \\{fnt\_num\_63} (opcodes 172 to 234). Set +|f:=1|, \dots, \hbox{|f:=63|}, respectively. + +\yskip\hang|fnt1| 235 |k[1]|. Set |f:=k|. \TeX82 uses this command for font +numbers in the range |64<=k<256|. + +\yskip\hang|@!fnt2| 236 |k[2]|. Same as |fnt1|, except that |k|~is two +bytes long, so it is in the range |0<=k<65536|. \TeX82 never generates this +command, but large font numbers may prove useful for specifications of +color or texture, or they may be used for special fonts that have fixed +numbers in some external coding scheme. + +\yskip\hang|@!fnt3| 237 |k[3]|. Same as |fnt1|, except that |k|~is three +bytes long, so it can be as large as $2^{24}-1$. + +\yskip\hang|@!fnt4| 238 |k[4]|. Same as |fnt1|, except that |k|~is four +bytes long; this is for the really big font numbers (and for the negative ones). + +\yskip\hang|xxx1| 239 |k[1]| |x[k]|. This command is undefined in +general; it functions as a $(k+2)$-byte |nop| unless special \.{DVI}-reading +programs are being used. \TeX82 generates |xxx1| when a short enough +\.{\\special} appears, setting |k| to the number of bytes being sent. It +is recommended that |x| be a string having the form of a keyword followed +by possible parameters relevant to that keyword. + +\yskip\hang|@!xxx2| 240 |k[2]| |x[k]|. Like |xxx1|, but |0<=k<65536|. + +\yskip\hang|@!xxx3| 241 |k[3]| |x[k]|. Like |xxx1|, but |0<=k<@t$2^{24}$@>|. + +\yskip\hang|xxx4| 242 |k[4]| |x[k]|. Like |xxx1|, but |k| can be ridiculously +large. \TeX82 uses |xxx4| when sending a string of length 256 or more. + +\yskip\hang|fnt_def1| 243 |k[1]| |c[4]| |s[4]| |d[4]| |a[1]| |l[1]| |n[a+l]|. +Define font |k|, where |0<=k<256|; font definitions will be explained shortly. + +\yskip\hang|@!fnt_def2| 244 |k[2]| |c[4]| |s[4]| |d[4]| |a[1]| |l[1]| |n[a+l]|. +Define font |k|, where |0<=k<65536|. + +\yskip\hang|@!fnt_def3| 245 |k[3]| |c[4]| |s[4]| |d[4]| |a[1]| |l[1]| |n[a+l]|. +Define font |k|, where |0<=k<@t$2^{24}$@>|. + +\yskip\hang|@!fnt_def4| 246 |k[4]| |c[4]| |s[4]| |d[4]| |a[1]| |l[1]| |n[a+l]|. +Define font |k|, where |@t$-2^{31}$@><=k<@t$2^{31}$@>|. + +\yskip\hang|pre| 247 |i[1]| |num[4]| |den[4]| |mag[4]| |k[1]| |x[k]|. +Beginning of the preamble; this must come at the very beginning of the +file. Parameters |i|, |num|, |den|, |mag|, |k|, and |x| are explained below. + +\yskip\hang|post| 248. Beginning of the postamble, see below. + +\yskip\hang|post_post| 249. Ending of the postamble, see below. + +\yskip\noindent Commands 250--255 are undefined at the present time. + +@ @d set_char_0=0 {typeset character 0 and move right} +@d set1=128 {typeset a character and move right} +@d set_rule=132 {typeset a rule and move right} +@d put_rule=137 {typeset a rule} +@d nop=138 {no operation} +@d bop=139 {beginning of page} +@d eop=140 {ending of page} +@d push=141 {save the current positions} +@d pop=142 {restore previous positions} +@d right1=143 {move right} +@d w0=147 {move right by |w|} +@d w1=148 {move right and set |w|} +@d x0=152 {move right by |x|} +@d x1=153 {move right and set |x|} +@d down1=157 {move down} +@d y0=161 {move down by |y|} +@d y1=162 {move down and set |y|} +@d z0=166 {move down by |z|} +@d z1=167 {move down and set |z|} +@d fnt_num_0=171 {set current font to 0} +@d fnt1=235 {set current font} +@d xxx1=239 {extension to \.{DVI} primitives} +@d xxx4=242 {potentially long extension to \.{DVI} primitives} +@d fnt_def1=243 {define the meaning of a font number} +@d pre=247 {preamble} +@d post=248 {postamble beginning} +@d post_post=249 {postamble ending} + +@ The preamble contains basic information about the file as a whole. As +stated above, there are six parameters: +$$\hbox{|@!i[1]| |@!num[4]| |@!den[4]| |@!mag[4]| |@!k[1]| |@!x[k]|.}$$ +The |i| byte identifies \.{DVI} format; currently this byte is always set +to~2. (The value |i=3| is currently used for an extended format that +allows a mixture of right-to-left and left-to-right typesetting. +Some day we will set |i=4|, when \.{DVI} format makes another +incompatible change---perhaps in the year 2048.) + +The next two parameters, |num| and |den|, are positive integers that define +the units of measurement; they are the numerator and denominator of a +fraction by which all dimensions in the \.{DVI} file could be multiplied +in order to get lengths in units of $10^{-7}$ meters. Since $\rm 7227{pt} = +254{cm}$, and since \TeX\ works with scaled points where there are $2^{16}$ +sp in a point, \TeX\ sets +$|num|/|den|=(254\cdot10^5)/(7227\cdot2^{16})=25400000/473628672$. +@^sp@> + +The |mag| parameter is what \TeX\ calls \.{\\mag}, i.e., 1000 times the +desired magnification. The actual fraction by which dimensions are +multiplied is therefore $|mag|\cdot|num|/1000|den|$. Note that if a \TeX\ +source document does not call for any `\.{true}' dimensions, and if you +change it only by specifying a different \.{\\mag} setting, the \.{DVI} +file that \TeX\ creates will be completely unchanged except for the value +of |mag| in the preamble and postamble. (Fancy \.{DVI}-reading programs allow +users to override the |mag|~setting when a \.{DVI} file is being printed.) + +Finally, |k| and |x| allow the \.{DVI} writer to include a comment, which is not +interpreted further. The length of comment |x| is |k|, where |0<=k<256|. + +@d id_byte=2 {identifies the kind of \.{DVI} files described here} + +@ Font definitions for a given font number |k| contain further parameters +$$\hbox{|c[4]| |s[4]| |d[4]| |a[1]| |l[1]| |n[a+l]|.}$$ +The four-byte value |c| is the check sum that \TeX\ found in the \.{TFM} +file for this font; |c| should match the check sum of the font found by +programs that read this \.{DVI} file. +@^check sum@> + +Parameter |s| contains a fixed-point scale factor that is applied to +the character widths in font |k|; font dimensions in \.{TFM} files and +other font files are relative to this quantity, which is called the +``at size'' elsewhere in this documentation. The value of |s| is +always positive and less than $2^{27}$. It is given in the same units +as the other \.{DVI} dimensions, i.e., in sp when \TeX82 has made the +file. Parameter |d| is similar to |s|; it is the ``design size,'' and +(like~|s|) it is given in \.{DVI} units. Thus, font |k| is to be used +at $|mag|\cdot s/1000d$ times its normal size. + +The remaining part of a font definition gives the external name of the font, +which is an ASCII string of length |a+l|. The number |a| is the length +of the ``area'' or directory, and |l| is the length of the font name itself; +the standard local system font area is supposed to be used when |a=0|. +The |n| field contains the area in its first |a| bytes. + +Font definitions must appear before the first use of a particular font number. +Once font |k| is defined, it must not be defined again; however, we +shall see below that font definitions appear in the postamble as well as +in the pages, so in this sense each font number is defined exactly twice, +if at all. Like |nop| commands, font definitions can +appear before the first |bop|, or between an |eop| and a |bop|. + +@ Sometimes it is desirable to make horizontal or vertical rules line up +precisely with certain features in characters of a font. It is possible to +guarantee the correct matching between \.{DVI} output and the characters +generated by \MF\ by adhering to the following principles: (1)~The \MF\ +characters should be positioned so that a bottom edge or left edge that is +supposed to line up with the bottom or left edge of a rule appears at the +reference point, i.e., in row~0 and column~0 of the \MF\ raster. This +ensures that the position of the rule will not be rounded differently when +the pixel size is not a perfect multiple of the units of measurement in +the \.{DVI} file. (2)~A typeset rule of height $a>0$ and width $b>0$ +should be equivalent to a \MF-generated character having black pixels in +precisely those raster positions whose \MF\ coordinates satisfy +|0<=x<@t$\alpha$@>b| and |0<=y<@t$\alpha$@>a|, where $\alpha$ is the number +of pixels per \.{DVI} unit. +@:METAFONT}{\MF@> +@^alignment of rules with characters@> +@^rules aligning with characters@> + +@ The last page in a \.{DVI} file is followed by `|post|'; this command +introduces the postamble, which summarizes important facts that \TeX\ has +accumulated about the file, making it possible to print subsets of the data +with reasonable efficiency. The postamble has the form +$$\vbox{\halign{\hbox{#\hfil}\cr + |post| |p[4]| |num[4]| |den[4]| |mag[4]| |l[4]| |u[4]| |s[2]| |t[2]|\cr + $\langle\,$font definitions$\,\rangle$\cr + |post_post| |q[4]| |i[1]| 223's$[{\G}4]$\cr}}$$ +Here |p| is a pointer to the final |bop| in the file. The next three +parameters, |num|, |den|, and |mag|, are duplicates of the quantities that +appeared in the preamble. + +Parameters |l| and |u| give respectively the height-plus-depth of the tallest +page and the width of the widest page, in the same units as other dimensions +of the file. These numbers might be used by a \.{DVI}-reading program to +position individual ``pages'' on large sheets of film or paper; however, +the standard convention for output on normal size paper is to position each +page so that the upper left-hand corner is exactly one inch from the left +and the top. Experience has shown that it is unwise to design \.{DVI}-to-printer +software that attempts cleverly to center the output; a fixed position of +the upper left corner is easiest for users to understand and to work with. +Therefore |l| and~|u| are often ignored. + +Parameter |s| is the maximum stack depth (i.e., the largest excess of +|push| commands over |pop| commands) needed to process this file. Then +comes |t|, the total number of pages (|bop| commands) present. + +The postamble continues with font definitions, which are any number of +\\{fnt\_def} commands as described above, possibly interspersed with |nop| +commands. Each font number that is used in the \.{DVI} file must be defined +exactly twice: Once before it is first selected by a \\{fnt} command, and once +in the postamble. + +@ The last part of the postamble, following the |post_post| byte that +signifies the end of the font definitions, contains |q|, a pointer to the +|post| command that started the postamble. An identification byte, |i|, +comes next; this currently equals~2, as in the preamble. + +The |i| byte is followed by four or more bytes that are all equal to +the decimal number 223 (i.e., @'337 in octal). \TeX\ puts out four to seven of +these trailing bytes, until the total length of the file is a multiple of +four bytes, since this works out best on machines that pack four bytes per +word; but any number of 223's is allowed, as long as there are at least four +of them. In effect, 223 is a sort of signature that is added at the very end. +@^Fuchs, David Raymond@> + +This curious way to finish off a \.{DVI} file makes it feasible for +\.{DVI}-reading programs to find the postamble first, on most computers, +even though \TeX\ wants to write the postamble last. Most operating +systems permit random access to individual words or bytes of a file, so +the \.{DVI} reader can start at the end and skip backwards over the 223's +until finding the identification byte. Then it can back up four bytes, read +|q|, and move to byte |q| of the file. This byte should, of course, +contain the value 248 (|post|); now the postamble can be read, so the +\.{DVI} reader can discover all the information needed for typesetting the +pages. Note that it is also possible to skip through the \.{DVI} file at +reasonably high speed to locate a particular page, if that proves +desirable. This saves a lot of time, since \.{DVI} files used in production +jobs tend to be large. + +Unfortunately, however, standard \PASCAL\ does not include the ability to +@^system dependencies@> +access a random position in a file, or even to determine the length of a file. +Almost all systems nowadays provide the necessary capabilities, so \.{DVI} +format has been designed to work most efficiently with modern operating systems. +But if \.{DVI} files have to be processed under the restrictions of standard +\PASCAL, one can simply read them from front to back, since the necessary +header information is present in the preamble and in the font definitions. +(The |l| and |u| and |s| and |t| parameters, which appear only in the +postamble, are ``frills'' that are handy but not absolutely necessary.) + +@* \[32] Shipping pages out. +After considering \TeX's eyes and stomach, we come now to the bowels. +@^bowels@> + +The |ship_out| procedure is given a pointer to a box; its mission is +to describe that box in \.{DVI} form, outputting a ``page'' to |dvi_file|. +The \.{DVI} coordinates $(h,v)=(0,0)$ should correspond to the upper left +corner of the box being shipped. + +Since boxes can be inside of boxes inside of boxes, the main work of +|ship_out| is done by two mutually recursive routines, |hlist_out| +and |vlist_out|, which traverse the hlists and vlists inside of horizontal +and vertical boxes. + +As individual pages are being processed, we need to accumulate +information about the entire set of pages, since such statistics must be +reported in the postamble. The global variables |total_pages|, |max_v|, +|max_h|, |max_push|, and |last_bop| are used to record this information. + +The variable |doing_leaders| is |true| while leaders are being output. +The variable |dead_cycles| contains the number of times an output routine +has been initiated since the last |ship_out|. + +A few additional global variables are also defined here for use in +|vlist_out| and |hlist_out|. They could have been local variables, but +that would waste stack space when boxes are deeply nested, since the +values of these variables are not needed during recursive calls. +@^recursion@> + +@<Glob...@>= +@!total_pages:integer; {the number of pages that have been shipped out} +@!max_v:scaled; {maximum height-plus-depth of pages shipped so far} +@!max_h:scaled; {maximum width of pages shipped so far} +@!max_push:integer; {deepest nesting of |push| commands encountered so far} +@!last_bop:integer; {location of previous |bop| in the \.{DVI} output} +@!dead_cycles:integer; {recent outputs that didn't ship anything out} +@!doing_leaders:boolean; {are we inside a leader box?} +@# +@!c,@!f:quarterword; {character and font in current |char_node|} +@!rule_ht,@!rule_dp,@!rule_wd:scaled; {size of current rule being output} +@!g:pointer; {current glue specification} +@!lq,@!lr:integer; {quantities used in calculations for leaders} + +@ @<Set init...@>= +total_pages:=0; max_v:=0; max_h:=0; max_push:=0; last_bop:=-1; +doing_leaders:=false; dead_cycles:=0; cur_s:=-1; + +@ The \.{DVI} bytes are output to a buffer instead of being written directly +to the output file. This makes it possible to reduce the overhead of +subroutine calls, thereby measurably speeding up the computation, since +output of \.{DVI} bytes is part of \TeX's inner loop. And it has another +advantage as well, since we can change instructions in the buffer in order to +make the output more compact. For example, a `|down2|' command can be +changed to a `|y2|', thereby making a subsequent `|y0|' command possible, +saving two bytes. + +The output buffer is divided into two parts of equal size; the bytes found +in |dvi_buf[0..half_buf-1]| constitute the first half, and those in +|dvi_buf[half_buf..dvi_buf_size-1]| constitute the second. The global +variable |dvi_ptr| points to the position that will receive the next +output byte. When |dvi_ptr| reaches |dvi_limit|, which is always equal +to one of the two values |half_buf| or |dvi_buf_size|, the half buffer that +is about to be invaded next is sent to the output and |dvi_limit| is +changed to its other value. Thus, there is always at least a half buffer's +worth of information present, except at the very beginning of the job. + +Bytes of the \.{DVI} file are numbered sequentially starting with 0; +the next byte to be generated will be number |dvi_offset+dvi_ptr|. +A byte is present in the buffer only if its number is |>=dvi_gone|. + +@<Types...@>= +@!dvi_index=0..dvi_buf_size; {an index into the output buffer} + +@ Some systems may find it more efficient to make |dvi_buf| a |packed| +array, since output of four bytes at once may be facilitated. +@^system dependencies@> + +@<Glob...@>= +@!dvi_buf:array[dvi_index] of eight_bits; {buffer for \.{DVI} output} +@!half_buf:dvi_index; {half of |dvi_buf_size|} +@!dvi_limit:dvi_index; {end of the current half buffer} +@!dvi_ptr:dvi_index; {the next available buffer address} +@!dvi_offset:integer; {|dvi_buf_size| times the number of times the + output buffer has been fully emptied} +@!dvi_gone:integer; {the number of bytes already output to |dvi_file|} + +@ Initially the buffer is all in one piece; we will output half of it only +after it first fills up. + +@<Set init...@>= +half_buf:=dvi_buf_size div 2; dvi_limit:=dvi_buf_size; dvi_ptr:=0; +dvi_offset:=0; dvi_gone:=0; + +@ The actual output of |dvi_buf[a..b]| to |dvi_file| is performed by calling +|write_dvi(a,b)|. For best results, this procedure should be optimized to +run as fast as possible on each particular system, since it is part of +\TeX's inner loop. It is safe to assume that |a| and |b+1| will both be +multiples of 4 when |write_dvi(a,b)| is called; therefore it is possible on +many machines to use efficient methods to pack four bytes per word and to +output an array of words with one system call. +@^system dependencies@> +@^inner loop@> +@^defecation@> + +@p procedure write_dvi(@!a,@!b:dvi_index); +var k:dvi_index; +begin for k:=a to b do write(dvi_file,dvi_buf[k]); +end; + +@ To put a byte in the buffer without paying the cost of invoking a procedure +each time, we use the macro |dvi_out|. + +@d dvi_out(#)==@+begin dvi_buf[dvi_ptr]:=#; incr(dvi_ptr); + if dvi_ptr=dvi_limit then dvi_swap; + end + +@p procedure dvi_swap; {outputs half of the buffer} +begin if dvi_limit=dvi_buf_size then + begin write_dvi(0,half_buf-1); dvi_limit:=half_buf; + dvi_offset:=dvi_offset+dvi_buf_size; dvi_ptr:=0; + end +else begin write_dvi(half_buf,dvi_buf_size-1); dvi_limit:=dvi_buf_size; + end; +dvi_gone:=dvi_gone+half_buf; +end; + +@ Here is how we clean out the buffer when \TeX\ is all through; |dvi_ptr| +will be a multiple of~4. + +@<Empty the last bytes out of |dvi_buf|@>= +if dvi_limit=half_buf then write_dvi(half_buf,dvi_buf_size-1); +if dvi_ptr>0 then write_dvi(0,dvi_ptr-1) + +@ The |dvi_four| procedure outputs four bytes in two's complement notation, +without risking arithmetic overflow. + +@p procedure dvi_four(@!x:integer); +begin if x>=0 then dvi_out(x div @'100000000) +else begin x:=x+@'10000000000; + x:=x+@'10000000000; + dvi_out((x div @'100000000) + 128); + end; +x:=x mod @'100000000; dvi_out(x div @'200000); +x:=x mod @'200000; dvi_out(x div @'400); +dvi_out(x mod @'400); +end; + +@ A mild optimization of the output is performed by the |dvi_pop| +routine, which issues a |pop| unless it is possible to cancel a +`|push| |pop|' pair. The parameter to |dvi_pop| is the byte address +following the old |push| that matches the new |pop|. + +@p procedure dvi_pop(@!l:integer); +begin if (l=dvi_offset+dvi_ptr)and(dvi_ptr>0) then decr(dvi_ptr) +else dvi_out(pop); +end; + +@ Here's a procedure that outputs a font definition. Since \TeX82 uses at +most 256 different fonts per job, |fnt_def1| is always used as the command code. + +@p procedure dvi_font_def(@!f:internal_font_number); +var k:pool_pointer; {index into |str_pool|} +begin dvi_out(fnt_def1); +dvi_out(f-font_base-1);@/ +dvi_out(qo(font_check[f].b0)); +dvi_out(qo(font_check[f].b1)); +dvi_out(qo(font_check[f].b2)); +dvi_out(qo(font_check[f].b3));@/ +dvi_four(font_size[f]); +dvi_four(font_dsize[f]);@/ +dvi_out(length(font_area[f])); +dvi_out(length(font_name[f])); +@<Output the font name whose internal number is |f|@>; +end; + +@ @<Output the font name whose internal number is |f|@>= +for k:=str_start[font_area[f]] to str_start[font_area[f]+1]-1 do + dvi_out(so(str_pool[k])); +for k:=str_start[font_name[f]] to str_start[font_name[f]+1]-1 do + dvi_out(so(str_pool[k])) + +@ Versions of \TeX\ intended for small computers might well choose to omit +the ideas in the next few parts of this program, since it is not really +necessary to optimize the \.{DVI} code by making use of the |w0|, |x0|, +|y0|, and |z0| commands. Furthermore, the algorithm that we are about to +describe does not pretend to give an optimum reduction in the length +of the \.{DVI} code; after all, speed is more important than compactness. +But the method is surprisingly effective, and it takes comparatively little +time. + +We can best understand the basic idea by first considering a simpler problem +that has the same essential characteristics. Given a sequence of digits, +say $3\,1\,4\,1\,5\,9\,2\,6\,5\,3\,5\,8\,9$, we want to assign subscripts +$d$, $y$, or $z$ to each digit so as to maximize the number of ``$y$-hits'' +and ``$z$-hits''; a $y$-hit is an instance of two appearances of the same +digit with the subscript $y$, where no $y$'s intervene between the two +appearances, and a $z$-hit is defined similarly. For example, the sequence +above could be decorated with subscripts as follows: +$$3_z\,1_y\,4_d\,1_y\,5_y\,9_d\,2_d\,6_d\,5_y\,3_z\,5_y\,8_d\,9_d.$$ +There are three $y$-hits ($1_y\ldots1_y$ and $5_y\ldots5_y\ldots5_y$) and +one $z$-hit ($3_z\ldots3_z$); there are no $d$-hits, since the two appearances +of $9_d$ have $d$'s between them, but we don't count $d$-hits so it doesn't +matter how many there are. These subscripts are analogous to the \.{DVI} +commands called \\{down}, $y$, and $z$, and the digits are analogous to +different amounts of vertical motion; a $y$-hit or $z$-hit corresponds to +the opportunity to use the one-byte commands |y0| or |z0| in a \.{DVI} file. + +\TeX's method of assigning subscripts works like this: Append a new digit, +say $\delta$, to the right of the sequence. Now look back through the +sequence until one of the following things happens: (a)~You see +$\delta_y$ or $\delta_z$, and this was the first time you encountered a +$y$ or $z$ subscript, respectively. Then assign $y$ or $z$ to the new +$\delta$; you have scored a hit. (b)~You see $\delta_d$, and no $y$ +subscripts have been encountered so far during this search. Then change +the previous $\delta_d$ to $\delta_y$ (this corresponds to changing a +command in the output buffer), and assign $y$ to the new $\delta$; it's +another hit. (c)~You see $\delta_d$, and a $y$ subscript has been seen +but not a $z$. Change the previous $\delta_d$ to $\delta_z$ and assign +$z$ to the new $\delta$. (d)~You encounter both $y$ and $z$ subscripts +before encountering a suitable $\delta$, or you scan all the way to the +front of the sequence. Assign $d$ to the new $\delta$; this assignment may +be changed later. + +The subscripts $3_z\,1_y\,4_d\ldots\,$ in the example above were, in fact, +produced by this procedure, as the reader can verify. (Go ahead and try it.) + +@ In order to implement such an idea, \TeX\ maintains a stack of pointers +to the \\{down}, $y$, and $z$ commands that have been generated for the +current page. And there is a similar stack for \\{right}, |w|, and |x| +commands. These stacks are called the down stack and right stack, and their +top elements are maintained in the variables |down_ptr| and |right_ptr|. + +Each entry in these stacks contains four fields: The |width| field is +the amount of motion down or to the right; the |location| field is the +byte number of the \.{DVI} command in question (including the appropriate +|dvi_offset|); the |link| field points to the next item below this one +on the stack; and the |info| field encodes the options for possible change +in the \.{DVI} command. + +@d movement_node_size=3 {number of words per entry in the down and right stacks} +@d location(#)==mem[#+2].int {\.{DVI} byte number for a movement command} + +@<Glob...@>= +@!down_ptr,@!right_ptr:pointer; {heads of the down and right stacks} + +@ @<Set init...@>= +down_ptr:=null; right_ptr:=null; + +@ Here is a subroutine that produces a \.{DVI} command for some specified +downward or rightward motion. It has two parameters: |w| is the amount +of motion, and |o| is either |down1| or |right1|. We use the fact that +the command codes have convenient arithmetic properties: |y1-down1=w1-right1| +and |z1-down1=x1-right1|. + +@p procedure movement(@!w:scaled;@!o:eight_bits); +label exit,found,not_found,2,1; +var mstate:small_number; {have we seen a |y| or |z|?} +@!p,@!q:pointer; {current and top nodes on the stack} +@!k:integer; {index into |dvi_buf|, modulo |dvi_buf_size|} +begin q:=get_node(movement_node_size); {new node for the top of the stack} +width(q):=w; location(q):=dvi_offset+dvi_ptr; +if o=down1 then + begin link(q):=down_ptr; down_ptr:=q; + end +else begin link(q):=right_ptr; right_ptr:=q; + end; +@<Look at the other stack entries until deciding what sort of \.{DVI} command + to generate; |goto found| if node |p| is a ``hit''@>; +@<Generate a |down| or |right| command for |w| and |return|@>; +found: @<Generate a |y0| or |z0| command in order to reuse a previous + appearance of~|w|@>; +exit:end; + +@ The |info| fields in the entries of the down stack or the right stack +have six possible settings: |y_here| or |z_here| mean that the \.{DVI} +command refers to |y| or |z|, respectively (or to |w| or |x|, in the +case of horizontal motion); |yz_OK| means that the \.{DVI} command is +\\{down} (or \\{right}) but can be changed to either |y| or |z| (or +to either |w| or |x|); |y_OK| means that it is \\{down} and can be changed +to |y| but not |z|; |z_OK| is similar; and |d_fixed| means it must stay +\\{down}. + +The four settings |yz_OK|, |y_OK|, |z_OK|, |d_fixed| would not need to +be distinguished from each other if we were simply solving the +digit-subscripting problem mentioned above. But in \TeX's case there is +a complication because of the nested structure of |push| and |pop| +commands. Suppose we add parentheses to the digit-subscripting problem, +redefining hits so that $\delta_y\ldots \delta_y$ is a hit if all $y$'s between +the $\delta$'s are enclosed in properly nested parentheses, and if the +parenthesis level of the right-hand $\delta_y$ is deeper than or equal to +that of the left-hand one. Thus, `(' and `)' correspond to `|push|' +and `|pop|'. Now if we want to assign a subscript to the final 1 in the +sequence +$$2_y\,7_d\,1_d\,(\,8_z\,2_y\,8_z\,)\,1$$ +we cannot change the previous $1_d$ to $1_y$, since that would invalidate +the $2_y\ldots2_y$ hit. But we can change it to $1_z$, scoring a hit +since the intervening $8_z$'s are enclosed in parentheses. + +The program below removes movement nodes that are introduced after a |push|, +before it outputs the corresponding |pop|. + +@d y_here=1 {|info| when the movement entry points to a |y| command} +@d z_here=2 {|info| when the movement entry points to a |z| command} +@d yz_OK=3 {|info| corresponding to an unconstrained \\{down} command} +@d y_OK=4 {|info| corresponding to a \\{down} that can't become a |z|} +@d z_OK=5 {|info| corresponding to a \\{down} that can't become a |y|} +@d d_fixed=6 {|info| corresponding to a \\{down} that can't change} + +@ When the |movement| procedure gets to the label |found|, the value of +|info(p)| will be either |y_here| or |z_here|. If it is, say, |y_here|, +the procedure generates a |y0| command (or a |w0| command), and marks +all |info| fields between |q| and |p| so that |y| is not OK in that range. + +@<Generate a |y0| or |z0| command...@>= +info(q):=info(p); +if info(q)=y_here then + begin dvi_out(o+y0-down1); {|y0| or |w0|} + while link(q)<>p do + begin q:=link(q); + case info(q) of + yz_OK: info(q):=z_OK; + y_OK: info(q):=d_fixed; + othercases do_nothing + endcases; + end; + end +else begin dvi_out(o+z0-down1); {|z0| or |x0|} + while link(q)<>p do + begin q:=link(q); + case info(q) of + yz_OK: info(q):=y_OK; + z_OK: info(q):=d_fixed; + othercases do_nothing + endcases; + end; + end + +@ @<Generate a |down| or |right|...@>= +info(q):=yz_OK; +if abs(w)>=@'40000000 then + begin dvi_out(o+3); {|down4| or |right4|} + dvi_four(w); return; + end; +if abs(w)>=@'100000 then + begin dvi_out(o+2); {|down3| or |right3|} + if w<0 then w:=w+@'100000000; + dvi_out(w div @'200000); w:=w mod @'200000; goto 2; + end; +if abs(w)>=@'200 then + begin dvi_out(o+1); {|down2| or |right2|} + if w<0 then w:=w+@'200000; + goto 2; + end; +dvi_out(o); {|down1| or |right1|} +if w<0 then w:=w+@'400; +goto 1; +2: dvi_out(w div @'400); +1: dvi_out(w mod @'400); return + +@ As we search through the stack, we are in one of three states, +|y_seen|, |z_seen|, or |none_seen|, depending on whether we have +encountered |y_here| or |z_here| nodes. These states are encoded as +multiples of 6, so that they can be added to the |info| fields for quick +decision-making. +@^inner loop@> + +@d none_seen=0 {no |y_here| or |z_here| nodes have been encountered yet} +@d y_seen=6 {we have seen |y_here| but not |z_here|} +@d z_seen=12 {we have seen |z_here| but not |y_here|} + +@<Look at the other stack entries until deciding...@>= +p:=link(q); mstate:=none_seen; +while p<>null do + begin if width(p)=w then @<Consider a node with matching width; + |goto found| if it's a hit@> + else case mstate+info(p) of + none_seen+y_here: mstate:=y_seen; + none_seen+z_here: mstate:=z_seen; + y_seen+z_here,z_seen+y_here: goto not_found; + othercases do_nothing + endcases; + p:=link(p); + end; +not_found: + +@ We might find a valid hit in a |y| or |z| byte that is already gone +from the buffer. But we can't change bytes that are gone forever; ``the +moving finger writes, $\ldots\,\,$.'' + +@<Consider a node with matching width...@>= +case mstate+info(p) of +none_seen+yz_OK,none_seen+y_OK,z_seen+yz_OK,z_seen+y_OK:@t@>@;@/ + if location(p)<dvi_gone then goto not_found + else @<Change buffered instruction to |y| or |w| and |goto found|@>; +none_seen+z_OK,y_seen+yz_OK,y_seen+z_OK:@t@>@;@/ + if location(p)<dvi_gone then goto not_found + else @<Change buffered instruction to |z| or |x| and |goto found|@>; +none_seen+y_here,none_seen+z_here,y_seen+z_here,z_seen+y_here: goto found; +othercases do_nothing +endcases + +@ @<Change buffered instruction to |y| or |w| and |goto found|@>= +begin k:=location(p)-dvi_offset; +if k<0 then k:=k+dvi_buf_size; +dvi_buf[k]:=dvi_buf[k]+y1-down1; +info(p):=y_here; goto found; +end + +@ @<Change buffered instruction to |z| or |x| and |goto found|@>= +begin k:=location(p)-dvi_offset; +if k<0 then k:=k+dvi_buf_size; +dvi_buf[k]:=dvi_buf[k]+z1-down1; +info(p):=z_here; goto found; +end + +@ In case you are wondering when all the movement nodes are removed from +\TeX's memory, the answer is that they are recycled just before +|hlist_out| and |vlist_out| finish outputting a box. This restores the +down and right stacks to the state they were in before the box was output, +except that some |info|'s may have become more restrictive. + +@p procedure prune_movements(@!l:integer); + {delete movement nodes with |location>=l|} +label done,exit; +var p:pointer; {node being deleted} +begin while down_ptr<>null do + begin if location(down_ptr)<l then goto done; + p:=down_ptr; down_ptr:=link(p); free_node(p,movement_node_size); + end; +done: while right_ptr<>null do + begin if location(right_ptr)<l then return; + p:=right_ptr; right_ptr:=link(p); free_node(p,movement_node_size); + end; +exit:end; + +@ The actual distances by which we want to move might be computed as the +sum of several separate movements. For example, there might be several +glue nodes in succession, or we might want to move right by the width of +some box plus some amount of glue. More importantly, the baselineskip +distances are computed in terms of glue together with the depth and +height of adjacent boxes, and we want the \.{DVI} file to lump these +three quantities together into a single motion. + +Therefore, \TeX\ maintains two pairs of global variables: |dvi_h| and |dvi_v| +are the |h| and |v| coordinates corresponding to the commands actually +output to the \.{DVI} file, while |cur_h| and |cur_v| are the coordinates +corresponding to the current state of the output routines. Coordinate +changes will accumulate in |cur_h| and |cur_v| without being reflected +in the output, until such a change becomes necessary or desirable; we +can call the |movement| procedure whenever we want to make |dvi_h=cur_h| +or |dvi_v=cur_v|. + +The current font reflected in the \.{DVI} output is called |dvi_f|; +there is no need for a `\\{cur\_f}' variable. + +The depth of nesting of |hlist_out| and |vlist_out| is called |cur_s|; +this is essentially the depth of |push| commands in the \.{DVI} output. + +@d synch_h==if cur_h<>dvi_h then + begin movement(cur_h-dvi_h,right1); dvi_h:=cur_h; + end +@d synch_v==if cur_v<>dvi_v then + begin movement(cur_v-dvi_v,down1); dvi_v:=cur_v; + end + +@<Glob...@>= +@!dvi_h,@!dvi_v:scaled; {a \.{DVI} reader program thinks we are here} +@!cur_h,@!cur_v:scaled; {\TeX\ thinks we are here} +@!dvi_f:internal_font_number; {the current font} +@!cur_s:integer; {current depth of output box nesting, initially $-1$} + +@ @<Initialize variables as |ship_out| begins@>= +dvi_h:=0; dvi_v:=0; cur_h:=h_offset; dvi_f:=null_font; +ensure_dvi_open; +if total_pages=0 then + begin dvi_out(pre); dvi_out(id_byte); {output the preamble} +@^preamble of \.{DVI} file@> + dvi_four(25400000); dvi_four(473628672); {conversion ratio for sp} + prepare_mag; dvi_four(mag); {magnification factor is frozen} + old_setting:=selector; selector:=new_string; + print(" TeX output "); print_int(year); print_char("."); + print_two(month); print_char("."); print_two(day); + print_char(":"); print_two(time div 60); + print_two(time mod 60); + selector:=old_setting; dvi_out(cur_length); + for s:=str_start[str_ptr] to pool_ptr-1 do dvi_out(so(str_pool[s])); + pool_ptr:=str_start[str_ptr]; {flush the current string} + end + +@ When |hlist_out| is called, its duty is to output the box represented +by the |hlist_node| pointed to by |temp_ptr|. The reference point of that +box has coordinates |(cur_h,cur_v)|. + +Similarly, when |vlist_out| is called, its duty is to output the box represented +by the |vlist_node| pointed to by |temp_ptr|. The reference point of that +box has coordinates |(cur_h,cur_v)|. +@^recursion@> + +@p procedure@?vlist_out; forward; {|hlist_out| and |vlist_out| are mutually + recursive} + +@ The recursive procedures |hlist_out| and |vlist_out| each have local variables +|save_h| and |save_v| to hold the values of |dvi_h| and |dvi_v| just before +entering a new level of recursion. In effect, the values of |save_h| and +|save_v| on \TeX's run-time stack correspond to the values of |h| and |v| +that a \.{DVI}-reading program will push onto its coordinate stack. + +@d move_past=13 {go to this label when advancing past glue or a rule} +@d fin_rule=14 {go to this label to finish processing a rule} +@d next_p=15 {go to this label when finished with node |p|} + +@p @t\4@>@<Declare procedures needed in |hlist_out|, |vlist_out|@>@t@>@/ +procedure hlist_out; {output an |hlist_node| box} +label reswitch, move_past, fin_rule, next_p; +var base_line: scaled; {the baseline coordinate for this box} +@!left_edge: scaled; {the left coordinate for this box} +@!save_h,@!save_v: scaled; {what |dvi_h| and |dvi_v| should pop to} +@!this_box: pointer; {pointer to containing box} +@!g_order: glue_ord; {applicable order of infinity for glue} +@!g_sign: normal..shrinking; {selects type of glue} +@!p:pointer; {current position in the hlist} +@!save_loc:integer; {\.{DVI} byte location upon entry} +@!leader_box:pointer; {the leader box being replicated} +@!leader_wd:scaled; {width of leader box being replicated} +@!lx:scaled; {extra space between leader boxes} +@!outer_doing_leaders:boolean; {were we doing leaders?} +@!edge:scaled; {left edge of sub-box, or right edge of leader space} +@!glue_temp:real; {glue value before rounding} +@!cur_glue:real; {glue seen so far} +@!cur_g:scaled; {rounded equivalent of |cur_glue| times the glue ratio} +begin cur_g:=0; cur_glue:=float_constant(0); +this_box:=temp_ptr; g_order:=glue_order(this_box); +g_sign:=glue_sign(this_box); p:=list_ptr(this_box); +incr(cur_s); +if cur_s>0 then dvi_out(push); +if cur_s>max_push then max_push:=cur_s; +save_loc:=dvi_offset+dvi_ptr; base_line:=cur_v; left_edge:=cur_h; +while p<>null do @<Output node |p| for |hlist_out| and move to the next node, + maintaining the condition |cur_v=base_line|@>; +prune_movements(save_loc); +if cur_s>0 then dvi_pop(save_loc); +decr(cur_s); +end; + +@ We ought to give special care to the efficiency of one part of |hlist_out|, +since it belongs to \TeX's inner loop. When a |char_node| is encountered, +we save a little time by processing several nodes in succession until +reaching a non-|char_node|. The program uses the fact that |set_char_0=0|. +@^inner loop@> + +@<Output node |p| for |hlist_out|...@>= +reswitch: if is_char_node(p) then + begin synch_h; synch_v; + repeat f:=font(p); c:=character(p); + if f<>dvi_f then @<Change font |dvi_f| to |f|@>; + if c>=qi(128) then dvi_out(set1); + dvi_out(qo(c));@/ + cur_h:=cur_h+char_width(f)(char_info(f)(c)); + p:=link(p); + until not is_char_node(p); + dvi_h:=cur_h; + end +else @<Output the non-|char_node| |p| for |hlist_out| + and move to the next node@> + +@ @<Change font |dvi_f| to |f|@>= +begin if not font_used[f] then + begin dvi_font_def(f); font_used[f]:=true; + end; +if f<=64+font_base then dvi_out(f-font_base-1+fnt_num_0) +else begin dvi_out(fnt1); dvi_out(f-font_base-1); + end; +dvi_f:=f; +end + +@ @<Output the non-|char_node| |p| for |hlist_out|...@>= +begin case type(p) of +hlist_node,vlist_node:@<Output a box in an hlist@>; +rule_node: begin rule_ht:=height(p); rule_dp:=depth(p); rule_wd:=width(p); + goto fin_rule; + end; +whatsit_node: @<Output the whatsit node |p| in an hlist@>; +glue_node: @<Move right or output leaders@>; +kern_node,math_node:cur_h:=cur_h+width(p); +ligature_node: @<Make node |p| look like a |char_node| and |goto reswitch|@>; +othercases do_nothing +endcases;@/ +goto next_p; +fin_rule: @<Output a rule in an hlist@>; +move_past: cur_h:=cur_h+rule_wd; +next_p:p:=link(p); +end + +@ @<Output a box in an hlist@>= +if list_ptr(p)=null then cur_h:=cur_h+width(p) +else begin save_h:=dvi_h; save_v:=dvi_v; + cur_v:=base_line+shift_amount(p); {shift the box down} + temp_ptr:=p; edge:=cur_h; + if type(p)=vlist_node then vlist_out@+else hlist_out; + dvi_h:=save_h; dvi_v:=save_v; + cur_h:=edge+width(p); cur_v:=base_line; + end + +@ @<Output a rule in an hlist@>= +if is_running(rule_ht) then rule_ht:=height(this_box); +if is_running(rule_dp) then rule_dp:=depth(this_box); +rule_ht:=rule_ht+rule_dp; {this is the rule thickness} +if (rule_ht>0)and(rule_wd>0) then {we don't output empty rules} + begin synch_h; cur_v:=base_line+rule_dp; synch_v; + dvi_out(set_rule); dvi_four(rule_ht); dvi_four(rule_wd); + cur_v:=base_line; dvi_h:=dvi_h+rule_wd; + end + +@ @d billion==float_constant(1000000000) +@d vet_glue(#)== glue_temp:=#; + if glue_temp>billion then + glue_temp:=billion + else if glue_temp<-billion then + glue_temp:=-billion + +@<Move right or output leaders@>= +begin g:=glue_ptr(p); rule_wd:=width(g)-cur_g; +if g_sign<>normal then + begin if g_sign=stretching then + begin if stretch_order(g)=g_order then + begin cur_glue:=cur_glue+stretch(g); + vet_glue(float(glue_set(this_box))*cur_glue); +@^real multiplication@> + cur_g:=round(glue_temp); + end; + end + else if shrink_order(g)=g_order then + begin cur_glue:=cur_glue-shrink(g); + vet_glue(float(glue_set(this_box))*cur_glue); + cur_g:=round(glue_temp); + end; + end; +rule_wd:=rule_wd+cur_g; +if subtype(p)>=a_leaders then + @<Output leaders in an hlist, |goto fin_rule| if a rule + or to |next_p| if done@>; +goto move_past; +end + +@ @<Output leaders in an hlist...@>= +begin leader_box:=leader_ptr(p); +if type(leader_box)=rule_node then + begin rule_ht:=height(leader_box); rule_dp:=depth(leader_box); + goto fin_rule; + end; +leader_wd:=width(leader_box); +if (leader_wd>0)and(rule_wd>0) then + begin rule_wd:=rule_wd+10; {compensate for floating-point rounding} + edge:=cur_h+rule_wd; lx:=0; + @<Let |cur_h| be the position of the first box, and set |leader_wd+lx| + to the spacing between corresponding parts of boxes@>; + while cur_h+leader_wd<=edge do + @<Output a leader box at |cur_h|, + then advance |cur_h| by |leader_wd+lx|@>; + cur_h:=edge-10; goto next_p; + end; +end + +@ The calculations related to leaders require a bit of care. First, in the +case of |a_leaders| (aligned leaders), we want to move |cur_h| to +|left_edge| plus the smallest multiple of |leader_wd| for which the result +is not less than the current value of |cur_h|; i.e., |cur_h| should become +$|left_edge|+|leader_wd|\times\lceil +(|cur_h|-|left_edge|)/|leader_wd|\rceil$. The program here should work in +all cases even though some implementations of \PASCAL\ give nonstandard +results for the |div| operation when |cur_h| is less than |left_edge|. + +In the case of |c_leaders| (centered leaders), we want to increase |cur_h| +by half of the excess space not occupied by the leaders; and in the +case of |x_leaders| (expanded leaders) we increase |cur_h| +by $1/(q+1)$ of this excess space, where $q$ is the number of times the +leader box will be replicated. Slight inaccuracies in the division might +accumulate; half of this rounding error is placed at each end of the leaders. + +@<Let |cur_h| be the position of the first box, ...@>= +if subtype(p)=a_leaders then + begin save_h:=cur_h; + cur_h:=left_edge+leader_wd*((cur_h-left_edge)@!div leader_wd); + if cur_h<save_h then cur_h:=cur_h+leader_wd; + end +else begin lq:=rule_wd div leader_wd; {the number of box copies} + lr:=rule_wd mod leader_wd; {the remaining space} + if subtype(p)=c_leaders then cur_h:=cur_h+(lr div 2) + else begin lx:=lr div (lq+1); + cur_h:=cur_h+((lr-(lq-1)*lx) div 2); + end; + end + +@ The `\\{synch}' operations here are intended to decrease the number of +bytes needed to specify horizontal and vertical motion in the \.{DVI} output. + +@<Output a leader box at |cur_h|, ...@>= +begin cur_v:=base_line+shift_amount(leader_box); synch_v; save_v:=dvi_v;@/ +synch_h; save_h:=dvi_h; temp_ptr:=leader_box; +outer_doing_leaders:=doing_leaders; doing_leaders:=true; +if type(leader_box)=vlist_node then vlist_out@+else hlist_out; +doing_leaders:=outer_doing_leaders; +dvi_v:=save_v; dvi_h:=save_h; cur_v:=base_line; +cur_h:=save_h+leader_wd+lx; +end + +@ The |vlist_out| routine is similar to |hlist_out|, but a bit simpler. + +@p procedure vlist_out; {output a |vlist_node| box} +label move_past, fin_rule, next_p; +var left_edge: scaled; {the left coordinate for this box} +@!top_edge: scaled; {the top coordinate for this box} +@!save_h,@!save_v: scaled; {what |dvi_h| and |dvi_v| should pop to} +@!this_box: pointer; {pointer to containing box} +@!g_order: glue_ord; {applicable order of infinity for glue} +@!g_sign: normal..shrinking; {selects type of glue} +@!p:pointer; {current position in the vlist} +@!save_loc:integer; {\.{DVI} byte location upon entry} +@!leader_box:pointer; {the leader box being replicated} +@!leader_ht:scaled; {height of leader box being replicated} +@!lx:scaled; {extra space between leader boxes} +@!outer_doing_leaders:boolean; {were we doing leaders?} +@!edge:scaled; {bottom boundary of leader space} +@!glue_temp:real; {glue value before rounding} +@!cur_glue:real; {glue seen so far} +@!cur_g:scaled; {rounded equivalent of |cur_glue| times the glue ratio} +begin cur_g:=0; cur_glue:=float_constant(0); +this_box:=temp_ptr; g_order:=glue_order(this_box); +g_sign:=glue_sign(this_box); p:=list_ptr(this_box); +incr(cur_s); +if cur_s>0 then dvi_out(push); +if cur_s>max_push then max_push:=cur_s; +save_loc:=dvi_offset+dvi_ptr; left_edge:=cur_h; cur_v:=cur_v-height(this_box); +top_edge:=cur_v; +while p<>null do @<Output node |p| for |vlist_out| and move to the next node, + maintaining the condition |cur_h=left_edge|@>; +prune_movements(save_loc); +if cur_s>0 then dvi_pop(save_loc); +decr(cur_s); +end; + +@ @<Output node |p| for |vlist_out|...@>= +begin if is_char_node(p) then confusion("vlistout") +@:this can't happen vlistout}{\quad vlistout@> +else @<Output the non-|char_node| |p| for |vlist_out|@>; +next_p:p:=link(p); +end + +@ @<Output the non-|char_node| |p| for |vlist_out|@>= +begin case type(p) of +hlist_node,vlist_node:@<Output a box in a vlist@>; +rule_node: begin rule_ht:=height(p); rule_dp:=depth(p); rule_wd:=width(p); + goto fin_rule; + end; +whatsit_node: @<Output the whatsit node |p| in a vlist@>; +glue_node: @<Move down or output leaders@>; +kern_node:cur_v:=cur_v+width(p); +othercases do_nothing +endcases;@/ +goto next_p; +fin_rule: @<Output a rule in a vlist, |goto next_p|@>; +move_past: cur_v:=cur_v+rule_ht; +end + +@ The |synch_v| here allows the \.{DVI} output to use one-byte commands +for adjusting |v| in most cases, since the baselineskip distance will +usually be constant. + +@<Output a box in a vlist@>= +if list_ptr(p)=null then cur_v:=cur_v+height(p)+depth(p) +else begin cur_v:=cur_v+height(p); synch_v; + save_h:=dvi_h; save_v:=dvi_v; + cur_h:=left_edge+shift_amount(p); {shift the box right} + temp_ptr:=p; + if type(p)=vlist_node then vlist_out@+else hlist_out; + dvi_h:=save_h; dvi_v:=save_v; + cur_v:=save_v+depth(p); cur_h:=left_edge; + end + +@ @<Output a rule in a vlist...@>= +if is_running(rule_wd) then rule_wd:=width(this_box); +rule_ht:=rule_ht+rule_dp; {this is the rule thickness} +cur_v:=cur_v+rule_ht; +if (rule_ht>0)and(rule_wd>0) then {we don't output empty rules} + begin synch_h; synch_v; + dvi_out(put_rule); dvi_four(rule_ht); dvi_four(rule_wd); + end; +goto next_p + +@ @<Move down or output leaders@>= +begin g:=glue_ptr(p); rule_ht:=width(g)-cur_g; +if g_sign<>normal then + begin if g_sign=stretching then + begin if stretch_order(g)=g_order then + begin cur_glue:=cur_glue+stretch(g); + vet_glue(float(glue_set(this_box))*cur_glue); +@^real multiplication@> + cur_g:=round(glue_temp); + end; + end + else if shrink_order(g)=g_order then + begin cur_glue:=cur_glue-shrink(g); + vet_glue(float(glue_set(this_box))*cur_glue); + cur_g:=round(glue_temp); + end; + end; +rule_ht:=rule_ht+cur_g; +if subtype(p)>=a_leaders then + @<Output leaders in a vlist, |goto fin_rule| if a rule + or to |next_p| if done@>; +goto move_past; +end + +@ @<Output leaders in a vlist...@>= +begin leader_box:=leader_ptr(p); +if type(leader_box)=rule_node then + begin rule_wd:=width(leader_box); rule_dp:=0; + goto fin_rule; + end; +leader_ht:=height(leader_box)+depth(leader_box); +if (leader_ht>0)and(rule_ht>0) then + begin rule_ht:=rule_ht+10; {compensate for floating-point rounding} + edge:=cur_v+rule_ht; lx:=0; + @<Let |cur_v| be the position of the first box, and set |leader_ht+lx| + to the spacing between corresponding parts of boxes@>; + while cur_v+leader_ht<=edge do + @<Output a leader box at |cur_v|, + then advance |cur_v| by |leader_ht+lx|@>; + cur_v:=edge-10; goto next_p; + end; +end + +@ @<Let |cur_v| be the position of the first box, ...@>= +if subtype(p)=a_leaders then + begin save_v:=cur_v; + cur_v:=top_edge+leader_ht*((cur_v-top_edge)@!div leader_ht); + if cur_v<save_v then cur_v:=cur_v+leader_ht; + end +else begin lq:=rule_ht div leader_ht; {the number of box copies} + lr:=rule_ht mod leader_ht; {the remaining space} + if subtype(p)=c_leaders then cur_v:=cur_v+(lr div 2) + else begin lx:=lr div (lq+1); + cur_v:=cur_v+((lr-(lq-1)*lx) div 2); + end; + end + +@ When we reach this part of the program, |cur_v| indicates the top of a +leader box, not its baseline. + +@<Output a leader box at |cur_v|, ...@>= +begin cur_h:=left_edge+shift_amount(leader_box); synch_h; save_h:=dvi_h;@/ +cur_v:=cur_v+height(leader_box); synch_v; save_v:=dvi_v; +temp_ptr:=leader_box; +outer_doing_leaders:=doing_leaders; doing_leaders:=true; +if type(leader_box)=vlist_node then vlist_out@+else hlist_out; +doing_leaders:=outer_doing_leaders; +dvi_v:=save_v; dvi_h:=save_h; cur_h:=left_edge; +cur_v:=save_v-height(leader_box)+leader_ht+lx; +end + +@ The |hlist_out| and |vlist_out| procedures are now complete, so we are +ready for the |ship_out| routine that gets them started in the first place. + +@p procedure ship_out(@!p:pointer); {output the box |p|} +label done; +var page_loc:integer; {location of the current |bop|} +@!j,@!k:0..9; {indices to first ten count registers} +@!s:pool_pointer; {index into |str_pool|} +@!old_setting:0..max_selector; {saved |selector| setting} +begin if tracing_output>0 then + begin print_nl(""); print_ln; + print("Completed box being shipped out"); +@.Completed box...@> + end; +if term_offset>max_print_line-9 then print_ln +else if (term_offset>0)or(file_offset>0) then print_char(" "); +print_char("["); j:=9; +while (count(j)=0)and(j>0) do decr(j); +for k:=0 to j do + begin print_int(count(k)); + if k<j then print_char("."); + end; +update_terminal; +if tracing_output>0 then + begin print_char("]"); + begin_diagnostic; show_box(p); end_diagnostic(true); + end; +@<Ship box |p| out@>; +if tracing_output<=0 then print_char("]"); +dead_cycles:=0; +update_terminal; {progress report} +@<Flush the box from memory, showing statistics if requested@>; +end; + +@ @<Flush the box from memory, showing statistics if requested@>= +@!stat if tracing_stats>1 then + begin print_nl("Memory usage before: "); +@.Memory usage...@> + print_int(var_used); print_char("&"); + print_int(dyn_used); print_char(";"); + end; +tats@/ +flush_node_list(p); +@!stat if tracing_stats>1 then + begin print(" after: "); + print_int(var_used); print_char("&"); + print_int(dyn_used); print("; still untouched: "); + print_int(hi_mem_min-lo_mem_max-1); print_ln; + end; +tats + +@ @<Ship box |p| out@>= +@<Update the values of |max_h| and |max_v|; but if the page is too large, + |goto done|@>; +@<Initialize variables as |ship_out| begins@>; +page_loc:=dvi_offset+dvi_ptr; +dvi_out(bop); +for k:=0 to 9 do dvi_four(count(k)); +dvi_four(last_bop); last_bop:=page_loc; +cur_v:=height(p)+v_offset; temp_ptr:=p; +if type(p)=vlist_node then vlist_out@+else hlist_out; +dvi_out(eop); incr(total_pages); cur_s:=-1; +done: + +@ Sometimes the user will generate a huge page because other error messages +are being ignored. Such pages are not output to the \.{dvi} file, since they +may confuse the printing software. + +@<Update the values of |max_h| and |max_v|; but if the page is too large...@>= +if (height(p)>max_dimen)or@|(depth(p)>max_dimen)or@| + (height(p)+depth(p)+v_offset>max_dimen)or@| + (width(p)+h_offset>max_dimen) then + begin print_err("Huge page cannot be shipped out"); +@.Huge page...@> + help2("The page just created is more than 18 feet tall or")@/ + ("more than 18 feet wide, so I suspect something went wrong."); + error; + if tracing_output<=0 then + begin begin_diagnostic; + print_nl("The following box has been deleted:"); +@.The following...deleted@> + show_box(p); + end_diagnostic(true); + end; + goto done; + end; +if height(p)+depth(p)+v_offset>max_v then max_v:=height(p)+depth(p)+v_offset; +if width(p)+h_offset>max_h then max_h:=width(p)+h_offset + +@ At the end of the program, we must finish things off by writing the +post\-amble. If |total_pages=0|, the \.{DVI} file was never opened. +If |total_pages>=65536|, the \.{DVI} file will lie. + +An integer variable |k| will be declared for use by this routine. + +@<Finish the \.{DVI} file@>= +while cur_s>-1 do + begin if cur_s>0 then dvi_out(pop) + else begin dvi_out(eop); incr(total_pages); + end; + decr(cur_s); + end; +if total_pages=0 then print_nl("No pages of output.") +@.No pages of output@> +else begin dvi_out(post); {beginning of the postamble} + dvi_four(last_bop); last_bop:=dvi_offset+dvi_ptr-5; {|post| location} + dvi_four(25400000); dvi_four(473628672); {conversion ratio for sp} + prepare_mag; dvi_four(mag); {magnification factor} + dvi_four(max_v); dvi_four(max_h);@/ + dvi_out(max_push div 256); dvi_out(max_push mod 256);@/ + dvi_out((total_pages div 256) mod 256); dvi_out(total_pages mod 256);@/ + @<Output the font definitions for all fonts that were used@>; + dvi_out(post_post); dvi_four(last_bop); dvi_out(id_byte);@/ + k:=4+((dvi_buf_size-dvi_ptr) mod 4); {the number of 223's} + while k>0 do + begin dvi_out(223); decr(k); + end; + @<Empty the last bytes out of |dvi_buf|@>; + print_nl("Output written on "); slow_print(output_file_name); +@.Output written on x@> + print(" ("); print_int(total_pages); print(" page"); + if total_pages<>1 then print_char("s"); + print(", "); print_int(dvi_offset+dvi_ptr); print(" bytes)."); + b_close(dvi_file); + end + +@ @<Output the font definitions...@>= +while font_ptr>font_base do + begin if font_used[font_ptr] then dvi_font_def(font_ptr); + decr(font_ptr); + end + +@* \[33] Packaging. +We're essentially done with the parts of \TeX\ that are concerned with +the input (|get_next|) and the output (|ship_out|). So it's time to +get heavily into the remaining part, which does the real work of typesetting. + +After lists are constructed, \TeX\ wraps them up and puts them into boxes. +Two major subroutines are given the responsibility for this task: |hpack| +applies to horizontal lists (hlists) and |vpack| applies to vertical lists +(vlists). The main duty of |hpack| and |vpack| is to compute the dimensions +of the resulting boxes, and to adjust the glue if one of those dimensions +is pre-specified. The computed sizes normally enclose all of the material +inside the new box; but some items may stick out if negative glue is used, +if the box is overfull, or if a \.{\\vbox} includes other boxes that have +been shifted left. + +The subroutine call |hpack(p,w,m)| returns a pointer to an |hlist_node| +for a box containing the hlist that starts at |p|. Parameter |w| specifies +a width; and parameter |m| is either `|exactly|' or `|additional|'. Thus, +|hpack(p,w,exactly)| produces a box whose width is exactly |w|, while +|hpack(p,w,additional)| yields a box whose width is the natural width plus +|w|. It is convenient to define a macro called `|natural|' to cover the +most common case, so that we can say |hpack(p,natural)| to get a box that +has the natural width of list |p|. + +Similarly, |vpack(p,w,m)| returns a pointer to a |vlist_node| for a +box containing the vlist that starts at |p|. In this case |w| represents +a height instead of a width; the parameter |m| is interpreted as in |hpack|. + +@d exactly=0 {a box dimension is pre-specified} +@d additional=1 {a box dimension is increased from the natural one} +@d natural==0,additional {shorthand for parameters to |hpack| and |vpack|} + +@ The parameters to |hpack| and |vpack| correspond to \TeX's primitives +like `\.{\\hbox} \.{to} \.{300pt}', `\.{\\hbox} \.{spread} \.{10pt}'; note +that `\.{\\hbox}' with no dimension following it is equivalent to +`\.{\\hbox} \.{spread} \.{0pt}'. The |scan_spec| subroutine scans such +constructions in the user's input, including the mandatory left brace that +follows them, and it puts the specification onto |save_stack| so that the +desired box can later be obtained by executing the following code: +$$\vbox{\halign{#\hfil\cr +|save_ptr:=save_ptr-2;|\cr +|hpack(p,saved(1),saved(0)).|\cr}}$$ +Special care is necessary to ensure that the special |save_stack| codes +are placed just below the new group code, because scanning can change +|save_stack| when \.{\\csname} appears. + +@p procedure scan_spec(@!c:group_code;@!three_codes:boolean); + {scans a box specification and left brace} +label found; +var @!s:integer; {temporarily saved value} +@!spec_code:exactly..additional; +begin if three_codes then s:=saved(0); +if scan_keyword("to") then spec_code:=exactly +@.to@> +else if scan_keyword("spread") then spec_code:=additional +@.spread@> +else begin spec_code:=additional; cur_val:=0; + goto found; + end; +scan_normal_dimen; +found: if three_codes then + begin saved(0):=s; incr(save_ptr); + end; +saved(0):=spec_code; saved(1):=cur_val; save_ptr:=save_ptr+2; +new_save_level(c); scan_left_brace; +end; + +@ To figure out the glue setting, |hpack| and |vpack| determine how much +stretchability and shrinkability are present, considering all four orders +of infinity. The highest order of infinity that has a nonzero coefficient +is then used as if no other orders were present. + +For example, suppose that the given list contains six glue nodes with +the respective stretchabilities 3pt, 8fill, 5fil, 6pt, $-3$fil, $-8$fill. +Then the total is essentially 2fil; and if a total additional space of 6pt +is to be achieved by stretching, the actual amounts of stretch will be +0pt, 0pt, 15pt, 0pt, $-9$pt, and 0pt, since only `fil' glue will be +considered. (The `fill' glue is therefore not really stretching infinitely +with respect to `fil'; nobody would actually want that to happen.) + +The arrays |total_stretch| and |total_shrink| are used to determine how much +glue of each kind is present. A global variable |last_badness| is used +to implement \.{\\badness}. + +@<Glob...@>= +@!total_stretch, @!total_shrink: array[glue_ord] of scaled; + {glue found by |hpack| or |vpack|} +@!last_badness:integer; {badness of the most recently packaged box} + +@ If the global variable |adjust_tail| is non-null, the |hpack| routine +also removes all occurrences of |ins_node|, |mark_node|, and |adjust_node| +items and appends the resulting material onto the list that ends at +location |adjust_tail|. + +@< Glob...@>= +@!adjust_tail:pointer; {tail of adjustment list} + +@ @<Set init...@>=adjust_tail:=null; last_badness:=0; + +@ Here now is |hpack|, which contains few if any surprises. + +@p function hpack(@!p:pointer;@!w:scaled;@!m:small_number):pointer; +label reswitch, common_ending, exit; +var r:pointer; {the box node that will be returned} +@!q:pointer; {trails behind |p|} +@!h,@!d,@!x:scaled; {height, depth, and natural width} +@!s:scaled; {shift amount} +@!g:pointer; {points to a glue specification} +@!o:glue_ord; {order of infinity} +@!f:internal_font_number; {the font in a |char_node|} +@!i:four_quarters; {font information about a |char_node|} +@!hd:eight_bits; {height and depth indices for a character} +begin last_badness:=0; r:=get_node(box_node_size); type(r):=hlist_node; +subtype(r):=min_quarterword; shift_amount(r):=0; +q:=r+list_offset; link(q):=p;@/ +h:=0; @<Clear dimensions to zero@>; +while p<>null do @<Examine node |p| in the hlist, taking account of its effect + on the dimensions of the new box, or moving it to the adjustment list; + then advance |p| to the next node@>; +if adjust_tail<>null then link(adjust_tail):=null; +height(r):=h; depth(r):=d;@/ +@<Determine the value of |width(r)| and the appropriate glue setting; + then |return| or |goto common_ending|@>; +common_ending: @<Finish issuing a diagnostic message + for an overfull or underfull hbox@>; +exit: hpack:=r; +end; + +@ @<Clear dimensions to zero@>= +d:=0; x:=0; +total_stretch[normal]:=0; total_shrink[normal]:=0; +total_stretch[fil]:=0; total_shrink[fil]:=0; +total_stretch[fill]:=0; total_shrink[fill]:=0; +total_stretch[filll]:=0; total_shrink[filll]:=0 + +@ @<Examine node |p| in the hlist, taking account of its effect...@>= +@^inner loop@> +begin reswitch: while is_char_node(p) do + @<Incorporate character dimensions into the dimensions of + the hbox that will contain~it, then move to the next node@>; +if p<>null then + begin case type(p) of + hlist_node,vlist_node,rule_node,unset_node: + @<Incorporate box dimensions into the dimensions of + the hbox that will contain~it@>; + ins_node,mark_node,adjust_node: if adjust_tail<>null then + @<Transfer node |p| to the adjustment list@>; + whatsit_node:@<Incorporate a whatsit node into an hbox@>; + glue_node:@<Incorporate glue into the horizontal totals@>; + kern_node,math_node: x:=x+width(p); + ligature_node: @<Make node |p| look like a |char_node| + and |goto reswitch|@>; + othercases do_nothing + endcases;@/ + p:=link(p); + end; +end + + +@ @<Make node |p| look like a |char_node| and |goto reswitch|@>= +begin mem[lig_trick]:=mem[lig_char(p)]; link(lig_trick):=link(p); +p:=lig_trick; goto reswitch; +end + +@ The code here implicitly uses the fact that running dimensions are +indicated by |null_flag|, which will be ignored in the calculations +because it is a highly negative number. + +@<Incorporate box dimensions into the dimensions of the hbox...@>= +begin x:=x+width(p); +if type(p)>=rule_node then s:=0 @+else s:=shift_amount(p); +if height(p)-s>h then h:=height(p)-s; +if depth(p)+s>d then d:=depth(p)+s; +end + +@ The following code is part of \TeX's inner loop; i.e., adding another +character of text to the user's input will cause each of these instructions +to be exercised one more time. +@^inner loop@> + +@<Incorporate character dimensions into the dimensions of the hbox...@>= +begin f:=font(p); i:=char_info(f)(character(p)); hd:=height_depth(i); +x:=x+char_width(f)(i);@/ +s:=char_height(f)(hd);@+if s>h then h:=s; +s:=char_depth(f)(hd);@+if s>d then d:=s; +p:=link(p); +end + +@ Although node |q| is not necessarily the immediate predecessor of node |p|, +it always points to some node in the list preceding |p|. Thus, we can delete +nodes by moving |q| when necessary. The algorithm takes linear time, and the +extra computation does not intrude on the inner loop unless it is necessary +to make a deletion. +@^inner loop@> + +@<Transfer node |p| to the adjustment list@>= +begin while link(q)<>p do q:=link(q); +if type(p)=adjust_node then + begin link(adjust_tail):=adjust_ptr(p); + while link(adjust_tail)<>null do adjust_tail:=link(adjust_tail); + p:=link(p); free_node(link(q),small_node_size); + end +else begin link(adjust_tail):=p; adjust_tail:=p; p:=link(p); + end; +link(q):=p; p:=q; +end + +@ @<Incorporate glue into the horizontal totals@>= +begin g:=glue_ptr(p); x:=x+width(g);@/ +o:=stretch_order(g); total_stretch[o]:=total_stretch[o]+stretch(g); +o:=shrink_order(g); total_shrink[o]:=total_shrink[o]+shrink(g); +if subtype(p)>=a_leaders then + begin g:=leader_ptr(p); + if height(g)>h then h:=height(g); + if depth(g)>d then d:=depth(g); + end; +end + +@ When we get to the present part of the program, |x| is the natural width +of the box being packaged. + +@<Determine the value of |width(r)| and the appropriate glue setting...@>= +if m=additional then w:=x+w; +width(r):=w; x:=w-x; {now |x| is the excess to be made up} +if x=0 then + begin glue_sign(r):=normal; glue_order(r):=normal; + set_glue_ratio_zero(glue_set(r)); + return; + end +else if x>0 then @<Determine horizontal glue stretch setting, then |return| + or \hbox{|goto common_ending|}@> +else @<Determine horizontal glue shrink setting, then |return| + or \hbox{|goto common_ending|}@> + +@ @<Determine horizontal glue stretch setting...@>= +begin @<Determine the stretch order@>; +glue_order(r):=o; glue_sign(r):=stretching; +if total_stretch[o]<>0 then glue_set(r):=unfloat(x/total_stretch[o]) +@^real division@> +else begin glue_sign(r):=normal; + set_glue_ratio_zero(glue_set(r)); {there's nothing to stretch} + end; +if o=normal then if list_ptr(r)<>null then + @<Report an underfull hbox and |goto common_ending|, if this box + is sufficiently bad@>; +return; +end + +@ @<Determine the stretch order@>= +if total_stretch[filll]<>0 then o:=filll +else if total_stretch[fill]<>0 then o:=fill +else if total_stretch[fil]<>0 then o:=fil +else o:=normal + +@ @<Report an underfull hbox and |goto common_ending|, if...@>= +begin last_badness:=badness(x,total_stretch[normal]); +if last_badness>hbadness then + begin print_ln; + if last_badness>100 then print_nl("Underfull")@+else print_nl("Loose"); + print(" \hbox (badness "); print_int(last_badness); +@.Underfull \\hbox...@> +@.Loose \\hbox...@> + goto common_ending; + end; +end + +@ In order to provide a decent indication of where an overfull or underfull +box originated, we use a global variable |pack_begin_line| that is +set nonzero only when |hpack| is being called by the paragraph builder +or the alignment finishing routine. + +@<Glob...@>= +@!pack_begin_line:integer; {source file line where the current paragraph + or alignment began; a negative value denotes alignment} + +@ @<Set init...@>= +pack_begin_line:=0; + +@ @<Finish issuing a diagnostic message for an overfull or underfull hbox@>= +if output_active then print(") has occurred while \output is active") +else begin if pack_begin_line<>0 then + begin if pack_begin_line>0 then print(") in paragraph at lines ") + else print(") in alignment at lines "); + print_int(abs(pack_begin_line)); + print("--"); + end + else print(") detected at line "); + print_int(line); + end; +print_ln;@/ +font_in_short_display:=null_font; short_display(list_ptr(r)); print_ln;@/ +begin_diagnostic; show_box(r); end_diagnostic(true) + +@ @<Determine horizontal glue shrink setting...@>= +begin @<Determine the shrink order@>; +glue_order(r):=o; glue_sign(r):=shrinking; +if total_shrink[o]<>0 then glue_set(r):=unfloat((-x)/total_shrink[o]) +@^real division@> +else begin glue_sign(r):=normal; + set_glue_ratio_zero(glue_set(r)); {there's nothing to shrink} + end; +if (total_shrink[o]<-x)and(o=normal)and(list_ptr(r)<>null) then + begin last_badness:=1000000; + set_glue_ratio_one(glue_set(r)); {use the maximum shrinkage} + @<Report an overfull hbox and |goto common_ending|, if this box + is sufficiently bad@>; + end +else if o=normal then if list_ptr(r)<>null then + @<Report a tight hbox and |goto common_ending|, if this box + is sufficiently bad@>; +return; +end + +@ @<Determine the shrink order@>= +if total_shrink[filll]<>0 then o:=filll +else if total_shrink[fill]<>0 then o:=fill +else if total_shrink[fil]<>0 then o:=fil +else o:=normal + +@ @<Report an overfull hbox and |goto common_ending|, if...@>= +if (-x-total_shrink[normal]>hfuzz)or(hbadness<100) then + begin if (overfull_rule>0)and(-x-total_shrink[normal]>hfuzz) then + begin while link(q)<>null do q:=link(q); + link(q):=new_rule; + width(link(q)):=overfull_rule; + end; + print_ln; print_nl("Overfull \hbox ("); +@.Overfull \\hbox...@> + print_scaled(-x-total_shrink[normal]); print("pt too wide"); + goto common_ending; + end + +@ @<Report a tight hbox and |goto common_ending|, if...@>= +begin last_badness:=badness(-x,total_shrink[normal]); +if last_badness>hbadness then + begin print_ln; print_nl("Tight \hbox (badness "); print_int(last_badness); +@.Tight \\hbox...@> + goto common_ending; + end; +end + +@ The |vpack| subroutine is actually a special case of a slightly more +general routine called |vpackage|, which has four parameters. The fourth +parameter, which is |max_dimen| in the case of |vpack|, specifies the +maximum depth of the page box that is constructed. The depth is first +computed by the normal rules; if it exceeds this limit, the reference +point is simply moved down until the limiting depth is attained. + +@d vpack(#)==vpackage(#,max_dimen) {special case of unconstrained depth} + +@p function vpackage(@!p:pointer;@!h:scaled;@!m:small_number;@!l:scaled): + pointer; +label common_ending, exit; +var r:pointer; {the box node that will be returned} +@!w,@!d,@!x:scaled; {width, depth, and natural height} +@!s:scaled; {shift amount} +@!g:pointer; {points to a glue specification} +@!o:glue_ord; {order of infinity} +begin last_badness:=0; r:=get_node(box_node_size); type(r):=vlist_node; +subtype(r):=min_quarterword; shift_amount(r):=0; +list_ptr(r):=p;@/ +w:=0; @<Clear dimensions to zero@>; +while p<>null do @<Examine node |p| in the vlist, taking account of its effect + on the dimensions of the new box; then advance |p| to the next node@>; +width(r):=w; +if d>l then + begin x:=x+d-l; depth(r):=l; + end +else depth(r):=d; +@<Determine the value of |height(r)| and the appropriate glue setting; + then |return| or |goto common_ending|@>; +common_ending: @<Finish issuing a diagnostic message + for an overfull or underfull vbox@>; +exit: vpackage:=r; +end; + +@ @<Examine node |p| in the vlist, taking account of its effect...@>= +begin if is_char_node(p) then confusion("vpack") +@:this can't happen vpack}{\quad vpack@> +else case type(p) of + hlist_node,vlist_node,rule_node,unset_node: + @<Incorporate box dimensions into the dimensions of + the vbox that will contain~it@>; + whatsit_node:@<Incorporate a whatsit node into a vbox@>; + glue_node: @<Incorporate glue into the vertical totals@>; + kern_node: begin x:=x+d+width(p); d:=0; + end; + othercases do_nothing + endcases; +p:=link(p); +end + +@ @<Incorporate box dimensions into the dimensions of the vbox...@>= +begin x:=x+d+height(p); d:=depth(p); +if type(p)>=rule_node then s:=0 @+else s:=shift_amount(p); +if width(p)+s>w then w:=width(p)+s; +end + +@ @<Incorporate glue into the vertical totals@>= +begin x:=x+d; d:=0;@/ +g:=glue_ptr(p); x:=x+width(g);@/ +o:=stretch_order(g); total_stretch[o]:=total_stretch[o]+stretch(g); +o:=shrink_order(g); total_shrink[o]:=total_shrink[o]+shrink(g); +if subtype(p)>=a_leaders then + begin g:=leader_ptr(p); + if width(g)>w then w:=width(g); + end; +end + +@ When we get to the present part of the program, |x| is the natural height +of the box being packaged. + +@<Determine the value of |height(r)| and the appropriate glue setting...@>= +if m=additional then h:=x+h; +height(r):=h; x:=h-x; {now |x| is the excess to be made up} +if x=0 then + begin glue_sign(r):=normal; glue_order(r):=normal; + set_glue_ratio_zero(glue_set(r)); + return; + end +else if x>0 then @<Determine vertical glue stretch setting, then |return| + or \hbox{|goto common_ending|}@> +else @<Determine vertical glue shrink setting, then |return| + or \hbox{|goto common_ending|}@> + +@ @<Determine vertical glue stretch setting...@>= +begin @<Determine the stretch order@>; +glue_order(r):=o; glue_sign(r):=stretching; +if total_stretch[o]<>0 then glue_set(r):=unfloat(x/total_stretch[o]) +@^real division@> +else begin glue_sign(r):=normal; + set_glue_ratio_zero(glue_set(r)); {there's nothing to stretch} + end; +if o=normal then if list_ptr(r)<>null then + @<Report an underfull vbox and |goto common_ending|, if this box + is sufficiently bad@>; +return; +end + +@ @<Report an underfull vbox and |goto common_ending|, if...@>= +begin last_badness:=badness(x,total_stretch[normal]); +if last_badness>vbadness then + begin print_ln; + if last_badness>100 then print_nl("Underfull")@+else print_nl("Loose"); + print(" \vbox (badness "); print_int(last_badness); +@.Underfull \\vbox...@> +@.Loose \\vbox...@> + goto common_ending; + end; +end + +@ @<Finish issuing a diagnostic message for an overfull or underfull vbox@>= +if output_active then print(") has occurred while \output is active") +else begin if pack_begin_line<>0 then {it's actually negative} + begin print(") in alignment at lines "); + print_int(abs(pack_begin_line)); + print("--"); + end + else print(") detected at line "); + print_int(line); + print_ln;@/ + end; +begin_diagnostic; show_box(r); end_diagnostic(true) + +@ @<Determine vertical glue shrink setting...@>= +begin @<Determine the shrink order@>; +glue_order(r):=o; glue_sign(r):=shrinking; +if total_shrink[o]<>0 then glue_set(r):=unfloat((-x)/total_shrink[o]) +@^real division@> +else begin glue_sign(r):=normal; + set_glue_ratio_zero(glue_set(r)); {there's nothing to shrink} + end; +if (total_shrink[o]<-x)and(o=normal)and(list_ptr(r)<>null) then + begin last_badness:=1000000; + set_glue_ratio_one(glue_set(r)); {use the maximum shrinkage} + @<Report an overfull vbox and |goto common_ending|, if this box + is sufficiently bad@>; + end +else if o=normal then if list_ptr(r)<>null then + @<Report a tight vbox and |goto common_ending|, if this box + is sufficiently bad@>; +return; +end + +@ @<Report an overfull vbox and |goto common_ending|, if...@>= +if (-x-total_shrink[normal]>vfuzz)or(vbadness<100) then + begin print_ln; print_nl("Overfull \vbox ("); +@.Overfull \\vbox...@> + print_scaled(-x-total_shrink[normal]); print("pt too high"); + goto common_ending; + end + +@ @<Report a tight vbox and |goto common_ending|, if...@>= +begin last_badness:=badness(-x,total_shrink[normal]); +if last_badness>vbadness then + begin print_ln; print_nl("Tight \vbox (badness "); print_int(last_badness); +@.Tight \\vbox...@> + goto common_ending; + end; +end + +@ When a box is being appended to the current vertical list, the +baselineskip calculation is handled by the |append_to_vlist| routine. + +@p procedure append_to_vlist(@!b:pointer); +var d:scaled; {deficiency of space between baselines} +@!p:pointer; {a new glue specification} +begin if prev_depth>ignore_depth then + begin d:=width(baseline_skip)-prev_depth-height(b); + if d<line_skip_limit then p:=new_param_glue(line_skip_code) + else begin p:=new_skip_param(baseline_skip_code); + width(temp_ptr):=d; {|temp_ptr=glue_ptr(p)|} + end; + link(tail):=p; tail:=p; + end; +link(tail):=b; tail:=b; prev_depth:=depth(b); +end; + +@* \[34] Data structures for math mode. +When \TeX\ reads a formula that is enclosed between \.\$'s, it constructs an +{\sl mlist}, which is essentially a tree structure representing that +formula. An mlist is a linear sequence of items, but we can regard it as +a tree structure because mlists can appear within mlists. For example, many +of the entries can be subscripted or superscripted, and such ``scripts'' +are mlists in their own right. + +An entire formula is parsed into such a tree before any of the actual +typesetting is done, because the current style of type is usually not +known until the formula has been fully scanned. For example, when the +formula `\.{\$a+b \\over c+d\$}' is being read, there is no way to tell +that `\.{a+b}' will be in script size until `\.{\\over}' has appeared. + +During the scanning process, each element of the mlist being built is +classified as a relation, a binary operator, an open parenthesis, etc., +or as a construct like `\.{\\sqrt}' that must be built up. This classification +appears in the mlist data structure. + +After a formula has been fully scanned, the mlist is converted to an hlist +so that it can be incorporated into the surrounding text. This conversion is +controlled by a recursive procedure that decides all of the appropriate +styles by a ``top-down'' process starting at the outermost level and working +in towards the subformulas. The formula is ultimately pasted together using +combinations of horizontal and vertical boxes, with glue and penalty nodes +inserted as necessary. + +An mlist is represented internally as a linked list consisting chiefly +of ``noads'' (pronounced ``no-adds''), to distinguish them from the somewhat +similar ``nodes'' in hlists and vlists. Certain kinds of ordinary nodes are +allowed to appear in mlists together with the noads; \TeX\ tells the difference +by means of the |type| field, since a noad's |type| is always greater than +that of a node. An mlist does not contain character nodes, hlist nodes, vlist +nodes, math nodes, ligature nodes, +or unset nodes; in particular, each mlist item appears in the +variable-size part of |mem|, so the |type| field is always present. + +@ Each noad is four or more words long. The first word contains the |type| +and |subtype| and |link| fields that are already so familiar to us; the +second, third, and fourth words are called the noad's |nucleus|, |subscr|, +and |supscr| fields. + +Consider, for example, the simple formula `\.{\$x\^2\$}', which would be +parsed into an mlist containing a single element called an |ord_noad|. +The |nucleus| of this noad is a representation of `\.x', the |subscr| is +empty, and the |supscr| is a representation of `\.2'. + +The |nucleus|, |subscr|, and |supscr| fields are further broken into +subfields. If |p| points to a noad, and if |q| is one of its principal +fields (e.g., |q=subscr(p)|), there are several possibilities for the +subfields, depending on the |math_type| of |q|. + +\yskip\hang|math_type(q)=math_char| means that |fam(q)| refers to one of +the sixteen font families, and |character(q)| is the number of a character +within a font of that family, as in a character node. + +\yskip\hang|math_type(q)=math_text_char| is similar, but the character is +unsubscripted and unsuperscripted and it is followed immediately by another +character from the same font. (This |math_type| setting appears only +briefly during the processing; it is used to suppress unwanted italic +corrections.) + +\yskip\hang|math_type(q)=empty| indicates a field with no value (the +corresponding attribute of noad |p| is not present). + +\yskip\hang|math_type(q)=sub_box| means that |info(q)| points to a box +node (either an |hlist_node| or a |vlist_node|) that should be used as the +value of the field. The |shift_amount| in the subsidiary box node is the +amount by which that box will be shifted downward. + +\yskip\hang|math_type(q)=sub_mlist| means that |info(q)| points to +an mlist; the mlist must be converted to an hlist in order to obtain +the value of this field. + +\yskip\noindent In the latter case, we might have |info(q)=null|. This +is not the same as |math_type(q)=empty|; for example, `\.{\$P\_\{\}\$}' +and `\.{\$P\$}' produce different results (the former will not have the +``italic correction'' added to the width of |P|, but the ``script skip'' +will be added). + +The definitions of subfields given here are evidently wasteful of space, +since a halfword is being used for the |math_type| although only three +bits would be needed. However, there are hardly ever many noads present at +once, since they are soon converted to nodes that take up even more space, +so we can afford to represent them in whatever way simplifies the +programming. + +@d noad_size=4 {number of words in a normal noad} +@d nucleus(#)==#+1 {the |nucleus| field of a noad} +@d supscr(#)==#+2 {the |supscr| field of a noad} +@d subscr(#)==#+3 {the |subscr| field of a noad} +@d math_type==link {a |halfword| in |mem|} +@d fam==font {a |quarterword| in |mem|} +@d math_char=1 {|math_type| when the attribute is simple} +@d sub_box=2 {|math_type| when the attribute is a box} +@d sub_mlist=3 {|math_type| when the attribute is a formula} +@d math_text_char=4 {|math_type| when italic correction is dubious} + +@ Each portion of a formula is classified as Ord, Op, Bin, Rel, Ope, +Clo, Pun, or Inn, for purposes of spacing and line breaking. An +|ord_noad|, |op_noad|, |bin_noad|, |rel_noad|, |open_noad|, |close_noad|, +|punct_noad|, or |inner_noad| is used to represent portions of the various +types. For example, an `\.=' sign in a formula leads to the creation of a +|rel_noad| whose |nucleus| field is a representation of an equals sign +(usually |fam=0|, |character=@'75|). A formula preceded by \.{\\mathrel} +also results in a |rel_noad|. When a |rel_noad| is followed by an +|op_noad|, say, and possibly separated by one or more ordinary nodes (not +noads), \TeX\ will insert a penalty node (with the current |rel_penalty|) +just after the formula that corresponds to the |rel_noad|, unless there +already was a penalty immediately following; and a ``thick space'' will be +inserted just before the formula that corresponds to the |op_noad|. + +A noad of type |ord_noad|, |op_noad|, \dots, |inner_noad| usually +has a |subtype=normal|. The only exception is that an |op_noad| might +have |subtype=limits| or |no_limits|, if the normal positioning of +limits has been overridden for this operator. + +@d ord_noad=unset_node+3 {|type| of a noad classified Ord} +@d op_noad=ord_noad+1 {|type| of a noad classified Op} +@d bin_noad=ord_noad+2 {|type| of a noad classified Bin} +@d rel_noad=ord_noad+3 {|type| of a noad classified Rel} +@d open_noad=ord_noad+4 {|type| of a noad classified Ope} +@d close_noad=ord_noad+5 {|type| of a noad classified Clo} +@d punct_noad=ord_noad+6 {|type| of a noad classified Pun} +@d inner_noad=ord_noad+7 {|type| of a noad classified Inn} +@d limits=1 {|subtype| of |op_noad| whose scripts are to be above, below} +@d no_limits=2 {|subtype| of |op_noad| whose scripts are to be normal} + +@ A |radical_noad| is five words long; the fifth word is the |left_delimiter| +field, which usually represents a square root sign. + +A |fraction_noad| is six words long; it has a |right_delimiter| field +as well as a |left_delimiter|. + +Delimiter fields are of type |four_quarters|, and they have four subfields +called |small_fam|, |small_char|, |large_fam|, |large_char|. These subfields +represent variable-size delimiters by giving the ``small'' and ``large'' +starting characters, as explained in Chapter~17 of {\sl The \TeX book}. +@:TeXbook}{\sl The \TeX book@> + +A |fraction_noad| is actually quite different from all other noads. Not +only does it have six words, it has |thickness|, |denominator|, and +|numerator| fields instead of |nucleus|, |subscr|, and |supscr|. The +|thickness| is a scaled value that tells how thick to make a fraction +rule; however, the special value |default_code| is used to stand for the +|default_rule_thickness| of the current size. The |numerator| and +|denominator| point to mlists that define a fraction; we always have +$$\hbox{|math_type(numerator)=math_type(denominator)=sub_mlist|}.$$ The +|left_delimiter| and |right_delimiter| fields specify delimiters that will +be placed at the left and right of the fraction. In this way, a +|fraction_noad| is able to represent all of \TeX's operators \.{\\over}, +\.{\\atop}, \.{\\above}, \.{\\overwithdelims}, \.{\\atopwithdelims}, and + \.{\\abovewithdelims}. + +@d left_delimiter(#)==#+4 {first delimiter field of a noad} +@d right_delimiter(#)==#+5 {second delimiter field of a fraction noad} +@d radical_noad=inner_noad+1 {|type| of a noad for square roots} +@d radical_noad_size=5 {number of |mem| words in a radical noad} +@d fraction_noad=radical_noad+1 {|type| of a noad for generalized fractions} +@d fraction_noad_size=6 {number of |mem| words in a fraction noad} +@d small_fam(#)==mem[#].qqqq.b0 {|fam| for ``small'' delimiter} +@d small_char(#)==mem[#].qqqq.b1 {|character| for ``small'' delimiter} +@d large_fam(#)==mem[#].qqqq.b2 {|fam| for ``large'' delimiter} +@d large_char(#)==mem[#].qqqq.b3 {|character| for ``large'' delimiter} +@d thickness==width {|thickness| field in a fraction noad} +@d default_code==@'10000000000 {denotes |default_rule_thickness|} +@d numerator==supscr {|numerator| field in a fraction noad} +@d denominator==subscr {|denominator| field in a fraction noad} + +@ The global variable |empty_field| is set up for initialization of empty +fields in new noads. Similarly, |null_delimiter| is for the initialization +of delimiter fields. + +@<Glob...@>= +@!empty_field:two_halves; +@!null_delimiter:four_quarters; + +@ @<Set init...@>= +empty_field.rh:=empty; empty_field.lh:=null;@/ +null_delimiter.b0:=0; null_delimiter.b1:=min_quarterword;@/ +null_delimiter.b2:=0; null_delimiter.b3:=min_quarterword; + +@ The |new_noad| function creates an |ord_noad| that is completely null. + +@p function new_noad:pointer; +var p:pointer; +begin p:=get_node(noad_size); +type(p):=ord_noad; subtype(p):=normal; +mem[nucleus(p)].hh:=empty_field; +mem[subscr(p)].hh:=empty_field; +mem[supscr(p)].hh:=empty_field; +new_noad:=p; +end; + +@ A few more kinds of noads will complete the set: An |under_noad| has its +nucleus underlined; an |over_noad| has it overlined. An |accent_noad| places +an accent over its nucleus; the accent character appears as +|fam(accent_chr(p))| and |character(accent_chr(p))|. A |vcenter_noad| +centers its nucleus vertically with respect to the axis of the formula; +in such noads we always have |math_type(nucleus(p))=sub_box|. + +And finally, we have |left_noad| and |right_noad| types, to implement +\TeX's \.{\\left} and \.{\\right}. The |nucleus| of such noads is +replaced by a |delimiter| field; thus, for example, `\.{\\left(}' produces +a |left_noad| such that |delimiter(p)| holds the family and character +codes for all left parentheses. A |left_noad| never appears in an mlist +except as the first element, and a |right_noad| never appears in an mlist +except as the last element; furthermore, we either have both a |left_noad| +and a |right_noad|, or neither one is present. The |subscr| and |supscr| +fields are always |empty| in a |left_noad| and a |right_noad|. + +@d under_noad=fraction_noad+1 {|type| of a noad for underlining} +@d over_noad=under_noad+1 {|type| of a noad for overlining} +@d accent_noad=over_noad+1 {|type| of a noad for accented subformulas} +@d accent_noad_size=5 {number of |mem| words in an accent noad} +@d accent_chr(#)==#+4 {the |accent_chr| field of an accent noad} +@d vcenter_noad=accent_noad+1 {|type| of a noad for \.{\\vcenter}} +@d left_noad=vcenter_noad+1 {|type| of a noad for \.{\\left}} +@d right_noad=left_noad+1 {|type| of a noad for \.{\\right}} +@d delimiter==nucleus {|delimiter| field in left and right noads} +@d scripts_allowed(#)==(type(#)>=ord_noad)and(type(#)<left_noad) + +@ Math formulas can also contain instructions like \.{\\textstyle} that +override \TeX's normal style rules. A |style_node| is inserted into the +data structure to record such instructions; it is three words long, so it +is considered a node instead of a noad. The |subtype| is either |display_style| +or |text_style| or |script_style| or |script_script_style|. The +second and third words of a |style_node| are not used, but they are +present because a |choice_node| is converted to a |style_node|. + +\TeX\ uses even numbers 0, 2, 4, 6 to encode the basic styles +|display_style|, \dots, |script_script_style|, and adds~1 to get the +``cramped'' versions of these styles. This gives a numerical order that +is backwards from the convention of Appendix~G in {\sl The \TeX book\/}; +i.e., a smaller style has a larger numerical value. +@:TeXbook}{\sl The \TeX book@> + +@d style_node=unset_node+1 {|type| of a style node} +@d style_node_size=3 {number of words in a style node} +@d display_style=0 {|subtype| for \.{\\displaystyle}} +@d text_style=2 {|subtype| for \.{\\textstyle}} +@d script_style=4 {|subtype| for \.{\\scriptstyle}} +@d script_script_style=6 {|subtype| for \.{\\scriptscriptstyle}} +@d cramped=1 {add this to an uncramped style if you want to cramp it} + +@p function new_style(@!s:small_number):pointer; {create a style node} +var p:pointer; {the new node} +begin p:=get_node(style_node_size); type(p):=style_node; +subtype(p):=s; width(p):=0; depth(p):=0; {the |width| and |depth| are not used} +new_style:=p; +end; + +@ Finally, the \.{\\mathchoice} primitive creates a |choice_node|, which +has special subfields |display_mlist|, |text_mlist|, |script_mlist|, +and |script_script_mlist| pointing to the mlists for each style. + +@d choice_node=unset_node+2 {|type| of a choice node} +@d display_mlist(#)==info(#+1) {mlist to be used in display style} +@d text_mlist(#)==link(#+1) {mlist to be used in text style} +@d script_mlist(#)==info(#+2) {mlist to be used in script style} +@d script_script_mlist(#)==link(#+2) {mlist to be used in scriptscript style} + +@p function new_choice:pointer; {create a choice node} +var p:pointer; {the new node} +begin p:=get_node(style_node_size); type(p):=choice_node; +subtype(p):=0; {the |subtype| is not used} +display_mlist(p):=null; text_mlist(p):=null; script_mlist(p):=null; +script_script_mlist(p):=null; +new_choice:=p; +end; + +@ Let's consider now the previously unwritten part of |show_node_list| +that displays the things that can only be present in mlists; this +program illustrates how to access the data structures just defined. + +In the context of the following program, |p| points to a node or noad that +should be displayed, and the current string contains the ``recursion history'' +that leads to this point. The recursion history consists of a dot for each +outer level in which |p| is subsidiary to some node, or in which |p| is +subsidiary to the |nucleus| field of some noad; the dot is replaced by +`\.\_' or `\.\^' or `\./' or `\.\\' if |p| is descended from the |subscr| +or |supscr| or |denominator| or |numerator| fields of noads. For example, +the current string would be `\.{.\^.\_/}' if |p| points to the |ord_noad| for +|x| in the (ridiculous) formula +`\.{\$\\sqrt\{a\^\{\\mathinner\{b\_\{c\\over x+y\}\}\}\}\$}'. + +@<Cases of |show_node_list| that arise...@>= +style_node:print_style(subtype(p)); +choice_node:@<Display choice node |p|@>; +ord_noad,op_noad,bin_noad,rel_noad,open_noad,close_noad,punct_noad,inner_noad, + radical_noad,over_noad,under_noad,vcenter_noad,accent_noad, + left_noad,right_noad:@<Display normal noad |p|@>; +fraction_noad:@<Display fraction noad |p|@>; + +@ Here are some simple routines used in the display of noads. + +@<Declare procedures needed for displaying the elements of mlists@>= +procedure print_fam_and_char(@!p:pointer); {prints family and character} +begin print_esc("fam"); print_int(fam(p)); print_char(" "); +print_ASCII(qo(character(p))); +end; +@# +procedure print_delimiter(@!p:pointer); {prints a delimiter as 24-bit hex value} +var a:integer; {accumulator} +begin a:=small_fam(p)*256+qo(small_char(p)); +a:=a*@"1000+large_fam(p)*256+qo(large_char(p)); +if a<0 then print_int(a) {this should never happen} +else print_hex(a); +end; + +@ The next subroutine will descend to another level of recursion when a +subsidiary mlist needs to be displayed. The parameter |c| indicates what +character is to become part of the recursion history. An empty mlist is +distinguished from a field with |math_type(p)=empty|, because these are +not equivalent (as explained above). +@^recursion@> + +@<Declare procedures needed for displaying...@>= +procedure@?show_info; forward;@t\2@>@?{|show_node_list(info(temp_ptr))|} +procedure print_subsidiary_data(@!p:pointer;@!c:ASCII_code); + {display a noad field} +begin if cur_length>=depth_threshold then + begin if math_type(p)<>empty then print(" []"); + end +else begin append_char(c); {include |c| in the recursion history} + temp_ptr:=p; {prepare for |show_info| if recursion is needed} + case math_type(p) of + math_char: begin print_ln; print_current_string; print_fam_and_char(p); + end; + sub_box: show_info; {recursive call} + sub_mlist: if info(p)=null then + begin print_ln; print_current_string; print("{}"); + end + else show_info; {recursive call} + othercases do_nothing {|empty|} + endcases;@/ + flush_char; {remove |c| from the recursion history} + end; +end; + +@ The inelegant introduction of |show_info| in the code above seems better +than the alternative of using \PASCAL's strange |forward| declaration for a +procedure with parameters. The \PASCAL\ convention about dropping parameters +from a post-|forward| procedure is, frankly, so intolerable to the author +of \TeX\ that he would rather stoop to communication via a global temporary +variable. (A similar stoopidity occurred with respect to |hlist_out| and +|vlist_out| above, and it will occur with respect to |mlist_to_hlist| below.) +@^Knuth, Donald Ervin@> +@:PASCAL}{\PASCAL@> + +@p procedure show_info; {the reader will kindly forgive this} +begin show_node_list(info(temp_ptr)); +end; + +@ @<Declare procedures needed for displaying...@>= +procedure print_style(@!c:integer); +begin case c div 2 of +0: print_esc("displaystyle"); {|display_style=0|} +1: print_esc("textstyle"); {|text_style=2|} +2: print_esc("scriptstyle"); {|script_style=4|} +3: print_esc("scriptscriptstyle"); {|script_script_style=6|} +othercases print("Unknown style!") +endcases; +end; + +@ @<Display choice node |p|@>= +begin print_esc("mathchoice"); +append_char("D"); show_node_list(display_mlist(p)); flush_char; +append_char("T"); show_node_list(text_mlist(p)); flush_char; +append_char("S"); show_node_list(script_mlist(p)); flush_char; +append_char("s"); show_node_list(script_script_mlist(p)); flush_char; +end + +@ @<Display normal noad |p|@>= +begin case type(p) of +ord_noad: print_esc("mathord"); +op_noad: print_esc("mathop"); +bin_noad: print_esc("mathbin"); +rel_noad: print_esc("mathrel"); +open_noad: print_esc("mathopen"); +close_noad: print_esc("mathclose"); +punct_noad: print_esc("mathpunct"); +inner_noad: print_esc("mathinner"); +over_noad: print_esc("overline"); +under_noad: print_esc("underline"); +vcenter_noad: print_esc("vcenter"); +radical_noad: begin print_esc("radical"); print_delimiter(left_delimiter(p)); + end; +accent_noad: begin print_esc("accent"); print_fam_and_char(accent_chr(p)); + end; +left_noad: begin print_esc("left"); print_delimiter(nucleus(p)); + end; +right_noad: begin print_esc("right"); print_delimiter(nucleus(p)); + end; +end; +if subtype(p)<>normal then + if subtype(p)=limits then print_esc("limits") + else print_esc("nolimits"); +if type(p)<left_noad then print_subsidiary_data(nucleus(p),"."); +print_subsidiary_data(supscr(p),"^"); +print_subsidiary_data(subscr(p),"_"); +end + +@ @<Display fraction noad |p|@>= +begin print_esc("fraction, thickness "); +if thickness(p)=default_code then print("= default") +else print_scaled(thickness(p)); +if (small_fam(left_delimiter(p))<>0)or@+ + (small_char(left_delimiter(p))<>min_quarterword)or@| + (large_fam(left_delimiter(p))<>0)or@| + (large_char(left_delimiter(p))<>min_quarterword) then + begin print(", left-delimiter "); print_delimiter(left_delimiter(p)); + end; +if (small_fam(right_delimiter(p))<>0)or@| + (small_char(right_delimiter(p))<>min_quarterword)or@| + (large_fam(right_delimiter(p))<>0)or@| + (large_char(right_delimiter(p))<>min_quarterword) then + begin print(", right-delimiter "); print_delimiter(right_delimiter(p)); + end; +print_subsidiary_data(numerator(p),"\"); +print_subsidiary_data(denominator(p),"/"); +end + +@ That which can be displayed can also be destroyed. + +@<Cases of |flush_node_list| that arise...@>= +style_node: begin free_node(p,style_node_size); goto done; + end; +choice_node:begin flush_node_list(display_mlist(p)); + flush_node_list(text_mlist(p)); + flush_node_list(script_mlist(p)); + flush_node_list(script_script_mlist(p)); + free_node(p,style_node_size); goto done; + end; +ord_noad,op_noad,bin_noad,rel_noad,open_noad,close_noad,punct_noad,inner_noad, + radical_noad,over_noad,under_noad,vcenter_noad,accent_noad:@t@>@;@/ + begin if math_type(nucleus(p))>=sub_box then + flush_node_list(info(nucleus(p))); + if math_type(supscr(p))>=sub_box then + flush_node_list(info(supscr(p))); + if math_type(subscr(p))>=sub_box then + flush_node_list(info(subscr(p))); + if type(p)=radical_noad then free_node(p,radical_noad_size) + else if type(p)=accent_noad then free_node(p,accent_noad_size) + else free_node(p,noad_size); + goto done; + end; +left_noad,right_noad: begin free_node(p,noad_size); goto done; + end; +fraction_noad: begin flush_node_list(info(numerator(p))); + flush_node_list(info(denominator(p))); + free_node(p,fraction_noad_size); goto done; + end; + +@* \[35] Subroutines for math mode. +In order to convert mlists to hlists, i.e., noads to nodes, we need several +subroutines that are conveniently dealt with now. + +Let us first introduce the macros that make it easy to get at the parameters and +other font information. A size code, which is a multiple of 16, is added to a +family number to get an index into the table of internal font numbers +for each combination of family and size. (Be alert: Size codes get +larger as the type gets smaller.) + +@d text_size=0 {size code for the largest size in a family} +@d script_size=16 {size code for the medium size in a family} +@d script_script_size=32 {size code for the smallest size in a family} + +@<Basic printing procedures@>= +procedure print_size(@!s:integer); +begin if s=0 then print_esc("textfont") +else if s=script_size then print_esc("scriptfont") +else print_esc("scriptscriptfont"); +end; + +@ Before an mlist is converted to an hlist, \TeX\ makes sure that +the fonts in family~2 have enough parameters to be math-symbol +fonts, and that the fonts in family~3 have enough parameters to be +math-extension fonts. The math-symbol parameters are referred to by using the +following macros, which take a size code as their parameter; for example, +|num1(cur_size)| gives the value of the |num1| parameter for the current size. +@^parameters for symbols@> +@^font parameters@> + +@d mathsy_end(#)==fam_fnt(2+#)]].sc +@d mathsy(#)==font_info[#+param_base[mathsy_end +@d math_x_height==mathsy(5) {height of `\.x'} +@d math_quad==mathsy(6) {\.{18mu}} +@d num1==mathsy(8) {numerator shift-up in display styles} +@d num2==mathsy(9) {numerator shift-up in non-display, non-\.{\\atop}} +@d num3==mathsy(10) {numerator shift-up in non-display \.{\\atop}} +@d denom1==mathsy(11) {denominator shift-down in display styles} +@d denom2==mathsy(12) {denominator shift-down in non-display styles} +@d sup1==mathsy(13) {superscript shift-up in uncramped display style} +@d sup2==mathsy(14) {superscript shift-up in uncramped non-display} +@d sup3==mathsy(15) {superscript shift-up in cramped styles} +@d sub1==mathsy(16) {subscript shift-down if superscript is absent} +@d sub2==mathsy(17) {subscript shift-down if superscript is present} +@d sup_drop==mathsy(18) {superscript baseline below top of large box} +@d sub_drop==mathsy(19) {subscript baseline below bottom of large box} +@d delim1==mathsy(20) {size of \.{\\atopwithdelims} delimiters + in display styles} +@d delim2==mathsy(21) {size of \.{\\atopwithdelims} delimiters in non-displays} +@d axis_height==mathsy(22) {height of fraction lines above the baseline} +@d total_mathsy_params=22 + +@ The math-extension parameters have similar macros, but the size code is +omitted (since it is always |cur_size| when we refer to such parameters). +@^parameters for symbols@> +@^font parameters@> + +@d mathex(#)==font_info[#+param_base[fam_fnt(3+cur_size)]].sc +@d default_rule_thickness==mathex(8) {thickness of \.{\\over} bars} +@d big_op_spacing1==mathex(9) {minimum clearance above a displayed op} +@d big_op_spacing2==mathex(10) {minimum clearance below a displayed op} +@d big_op_spacing3==mathex(11) {minimum baselineskip above displayed op} +@d big_op_spacing4==mathex(12) {minimum baselineskip below displayed op} +@d big_op_spacing5==mathex(13) {padding above and below displayed limits} +@d total_mathex_params=13 + +@ We also need to compute the change in style between mlists and their +subsidiaries. The following macros define the subsidiary style for +an overlined nucleus (|cramped_style|), for a subscript or a superscript +(|sub_style| or |sup_style|), or for a numerator or denominator (|num_style| +or |denom_style|). + +@d cramped_style(#)==2*(# div 2)+cramped {cramp the style} +@d sub_style(#)==2*(# div 4)+script_style+cramped {smaller and cramped} +@d sup_style(#)==2*(# div 4)+script_style+(# mod 2) {smaller} +@d num_style(#)==#+2-2*(# div 6) {smaller unless already script-script} +@d denom_style(#)==2*(# div 2)+cramped+2-2*(# div 6) {smaller, cramped} + +@ When the style changes, the following piece of program computes associated +information: + +@<Set up the values of |cur_size| and |cur_mu|, based on |cur_style|@>= +begin if cur_style<script_style then cur_size:=text_size +else cur_size:=16*((cur_style-text_style) div 2); +cur_mu:=x_over_n(math_quad(cur_size),18); +end + +@ Here is a function that returns a pointer to a rule node having a given +thickness |t|. The rule will extend horizontally to the boundary of the vlist +that eventually contains it. + +@p function fraction_rule(@!t:scaled):pointer; + {construct the bar for a fraction} +var p:pointer; {the new node} +begin p:=new_rule; height(p):=t; depth(p):=0; fraction_rule:=p; +end; + +@ The |overbar| function returns a pointer to a vlist box that consists of +a given box |b|, above which has been placed a kern of height |k| under a +fraction rule of thickness |t| under additional space of height |t|. + +@p function overbar(@!b:pointer;@!k,@!t:scaled):pointer; +var p,@!q:pointer; {nodes being constructed} +begin p:=new_kern(k); link(p):=b; q:=fraction_rule(t); link(q):=p; +p:=new_kern(t); link(p):=q; overbar:=vpack(p,natural); +end; + +@ The |var_delimiter| function, which finds or constructs a sufficiently +large delimiter, is the most interesting of the auxiliary functions that +currently concern us. Given a pointer |d| to a delimiter field in some noad, +together with a size code |s| and a vertical distance |v|, this function +returns a pointer to a box that contains the smallest variant of |d| whose +height plus depth is |v| or more. (And if no variant is large enough, it +returns the largest available variant.) In particular, this routine will +construct arbitrarily large delimiters from extensible components, if +|d| leads to such characters. + +The value returned is a box whose |shift_amount| has been set so that +the box is vertically centered with respect to the axis in the given size. +If a built-up symbol is returned, the height of the box before shifting +will be the height of its topmost component. + +@p@t\4@>@<Declare subprocedures for |var_delimiter|@> +function var_delimiter(@!d:pointer;@!s:small_number;@!v:scaled):pointer; +label found,continue; +var b:pointer; {the box that will be constructed} +@!f,@!g: internal_font_number; {best-so-far and tentative font codes} +@!c,@!x,@!y: quarterword; {best-so-far and tentative character codes} +@!m,@!n: integer; {the number of extensible pieces} +@!u: scaled; {height-plus-depth of a tentative character} +@!w: scaled; {largest height-plus-depth so far} +@!q: four_quarters; {character info} +@!hd: eight_bits; {height-depth byte} +@!r: four_quarters; {extensible pieces} +@!z: small_number; {runs through font family members} +@!large_attempt: boolean; {are we trying the ``large'' variant?} +begin f:=null_font; w:=0; large_attempt:=false; +z:=small_fam(d); x:=small_char(d); +loop@+ begin @<Look at the variants of |(z,x)|; set |f| and |c| whenever + a better character is found; |goto found| as soon as a + large enough variant is encountered@>; + if large_attempt then goto found; {there were none large enough} + large_attempt:=true; z:=large_fam(d); x:=large_char(d); + end; +found: if f<>null_font then + @<Make variable |b| point to a box for |(f,c)|@> +else begin b:=new_null_box; + width(b):=null_delimiter_space; {use this width if no delimiter was found} + end; +shift_amount(b):=half(height(b)-depth(b)) - axis_height(s); +var_delimiter:=b; +end; + +@ The search process is complicated slightly by the facts that some of the +characters might not be present in some of the fonts, and they might not +be probed in increasing order of height. + +@<Look at the variants of |(z,x)|; set |f| and |c|...@>= +if (z<>0)or(x<>min_quarterword) then + begin z:=z+s+16; + repeat z:=z-16; g:=fam_fnt(z); + if g<>null_font then + @<Look at the list of characters starting with |x| in + font |g|; set |f| and |c| whenever + a better character is found; |goto found| as soon as a + large enough variant is encountered@>; + until z<16; + end + +@ @<Look at the list of characters starting with |x|...@>= +begin y:=x; +if (qo(y)>=font_bc[g])and(qo(y)<=font_ec[g]) then + begin continue: q:=char_info(g)(y); + if char_exists(q) then + begin if char_tag(q)=ext_tag then + begin f:=g; c:=y; goto found; + end; + hd:=height_depth(q); + u:=char_height(g)(hd)+char_depth(g)(hd); + if u>w then + begin f:=g; c:=y; w:=u; + if u>=v then goto found; + end; + if char_tag(q)=list_tag then + begin y:=rem_byte(q); goto continue; + end; + end; + end; +end + +@ Here is a subroutine that creates a new box, whose list contains a +single character, and whose width includes the italic correction for +that character. The height or depth of the box will be negative, if +the height or depth of the character is negative; thus, this routine +may deliver a slightly different result than |hpack| would produce. + +@<Declare subprocedures for |var_delimiter|@>= +function char_box(@!f:internal_font_number;@!c:quarterword):pointer; +var q:four_quarters; +@!hd:eight_bits; {|height_depth| byte} +@!b,@!p:pointer; {the new box and its character node} +begin q:=char_info(f)(c); hd:=height_depth(q); +b:=new_null_box; width(b):=char_width(f)(q)+char_italic(f)(q); +height(b):=char_height(f)(hd); depth(b):=char_depth(f)(hd); +p:=get_avail; character(p):=c; font(p):=f; list_ptr(b):=p; char_box:=b; +end; + +@ When the following code is executed, |char_tag(q)| will be equal to +|ext_tag| if and only if a built-up symbol is supposed to be returned. + +@<Make variable |b| point to a box for |(f,c)|@>= +if char_tag(q)=ext_tag then + @<Construct an extensible character in a new box |b|, + using recipe |rem_byte(q)| and font |f|@> +else b:=char_box(f,c) + +@ When we build an extensible character, it's handy to have the +following subroutine, which puts a given character on top +of the characters already in box |b|: + +@<Declare subprocedures for |var_delimiter|@>= +procedure stack_into_box(@!b:pointer;@!f:internal_font_number; + @!c:quarterword); +var p:pointer; {new node placed into |b|} +begin p:=char_box(f,c); link(p):=list_ptr(b); list_ptr(b):=p; +height(b):=height(p); +end; + +@ Another handy subroutine computes the height plus depth of +a given character: + +@<Declare subprocedures for |var_delimiter|@>= +function height_plus_depth(@!f:internal_font_number;@!c:quarterword):scaled; +var q:four_quarters; +@!hd:eight_bits; {|height_depth| byte} +begin q:=char_info(f)(c); hd:=height_depth(q); +height_plus_depth:=char_height(f)(hd)+char_depth(f)(hd); +end; + +@ @<Construct an extensible...@>= +begin b:=new_null_box; +type(b):=vlist_node; +r:=font_info[exten_base[f]+rem_byte(q)].qqqq;@/ +@<Compute the minimum suitable height, |w|, and the corresponding + number of extension steps, |n|; also set |width(b)|@>; +c:=ext_bot(r); +if c<>min_quarterword then stack_into_box(b,f,c); +c:=ext_rep(r); +for m:=1 to n do stack_into_box(b,f,c); +c:=ext_mid(r); +if c<>min_quarterword then + begin stack_into_box(b,f,c); c:=ext_rep(r); + for m:=1 to n do stack_into_box(b,f,c); + end; +c:=ext_top(r); +if c<>min_quarterword then stack_into_box(b,f,c); +depth(b):=w-height(b); +end + +@ The width of an extensible character is the width of the repeatable +module. If this module does not have positive height plus depth, +we don't use any copies of it, otherwise we use as few as possible +(in groups of two if there is a middle part). + +@<Compute the minimum suitable height, |w|, and...@>= +c:=ext_rep(r); u:=height_plus_depth(f,c); +w:=0; q:=char_info(f)(c); width(b):=char_width(f)(q)+char_italic(f)(q);@/ +c:=ext_bot(r);@+if c<>min_quarterword then w:=w+height_plus_depth(f,c); +c:=ext_mid(r);@+if c<>min_quarterword then w:=w+height_plus_depth(f,c); +c:=ext_top(r);@+if c<>min_quarterword then w:=w+height_plus_depth(f,c); +n:=0; +if u>0 then while w<v do + begin w:=w+u; incr(n); + if ext_mid(r)<>min_quarterword then w:=w+u; + end + +@ The next subroutine is much simpler; it is used for numerators and +denominators of fractions as well as for displayed operators and +their limits above and below. It takes a given box~|b| and +changes it so that the new box is centered in a box of width~|w|. +The centering is done by putting \.{\\hss} glue at the left and right +of the list inside |b|, then packaging the new box; thus, the +actual box might not really be centered, if it already contains +infinite glue. + +The given box might contain a single character whose italic correction +has been added to the width of the box; in this case a compensating +kern is inserted. + +@p function rebox(@!b:pointer;@!w:scaled):pointer; +var p:pointer; {temporary register for list manipulation} +@!f:internal_font_number; {font in a one-character box} +@!v:scaled; {width of a character without italic correction} +begin if (width(b)<>w)and(list_ptr(b)<>null) then + begin if type(b)=vlist_node then b:=hpack(b,natural); + p:=list_ptr(b); + if (is_char_node(p))and(link(p)=null) then + begin f:=font(p); v:=char_width(f)(char_info(f)(character(p))); + if v<>width(b) then link(p):=new_kern(width(b)-v); + end; + free_node(b,box_node_size); + b:=new_glue(ss_glue); link(b):=p; + while link(p)<>null do p:=link(p); + link(p):=new_glue(ss_glue); + rebox:=hpack(b,w,exactly); + end +else begin width(b):=w; rebox:=b; + end; +end; + +@ Here is a subroutine that creates a new glue specification from another +one that is expressed in `\.{mu}', given the value of the math unit. + +@d mu_mult(#)==nx_plus_y(n,#,xn_over_d(#,f,@'200000)) + +@p function math_glue(@!g:pointer;@!m:scaled):pointer; +var p:pointer; {the new glue specification} +@!n:integer; {integer part of |m|} +@!f:scaled; {fraction part of |m|} +begin n:=x_over_n(m,@'200000); f:=remainder;@/ +if f<0 then + begin decr(n); f:=f+@'200000; + end; +p:=get_node(glue_spec_size); +width(p):=mu_mult(width(g)); {convert \.{mu} to \.{pt}} +stretch_order(p):=stretch_order(g); +if stretch_order(p)=normal then stretch(p):=mu_mult(stretch(g)) +else stretch(p):=stretch(g); +shrink_order(p):=shrink_order(g); +if shrink_order(p)=normal then shrink(p):=mu_mult(shrink(g)) +else shrink(p):=shrink(g); +math_glue:=p; +end; + +@ The |math_kern| subroutine removes |mu_glue| from a kern node, given +the value of the math unit. + +@p procedure math_kern(@!p:pointer;@!m:scaled); +var @!n:integer; {integer part of |m|} +@!f:scaled; {fraction part of |m|} +begin if subtype(p)=mu_glue then + begin n:=x_over_n(m,@'200000); f:=remainder;@/ + if f<0 then + begin decr(n); f:=f+@'200000; + end; + width(p):=mu_mult(width(p)); subtype(p):=explicit; + end; +end; + +@ Sometimes it is necessary to destroy an mlist. The following +subroutine empties the current list, assuming that |abs(mode)=mmode|. + +@p procedure flush_math; +begin flush_node_list(link(head)); flush_node_list(incompleat_noad); +link(head):=null; tail:=head; incompleat_noad:=null; +end; + +@* \[36] Typesetting math formulas. +\TeX's most important routine for dealing with formulas is called +|mlist_to_hlist|. After a formula has been scanned and represented as an +mlist, this routine converts it to an hlist that can be placed into a box +or incorporated into the text of a paragraph. There are three implicit +parameters, passed in global variables: |cur_mlist| points to the first +node or noad in the given mlist (and it might be |null|); |cur_style| is a +style code; and |mlist_penalties| is |true| if penalty nodes for potential +line breaks are to be inserted into the resulting hlist. After +|mlist_to_hlist| has acted, |link(temp_head)| points to the translated hlist. + +Since mlists can be inside mlists, the procedure is recursive. And since this +is not part of \TeX's inner loop, the program has been written in a manner +that stresses compactness over efficiency. +@^recursion@> + +@<Glob...@>= +@!cur_mlist:pointer; {beginning of mlist to be translated} +@!cur_style:small_number; {style code at current place in the list} +@!cur_size:small_number; {size code corresponding to |cur_style|} +@!cur_mu:scaled; {the math unit width corresponding to |cur_size|} +@!mlist_penalties:boolean; {should |mlist_to_hlist| insert penalties?} + +@ The recursion in |mlist_to_hlist| is due primarily to a subroutine +called |clean_box| that puts a given noad field into a box using a given +math style; |mlist_to_hlist| can call |clean_box|, which can call +|mlist_to_hlist|. +@^recursion@> + +The box returned by |clean_box| is ``clean'' in the +sense that its |shift_amount| is zero. + +@p procedure@?mlist_to_hlist; forward;@t\2@>@/ +function clean_box(@!p:pointer;@!s:small_number):pointer; +label found; +var q:pointer; {beginning of a list to be boxed} +@!save_style:small_number; {|cur_style| to be restored} +@!x:pointer; {box to be returned} +@!r:pointer; {temporary pointer} +begin case math_type(p) of +math_char: begin cur_mlist:=new_noad; mem[nucleus(cur_mlist)]:=mem[p]; + end; +sub_box: begin q:=info(p); goto found; + end; +sub_mlist: cur_mlist:=info(p); +othercases begin q:=new_null_box; goto found; + end +endcases;@/ +save_style:=cur_style; cur_style:=s; mlist_penalties:=false;@/ +mlist_to_hlist; q:=link(temp_head); {recursive call} +cur_style:=save_style; {restore the style} +@<Set up the values of |cur_size| and |cur_mu|, based on |cur_style|@>; +found: if is_char_node(q)or(q=null) then x:=hpack(q,natural) + else if (link(q)=null)and(type(q)<=vlist_node)and(shift_amount(q)=0) then + x:=q {it's already clean} + else x:=hpack(q,natural); +@<Simplify a trivial box@>; +clean_box:=x; +end; + +@ Here we save memory space in a common case. + +@<Simplify a trivial box@>= +q:=list_ptr(x); +if is_char_node(q) then + begin r:=link(q); + if r<>null then if link(r)=null then if not is_char_node(r) then + if type(r)=kern_node then {unneeded italic correction} + begin free_node(r,small_node_size); link(q):=null; + end; + end + +@ It is convenient to have a procedure that converts a |math_char| +field to an ``unpacked'' form. The |fetch| routine sets |cur_f|, |cur_c|, +and |cur_i| to the font code, character code, and character information bytes of +a given noad field. It also takes care of issuing error messages for +nonexistent characters; in such cases, |char_exists(cur_i)| will be |false| +after |fetch| has acted, and the field will also have been reset to |empty|. + +@p procedure fetch(@!a:pointer); {unpack the |math_char| field |a|} +begin cur_c:=character(a); cur_f:=fam_fnt(fam(a)+cur_size); +if cur_f=null_font then + @<Complain about an undefined family and set |cur_i| null@> +else begin if (qo(cur_c)>=font_bc[cur_f])and(qo(cur_c)<=font_ec[cur_f]) then + cur_i:=char_info(cur_f)(cur_c) + else cur_i:=null_character; + if not(char_exists(cur_i)) then + begin char_warning(cur_f,qo(cur_c)); + math_type(a):=empty; + end; + end; +end; + +@ @<Complain about an undefined family...@>= +begin print_err(""); print_size(cur_size); print_char(" "); +print_int(fam(a)); print(" is undefined (character "); +print_ASCII(qo(cur_c)); print_char(")"); +help4("Somewhere in the math formula just ended, you used the")@/ +("stated character from an undefined font family. For example,")@/ +("plain TeX doesn't allow \it or \sl in subscripts. Proceed,")@/ +("and I'll try to forget that I needed that character."); +error; cur_i:=null_character; math_type(a):=empty; +end + +@ The outputs of |fetch| are placed in global variables. + +@<Glob...@>= +@!cur_f:internal_font_number; {the |font| field of a |math_char|} +@!cur_c:quarterword; {the |character| field of a |math_char|} +@!cur_i:four_quarters; {the |char_info| of a |math_char|, + or a lig/kern instruction} + +@ We need to do a lot of different things, so |mlist_to_hlist| makes two +passes over the given mlist. + +The first pass does most of the processing: It removes ``mu'' spacing from +glue, it recursively evaluates all subsidiary mlists so that only the +top-level mlist remains to be handled, it puts fractions and square roots +and such things into boxes, it attaches subscripts and superscripts, and +it computes the overall height and depth of the top-level mlist so that +the size of delimiters for a |left_noad| and a |right_noad| will be known. +The hlist resulting from each noad is recorded in that noad's |new_hlist| +field, an integer field that replaces the |nucleus| or |thickness|. +@^recursion@> + +The second pass eliminates all noads and inserts the correct glue and +penalties between nodes. + +@d new_hlist(#)==mem[nucleus(#)].int {the translation of an mlist} + +@ Here is the overall plan of |mlist_to_hlist|, and the list of its +local variables. + +@d done_with_noad=80 {go here when a noad has been fully translated} +@d done_with_node=81 {go here when a node has been fully converted} +@d check_dimensions=82 {go here to update |max_h| and |max_d|} +@d delete_q=83 {go here to delete |q| and move to the next node} + +@p@t\4@>@<Declare math construction procedures@> +procedure mlist_to_hlist; +label reswitch, check_dimensions, done_with_noad, done_with_node, delete_q, + done; +var mlist:pointer; {beginning of the given list} +@!penalties:boolean; {should penalty nodes be inserted?} +@!style:small_number; {the given style} +@!save_style:small_number; {holds |cur_style| during recursion} +@!q:pointer; {runs through the mlist} +@!r:pointer; {the most recent noad preceding |q|} +@!r_type:small_number; {the |type| of noad |r|, or |op_noad| if |r=null|} +@!t:small_number; {the effective |type| of noad |q| during the second pass} +@!p,@!x,@!y,@!z: pointer; {temporary registers for list construction} +@!pen:integer; {a penalty to be inserted} +@!s:small_number; {the size of a noad to be deleted} +@!max_h,@!max_d:scaled; {maximum height and depth of the list translated so far} +@!delta:scaled; {offset between subscript and superscript} +begin mlist:=cur_mlist; penalties:=mlist_penalties; +style:=cur_style; {tuck global parameters away as local variables} +q:=mlist; r:=null; r_type:=op_noad; max_h:=0; max_d:=0; +@<Set up the values of |cur_size| and |cur_mu|, based on |cur_style|@>; +while q<>null do @<Process node-or-noad |q| as much as possible in preparation + for the second pass of |mlist_to_hlist|, then move to the next + item in the mlist@>; +@<Convert \(a)a final |bin_noad| to an |ord_noad|@>; +@<Make a second pass over the mlist, removing all noads and inserting the + proper spacing and penalties@>; +end; + +@ We use the fact that no character nodes appear in an mlist, hence +the field |type(q)| is always present. + +@<Process node-or-noad...@>= +begin @<Do first-pass processing based on |type(q)|; |goto done_with_noad| + if a noad has been fully processed, |goto check_dimensions| if it + has been translated into |new_hlist(q)|, or |goto done_with_node| + if a node has been fully processed@>; +check_dimensions: z:=hpack(new_hlist(q),natural); +if height(z)>max_h then max_h:=height(z); +if depth(z)>max_d then max_d:=depth(z); +free_node(z,box_node_size); +done_with_noad: r:=q; r_type:=type(r); +done_with_node: q:=link(q); +end + +@ One of the things we must do on the first pass is change a |bin_noad| to +an |ord_noad| if the |bin_noad| is not in the context of a binary operator. +The values of |r| and |r_type| make this fairly easy. + +@<Do first-pass processing...@>= +reswitch: delta:=0; +case type(q) of +bin_noad: case r_type of + bin_noad,op_noad,rel_noad,open_noad,punct_noad,left_noad: + begin type(q):=ord_noad; goto reswitch; + end; + othercases do_nothing + endcases; +rel_noad,close_noad,punct_noad,right_noad: begin@t@>@;@/ + @<Convert \(a)a final |bin_noad| to an |ord_noad|@>; + if type(q)=right_noad then goto done_with_noad; + end; +@t\4@>@<Cases for noads that can follow a |bin_noad|@>@; +@t\4@>@<Cases for nodes that can appear in an mlist, after which we + |goto done_with_node|@>@; +othercases confusion("mlist1") +@:this can't happen mlist1}{\quad mlist1@> +endcases;@/ +@<Convert \(n)|nucleus(q)| to an hlist and attach the sub/superscripts@> + +@ @<Convert \(a)a final |bin_noad| to an |ord_noad|@>= +if r_type=bin_noad then type(r):=ord_noad + +@ @<Cases for nodes that can appear in an mlist...@>= +style_node: begin cur_style:=subtype(q); + @<Set up the values of |cur_size| and |cur_mu|, based on |cur_style|@>; + goto done_with_node; + end; +choice_node: @<Change this node to a style node followed by the correct choice, + then |goto done_with_node|@>; +ins_node,mark_node,adjust_node, + whatsit_node,penalty_node,disc_node: goto done_with_node; +rule_node: begin if height(q)>max_h then max_h:=height(q); + if depth(q)>max_d then max_d:=depth(q); goto done_with_node; + end; +glue_node: begin @<Convert \(m)math glue to ordinary glue@>; + goto done_with_node; + end; +kern_node: begin math_kern(q,cur_mu); goto done_with_node; + end; + +@ @d choose_mlist(#)==begin p:=#(q); #(q):=null;@+end + +@<Change this node to a style node...@>= +begin case cur_style div 2 of +0: choose_mlist(display_mlist); {|display_style=0|} +1: choose_mlist(text_mlist); {|text_style=2|} +2: choose_mlist(script_mlist); {|script_style=4|} +3: choose_mlist(script_script_mlist); {|script_script_style=6|} +end; {there are no other cases} +flush_node_list(display_mlist(q)); +flush_node_list(text_mlist(q)); +flush_node_list(script_mlist(q)); +flush_node_list(script_script_mlist(q));@/ +type(q):=style_node; subtype(q):=cur_style; width(q):=0; depth(q):=0; +if p<>null then + begin z:=link(q); link(q):=p; + while link(p)<>null do p:=link(p); + link(p):=z; + end; +goto done_with_node; +end + +@ Conditional math glue (`\.{\\nonscript}') results in a |glue_node| +pointing to |zero_glue|, with |subtype(q)=cond_math_glue|; in such a case +the node following will be eliminated if it is a glue or kern node and if the +current size is different from |text_size|. Unconditional math glue +(`\.{\\muskip}') is converted to normal glue by multiplying the dimensions +by |cur_mu|. +@!@:non_script_}{\.{\\nonscript} primitive@> + +@<Convert \(m)math glue to ordinary glue@>= +if subtype(q)=mu_glue then + begin x:=glue_ptr(q); + y:=math_glue(x,cur_mu); delete_glue_ref(x); glue_ptr(q):=y; + subtype(q):=normal; + end +else if (cur_size<>text_size)and(subtype(q)=cond_math_glue) then + begin p:=link(q); + if p<>null then if (type(p)=glue_node)or(type(p)=kern_node) then + begin link(q):=link(p); link(p):=null; flush_node_list(p); + end; + end + +@ @<Cases for noads that can follow a |bin_noad|@>= +left_noad: goto done_with_noad; +fraction_noad: begin make_fraction(q); goto check_dimensions; + end; +op_noad: begin delta:=make_op(q); + if subtype(q)=limits then goto check_dimensions; + end; +ord_noad: make_ord(q); +open_noad,inner_noad: do_nothing; +radical_noad: make_radical(q); +over_noad: make_over(q); +under_noad: make_under(q); +accent_noad: make_math_accent(q); +vcenter_noad: make_vcenter(q); + +@ Most of the actual construction work of |mlist_to_hlist| is done +by procedures with names +like |make_fraction|, |make_radical|, etc. To illustrate +the general setup of such procedures, let's begin with a couple of +simple ones. + +@<Declare math...@>= +procedure make_over(@!q:pointer); +begin info(nucleus(q)):=@| + overbar(clean_box(nucleus(q),cramped_style(cur_style)),@| + 3*default_rule_thickness,default_rule_thickness); +math_type(nucleus(q)):=sub_box; +end; + +@ @<Declare math...@>= +procedure make_under(@!q:pointer); +var p,@!x,@!y: pointer; {temporary registers for box construction} +@!delta:scaled; {overall height plus depth} +begin x:=clean_box(nucleus(q),cur_style); +p:=new_kern(3*default_rule_thickness); link(x):=p; +link(p):=fraction_rule(default_rule_thickness); +y:=vpack(x,natural); +delta:=height(y)+depth(y)+default_rule_thickness; +height(y):=height(x); depth(y):=delta-height(y); +info(nucleus(q)):=y; math_type(nucleus(q)):=sub_box; +end; + +@ @<Declare math...@>= +procedure make_vcenter(@!q:pointer); +var v:pointer; {the box that should be centered vertically} +@!delta:scaled; {its height plus depth} +begin v:=info(nucleus(q)); +if type(v)<>vlist_node then confusion("vcenter"); +@:this can't happen vcenter}{\quad vcenter@> +delta:=height(v)+depth(v); +height(v):=axis_height(cur_size)+half(delta); +depth(v):=delta-height(v); +end; + +@ According to the rules in the \.{DVI} file specifications, we ensure alignment +@^square roots@> +between a square root sign and the rule above its nucleus by assuming that the +baseline of the square-root symbol is the same as the bottom of the rule. The +height of the square-root symbol will be the thickness of the rule, and the +depth of the square-root symbol should exceed or equal the height-plus-depth +of the nucleus plus a certain minimum clearance~|clr|. The symbol will be +placed so that the actual clearance is |clr| plus half the excess. + +@<Declare math...@>= +procedure make_radical(@!q:pointer); +var x,@!y:pointer; {temporary registers for box construction} +@!delta,@!clr:scaled; {dimensions involved in the calculation} +begin x:=clean_box(nucleus(q),cramped_style(cur_style)); +if cur_style<text_style then {display style} + clr:=default_rule_thickness+(abs(math_x_height(cur_size)) div 4) +else begin clr:=default_rule_thickness; clr:=clr + (abs(clr) div 4); + end; +y:=var_delimiter(left_delimiter(q),cur_size,height(x)+depth(x)+clr+ + default_rule_thickness); +delta:=depth(y)-(height(x)+depth(x)+clr); +if delta>0 then clr:=clr+half(delta); {increase the actual clearance} +shift_amount(y):=-(height(x)+clr); +link(y):=overbar(x,clr,height(y)); +info(nucleus(q)):=hpack(y,natural); math_type(nucleus(q)):=sub_box; +end; + +@ Slants are not considered when placing accents in math mode. The accenter is +centered over the accentee, and the accent width is treated as zero with +respect to the size of the final box. + +@<Declare math...@>= +procedure make_math_accent(@!q:pointer); +label done,done1; +var p,@!x,@!y:pointer; {temporary registers for box construction} +@!a:integer; {address of lig/kern instruction} +@!c:quarterword; {accent character} +@!f:internal_font_number; {its font} +@!i:four_quarters; {its |char_info|} +@!s:scaled; {amount to skew the accent to the right} +@!h:scaled; {height of character being accented} +@!delta:scaled; {space to remove between accent and accentee} +@!w:scaled; {width of the accentee, not including sub/superscripts} +begin fetch(accent_chr(q)); +if char_exists(cur_i) then + begin i:=cur_i; c:=cur_c; f:=cur_f;@/ + @<Compute the amount of skew@>; + x:=clean_box(nucleus(q),cramped_style(cur_style)); w:=width(x); h:=height(x); + @<Switch to a larger accent if available and appropriate@>; + if h<x_height(f) then delta:=h@+else delta:=x_height(f); + if (math_type(supscr(q))<>empty)or(math_type(subscr(q))<>empty) then + if math_type(nucleus(q))=math_char then + @<Swap the subscript and superscript into box |x|@>; + y:=char_box(f,c); + shift_amount(y):=s+half(w-width(y)); + width(y):=0; p:=new_kern(-delta); link(p):=x; link(y):=p; + y:=vpack(y,natural); width(y):=width(x); + if height(y)<h then @<Make the height of box |y| equal to |h|@>; + info(nucleus(q)):=y; + math_type(nucleus(q)):=sub_box; + end; +end; + +@ @<Make the height of box |y|...@>= +begin p:=new_kern(h-height(y)); link(p):=list_ptr(y); list_ptr(y):=p; +height(y):=h; +end + +@ @<Switch to a larger accent if available and appropriate@>= +loop@+ begin if char_tag(i)<>list_tag then goto done; + y:=rem_byte(i); + i:=char_info(f)(y); + if not char_exists(i) then goto done; + if char_width(f)(i)>w then goto done; + c:=y; + end; +done: + +@ @<Compute the amount of skew@>= +s:=0; +if math_type(nucleus(q))=math_char then + begin fetch(nucleus(q)); + if char_tag(cur_i)=lig_tag then + begin a:=lig_kern_start(cur_f)(cur_i); + cur_i:=font_info[a].qqqq; + if skip_byte(cur_i)>stop_flag then + begin a:=lig_kern_restart(cur_f)(cur_i); + cur_i:=font_info[a].qqqq; + end; + loop@+ begin if qo(next_char(cur_i))=skew_char[cur_f] then + begin if op_byte(cur_i)>=kern_flag then + if skip_byte(cur_i)<=stop_flag then s:=char_kern(cur_f)(cur_i); + goto done1; + end; + if skip_byte(cur_i)>=stop_flag then goto done1; + a:=a+qo(skip_byte(cur_i))+1; + cur_i:=font_info[a].qqqq; + end; + end; + end; +done1: + +@ @<Swap the subscript and superscript into box |x|@>= +begin flush_node_list(x); x:=new_noad; +mem[nucleus(x)]:=mem[nucleus(q)]; +mem[supscr(x)]:=mem[supscr(q)]; +mem[subscr(x)]:=mem[subscr(q)];@/ +mem[supscr(q)].hh:=empty_field; +mem[subscr(q)].hh:=empty_field;@/ +math_type(nucleus(q)):=sub_mlist; info(nucleus(q)):=x; +x:=clean_box(nucleus(q),cur_style); delta:=delta+height(x)-h; h:=height(x); +end + +@ The |make_fraction| procedure is a bit different because it sets +|new_hlist(q)| directly rather than making a sub-box. + +@<Declare math...@>= +procedure make_fraction(@!q:pointer); +var p,@!v,@!x,@!y,@!z:pointer; {temporary registers for box construction} +@!delta,@!delta1,@!delta2,@!shift_up,@!shift_down,@!clr:scaled; + {dimensions for box calculations} +begin if thickness(q)=default_code then thickness(q):=default_rule_thickness; +@<Create equal-width boxes |x| and |z| for the numerator and denominator, + and compute the default amounts |shift_up| and |shift_down| by which they + are displaced from the baseline@>; +if thickness(q)=0 then @<Adjust \(s)|shift_up| and |shift_down| for the case + of no fraction line@> +else @<Adjust \(s)|shift_up| and |shift_down| for the case of a fraction line@>; +@<Construct a vlist box for the fraction, according to |shift_up| and + |shift_down|@>; +@<Put the \(f)fraction into a box with its delimiters, and make |new_hlist(q)| + point to it@>; +end; + +@ @<Create equal-width boxes |x| and |z| for the numerator and denom...@>= +x:=clean_box(numerator(q),num_style(cur_style)); +z:=clean_box(denominator(q),denom_style(cur_style)); +if width(x)<width(z) then x:=rebox(x,width(z)) +else z:=rebox(z,width(x)); +if cur_style<text_style then {display style} + begin shift_up:=num1(cur_size); shift_down:=denom1(cur_size); + end +else begin shift_down:=denom2(cur_size); + if thickness(q)<>0 then shift_up:=num2(cur_size) + else shift_up:=num3(cur_size); + end + +@ The numerator and denominator must be separated by a certain minimum +clearance, called |clr| in the following program. The difference between +|clr| and the actual clearance is |2delta|. + +@<Adjust \(s)|shift_up| and |shift_down| for the case of no fraction line@>= +begin if cur_style<text_style then clr:=7*default_rule_thickness +else clr:=3*default_rule_thickness; +delta:=half(clr-((shift_up-depth(x))-(height(z)-shift_down))); +if delta>0 then + begin shift_up:=shift_up+delta; + shift_down:=shift_down+delta; + end; +end + +@ In the case of a fraction line, the minimum clearance depends on the actual +thickness of the line. + +@<Adjust \(s)|shift_up| and |shift_down| for the case of a fraction line@>= +begin if cur_style<text_style then clr:=3*thickness(q) +else clr:=thickness(q); +delta:=half(thickness(q)); +delta1:=clr-((shift_up-depth(x))-(axis_height(cur_size)+delta)); +delta2:=clr-((axis_height(cur_size)-delta)-(height(z)-shift_down)); +if delta1>0 then shift_up:=shift_up+delta1; +if delta2>0 then shift_down:=shift_down+delta2; +end + +@ @<Construct a vlist box for the fraction...@>= +v:=new_null_box; type(v):=vlist_node; +height(v):=shift_up+height(x); depth(v):=depth(z)+shift_down; +width(v):=width(x); {this also equals |width(z)|} +if thickness(q)=0 then + begin p:=new_kern((shift_up-depth(x))-(height(z)-shift_down)); + link(p):=z; + end +else begin y:=fraction_rule(thickness(q));@/ + p:=new_kern((axis_height(cur_size)-delta)-@|(height(z)-shift_down));@/ + link(y):=p; link(p):=z;@/ + p:=new_kern((shift_up-depth(x))-(axis_height(cur_size)+delta)); + link(p):=y; + end; +link(x):=p; list_ptr(v):=x + +@ @<Put the \(f)fraction into a box with its delimiters...@>= +if cur_style<text_style then delta:=delim1(cur_size) +else delta:=delim2(cur_size); +x:=var_delimiter(left_delimiter(q), cur_size, delta); link(x):=v;@/ +z:=var_delimiter(right_delimiter(q), cur_size, delta); link(v):=z;@/ +new_hlist(q):=hpack(x,natural) + +@ If the nucleus of an |op_noad| is a single character, it is to be +centered vertically with respect to the axis, after first being enlarged +(via a character list in the font) if we are in display style. The normal +convention for placing displayed limits is to put them above and below the +operator in display style. + +The italic correction is removed from the character if there is a subscript +and the limits are not being displayed. The |make_op| +routine returns the value that should be used as an offset between +subscript and superscript. + +After |make_op| has acted, |subtype(q)| will be |limits| if and only if +the limits have been set above and below the operator. In that case, +|new_hlist(q)| will already contain the desired final box. + +@<Declare math...@>= +function make_op(@!q:pointer):scaled; +var delta:scaled; {offset between subscript and superscript} +@!p,@!v,@!x,@!y,@!z:pointer; {temporary registers for box construction} +@!c:quarterword;@+@!i:four_quarters; {registers for character examination} +@!shift_up,@!shift_down:scaled; {dimensions for box calculation} +begin if (subtype(q)=normal)and(cur_style<text_style) then + subtype(q):=limits; +if math_type(nucleus(q))=math_char then + begin fetch(nucleus(q)); + if (cur_style<text_style)and(char_tag(cur_i)=list_tag) then {make it larger} + begin c:=rem_byte(cur_i); i:=char_info(cur_f)(c); + if char_exists(i) then + begin cur_c:=c; cur_i:=i; character(nucleus(q)):=c; + end; + end; + delta:=char_italic(cur_f)(cur_i); x:=clean_box(nucleus(q),cur_style); + if (math_type(subscr(q))<>empty)and(subtype(q)<>limits) then + width(x):=width(x)-delta; {remove italic correction} + shift_amount(x):=half(height(x)-depth(x)) - axis_height(cur_size); + {center vertically} + math_type(nucleus(q)):=sub_box; info(nucleus(q)):=x; + end +else delta:=0; +if subtype(q)=limits then + @<Construct a box with limits above and below it, skewed by |delta|@>; +make_op:=delta; +end; + +@ The following program builds a vlist box |v| for displayed limits. The +width of the box is not affected by the fact that the limits may be skewed. + +@<Construct a box with limits above and below it...@>= +begin x:=clean_box(supscr(q),sup_style(cur_style)); +y:=clean_box(nucleus(q),cur_style); +z:=clean_box(subscr(q),sub_style(cur_style)); +v:=new_null_box; type(v):=vlist_node; width(v):=width(y); +if width(x)>width(v) then width(v):=width(x); +if width(z)>width(v) then width(v):=width(z); +x:=rebox(x,width(v)); y:=rebox(y,width(v)); z:=rebox(z,width(v));@/ +shift_amount(x):=half(delta); shift_amount(z):=-shift_amount(x); +height(v):=height(y); depth(v):=depth(y); +@<Attach the limits to |y| and adjust |height(v)|, |depth(v)| to + account for their presence@>; +new_hlist(q):=v; +end + +@ We use |shift_up| and |shift_down| in the following program for the +amount of glue between the displayed operator |y| and its limits |x| and +|z|. The vlist inside box |v| will consist of |x| followed by |y| followed +by |z|, with kern nodes for the spaces between and around them. + +@<Attach the limits to |y| and adjust |height(v)|, |depth(v)|...@>= +if math_type(supscr(q))=empty then + begin free_node(x,box_node_size); list_ptr(v):=y; + end +else begin shift_up:=big_op_spacing3-depth(x); + if shift_up<big_op_spacing1 then shift_up:=big_op_spacing1; + p:=new_kern(shift_up); link(p):=y; link(x):=p;@/ + p:=new_kern(big_op_spacing5); link(p):=x; list_ptr(v):=p; + height(v):=height(v)+big_op_spacing5+height(x)+depth(x)+shift_up; + end; +if math_type(subscr(q))=empty then free_node(z,box_node_size) +else begin shift_down:=big_op_spacing4-height(z); + if shift_down<big_op_spacing2 then shift_down:=big_op_spacing2; + p:=new_kern(shift_down); link(y):=p; link(p):=z;@/ + p:=new_kern(big_op_spacing5); link(z):=p; + depth(v):=depth(v)+big_op_spacing5+height(z)+depth(z)+shift_down; + end + +@ A ligature found in a math formula does not create a |ligature_node|, because +there is no question of hyphenation afterwards; the ligature will simply be +stored in an ordinary |char_node|, after residing in an |ord_noad|. + +The |math_type| is converted to |math_text_char| here if we would not want to +apply an italic correction to the current character unless it belongs +to a math font (i.e., a font with |space=0|). + +No boundary characters enter into these ligatures. + +@<Declare math...@>= +procedure make_ord(@!q:pointer); +label restart,exit; +var a:integer; {address of lig/kern instruction} +@!p,@!r:pointer; {temporary registers for list manipulation} +begin restart:@t@>@;@/ +if math_type(subscr(q))=empty then if math_type(supscr(q))=empty then + if math_type(nucleus(q))=math_char then + begin p:=link(q); + if p<>null then if (type(p)>=ord_noad)and(type(p)<=punct_noad) then + if math_type(nucleus(p))=math_char then + if fam(nucleus(p))=fam(nucleus(q)) then + begin math_type(nucleus(q)):=math_text_char; + fetch(nucleus(q)); + if char_tag(cur_i)=lig_tag then + begin a:=lig_kern_start(cur_f)(cur_i); + cur_c:=character(nucleus(p)); + cur_i:=font_info[a].qqqq; + if skip_byte(cur_i)>stop_flag then + begin a:=lig_kern_restart(cur_f)(cur_i); + cur_i:=font_info[a].qqqq; + end; + loop@+ begin @<If instruction |cur_i| is a kern with |cur_c|, attach + the kern after~|q|; or if it is a ligature with |cur_c|, combine + noads |q| and~|p| appropriately; then |return| if the cursor has + moved past a noad, or |goto restart|@>; + if skip_byte(cur_i)>=stop_flag then return; + a:=a+qo(skip_byte(cur_i))+1; + cur_i:=font_info[a].qqqq; + end; + end; + end; + end; +exit:end; + +@ Note that a ligature between an |ord_noad| and another kind of noad +is replaced by an |ord_noad|, when the two noads collapse into one. +But we could make a parenthesis (say) change shape when it follows +certain letters. Presumably a font designer will define such +ligatures only when this convention makes sense. + +\chardef\?='174 % vertical line to indicate character retention + +@<If instruction |cur_i| is a kern with |cur_c|, ...@>= +if next_char(cur_i)=cur_c then if skip_byte(cur_i)<=stop_flag then + if op_byte(cur_i)>=kern_flag then + begin p:=new_kern(char_kern(cur_f)(cur_i)); + link(p):=link(q); link(q):=p; return; + end + else begin check_interrupt; {allow a way out of infinite ligature loop} + case op_byte(cur_i) of + qi(1),qi(5): character(nucleus(q)):=rem_byte(cur_i); {\.{=:\?}, \.{=:\?>}} + qi(2),qi(6): character(nucleus(p)):=rem_byte(cur_i); {\.{\?=:}, \.{\?=:>}} + qi(3),qi(7),qi(11):begin r:=new_noad; {\.{\?=:\?}, \.{\?=:\?>}, \.{\?=:\?>>}} + character(nucleus(r)):=rem_byte(cur_i); + fam(nucleus(r)):=fam(nucleus(q));@/ + link(q):=r; link(r):=p; + if op_byte(cur_i)<qi(11) then math_type(nucleus(r)):=math_char + else math_type(nucleus(r)):=math_text_char; {prevent combination} + end; + othercases begin link(q):=link(p); + character(nucleus(q)):=rem_byte(cur_i); {\.{=:}} + mem[subscr(q)]:=mem[subscr(p)]; mem[supscr(q)]:=mem[supscr(p)];@/ + free_node(p,noad_size); + end + endcases; + if op_byte(cur_i)>qi(3) then return; + math_type(nucleus(q)):=math_char; goto restart; + end + +@ When we get to the following part of the program, we have ``fallen through'' +from cases that did not lead to |check_dimensions| or |done_with_noad| or +|done_with_node|. Thus, |q|~points to a noad whose nucleus may need to be +converted to an hlist, and whose subscripts and superscripts need to be +appended if they are present. + +If |nucleus(q)| is not a |math_char|, the variable |delta| is the amount +by which a superscript should be moved right with respect to a subscript +when both are present. +@^subscripts@> +@^superscripts@> + +@<Convert \(n)|nucleus(q)| to an hlist and attach the sub/superscripts@>= +case math_type(nucleus(q)) of +math_char, math_text_char: + @<Create a character node |p| for |nucleus(q)|, possibly followed + by a kern node for the italic correction, and set |delta| to the + italic correction if a subscript is present@>; +empty: p:=null; +sub_box: p:=info(nucleus(q)); +sub_mlist: begin cur_mlist:=info(nucleus(q)); save_style:=cur_style; + mlist_penalties:=false; mlist_to_hlist; {recursive call} +@^recursion@> + cur_style:=save_style; @<Set up the values...@>; + p:=hpack(link(temp_head),natural); + end; +othercases confusion("mlist2") +@:this can't happen mlist2}{\quad mlist2@> +endcases;@/ +new_hlist(q):=p; +if (math_type(subscr(q))=empty)and(math_type(supscr(q))=empty) then + goto check_dimensions; +make_scripts(q,delta) + +@ @<Create a character node |p| for |nucleus(q)|...@>= +begin fetch(nucleus(q)); +if char_exists(cur_i) then + begin delta:=char_italic(cur_f)(cur_i); p:=new_character(cur_f,qo(cur_c)); + if (math_type(nucleus(q))=math_text_char)and(space(cur_f)<>0) then + delta:=0; {no italic correction in mid-word of text font} + if (math_type(subscr(q))=empty)and(delta<>0) then + begin link(p):=new_kern(delta); delta:=0; + end; + end +else p:=null; +end + +@ The purpose of |make_scripts(q,delta)| is to attach the subscript and/or +superscript of noad |q| to the list that starts at |new_hlist(q)|, +given that subscript and superscript aren't both empty. The superscript +will appear to the right of the subscript by a given distance |delta|. + +We set |shift_down| and |shift_up| to the minimum amounts to shift the +baseline of subscripts and superscripts based on the given nucleus. + +@<Declare math...@>= +procedure make_scripts(@!q:pointer;@!delta:scaled); +var p,@!x,@!y,@!z:pointer; {temporary registers for box construction} +@!shift_up,@!shift_down,@!clr:scaled; {dimensions in the calculation} +@!t:small_number; {subsidiary size code} +begin p:=new_hlist(q); +if is_char_node(p) then + begin shift_up:=0; shift_down:=0; + end +else begin z:=hpack(p,natural); + if cur_style<script_style then t:=script_size@+else t:=script_script_size; + shift_up:=height(z)-sup_drop(t); + shift_down:=depth(z)+sub_drop(t); + free_node(z,box_node_size); + end; +if math_type(supscr(q))=empty then + @<Construct a subscript box |x| when there is no superscript@> +else begin @<Construct a superscript box |x|@>; + if math_type(subscr(q))=empty then shift_amount(x):=-shift_up + else @<Construct a sub/superscript combination box |x|, with the + superscript offset by |delta|@>; + end; +if new_hlist(q)=null then new_hlist(q):=x +else begin p:=new_hlist(q); + while link(p)<>null do p:=link(p); + link(p):=x; + end; +end; + +@ When there is a subscript without a superscript, the top of the subscript +should not exceed the baseline plus four-fifths of the x-height. + +@<Construct a subscript box |x| when there is no superscript@>= +begin x:=clean_box(subscr(q),sub_style(cur_style)); +width(x):=width(x)+script_space; +if shift_down<sub1(cur_size) then shift_down:=sub1(cur_size); +clr:=height(x)-(abs(math_x_height(cur_size)*4) div 5); +if shift_down<clr then shift_down:=clr; +shift_amount(x):=shift_down; +end + +@ The bottom of a superscript should never descend below the baseline plus +one-fourth of the x-height. + +@<Construct a superscript box |x|@>= +begin x:=clean_box(supscr(q),sup_style(cur_style)); +width(x):=width(x)+script_space; +if odd(cur_style) then clr:=sup3(cur_size) +else if cur_style<text_style then clr:=sup1(cur_size) +else clr:=sup2(cur_size); +if shift_up<clr then shift_up:=clr; +clr:=depth(x)+(abs(math_x_height(cur_size)) div 4); +if shift_up<clr then shift_up:=clr; +end + +@ When both subscript and superscript are present, the subscript must be +separated from the superscript by at least four times |default_rule_thickness|. +If this condition would be violated, the subscript moves down, after which +both subscript and superscript move up so that the bottom of the superscript +is at least as high as the baseline plus four-fifths of the x-height. + +@<Construct a sub/superscript combination box |x|...@>= +begin y:=clean_box(subscr(q),sub_style(cur_style)); +width(y):=width(y)+script_space; +if shift_down<sub2(cur_size) then shift_down:=sub2(cur_size); +clr:=4*default_rule_thickness- + ((shift_up-depth(x))-(height(y)-shift_down)); +if clr>0 then + begin shift_down:=shift_down+clr; + clr:=(abs(math_x_height(cur_size)*4) div 5)-(shift_up-depth(x)); + if clr>0 then + begin shift_up:=shift_up+clr; + shift_down:=shift_down-clr; + end; + end; +shift_amount(x):=delta; {superscript is |delta| to the right of the subscript} +p:=new_kern((shift_up-depth(x))-(height(y)-shift_down)); link(x):=p; link(p):=y; +x:=vpack(x,natural); shift_amount(x):=shift_down; +end + +@ We have now tied up all the loose ends of the first pass of |mlist_to_hlist|. +The second pass simply goes through and hooks everything together with the +proper glue and penalties. It also handles the |left_noad| and |right_noad| that +might be present, since |max_h| and |max_d| are now known. Variable |p| points +to a node at the current end of the final hlist. + +@<Make a second pass over the mlist, ...@>= +p:=temp_head; link(p):=null; q:=mlist; r_type:=0; cur_style:=style; +@<Set up the values of |cur_size| and |cur_mu|, based on |cur_style|@>; +while q<>null do + begin @<If node |q| is a style node, change the style and |goto delete_q|; + otherwise if it is not a noad, put it into the hlist, + advance |q|, and |goto done|; otherwise set |s| to the size + of noad |q|, set |t| to the associated type (|ord_noad.. + inner_noad|), and set |pen| to the associated penalty@>; + @<Append inter-element spacing based on |r_type| and |t|@>; + @<Append any |new_hlist| entries for |q|, and any appropriate penalties@>; + r_type:=t; + delete_q: r:=q; q:=link(q); free_node(r,s); + done: end + +@ Just before doing the big |case| switch in the second pass, the program +sets up default values so that most of the branches are short. + +@<If node |q| is a style node, change the style...@>= +t:=ord_noad; s:=noad_size; pen:=inf_penalty; +case type(q) of +op_noad,open_noad,close_noad,punct_noad,inner_noad: t:=type(q); +bin_noad: begin t:=bin_noad; pen:=bin_op_penalty; + end; +rel_noad: begin t:=rel_noad; pen:=rel_penalty; + end; +ord_noad,vcenter_noad,over_noad,under_noad: do_nothing; +radical_noad: s:=radical_noad_size; +accent_noad: s:=accent_noad_size; +fraction_noad: begin t:=inner_noad; s:=fraction_noad_size; + end; +left_noad,right_noad: t:=make_left_right(q,style,max_d,max_h); +style_node: @<Change the current style and |goto delete_q|@>; +whatsit_node,penalty_node,rule_node,disc_node,adjust_node,ins_node,mark_node, + glue_node,kern_node:@t@>@;@/ + begin link(p):=q; p:=q; q:=link(q); link(p):=null; goto done; + end; +othercases confusion("mlist3") +@:this can't happen mlist3}{\quad mlist3@> +endcases + +@ The |make_left_right| function constructs a left or right delimiter of +the required size and returns the value |open_noad| or |close_noad|. The +|right_noad| and |left_noad| will both be based on the original |style|, +so they will have consistent sizes. + +We use the fact that |right_noad-left_noad=close_noad-open_noad|. + +@<Declare math...@>= +function make_left_right(@!q:pointer;@!style:small_number; + @!max_d,@!max_h:scaled):small_number; +var delta,@!delta1,@!delta2:scaled; {dimensions used in the calculation} +begin if style<script_style then cur_size:=text_size +else cur_size:=16*((style-text_style) div 2); +delta2:=max_d+axis_height(cur_size); +delta1:=max_h+max_d-delta2; +if delta2>delta1 then delta1:=delta2; {|delta1| is max distance from axis} +delta:=(delta1 div 500)*delimiter_factor; +delta2:=delta1+delta1-delimiter_shortfall; +if delta<delta2 then delta:=delta2; +new_hlist(q):=var_delimiter(delimiter(q),cur_size,delta); +make_left_right:=type(q)-(left_noad-open_noad); {|open_noad| or |close_noad|} +end; + +@ @<Change the current style and |goto delete_q|@>= +begin cur_style:=subtype(q); s:=style_node_size; +@<Set up the values of |cur_size| and |cur_mu|, based on |cur_style|@>; +goto delete_q; +end + +@ The inter-element spacing in math formulas depends on a $8\times8$ table that +\TeX\ preloads as a 64-digit string. The elements of this string have the +following significance: +$$\vbox{\halign{#\hfil\cr +\.0 means no space;\cr +\.1 means a conditional thin space (\.{\\nonscript\\mskip\\thinmuskip});\cr +\.2 means a thin space (\.{\\mskip\\thinmuskip});\cr +\.3 means a conditional medium space + (\.{\\nonscript\\mskip\\medmuskip});\cr +\.4 means a conditional thick space + (\.{\\nonscript\\mskip\\thickmuskip});\cr +\.* means an impossible case.\cr}}$$ +This is all pretty cryptic, but {\sl The \TeX book\/} explains what is +supposed to happen, and the string makes it happen. +@:TeXbook}{\sl The \TeX book@> + +A global variable |magic_offset| is computed so that if |a| and |b| are +in the range |ord_noad..inner_noad|, then |str_pool[a*8+b+magic_offset]| +is the digit for spacing between noad types |a| and |b|. + +If \PASCAL\ had provided a good way to preload constant arrays, this part of +the program would not have been so strange. +@:PASCAL}{\PASCAL@> + +@d math_spacing=@;@/ +@t\hskip-35pt@> +"0234000122*4000133**3**344*0400400*000000234000111*1111112341011" +@t$ \hskip-35pt$@> + +@<Glob...@>= +@!magic_offset:integer; {used to find inter-element spacing} + +@ @<Compute the magic offset@>= +magic_offset:=str_start[math_spacing]-9*ord_noad + +@ @<Append inter-element spacing based on |r_type| and |t|@>= +if r_type>0 then {not the first noad} + begin case so(str_pool[r_type*8+t+magic_offset]) of + "0": x:=0; + "1": if cur_style<script_style then x:=thin_mu_skip_code@+else x:=0; + "2": x:=thin_mu_skip_code; + "3": if cur_style<script_style then x:=med_mu_skip_code@+else x:=0; + "4": if cur_style<script_style then x:=thick_mu_skip_code@+else x:=0; + othercases confusion("mlist4") +@:this can't happen mlist4}{\quad mlist4@> + endcases; + if x<>0 then + begin y:=math_glue(glue_par(x),cur_mu); + z:=new_glue(y); glue_ref_count(y):=null; link(p):=z; p:=z;@/ + subtype(z):=x+1; {store a symbolic subtype} + end; + end + +@ We insert a penalty node after the hlist entries of noad |q| if |pen| +is not an ``infinite'' penalty, and if the node immediately following |q| +is not a penalty node or a |rel_noad| or absent entirely. + +@<Append any |new_hlist| entries for |q|, and any appropriate penalties@>= +if new_hlist(q)<>null then + begin link(p):=new_hlist(q); + repeat p:=link(p); + until link(p)=null; + end; +if penalties then if link(q)<>null then if pen<inf_penalty then + begin r_type:=type(link(q)); + if r_type<>penalty_node then if r_type<>rel_noad then + begin z:=new_penalty(pen); link(p):=z; p:=z; + end; + end + +@* \[37] Alignment. +It's sort of a miracle whenever \.{\\halign} and \.{\\valign} work, because +they cut across so many of the control structures of \TeX. + +Therefore the +present page is probably not the best place for a beginner to start reading +this program; it is better to master everything else first. + +Let us focus our thoughts on an example of what the input might be, in order +to get some idea about how the alignment miracle happens. The example doesn't +do anything useful, but it is sufficiently general to indicate all of the +special cases that must be dealt with; please do not be disturbed by its +apparent complexity and meaninglessness. +$$\vbox{\halign{\.{#}\hfil\cr +{}\\tabskip 2pt plus 3pt\cr +{}\\halign to 300pt\{u1\#v1\&\cr +\hskip 50pt\\tabskip 1pt plus 1fil u2\#v2\&\cr +\hskip 50pt u3\#v3\\cr\cr +\hskip 25pt a1\&\\omit a2\&\\vrule\\cr\cr +\hskip 25pt \\noalign\{\\vskip 3pt\}\cr +\hskip 25pt b1\\span b2\\cr\cr +\hskip 25pt \\omit\&c2\\span\\omit\\cr\}\cr}}$$ +Here's what happens: + +\yskip +(0) When `\.{\\halign to 300pt\{}' is scanned, the |scan_spec| routine +places the 300pt dimension onto the |save_stack|, and an |align_group| +code is placed above it. This will make it possible to complete the alignment +when the matching `\.\}' is found. + +(1) The preamble is scanned next. Macros in the preamble are not expanded, +@^preamble@> +except as part of a tabskip specification. For example, if \.{u2} had been +a macro in the preamble above, it would have been expanded, since \TeX\ +must look for `\.{minus...}' as part of the tabskip glue. A ``preamble list'' +is constructed based on the user's preamble; in our case it contains the +following seven items: +$$\vbox{\halign{\.{#}\hfil\qquad&(#)\hfil\cr +{}\\glue 2pt plus 3pt&the tabskip preceding column 1\cr +{}\\alignrecord, width $-\infty$&preamble info for column 1\cr +{}\\glue 2pt plus 3pt&the tabskip between columns 1 and 2\cr +{}\\alignrecord, width $-\infty$&preamble info for column 2\cr +{}\\glue 1pt plus 1fil&the tabskip between columns 2 and 3\cr +{}\\alignrecord, width $-\infty$&preamble info for column 3\cr +{}\\glue 1pt plus 1fil&the tabskip following column 3\cr}}$$ +These ``alignrecord'' entries have the same size as an |unset_node|, +since they will later be converted into such nodes. However, at the +moment they have no |type| or |subtype| fields; they have |info| fields +instead, and these |info| fields are initially set to the value |end_span|, +for reasons explained below. Furthermore, the alignrecord nodes have no +|height| or |depth| fields; these are renamed |u_part| and |v_part|, +and they point to token lists for the templates of the alignment. +For example, the |u_part| field in the first alignrecord points to the +token list `\.{u1}', i.e., the template preceding the `\.\#' for column~1. + +(2) \TeX\ now looks at what follows the \.{\\cr} that ended the preamble. +It is not `\.{\\noalign}' or `\.{\\omit}', so this input is put back to +be read again, and the template `\.{u1}' is fed to the scanner. Just +before reading `\.{u1}', \TeX\ goes into restricted horizontal mode. +Just after reading `\.{u1}', \TeX\ will see `\.{a1}', and then (when the +{\.\&} is sensed) \TeX\ will see `\.{v1}'. Then \TeX\ scans an |endv| +token, indicating the end of a column. At this point an |unset_node| is +created, containing the contents of the current hlist (i.e., `\.{u1a1v1}'). +The natural width of this unset node replaces the |width| field of the +alignrecord for column~1; in general, the alignrecords will record the +maximum natural width that has occurred so far in a given column. + +(3) Since `\.{\\omit}' follows the `\.\&', the templates for column~2 +are now bypassed. Again \TeX\ goes into restricted horizontal mode and +makes an |unset_node| from the resulting hlist; but this time the +hlist contains simply `\.{a2}'. The natural width of the new unset box +is remembered in the |width| field of the alignrecord for column~2. + +(4) A third |unset_node| is created for column 3, using essentially the +mechanism that worked for column~1; this unset box contains `\.{u3\\vrule +v3}'. The vertical rule in this case has running dimensions that will later +extend to the height and depth of the whole first row, since each |unset_node| +in a row will eventually inherit the height and depth of its enclosing box. + +(5) The first row has now ended; it is made into a single unset box +comprising the following seven items: +$$\vbox{\halign{\hbox to 325pt{\qquad\.{#}\hfil}\cr +{}\\glue 2pt plus 3pt\cr +{}\\unsetbox for 1 column: u1a1v1\cr +{}\\glue 2pt plus 3pt\cr +{}\\unsetbox for 1 column: a2\cr +{}\\glue 1pt plus 1fil\cr +{}\\unsetbox for 1 column: u3\\vrule v3\cr +{}\\glue 1pt plus 1fil\cr}}$$ +The width of this unset row is unimportant, but it has the correct height +and depth, so the correct baselineskip glue will be computed as the row +is inserted into a vertical list. + +(6) Since `\.{\\noalign}' follows the current \.{\\cr}, \TeX\ appends +additional material (in this case \.{\\vskip 3pt}) to the vertical list. +While processing this material, \TeX\ will be in internal vertical +mode, and |no_align_group| will be on |save_stack|. + +(7) The next row produces an unset box that looks like this: +$$\vbox{\halign{\hbox to 325pt{\qquad\.{#}\hfil}\cr +{}\\glue 2pt plus 3pt\cr +{}\\unsetbox for 2 columns: u1b1v1u2b2v2\cr +{}\\glue 1pt plus 1fil\cr +{}\\unsetbox for 1 column: {\rm(empty)}\cr +{}\\glue 1pt plus 1fil\cr}}$$ +The natural width of the unset box that spans columns 1~and~2 is stored +in a ``span node,'' which we will explain later; the |info| field of the +alignrecord for column~1 now points to the new span node, and the |info| +of the span node points to |end_span|. + +(8) The final row produces the unset box +$$\vbox{\halign{\hbox to 325pt{\qquad\.{#}\hfil}\cr +{}\\glue 2pt plus 3pt\cr +{}\\unsetbox for 1 column: {\rm(empty)}\cr +{}\\glue 2pt plus 3pt\cr +{}\\unsetbox for 2 columns: u2c2v2\cr +{}\\glue 1pt plus 1fil\cr}}$$ +A new span node is attached to the alignrecord for column 2. + +(9) The last step is to compute the true column widths and to change all the +unset boxes to hboxes, appending the whole works to the vertical list that +encloses the \.{\\halign}. The rules for deciding on the final widths of +each unset column box will be explained below. + +\yskip\noindent +Note that as \.{\\halign} is being processed, we fearlessly give up control +to the rest of \TeX. At critical junctures, an alignment routine is +called upon to step in and do some little action, but most of the time +these routines just lurk in the background. It's something like +post-hypnotic suggestion. + +@ We have mentioned that alignrecords contain no |height| or |depth| fields. +Their |glue_sign| and |glue_order| are pre-empted as well, since it +is necessary to store information about what to do when a template ends. +This information is called the |extra_info| field. + +@d u_part(#)==mem[#+height_offset].int {pointer to \<u_j> token list} +@d v_part(#)==mem[#+depth_offset].int {pointer to \<v_j> token list} +@d extra_info(#)==info(#+list_offset) {info to remember during template} + +@ Alignments can occur within alignments, so a small stack is used to access +the alignrecord information. At each level we have a |preamble| pointer, +indicating the beginning of the preamble list; a |cur_align| pointer, +indicating the current position in the preamble list; a |cur_span| pointer, +indicating the value of |cur_align| at the beginning of a sequence of +spanned columns; a |cur_loop| pointer, indicating the tabskip glue before +an alignrecord that should be copied next if the current list is extended; +and the |align_state| variable, which indicates the nesting of braces so +that \.{\\cr} and \.{\\span} and tab marks are properly intercepted. +There also are pointers |cur_head| and |cur_tail| to the head and tail +of a list of adjustments being moved out from horizontal mode to +vertical~mode. + +The current values of these seven quantities appear in global variables; +when they have to be pushed down, they are stored in 5-word nodes, and +|align_ptr| points to the topmost such node. + +@d preamble==link(align_head) {the current preamble list} +@d align_stack_node_size=5 {number of |mem| words to save alignment states} + +@<Glob...@>= +@!cur_align:pointer; {current position in preamble list} +@!cur_span:pointer; {start of currently spanned columns in preamble list} +@!cur_loop:pointer; {place to copy when extending a periodic preamble} +@!align_ptr:pointer; {most recently pushed-down alignment stack node} +@!cur_head,@!cur_tail:pointer; {adjustment list pointers} + +@ The |align_state| and |preamble| variables are initialized elsewhere. + +@<Set init...@>= +align_ptr:=null; cur_align:=null; cur_span:=null; cur_loop:=null; +cur_head:=null; cur_tail:=null; + +@ Alignment stack maintenance is handled by a pair of trivial routines +called |push_alignment| and |pop_alignment|. + +@p procedure push_alignment; +var p:pointer; {the new alignment stack node} +begin p:=get_node(align_stack_node_size); +link(p):=align_ptr; info(p):=cur_align; +llink(p):=preamble; rlink(p):=cur_span; +mem[p+2].int:=cur_loop; mem[p+3].int:=align_state; +info(p+4):=cur_head; link(p+4):=cur_tail; +align_ptr:=p; +cur_head:=get_avail; +end; +@# +procedure pop_alignment; +var p:pointer; {the top alignment stack node} +begin free_avail(cur_head); +p:=align_ptr; +cur_tail:=link(p+4); cur_head:=info(p+4); +align_state:=mem[p+3].int; cur_loop:=mem[p+2].int; +cur_span:=rlink(p); preamble:=llink(p); +cur_align:=info(p); align_ptr:=link(p); +free_node(p,align_stack_node_size); +end; + +@ \TeX\ has eight procedures that govern alignments: |init_align| and +|fin_align| are used at the very beginning and the very end; |init_row| and +|fin_row| are used at the beginning and end of individual rows; |init_span| +is used at the beginning of a sequence of spanned columns (possibly involving +only one column); |init_col| and |fin_col| are used at the beginning and +end of individual columns; and |align_peek| is used after \.{\\cr} to see +whether the next item is \.{\\noalign}. + +We shall consider these routines in the order they are first used during +the course of a complete \.{\\halign}, namely |init_align|, |align_peek|, +|init_row|, |init_span|, |init_col|, |fin_col|, |fin_row|, |fin_align|. + +@ When \.{\\halign} or \.{\\valign} has been scanned in an appropriate +mode, \TeX\ calls |init_align|, whose task is to get everything off to a +good start. This mostly involves scanning the preamble and putting its +information into the preamble list. +@^preamble@> + +@p @t\4@>@<Declare the procedure called |get_preamble_token|@>@t@>@/ +procedure@?align_peek; forward;@t\2@>@/ +procedure@?normal_paragraph; forward;@t\2@>@/ +procedure init_align; +label done, done1, done2, continue; +var save_cs_ptr:pointer; {|warning_index| value for error messages} +@!p:pointer; {for short-term temporary use} +begin save_cs_ptr:=cur_cs; {\.{\\halign} or \.{\\valign}, usually} +push_alignment; align_state:=-1000000; {enter a new alignment level} +@<Check for improper alignment in displayed math@>; +push_nest; {enter a new semantic level} +@<Change current mode to |-vmode| for \.{\\halign}, |-hmode| for \.{\\valign}@>; +scan_spec(align_group,false);@/ +@<Scan the preamble and record it in the |preamble| list@>; +new_save_level(align_group); +if every_cr<>null then begin_token_list(every_cr,every_cr_text); +align_peek; {look for \.{\\noalign} or \.{\\omit}} +end; + +@ In vertical modes, |prev_depth| already has the correct value. But +if we are in |mmode| (displayed formula mode), we reach out to the +enclosing vertical mode for the |prev_depth| value that produces the +correct baseline calculations. + +@<Change current mode...@>= +if mode=mmode then + begin mode:=-vmode; prev_depth:=nest[nest_ptr-2].aux_field.sc; + end +else if mode>0 then negate(mode) + +@ When \.{\\halign} is used as a displayed formula, there should be +no other pieces of mlists present. + +@<Check for improper alignment in displayed math@>= +if (mode=mmode)and((tail<>head)or(incompleat_noad<>null)) then + begin print_err("Improper "); print_esc("halign"); print(" inside $$'s"); +@.Improper \\halign...@> + help3("Displays can use special alignments (like \eqalignno)")@/ + ("only if nothing but the alignment itself is between $$'s.")@/ + ("So I've deleted the formulas that preceded this alignment."); + error; flush_math; + end + +@ @<Scan the preamble and record it in the |preamble| list@>= +preamble:=null; cur_align:=align_head; cur_loop:=null; scanner_status:=aligning; +warning_index:=save_cs_ptr; align_state:=-1000000; + {at this point, |cur_cmd=left_brace|} +loop@+ begin @<Append the current tabskip glue to the preamble list@>; + if cur_cmd=car_ret then goto done; {\.{\\cr} ends the preamble} + @<Scan preamble text until |cur_cmd| is |tab_mark| or |car_ret|, + looking for changes in the tabskip glue; append an + alignrecord to the preamble list@>; + end; +done: scanner_status:=normal + +@ @<Append the current tabskip glue to the preamble list@>= +link(cur_align):=new_param_glue(tab_skip_code); +cur_align:=link(cur_align) + +@ @<Scan preamble text until |cur_cmd| is |tab_mark| or |car_ret|...@>= +@<Scan the template \<u_j>, putting the resulting token list in |hold_head|@>; +link(cur_align):=new_null_box; cur_align:=link(cur_align); {a new alignrecord} +info(cur_align):=end_span; width(cur_align):=null_flag; +u_part(cur_align):=link(hold_head); +@<Scan the template \<v_j>, putting the resulting token list in |hold_head|@>; +v_part(cur_align):=link(hold_head) + +@ We enter `\.{\\span}' into |eqtb| with |tab_mark| as its command code, +and with |span_code| as the command modifier. This makes \TeX\ interpret it +essentially the same as an alignment delimiter like `\.\&', yet it is +recognizably different when we need to distinguish it from a normal delimiter. +It also turns out to be useful to give a special |cr_code| to `\.{\\cr}', +and an even larger |cr_cr_code| to `\.{\\crcr}'. + +The end of a template is represented by two ``frozen'' control sequences +called \.{\\endtemplate}. The first has the command code |end_template|, which +is |>outer_call|, so it will not easily disappear in the presence of errors. +The |get_x_token| routine converts the first into the second, which has |endv| +as its command code. + +@d span_code=256 {distinct from any character} +@d cr_code=257 {distinct from |span_code| and from any character} +@d cr_cr_code=cr_code+1 {this distinguishes \.{\\crcr} from \.{\\cr}} +@d end_template_token==cs_token_flag+frozen_end_template + +@<Put each of \TeX's primitives into the hash table@>= +primitive("span",tab_mark,span_code);@/ +@!@:span_}{\.{\\span} primitive@> +primitive("cr",car_ret,cr_code); +@!@:cr_}{\.{\\cr} primitive@> +text(frozen_cr):="cr"; eqtb[frozen_cr]:=eqtb[cur_val];@/ +primitive("crcr",car_ret,cr_cr_code); +@!@:cr_cr_}{\.{\\crcr} primitive@> +text(frozen_end_template):="endtemplate"; text(frozen_endv):="endtemplate"; +eq_type(frozen_endv):=endv; equiv(frozen_endv):=null_list; +eq_level(frozen_endv):=level_one;@/ +eqtb[frozen_end_template]:=eqtb[frozen_endv]; +eq_type(frozen_end_template):=end_template; + +@ @<Cases of |print_cmd_chr|...@>= +tab_mark: if chr_code=span_code then print_esc("span") + else chr_cmd("alignment tab character "); +car_ret: if chr_code=cr_code then print_esc("cr") + else print_esc("crcr"); + +@ The preamble is copied directly, except that \.{\\tabskip} causes a change +to the tabskip glue, thereby possibly expanding macros that immediately +follow it. An appearance of \.{\\span} also causes such an expansion. + +Note that if the preamble contains `\.{\\global\\tabskip}', the `\.{\\global}' +token survives in the preamble and the `\.{\\tabskip}' defines new +tabskip glue (locally). + +@<Declare the procedure called |get_preamble_token|@>= +procedure get_preamble_token; +label restart; +begin restart: get_token; +while (cur_chr=span_code)and(cur_cmd=tab_mark) do + begin get_token; {this token will be expanded once} + if cur_cmd>max_command then + begin expand; get_token; + end; + end; +if cur_cmd=endv then + fatal_error("(interwoven alignment preambles are not allowed)"); +@.interwoven alignment preambles...@> +if (cur_cmd=assign_glue)and(cur_chr=glue_base+tab_skip_code) then + begin scan_optional_equals; scan_glue(glue_val); + if global_defs>0 then geq_define(glue_base+tab_skip_code,glue_ref,cur_val) + else eq_define(glue_base+tab_skip_code,glue_ref,cur_val); + goto restart; + end; +end; + +@ Spaces are eliminated from the beginning of a template. + +@<Scan the template \<u_j>...@>= +p:=hold_head; link(p):=null; +loop@+ begin get_preamble_token; + if cur_cmd=mac_param then goto done1; + if (cur_cmd<=car_ret)and(cur_cmd>=tab_mark)and(align_state=-1000000) then + if (p=hold_head)and(cur_loop=null)and(cur_cmd=tab_mark) + then cur_loop:=cur_align + else begin print_err("Missing # inserted in alignment preamble"); +@.Missing \# inserted...@> + help3("There should be exactly one # between &'s, when an")@/ + ("\halign or \valign is being set up. In this case you had")@/ + ("none, so I've put one in; maybe that will work."); + back_error; goto done1; + end + else if (cur_cmd<>spacer)or(p<>hold_head) then + begin link(p):=get_avail; p:=link(p); info(p):=cur_tok; + end; + end; +done1: + +@ @<Scan the template \<v_j>...@>= +p:=hold_head; link(p):=null; +loop@+ begin continue: get_preamble_token; + if (cur_cmd<=car_ret)and(cur_cmd>=tab_mark)and(align_state=-1000000) then + goto done2; + if cur_cmd=mac_param then + begin print_err("Only one # is allowed per tab"); +@.Only one \# is allowed...@> + help3("There should be exactly one # between &'s, when an")@/ + ("\halign or \valign is being set up. In this case you had")@/ + ("more than one, so I'm ignoring all but the first."); + error; goto continue; + end; + link(p):=get_avail; p:=link(p); info(p):=cur_tok; + end; +done2: link(p):=get_avail; p:=link(p); +info(p):=end_template_token {put \.{\\endtemplate} at the end} + +@ The tricky part about alignments is getting the templates into the +scanner at the right time, and recovering control when a row or column +is finished. + +We usually begin a row after each \.{\\cr} has been sensed, unless that +\.{\\cr} is followed by \.{\\noalign} or by the right brace that terminates +the alignment. The |align_peek| routine is used to look ahead and do +the right thing; it either gets a new row started, or gets a \.{\\noalign} +started, or finishes off the alignment. + +@<Declare the procedure called |align_peek|@>= +procedure align_peek; +label restart; +begin restart: align_state:=1000000; @<Get the next non-blank non-call token@>; +if cur_cmd=no_align then + begin scan_left_brace; new_save_level(no_align_group); + if mode=-vmode then normal_paragraph; + end +else if cur_cmd=right_brace then fin_align +else if (cur_cmd=car_ret)and(cur_chr=cr_cr_code) then + goto restart {ignore \.{\\crcr}} +else begin init_row; {start a new row} + init_col; {start a new column and replace what we peeked at} + end; +end; + +@ To start a row (i.e., a `row' that rhymes with `dough' but not with `bough'), +we enter a new semantic level, copy the first tabskip glue, and change +from internal vertical mode to restricted horizontal mode or vice versa. +The |space_factor| and |prev_depth| are not used on this semantic level, +but we clear them to zero just to be tidy. + +@p @t\4@>@<Declare the procedure called |init_span|@>@t@>@/ +procedure init_row; +begin push_nest; mode:=(-hmode-vmode)-mode; +if mode=-hmode then space_factor:=0 @+else prev_depth:=0; +tail_append(new_glue(glue_ptr(preamble))); +subtype(tail):=tab_skip_code+1;@/ +cur_align:=link(preamble); cur_tail:=cur_head; init_span(cur_align); +end; + +@ The parameter to |init_span| is a pointer to the alignrecord where the +next column or group of columns will begin. A new semantic level is +entered, so that the columns will generate a list for subsequent packaging. + +@<Declare the procedure called |init_span|@>= +procedure init_span(@!p:pointer); +begin push_nest; +if mode=-hmode then space_factor:=1000 +else begin prev_depth:=ignore_depth; normal_paragraph; + end; +cur_span:=p; +end; + +@ When a column begins, we assume that |cur_cmd| is either |omit| or else +the current token should be put back into the input until the \<u_j> +template has been scanned. (Note that |cur_cmd| might be |tab_mark| or +|car_ret|.) We also assume that |align_state| is approximately 1000000 at +this time. We remain in the same mode, and start the template if it is +called for. + +@p procedure init_col; +begin extra_info(cur_align):=cur_cmd; +if cur_cmd=omit then align_state:=0 +else begin back_input; begin_token_list(u_part(cur_align),u_template); + end; {now |align_state=1000000|} +end; + +@ The scanner sets |align_state| to zero when the \<u_j> template ends. When +a subsequent \.{\\cr} or \.{\\span} or tab mark occurs with |align_state=0|, +the scanner activates the following code, which fires up the \<v_j> template. +We need to remember the |cur_chr|, which is either |cr_cr_code|, |cr_code|, +|span_code|, or a character code, depending on how the column text has ended. + +This part of the program had better not be activated when the preamble +to another alignment is being scanned, or when no alignment preamble is active. + +@<Insert the \(v)\<v_j>...@>= +begin if (scanner_status=aligning) or (cur_align=null) then + fatal_error("(interwoven alignment preambles are not allowed)"); +@.interwoven alignment preambles...@> +cur_cmd:=extra_info(cur_align); extra_info(cur_align):=cur_chr; +if cur_cmd=omit then begin_token_list(omit_template,v_template) +else begin_token_list(v_part(cur_align),v_template); +align_state:=1000000; goto restart; +end + +@ The token list |omit_template| just referred to is a constant token +list that contains the special control sequence \.{\\endtemplate} only. + +@<Initialize the special...@>= +info(omit_template):=end_template_token; {|link(omit_template)=null|} + +@ When the |endv| command at the end of a \<v_j> template comes through the +scanner, things really start to happen; and it is the |fin_col| routine +that makes them happen. This routine returns |true| if a row as well as a +column has been finished. + +@p function fin_col:boolean; +label exit; +var p:pointer; {the alignrecord after the current one} +@!q,@!r:pointer; {temporary pointers for list manipulation} +@!s:pointer; {a new span node} +@!u:pointer; {a new unset box} +@!w:scaled; {natural width} +@!o:glue_ord; {order of infinity} +@!n:halfword; {span counter} +begin if cur_align=null then confusion("endv"); +q:=link(cur_align);@+if q=null then confusion("endv"); +@:this can't happen endv}{\quad endv@> +if align_state<500000 then + fatal_error("(interwoven alignment preambles are not allowed)"); +@.interwoven alignment preambles...@> +p:=link(q); +@<If the preamble list has been traversed, check that the row has ended@>; +if extra_info(cur_align)<>span_code then + begin unsave; new_save_level(align_group);@/ + @<Package an unset box for the current column and record its width@>; + @<Copy the tabskip glue between columns@>; + if extra_info(cur_align)>=cr_code then + begin fin_col:=true; return; + end; + init_span(p); + end; +align_state:=1000000; @<Get the next non-blank non-call token@>; +cur_align:=p; +init_col; fin_col:=false; +exit: end; + +@ @<If the preamble list has been traversed, check that the row has ended@>= +if (p=null)and(extra_info(cur_align)<cr_code) then + if cur_loop<>null then @<Lengthen the preamble periodically@> + else begin print_err("Extra alignment tab has been changed to "); +@.Extra alignment tab...@> + print_esc("cr"); + help3("You have given more \span or & marks than there were")@/ + ("in the preamble to the \halign or \valign now in progress.")@/ + ("So I'll assume that you meant to type \cr instead."); + extra_info(cur_align):=cr_code; error; + end + +@ @<Lengthen the preamble...@>= +begin link(q):=new_null_box; p:=link(q); {a new alignrecord} +info(p):=end_span; width(p):=null_flag; cur_loop:=link(cur_loop); +@<Copy the templates from node |cur_loop| into node |p|@>; +cur_loop:=link(cur_loop); +link(p):=new_glue(glue_ptr(cur_loop)); +end + +@ @<Copy the templates from node |cur_loop| into node |p|@>= +q:=hold_head; r:=u_part(cur_loop); +while r<>null do + begin link(q):=get_avail; q:=link(q); info(q):=info(r); r:=link(r); + end; +link(q):=null; u_part(p):=link(hold_head); +q:=hold_head; r:=v_part(cur_loop); +while r<>null do + begin link(q):=get_avail; q:=link(q); info(q):=info(r); r:=link(r); + end; +link(q):=null; v_part(p):=link(hold_head) + +@ @<Copy the tabskip glue...@>= +tail_append(new_glue(glue_ptr(link(cur_align)))); +subtype(tail):=tab_skip_code+1 + +@ @<Package an unset...@>= +begin if mode=-hmode then + begin adjust_tail:=cur_tail; u:=hpack(link(head),natural); w:=width(u); + cur_tail:=adjust_tail; adjust_tail:=null; + end +else begin u:=vpackage(link(head),natural,0); w:=height(u); + end; +n:=min_quarterword; {this represents a span count of 1} +if cur_span<>cur_align then @<Update width entry for spanned columns@> +else if w>width(cur_align) then width(cur_align):=w; +type(u):=unset_node; span_count(u):=n;@/ +@<Determine the stretch order@>; +glue_order(u):=o; glue_stretch(u):=total_stretch[o];@/ +@<Determine the shrink order@>; +glue_sign(u):=o; glue_shrink(u):=total_shrink[o];@/ +pop_nest; link(tail):=u; tail:=u; +end + +@ A span node is a 2-word record containing |width|, |info|, and |link| +fields. The |link| field is not really a link, it indicates the number of +spanned columns; the |info| field points to a span node for the same +starting column, having a greater extent of spanning, or to |end_span|, +which has the largest possible |link| field; the |width| field holds the +largest natural width corresponding to a particular set of spanned columns. + +A list of the maximum widths so far, for spanned columns starting at a +given column, begins with the |info| field of the alignrecord for that +column. + +@d span_node_size=2 {number of |mem| words for a span node} + +@<Initialize the special list heads...@>= +link(end_span):=max_quarterword+1; info(end_span):=null; + +@ @<Update width entry for spanned columns@>= +begin q:=cur_span; +repeat incr(n); q:=link(link(q)); +until q=cur_align; +if n>max_quarterword then confusion("256 spans"); {this can happen, but won't} +@^system dependencies@> +@:this can't happen 256 spans}{\quad 256 spans@> +q:=cur_span; while link(info(q))<n do q:=info(q); +if link(info(q))>n then + begin s:=get_node(span_node_size); info(s):=info(q); link(s):=n; + info(q):=s; width(s):=w; + end +else if width(info(q))<w then width(info(q)):=w; +end + +@ At the end of a row, we append an unset box to the current vlist (for +\.{\\halign}) or the current hlist (for \.{\\valign}). This unset box +contains the unset boxes for the columns, separated by the tabskip glue. +Everything will be set later. + +@p procedure fin_row; +var p:pointer; {the new unset box} +begin if mode=-hmode then + begin p:=hpack(link(head),natural); + pop_nest; append_to_vlist(p); + if cur_head<>cur_tail then + begin link(tail):=link(cur_head); tail:=cur_tail; + end; + end +else begin p:=vpack(link(head),natural); pop_nest; + link(tail):=p; tail:=p; space_factor:=1000; + end; +type(p):=unset_node; glue_stretch(p):=0; +if every_cr<>null then begin_token_list(every_cr,every_cr_text); +align_peek; +end; {note that |glue_shrink(p)=0| since |glue_shrink==shift_amount|} + +@ Finally, we will reach the end of the alignment, and we can breathe a +sigh of relief that memory hasn't overflowed. All the unset boxes will now be +set so that the columns line up, taking due account of spanned columns. + +@p procedure@?do_assignments; forward;@t\2@>@/ +procedure@?resume_after_display; forward;@t\2@>@/ +procedure@?build_page; forward;@t\2@>@/ +procedure fin_align; +var @!p,@!q,@!r,@!s,@!u,@!v: pointer; {registers for the list operations} +@!t,@!w:scaled; {width of column} +@!o:scaled; {shift offset for unset boxes} +@!n:halfword; {matching span amount} +@!rule_save:scaled; {temporary storage for |overfull_rule|} +@!aux_save:memory_word; {temporary storage for |aux|} +begin if cur_group<>align_group then confusion("align1"); +@:this can't happen align}{\quad align@> +unsave; {that |align_group| was for individual entries} +if cur_group<>align_group then confusion("align0"); +unsave; {that |align_group| was for the whole alignment} +if nest[nest_ptr-1].mode_field=mmode then o:=display_indent + else o:=0; +@<Go through the preamble list, determining the column widths and + changing the alignrecords to dummy unset boxes@>; +@<Package the preamble list, to determine the actual tabskip glue amounts, + and let |p| point to this prototype box@>; +@<Set the glue in all the unset boxes of the current list@>; +flush_node_list(p); pop_alignment; +@<Insert the \(c)current list into its environment@>; +end;@/ +@t\4@>@<Declare the procedure called |align_peek|@> + +@ It's time now to dismantle the preamble list and to compute the column +widths. Let $w_{ij}$ be the maximum of the natural widths of all entries +that span columns $i$ through $j$, inclusive. The alignrecord for column~$i$ +contains $w_{ii}$ in its |width| field, and there is also a linked list of +the nonzero $w_{ij}$ for increasing $j$, accessible via the |info| field; +these span nodes contain the value $j-i-1+|min_quarterword|$ in their +|link| fields. The values of $w_{ii}$ were initialized to |null_flag|, which +we regard as $-\infty$. + +The final column widths are defined by the formula +$$w_j=\max_{1\L i\L j}\biggl( w_{ij}-\sum_{i\L k<j}(t_k+w_k)\biggr),$$ +where $t_k$ is the natural width of the tabskip glue between columns +$k$ and~$k+1$. However, if $w_{ij}=-\infty$ for all |i| in the range +|1<=i<=j| (i.e., if every entry that involved column~|j| also involved +column~|j+1|), we let $w_j=0$, and we zero out the tabskip glue after +column~|j|. + +\TeX\ computes these values by using the following scheme: First $w_1=w_{11}$. +Then replace $w_{2j}$ by $\max(w_{2j},w_{1j}-t_1-w_1)$, for all $j>1$. +Then $w_2=w_{22}$. Then replace $w_{3j}$ by $\max(w_{3j},w_{2j}-t_2-w_2)$ +for all $j>2$; and so on. If any $w_j$ turns out to be $-\infty$, its +value is changed to zero and so is the next tabskip. + +@<Go through the preamble list,...@>= +q:=link(preamble); +repeat flush_list(u_part(q)); flush_list(v_part(q)); +p:=link(link(q)); +if width(q)=null_flag then + @<Nullify |width(q)| and the tabskip glue following this column@>; +if info(q)<>end_span then + @<Merge the widths in the span nodes of |q| with those of |p|, + destroying the span nodes of |q|@>; +type(q):=unset_node; span_count(q):=min_quarterword; height(q):=0; +depth(q):=0; glue_order(q):=normal; glue_sign(q):=normal; +glue_stretch(q):=0; glue_shrink(q):=0; q:=p; +until q=null + +@ @<Nullify |width(q)| and the tabskip glue following this column@>= +begin width(q):=0; r:=link(q); s:=glue_ptr(r); +if s<>zero_glue then + begin add_glue_ref(zero_glue); delete_glue_ref(s); + glue_ptr(r):=zero_glue; + end; +end + +@ Merging of two span-node lists is a typical exercise in the manipulation of +linearly linked data structures. The essential invariant in the following +|repeat| loop is that we want to dispense with node |r|, in |q|'s list, +and |u| is its successor; all nodes of |p|'s list up to and including |s| +have been processed, and the successor of |s| matches |r| or precedes |r| +or follows |r|, according as |link(r)=n| or |link(r)>n| or |link(r)<n|. + +@<Merge the widths...@>= +begin t:=width(q)+width(glue_ptr(link(q))); +r:=info(q); s:=end_span; info(s):=p; n:=min_quarterword+1; +repeat width(r):=width(r)-t; u:=info(r); +while link(r)>n do + begin s:=info(s); n:=link(info(s))+1; + end; +if link(r)<n then + begin info(r):=info(s); info(s):=r; decr(link(r)); s:=r; + end +else begin if width(r)>width(info(s)) then width(info(s)):=width(r); + free_node(r,span_node_size); + end; +r:=u; +until r=end_span; +end + +@ Now the preamble list has been converted to a list of alternating unset +boxes and tabskip glue, where the box widths are equal to the final +column sizes. In case of \.{\\valign}, we change the widths to heights, +so that a correct error message will be produced if the alignment is +overfull or underfull. + +@<Package the preamble list...@>= +save_ptr:=save_ptr-2; pack_begin_line:=-mode_line; +if mode=-vmode then + begin rule_save:=overfull_rule; + overfull_rule:=0; {prevent rule from being packaged} + p:=hpack(preamble,saved(1),saved(0)); overfull_rule:=rule_save; + end +else begin q:=link(preamble); + repeat height(q):=width(q); width(q):=0; q:=link(link(q)); + until q=null; + p:=vpack(preamble,saved(1),saved(0)); + q:=link(preamble); + repeat width(q):=height(q); height(q):=0; q:=link(link(q)); + until q=null; + end; +pack_begin_line:=0 + +@ @<Set the glue in all the unset...@>= +q:=link(head); s:=head; +while q<>null do + begin if not is_char_node(q) then + if type(q)=unset_node then + @<Set the unset box |q| and the unset boxes in it@> + else if type(q)=rule_node then + @<Make the running dimensions in rule |q| extend to the + boundaries of the alignment@>; + s:=q; q:=link(q); + end + +@ @<Make the running dimensions in rule |q| extend...@>= +begin if is_running(width(q)) then width(q):=width(p); +if is_running(height(q)) then height(q):=height(p); +if is_running(depth(q)) then depth(q):=depth(p); +if o<>0 then + begin r:=link(q); link(q):=null; q:=hpack(q,natural); + shift_amount(q):=o; link(q):=r; link(s):=q; + end; +end + +@ The unset box |q| represents a row that contains one or more unset boxes, +depending on how soon \.{\\cr} occurred in that row. + +@<Set the unset box |q| and the unset boxes in it@>= +begin if mode=-vmode then + begin type(q):=hlist_node; width(q):=width(p); + end +else begin type(q):=vlist_node; height(q):=height(p); + end; +glue_order(q):=glue_order(p); glue_sign(q):=glue_sign(p); +glue_set(q):=glue_set(p); shift_amount(q):=o; +r:=link(list_ptr(q)); s:=link(list_ptr(p)); +repeat @<Set the glue in node |r| and change it from an unset node@>; +r:=link(link(r)); s:=link(link(s)); +until r=null; +end + +@ A box made from spanned columns will be followed by tabskip glue nodes and +by empty boxes as if there were no spanning. This permits perfect alignment +of subsequent entries, and it prevents values that depend on floating point +arithmetic from entering into the dimensions of any boxes. + +@<Set the glue in node |r|...@>= +n:=span_count(r); t:=width(s); w:=t; u:=hold_head; +while n>min_quarterword do + begin decr(n); + @<Append tabskip glue and an empty box to list |u|, + and update |s| and |t| as the prototype nodes are passed@>; + end; +if mode=-vmode then + @<Make the unset node |r| into an |hlist_node| of width |w|, + setting the glue as if the width were |t|@> +else @<Make the unset node |r| into a |vlist_node| of height |w|, + setting the glue as if the height were |t|@>; +shift_amount(r):=0; +if u<>hold_head then {append blank boxes to account for spanned nodes} + begin link(u):=link(r); link(r):=link(hold_head); r:=u; + end + +@ @<Append tabskip glue and an empty box to list |u|...@>= +s:=link(s); v:=glue_ptr(s); link(u):=new_glue(v); u:=link(u); +subtype(u):=tab_skip_code+1; t:=t+width(v); +if glue_sign(p)=stretching then + begin if stretch_order(v)=glue_order(p) then + t:=t+round(float(glue_set(p))*stretch(v)); +@^real multiplication@> + end +else if glue_sign(p)=shrinking then + begin if shrink_order(v)=glue_order(p) then + t:=t-round(float(glue_set(p))*shrink(v)); + end; +s:=link(s); link(u):=new_null_box; u:=link(u); t:=t+width(s); +if mode=-vmode then width(u):=width(s)@+else + begin type(u):=vlist_node; height(u):=width(s); + end + +@ @<Make the unset node |r| into an |hlist_node| of width |w|...@>= +begin height(r):=height(q); depth(r):=depth(q); +if t=width(r) then + begin glue_sign(r):=normal; glue_order(r):=normal; + set_glue_ratio_zero(glue_set(r)); + end +else if t>width(r) then + begin glue_sign(r):=stretching; + if glue_stretch(r)=0 then set_glue_ratio_zero(glue_set(r)) + else glue_set(r):=unfloat((t-width(r))/glue_stretch(r)); +@^real division@> + end +else begin glue_order(r):=glue_sign(r); glue_sign(r):=shrinking; + if glue_shrink(r)=0 then set_glue_ratio_zero(glue_set(r)) + else if (glue_order(r)=normal)and(width(r)-t>glue_shrink(r)) then + set_glue_ratio_one(glue_set(r)) + else glue_set(r):=unfloat((width(r)-t)/glue_shrink(r)); + end; +width(r):=w; type(r):=hlist_node; +end + +@ @<Make the unset node |r| into a |vlist_node| of height |w|...@>= +begin width(r):=width(q); +if t=height(r) then + begin glue_sign(r):=normal; glue_order(r):=normal; + set_glue_ratio_zero(glue_set(r)); + end +else if t>height(r) then + begin glue_sign(r):=stretching; + if glue_stretch(r)=0 then set_glue_ratio_zero(glue_set(r)) + else glue_set(r):=unfloat((t-height(r))/glue_stretch(r)); +@^real division@> + end +else begin glue_order(r):=glue_sign(r); glue_sign(r):=shrinking; + if glue_shrink(r)=0 then set_glue_ratio_zero(glue_set(r)) + else if (glue_order(r)=normal)and(height(r)-t>glue_shrink(r)) then + set_glue_ratio_one(glue_set(r)) + else glue_set(r):=unfloat((height(r)-t)/glue_shrink(r)); + end; +height(r):=w; type(r):=vlist_node; +end + +@ We now have a completed alignment, in the list that starts at |head| +and ends at |tail|. This list will be merged with the one that encloses +it. (In case the enclosing mode is |mmode|, for displayed formulas, +we will need to insert glue before and after the display; that part of the +program will be deferred until we're more familiar with such operations.) + +In horizontal mode, the |clang| part of |aux| is undefined; an over-cautious +\PASCAL\ runtime system may complain about this. +@^dirty \PASCAL@> + +@<Insert the \(c)current list into its environment@>= +aux_save:=aux; p:=link(head); q:=tail; pop_nest; +if mode=mmode then @<Finish an alignment in a display@> +else begin aux:=aux_save; link(tail):=p; + if p<>null then tail:=q; + if mode=vmode then build_page; + end + +@* \[38] Breaking paragraphs into lines. +We come now to what is probably the most interesting algorithm of \TeX: +the mechanism for choosing the ``best possible'' breakpoints that yield +the individual lines of a paragraph. \TeX's line-breaking algorithm takes +a given horizontal list and converts it to a sequence of boxes that are +appended to the current vertical list. In the course of doing this, it +creates a special data structure containing three kinds of records that are +not used elsewhere in \TeX. Such nodes are created while a paragraph is +being processed, and they are destroyed afterwards; thus, the other parts +of \TeX\ do not need to know anything about how line-breaking is done. + +The method used here is based on an approach devised by Michael F. Plass and +@^Plass, Michael Frederick@> +@^Knuth, Donald Ervin@> +the author in 1977, subsequently generalized and improved by the same two +people in 1980. A detailed discussion appears in {\sl SOFTWARE---Practice +\AM\ Experience \bf11} (1981), 1119--1184, where it is shown that the +line-breaking problem can be regarded as a special case of the problem of +computing the shortest path in an acyclic network. The cited paper includes +numerous examples and describes the history of line breaking as it has been +practiced by printers through the ages. The present implementation adds two +new ideas to the algorithm of 1980: memory space requirements are considerably +reduced by using smaller records for inactive nodes than for active ones, +and arithmetic overflow is avoided by using ``delta distances'' instead of +keeping track of the total distance from the beginning of the paragraph to the +current point. + +@ The |line_break| procedure should be invoked only in horizontal mode; it +leaves that mode and places its output into the current vlist of the +enclosing vertical mode (or internal vertical mode). +There is one explicit parameter: |final_widow_penalty| is the amount of +additional penalty to be inserted before the final line of the paragraph. + +There are also a number of implicit parameters: The hlist to be broken +starts at |link(head)|, and it is nonempty. The value of |prev_graf| in the +enclosing semantic level tells where the paragraph should begin in the +sequence of line numbers, in case hanging indentation or \.{\\parshape} +are in use; |prev_graf| is zero unless this paragraph is being continued +after a displayed formula. Other implicit parameters, such as the +|par_shape_ptr| and various penalties to use for hyphenation, etc., appear +in |eqtb|. + +After |line_break| has acted, it will have updated the current vlist and the +value of |prev_graf|. Furthermore, the global variable |just_box| will +point to the final box created by |line_break|, so that the width of this +line can be ascertained when it is necessary to decide whether to use +|above_display_skip| or |above_display_short_skip| before a displayed formula. + +@<Glob...@>= +@!just_box:pointer; {the |hlist_node| for the last line of the new paragraph} + +@ Since |line_break| is a rather lengthy procedure---sort of a small world unto +itself---we must build it up little by little, somewhat more cautiously +than we have done with the simpler procedures of \TeX. Here is the +general outline. + +@p@t\4@>@<Declare subprocedures for |line_break|@> +procedure line_break(@!final_widow_penalty:integer); +label done,done1,done2,done3,done4,done5,continue; +var @<Local variables for line breaking@>@; +begin pack_begin_line:=mode_line; {this is for over/underfull box messages} +@<Get ready to start line breaking@>; +@<Find optimal breakpoints@>; +@<Break the paragraph at the chosen breakpoints, justify the resulting lines +to the correct widths, and append them to the current vertical list@>; +@<Clean up the memory by removing the break nodes@>; +pack_begin_line:=0; +end; + +@ The first task is to move the list from |head| to |temp_head| and go +into the enclosing semantic level. We also append the \.{\\parfillskip} +glue to the end of the paragraph, removing a space (or other glue node) if +it was there, since spaces usually precede blank lines and instances of +`\.{\$\$}'. The |par_fill_skip| is preceded by an infinite penalty, so +it will never be considered as a potential breakpoint. + +This code assumes that a |glue_node| and a |penalty_node| occupy the +same number of |mem|~words. +@^data structure assumptions@> + +@<Get ready to start...@>= +link(temp_head):=link(head); +if is_char_node(tail) then tail_append(new_penalty(inf_penalty)) +else if type(tail)<>glue_node then tail_append(new_penalty(inf_penalty)) +else begin type(tail):=penalty_node; delete_glue_ref(glue_ptr(tail)); + flush_node_list(leader_ptr(tail)); penalty(tail):=inf_penalty; + end; +link(tail):=new_param_glue(par_fill_skip_code); +init_cur_lang:=prev_graf mod @'200000; +init_l_hyf:=prev_graf div @'20000000; +init_r_hyf:=(prev_graf div @'200000) mod @'100; +pop_nest; + +@ When looking for optimal line breaks, \TeX\ creates a ``break node'' for +each break that is {\sl feasible}, in the sense that there is a way to end +a line at the given place without requiring any line to stretch more than +a given tolerance. A break node is characterized by three things: the position +of the break (which is a pointer to a |glue_node|, |math_node|, |penalty_node|, +or |disc_node|); the ordinal number of the line that will follow this +breakpoint; and the fitness classification of the line that has just +ended, i.e., |tight_fit|, |decent_fit|, |loose_fit|, or |very_loose_fit|. + +@d tight_fit=3 {fitness classification for lines shrinking 0.5 to 1.0 of their + shrinkability} +@d loose_fit=1 {fitness classification for lines stretching 0.5 to 1.0 of their + stretchability} +@d very_loose_fit=0 {fitness classification for lines stretching more than + their stretchability} +@d decent_fit=2 {fitness classification for all other lines} + +@ The algorithm essentially determines the best possible way to achieve +each feasible combination of position, line, and fitness. Thus, it answers +questions like, ``What is the best way to break the opening part of the +paragraph so that the fourth line is a tight line ending at such-and-such +a place?'' However, the fact that all lines are to be the same length +after a certain point makes it possible to regard all sufficiently large +line numbers as equivalent, when the looseness parameter is zero, and this +makes it possible for the algorithm to save space and time. + +An ``active node'' and a ``passive node'' are created in |mem| for each +feasible breakpoint that needs to be considered. Active nodes are three +words long and passive nodes are two words long. We need active nodes only +for breakpoints near the place in the paragraph that is currently being +examined, so they are recycled within a comparatively short time after +they are created. + +@ An active node for a given breakpoint contains six fields: + +\yskip\hang|link| points to the next node in the list of active nodes; the +last active node has |link=last_active|. + +\yskip\hang|break_node| points to the passive node associated with this +breakpoint. + +\yskip\hang|line_number| is the number of the line that follows this +breakpoint. + +\yskip\hang|fitness| is the fitness classification of the line ending at this +breakpoint. + +\yskip\hang|type| is either |hyphenated| or |unhyphenated|, depending on +whether this breakpoint is a |disc_node|. + +\yskip\hang|total_demerits| is the minimum possible sum of demerits over all +lines leading from the beginning of the paragraph to this breakpoint. + +\yskip\noindent +The value of |link(active)| points to the first active node on a linked list +of all currently active nodes. This list is in order by |line_number|, +except that nodes with |line_number>easy_line| may be in any order relative +to each other. + +@d active_node_size=3 {number of words in active nodes} +@d fitness==subtype {|very_loose_fit..tight_fit| on final line for this break} +@d break_node==rlink {pointer to the corresponding passive node} +@d line_number==llink {line that begins at this breakpoint} +@d total_demerits(#)==mem[#+2].int {the quantity that \TeX\ minimizes} +@d unhyphenated=0 {the |type| of a normal active break node} +@d hyphenated=1 {the |type| of an active node that breaks at a |disc_node|} +@d last_active==active {the active list ends where it begins} + +@ @<Initialize the special list heads...@>= +type(last_active):=hyphenated; line_number(last_active):=max_halfword; +subtype(last_active):=0; {the |subtype| is never examined by the algorithm} + +@ The passive node for a given breakpoint contains only four fields: + +\yskip\hang|link| points to the passive node created just before this one, +if any, otherwise it is |null|. + +\yskip\hang|cur_break| points to the position of this breakpoint in the +horizontal list for the paragraph being broken. + +\yskip\hang|prev_break| points to the passive node that should precede this +one in an optimal path to this breakpoint. + +\yskip\hang|serial| is equal to |n| if this passive node is the |n|th +one created during the current pass. (This field is used only when +printing out detailed statistics about the line-breaking calculations.) + +\yskip\noindent +There is a global variable called |passive| that points to the most +recently created passive node. Another global variable, |printed_node|, +is used to help print out the paragraph when detailed information about +the line-breaking computation is being displayed. + +@d passive_node_size=2 {number of words in passive nodes} +@d cur_break==rlink {in passive node, points to position of this breakpoint} +@d prev_break==llink {points to passive node that should precede this one} +@d serial==info {serial number for symbolic identification} + +@<Glob...@>= +@!passive:pointer; {most recent node on passive list} +@!printed_node:pointer; {most recent node that has been printed} +@!pass_number:halfword; {the number of passive nodes allocated on this pass} + +@ The active list also contains ``delta'' nodes that help the algorithm +compute the badness of individual lines. Such nodes appear only between two +active nodes, and they have |type=delta_node|. If |p| and |r| are active nodes +and if |q| is a delta node between them, so that |link(p)=q| and |link(q)=r|, +then |q| tells the space difference between lines in the horizontal list that +start after breakpoint |p| and lines that start after breakpoint |r|. In +other words, if we know the length of the line that starts after |p| and +ends at our current position, then the corresponding length of the line that +starts after |r| is obtained by adding the amounts in node~|q|. A delta node +contains six scaled numbers, since it must record the net change in glue +stretchability with respect to all orders of infinity. The natural width +difference appears in |mem[q+1].sc|; the stretch differences in units of +pt, fil, fill, and filll appear in |mem[q+2..q+5].sc|; and the shrink difference +appears in |mem[q+6].sc|. The |subtype| field of a delta node is not used. + +@d delta_node_size=7 {number of words in a delta node} +@d delta_node=2 {|type| field in a delta node} + +@ As the algorithm runs, it maintains a set of six delta-like registers +for the length of the line following the first active breakpoint to the +current position in the given hlist. When it makes a pass through the +active list, it also maintains a similar set of six registers for the +length following the active breakpoint of current interest. A third set +holds the length of an empty line (namely, the sum of \.{\\leftskip} and +\.{\\rightskip}); and a fourth set is used to create new delta nodes. + +When we pass a delta node we want to do operations like +$$\hbox{\ignorespaces|for +k:=1 to 6 do cur_active_width[k]:=cur_active_width[k]+mem[q+k].sc|};$$ and we +want to do this without the overhead of |for| loops. The |do_all_six| +macro makes such six-tuples convenient. + +@d do_all_six(#)==#(1);#(2);#(3);#(4);#(5);#(6) + +@<Glo...@>= +@!active_width:array[1..6] of scaled; + {distance from first active node to~|cur_p|} +@!cur_active_width:array[1..6] of scaled; {distance from current active node} +@!background:array[1..6] of scaled; {length of an ``empty'' line} +@!break_width:array[1..6] of scaled; {length being computed after current break} + +@ Let's state the principles of the delta nodes more precisely and concisely, +so that the following programs will be less obscure. For each legal +breakpoint~|p| in the paragraph, we define two quantities $\alpha(p)$ and +$\beta(p)$ such that the length of material in a line from breakpoint~|p| +to breakpoint~|q| is $\gamma+\beta(q)-\alpha(p)$, for some fixed $\gamma$. +Intuitively, $\alpha(p)$ and $\beta(q)$ are the total length of material from +the beginning of the paragraph to a point ``after'' a break at |p| and to a +point ``before'' a break at |q|; and $\gamma$ is the width of an empty line, +namely the length contributed by \.{\\leftskip} and \.{\\rightskip}. + +Suppose, for example, that the paragraph consists entirely of alternating +boxes and glue skips; let the boxes have widths $x_1\ldots x_n$ and +let the skips have widths $y_1\ldots y_n$, so that the paragraph can be +represented by $x_1y_1\ldots x_ny_n$. Let $p_i$ be the legal breakpoint +at $y_i$; then $\alpha(p_i)=x_1+y_1+\cdots+x_i+y_i$, and $\beta(p_i)= +x_1+y_1+\cdots+x_i$. To check this, note that the length of material from +$p_2$ to $p_5$, say, is $\gamma+x_3+y_3+x_4+y_4+x_5=\gamma+\beta(p_5) +-\alpha(p_2)$. + +The quantities $\alpha$, $\beta$, $\gamma$ involve glue stretchability and +shrinkability as well as a natural width. If we were to compute $\alpha(p)$ +and $\beta(p)$ for each |p|, we would need multiple precision arithmetic, and +the multiprecise numbers would have to be kept in the active nodes. +\TeX\ avoids this problem by working entirely with relative differences +or ``deltas.'' Suppose, for example, that the active list contains +$a_1\,\delta_1\,a_2\,\delta_2\,a_3$, where the |a|'s are active breakpoints +and the $\delta$'s are delta nodes. Then $\delta_1=\alpha(a_1)-\alpha(a_2)$ +and $\delta_2=\alpha(a_2)-\alpha(a_3)$. If the line breaking algorithm is +currently positioned at some other breakpoint |p|, the |active_width| array +contains the value $\gamma+\beta(p)-\alpha(a_1)$. If we are scanning through +the list of active nodes and considering a tentative line that runs from +$a_2$ to~|p|, say, the |cur_active_width| array will contain the value +$\gamma+\beta(p)-\alpha(a_2)$. Thus, when we move from $a_2$ to $a_3$, +we want to add $\alpha(a_2)-\alpha(a_3)$ to |cur_active_width|; and this +is just $\delta_2$, which appears in the active list between $a_2$ and +$a_3$. The |background| array contains $\gamma$. The |break_width| array +will be used to calculate values of new delta nodes when the active +list is being updated. + +@ Glue nodes in a horizontal list that is being paragraphed are not supposed to +include ``infinite'' shrinkability; that is why the algorithm maintains +four registers for stretching but only one for shrinking. If the user tries to +introduce infinite shrinkability, the shrinkability will be reset to finite +and an error message will be issued. A boolean variable |no_shrink_error_yet| +prevents this error message from appearing more than once per paragraph. + +@d check_shrinkage(#)==if (shrink_order(#)<>normal)and(shrink(#)<>0) then + begin #:=finite_shrink(#); + end + +@<Glob...@>= +@!no_shrink_error_yet:boolean; {have we complained about infinite shrinkage?} + +@ @<Declare subprocedures for |line_break|@>= +function finite_shrink(@!p:pointer):pointer; {recovers from infinite shrinkage} +var q:pointer; {new glue specification} +begin if no_shrink_error_yet then + begin no_shrink_error_yet:=false; + print_err("Infinite glue shrinkage found in a paragraph"); +@.Infinite glue shrinkage...@> + help5("The paragraph just ended includes some glue that has")@/ + ("infinite shrinkability, e.g., `\hskip 0pt minus 1fil'.")@/ + ("Such glue doesn't belong there---it allows a paragraph")@/ + ("of any length to fit on one line. But it's safe to proceed,")@/ + ("since the offensive shrinkability has been made finite."); + error; + end; +q:=new_spec(p); shrink_order(q):=normal; +delete_glue_ref(p); finite_shrink:=q; +end; + +@ @<Get ready to start...@>= +no_shrink_error_yet:=true;@/ +check_shrinkage(left_skip); check_shrinkage(right_skip);@/ +q:=left_skip; r:=right_skip; background[1]:=width(q)+width(r);@/ +background[2]:=0; background[3]:=0; background[4]:=0; background[5]:=0;@/ +background[2+stretch_order(q)]:=stretch(q);@/ +background[2+stretch_order(r)]:=@|background[2+stretch_order(r)]+stretch(r);@/ +background[6]:=shrink(q)+shrink(r); + +@ A pointer variable |cur_p| runs through the given horizontal list as we look +for breakpoints. This variable is global, since it is used both by |line_break| +and by its subprocedure |try_break|. + +Another global variable called |threshold| is used to determine the feasibility +of individual lines: breakpoints are feasible if there is a way to reach +them without creating lines whose badness exceeds |threshold|. (The +badness is compared to |threshold| before penalties are added, so that +penalty values do not affect the feasibility of breakpoints, except that +no break is allowed when the penalty is 10000 or more.) If |threshold| +is 10000 or more, all legal breaks are considered feasible, since the +|badness| function specified above never returns a value greater than~10000. + +Up to three passes might be made through the paragraph in an attempt to find at +least one set of feasible breakpoints. On the first pass, we have +|threshold=pretolerance| and |second_pass=final_pass=false|. +If this pass fails to find a +feasible solution, |threshold| is set to |tolerance|, |second_pass| is set +|true|, and an attempt is made to hyphenate as many words as possible. +If that fails too, we add |emergency_stretch| to the background +stretchability and set |final_pass=true|. + +@<Glob...@>= +@!cur_p:pointer; {the current breakpoint under consideration} +@!second_pass:boolean; {is this our second attempt to break this paragraph?} +@!final_pass:boolean; {is this our final attempt to break this paragraph?} +@!threshold:integer; {maximum badness on feasible lines} + +@ The heart of the line-breaking procedure is `|try_break|', a subroutine +that tests if the current breakpoint |cur_p| is feasible, by running +through the active list to see what lines of text can be made from active +nodes to~|cur_p|. If feasible breaks are possible, new break nodes are +created. If |cur_p| is too far from an active node, that node is +deactivated. + +The parameter |pi| to |try_break| is the penalty associated +with a break at |cur_p|; we have |pi=eject_penalty| if the break is forced, +and |pi=inf_penalty| if the break is illegal. + +The other parameter, |break_type|, is set to |hyphenated| or |unhyphenated|, +depending on whether or not the current break is at a |disc_node|. The +end of a paragraph is also regarded as `|hyphenated|'; this case is +distinguishable by the condition |cur_p=null|. + +@d copy_to_cur_active(#)==cur_active_width[#]:=active_width[#] +@d deactivate=60 {go here when node |r| should be deactivated} + +@<Declare subprocedures for |line_break|@>= +procedure try_break(@!pi:integer;@!break_type:small_number); +label exit,done,done1,continue,deactivate; +var r:pointer; {runs through the active list} +@!prev_r:pointer; {stays a step behind |r|} +@!old_l:halfword; {maximum line number in current equivalence class of lines} +@!no_break_yet:boolean; {have we found a feasible break at |cur_p|?} +@<Other local variables for |try_break|@>@; +begin @<Make sure that |pi| is in the proper range@>; +no_break_yet:=true; prev_r:=active; old_l:=0; +do_all_six(copy_to_cur_active); +loop@+ begin continue: r:=link(prev_r); + @<If node |r| is of type |delta_node|, update |cur_active_width|, + set |prev_r| and |prev_prev_r|, then |goto continue|@>; + @<If a line number class has ended, create new active nodes for + the best feasible breaks in that class; then |return| + if |r=last_active|, otherwise compute the new |line_width|@>; + @<Consider the demerits for a line from |r| to |cur_p|; + deactivate node |r| if it should no longer be active; + then |goto continue| if a line from |r| to |cur_p| is infeasible, + otherwise record a new feasible break@>; + end; +exit: @!stat @<Update the value of |printed_node| for + symbolic displays@>@+tats@; +end; + +@ @<Other local variables for |try_break|@>= +@!prev_prev_r:pointer; {a step behind |prev_r|, if |type(prev_r)=delta_node|} +@!s:pointer; {runs through nodes ahead of |cur_p|} +@!q:pointer; {points to a new node being created} +@!v:pointer; {points to a glue specification or a node ahead of |cur_p|} +@!t:integer; {node count, if |cur_p| is a discretionary node} +@!f:internal_font_number; {used in character width calculation} +@!l:halfword; {line number of current active node} +@!node_r_stays_active:boolean; {should node |r| remain in the active list?} +@!line_width:scaled; {the current line will be justified to this width} +@!fit_class:very_loose_fit..tight_fit; {possible fitness class of test line} +@!b:halfword; {badness of test line} +@!d:integer; {demerits of test line} +@!artificial_demerits:boolean; {has |d| been forced to zero?} +@!save_link:pointer; {temporarily holds value of |link(cur_p)|} +@!shortfall:scaled; {used in badness calculations} + +@ @<Make sure that |pi| is in the proper range@>= +if abs(pi)>=inf_penalty then + if pi>0 then return {this breakpoint is inhibited by infinite penalty} + else pi:=eject_penalty {this breakpoint will be forced} + +@ The following code uses the fact that |type(last_active)<>delta_node|. + +@d update_width(#)==@| + cur_active_width[#]:=cur_active_width[#]+mem[r+#].sc + +@<If node |r|...@>= +@^inner loop@> +if type(r)=delta_node then + begin do_all_six(update_width); + prev_prev_r:=prev_r; prev_r:=r; goto continue; + end + +@ As we consider various ways to end a line at |cur_p|, in a given line number +class, we keep track of the best total demerits known, in an array with +one entry for each of the fitness classifications. For example, +|minimal_demerits[tight_fit]| contains the fewest total demerits of feasible +line breaks ending at |cur_p| with a |tight_fit| line; |best_place[tight_fit]| +points to the passive node for the break before~|cur_p| that achieves such +an optimum; and |best_pl_line[tight_fit]| is the |line_number| field in the +active node corresponding to |best_place[tight_fit]|. When no feasible break +sequence is known, the |minimal_demerits| entries will be equal to +|awful_bad|, which is $2^{30}-1$. Another variable, |minimum_demerits|, +keeps track of the smallest value in the |minimal_demerits| array. + +@d awful_bad==@'7777777777 {more than a billion demerits} + +@<Global...@>= +@!minimal_demerits:array[very_loose_fit..tight_fit] of integer; {best total + demerits known for current line class and position, given the fitness} +@!minimum_demerits:integer; {best total demerits known for current line class + and position} +@!best_place:array[very_loose_fit..tight_fit] of pointer; {how to achieve + |minimal_demerits|} +@!best_pl_line:array[very_loose_fit..tight_fit] of halfword; {corresponding + line number} + +@ @<Get ready to start...@>= +minimum_demerits:=awful_bad; +minimal_demerits[tight_fit]:=awful_bad; +minimal_demerits[decent_fit]:=awful_bad; +minimal_demerits[loose_fit]:=awful_bad; +minimal_demerits[very_loose_fit]:=awful_bad; + +@ The first part of the following code is part of \TeX's inner loop, so +we don't want to waste any time. The current active node, namely node |r|, +contains the line number that will be considered next. At the end of the +list we have arranged the data structure so that |r=last_active| and +|line_number(last_active)>old_l|. +@^inner loop@> + +@<If a line number class...@>= +begin l:=line_number(r); +if l>old_l then + begin {now we are no longer in the inner loop} + if (minimum_demerits<awful_bad)and@| + ((old_l<>easy_line)or(r=last_active)) then + @<Create new active nodes for the best feasible breaks + just found@>; + if r=last_active then return; + @<Compute the new line width@>; + end; +end + +@ It is not necessary to create new active nodes having |minimal_demerits| +greater than +|minimum_demerits+abs(adj_demerits)|, since such active nodes will never +be chosen in the final paragraph breaks. This observation allows us to +omit a substantial number of feasible breakpoints from further consideration. + +@<Create new active nodes...@>= +begin if no_break_yet then @<Compute the values of |break_width|@>; +@<Insert a delta node to prepare for breaks at |cur_p|@>; +if abs(adj_demerits)>=awful_bad-minimum_demerits then + minimum_demerits:=awful_bad-1 +else minimum_demerits:=minimum_demerits+abs(adj_demerits); +for fit_class:=very_loose_fit to tight_fit do + begin if minimal_demerits[fit_class]<=minimum_demerits then + @<Insert a new active node + from |best_place[fit_class]| to |cur_p|@>; + minimal_demerits[fit_class]:=awful_bad; + end; +minimum_demerits:=awful_bad; +@<Insert a delta node to prepare for the next active node@>; +end + +@ When we insert a new active node for a break at |cur_p|, suppose this +new node is to be placed just before active node |a|; then we essentially +want to insert `$\delta\,|cur_p|\,\delta^\prime$' before |a|, where +$\delta=\alpha(a)-\alpha(|cur_p|)$ and $\delta^\prime=\alpha(|cur_p|)-\alpha(a)$ +in the notation explained above. The |cur_active_width| array now holds +$\gamma+\beta(|cur_p|)-\alpha(a)$; so $\delta$ can be obtained by +subtracting |cur_active_width| from the quantity $\gamma+\beta(|cur_p|)- +\alpha(|cur_p|)$. The latter quantity can be regarded as the length of a +line ``from |cur_p| to |cur_p|''; we call it the |break_width| at |cur_p|. + +The |break_width| is usually negative, since it consists of the background +(which is normally zero) minus the width of nodes following~|cur_p| that are +eliminated after a break. If, for example, node |cur_p| is a glue node, the +width of this glue is subtracted from the background; and we also look +ahead to eliminate all subsequent glue and penalty and kern and math +nodes, subtracting their widths as well. + +Kern nodes do not disappear at a line break unless they are |explicit|. + +@d set_break_width_to_background(#)==break_width[#]:=background[#] + +@<Compute the values of |break...@>= +begin no_break_yet:=false; do_all_six(set_break_width_to_background); +s:=cur_p; +if break_type>unhyphenated then if cur_p<>null then + @<Compute the discretionary |break_width| values@>; +while s<>null do + begin if is_char_node(s) then goto done; + case type(s) of + glue_node:@<Subtract glue from |break_width|@>; + penalty_node: do_nothing; + math_node: break_width[1]:=break_width[1]-width(s); + kern_node: if subtype(s)<>explicit then goto done + else break_width[1]:=break_width[1]-width(s); + othercases goto done + endcases;@/ + s:=link(s); + end; +done: end + +@ @<Subtract glue from |break...@>= +begin v:=glue_ptr(s); break_width[1]:=break_width[1]-width(v); +break_width[2+stretch_order(v)]:=break_width[2+stretch_order(v)]-stretch(v); +break_width[6]:=break_width[6]-shrink(v); +end + +@ When |cur_p| is a discretionary break, the length of a line ``from |cur_p| to +|cur_p|'' has to be defined properly so that the other calculations work out. +Suppose that the pre-break text at |cur_p| has length $l_0$, the post-break +text has length $l_1$, and the replacement text has length |l|. Suppose +also that |q| is the node following the replacement text. Then length of a +line from |cur_p| to |q| will be computed as $\gamma+\beta(q)-\alpha(|cur_p|)$, +where $\beta(q)=\beta(|cur_p|)-l_0+l$. The actual length will be the background +plus $l_1$, so the length from |cur_p| to |cur_p| should be $\gamma+l_0+l_1-l$. +If the post-break text of the discretionary is empty, a break may also +discard~|q|; in that unusual case we subtract the length of~|q| and any +other nodes that will be discarded after the discretionary break. + +The value of $l_0$ need not be computed, since |line_break| will put +it into the global variable |disc_width| before calling |try_break|. + +@<Glob...@>= +@!disc_width:scaled; {the length of discretionary material preceding a break} + +@ @<Compute the discretionary |break...@>= +begin t:=replace_count(cur_p); v:=cur_p; s:=post_break(cur_p); +while t>0 do + begin decr(t); v:=link(v); + @<Subtract the width of node |v| from |break_width|@>; + end; +while s<>null do + begin @<Add the width of node |s| to |break_width|@>; + s:=link(s); + end; +break_width[1]:=break_width[1]+disc_width; +if post_break(cur_p)=null then s:=link(v); + {nodes may be discardable after the break} +end + +@ Replacement texts and discretionary texts are supposed to contain +only character nodes, kern nodes, ligature nodes, and box or rule nodes. + +@<Subtract the width of node |v|...@>= +if is_char_node(v) then + begin f:=font(v); + break_width[1]:=break_width[1]-char_width(f)(char_info(f)(character(v))); + end +else case type(v) of + ligature_node: begin f:=font(lig_char(v));@/ + break_width[1]:=@|break_width[1]- + char_width(f)(char_info(f)(character(lig_char(v)))); + end; + hlist_node,vlist_node,rule_node,kern_node: + break_width[1]:=break_width[1]-width(v); + othercases confusion("disc1") +@:this can't happen disc1}{\quad disc1@> + endcases + +@ @<Add the width of node |s| to |b...@>= +if is_char_node(s) then + begin f:=font(s); + break_width[1]:=@|break_width[1]+char_width(f)(char_info(f)(character(s))); + end +else case type(s) of + ligature_node: begin f:=font(lig_char(s)); + break_width[1]:=break_width[1]+ + char_width(f)(char_info(f)(character(lig_char(s)))); + end; + hlist_node,vlist_node,rule_node,kern_node: + break_width[1]:=break_width[1]+width(s); + othercases confusion("disc2") +@:this can't happen disc2}{\quad disc2@> + endcases + +@ We use the fact that |type(active)<>delta_node|. + +@d convert_to_break_width(#)==@| + mem[prev_r+#].sc:=@|@t\hskip10pt@>mem[prev_r+#].sc + -cur_active_width[#]+break_width[#] +@d store_break_width(#)==active_width[#]:=break_width[#] +@d new_delta_to_break_width(#)==@| + mem[q+#].sc:=break_width[#]-cur_active_width[#] + +@<Insert a delta node to prepare for breaks at |cur_p|@>= +if type(prev_r)=delta_node then {modify an existing delta node} + begin do_all_six(convert_to_break_width); + end +else if prev_r=active then {no delta node needed at the beginning} + begin do_all_six(store_break_width); + end +else begin q:=get_node(delta_node_size); link(q):=r; type(q):=delta_node;@/ + subtype(q):=0; {the |subtype| is not used} + do_all_six(new_delta_to_break_width); + link(prev_r):=q; prev_prev_r:=prev_r; prev_r:=q; + end + +@ When the following code is performed, we will have just inserted at +least one active node before |r|, so |type(prev_r)<>delta_node|. + +@d new_delta_from_break_width(#)==@|mem[q+#].sc:= + cur_active_width[#]-break_width[#] + +@<Insert a delta node to prepare for the next active node@>= +if r<>last_active then + begin q:=get_node(delta_node_size); link(q):=r; type(q):=delta_node;@/ + subtype(q):=0; {the |subtype| is not used} + do_all_six(new_delta_from_break_width); + link(prev_r):=q; prev_prev_r:=prev_r; prev_r:=q; + end + +@ When we create an active node, we also create the corresponding +passive node. + +@<Insert a new active node from |best_place[fit_class]| to |cur_p|@>= +begin q:=get_node(passive_node_size); +link(q):=passive; passive:=q; cur_break(q):=cur_p; +@!stat incr(pass_number); serial(q):=pass_number;@+tats@;@/ +prev_break(q):=best_place[fit_class];@/ +q:=get_node(active_node_size); break_node(q):=passive; +line_number(q):=best_pl_line[fit_class]+1; +fitness(q):=fit_class; type(q):=break_type; +total_demerits(q):=minimal_demerits[fit_class]; +link(q):=r; link(prev_r):=q; prev_r:=q; +@!stat if tracing_paragraphs>0 then + @<Print a symbolic description of the new break node@>; +tats@;@/ +end + +@ @<Print a symbolic description of the new break node@>= +begin print_nl("@@@@"); print_int(serial(passive)); +@.\AT!\AT!@> +print(": line "); print_int(line_number(q)-1); +print_char("."); print_int(fit_class); +if break_type=hyphenated then print_char("-"); +print(" t="); print_int(total_demerits(q)); +print(" -> @@@@"); +if prev_break(passive)=null then print_char("0") +else print_int(serial(prev_break(passive))); +end + +@ The length of lines depends on whether the user has specified +\.{\\parshape} or \.{\\hangindent}. If |par_shape_ptr| is not null, it +points to a $(2n+1)$-word record in |mem|, where the |info| in the first +word contains the value of |n|, and the other $2n$ words contain the left +margins and line lengths for the first |n| lines of the paragraph; the +specifications for line |n| apply to all subsequent lines. If +|par_shape_ptr=null|, the shape of the paragraph depends on the value of +|n=hang_after|; if |n>=0|, hanging indentation takes place on lines |n+1|, +|n+2|, \dots, otherwise it takes place on lines 1, \dots, $\vert +n\vert$. When hanging indentation is active, the left margin is +|hang_indent|, if |hang_indent>=0|, else it is 0; the line length is +$|hsize|-\vert|hang_indent|\vert$. The normal setting is +|par_shape_ptr=null|, |hang_after=1|, and |hang_indent=0|. +Note that if |hang_indent=0|, the value of |hang_after| is irrelevant. +@^length of lines@> @^hanging indentation@> + +@<Glob...@>= +@!easy_line:halfword; {line numbers |>easy_line| are equivalent in break nodes} +@!last_special_line:halfword; {line numbers |>last_special_line| all have + the same width} +@!first_width:scaled; {the width of all lines |<=last_special_line|, if + no \.{\\parshape} has been specified} +@!second_width:scaled; {the width of all lines |>last_special_line|} +@!first_indent:scaled; {left margin to go with |first_width|} +@!second_indent:scaled; {left margin to go with |second_width|} + +@ We compute the values of |easy_line| and the other local variables relating +to line length when the |line_break| procedure is initializing itself. + +@<Get ready to start...@>= +if par_shape_ptr=null then + if hang_indent=0 then + begin last_special_line:=0; second_width:=hsize; + second_indent:=0; + end + else @<Set line length parameters in preparation for hanging indentation@> +else begin last_special_line:=info(par_shape_ptr)-1; + second_width:=mem[par_shape_ptr+2*(last_special_line+1)].sc; + second_indent:=mem[par_shape_ptr+2*last_special_line+1].sc; + end; +if looseness=0 then easy_line:=last_special_line +else easy_line:=max_halfword + +@ @<Set line length parameters in preparation for hanging indentation@>= +begin last_special_line:=abs(hang_after); +if hang_after<0 then + begin first_width:=hsize-abs(hang_indent); + if hang_indent>=0 then first_indent:=hang_indent + else first_indent:=0; + second_width:=hsize; second_indent:=0; + end +else begin first_width:=hsize; first_indent:=0; + second_width:=hsize-abs(hang_indent); + if hang_indent>=0 then second_indent:=hang_indent + else second_indent:=0; + end; +end + +@ When we come to the following code, we have just encountered the first +active node~|r| whose |line_number| field contains |l|. Thus we want to +compute the length of the $l\mskip1mu$th line of the current paragraph. Furthermore, +we want to set |old_l| to the last number in the class of line numbers +equivalent to~|l|. + +@<Compute the new line width@>= +if l>easy_line then + begin line_width:=second_width; old_l:=max_halfword-1; + end +else begin old_l:=l; + if l>last_special_line then line_width:=second_width + else if par_shape_ptr=null then line_width:=first_width + else line_width:=mem[par_shape_ptr+2*l@,].sc; + end + +@ The remaining part of |try_break| deals with the calculation of +demerits for a break from |r| to |cur_p|. + +The first thing to do is calculate the badness, |b|. This value will always +be between zero and |inf_bad+1|; the latter value occurs only in the +case of lines from |r| to |cur_p| that cannot shrink enough to fit the necessary +width. In such cases, node |r| will be deactivated. +We also deactivate node~|r| when a break at~|cur_p| is forced, since future +breaks must go through a forced break. + +@<Consider the demerits for a line from |r| to |cur_p|...@>= +begin artificial_demerits:=false;@/ +@^inner loop@> +shortfall:=line_width-cur_active_width[1]; {we're this much too short} +if shortfall>0 then + @<Set the value of |b| to the badness for stretching the line, + and compute the corresponding |fit_class|@> +else @<Set the value of |b| to the badness for shrinking the line, + and compute the corresponding |fit_class|@>; +if (b>inf_bad)or(pi=eject_penalty) then + @<Prepare to deactivate node~|r|, and |goto deactivate| unless + there is a reason to consider lines of text from |r| to |cur_p|@> +else begin prev_r:=r; + if b>threshold then goto continue; + node_r_stays_active:=true; + end; +@<Record a new feasible break@>; +if node_r_stays_active then goto continue; {|prev_r| has been set to |r|} +deactivate: @<Deactivate node |r|@>; +end + +@ When a line must stretch, the available stretchability can be found in the +subarray |cur_active_width[2..5]|, in units of points, fil, fill, and filll. + +The present section is part of \TeX's inner loop, and it is most often performed +when the badness is infinite; therefore it is worth while to make a quick +test for large width excess and small stretchability, before calling the +|badness| subroutine. +@^inner loop@> + +@<Set the value of |b| to the badness for stretching...@>= +if (cur_active_width[3]<>0)or(cur_active_width[4]<>0)or@| + (cur_active_width[5]<>0) then + begin b:=0; fit_class:=decent_fit; {infinite stretch} + end +else begin if shortfall>7230584 then if cur_active_width[2]<1663497 then + begin b:=inf_bad; fit_class:=very_loose_fit; goto done1; + end; + b:=badness(shortfall,cur_active_width[2]); + if b>12 then + if b>99 then fit_class:=very_loose_fit + else fit_class:=loose_fit + else fit_class:=decent_fit; + done1: + end + +@ Shrinkability is never infinite in a paragraph; +we can shrink the line from |r| to |cur_p| by at most |cur_active_width[6]|. + +@<Set the value of |b| to the badness for shrinking...@>= +begin if -shortfall>cur_active_width[6] then b:=inf_bad+1 +else b:=badness(-shortfall,cur_active_width[6]); +if b>12 then fit_class:=tight_fit@+else fit_class:=decent_fit; +end + +@ During the final pass, we dare not lose all active nodes, lest we lose +touch with the line breaks already found. The code shown here makes sure +that such a catastrophe does not happen, by permitting overfull boxes as +a last resort. This particular part of \TeX\ was a source of several subtle +bugs before the correct program logic was finally discovered; readers +who seek to ``improve'' \TeX\ should therefore think thrice before daring +to make any changes here. +@^overfull boxes@> + +@<Prepare to deactivate node~|r|, and |goto deactivate| unless...@>= +begin if final_pass and (minimum_demerits=awful_bad) and@| + (link(r)=last_active) and + (prev_r=active) then + artificial_demerits:=true {set demerits zero, this break is forced} +else if b>threshold then goto deactivate; +node_r_stays_active:=false; +end + +@ When we get to this part of the code, the line from |r| to |cur_p| is +feasible, its badness is~|b|, and its fitness classification is |fit_class|. +We don't want to make an active node for this break yet, but we will +compute the total demerits and record them in the |minimal_demerits| array, +if such a break is the current champion among all ways to get to |cur_p| +in a given line-number class and fitness class. + +@<Record a new feasible break@>= +if artificial_demerits then d:=0 +else @<Compute the demerits, |d|, from |r| to |cur_p|@>; +@!stat if tracing_paragraphs>0 then + @<Print a symbolic description of this feasible break@>; +tats@;@/ +d:=d+total_demerits(r); {this is the minimum total demerits + from the beginning to |cur_p| via |r|} +if d<=minimal_demerits[fit_class] then + begin minimal_demerits[fit_class]:=d; + best_place[fit_class]:=break_node(r); best_pl_line[fit_class]:=l; + if d<minimum_demerits then minimum_demerits:=d; + end + +@ @<Print a symbolic description of this feasible break@>= +begin if printed_node<>cur_p then + @<Print the list between |printed_node| and |cur_p|, + then set |printed_node:=cur_p|@>; +print_nl("@@"); +@.\AT!@> +if cur_p=null then print_esc("par") +else if type(cur_p)<>glue_node then + begin if type(cur_p)=penalty_node then print_esc("penalty") + else if type(cur_p)=disc_node then print_esc("discretionary") + else if type(cur_p)=kern_node then print_esc("kern") + else print_esc("math"); + end; +print(" via @@@@"); +if break_node(r)=null then print_char("0") +else print_int(serial(break_node(r))); +print(" b="); +if b>inf_bad then print_char("*")@+else print_int(b); +@.*\relax@> +print(" p="); print_int(pi); print(" d="); +if artificial_demerits then print_char("*")@+else print_int(d); +end + +@ @<Print the list between |printed_node| and |cur_p|...@>= +begin print_nl(""); +if cur_p=null then short_display(link(printed_node)) +else begin save_link:=link(cur_p); + link(cur_p):=null; print_nl(""); short_display(link(printed_node)); + link(cur_p):=save_link; + end; +printed_node:=cur_p; +end + +@ When the data for a discretionary break is being displayed, we will have +printed the |pre_break| and |post_break| lists; we want to skip over the +third list, so that the discretionary data will not appear twice. The +following code is performed at the very end of |try_break|. + +@<Update the value of |printed_node|...@>= +if cur_p=printed_node then if cur_p<>null then if type(cur_p)=disc_node then + begin t:=replace_count(cur_p); + while t>0 do + begin decr(t); printed_node:=link(printed_node); + end; + end + +@ @<Compute the demerits, |d|, from |r| to |cur_p|@>= +begin d:=line_penalty+b; +if abs(d)>=10000 then d:=100000000@+else d:=d*d; +if pi<>0 then + if pi>0 then d:=d+pi*pi + else if pi>eject_penalty then d:=d-pi*pi; +if (break_type=hyphenated)and(type(r)=hyphenated) then + if cur_p<>null then d:=d+double_hyphen_demerits + else d:=d+final_hyphen_demerits; +if abs(fit_class-fitness(r))>1 then d:=d+adj_demerits; +end + +@ When an active node disappears, we must delete an adjacent delta node if the +active node was at the beginning or the end of the active list, or if it +was surrounded by delta nodes. We also must preserve the property that +|cur_active_width| represents the length of material from |link(prev_r)| +to~|cur_p|. + +@d combine_two_deltas(#)==@|mem[prev_r+#].sc:=mem[prev_r+#].sc+mem[r+#].sc +@d downdate_width(#)==@|cur_active_width[#]:=cur_active_width[#]- + mem[prev_r+#].sc + +@<Deactivate node |r|@>= +link(prev_r):=link(r); free_node(r,active_node_size); +if prev_r=active then @<Update the active widths, since the first active + node has been deleted@> +else if type(prev_r)=delta_node then + begin r:=link(prev_r); + if r=last_active then + begin do_all_six(downdate_width); + link(prev_prev_r):=last_active; + free_node(prev_r,delta_node_size); prev_r:=prev_prev_r; + end + else if type(r)=delta_node then + begin do_all_six(update_width); + do_all_six(combine_two_deltas); + link(prev_r):=link(r); free_node(r,delta_node_size); + end; + end + +@ The following code uses the fact that |type(last_active)<>delta_node|. If the +active list has just become empty, we do not need to update the +|active_width| array, since it will be initialized when an active +node is next inserted. + +@d update_active(#)==active_width[#]:=active_width[#]+mem[r+#].sc + +@<Update the active widths,...@>= +begin r:=link(active); +if type(r)=delta_node then + begin do_all_six(update_active); + do_all_six(copy_to_cur_active); + link(active):=link(r); free_node(r,delta_node_size); + end; +end + +@* \[39] Breaking paragraphs into lines, continued. +So far we have gotten a little way into the |line_break| routine, having +covered its important |try_break| subroutine. Now let's consider the +rest of the process. + +The main loop of |line_break| traverses the given hlist, +starting at |link(temp_head)|, and calls |try_break| at each legal +breakpoint. A variable called |auto_breaking| is set to true except +within math formulas, since glue nodes are not legal breakpoints when +they appear in formulas. + +The current node of interest in the hlist is pointed to by |cur_p|. Another +variable, |prev_p|, is usually one step behind |cur_p|, but the real +meaning of |prev_p| is this: If |type(cur_p)=glue_node| then |cur_p| is a legal +breakpoint if and only if |auto_breaking| is true and |prev_p| does not +point to a glue node, penalty node, explicit kern node, or math node. + +The following declarations provide for a few other local variables that are +used in special calculations. + +@<Local variables for line breaking@>= +@!auto_breaking:boolean; {is node |cur_p| outside a formula?} +@!prev_p:pointer; {helps to determine when glue nodes are breakpoints} +@!q,@!r,@!s,@!prev_s:pointer; {miscellaneous nodes of temporary interest} +@!f:internal_font_number; {used when calculating character widths} + +@ The `\ignorespaces|loop|\unskip' in the following code is performed at most +thrice per call of |line_break|, since it is actually a pass over the +entire paragraph. + +@<Find optimal breakpoints@>= +threshold:=pretolerance; +if threshold>=0 then + begin @!stat if tracing_paragraphs>0 then + begin begin_diagnostic; print_nl("@@firstpass");@+end;@;@+tats@;@/ + second_pass:=false; final_pass:=false; + end +else begin threshold:=tolerance; second_pass:=true; + final_pass:=(emergency_stretch<=0); + @!stat if tracing_paragraphs>0 then begin_diagnostic;@+tats@; + end; +loop@+ begin if threshold>inf_bad then threshold:=inf_bad; + if second_pass then @<Initialize for hyphenating a paragraph@>; + @<Create an active breakpoint representing the beginning of the paragraph@>; + cur_p:=link(temp_head); auto_breaking:=true;@/ + prev_p:=cur_p; {glue at beginning is not a legal breakpoint} + while (cur_p<>null)and(link(active)<>last_active) do + @<Call |try_break| if |cur_p| is a legal breakpoint; + on the second pass, also try to hyphenate the next + word, if |cur_p| is a glue node; + then advance |cur_p| to the next node of the paragraph + that could possibly be a legal breakpoint@>; + if cur_p=null then + @<Try the final line break at the end of the paragraph, + and |goto done| if the desired breakpoints have been found@>; + @<Clean up the memory by removing the break nodes@>; + if not second_pass then + begin@!stat if tracing_paragraphs>0 then print_nl("@@secondpass");@;@+tats@/ + threshold:=tolerance; second_pass:=true; final_pass:=(emergency_stretch<=0); + end {if at first you don't succeed, \dots} + else begin @!stat if tracing_paragraphs>0 then + print_nl("@@emergencypass");@;@+tats@/ + background[2]:=background[2]+emergency_stretch; final_pass:=true; + end; + end; +done: @!stat if tracing_paragraphs>0 then + begin end_diagnostic(true); normalize_selector; + end;@+tats@/ + +@ The active node that represents the starting point does not need a +corresponding passive node. + +@d store_background(#)==active_width[#]:=background[#] + +@<Create an active breakpoint representing the beginning of the paragraph@>= +q:=get_node(active_node_size); +type(q):=unhyphenated; fitness(q):=decent_fit; +link(q):=last_active; break_node(q):=null; +line_number(q):=prev_graf+1; total_demerits(q):=0; link(active):=q; +do_all_six(store_background);@/ +passive:=null; printed_node:=temp_head; pass_number:=0; +font_in_short_display:=null_font + +@ @<Clean...@>= +q:=link(active); +while q<>last_active do + begin cur_p:=link(q); + if type(q)=delta_node then free_node(q,delta_node_size) + else free_node(q,active_node_size); + q:=cur_p; + end; +q:=passive; +while q<>null do + begin cur_p:=link(q); + free_node(q,passive_node_size); + q:=cur_p; + end + +@ Here is the main switch in the |line_break| routine, where legal breaks +are determined. As we move through the hlist, we need to keep the |active_width| +array up to date, so that the badness of individual lines is readily calculated +by |try_break|. It is convenient to use the short name |act_width| for +the component of active width that represents real width as opposed to glue. + +@d act_width==active_width[1] {length from first active node to current node} +@d kern_break==begin if not is_char_node(link(cur_p)) and auto_breaking then + if type(link(cur_p))=glue_node then try_break(0,unhyphenated); + act_width:=act_width+width(cur_p); + end + +@<Call |try_break| if |cur_p| is a legal breakpoint...@>= +begin if is_char_node(cur_p) then + @<Advance \(c)|cur_p| to the node following the present + string of characters@>; +case type(cur_p) of +hlist_node,vlist_node,rule_node: act_width:=act_width+width(cur_p); +whatsit_node: @<Advance \(p)past a whatsit node in the \(l)|line_break| loop@>; +glue_node: begin @<If node |cur_p| is a legal breakpoint, call |try_break|; + then update the active widths by including the glue in |glue_ptr(cur_p)|@>; + if second_pass and auto_breaking then + @<Try to hyphenate the following word@>; + end; +kern_node: if subtype(cur_p)=explicit then kern_break + else act_width:=act_width+width(cur_p); +ligature_node: begin f:=font(lig_char(cur_p)); + act_width:=act_width+char_width(f)(char_info(f)(character(lig_char(cur_p)))); + end; +disc_node: @<Try to break after a discretionary fragment, then |goto done5|@>; +math_node: begin auto_breaking:=(subtype(cur_p)=after); kern_break; + end; +penalty_node: try_break(penalty(cur_p),unhyphenated); +mark_node,ins_node,adjust_node: do_nothing; +othercases confusion("paragraph") +@:this can't happen paragraph}{\quad paragraph@> +endcases;@/ +prev_p:=cur_p; cur_p:=link(cur_p); +done5:end + +@ The code that passes over the characters of words in a paragraph is +part of \TeX's inner loop, so it has been streamlined for speed. We use +the fact that `\.{\\parfillskip}' glue appears at the end of each paragraph; +it is therefore unnecessary to check if |link(cur_p)=null| when |cur_p| is a +character node. +@^inner loop@> + +@<Advance \(c)|cur_p| to the node following the present string...@>= +begin prev_p:=cur_p; +repeat f:=font(cur_p); +act_width:=act_width+char_width(f)(char_info(f)(character(cur_p))); +cur_p:=link(cur_p); +until not is_char_node(cur_p); +end + +@ When node |cur_p| is a glue node, we look at |prev_p| to see whether or not +a breakpoint is legal at |cur_p|, as explained above. + +@<If node |cur_p| is a legal breakpoint, call...@>= +if auto_breaking then + begin if is_char_node(prev_p) then try_break(0,unhyphenated) + else if precedes_break(prev_p) then try_break(0,unhyphenated) + else if (type(prev_p)=kern_node)and(subtype(prev_p)<>explicit) then + try_break(0,unhyphenated); + end; +check_shrinkage(glue_ptr(cur_p)); q:=glue_ptr(cur_p); +act_width:=act_width+width(q);@| +active_width[2+stretch_order(q)]:=@| + active_width[2+stretch_order(q)]+stretch(q);@/ +active_width[6]:=active_width[6]+shrink(q) + +@ The following code knows that discretionary texts contain +only character nodes, kern nodes, box nodes, rule nodes, and ligature nodes. + +@<Try to break after a discretionary fragment...@>= +begin s:=pre_break(cur_p); disc_width:=0; +if s=null then try_break(ex_hyphen_penalty,hyphenated) +else begin repeat @<Add the width of node |s| to |disc_width|@>; + s:=link(s); + until s=null; + act_width:=act_width+disc_width; + try_break(hyphen_penalty,hyphenated); + act_width:=act_width-disc_width; + end; +r:=replace_count(cur_p); s:=link(cur_p); +while r>0 do + begin @<Add the width of node |s| to |act_width|@>; + decr(r); s:=link(s); + end; +prev_p:=cur_p; cur_p:=s; goto done5; +end + +@ @<Add the width of node |s| to |disc_width|@>= +if is_char_node(s) then + begin f:=font(s); + disc_width:=disc_width+char_width(f)(char_info(f)(character(s))); + end +else case type(s) of + ligature_node: begin f:=font(lig_char(s)); + disc_width:=disc_width+ + char_width(f)(char_info(f)(character(lig_char(s)))); + end; + hlist_node,vlist_node,rule_node,kern_node: + disc_width:=disc_width+width(s); + othercases confusion("disc3") +@:this can't happen disc3}{\quad disc3@> + endcases + +@ @<Add the width of node |s| to |act_width|@>= +if is_char_node(s) then + begin f:=font(s); + act_width:=act_width+char_width(f)(char_info(f)(character(s))); + end +else case type(s) of + ligature_node: begin f:=font(lig_char(s)); + act_width:=act_width+ + char_width(f)(char_info(f)(character(lig_char(s)))); + end; + hlist_node,vlist_node,rule_node,kern_node: + act_width:=act_width+width(s); + othercases confusion("disc4") +@:this can't happen disc4}{\quad disc4@> + endcases + +@ The forced line break at the paragraph's end will reduce the list of +breakpoints so that all active nodes represent breaks at |cur_p=null|. +On the first pass, we insist on finding an active node that has the +correct ``looseness.'' On the final pass, there will be at least one active +node, and we will match the desired looseness as well as we can. + +The global variable |best_bet| will be set to the active node for the best +way to break the paragraph, and a few other variables are used to +help determine what is best. + +@<Glob...@>= +@!best_bet:pointer; {use this passive node and its predecessors} +@!fewest_demerits:integer; {the demerits associated with |best_bet|} +@!best_line:halfword; {line number following the last line of the new paragraph} +@!actual_looseness:integer; {the difference between |line_number(best_bet)| + and the optimum |best_line|} +@!line_diff:integer; {the difference between the current line number and + the optimum |best_line|} + +@ @<Try the final line break at the end of the paragraph...@>= +begin try_break(eject_penalty,hyphenated); +if link(active)<>last_active then + begin @<Find an active node with fewest demerits@>; + if looseness=0 then goto done; + @<Find the best active node for the desired looseness@>; + if (actual_looseness=looseness)or final_pass then goto done; + end; +end + +@ @<Find an active node...@>= +r:=link(active); fewest_demerits:=awful_bad; +repeat if type(r)<>delta_node then if total_demerits(r)<fewest_demerits then + begin fewest_demerits:=total_demerits(r); best_bet:=r; + end; +r:=link(r); +until r=last_active; +best_line:=line_number(best_bet) + +@ The adjustment for a desired looseness is a slightly more complicated +version of the loop just considered. Note that if a paragraph is broken +into segments by displayed equations, each segment will be subject to the +looseness calculation, independently of the other segments. + +@<Find the best active node...@>= +begin r:=link(active); actual_looseness:=0; +repeat if type(r)<>delta_node then + begin line_diff:=line_number(r)-best_line; + if ((line_diff<actual_looseness)and(looseness<=line_diff))or@| + ((line_diff>actual_looseness)and(looseness>=line_diff)) then + begin best_bet:=r; actual_looseness:=line_diff; + fewest_demerits:=total_demerits(r); + end + else if (line_diff=actual_looseness)and@| + (total_demerits(r)<fewest_demerits) then + begin best_bet:=r; fewest_demerits:=total_demerits(r); + end; + end; +r:=link(r); +until r=last_active; +best_line:=line_number(best_bet); +end + +@ Once the best sequence of breakpoints has been found (hurray), we call on the +procedure |post_line_break| to finish the remainder of the work. +(By introducing this subprocedure, we are able to keep |line_break| +from getting extremely long.) + +@<Break the paragraph at the chosen...@>= +post_line_break(final_widow_penalty) + +@ The total number of lines that will be set by |post_line_break| +is |best_line-prev_graf-1|. The last breakpoint is specified by +|break_node(best_bet)|, and this passive node points to the other breakpoints +via the |prev_break| links. The finishing-up phase starts by linking the +relevant passive nodes in forward order, changing |prev_break| to +|next_break|. (The |next_break| fields actually reside in the same memory +space as the |prev_break| fields did, but we give them a new name because +of their new significance.) Then the lines are justified, one by one. + +@d next_break==prev_break {new name for |prev_break| after links are reversed} + +@<Declare subprocedures for |line_break|@>= +procedure post_line_break(@!final_widow_penalty:integer); +label done,done1; +var q,@!r,@!s:pointer; {temporary registers for list manipulation} +@!disc_break:boolean; {was the current break at a discretionary node?} +@!post_disc_break:boolean; {and did it have a nonempty post-break part?} +@!cur_width:scaled; {width of line number |cur_line|} +@!cur_indent:scaled; {left margin of line number |cur_line|} +@!t:quarterword; {used for replacement counts in discretionary nodes} +@!pen:integer; {use when calculating penalties between lines} +@!cur_line: halfword; {the current line number being justified} +begin @<Reverse the links of the relevant passive nodes, setting |cur_p| to the + first breakpoint@>; +cur_line:=prev_graf+1; +repeat @<Justify the line ending at breakpoint |cur_p|, and append it to the + current vertical list, together with associated penalties and other + insertions@>; +incr(cur_line); cur_p:=next_break(cur_p); +if cur_p<>null then if not post_disc_break then + @<Prune unwanted nodes at the beginning of the next line@>; +until cur_p=null; +if (cur_line<>best_line)or(link(temp_head)<>null) then + confusion("line breaking"); +@:this can't happen line breaking}{\quad line breaking@> +prev_graf:=best_line-1; +end; + +@ The job of reversing links in a list is conveniently regarded as the job +of taking items off one stack and putting them on another. In this case we +take them off a stack pointed to by |q| and having |prev_break| fields; +we put them on a stack pointed to by |cur_p| and having |next_break| fields. +Node |r| is the passive node being moved from stack to stack. + +@<Reverse the links of the relevant passive nodes...@>= +q:=break_node(best_bet); cur_p:=null; +repeat r:=q; q:=prev_break(q); next_break(r):=cur_p; cur_p:=r; +until q=null + +@ Glue and penalty and kern and math nodes are deleted at the beginning of +a line, except in the anomalous case that the node to be deleted is actually +one of the chosen breakpoints. Otherwise +the pruning done here is designed to match +the lookahead computation in |try_break|, where the |break_width| values +are computed for non-discretionary breakpoints. + +@<Prune unwanted nodes at the beginning of the next line@>= +begin r:=temp_head; +loop@+ begin q:=link(r); + if q=cur_break(cur_p) then goto done1; + {|cur_break(cur_p)| is the next breakpoint} + {now |q| cannot be |null|} + if is_char_node(q) then goto done1; + if non_discardable(q) then goto done1; + if type(q)=kern_node then if subtype(q)<>explicit then goto done1; + r:=q; {now |type(q)=glue_node|, |kern_node|, |math_node| or |penalty_node|} + end; +done1: if r<>temp_head then + begin link(r):=null; flush_node_list(link(temp_head)); + link(temp_head):=q; + end; +end + +@ The current line to be justified appears in a horizontal list starting +at |link(temp_head)| and ending at |cur_break(cur_p)|. If |cur_break(cur_p)| is +a glue node, we reset the glue to equal the |right_skip| glue; otherwise +we append the |right_skip| glue at the right. If |cur_break(cur_p)| is a +discretionary node, we modify the list so that the discretionary break +is compulsory, and we set |disc_break| to |true|. We also append +the |left_skip| glue at the left of the line, unless it is zero. + +@<Justify the line ending at breakpoint |cur_p|, and append it...@>= +@<Modify the end of the line to reflect the nature of the break and to include + \.{\\rightskip}; also set the proper value of |disc_break|@>; +@<Put the \(l)\.{\\leftskip} glue at the left and detach this line@>; +@<Call the packaging subroutine, setting |just_box| to the justified box@>; +@<Append the new box to the current vertical list, followed by the list of + special nodes taken out of the box by the packager@>; +@<Append a penalty node, if a nonzero penalty is appropriate@> + +@ At the end of the following code, |q| will point to the final node on the +list about to be justified. + +@<Modify the end of the line...@>= +q:=cur_break(cur_p); disc_break:=false; post_disc_break:=false; +if q<>null then {|q| cannot be a |char_node|} + if type(q)=glue_node then + begin delete_glue_ref(glue_ptr(q)); + glue_ptr(q):=right_skip; + subtype(q):=right_skip_code+1; add_glue_ref(right_skip); + goto done; + end + else begin if type(q)=disc_node then + @<Change discretionary to compulsory and set + |disc_break:=true|@> + else if (type(q)=math_node)or(type(q)=kern_node) then width(q):=0; + end +else begin q:=temp_head; + while link(q)<>null do q:=link(q); + end; +@<Put the \(r)\.{\\rightskip} glue after node |q|@>; +done: + +@ @<Change discretionary to compulsory...@>= +begin t:=replace_count(q); +@<Destroy the |t| nodes following |q|, and + make |r| point to the following node@>; +if post_break(q)<>null then @<Transplant the post-break list@>; +if pre_break(q)<>null then @<Transplant the pre-break list@>; +link(q):=r; disc_break:=true; +end + +@ @<Destroy the |t| nodes following |q|...@>= +if t=0 then r:=link(q) +else begin r:=q; + while t>1 do + begin r:=link(r); decr(t); + end; + s:=link(r); + r:=link(s); link(s):=null; + flush_node_list(link(q)); replace_count(q):=0; + end + +@ We move the post-break list from inside node |q| to the main list by +re\-attaching it just before the present node |r|, then resetting |r|. + +@<Transplant the post-break list@>= +begin s:=post_break(q); +while link(s)<>null do s:=link(s); +link(s):=r; r:=post_break(q); post_break(q):=null; post_disc_break:=true; +end + +@ We move the pre-break list from inside node |q| to the main list by +re\-attaching it just after the present node |q|, then resetting |q|. + +@<Transplant the pre-break list@>= +begin s:=pre_break(q); link(q):=s; +while link(s)<>null do s:=link(s); +pre_break(q):=null; q:=s; +end + +@ @<Put the \(r)\.{\\rightskip} glue after node |q|@>= +r:=new_param_glue(right_skip_code); link(r):=link(q); link(q):=r; q:=r + +@ The following code begins with |q| at the end of the list to be +justified. It ends with |q| at the beginning of that list, and with +|link(temp_head)| pointing to the remainder of the paragraph, if any. + +@<Put the \(l)\.{\\leftskip} glue at the left...@>= +r:=link(q); link(q):=null; q:=link(temp_head); link(temp_head):=r; +if left_skip<>zero_glue then + begin r:=new_param_glue(left_skip_code); + link(r):=q; q:=r; + end + +@ @<Append the new box to the current vertical list...@>= +append_to_vlist(just_box); +if adjust_head<>adjust_tail then + begin link(tail):=link(adjust_head); tail:=adjust_tail; + end; +adjust_tail:=null + +@ Now |q| points to the hlist that represents the current line of the +paragraph. We need to compute the appropriate line width, pack the +line into a box of this size, and shift the box by the appropriate +amount of indentation. + +@<Call the packaging subroutine...@>= +if cur_line>last_special_line then + begin cur_width:=second_width; cur_indent:=second_indent; + end +else if par_shape_ptr=null then + begin cur_width:=first_width; cur_indent:=first_indent; + end +else begin cur_width:=mem[par_shape_ptr+2*cur_line].sc; + cur_indent:=mem[par_shape_ptr+2*cur_line-1].sc; + end; +adjust_tail:=adjust_head; just_box:=hpack(q,cur_width,exactly); +shift_amount(just_box):=cur_indent + +@ Penalties between the lines of a paragraph come from club and widow lines, +from the |inter_line_penalty| parameter, and from lines that end at +discretionary breaks. Breaking between lines of a two-line paragraph gets +both club-line and widow-line penalties. The local variable |pen| will +be set to the sum of all relevant penalties for the current line, except +that the final line is never penalized. + +@<Append a penalty node, if a nonzero penalty is appropriate@>= +if cur_line+1<>best_line then + begin pen:=inter_line_penalty; + if cur_line=prev_graf+1 then pen:=pen+club_penalty; + if cur_line+2=best_line then pen:=pen+final_widow_penalty; + if disc_break then pen:=pen+broken_penalty; + if pen<>0 then + begin r:=new_penalty(pen); + link(tail):=r; tail:=r; + end; + end + +@* \[40] Pre-hyphenation. +When the line-breaking routine is unable to find a feasible sequence of +breakpoints, it makes a second pass over the paragraph, attempting to +hyphenate the hyphenatable words. The goal of hyphenation is to insert +discretionary material into the paragraph so that there are more +potential places to break. + +The general rules for hyphenation are somewhat complex and technical, +because we want to be able to hyphenate words that are preceded or +followed by punctuation marks, and because we want the rules to work +for languages other than English. We also must contend with the fact +that hyphens might radically alter the ligature and kerning structure +of a word. + +A sequence of characters will be considered for hyphenation only if it +belongs to a ``potentially hyphenatable part'' of the current paragraph. +This is a sequence of nodes $p_0p_1\ldots p_m$ where $p_0$ is a glue node, +$p_1\ldots p_{m-1}$ are either character or ligature or whatsit or +implicit kern nodes, and $p_m$ is a glue or penalty or insertion or adjust +or mark or whatsit or explicit kern node. (Therefore hyphenation is +disabled by boxes, math formulas, and discretionary nodes already inserted +by the user.) The ligature nodes among $p_1\ldots p_{m-1}$ are effectively +expanded into the original non-ligature characters; the kern nodes and +whatsits are ignored. Each character |c| is now classified as either a +nonletter (if |lc_code(c)=0|), a lowercase letter (if +|lc_code(c)=c|), or an uppercase letter (otherwise); an uppercase letter +is treated as if it were |lc_code(c)| for purposes of hyphenation. The +characters generated by $p_1\ldots p_{m-1}$ may begin with nonletters; let +$c_1$ be the first letter that is not in the middle of a ligature. Whatsit +nodes preceding $c_1$ are ignored; a whatsit found after $c_1$ will be the +terminating node $p_m$. All characters that do not have the same font as +$c_1$ will be treated as nonletters. The |hyphen_char| for that font +must be between 0 and 255, otherwise hyphenation will not be attempted. +\TeX\ looks ahead for as many consecutive letters $c_1\ldots c_n$ as +possible; however, |n| must be less than 64, so a character that would +otherwise be $c_{64}$ is effectively not a letter. Furthermore $c_n$ must +not be in the middle of a ligature. In this way we obtain a string of +letters $c_1\ldots c_n$ that are generated by nodes $p_a\ldots p_b$, where +|1<=a<=b+1<=m|. If |n>=l_hyf+r_hyf|, this string qualifies for hyphenation; +however, |uc_hyph| must be positive, if $c_1$ is uppercase. + +The hyphenation process takes place in three stages. First, the candidate +sequence $c_1\ldots c_n$ is found; then potential positions for hyphens +are determined by referring to hyphenation tables; and finally, the nodes +$p_a\ldots p_b$ are replaced by a new sequence of nodes that includes the +discretionary breaks found. + +Fortunately, we do not have to do all this calculation very often, because +of the way it has been taken out of \TeX's inner loop. For example, when +the second edition of the author's 700-page book {\sl Seminumerical +Algorithms} was typeset by \TeX, only about 1.2 hyphenations needed to be +@^Knuth, Donald Ervin@> +tried per paragraph, since the line breaking algorithm needed to use two +passes on only about 5 per cent of the paragraphs. + +@<Initialize for hyphenating...@>= +begin @!init if trie_not_ready then init_trie;@+tini@;@/ +cur_lang:=init_cur_lang; l_hyf:=init_l_hyf; r_hyf:=init_r_hyf; +end + +@ The letters $c_1\ldots c_n$ that are candidates for hyphenation are placed +into an array called |hc|; the number |n| is placed into |hn|; pointers to +nodes $p_{a-1}$ and~$p_b$ in the description above are placed into variables +|ha| and |hb|; and the font number is placed into |hf|. + +@<Glob...@>= +@!hc:array[0..65] of 0..256; {word to be hyphenated} +@!hn:small_number; {the number of positions occupied in |hc|} +@!ha,@!hb:pointer; {nodes |ha..hb| should be replaced by the hyphenated result} +@!hf:internal_font_number; {font number of the letters in |hc|} +@!hu:array[0..63] of 0..256; {like |hc|, before conversion to lowercase} +@!hyf_char:integer; {hyphen character of the relevant font} +@!cur_lang,@!init_cur_lang:ASCII_code; {current hyphenation table of interest} +@!l_hyf,@!r_hyf,@!init_l_hyf,@!init_r_hyf:integer; {limits on fragment sizes} +@!hyf_bchar:halfword; {boundary character after $c_n$} + +@ Hyphenation routines need a few more local variables. + +@<Local variables for line...@>= +@!j:small_number; {an index into |hc| or |hu|} +@!c:0..255; {character being considered for hyphenation} + +@ When the following code is activated, the |line_break| procedure is in its +second pass, and |cur_p| points to a glue node. + +@<Try to hyphenate...@>= +begin prev_s:=cur_p; s:=link(prev_s); +if s<>null then + begin @<Skip to node |ha|, or |goto done1| if no hyphenation + should be attempted@>; + if l_hyf+r_hyf>63 then goto done1; + @<Skip to node |hb|, putting letters into |hu| and |hc|@>; + @<Check that the nodes following |hb| permit hyphenation and that at least + |l_hyf+r_hyf| letters have been found, otherwise |goto done1|@>; + hyphenate; + end; +done1: end + +@ @<Declare subprocedures for |line_break|@>= +@t\4@>@<Declare the function called |reconstitute|@> +procedure hyphenate; +label common_ending,done,found,found1,found2,not_found,exit; +var @<Local variables for hyphenation@>@; +begin @<Find hyphen locations for the word in |hc|, or |return|@>; +@<If no hyphens were found, |return|@>; +@<Replace nodes |ha..hb| by a sequence of nodes that includes + the discretionary hyphens@>; +exit:end; + +@ The first thing we need to do is find the node |ha| just before the +first letter. + +@<Skip to node |ha|, or |goto done1|...@>= +loop@+ begin if is_char_node(s) then + begin c:=qo(character(s)); hf:=font(s); + end + else if type(s)=ligature_node then + if lig_ptr(s)=null then goto continue + else begin q:=lig_ptr(s); c:=qo(character(q)); hf:=font(q); + end + else if (type(s)=kern_node)and(subtype(s)=normal) then goto continue + else if type(s)=whatsit_node then + begin @<Advance \(p)past a whatsit node in the \(p)pre-hyphenation loop@>; + goto continue; + end + else goto done1; + if lc_code(c)<>0 then + if (lc_code(c)=c)or(uc_hyph>0) then goto done2 + else goto done1; +continue: prev_s:=s; s:=link(prev_s); + end; +done2: hyf_char:=hyphen_char[hf]; +if hyf_char<0 then goto done1; +if hyf_char>255 then goto done1; +ha:=prev_s + +@ The word to be hyphenated is now moved to the |hu| and |hc| arrays. + +@<Skip to node |hb|, putting letters...@>= +hn:=0; +loop@+ begin if is_char_node(s) then + begin if font(s)<>hf then goto done3; + hyf_bchar:=character(s); c:=qo(hyf_bchar); + if lc_code(c)=0 then goto done3; + if hn=63 then goto done3; + hb:=s; incr(hn); hu[hn]:=c; hc[hn]:=lc_code(c); hyf_bchar:=non_char; + end + else if type(s)=ligature_node then + @<Move the characters of a ligature node to |hu| and |hc|; + but |goto done3| if they are not all letters@> + else if (type(s)=kern_node)and(subtype(s)=normal) then + begin hb:=s; + hyf_bchar:=font_bchar[hf]; + end + else goto done3; + s:=link(s); + end; +done3: + +@ We let |j| be the index of the character being stored when a ligature node +is being expanded, since we do not want to advance |hn| until we are sure +that the entire ligature consists of letters. Note that it is possible +to get to |done3| with |hn=0| and |hb| not set to any value. + +@<Move the characters of a ligature node to |hu| and |hc|...@>= +begin if font(lig_char(s))<>hf then goto done3; +j:=hn; q:=lig_ptr(s);@+if q>null then hyf_bchar:=character(q); +while q>null do + begin c:=qo(character(q)); + if lc_code(c)=0 then goto done3; + if j=63 then goto done3; + incr(j); hu[j]:=c; hc[j]:=lc_code(c);@/ + q:=link(q); + end; +hb:=s; hn:=j; +if odd(subtype(s)) then hyf_bchar:=font_bchar[hf]@+else hyf_bchar:=non_char; +end + +@ @<Check that the nodes following |hb| permit hyphenation...@>= +if hn<l_hyf+r_hyf then goto done1; {|l_hyf| and |r_hyf| are |>=1|} +loop@+ begin if not(is_char_node(s)) then + case type(s) of + ligature_node: do_nothing; + kern_node: if subtype(s)<>normal then goto done4; + whatsit_node,glue_node,penalty_node,ins_node,adjust_node,mark_node: + goto done4; + othercases goto done1 + endcases; + s:=link(s); + end; +done4: + +@* \[41] Post-hyphenation. +If a hyphen may be inserted between |hc[j]| and |hc[j+1]|, the hyphenation +procedure will set |hyf[j]| to some small odd number. But before we look +at \TeX's hyphenation procedure, which is independent of the rest of the +line-breaking algorithm, let us consider what we will do with the hyphens +it finds, since it is better to work on this part of the program before +forgetting what |ha| and |hb|, etc., are all about. + +@<Glob...@>= +@!hyf:array [0..64] of 0..9; {odd values indicate discretionary hyphens} +@!init_list:pointer; {list of punctuation characters preceding the word} +@!init_lig:boolean; {does |init_list| represent a ligature?} +@!init_lft:boolean; {if so, did the ligature involve a left boundary?} + +@ @<Local variables for hyphenation@>= +@!i,@!j,@!l:0..65; {indices into |hc| or |hu|} +@!q,@!r,@!s:pointer; {temporary registers for list manipulation} +@!bchar:halfword; {right boundary character of hyphenated word, or |non_char|} + +@ \TeX\ will never insert a hyphen that has fewer than +\.{\\lefthyphenmin} letters before it or fewer than +\.{\\righthyphenmin} after it; hence, a short word has +comparatively little chance of being hyphenated. If no hyphens have +been found, we can save time by not having to make any changes to the +paragraph. + +@<If no hyphens were found, |return|@>= +for j:=l_hyf to hn-r_hyf do if odd(hyf[j]) then goto found1; +return; +found1: + +@ If hyphens are in fact going to be inserted, \TeX\ first deletes the +subsequence of nodes between |ha| and~|hb|. An attempt is made to +preserve the effect that implicit boundary characters and punctuation marks +had on ligatures inside the hyphenated word, by storing a left boundary or +preceding character in |hu[0]| and by storing a possible right boundary +in |bchar|. We set |j:=0| if |hu[0]| is to be part of the reconstruction; +otherwise |j:=1|. +The variable |s| will point to the tail of the current hlist, and +|q| will point to the node following |hb|, so that +things can be hooked up after we reconstitute the hyphenated word. + +@<Replace nodes |ha..hb| by a sequence of nodes...@>= +q:=link(hb); link(hb):=null; r:=link(ha); link(ha):=null; bchar:=hyf_bchar; +if is_char_node(ha) then + if font(ha)<>hf then goto found2 + else begin init_list:=ha; init_lig:=false; hu[0]:=qo(character(ha)); + end +else if type(ha)=ligature_node then + if font(lig_char(ha))<>hf then goto found2 + else begin init_list:=lig_ptr(ha); init_lig:=true; init_lft:=(subtype(ha)>1); + hu[0]:=qo(character(lig_char(ha))); + if init_list=null then if init_lft then + begin hu[0]:=256; init_lig:=false; + end; {in this case a ligature will be reconstructed from scratch} + free_node(ha,small_node_size); + end +else begin {no punctuation found; look for left boundary} + if not is_char_node(r) then if type(r)=ligature_node then + if subtype(r)>1 then goto found2; + j:=1; s:=ha; init_list:=null; goto common_ending; + end; +s:=cur_p; {we have |cur_p<>ha| because |type(cur_p)=glue_node|} +while link(s)<>ha do s:=link(s); +j:=0; goto common_ending; +found2: s:=ha; j:=0; hu[0]:=256; init_lig:=false; init_list:=null; +common_ending: flush_node_list(r); +@<Reconstitute nodes for the hyphenated word, inserting discretionary hyphens@>; +flush_list(init_list) + +@ We must now face the fact that the battle is not over, even though the +{\def\!{\kern-1pt}% +hyphens have been found: The process of reconstituting a word can be nontrivial +because ligatures might change when a hyphen is present. {\sl The \TeX book\/} +discusses the difficulties of the word ``difficult'', and +the discretionary material surrounding a +hyphen can be considerably more complex than that. Suppose +\.{abcdef} is a word in a font for which the only ligatures are \.{b\!c}, +\.{c\!d}, \.{d\!e}, and \.{e\!f}. If this word permits hyphenation +between \.b and \.c, the two patterns with and without hyphenation are +$\.a\,\.b\,\.-\,\.{c\!d}\,\.{e\!f}$ and $\.a\,\.{b\!c}\,\.{d\!e}\,\.f$. +Thus the insertion of a hyphen might cause effects to ripple arbitrarily +far into the rest of the word. A further complication arises if additional +hyphens appear together with such rippling, e.g., if the word in the +example just given could also be hyphenated between \.c and \.d; \TeX\ +avoids this by simply ignoring the additional hyphens in such weird cases.} + +Still further complications arise in the presence of ligatures that do not +delete the original characters. When punctuation precedes the word being +hyphenated, \TeX's method is not perfect under all possible scenarios, +because punctuation marks and letters can propagate information back and forth. +For example, suppose the original pre-hyphenation pair +\.{*a} changes to \.{*y} via a \.{\?=:} ligature, which changes to \.{xy} +via a \.{=:\?} ligature; if $p_{a-1}=\.x$ and $p_a=\.y$, the reconstitution +procedure isn't smart enough to obtain \.{xy} again. In such cases the +font designer should include a ligature that goes from \.{xa} to \.{xy}. + +@ The processing is facilitated by a subroutine called |reconstitute|. Given +a string of characters $x_j\ldots x_n$, there is a smallest index $m\ge j$ +such that the ``translation'' of $x_j\ldots x_n$ by ligatures and kerning +has the form $y_1\ldots y_t$ followed by the translation of $x_{m+1}\ldots x_n$, +where $y_1\ldots y_t$ is some nonempty sequence of character, ligature, and +kern nodes. We call $x_j\ldots x_m$ a ``cut prefix'' of $x_j\ldots x_n$. +For example, if $x_1x_2x_3=\.{fly}$, and if the font contains `fl' as a +ligature and a kern between `fl' and `y', then $m=2$, $t=2$, and $y_1$ will +be a ligature node for `fl' followed by an appropriate kern node~$y_2$. +In the most common case, $x_j$~forms no ligature with $x_{j+1}$ and we +simply have $m=j$, $y_1=x_j$. If $m<n$ we can repeat the procedure on +$x_{m+1}\ldots x_n$ until the entire translation has been found. + +The |reconstitute| function returns the integer $m$ and puts the nodes +$y_1\ldots y_t$ into a linked list starting at |link(hold_head)|, +getting the input $x_j\ldots x_n$ from the |hu| array. If $x_j=256$, +we consider $x_j$ to be an implicit left boundary character; in this +case |j| must be strictly less than~|n|. There is a +parameter |bchar|, which is either 256 or an implicit right boundary character +assumed to be present just following~$x_n$. (The value |hu[n+1]| is never +explicitly examined, but the algorithm imagines that |bchar| is there.) + +If there exists an index |k| in the range $j\le k\le m$ such that |hyf[k]| +is odd and such that the result of |reconstitute| would have been different +if $x_{k+1}$ had been |hchar|, then |reconstitute| sets |hyphen_passed| +to the smallest such~|k|. Otherwise it sets |hyphen_passed| to zero. + +A special convention is used in the case |j=0|: Then we assume that the +translation of |hu[0]| appears in a special list of charnodes starting at +|init_list|; moreover, if |init_lig| is |true|, then |hu[0]| will be +a ligature character, involving a left boundary if |init_lft| is |true|. +This facility is provided for cases when a hyphenated +word is preceded by punctuation (like single or double quotes) that might +affect the translation of the beginning of the word. + +@<Glob...@>= +@!hyphen_passed:small_number; {first hyphen in a ligature, if any} + +@ @<Declare the function called |reconstitute|@>= +function reconstitute(@!j,@!n:small_number;@!bchar,@!hchar:halfword): + small_number; +label continue,done; +var @!p:pointer; {temporary register for list manipulation} +@!t:pointer; {a node being appended to} +@!q:four_quarters; {character information or a lig/kern instruction} +@!cur_rh:halfword; {hyphen character for ligature testing} +@!test_char:halfword; {hyphen or other character for ligature testing} +@!w:scaled; {amount of kerning} +@!k:font_index; {position of current lig/kern instruction} +begin hyphen_passed:=0; t:=hold_head; w:=0; link(hold_head):=null; + {at this point |ligature_present=lft_hit=rt_hit=false|} +@<Set up data structures with the cursor following position |j|@>; +continue:@<If there's a ligature or kern at the cursor position, update the data + structures, possibly advancing~|j|; continue until the cursor moves@>; +@<Append a ligature and/or kern to the translation; + |goto continue| if the stack of inserted ligatures is nonempty@>; +reconstitute:=j; +end; + +@ The reconstitution procedure shares many of the global data structures +by which \TeX\ has processed the words before they were hyphenated. +There is an implied ``cursor'' between characters |cur_l| and |cur_r|; +these characters will be tested for possible ligature activity. If +|ligature_present| then |cur_l| is a ligature character formed from the +original characters following |cur_q| in the current translation list. +There is a ``ligature stack'' between the cursor and character |j+1|, +consisting of pseudo-ligature nodes linked together by their |link| fields. +This stack is normally empty unless a ligature command has created a new +character that will need to be processed later. A pseudo-ligature is +a special node having a |character| field that represents a potential +ligature and a |lig_ptr| field that points to a |char_node| or is |null|. +We have +$$|cur_r|=\cases{|character(lig_stack)|,&if |lig_stack>null|;\cr + |qi(hu[j+1])|,&if |lig_stack=null| and |j<n|;\cr + bchar,&if |lig_stack=null| and |j=n|.\cr}$$ + +@<Glob...@>= +@!cur_l,@!cur_r:halfword; {characters before and after the cursor} +@!cur_q:pointer; {where a ligature should be detached} +@!lig_stack:pointer; {unfinished business to the right of the cursor} +@!ligature_present:boolean; {should a ligature node be made for |cur_l|?} +@!lft_hit,@!rt_hit:boolean; {did we hit a ligature with a boundary character?} + +@ @d append_charnode_to_t(#)== begin link(t):=get_avail; t:=link(t); + font(t):=hf; character(t):=#; + end +@d set_cur_r==begin if j<n then cur_r:=qi(hu[j+1])@+else cur_r:=bchar; + if odd(hyf[j]) then cur_rh:=hchar@+else cur_rh:=non_char; + end + +@<Set up data structures with the cursor following position |j|@>= +cur_l:=qi(hu[j]); cur_q:=t; +if j=0 then + begin ligature_present:=init_lig; p:=init_list; + if ligature_present then lft_hit:=init_lft; + while p>null do + begin append_charnode_to_t(character(p)); p:=link(p); + end; + end +else if cur_l<non_char then append_charnode_to_t(cur_l); +lig_stack:=null; set_cur_r + +@ We may want to look at the lig/kern program twice, once for a hyphen +and once for a normal letter. (The hyphen might appear after the letter +in the program, so we'd better not try to look for both at once.) + +@<If there's a ligature or kern at the cursor position, update...@>= +if cur_l=non_char then + begin k:=bchar_label[hf]; + if k=non_address then goto done@+else q:=font_info[k].qqqq; + end +else begin q:=char_info(hf)(cur_l); + if char_tag(q)<>lig_tag then goto done; + k:=lig_kern_start(hf)(q); q:=font_info[k].qqqq; + if skip_byte(q)>stop_flag then + begin k:=lig_kern_restart(hf)(q); q:=font_info[k].qqqq; + end; + end; {now |k| is the starting address of the lig/kern program} +if cur_rh<non_char then test_char:=cur_rh@+else test_char:=cur_r; +loop@+begin if next_char(q)=test_char then if skip_byte(q)<=stop_flag then + if cur_rh<non_char then + begin hyphen_passed:=j; hchar:=non_char; cur_rh:=non_char; + goto continue; + end + else begin if hchar<non_char then if odd(hyf[j]) then + begin hyphen_passed:=j; hchar:=non_char; + end; + if op_byte(q)<kern_flag then + @<Carry out a ligature replacement, updating the cursor structure + and possibly advancing~|j|; |goto continue| if the cursor doesn't + advance, otherwise |goto done|@>; + w:=char_kern(hf)(q); goto done; {this kern will be inserted below} + end; + if skip_byte(q)>=stop_flag then + if cur_rh=non_char then goto done + else begin cur_rh:=non_char; goto continue; + end; + k:=k+qo(skip_byte(q))+1; q:=font_info[k].qqqq; + end; +done: + +@ @d wrap_lig(#)==if ligature_present then + begin p:=new_ligature(hf,cur_l,link(cur_q)); + if lft_hit then + begin subtype(p):=2; lft_hit:=false; + end; + if # then if lig_stack=null then + begin incr(subtype(p)); rt_hit:=false; + end; + link(cur_q):=p; t:=p; ligature_present:=false; + end +@d pop_lig_stack==begin if lig_ptr(lig_stack)>null then + begin link(t):=lig_ptr(lig_stack); {this is a charnode for |hu[j+1]|} + t:=link(t); incr(j); + end; + p:=lig_stack; lig_stack:=link(p); free_node(p,small_node_size); + if lig_stack=null then set_cur_r@+else cur_r:=character(lig_stack); + end {if |lig_stack| isn't |null| we have |cur_rh=non_char|} + +@<Append a ligature and/or kern to the translation...@>= +wrap_lig(rt_hit); +if w<>0 then + begin link(t):=new_kern(w); t:=link(t); w:=0; + end; +if lig_stack>null then + begin cur_q:=t; cur_l:=character(lig_stack); ligature_present:=true; + pop_lig_stack; goto continue; + end + +@ @<Carry out a ligature replacement, updating the cursor structure...@>= +begin if cur_l=non_char then lft_hit:=true; +if j=n then if lig_stack=null then rt_hit:=true; +check_interrupt; {allow a way out in case there's an infinite ligature loop} +case op_byte(q) of +qi(1),qi(5):begin cur_l:=rem_byte(q); {\.{=:\?}, \.{=:\?>}} + ligature_present:=true; + end; +qi(2),qi(6):begin cur_r:=rem_byte(q); {\.{\?=:}, \.{\?=:>}} + if lig_stack>null then character(lig_stack):=cur_r + else begin lig_stack:=new_lig_item(cur_r); + if j=n then bchar:=non_char + else begin p:=get_avail; lig_ptr(lig_stack):=p; + character(p):=qi(hu[j+1]); font(p):=hf; + end; + end; + end; +qi(3):begin cur_r:=rem_byte(q); {\.{\?=:\?}} + p:=lig_stack; lig_stack:=new_lig_item(cur_r); link(lig_stack):=p; + end; +qi(7),qi(11):begin wrap_lig(false); {\.{\?=:\?>}, \.{\?=:\?>>}} + cur_q:=t; cur_l:=rem_byte(q); ligature_present:=true; + end; +othercases begin cur_l:=rem_byte(q); ligature_present:=true; {\.{=:}} + if lig_stack>null then pop_lig_stack + else if j=n then goto done + else begin append_charnode_to_t(cur_r); incr(j); set_cur_r; + end; + end +endcases; +if op_byte(q)>qi(4) then if op_byte(q)<>qi(7) then goto done; +goto continue; +end + +@ Okay, we're ready to insert the potential hyphenations that were found. +When the following program is executed, we want to append the word +|hu[1..hn]| after node |ha|, and node |q| should be appended to the result. +During this process, the variable |i| will be a temporary +index into |hu|; the variable |j| will be an index to our current position +in |hu|; the variable |l| will be the counterpart of |j|, in a discretionary +branch; the variable |r| will point to new nodes being created; and +we need a few new local variables: + +@<Local variables for hyph...@>= +@!major_tail,@!minor_tail:pointer; {the end of lists in the main and + discretionary branches being reconstructed} +@!c:ASCII_code; {character temporarily replaced by a hyphen} +@!c_loc:0..63; {where that character came from} +@!r_count:integer; {replacement count for discretionary} +@!hyf_node:pointer; {the hyphen, if it exists} + +@ When the following code is performed, |hyf[0]| and |hyf[hn]| will be zero. + +@<Reconstitute nodes for the hyphenated word...@>= +repeat l:=j; j:=reconstitute(j,hn,bchar,qi(hyf_char))+1; +if hyphen_passed=0 then + begin link(s):=link(hold_head); + while link(s)>null do s:=link(s); + if odd(hyf[j-1]) then + begin l:=j; hyphen_passed:=j-1; link(hold_head):=null; + end; + end; +if hyphen_passed>0 then + @<Create and append a discretionary node as an alternative to the + unhyphenated word, and continue to develop both branches until they + become equivalent@>; +until j>hn; +link(s):=q + +@ In this repeat loop we will insert another discretionary if |hyf[j-1]| is +odd, when both branches of the previous discretionary end at position |j-1|. +Strictly speaking, we aren't justified in doing this, because we don't know +that a hyphen after |j-1| is truly independent of those branches. But in almost +all applications we would rather not lose a potentially valuable hyphenation +point. (Consider the word `difficult', where the letter `c' is in position |j|.) + +@d advance_major_tail==begin major_tail:=link(major_tail); incr(r_count); + end + +@<Create and append a discretionary node as an alternative...@>= +repeat r:=get_node(small_node_size); +link(r):=link(hold_head); type(r):=disc_node; +major_tail:=r; r_count:=0; +while link(major_tail)>null do advance_major_tail; +i:=hyphen_passed; hyf[i]:=0; +@<Put the \(c)characters |hu[l..i]| and a hyphen into |pre_break(r)|@>; +@<Put the \(c)characters |hu[i+1..@,]| into |post_break(r)|, appending to this + list and to |major_tail| until synchronization has been achieved@>; +@<Move pointer |s| to the end of the current list, and set |replace_count(r)| + appropriately@>; +hyphen_passed:=j-1; link(hold_head):=null; +until not odd(hyf[j-1]) + +@ The new hyphen might combine with the previous character via ligature +or kern. At this point we have |l-1<=i<j| and |i<hn|. + +@<Put the \(c)characters |hu[l..i]| and a hyphen into |pre_break(r)|@>= +minor_tail:=null; pre_break(r):=null; hyf_node:=new_character(hf,hyf_char); +if hyf_node<>null then + begin incr(i); c:=hu[i]; hu[i]:=hyf_char; free_avail(hyf_node); + end; +while l<=i do + begin l:=reconstitute(l,i,font_bchar[hf],non_char)+1; + if link(hold_head)>null then + begin if minor_tail=null then pre_break(r):=link(hold_head) + else link(minor_tail):=link(hold_head); + minor_tail:=link(hold_head); + while link(minor_tail)>null do minor_tail:=link(minor_tail); + end; + end; +if hyf_node<>null then + begin hu[i]:=c; {restore the character in the hyphen position} + l:=i; decr(i); + end + +@ The synchronization algorithm begins with |l=i+1<=j|. + +@<Put the \(c)characters |hu[i+1..@,]| into |post_break(r)|...@>= +minor_tail:=null; post_break(r):=null; c_loc:=0; +if bchar_label[hf]<>non_address then {put left boundary at beginning of new line} + begin decr(l); c:=hu[l]; c_loc:=l; hu[l]:=256; + end; +while l<j do + begin repeat l:=reconstitute(l,hn,bchar,non_char)+1; + if c_loc>0 then + begin hu[c_loc]:=c; c_loc:=0; + end; + if link(hold_head)>null then + begin if minor_tail=null then post_break(r):=link(hold_head) + else link(minor_tail):=link(hold_head); + minor_tail:=link(hold_head); + while link(minor_tail)>null do minor_tail:=link(minor_tail); + end; + until l>=j; + while l>j do + @<Append characters of |hu[j..@,]| to |major_tail|, advancing~|j|@>; + end + +@ @<Append characters of |hu[j..@,]|...@>= +begin j:=reconstitute(j,hn,bchar,non_char)+1; +link(major_tail):=link(hold_head); +while link(major_tail)>null do advance_major_tail; +end + +@ Ligature insertion can cause a word to grow exponentially in size. Therefore +we must test the size of |r_count| here, even though the hyphenated text +was at most 63 characters long. + +@<Move pointer |s| to the end of the current list...@>= +if r_count>127 then {we have to forget the discretionary hyphen} + begin link(s):=link(r); link(r):=null; flush_node_list(r); + end +else begin link(s):=r; replace_count(r):=r_count; + end; +s:=major_tail + +@* \[42] Hyphenation. +When a word |hc[1..hn]| has been set up to contain a candidate for hyphenation, +\TeX\ first looks to see if it is in the user's exception dictionary. If not, +hyphens are inserted based on patterns that appear within the given word, +using an algorithm due to Frank~M. Liang. +@^Liang, Franklin Mark@> + +Let's consider Liang's method first, since it is much more interesting than the +exception-lookup routine. The algorithm begins by setting |hyf[j]| to zero +for all |j|, and invalid characters are inserted into |hc[0]| +and |hc[hn+1]| to serve as delimiters. Then a reasonably fast method is +used to see which of a given set of patterns occurs in the word +|hc[0..(hn+1)]|. Each pattern $p_1\ldots p_k$ of length |k| has an associated +sequence of |k+1| numbers $n_0\ldots n_k$; and if the pattern occurs in +|hc[(j+1)..(j+k)]|, \TeX\ will set |hyf[j+i]:=@tmax@>(hyf[j+i],@t$n_i$@>)| for +|0<=i<=k|. After this has been done for each pattern that occurs, a +discretionary hyphen will be inserted between |hc[j]| and |hc[j+1]| when +|hyf[j]| is odd, as we have already seen. + +The set of patterns $p_1\ldots p_k$ and associated numbers $n_0\ldots n_k$ +depends, of course, on the language whose words are being hyphenated, and +on the degree of hyphenation that is desired. A method for finding +appropriate |p|'s and |n|'s, from a given dictionary of words and acceptable +hyphenations, is discussed in Liang's Ph.D. thesis (Stanford University, +1983); \TeX\ simply starts with the patterns and works from there. + +@ The patterns are stored in a compact table that is also efficient for +retrieval, using a variant of ``trie memory'' [cf.\ {\sl The Art of +Computer Programming \bf3} (1973), 481--505]. We can find each pattern +$p_1\ldots p_k$ by letting $z_0$ be one greater than the relevant language +index and then, for |1<=i<=k|, +setting |@t$z_i$@>:=trie_link@t$(z_{i-1})+p_i$@>|; the pattern will be +identified by the number $z_k$. Since all the pattern information is +packed together into a single |trie_link| array, it is necessary to +prevent confusion between the data from inequivalent patterns, so another +table is provided such that |trie_char@t$(z_i)=p_i$@>| for all |i|. There +is also a table |trie_op|$(z_k)$ to identify the numbers $n_0\ldots n_k$ +associated with $p_1\ldots p_k$. + +Comparatively few different number sequences $n_0\ldots n_k$ actually occur, +since most of the |n|'s are generally zero. Therefore the number sequences +are encoded in such a way that |trie_op|$(z_k)$ is only one byte long. +If |trie_op(@t$z_k$@>)<>min_quarterword|, when $p_1\ldots p_k$ has matched +the letters in |hc[(l-k+1)..l@,]| of language |t|, +we perform all of the required operations +for this pattern by carrying out the following little program: Set +|v:=trie_op(@t$z_k$@>)|. Then set |v:=v+op_start[t]|, +|hyf[l-hyf_distance[v]]:=@tmax@>(hyf[l-hyf_distance[v]], hyf_num[v])|, +and |v:=hyf_next[v]|; repeat, if necessary, until |v=min_quarterword|. + +@<Types...@>= +@!trie_pointer=0..trie_size; {an index into |trie|} + +@ @d trie_link(#)==trie[#].rh {``downward'' link in a trie} +@d trie_char(#)==trie[#].b1 {character matched at this trie location} +@d trie_op(#)==trie[#].b0 {program for hyphenation at this trie location} + +@<Glob...@>= +@!trie:array[trie_pointer] of two_halves; {|trie_link|, |trie_char|, |trie_op|} +@!hyf_distance:array[1..trie_op_size] of small_number; {position |k-j| of $n_j$} +@!hyf_num:array[1..trie_op_size] of small_number; {value of $n_j$} +@!hyf_next:array[1..trie_op_size] of quarterword; {continuation code} +@!op_start:array[ASCII_code] of 0..trie_op_size; {offset for current language} + +@ @<Local variables for hyph...@>= +@!z:trie_pointer; {an index into |trie|} +@!v:integer; {an index into |hyf_distance|, etc.} + +@ Assuming that these auxiliary tables have been set up properly, the +hyphenation algorithm is quite short. In the following code we set |hc[hn+2]| +to the impossible value 256, in order to guarantee that |hc[hn+3]| will +never be fetched. + +@<Find hyphen locations for the word in |hc|...@>= +for j:=0 to hn do hyf[j]:=0; +@<Look for the word |hc[1..hn]| in the exception table, and |goto found| (with + |hyf| containing the hyphens) if an entry is found@>; +if trie_char(cur_lang+1)<>qi(cur_lang) then return; {no patterns for |cur_lang|} +hc[0]:=0; hc[hn+1]:=0; hc[hn+2]:=256; {insert delimiters} +for j:=0 to hn-r_hyf+1 do + begin z:=trie_link(cur_lang+1)+hc[j]; l:=j; + while hc[l]=qo(trie_char(z)) do + begin if trie_op(z)<>min_quarterword then + @<Store \(m)maximum values in the |hyf| table@>; + incr(l); z:=trie_link(z)+hc[l]; + end; + end; +found: for j:=0 to l_hyf-1 do hyf[j]:=0; +for j:=0 to r_hyf-1 do hyf[hn-j]:=0 + +@ @<Store \(m)maximum values in the |hyf| table@>= +begin v:=trie_op(z); +repeat v:=v+op_start[cur_lang]; i:=l-hyf_distance[v]; +if hyf_num[v]>hyf[i] then hyf[i]:=hyf_num[v]; +v:=hyf_next[v]; +until v=min_quarterword; +end + +@ The exception table that is built by \TeX's \.{\\hyphenation} primitive is +organized as an ordered hash table [cf.\ Amble and Knuth, {\sl The Computer +@^Amble, Ole@> @^Knuth, Donald Ervin@> +Journal\/ \bf17} (1974), 135--142] using linear probing. If $\alpha$ and +$\beta$ are words, we will say that $\alpha<\beta$ if $\vert\alpha\vert< +\vert\beta\vert$ or if $\vert\alpha\vert=\vert\beta\vert$ and +$\alpha$ is lexicographically smaller than $\beta$. (The notation $\vert +\alpha\vert$ stands for the length of $\alpha$.) The idea of ordered hashing +is to arrange the table so that a given word $\alpha$ can be sought by computing +a hash address $h=h(\alpha)$ and then looking in table positions |h|, |h-1|, +\dots, until encountering the first word $\L\alpha$. If this word is +different from $\alpha$, we can conclude that $\alpha$ is not in the table. + +The words in the table point to lists in |mem| that specify hyphen positions +in their |info| fields. The list for $c_1\ldots c_n$ contains the number |k| if +the word $c_1\ldots c_n$ has a discretionary hyphen between $c_k$ and +$c_{k+1}$. + +@<Types...@>= +@!hyph_pointer=0..hyph_size; {an index into the ordered hash table} + +@ @<Glob...@>= +@!hyph_word:array[hyph_pointer] of str_number; {exception words} +@!hyph_list:array[hyph_pointer] of pointer; {list of hyphen positions} +@!hyph_count:hyph_pointer; {the number of words in the exception dictionary} + +@ @<Local variables for init...@>= +@!z:hyph_pointer; {runs through the exception dictionary} + +@ @<Set init...@>= +for z:=0 to hyph_size do + begin hyph_word[z]:=0; hyph_list[z]:=null; + end; +hyph_count:=0; + +@ The algorithm for exception lookup is quite simple, as soon as we have +a few more local variables to work with. + +@<Local variables for hyph...@>= +@!h:hyph_pointer; {an index into |hyph_word| and |hyph_list|} +@!k:str_number; {an index into |str_start|} +@!u:pool_pointer; {an index into |str_pool|} + +@ First we compute the hash code |h|, then we search until we either +find the word or we don't. Words from different languages are kept +separate by appending the language code to the string. + +@<Look for the word |hc[1...@>= +h:=hc[1]; incr(hn); hc[hn]:=cur_lang; +for j:=2 to hn do h:=(h+h+hc[j]) mod hyph_size; +loop@+ begin @<If the string |hyph_word[h]| is less than \(hc)|hc[1..hn]|, + |goto not_found|; but if the two strings are equal, + set |hyf| to the hyphen positions and |goto found|@>; + if h>0 then decr(h)@+else h:=hyph_size; + end; +not_found: decr(hn) + +@ @<If the string |hyph_word[h]| is less than \(hc)...@>= +k:=hyph_word[h]; if k=0 then goto not_found; +if length(k)<hn then goto not_found; +if length(k)=hn then + begin j:=1; u:=str_start[k]; + repeat if so(str_pool[u])<hc[j] then goto not_found; + if so(str_pool[u])>hc[j] then goto done; + incr(j); incr(u); + until j>hn; + @<Insert hyphens as specified in |hyph_list[h]|@>; + decr(hn); goto found; + end; +done: + +@ @<Insert hyphens as specified...@>= +s:=hyph_list[h]; +while s<>null do + begin hyf[info(s)]:=1; s:=link(s); + end + +@ @<Search |hyph_list| for pointers to |p|@>= +for q:=0 to hyph_size do + begin if hyph_list[q]=p then + begin print_nl("HYPH("); print_int(q); print_char(")"); + end; + end + +@ We have now completed the hyphenation routine, so the |line_break| procedure +is finished at last. Since the hyphenation exception table is fresh in our +minds, it's a good time to deal with the routine that adds new entries to it. + +When \TeX\ has scanned `\.{\\hyphenation}', it calls on a procedure named +|new_hyph_exceptions| to do the right thing. + +@d set_cur_lang==if language<=0 then cur_lang:=0 + else if language>255 then cur_lang:=0 + else cur_lang:=language + +@p procedure new_hyph_exceptions; {enters new exceptions} +label reswitch, exit, found, not_found; +var n:0..64; {length of current word; not always a |small_number|} +@!j:0..64; {an index into |hc|} +@!h:hyph_pointer; {an index into |hyph_word| and |hyph_list|} +@!k:str_number; {an index into |str_start|} +@!p:pointer; {head of a list of hyphen positions} +@!q:pointer; {used when creating a new node for list |p|} +@!s,@!t:str_number; {strings being compared or stored} +@!u,@!v:pool_pointer; {indices into |str_pool|} +begin scan_left_brace; {a left brace must follow \.{\\hyphenation}} +set_cur_lang; +@<Enter as many hyphenation exceptions as are listed, +until coming to a right brace; then |return|@>; +exit:end; + +@ @<Enter as many...@>= +n:=0; p:=null; +loop@+ begin get_x_token; + reswitch: case cur_cmd of + letter,other_char,char_given:@<Append a new letter or hyphen@>; + char_num: begin scan_char_num; cur_chr:=cur_val; cur_cmd:=char_given; + goto reswitch; + end; + spacer,right_brace: begin if n>1 then @<Enter a hyphenation exception@>; + if cur_cmd=right_brace then return; + n:=0; p:=null; + end; + othercases @<Give improper \.{\\hyphenation} error@> + endcases; + end + +@ @<Give improper \.{\\hyph...@>= +begin print_err("Improper "); print_esc("hyphenation"); +@.Improper \\hyphenation...@> + print(" will be flushed"); +help2("Hyphenation exceptions must contain only letters")@/ + ("and hyphens. But continue; I'll forgive and forget."); +error; +end + +@ @<Append a new letter or hyphen@>= +if cur_chr="-" then @<Append the value |n| to list |p|@> +else begin if lc_code(cur_chr)=0 then + begin print_err("Not a letter"); +@.Not a letter@> + help2("Letters in \hyphenation words must have \lccode>0.")@/ + ("Proceed; I'll ignore the character I just read."); + error; + end + else if n<63 then + begin incr(n); hc[n]:=lc_code(cur_chr); + end; + end + +@ @<Append the value |n| to list |p|@>= +begin if n<63 then + begin q:=get_avail; link(q):=p; info(q):=n; p:=q; + end; +end + +@ @<Enter a hyphenation exception@>= +begin incr(n); hc[n]:=cur_lang; str_room(n); h:=0; +for j:=1 to n do + begin h:=(h+h+hc[j]) mod hyph_size; + append_char(hc[j]); + end; +s:=make_string; +@<Insert the \(p)pair |(s,p)| into the exception table@>; +end + +@ @<Insert the \(p)pair |(s,p)|...@>= +if hyph_count=hyph_size then overflow("exception dictionary",hyph_size); +@:TeX capacity exceeded exception dictionary}{\quad exception dictionary@> +incr(hyph_count); +while hyph_word[h]<>0 do + begin @<If the string |hyph_word[h]| is less than \(or)or equal to + |s|, interchange |(hyph_word[h],hyph_list[h])| with |(s,p)|@>; + if h>0 then decr(h)@+else h:=hyph_size; + end; +hyph_word[h]:=s; hyph_list[h]:=p + +@ @<If the string |hyph_word[h]| is less than \(or)...@>= +k:=hyph_word[h]; +if length(k)<length(s) then goto found; +if length(k)>length(s) then goto not_found; +u:=str_start[k]; v:=str_start[s]; +repeat if str_pool[u]<str_pool[v] then goto found; +if str_pool[u]>str_pool[v] then goto not_found; +incr(u); incr(v); +until u=str_start[k+1]; +found:q:=hyph_list[h]; hyph_list[h]:=p; p:=q;@/ +t:=hyph_word[h]; hyph_word[h]:=s; s:=t; +not_found: + +@* \[43] Initializing the hyphenation tables. +The trie for \TeX's hyphenation algorithm is built from a sequence of +patterns following a \.{\\patterns} specification. Such a specification +is allowed only in \.{INITEX}, since the extra memory for auxiliary tables +and for the initialization program itself would only clutter up the +production version of \TeX\ with a lot of deadwood. + +The first step is to build a trie that is linked, instead of packed +into sequential storage, so that insertions are readily made. +After all patterns have been processed, \.{INITEX} +compresses the linked trie by identifying common subtries. Finally the +trie is packed into the efficient sequential form that the hyphenation +algorithm actually uses. + +@<Declare subprocedures for |line_break|@>= +@!init @<Declare procedures for preprocessing hyphenation patterns@>@; +tini + +@ Before we discuss trie building in detail, let's consider the simpler +problem of creating the |hyf_distance|, |hyf_num|, and |hyf_next| arrays. + +Suppose, for example, that \TeX\ reads the pattern `\.{ab2cde1}'. This is +a pattern of length 5, with $n_0\ldots n_5=0\,0\,2\,0\,0\,1$ in the +notation above. We want the corresponding |trie_op| code |v| to have +|hyf_distance[v]=3|, |hyf_num[v]=2|, and |hyf_next[v]=@t$v^\prime$@>|, +where the auxiliary |trie_op| code $v^\prime$ has +|hyf_distance[@t$v^\prime$@>]=0|, |hyf_num[@t$v^\prime$@>]=1|, and +|hyf_next[@t$v^\prime$@>]=min_quarterword|. + +\TeX\ computes an appropriate value |v| with the |new_trie_op| subroutine +below, by setting +$$\hbox{|@t$v^\prime$@>:=new_trie_op(0,1,min_quarterword)|,\qquad +|v:=new_trie_op(3,2,@t$v^\prime$@>)|.}$$ +This subroutine looks up its three +parameters in a special hash table, assigning a new value only if these +three have not appeared before for the current language. + +The hash table is called |trie_op_hash|, and the number of entries it contains +is |trie_op_ptr|. + +@<Glob...@>= +@!init@! trie_op_hash:array[-trie_op_size..trie_op_size] of 0..trie_op_size; + {trie op codes for quadruples} +@!trie_used:array[ASCII_code] of quarterword; + {largest opcode used so far for this language} +@!trie_op_lang:array[1..trie_op_size] of ASCII_code; + {language part of a hashed quadruple} +@!trie_op_val:array[1..trie_op_size] of quarterword; + {opcode corresponding to a hashed quadruple} +@!trie_op_ptr:0..trie_op_size; {number of stored ops so far} +tini + +@ It's tempting to remove the |overflow| stops in the following procedure; +|new_trie_op| could return |min_quarterword| (thereby simply ignoring +part of a hyphenation pattern) instead of aborting the job. However, that would +lead to different hyphenation results on different installations of \TeX\ +using the same patterns. The |overflow| stops are necessary for portability +of patterns. + +@<Declare procedures for preprocessing hyph...@>= +function new_trie_op(@!d,@!n:small_number;@!v:quarterword):quarterword; +label exit; +var h:-trie_op_size..trie_op_size; {trial hash location} +@!u:quarterword; {trial op code} +@!l:0..trie_op_size; {pointer to stored data} +begin h:=abs(n+313*d+361*v+1009*cur_lang) mod (trie_op_size+trie_op_size) + - trie_op_size; +loop@+ begin l:=trie_op_hash[h]; + if l=0 then {empty position found for a new op} + begin if trie_op_ptr=trie_op_size then + overflow("pattern memory ops",trie_op_size); + u:=trie_used[cur_lang]; + if u=max_quarterword then + overflow("pattern memory ops per language", + max_quarterword-min_quarterword); + incr(trie_op_ptr); incr(u); trie_used[cur_lang]:=u; + hyf_distance[trie_op_ptr]:=d; + hyf_num[trie_op_ptr]:=n; hyf_next[trie_op_ptr]:=v; + trie_op_lang[trie_op_ptr]:=cur_lang; trie_op_hash[h]:=trie_op_ptr; + trie_op_val[trie_op_ptr]:=u; new_trie_op:=u; return; + end; + if (hyf_distance[l]=d)and(hyf_num[l]=n)and(hyf_next[l]=v) + and(trie_op_lang[l]=cur_lang) then + begin new_trie_op:=trie_op_val[l]; return; + end; + if h>-trie_op_size then decr(h)@+else h:=trie_op_size; + end; +exit:end; + +@ After |new_trie_op| has compressed the necessary opcode information, +plenty of information is available to unscramble the data into the +final form needed by our hyphenation algorithm. + +@<Sort \(t)the hyphenation op tables into proper order@>= +op_start[0]:=-min_quarterword; +for j:=1 to 255 do op_start[j]:=op_start[j-1]+qo(trie_used[j-1]); +for j:=1 to trie_op_ptr do + trie_op_hash[j]:=op_start[trie_op_lang[j]]+trie_op_val[j]; {destination} +for j:=1 to trie_op_ptr do while trie_op_hash[j]>j do + begin k:=trie_op_hash[j];@/ + t:=hyf_distance[k]; hyf_distance[k]:=hyf_distance[j]; hyf_distance[j]:=t;@/ + t:=hyf_num[k]; hyf_num[k]:=hyf_num[j]; hyf_num[j]:=t;@/ + t:=hyf_next[k]; hyf_next[k]:=hyf_next[j]; hyf_next[j]:=t;@/ + trie_op_hash[j]:=trie_op_hash[k]; trie_op_hash[k]:=k; + end + +@ Before we forget how to initialize the data structures that have been +mentioned so far, let's write down the code that gets them started. + +@<Initialize table entries...@>= +for k:=-trie_op_size to trie_op_size do trie_op_hash[k]:=0; +for k:=0 to 255 do trie_used[k]:=min_quarterword; +trie_op_ptr:=0; + +@ The linked trie that is used to preprocess hyphenation patterns appears +in several global arrays. Each node represents an instruction of the form +``if you see character |c|, then perform operation |o|, move to the +next character, and go to node |l|; otherwise go to node |r|.'' +The four quantities |c|, |o|, |l|, and |r| are stored in four arrays +|trie_c|, |trie_o|, |trie_l|, and |trie_r|. The root of the trie +is |trie_l[0]|, and the number of nodes is |trie_ptr|. Null trie +pointers are represented by zero. To initialize the trie, we simply +set |trie_l[0]| and |trie_ptr| to zero. We also set |trie_c[0]| to some +arbitrary value, since the algorithm may access it. + +The algorithms maintain the condition +$$\hbox{|trie_c[trie_r[z]]>trie_c[z]|\qquad +whenever |z<>0| and |trie_r[z]<>0|};$$ in other words, sibling nodes are +ordered by their |c| fields. + +@d trie_root==trie_l[0] {root of the linked trie} + +@<Glob...@>= +@!init @!trie_c:packed array[trie_pointer] of packed_ASCII_code; + {characters to match} +@t\hskip10pt@>@!trie_o:packed array[trie_pointer] of quarterword; + {operations to perform} +@t\hskip10pt@>@!trie_l:packed array[trie_pointer] of trie_pointer; + {left subtrie links} +@t\hskip10pt@>@!trie_r:packed array[trie_pointer] of trie_pointer; + {right subtrie links} +@t\hskip10pt@>@!trie_ptr:trie_pointer; {the number of nodes in the trie} +@t\hskip10pt@>@!trie_hash:packed array[trie_pointer] of trie_pointer; + {used to identify equivalent subtries} +tini + +@ Let us suppose that a linked trie has already been constructed. +Experience shows that we can often reduce its size by recognizing common +subtries; therefore another hash table is introduced for this purpose, +somewhat similar to |trie_op_hash|. The new hash table will be +initialized to zero. + +The function |trie_node(p)| returns |p| if |p| is distinct from other nodes +that it has seen, otherwise it returns the number of the first equivalent +node that it has seen. + +Notice that we might make subtries equivalent even if they correspond to +patterns for different languages, in which the trie ops might mean quite +different things. That's perfectly all right. + +@<Declare procedures for preprocessing hyph...@>= +function trie_node(@!p:trie_pointer):trie_pointer; {converts + to a canonical form} +label exit; +var h:trie_pointer; {trial hash location} +@!q:trie_pointer; {trial trie node} +begin h:=abs(trie_c[p]+1009*trie_o[p]+@| + 2718*trie_l[p]+3142*trie_r[p]) mod trie_size; +loop@+ begin q:=trie_hash[h]; + if q=0 then + begin trie_hash[h]:=p; trie_node:=p; return; + end; + if (trie_c[q]=trie_c[p])and(trie_o[q]=trie_o[p])and@| + (trie_l[q]=trie_l[p])and(trie_r[q]=trie_r[p]) then + begin trie_node:=q; return; + end; + if h>0 then decr(h)@+else h:=trie_size; + end; +exit:end; + +@ A neat recursive procedure is now able to compress a trie by +traversing it and applying |trie_node| to its nodes in ``bottom up'' +fashion. We will compress the entire trie by clearing |trie_hash| to +zero and then saying `|trie_root:=compress_trie(trie_root)|'. +@^recursion@> + +@<Declare procedures for preprocessing hyph...@>= +function compress_trie(@!p:trie_pointer):trie_pointer; +begin if p=0 then compress_trie:=0 +else begin trie_l[p]:=compress_trie(trie_l[p]); + trie_r[p]:=compress_trie(trie_r[p]); + compress_trie:=trie_node(p); + end; +end; + +@ The compressed trie will be packed into the |trie| array using a +``top-down first-fit'' procedure. This is a little tricky, so the reader +should pay close attention: The |trie_hash| array is cleared to zero +again and renamed |trie_ref| for this phase of the operation; later on, +|trie_ref[p]| will be nonzero only if the linked trie node |p| is the +smallest character +in a family and if the characters |c| of that family have been allocated to +locations |trie_ref[p]+c| in the |trie| array. Locations of |trie| that +are in use will have |trie_link=0|, while the unused holes in |trie| +will be doubly linked with |trie_link| pointing to the next larger vacant +location and |trie_back| pointing to the next smaller one. This double +linking will have been carried out only as far as |trie_max|, where +|trie_max| is the largest index of |trie| that will be needed. +To save time at the low end of the trie, we maintain array entries +|trie_min[c]| pointing to the smallest hole that is greater than~|c|. +Another array |trie_taken| tells whether or not a given location is +equal to |trie_ref[p]| for some |p|; this array is used to ensure that +distinct nodes in the compressed trie will have distinct |trie_ref| +entries. + +@d trie_ref==trie_hash {where linked trie families go into |trie|} +@d trie_back(#)==trie[#].lh {backward links in |trie| holes} + +@<Glob...@>= +@!init@!trie_taken:packed array[1..trie_size] of boolean; + {does a family start here?} +@t\hskip10pt@>@!trie_min:array[ASCII_code] of trie_pointer; + {the first possible slot for each character} +@t\hskip10pt@>@!trie_max:trie_pointer; {largest location used in |trie|} +@t\hskip10pt@>@!trie_not_ready:boolean; {is the trie still in linked form?} +tini + +@ Each time \.{\\patterns} appears, it contributes further patterns to +the future trie, which will be built only when hyphenation is attempted or +when a format file is dumped. The boolean variable |trie_not_ready| +will change to |false| when the trie is compressed; this will disable +further patterns. + +@<Initialize table entries...@>= +trie_not_ready:=true; trie_root:=0; trie_c[0]:=si(0); trie_ptr:=0; + +@ Here is how the trie-compression data structures are initialized. +If storage is tight, it would be possible to overlap |trie_op_hash|, +|trie_op_lang|, and |trie_op_val| with |trie|, |trie_hash|, and |trie_taken|, +because we finish with the former just before we need the latter. + +@<Get ready to compress the trie@>= +@<Sort \(t)the hyphenation...@>; +for p:=0 to trie_size do trie_hash[p]:=0; +trie_root:=compress_trie(trie_root); {identify equivalent subtries} +for p:=0 to trie_ptr do trie_ref[p]:=0; +for p:=0 to 255 do trie_min[p]:=p+1; +trie_link(0):=1; trie_max:=0 + +@ The |first_fit| procedure finds the smallest hole |z| in |trie| such that +a trie family starting at a given node |p| will fit into vacant positions +starting at |z|. If |c=trie_c[p]|, this means that location |z-c| must +not already be taken by some other family, and that |z-c+@t$c^\prime$@>| +must be vacant for all characters $c^\prime$ in the family. The procedure +sets |trie_ref[p]| to |z-c| when the first fit has been found. + +@<Declare procedures for preprocessing hyph...@>= +procedure first_fit(@!p:trie_pointer); {packs a family into |trie|} +label not_found,found; +var h:trie_pointer; {candidate for |trie_ref[p]|} +@!z:trie_pointer; {runs through holes} +@!q:trie_pointer; {runs through the family starting at |p|} +@!c:ASCII_code; {smallest character in the family} +@!l,@!r:trie_pointer; {left and right neighbors} +@!ll:1..256; {upper limit of |trie_min| updating} +begin c:=so(trie_c[p]); +z:=trie_min[c]; {get the first conceivably good hole} +loop@+ begin h:=z-c;@/ + @<Ensure that |trie_max>=h+256|@>; + if trie_taken[h] then goto not_found; + @<If all characters of the family fit relative to |h|, then + |goto found|,\30\ otherwise |goto not_found|@>; + not_found: z:=trie_link(z); {move to the next hole} + end; +found: @<Pack the family into |trie| relative to |h|@>; +end; + +@ By making sure that |trie_max| is at least |h+256|, we can be sure that +|trie_max>z|, since |h=z-c|. It follows that location |trie_max| will +never be occupied in |trie|, and we will have |trie_max>=trie_link(z)|. + +@<Ensure that |trie_max>=h+256|@>= +if trie_max<h+256 then + begin if trie_size<=h+256 then overflow("pattern memory",trie_size); +@:TeX capacity exceeded pattern memory}{\quad pattern memory@> + repeat incr(trie_max); trie_taken[trie_max]:=false; + trie_link(trie_max):=trie_max+1; trie_back(trie_max):=trie_max-1; + until trie_max=h+256; + end + +@ @<If all characters of the family fit relative to |h|...@>= +q:=trie_r[p]; +while q>0 do + begin if trie_link(h+so(trie_c[q]))=0 then goto not_found; + q:=trie_r[q]; + end; +goto found + +@ @<Pack the family into |trie| relative to |h|@>= +trie_taken[h]:=true; trie_ref[p]:=h; q:=p; +repeat z:=h+so(trie_c[q]); l:=trie_back(z); r:=trie_link(z); +trie_back(r):=l; trie_link(l):=r; trie_link(z):=0; +if l<256 then + begin if z<256 then ll:=z @+else ll:=256; + repeat trie_min[l]:=r; incr(l); + until l=ll; + end; +q:=trie_r[q]; +until q=0 + +@ To pack the entire linked trie, we use the following recursive procedure. +@^recursion@> + +@<Declare procedures for preprocessing hyph...@>= +procedure trie_pack(@!p:trie_pointer); {pack subtries of a family} +var q:trie_pointer; {a local variable that need not be saved on recursive calls} +begin repeat q:=trie_l[p]; +if (q>0)and(trie_ref[q]=0) then + begin first_fit(q); trie_pack(q); + end; +p:=trie_r[p]; +until p=0; +end; + +@ When the whole trie has been allocated into the sequential table, we +must go through it once again so that |trie| contains the correct +information. Null pointers in the linked trie will be represented by the +value~0, which properly implements an ``empty'' family. + +@<Move the data into |trie|@>= +h.rh:=0; h.b0:=min_quarterword; h.b1:=min_quarterword; {|trie_link:=0|, + |trie_op:=min_quarterword|, |trie_char:=qi(0)|} +if trie_root=0 then {no patterns were given} + begin for r:=0 to 256 do trie[r]:=h; + trie_max:=256; + end +else begin trie_fix(trie_root); {this fixes the non-holes in |trie|} + r:=0; {now we will zero out all the holes} + repeat s:=trie_link(r); trie[r]:=h; r:=s; + until r>trie_max; + end; +trie_char(0):=qi("?"); {make |trie_char(c)<>c| for all |c|} + +@ The fixing-up procedure is, of course, recursive. Since the linked trie +usually has overlapping subtries, the same data may be moved several +times; but that causes no harm, and at most as much work is done as it +took to build the uncompressed trie. +@^recursion@> + +@<Declare procedures for preprocessing hyph...@>= +procedure trie_fix(@!p:trie_pointer); {moves |p| and its siblings into |trie|} +var q:trie_pointer; {a local variable that need not be saved on recursive calls} +@!c:ASCII_code; {another one that need not be saved} +@!z:trie_pointer; {|trie| reference; this local variable must be saved} +begin z:=trie_ref[p]; +repeat q:=trie_l[p]; c:=so(trie_c[p]); +trie_link(z+c):=trie_ref[q]; trie_char(z+c):=qi(c); trie_op(z+c):=trie_o[p]; +if q>0 then trie_fix(q); +p:=trie_r[p]; +until p=0; +end; + +@ Now let's go back to the easier problem, of building the linked +trie. When \.{INITEX} has scanned the `\.{\\patterns}' control +sequence, it calls on |new_patterns| to do the right thing. + +@<Declare procedures for preprocessing hyph...@>= +procedure new_patterns; {initializes the hyphenation pattern data} +label done, done1; +var k,@!l:0..64; {indices into |hc| and |hyf|; + not always in |small_number| range} +@!digit_sensed:boolean; {should the next digit be treated as a letter?} +@!v:quarterword; {trie op code} +@!p,@!q:trie_pointer; {nodes of trie traversed during insertion} +@!first_child:boolean; {is |p=trie_l[q]|?} +@!c:ASCII_code; {character being inserted} +begin if trie_not_ready then + begin set_cur_lang; scan_left_brace; {a left brace must follow \.{\\patterns}} + @<Enter all of the patterns into a linked trie, until coming to a right + brace@>; + end +else begin print_err("Too late for "); print_esc("patterns"); + help1("All patterns must be given before typesetting begins."); + error; link(garbage):=scan_toks(false,false); flush_list(def_ref); + end; +end; + +@ Novices are not supposed to be using \.{\\patterns}, so the error +messages are terse. (Note that all error messages appear in \TeX's string +pool, even if they are used only by \.{INITEX}.) + +@<Enter all of the patterns into a linked trie...@>= +k:=0; hyf[0]:=0; digit_sensed:=false; +loop@+ begin get_x_token; + case cur_cmd of + letter,other_char:@<Append a new letter or a hyphen level@>; + spacer,right_brace: begin if k>0 then + @<Insert a new pattern into the linked trie@>; + if cur_cmd=right_brace then goto done; + k:=0; hyf[0]:=0; digit_sensed:=false; + end; + othercases begin print_err("Bad "); print_esc("patterns"); +@.Bad \\patterns@> + help1("(See Appendix H.)"); error; + end + endcases; + end; +done: + +@ @<Append a new letter or a hyphen level@>= +if digit_sensed or(cur_chr<"0")or(cur_chr>"9") then + begin if cur_chr="." then cur_chr:=0 {edge-of-word delimiter} + else begin cur_chr:=lc_code(cur_chr); + if cur_chr=0 then + begin print_err("Nonletter"); +@.Nonletter@> + help1("(See Appendix H.)"); error; + end; + end; + if k<63 then + begin incr(k); hc[k]:=cur_chr; hyf[k]:=0; digit_sensed:=false; + end; + end +else if k<63 then + begin hyf[k]:=cur_chr-"0"; digit_sensed:=true; + end + +@ When the following code comes into play, the pattern $p_1\ldots p_k$ +appears in |hc[1..k]|, and the corresponding sequence of numbers $n_0\ldots +n_k$ appears in |hyf[0..k]|. + +@<Insert a new pattern into the linked trie@>= +begin @<Compute the trie op code, |v|, and set |l:=0|@>; +q:=0; hc[0]:=cur_lang; +while l<=k do + begin c:=hc[l]; incr(l); p:=trie_l[q]; first_child:=true; + while (p>0)and(c>so(trie_c[p])) do + begin q:=p; p:=trie_r[q]; first_child:=false; + end; + if (p=0)or(c<so(trie_c[p])) then + @<Insert a new trie node between |q| and |p|, and + make |p| point to it@>; + q:=p; {now node |q| represents $p_1\ldots p_{l-1}$} + end; +if trie_o[q]<>min_quarterword then + begin print_err("Duplicate pattern"); +@.Duplicate pattern@> + help1("(See Appendix H.)"); error; + end; +trie_o[q]:=v; +end + +@ @<Insert a new trie node between |q| and |p|...@>= +begin if trie_ptr=trie_size then overflow("pattern memory",trie_size); +@:TeX capacity exceeded pattern memory}{\quad pattern memory@> +incr(trie_ptr); trie_r[trie_ptr]:=p; p:=trie_ptr; trie_l[p]:=0; +if first_child then trie_l[q]:=p@+else trie_r[q]:=p; +trie_c[p]:=si(c); trie_o[p]:=min_quarterword; +end + +@ @<Compute the trie op code, |v|...@>= +if hc[1]=0 then hyf[0]:=0; +if hc[k]=0 then hyf[k]:=0; +l:=k; v:=min_quarterword; +loop@+ begin if hyf[l]<>0 then v:=new_trie_op(k-l,hyf[l],v); + if l>0 then decr(l)@+else goto done1; + end; +done1: + +@ Finally we put everything together: Here is how the trie gets to its +final, efficient form. +The following packing routine is rigged so that the root of the linked +tree gets mapped into location 1 of |trie|, as required by the hyphenation +algorithm. This happens because the first call of |first_fit| will +``take'' location~1. + +@<Declare procedures for preprocessing hyphenation patterns@>= +procedure init_trie; +var @!p:trie_pointer; {pointer for initialization} +@!j,@!k,@!t:integer; {all-purpose registers for initialization} +@!r,@!s:trie_pointer; {used to clean up the packed |trie|} +@!h:two_halves; {template used to zero out |trie|'s holes} +begin @<Get ready to compress the trie@>; +if trie_root<>0 then + begin first_fit(trie_root); trie_pack(trie_root); + end; +@<Move the data into |trie|@>; +trie_not_ready:=false; +end; + +@* \[44] Breaking vertical lists into pages. +The |vsplit| procedure, which implements \TeX's \.{\\vsplit} operation, +is considerably simpler than |line_break| because it doesn't have to +worry about hyphenation, and because its mission is to discover a single +break instead of an optimum sequence of breakpoints. But before we get +into the details of |vsplit|, we need to consider a few more basic things. + +@ A subroutine called |prune_page_top| takes a pointer to a vlist and +returns a pointer to a modified vlist in which all glue, kern, and penalty nodes +have been deleted before the first box or rule node. However, the first +box or rule is actually preceded by a newly created glue node designed so that +the topmost baseline will be at distance |split_top_skip| from the top, +whenever this is possible without backspacing. + +In this routine and those that follow, we make use of the fact that a +vertical list contains no character nodes, hence the |type| field exists +for each node in the list. +@^data structure assumptions@> + +@p function prune_page_top(@!p:pointer):pointer; {adjust top after page break} +var prev_p:pointer; {lags one step behind |p|} +@!q:pointer; {temporary variable for list manipulation} +begin prev_p:=temp_head; link(temp_head):=p; +while p<>null do + case type(p) of + hlist_node,vlist_node,rule_node:@<Insert glue for |split_top_skip| + and set~|p:=null|@>; + whatsit_node,mark_node,ins_node: begin prev_p:=p; p:=link(prev_p); + end; + glue_node,kern_node,penalty_node: begin q:=p; p:=link(q); link(q):=null; + link(prev_p):=p; flush_node_list(q); + end; + othercases confusion("pruning") +@:this can't happen pruning}{\quad pruning@> + endcases; +prune_page_top:=link(temp_head); +end; + +@ @<Insert glue for |split_top_skip|...@>= +begin q:=new_skip_param(split_top_skip_code); link(prev_p):=q; link(q):=p; + {now |temp_ptr=glue_ptr(q)|} +if width(temp_ptr)>height(p) then width(temp_ptr):=width(temp_ptr)-height(p) +else width(temp_ptr):=0; +p:=null; +end + +@ The next subroutine finds the best place to break a given vertical list +so as to obtain a box of height~|h|, with maximum depth~|d|. +A pointer to the beginning of the vertical list is given, +and a pointer to the optimum breakpoint is returned. The list is effectively +followed by a forced break, i.e., a penalty node with the |eject_penalty|; +if the best break occurs at this artificial node, the value |null| is returned. + +An array of six |scaled| distances is used to keep track of the height +from the beginning of the list to the current place, just as in |line_break|. +In fact, we use one of the same arrays, only changing its name to reflect +its new significance. + +@d active_height==active_width {new name for the six distance variables} +@d cur_height==active_height[1] {the natural height} +@d set_height_zero(#)==active_height[#]:=0 {initialize the height to zero} +@# +@d update_heights=90 {go here to record glue in the |active_height| table} + +@p function vert_break(@!p:pointer; @!h,@!d:scaled):pointer; + {finds optimum page break} +label done,not_found,update_heights; +var prev_p:pointer; {if |p| is a glue node, |type(prev_p)| determines + whether |p| is a legal breakpoint} +@!q,@!r:pointer; {glue specifications} +@!pi:integer; {penalty value} +@!b:integer; {badness at a trial breakpoint} +@!least_cost:integer; {the smallest badness plus penalties found so far} +@!best_place:pointer; {the most recent break that leads to |least_cost|} +@!prev_dp:scaled; {depth of previous box in the list} +@!t:small_number; {|type| of the node following a kern} +begin prev_p:=p; {an initial glue node is not a legal breakpoint} +least_cost:=awful_bad; do_all_six(set_height_zero); prev_dp:=0; +loop@+ begin @<If node |p| is a legal breakpoint, check if this break is + the best known, and |goto done| if |p| is null or + if the page-so-far is already too full to accept more stuff@>; + prev_p:=p; p:=link(prev_p); + end; +done: vert_break:=best_place; +end; + +@ A global variable |best_height_plus_depth| will be set to the natural size +of the box that corresponds to the optimum breakpoint found by |vert_break|. +(This value is used by the insertion-splitting algorithm of the page builder.) + +@<Glob...@>= +@!best_height_plus_depth:scaled; {height of the best box, without stretching or + shrinking} + +@ A subtle point to be noted here is that the maximum depth~|d| might be +negative, so |cur_height| and |prev_dp| might need to be corrected even +after a glue or kern node. + +@<If node |p| is a legal breakpoint, check...@>= +if p=null then pi:=eject_penalty +else @<Use node |p| to update the current height and depth measurements; + if this node is not a legal breakpoint, |goto not_found| + or |update_heights|, + otherwise set |pi| to the associated penalty at the break@>; +@<Check if node |p| is a new champion breakpoint; then \(go)|goto done| + if |p| is a forced break or if the page-so-far is already too full@>; +if (type(p)<glue_node)or(type(p)>kern_node) then goto not_found; +update_heights: @<Update the current height and depth measurements with + respect to a glue or kern node~|p|@>; +not_found: if prev_dp>d then + begin cur_height:=cur_height+prev_dp-d; + prev_dp:=d; + end; + +@ @<Use node |p| to update the current height and depth measurements...@>= +case type(p) of +hlist_node,vlist_node,rule_node: begin@t@>@;@/ + cur_height:=cur_height+prev_dp+height(p); prev_dp:=depth(p); + goto not_found; + end; +whatsit_node:@<Process whatsit |p| in |vert_break| loop, |goto not_found|@>; +glue_node: if precedes_break(prev_p) then pi:=0 + else goto update_heights; +kern_node: begin if link(p)=null then t:=penalty_node + else t:=type(link(p)); + if t=glue_node then pi:=0@+else goto update_heights; + end; +penalty_node: pi:=penalty(p); +mark_node,ins_node: goto not_found; +othercases confusion("vertbreak") +@:this can't happen vertbreak}{\quad vertbreak@> +endcases + +@ @d deplorable==100000 {more than |inf_bad|, but less than |awful_bad|} + +@<Check if node |p| is a new champion breakpoint; then \(go)...@>= +if pi<inf_penalty then + begin @<Compute the badness, |b|, using |awful_bad| + if the box is too full@>; + if b<awful_bad then + if pi<=eject_penalty then b:=pi + else if b<inf_bad then b:=b+pi + else b:=deplorable; + if b<=least_cost then + begin best_place:=p; least_cost:=b; + best_height_plus_depth:=cur_height+prev_dp; + end; + if (b=awful_bad)or(pi<=eject_penalty) then goto done; + end + +@ @<Compute the badness, |b|, using |awful_bad| if the box is too full@>= +if cur_height<h then + if (active_height[3]<>0) or (active_height[4]<>0) or + (active_height[5]<>0) then b:=0 + else b:=badness(h-cur_height,active_height[2]) +else if cur_height-h>active_height[6] then b:=awful_bad +else b:=badness(cur_height-h,active_height[6]) + +@ Vertical lists that are subject to the |vert_break| procedure should not +contain infinite shrinkability, since that would permit any amount of +information to ``fit'' on one page. + +@<Update the current height and depth measurements with...@>= +if type(p)=kern_node then q:=p +else begin q:=glue_ptr(p); + active_height[2+stretch_order(q)]:=@| + active_height[2+stretch_order(q)]+stretch(q);@/ + active_height[6]:=active_height[6]+shrink(q); + if (shrink_order(q)<>normal)and(shrink(q)<>0) then + begin@t@>@;@/ + print_err("Infinite glue shrinkage found in box being split");@/ +@.Infinite glue shrinkage...@> + help4("The box you are \vsplitting contains some infinitely")@/ + ("shrinkable glue, e.g., `\vss' or `\vskip 0pt minus 1fil'.")@/ + ("Such glue doesn't belong there; but you can safely proceed,")@/ + ("since the offensive shrinkability has been made finite."); + error; r:=new_spec(q); shrink_order(r):=normal; delete_glue_ref(q); + glue_ptr(p):=r; q:=r; + end; + end; +cur_height:=cur_height+prev_dp+width(q); prev_dp:=0 + +@ Now we are ready to consider |vsplit| itself. Most of +its work is accomplished by the two subroutines that we have just considered. + +Given the number of a vlist box |n|, and given a desired page height |h|, +the |vsplit| function finds the best initial segment of the vlist and +returns a box for a page of height~|h|. The remainder of the vlist, if +any, replaces the original box, after removing glue and penalties and +adjusting for |split_top_skip|. Mark nodes in the split-off box are used to +set the values of |split_first_mark| and |split_bot_mark|; we use the +fact that |split_first_mark=null| if and only if |split_bot_mark=null|. + +The original box becomes ``void'' if and only if it has been entirely +extracted. The extracted box is ``void'' if and only if the original +box was void (or if it was, erroneously, an hlist box). + +@p function vsplit(@!n:eight_bits; @!h:scaled):pointer; + {extracts a page of height |h| from box |n|} +label exit,done; +var v:pointer; {the box to be split} +p:pointer; {runs through the vlist} +q:pointer; {points to where the break occurs} +begin v:=box(n); +if split_first_mark<>null then + begin delete_token_ref(split_first_mark); split_first_mark:=null; + delete_token_ref(split_bot_mark); split_bot_mark:=null; + end; +@<Dispense with trivial cases of void or bad boxes@>; +q:=vert_break(list_ptr(v),h,split_max_depth); +@<Look at all the marks in nodes before the break, and set the final + link to |null| at the break@>; +q:=prune_page_top(q); p:=list_ptr(v); free_node(v,box_node_size); +if q=null then box(n):=null {the |eq_level| of the box stays the same} +else box(n):=vpack(q,natural); +vsplit:=vpackage(p,h,exactly,split_max_depth); +exit: end; + +@ @<Dispense with trivial cases of void or bad boxes@>= +if v=null then + begin vsplit:=null; return; + end; +if type(v)<>vlist_node then + begin print_err(""); print_esc("vsplit"); print(" needs a "); + print_esc("vbox"); +@:vsplit_}{\.{\\vsplit needs a \\vbox}@> + help2("The box you are trying to split is an \hbox.")@/ + ("I can't split such a box, so I'll leave it alone."); + error; vsplit:=null; return; + end + +@ It's possible that the box begins with a penalty node that is the +``best'' break, so we must be careful to handle this special case correctly. + +@<Look at all the marks...@>= +p:=list_ptr(v); +if p=q then list_ptr(v):=null +else loop@+begin if type(p)=mark_node then + if split_first_mark=null then + begin split_first_mark:=mark_ptr(p); + split_bot_mark:=split_first_mark; + token_ref_count(split_first_mark):=@| + token_ref_count(split_first_mark)+2; + end + else begin delete_token_ref(split_bot_mark); + split_bot_mark:=mark_ptr(p); + add_token_ref(split_bot_mark); + end; + if link(p)=q then + begin link(p):=null; goto done; + end; + p:=link(p); + end; +done: + +@* \[45] The page builder. +When \TeX\ appends new material to its main vlist in vertical mode, it uses +a method something like |vsplit| to decide where a page ends, except that +the calculations are done ``on line'' as new items come in. +The main complication in this process is that insertions must be put +into their boxes and removed from the vlist, in a more-or-less optimum manner. + +We shall use the term ``current page'' for that part of the main vlist that +is being considered as a candidate for being broken off and sent to the +user's output routine. The current page starts at |link(page_head)|, and +it ends at |page_tail|. We have |page_head=page_tail| if this list is empty. +@^current page@> + +Utter chaos would reign if the user kept changing page specifications +while a page is being constructed, so the page builder keeps the pertinent +specifications frozen as soon as the page receives its first box or +insertion. The global variable |page_contents| is |empty| when the +current page contains only mark nodes and content-less whatsit nodes; it +is |inserts_only| if the page contains only insertion nodes in addition to +marks and whatsits. Glue nodes, kern nodes, and penalty nodes are +discarded until a box or rule node appears, at which time |page_contents| +changes to |box_there|. As soon as |page_contents| becomes non-|empty|, +the current |vsize| and |max_depth| are squirreled away into |page_goal| +and |page_max_depth|; the latter values will be used until the page has +been forwarded to the user's output routine. The \.{\\topskip} adjustment +is made when |page_contents| changes to |box_there|. + +Although |page_goal| starts out equal to |vsize|, it is decreased by the +scaled natural height-plus-depth of the insertions considered so far, and by +the \.{\\skip} corrections for those insertions. Therefore it represents +the size into which the non-inserted material should fit, assuming that +all insertions in the current page have been made. + +The global variables |best_page_break| and |least_page_cost| correspond +respectively to the local variables |best_place| and |least_cost| in the +|vert_break| routine that we have already studied; i.e., they record the +location and value of the best place currently known for breaking the +current page. The value of |page_goal| at the time of the best break is +stored in |best_size|. + +@d inserts_only=1 + {|page_contents| when an insert node has been contributed, but no boxes} +@d box_there=2 {|page_contents| when a box or rule has been contributed} + +@<Glob...@>= +@!page_tail:pointer; {the final node on the current page} +@!page_contents:empty..box_there; {what is on the current page so far?} +@!page_max_depth:scaled; {maximum box depth on page being built} +@!best_page_break:pointer; {break here to get the best page known so far} +@!least_page_cost:integer; {the score for this currently best page} +@!best_size:scaled; {its |page_goal|} + +@ The page builder has another data structure to keep track of insertions. +This is a list of four-word nodes, starting and ending at |page_ins_head|. +That is, the first element of the list is node |r@t$_1$@>=link(page_ins_head)|; +node $r_j$ is followed by |r@t$_{j+1}$@>=link(r@t$_j$@>)|; and if there are +|n| items we have |r@t$_{n+1}$@>=page_ins_head|. The |subtype| field of +each node in this list refers to an insertion number; for example, `\.{\\insert +250}' would correspond to a node whose |subtype| is |qi(250)| +(the same as the |subtype| field of the relevant |ins_node|). These |subtype| +fields are in increasing order, and |subtype(page_ins_head)= +qi(255)|, so |page_ins_head| serves as a convenient sentinel +at the end of the list. A record is present for each insertion number that +appears in the current page. + +The |type| field in these nodes distinguishes two possibilities that +might occur as we look ahead before deciding on the optimum page break. +If |type(r)=inserting|, then |height(r)| contains the total of the +height-plus-depth dimensions of the box and all its inserts seen so far. +If |type(r)=split_up|, then no more insertions will be made into this box, +because at least one previous insertion was too big to fit on the current +page; |broken_ptr(r)| points to the node where that insertion will be +split, if \TeX\ decides to split it, |broken_ins(r)| points to the +insertion node that was tentatively split, and |height(r)| includes also the +natural height plus depth of the part that would be split off. + +In both cases, |last_ins_ptr(r)| points to the last |ins_node| +encountered for box |qo(subtype(r))| that would be at least partially +inserted on the next page; and |best_ins_ptr(r)| points to the last +such |ins_node| that should actually be inserted, to get the page with +minimum badness among all page breaks considered so far. We have +|best_ins_ptr(r)=null| if and only if no insertion for this box should +be made to produce this optimum page. + +The data structure definitions here use the fact that the |@!height| field +appears in the fourth word of a box node. +@^data structure assumptions@> + +@d page_ins_node_size=4 {number of words for a page insertion node} +@d inserting=0 {an insertion class that has not yet overflowed} +@d split_up=1 {an overflowed insertion class} +@d broken_ptr(#)==link(#+1) + {an insertion for this class will break here if anywhere} +@d broken_ins(#)==info(#+1) {this insertion might break at |broken_ptr|} +@d last_ins_ptr(#)==link(#+2) {the most recent insertion for this |subtype|} +@d best_ins_ptr(#)==info(#+2) {the optimum most recent insertion} + +@<Initialize the special list heads...@>= +subtype(page_ins_head):=qi(255); +type(page_ins_head):=split_up; link(page_ins_head):=page_ins_head; + +@ An array |page_so_far| records the heights and depths of everything +on the current page. This array contains six |scaled| numbers, like the +similar arrays already considered in |line_break| and |vert_break|; and it +also contains |page_goal| and |page_depth|, since these values are +all accessible to the user via |set_page_dimen| commands. The +value of |page_so_far[1]| is also called |page_total|. The stretch +and shrink components of the \.{\\skip} corrections for each insertion are +included in |page_so_far|, but the natural space components of these +corrections are not, since they have been subtracted from |page_goal|. + +The variable |page_depth| records the depth of the current page; it has been +adjusted so that it is at most |page_max_depth|. The variable +|last_glue| points to the glue specification of the most recent node +contributed from the contribution list, if this was a glue node; otherwise +|last_glue=max_halfword|. (If the contribution list is nonempty, +however, the value of |last_glue| is not necessarily accurate.) +The variables |last_penalty| and |last_kern| are similar. And +finally, |insert_penalties| holds the sum of the penalties associated with +all split and floating insertions. + +@d page_goal==page_so_far[0] {desired height of information on page being built} +@d page_total==page_so_far[1] {height of the current page} +@d page_shrink==page_so_far[6] {shrinkability of the current page} +@d page_depth==page_so_far[7] {depth of the current page} + +@<Glob...@>= +@!page_so_far:array [0..7] of scaled; {height and glue of the current page} +@!last_glue:pointer; {used to implement \.{\\lastskip}} +@!last_penalty:integer; {used to implement \.{\\lastpenalty}} +@!last_kern:scaled; {used to implement \.{\\lastkern}} +@!insert_penalties:integer; {sum of the penalties for held-over insertions} + +@ @<Put each...@>= +primitive("pagegoal",set_page_dimen,0); +@!@:page_goal_}{\.{\\pagegoal} primitive@> +primitive("pagetotal",set_page_dimen,1); +@!@:page_total_}{\.{\\pagetotal} primitive@> +primitive("pagestretch",set_page_dimen,2); +@!@:page_stretch_}{\.{\\pagestretch} primitive@> +primitive("pagefilstretch",set_page_dimen,3); +@!@:page_fil_stretch_}{\.{\\pagefilstretch} primitive@> +primitive("pagefillstretch",set_page_dimen,4); +@!@:page_fill_stretch_}{\.{\\pagefillstretch} primitive@> +primitive("pagefilllstretch",set_page_dimen,5); +@!@:page_filll_stretch_}{\.{\\pagefilllstretch} primitive@> +primitive("pageshrink",set_page_dimen,6); +@!@:page_shrink_}{\.{\\pageshrink} primitive@> +primitive("pagedepth",set_page_dimen,7); +@!@:page_depth_}{\.{\\pagedepth} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +set_page_dimen: case chr_code of +0: print_esc("pagegoal"); +1: print_esc("pagetotal"); +2: print_esc("pagestretch"); +3: print_esc("pagefilstretch"); +4: print_esc("pagefillstretch"); +5: print_esc("pagefilllstretch"); +6: print_esc("pageshrink"); +othercases print_esc("pagedepth") +endcases; + +@ @d print_plus_end(#)==print(#);@+end +@d print_plus(#)==if page_so_far[#]<>0 then + begin print(" plus "); print_scaled(page_so_far[#]); print_plus_end + +@p procedure print_totals; +begin print_scaled(page_total); +print_plus(2)(""); +print_plus(3)("fil"); +print_plus(4)("fill"); +print_plus(5)("filll"); +if page_shrink<>0 then + begin print(" minus "); print_scaled(page_shrink); + end; +end; + +@ @<Show the status of the current page@>= +if page_head<>page_tail then + begin print_nl("### current page:"); + if output_active then print(" (held over for next output)"); +@.held over for next output@> + show_box(link(page_head)); + if page_contents>empty then + begin print_nl("total height "); print_totals; +@:total_height}{\.{total height}@> + print_nl(" goal height "); print_scaled(page_goal); +@.goal height@> + r:=link(page_ins_head); + while r<>page_ins_head do + begin print_ln; print_esc("insert"); t:=qo(subtype(r)); + print_int(t); print(" adds "); + t:=x_over_n(height(r),1000)*count(t); print_scaled(t); + if type(r)=split_up then + begin q:=page_head; t:=0; + repeat q:=link(q); + if (type(q)=ins_node)and(subtype(q)=subtype(r)) then incr(t); + until q=broken_ins(r); + print(", #"); print_int(t); print(" might split"); + end; + r:=link(r); + end; + end; + end + +@ Here is a procedure that is called when the |page_contents| is changing +from |empty| to |inserts_only| or |box_there|. + +@d set_page_so_far_zero(#)==page_so_far[#]:=0 + +@p procedure freeze_page_specs(@!s:small_number); +begin page_contents:=s; +page_goal:=vsize; page_max_depth:=max_depth; +page_depth:=0; do_all_six(set_page_so_far_zero); +least_page_cost:=awful_bad; +@!stat if tracing_pages>0 then + begin begin_diagnostic; + print_nl("%% goal height="); print_scaled(page_goal); +@.goal height@> + print(", max depth="); print_scaled(page_max_depth); + end_diagnostic(false); + end;@;@+tats@;@/ +end; + +@ Pages are built by appending nodes to the current list in \TeX's +vertical mode, which is at the outermost level of the semantic nest. This +vlist is split into two parts; the ``current page'' that we have been +talking so much about already, and the ``contribution list'' that receives +new nodes as they are created. The current page contains everything that +the page builder has accounted for in its data structures, as described +above, while the contribution list contains other things that have been +generated by other parts of \TeX\ but have not yet been +seen by the page builder. +The contribution list starts at |link(contrib_head)|, and it ends at the +current node in \TeX's vertical mode. + +When \TeX\ has appended new material in vertical mode, it calls the procedure +|build_page|, which tries to catch up by moving nodes from the contribution +list to the current page. This procedure will succeed in its goal of +emptying the contribution list, unless a page break is discovered, i.e., +unless the current page has grown to the point where the optimum next +page break has been determined. In the latter case, the nodes after the +optimum break will go back onto the contribution list, and control will +effectively pass to the user's output routine. + +We make |type(page_head)=glue_node|, so that an initial glue node on +the current page will not be considered a valid breakpoint. + +@<Initialize the special list...@>= +type(page_head):=glue_node; subtype(page_head):=normal; + +@ The global variable |output_active| is true during the time the +user's output routine is driving \TeX. + +@<Glob...@>= +@!output_active:boolean; {are we in the midst of an output routine?} + +@ @<Set init...@>= +output_active:=false; insert_penalties:=0; + +@ The page builder is ready to start a fresh page if we initialize +the following state variables. (However, the page insertion list is initialized +elsewhere.) + +@<Start a new current page@>= +page_contents:=empty; page_tail:=page_head; link(page_head):=null;@/ +last_glue:=max_halfword; last_penalty:=0; last_kern:=0; +page_depth:=0; page_max_depth:=0 + +@ At certain times box 255 is supposed to be void (i.e., |null|), +or an insertion box is supposed to be ready to accept a vertical list. +If not, an error message is printed, and the following subroutine +flushes the unwanted contents, reporting them to the user. + +@p procedure box_error(@!n:eight_bits); +begin error; begin_diagnostic; +print_nl("The following box has been deleted:"); +@.The following...deleted@> +show_box(box(n)); end_diagnostic(true); +flush_node_list(box(n)); box(n):=null; +end; + +@ The following procedure guarantees that a given box register +does not contain an \.{\\hbox}. + +@p procedure ensure_vbox(@!n:eight_bits); +var p:pointer; {the box register contents} +begin p:=box(n); +if p<>null then if type(p)=hlist_node then + begin print_err("Insertions can only be added to a vbox"); +@.Insertions can only...@> + help3("Tut tut: You're trying to \insert into a")@/ + ("\box register that now contains an \hbox.")@/ + ("Proceed, and I'll discard its present contents."); + box_error(n); + end; +end; + +@ \TeX\ is not always in vertical mode at the time |build_page| +is called; the current mode reflects what \TeX\ should return to, after +the contribution list has been emptied. A call on |build_page| should +be immediately followed by `|goto big_switch|', which is \TeX's central +control point. + +@d contribute=80 {go here to link a node into the current page} + +@p @t\4@>@<Declare the procedure called |fire_up|@>@;@/ +procedure build_page; {append contributions to the current page} +label exit,done,done1,continue,contribute,update_heights; +var p:pointer; {the node being appended} +@!q,@!r:pointer; {nodes being examined} +@!b,@!c:integer; {badness and cost of current page} +@!pi:integer; {penalty to be added to the badness} +@!n:min_quarterword..255; {insertion box number} +@!delta,@!h,@!w:scaled; {sizes used for insertion calculations} +begin if (link(contrib_head)=null)or output_active then return; +repeat continue: p:=link(contrib_head);@/ +@<Update the values of |last_glue|, |last_penalty|, and |last_kern|@>; +@<Move node |p| to the current page; if it is time for a page break, + put the nodes following the break back onto the contribution list, + and |return| to the user's output routine if there is one@>; +until link(contrib_head)=null; +@<Make the contribution list empty by setting its tail to |contrib_head|@>; +exit:end; + +@ @d contrib_tail==nest[0].tail_field {tail of the contribution list} + +@<Make the contribution list empty...@>= +if nest_ptr=0 then tail:=contrib_head {vertical mode} +else contrib_tail:=contrib_head {other modes} + +@ @<Update the values of |last_glue|...@>= +if last_glue<>max_halfword then delete_glue_ref(last_glue); +last_penalty:=0; last_kern:=0; +if type(p)=glue_node then + begin last_glue:=glue_ptr(p); add_glue_ref(last_glue); + end +else begin last_glue:=max_halfword; + if type(p)=penalty_node then last_penalty:=penalty(p) + else if type(p)=kern_node then last_kern:=width(p); + end + +@ The code here is an example of a many-way switch into routines that +merge together in different places. Some people call this unstructured +programming, but the author doesn't see much wrong with it, as long as +@^Knuth, Donald Ervin@> +the various labels have a well-understood meaning. + +@<Move node |p| to the current page; ...@>= +@<If the current page is empty and node |p| is to be deleted, |goto done1|; + otherwise use node |p| to update the state of the current page; + if this node is an insertion, |goto contribute|; otherwise if this node + is not a legal breakpoint, |goto contribute| or |update_heights|; + otherwise set |pi| to the penalty associated with this breakpoint@>; +@<Check if node |p| is a new champion breakpoint; then \(if)if it is time for + a page break, prepare for output, and either fire up the user's + output routine and |return| or ship out the page and |goto done|@>; +if (type(p)<glue_node)or(type(p)>kern_node) then goto contribute; +update_heights:@<Update the current page measurements with respect to the + glue or kern specified by node~|p|@>; +contribute: @<Make sure that |page_max_depth| is not exceeded@>; +@<Link node |p| into the current page and |goto done|@>; +done1:@<Recycle node |p|@>; +done: + +@ @<Link node |p| into the current page and |goto done|@>= +link(page_tail):=p; page_tail:=p; +link(contrib_head):=link(p); link(p):=null; goto done + +@ @<Recycle node |p|@>= +link(contrib_head):=link(p); link(p):=null; flush_node_list(p) + +@ The title of this section is already so long, it seems best to avoid +making it more accurate but still longer, by mentioning the fact that a +kern node at the end of the contribution list will not be contributed until +we know its successor. + +@<If the current page is empty...@>= +case type(p) of +hlist_node,vlist_node,rule_node: if page_contents<box_there then + @<Initialize the current page, insert the \.{\\topskip} glue + ahead of |p|, and |goto continue|@> + else @<Prepare to move a box or rule node to the current page, + then |goto contribute|@>; +whatsit_node: @<Prepare to move whatsit |p| to the current page, + then |goto contribute|@>; +glue_node: if page_contents<box_there then goto done1 + else if precedes_break(page_tail) then pi:=0 + else goto update_heights; +kern_node: if page_contents<box_there then goto done1 + else if link(p)=null then return + else if type(link(p))=glue_node then pi:=0 + else goto update_heights; +penalty_node: if page_contents<box_there then goto done1@+else pi:=penalty(p); +mark_node: goto contribute; +ins_node: @<Append an insertion to the current page and |goto contribute|@>; +othercases confusion("page") +@:this can't happen page}{\quad page@> +endcases + +@ @<Initialize the current page, insert the \.{\\topskip} glue...@>= +begin if page_contents=empty then freeze_page_specs(box_there) +else page_contents:=box_there; +q:=new_skip_param(top_skip_code); {now |temp_ptr=glue_ptr(q)|} +if width(temp_ptr)>height(p) then width(temp_ptr):=width(temp_ptr)-height(p) +else width(temp_ptr):=0; +link(q):=p; link(contrib_head):=q; goto continue; +end + +@ @<Prepare to move a box or rule node to the current page...@>= +begin page_total:=page_total+page_depth+height(p); +page_depth:=depth(p); +goto contribute; +end + +@ @<Make sure that |page_max_depth| is not exceeded@>= +if page_depth>page_max_depth then + begin page_total:=@| + page_total+page_depth-page_max_depth;@/ + page_depth:=page_max_depth; + end; + +@ @<Update the current page measurements with respect to the glue...@>= +if type(p)=kern_node then q:=p +else begin q:=glue_ptr(p); + page_so_far[2+stretch_order(q)]:=@| + page_so_far[2+stretch_order(q)]+stretch(q);@/ + page_shrink:=page_shrink+shrink(q); + if (shrink_order(q)<>normal)and(shrink(q)<>0) then + begin@t@>@;@/ + print_err("Infinite glue shrinkage found on current page");@/ +@.Infinite glue shrinkage...@> + help4("The page about to be output contains some infinitely")@/ + ("shrinkable glue, e.g., `\vss' or `\vskip 0pt minus 1fil'.")@/ + ("Such glue doesn't belong there; but you can safely proceed,")@/ + ("since the offensive shrinkability has been made finite."); + error; + r:=new_spec(q); shrink_order(r):=normal; delete_glue_ref(q); + glue_ptr(p):=r; q:=r; + end; + end; +page_total:=page_total+page_depth+width(q); page_depth:=0 + +@ @<Check if node |p| is a new champion breakpoint; then \(if)...@>= +if pi<inf_penalty then + begin @<Compute the badness, |b|, of the current page, + using |awful_bad| if the box is too full@>; + if b<awful_bad then + if pi<=eject_penalty then c:=pi + else if b<inf_bad then c:=b+pi+insert_penalties + else c:=deplorable + else c:=b; + if insert_penalties>=10000 then c:=awful_bad; + @!stat if tracing_pages>0 then @<Display the page break cost@>;@+tats@;@/ + if c<=least_page_cost then + begin best_page_break:=p; best_size:=page_goal; + least_page_cost:=c; + r:=link(page_ins_head); + while r<>page_ins_head do + begin best_ins_ptr(r):=last_ins_ptr(r); + r:=link(r); + end; + end; + if (c=awful_bad)or(pi<=eject_penalty) then + begin fire_up(p); {output the current page at the best place} + if output_active then return; {user's output routine will act} + goto done; {the page has been shipped out by default output routine} + end; + end + +@ @<Display the page break cost@>= +begin begin_diagnostic; print_nl("%"); +print(" t="); print_totals;@/ +print(" g="); print_scaled(page_goal);@/ +print(" b="); +if b=awful_bad then print_char("*")@+else print_int(b); +@.*\relax@> +print(" p="); print_int(pi); +print(" c="); +if c=awful_bad then print_char("*")@+else print_int(c); +if c<=least_page_cost then print_char("#"); +end_diagnostic(false); +end + +@ @<Compute the badness, |b|, of the current page...@>= +if page_total<page_goal then + if (page_so_far[3]<>0) or (page_so_far[4]<>0) or@| + (page_so_far[5]<>0) then b:=0 + else b:=badness(page_goal-page_total,page_so_far[2]) +else if page_total-page_goal>page_shrink then b:=awful_bad +else b:=badness(page_total-page_goal,page_shrink) + +@ @<Append an insertion to the current page and |goto contribute|@>= +begin if page_contents=empty then freeze_page_specs(inserts_only); +n:=subtype(p); r:=page_ins_head; +while n>=subtype(link(r)) do r:=link(r); +n:=qo(n); +if subtype(r)<>qi(n) then + @<Create a page insertion node with |subtype(r)=qi(n)|, and + include the glue correction for box |n| in the + current page state@>; +if type(r)=split_up then insert_penalties:=insert_penalties+float_cost(p) +else begin last_ins_ptr(r):=p; + delta:=page_goal-page_total-page_depth+page_shrink; + {this much room is left if we shrink the maximum} + if count(n)=1000 then h:=height(p) + else h:=x_over_n(height(p),1000)*count(n); {this much room is needed} + if ((h<=0)or(h<=delta))and(height(p)+height(r)<=dimen(n)) then + begin page_goal:=page_goal-h; height(r):=height(r)+height(p); + end + else @<Find the best way to split the insertion, and change + |type(r)| to |split_up|@>; + end; +goto contribute; +end + +@ We take note of the value of \.{\\skip} |n| and the height plus depth +of \.{\\box}~|n| only when the first \.{\\insert}~|n| node is +encountered for a new page. A user who changes the contents of \.{\\box}~|n| +after that first \.{\\insert}~|n| had better be either extremely careful +or extremely lucky, or both. + +@<Create a page insertion node...@>= +begin q:=get_node(page_ins_node_size); link(q):=link(r); link(r):=q; r:=q; +subtype(r):=qi(n); type(r):=inserting; ensure_vbox(n); +if box(n)=null then height(r):=0 +else height(r):=height(box(n))+depth(box(n)); +best_ins_ptr(r):=null;@/ +q:=skip(n); +if count(n)=1000 then h:=height(r) +else h:=x_over_n(height(r),1000)*count(n); +page_goal:=page_goal-h-width(q);@/ +page_so_far[2+stretch_order(q)]:=@|page_so_far[2+stretch_order(q)]+stretch(q);@/ +page_shrink:=page_shrink+shrink(q); +if (shrink_order(q)<>normal)and(shrink(q)<>0) then + begin print_err("Infinite glue shrinkage inserted from "); print_esc("skip"); +@.Infinite glue shrinkage...@> + print_int(n); + help3("The correction glue for page breaking with insertions")@/ + ("must have finite shrinkability. But you may proceed,")@/ + ("since the offensive shrinkability has been made finite."); + error; + end; +end + +@ Here is the code that will split a long footnote between pages, in an +emergency. The current situation deserves to be recapitulated: Node |p| +is an insertion into box |n|; the insertion will not fit, in its entirety, +either because it would make the total contents of box |n| greater than +\.{\\dimen} |n|, or because it would make the incremental amount of growth +|h| greater than the available space |delta|, or both. (This amount |h| has +been weighted by the insertion scaling factor, i.e., by \.{\\count} |n| +over 1000.) Now we will choose the best way to break the vlist of the +insertion, using the same criteria as in the \.{\\vsplit} operation. + +@<Find the best way to split the insertion...@>= +begin if count(n)<=0 then w:=max_dimen +else begin w:=page_goal-page_total-page_depth; + if count(n)<>1000 then w:=x_over_n(w,count(n))*1000; + end; +if w>dimen(n)-height(r) then w:=dimen(n)-height(r); +q:=vert_break(ins_ptr(p),w,depth(p)); +height(r):=height(r)+best_height_plus_depth; +@!stat if tracing_pages>0 then @<Display the insertion split cost@>;@+tats@;@/ +if count(n)<>1000 then + best_height_plus_depth:=x_over_n(best_height_plus_depth,1000)*count(n); +page_goal:=page_goal-best_height_plus_depth; +type(r):=split_up; broken_ptr(r):=q; broken_ins(r):=p; +if q=null then insert_penalties:=insert_penalties+eject_penalty +else if type(q)=penalty_node then insert_penalties:=insert_penalties+penalty(q); +end + +@ @<Display the insertion split cost@>= +begin begin_diagnostic; print_nl("% split"); print_int(n); +@.split@> +print(" to "); print_scaled(w); +print_char(","); print_scaled(best_height_plus_depth);@/ +print(" p="); +if q=null then print_int(eject_penalty) +else if type(q)=penalty_node then print_int(penalty(q)) +else print_char("0"); +end_diagnostic(false); +end + +@ When the page builder has looked at as much material as could appear before +the next page break, it makes its decision. The break that gave minimum +badness will be used to put a completed ``page'' into box 255, with insertions +appended to their other boxes. + +We also set the values of |top_mark|, |first_mark|, and |bot_mark|. The +program uses the fact that |bot_mark<>null| implies |first_mark<>null|; +it also knows that |bot_mark=null| implies |top_mark=first_mark=null|. + +The |fire_up| subroutine prepares to output the current page at the best +place; then it fires up the user's output routine, if there is one, +or it simply ships out the page. There is one parameter, |c|, which represents +the node that was being contributed to the page when the decision to +force an output was made. + +@<Declare the procedure called |fire_up|@>= +procedure fire_up(@!c:pointer); +label exit; +var p,@!q,@!r,@!s:pointer; {nodes being examined and/or changed} +@!prev_p:pointer; {predecessor of |p|} +@!n:min_quarterword..255; {insertion box number} +@!wait:boolean; {should the present insertion be held over?} +@!save_vbadness:integer; {saved value of |vbadness|} +@!save_vfuzz: scaled; {saved value of |vfuzz|} +@!save_split_top_skip: pointer; {saved value of |split_top_skip|} +begin @<Set the value of |output_penalty|@>; +if bot_mark<>null then + begin if top_mark<>null then delete_token_ref(top_mark); + top_mark:=bot_mark; add_token_ref(top_mark); + delete_token_ref(first_mark); first_mark:=null; + end; +@<Put the \(o)optimal current page into box 255, update |first_mark| and + |bot_mark|, append insertions to their boxes, and put the + remaining nodes back on the contribution list@>; +if (top_mark<>null)and(first_mark=null) then + begin first_mark:=top_mark; add_token_ref(top_mark); + end; +if output_routine<>null then + if dead_cycles>=max_dead_cycles then + @<Explain that too many dead cycles have occurred in a row@> + else @<Fire up the user's output routine and |return|@>; +@<Perform the default output routine@>; +exit:end; + +@ @<Set the value of |output_penalty|@>= +if type(best_page_break)=penalty_node then + begin geq_word_define(int_base+output_penalty_code,penalty(best_page_break)); + penalty(best_page_break):=inf_penalty; + end +else geq_word_define(int_base+output_penalty_code,inf_penalty) + +@ As the page is finally being prepared for output, +pointer |p| runs through the vlist, with |prev_p| trailing behind; +pointer |q| is the tail of a list of insertions that +are being held over for a subsequent page. + +@<Put the \(o)optimal current page into box 255...@>= +if c=best_page_break then best_page_break:=null; {|c| not yet linked in} +@<Ensure that box 255 is empty before output@>; +insert_penalties:=0; {this will count the number of insertions held over} +save_split_top_skip:=split_top_skip; +if holding_inserts<=0 then + @<Prepare all the boxes involved in insertions to act as queues@>; +q:=hold_head; link(q):=null; prev_p:=page_head; p:=link(prev_p); +while p<>best_page_break do + begin if type(p)=ins_node then + begin if holding_inserts<=0 then + @<Either insert the material specified by node |p| into the + appropriate box, or hold it for the next page; + also delete node |p| from the current page@>; + end + else if type(p)=mark_node then @<Update the values of + |first_mark| and |bot_mark|@>; + prev_p:=p; p:=link(prev_p); + end; +split_top_skip:=save_split_top_skip; +@<Break the current page at node |p|, put it in box~255, + and put the remaining nodes on the contribution list@>; +@<Delete \(t)the page-insertion nodes@> + +@ @<Ensure that box 255 is empty before output@>= +if box(255)<>null then + begin print_err(""); print_esc("box"); print("255 is not void"); +@:box255}{\.{\\box255 is not void}@> + help2("You shouldn't use \box255 except in \output routines.")@/ + ("Proceed, and I'll discard its present contents."); + box_error(255); + end + +@ @<Update the values of |first_mark| and |bot_mark|@>= +begin if first_mark=null then + begin first_mark:=mark_ptr(p); + add_token_ref(first_mark); + end; +if bot_mark<>null then delete_token_ref(bot_mark); +bot_mark:=mark_ptr(p); add_token_ref(bot_mark); +end + +@ When the following code is executed, the current page runs from node +|link(page_head)| to node |prev_p|, and the nodes from |p| to |page_tail| +are to be placed back at the front of the contribution list. Furthermore +the heldover insertions appear in a list from |link(hold_head)| to |q|; we +will put them into the current page list for safekeeping while the user's +output routine is active. We might have |q=hold_head|; and |p=null| if +and only if |prev_p=page_tail|. Error messages are suppressed within +|vpackage|, since the box might appear to be overfull or underfull simply +because the stretch and shrink from the \.{\\skip} registers for inserts +are not actually present in the box. + +@<Break the current page at node |p|, put it...@>= +if p<>null then + begin if link(contrib_head)=null then + if nest_ptr=0 then tail:=page_tail + else contrib_tail:=page_tail; + link(page_tail):=link(contrib_head); + link(contrib_head):=p; + link(prev_p):=null; + end; +save_vbadness:=vbadness; vbadness:=inf_bad; +save_vfuzz:=vfuzz; vfuzz:=max_dimen; {inhibit error messages} +box(255):=vpackage(link(page_head),best_size,exactly,page_max_depth); +vbadness:=save_vbadness; vfuzz:=save_vfuzz; +if last_glue<>max_halfword then delete_glue_ref(last_glue); +@<Start a new current page@>; {this sets |last_glue:=max_halfword|} +if q<>hold_head then + begin link(page_head):=link(hold_head); page_tail:=q; + end + +@ If many insertions are supposed to go into the same box, we want to know +the position of the last node in that box, so that we don't need to waste time +when linking further information into it. The |last_ins_ptr| fields of the +page insertion nodes are therefore used for this purpose during the +packaging phase. + +@<Prepare all the boxes involved in insertions to act as queues@>= +begin r:=link(page_ins_head); +while r<>page_ins_head do + begin if best_ins_ptr(r)<>null then + begin n:=qo(subtype(r)); ensure_vbox(n); + if box(n)=null then box(n):=new_null_box; + p:=box(n)+list_offset; + while link(p)<>null do p:=link(p); + last_ins_ptr(r):=p; + end; + r:=link(r); + end; +end + +@ @<Delete \(t)the page-insertion nodes@>= +r:=link(page_ins_head); +while r<>page_ins_head do + begin q:=link(r); free_node(r,page_ins_node_size); r:=q; + end; +link(page_ins_head):=page_ins_head + +@ We will set |best_ins_ptr:=null| and package the box corresponding to +insertion node~|r|, just after making the final insertion into that box. +If this final insertion is `|split_up|', the remainder after splitting +and pruning (if any) will be carried over to the next page. + +@<Either insert the material specified by node |p| into...@>= +begin r:=link(page_ins_head); +while subtype(r)<>subtype(p) do r:=link(r); +if best_ins_ptr(r)=null then wait:=true +else begin wait:=false; s:=last_ins_ptr(r); link(s):=ins_ptr(p); + if best_ins_ptr(r)=p then + @<Wrap up the box specified by node |r|, splitting node |p| if + called for; set |wait:=true| if node |p| holds a remainder after + splitting@> + else begin while link(s)<>null do s:=link(s); + last_ins_ptr(r):=s; + end; + end; +@<Either append the insertion node |p| after node |q|, and remove it + from the current page, or delete |node(p)|@>; +end + +@ @<Wrap up the box specified by node |r|, splitting node |p| if...@>= +begin if type(r)=split_up then + if (broken_ins(r)=p)and(broken_ptr(r)<>null) then + begin while link(s)<>broken_ptr(r) do s:=link(s); + link(s):=null; + split_top_skip:=split_top_ptr(p); + ins_ptr(p):=prune_page_top(broken_ptr(r)); + if ins_ptr(p)<>null then + begin temp_ptr:=vpack(ins_ptr(p),natural); + height(p):=height(temp_ptr)+depth(temp_ptr); + free_node(temp_ptr,box_node_size); wait:=true; + end; + end; +best_ins_ptr(r):=null; +n:=qo(subtype(r)); +temp_ptr:=list_ptr(box(n)); +free_node(box(n),box_node_size); +box(n):=vpack(temp_ptr,natural); +end + +@ @<Either append the insertion node |p|...@>= +link(prev_p):=link(p); link(p):=null; +if wait then + begin link(q):=p; q:=p; incr(insert_penalties); + end +else begin delete_glue_ref(split_top_ptr(p)); + free_node(p,ins_node_size); + end; +p:=prev_p + +@ The list of heldover insertions, running from |link(page_head)| to +|page_tail|, must be moved to the contribution list when the user has +specified no output routine. + +@<Perform the default output routine@>= +begin if link(page_head)<>null then + begin if link(contrib_head)=null then + if nest_ptr=0 then tail:=page_tail@+else contrib_tail:=page_tail + else link(page_tail):=link(contrib_head); + link(contrib_head):=link(page_head); + link(page_head):=null; page_tail:=page_head; + end; +ship_out(box(255)); box(255):=null; +end + +@ @<Explain that too many dead cycles have occurred in a row@>= +begin print_err("Output loop---"); print_int(dead_cycles); +@.Output loop...@> +print(" consecutive dead cycles"); +help3("I've concluded that your \output is awry; it never does a")@/ +("\shipout, so I'm shipping \box255 out myself. Next time")@/ +("increase \maxdeadcycles if you want me to be more patient!"); error; +end + +@ @<Fire up the user's output routine and |return|@>= +begin output_active:=true; +incr(dead_cycles); +push_nest; mode:=-vmode; prev_depth:=ignore_depth; mode_line:=-line; +begin_token_list(output_routine,output_text); +new_save_level(output_group); normal_paragraph; +scan_left_brace; +return; +end + +@ When the user's output routine finishes, it has constructed a vlist +in internal vertical mode, and \TeX\ will do the following: + +@<Resume the page builder after an output routine has come to an end@>= +begin if (loc<>null) or + ((token_type<>output_text)and(token_type<>backed_up)) then + @<Recover from an unbalanced output routine@>; +end_token_list; {conserve stack space in case more outputs are triggered} +end_graf; unsave; output_active:=false; insert_penalties:=0;@/ +@<Ensure that box 255 is empty after output@>; +if tail<>head then {current list goes after heldover insertions} + begin link(page_tail):=link(head); + page_tail:=tail; + end; +if link(page_head)<>null then {and both go before heldover contributions} + begin if link(contrib_head)=null then contrib_tail:=page_tail; + link(page_tail):=link(contrib_head); + link(contrib_head):=link(page_head); + link(page_head):=null; page_tail:=page_head; + end; +pop_nest; build_page; +end + +@ @<Recover from an unbalanced output routine@>= +begin print_err("Unbalanced output routine"); +@.Unbalanced output routine@> +help2("Your sneaky output routine has problematic {'s and/or }'s.")@/ +("I can't handle that very well; good luck."); error; +repeat get_token; +until loc=null; +end {loops forever if reading from a file, since |null=min_halfword<=0|} + +@ @<Ensure that box 255 is empty after output@>= +if box(255)<>null then + begin print_err("Output routine didn't use all of "); + print_esc("box"); print_int(255); +@.Output routine didn't use...@> + help3("Your \output commands should empty \box255,")@/ + ("e.g., by saying `\shipout\box255'.")@/ + ("Proceed; I'll discard its present contents."); + box_error(255); + end + +@* \[46] The chief executive. +We come now to the |main_control| routine, which contains the master +switch that causes all the various pieces of \TeX\ to do their things, +in the right order. + +In a sense, this is the grand climax of the program: It applies all the +tools that we have worked so hard to construct. In another sense, this is +the messiest part of the program: It necessarily refers to other pieces +of code all over the place, so that a person can't fully understand what is +going on without paging back and forth to be reminded of conventions that +are defined elsewhere. We are now at the hub of the web, the central nervous +system that touches most of the other parts and ties them together. +@^brain@> + +The structure of |main_control| itself is quite simple. There's a label +called |big_switch|, at which point the next token of input is fetched +using |get_x_token|. Then the program branches at high speed into one of +about 100 possible directions, based on the value of the current +mode and the newly fetched command code; the sum |abs(mode)+cur_cmd| +indicates what to do next. For example, the case `|vmode+letter|' arises +when a letter occurs in vertical mode (or internal vertical mode); this +case leads to instructions that initialize a new paragraph and enter +horizontal mode. + +The big |case| statement that contains this multiway switch has been labeled +|reswitch|, so that the program can |goto reswitch| when the next token +has already been fetched. Most of the cases are quite short; they call +an ``action procedure'' that does the work for that case, and then they +either |goto reswitch| or they ``fall through'' to the end of the |case| +statement, which returns control back to |big_switch|. Thus, |main_control| +is not an extremely large procedure, in spite of the multiplicity of things +it must do; it is small enough to be handled by \PASCAL\ compilers that put +severe restrictions on procedure size. +@!@^action procedure@> + +One case is singled out for special treatment, because it accounts for most +of \TeX's activities in typical applications. The process of reading simple +text and converting it into |char_node| records, while looking for ligatures +and kerns, is part of \TeX's ``inner loop''; the whole program runs +efficiently when its inner loop is fast, so this part has been written +with particular care. + +@ We shall concentrate first on the inner loop of |main_control|, deferring +consideration of the other cases until later. +@^inner loop@> + +@d big_switch=60 {go here to branch on the next token of input} +@d main_loop=70 {go here to typeset a string of consecutive characters} +@d main_loop_wrapup=80 {go here to finish a character or ligature} +@d main_loop_move=90 {go here to advance the ligature cursor} +@d main_loop_move_lig=95 {same, when advancing past a generated ligature} +@d main_loop_lookahead=100 {go here to bring in another character, if any} +@d main_lig_loop=110 {go here to check for ligatures or kerning} +@d append_normal_space=120 {go here to append a normal space between words} + +@p @t\4@>@<Declare action procedures for use by |main_control|@>@; +@t\4@>@<Declare the procedure called |handle_right_brace|@>@; +procedure main_control; {governs \TeX's activities} +label big_switch,reswitch,main_loop,main_loop_wrapup, + main_loop_move,main_loop_move+1,main_loop_move+2,main_loop_move_lig, + main_loop_lookahead,main_loop_lookahead+1, + main_lig_loop,main_lig_loop+1,main_lig_loop+2, + append_normal_space,exit; +var@!t:integer; {general-purpose temporary variable} +begin if every_job<>null then begin_token_list(every_job,every_job_text); +big_switch: get_x_token;@/ +reswitch: @<Give diagnostic information, if requested@>; +case abs(mode)+cur_cmd of +hmode+letter,hmode+other_char,hmode+char_given: goto main_loop; +hmode+char_num: begin scan_char_num; cur_chr:=cur_val; goto main_loop;@+end; +hmode+no_boundary: begin get_x_token; + if (cur_cmd=letter)or(cur_cmd=other_char)or(cur_cmd=char_given)or + (cur_cmd=char_num) then cancel_boundary:=true; + goto reswitch; + end; +hmode+spacer: if space_factor=1000 then goto append_normal_space + else app_space; +hmode+ex_space,mmode+ex_space: goto append_normal_space; +@t\4@>@<Cases of |main_control| that are not part of the inner loop@>@; +end; {of the big |case| statement} +goto big_switch; +main_loop:@<Append character |cur_chr| and the following characters (if~any) + to the current hlist in the current font; |goto reswitch| when + a non-character has been fetched@>; +append_normal_space:@<Append a normal inter-word space to the current list, + then |goto big_switch|@>; +exit:end; + +@ When a new token has just been fetched at |big_switch|, we have an +ideal place to monitor \TeX's activity. +@^debugging@> + +@<Give diagnostic information, if requested@>= +if interrupt<>0 then if OK_to_interrupt then + begin back_input; check_interrupt; goto big_switch; + end; +@!debug if panicking then check_mem(false);@+@;@+gubed +if tracing_commands>0 then show_cur_cmd_chr + +@ The following part of the program was first written in a structured +manner, according to the philosophy that ``premature optimization is +the root of all evil.'' Then it was rearranged into pieces of +spaghetti so that the most common actions could proceed with little or +no redundancy. + +The original unoptimized form of this algorithm resembles the +|reconstitute| procedure, which was described earlier in connection with +hyphenation. Again we have an implied ``cursor'' between characters +|cur_l| and |cur_r|. The main difference is that the |lig_stack| can now +contain a charnode as well as pseudo-ligatures; that stack is now +usually nonempty, because the next character of input (if any) has been +appended to it. In |main_control| we have +$$|cur_r|=\cases{|character(lig_stack)|,&if |lig_stack>null|;\cr + |font_bchar[cur_font]|,&otherwise;\cr}$$ +except when |character(lig_stack)=font_false_bchar[cur_font]|. +Several additional global variables are needed. + +@<Glob...@>= +@!main_f:internal_font_number; {the current font} +@!main_i:four_quarters; {character information bytes for |cur_l|} +@!main_j:four_quarters; {ligature/kern command} +@!main_k:font_index; {index into |font_info|} +@!main_p:pointer; {temporary register for list manipulation} +@!main_s:integer; {space factor value} +@!bchar:halfword; {right boundary character of current font, or |non_char|} +@!false_bchar:halfword; {nonexistent character matching |bchar|, or |non_char|} +@!cancel_boundary:boolean; {should the left boundary be ignored?} +@!ins_disc:boolean; {should we insert a discretionary node?} + +@ The boolean variables of the main loop are normally false, and always reset +to false before the loop is left. That saves us the extra work of initializing +each time. + +@<Set init...@>= +ligature_present:=false; cancel_boundary:=false; lft_hit:=false; rt_hit:=false; +ins_disc:=false; + +@ We leave the |space_factor| unchanged if |sf_code(cur_chr)=0|; otherwise we +set it equal to |sf_code(cur_chr)|, except that it should never change +from a value less than 1000 to a value exceeding 1000. The most common +case is |sf_code(cur_chr)=1000|, so we want that case to be fast. + +The overall structure of the main loop is presented here. Some program labels +are inside the individual sections. + +@d adjust_space_factor==@t@>@;@/ + main_s:=sf_code(cur_chr); + if main_s=1000 then space_factor:=1000 + else if main_s<1000 then + begin if main_s>0 then space_factor:=main_s; + end + else if space_factor<1000 then space_factor:=1000 + else space_factor:=main_s + +@<Append character |cur_chr|...@>= +adjust_space_factor;@/ +main_f:=cur_font; +bchar:=font_bchar[main_f]; false_bchar:=font_false_bchar[main_f]; +if mode>0 then if language<>clang then fix_language; +fast_get_avail(lig_stack); font(lig_stack):=main_f; cur_l:=qi(cur_chr); +character(lig_stack):=cur_l;@/ +cur_q:=tail; +if cancel_boundary then + begin cancel_boundary:=false; main_k:=non_address; + end +else main_k:=bchar_label[main_f]; +if main_k=non_address then goto main_loop_move+2; {no left boundary processing} +cur_r:=cur_l; cur_l:=non_char; +goto main_lig_loop+1; {begin with cursor after left boundary} +@# +main_loop_wrapup:@<Make a ligature node, if |ligature_present|; + insert a null discretionary, if appropriate@>; +main_loop_move:@<If the cursor is immediately followed by the right boundary, + |goto reswitch|; if it's followed by an invalid character, |goto big_switch|; + otherwise move the cursor one step to the right and |goto main_lig_loop|@>; +main_loop_lookahead:@<Look ahead for another character, or leave |lig_stack| + empty if there's none there@>; +main_lig_loop:@<If there's a ligature/kern command relevant to |cur_l| and + |cur_r|, adjust the text appropriately; exit to |main_loop_wrapup|@>; +main_loop_move_lig:@<Move the cursor past a pseudo-ligature, then + |goto main_loop_lookahead| or |main_lig_loop|@> + +@ If the current horizontal list is empty, the reference to |character(tail)| +here is not strictly legal, since |tail| will be a node freshly returned by +|get_avail|. But this should cause no problem on most implementations, and we +do want the inner loop to be fast. +@^dirty \PASCAL@> + +A discretionary break is not inserted for an explicit hyphen when we are in +restricted horizontal mode. In particular, this avoids putting discretionary +nodes inside of other discretionaries. + +@d pack_lig(#)== {the parameter is either |rt_hit| or |false|} + begin main_p:=new_ligature(main_f,cur_l,link(cur_q)); + if lft_hit then + begin subtype(main_p):=2; lft_hit:=false; + end; + if # then if lig_stack=null then + begin incr(subtype(main_p)); rt_hit:=false; + end; + link(cur_q):=main_p; tail:=main_p; ligature_present:=false; + end + +@d wrapup(#)==if cur_l<non_char then + begin if character(tail)=qi(hyphen_char[main_f]) then if link(cur_q)>null then + ins_disc:=true; + if ligature_present then pack_lig(#); + if ins_disc then + begin ins_disc:=false; + if mode>0 then tail_append(new_disc); + end; + end + +@<Make a ligature node, if |ligature_present|;...@>= +wrapup(rt_hit) + +@ @<If the cursor is immediately followed by the right boundary...@>= +if lig_stack=null then goto reswitch; +cur_q:=tail; cur_l:=character(lig_stack); +main_loop_move+1:if not is_char_node(lig_stack) then goto main_loop_move_lig; +main_loop_move+2:if(cur_chr<font_bc[main_f])or(cur_chr>font_ec[main_f]) then + begin char_warning(main_f,cur_chr); free_avail(lig_stack); goto big_switch; + end; +main_i:=char_info(main_f)(cur_l); +if not char_exists(main_i) then + begin char_warning(main_f,cur_chr); free_avail(lig_stack); goto big_switch; + end; +tail_append(lig_stack) {|main_loop_lookahead| is next} + +@ Here we are at |main_loop_move_lig|. +When we begin this code we have |cur_q=tail| and |cur_l=character(lig_stack)|. + +@<Move the cursor past a pseudo-ligature...@>= +main_p:=lig_ptr(lig_stack); +if main_p>null then tail_append(main_p); +temp_ptr:=lig_stack; lig_stack:=link(temp_ptr); +free_node(temp_ptr,small_node_size); +main_i:=char_info(main_f)(cur_l); ligature_present:=true; +if lig_stack=null then + if main_p>null then goto main_loop_lookahead + else cur_r:=bchar +else cur_r:=character(lig_stack); +goto main_lig_loop + +@ The result of \.{\\char} can participate in a ligature or kern, so we must +look ahead for it. + +@<Look ahead for another character...@>= +get_next; {set only |cur_cmd| and |cur_chr|, for speed} +if cur_cmd=letter then goto main_loop_lookahead+1; +if cur_cmd=other_char then goto main_loop_lookahead+1; +if cur_cmd=char_given then goto main_loop_lookahead+1; +x_token; {now expand and set |cur_cmd|, |cur_chr|, |cur_tok|} +if cur_cmd=letter then goto main_loop_lookahead+1; +if cur_cmd=other_char then goto main_loop_lookahead+1; +if cur_cmd=char_given then goto main_loop_lookahead+1; +if cur_cmd=char_num then + begin scan_char_num; cur_chr:=cur_val; goto main_loop_lookahead+1; + end; +if cur_cmd=no_boundary then bchar:=non_char; +cur_r:=bchar; lig_stack:=null; goto main_lig_loop; +main_loop_lookahead+1: adjust_space_factor; +fast_get_avail(lig_stack); font(lig_stack):=main_f; +cur_r:=qi(cur_chr); character(lig_stack):=cur_r; +if cur_r=false_bchar then cur_r:=non_char {this prevents spurious ligatures} + +@ Even though comparatively few characters have a lig/kern program, several +of the instructions here count as part of \TeX's inner loop, since a +@^inner loop@> +potentially long sequential search must be performed. For example, tests with +Computer Modern Roman showed that about 40 per cent of all characters +actually encountered in practice had a lig/kern program, and that about four +lig/kern commands were investigated for every such character. + +At the beginning of this code we have |main_i=char_info(main_f)(cur_l)|. + +@<If there's a ligature/kern command...@>= +if char_tag(main_i)<>lig_tag then goto main_loop_wrapup; +main_k:=lig_kern_start(main_f)(main_i); main_j:=font_info[main_k].qqqq; +if skip_byte(main_j)<=stop_flag then goto main_lig_loop+2; +main_k:=lig_kern_restart(main_f)(main_j); +main_lig_loop+1:main_j:=font_info[main_k].qqqq; +main_lig_loop+2:if next_char(main_j)=cur_r then + if skip_byte(main_j)<=stop_flag then + @<Do ligature or kern command, returning to |main_lig_loop| + or |main_loop_wrapup| or |main_loop_move|@>; +if skip_byte(main_j)=qi(0) then incr(main_k) +else begin if skip_byte(main_j)>=stop_flag then goto main_loop_wrapup; + main_k:=main_k+qo(skip_byte(main_j))+1; + end; +goto main_lig_loop+1 + +@ When a ligature or kern instruction matches a character, we know from +|read_font_info| that the character exists in the font, even though we +haven't verified its existence in the normal way. + +This section could be made into a subroutine, if the code inside +|main_control| needs to be shortened. + +\chardef\?='174 % vertical line to indicate character retention + +@<Do ligature or kern command...@>= +begin if op_byte(main_j)>=kern_flag then + begin wrapup(rt_hit); + tail_append(new_kern(char_kern(main_f)(main_j))); goto main_loop_move; + end; +if cur_l=non_char then lft_hit:=true +else if lig_stack=null then rt_hit:=true; +check_interrupt; {allow a way out in case there's an infinite ligature loop} +case op_byte(main_j) of +qi(1),qi(5):begin cur_l:=rem_byte(main_j); {\.{=:\?}, \.{=:\?>}} + main_i:=char_info(main_f)(cur_l); ligature_present:=true; + end; +qi(2),qi(6):begin cur_r:=rem_byte(main_j); {\.{\?=:}, \.{\?=:>}} + if lig_stack=null then {right boundary character is being consumed} + begin lig_stack:=new_lig_item(cur_r); bchar:=non_char; + end + else if is_char_node(lig_stack) then {|link(lig_stack)=null|} + begin main_p:=lig_stack; lig_stack:=new_lig_item(cur_r); + lig_ptr(lig_stack):=main_p; + end + else character(lig_stack):=cur_r; + end; +qi(3):begin cur_r:=rem_byte(main_j); {\.{\?=:\?}} + main_p:=lig_stack; lig_stack:=new_lig_item(cur_r); + link(lig_stack):=main_p; + end; +qi(7),qi(11):begin wrapup(false); {\.{\?=:\?>}, \.{\?=:\?>>}} + cur_q:=tail; cur_l:=rem_byte(main_j); + main_i:=char_info(main_f)(cur_l); ligature_present:=true; + end; +othercases begin cur_l:=rem_byte(main_j); ligature_present:=true; {\.{=:}} + if lig_stack=null then goto main_loop_wrapup + else goto main_loop_move+1; + end +endcases; +if op_byte(main_j)>qi(4) then + if op_byte(main_j)<>qi(7) then goto main_loop_wrapup; +if cur_l<non_char then goto main_lig_loop; +main_k:=bchar_label[main_f]; goto main_lig_loop+1; +end + +@ The occurrence of blank spaces is almost part of \TeX's inner loop, +@^inner loop@> +since we usually encounter about one space for every five non-blank characters. +Therefore |main_control| gives second-highest priority to ordinary spaces. + +When a glue parameter like \.{\\spaceskip} is set to `\.{0pt}', we will +see to it later that the corresponding glue specification is precisely +|zero_glue|, not merely a pointer to some specification that happens +to be full of zeroes. Therefore it is simple to test whether a glue parameter +is zero or~not. + +@<Append a normal inter-word space...@>= +if space_skip=zero_glue then + begin @<Find the glue specification, |main_p|, for + text spaces in the current font@>; + temp_ptr:=new_glue(main_p); + end +else temp_ptr:=new_param_glue(space_skip_code); +link(tail):=temp_ptr; tail:=temp_ptr; +goto big_switch + +@ Having |font_glue| allocated for each text font saves both time and memory. +If any of the three spacing parameters are subsequently changed by the +use of \.{\\fontdimen}, the |find_font_dimen| procedure deallocates the +|font_glue| specification allocated here. + +@<Find the glue specification...@>= +begin main_p:=font_glue[cur_font]; +if main_p=null then + begin main_p:=new_spec(zero_glue); main_k:=param_base[cur_font]+space_code; + width(main_p):=font_info[main_k].sc; {that's |space(cur_font)|} + stretch(main_p):=font_info[main_k+1].sc; {and |space_stretch(cur_font)|} + shrink(main_p):=font_info[main_k+2].sc; {and |space_shrink(cur_font)|} + font_glue[cur_font]:=main_p; + end; +end + +@ @<Declare act...@>= +procedure app_space; {handle spaces when |space_factor<>1000|} +var@!q:pointer; {glue node} +begin if (space_factor>=2000)and(xspace_skip<>zero_glue) then + q:=new_param_glue(xspace_skip_code) +else begin if space_skip<>zero_glue then main_p:=space_skip + else @<Find the glue specification...@>; + main_p:=new_spec(main_p); + @<Modify the glue specification in |main_p| according to the space factor@>; + q:=new_glue(main_p); glue_ref_count(main_p):=null; + end; +link(tail):=q; tail:=q; +end; + +@ @<Modify the glue specification in |main_p| according to the space factor@>= +if space_factor>=2000 then width(main_p):=width(main_p)+extra_space(cur_font); +stretch(main_p):=xn_over_d(stretch(main_p),space_factor,1000); +shrink(main_p):=xn_over_d(shrink(main_p),1000,space_factor) + +@ Whew---that covers the main loop. We can now proceed at a leisurely +pace through the other combinations of possibilities. + +@d any_mode(#)==vmode+#,hmode+#,mmode+# {for mode-independent commands} + +@<Cases of |main_control| that are not part of the inner loop@>= +any_mode(relax),vmode+spacer,mmode+spacer,mmode+no_boundary:do_nothing; +any_mode(ignore_spaces): begin @<Get the next non-blank non-call...@>; + goto reswitch; + end; +vmode+stop: if its_all_over then return; {this is the only way out} +@t\4@>@<Forbidden cases detected in |main_control|@>@+@,any_mode(mac_param): + report_illegal_case; +@<Math-only cases in non-math modes, or vice versa@>: insert_dollar_sign; +@t\4@>@<Cases of |main_control| that build boxes and lists@>@; +@t\4@>@<Cases of |main_control| that don't depend on |mode|@>@; +@t\4@>@<Cases of |main_control| that are for extensions to \TeX@>@; + +@ Here is a list of cases where the user has probably gotten into or out of math +mode by mistake. \TeX\ will insert a dollar sign and rescan the current token. + +@d non_math(#)==vmode+#,hmode+# + +@<Math-only cases in non-math modes...@>= +non_math(sup_mark), non_math(sub_mark), non_math(math_char_num), +non_math(math_given), non_math(math_comp), non_math(delim_num), +non_math(left_right), non_math(above), non_math(radical), +non_math(math_style), non_math(math_choice), non_math(vcenter), +non_math(non_script), non_math(mkern), non_math(limit_switch), +non_math(mskip), non_math(math_accent), +mmode+endv, mmode+par_end, mmode+stop, mmode+vskip, mmode+un_vbox, +mmode+valign, mmode+hrule + +@ @<Declare action...@>= +procedure insert_dollar_sign; +begin back_input; cur_tok:=math_shift_token+"$"; +print_err("Missing $ inserted"); +@.Missing \$ inserted@> +help2("I've inserted a begin-math/end-math symbol since I think")@/ +("you left one out. Proceed, with fingers crossed."); ins_error; +end; + +@ When erroneous situations arise, \TeX\ usually issues an error message +specific to the particular error. For example, `\.{\\noalign}' should +not appear in any mode, since it is recognized by the |align_peek| routine +in all of its legitimate appearances; a special error message is given +when `\.{\\noalign}' occurs elsewhere. But sometimes the most appropriate +error message is simply that the user is not allowed to do what he or she +has attempted. For example, `\.{\\moveleft}' is allowed only in vertical mode, +and `\.{\\lower}' only in non-vertical modes. Such cases are enumerated +here and in the other sections referred to under `See also \dots.' + +@<Forbidden cases...@>= +vmode+vmove,hmode+hmove,mmode+hmove,any_mode(last_item), + +@ The `|you_cant|' procedure prints a line saying that the current command +is illegal in the current mode; it identifies these things symbolically. + +@<Declare action...@>= +procedure you_cant; +begin print_err("You can't use `"); +@.You can't use x in y mode@> +print_cmd_chr(cur_cmd,cur_chr); +print("' in "); print_mode(mode); +end; + +@ @<Declare act...@>= +procedure report_illegal_case; +begin you_cant; +help4("Sorry, but I'm not programmed to handle this case;")@/ +("I'll just pretend that you didn't ask for it.")@/ +("If you're in the wrong mode, you might be able to")@/ +("return to the right one by typing `I}' or `I$' or `I\par'.");@/ +error; +end; + +@ Some operations are allowed only in privileged modes, i.e., in cases +that |mode>0|. The |privileged| function is used to detect violations +of this rule; it issues an error message and returns |false| if the +current |mode| is negative. + +@<Declare act...@>= +function privileged:boolean; +begin if mode>0 then privileged:=true +else begin report_illegal_case; privileged:=false; + end; +end; + +@ Either \.{\\dump} or \.{\\end} will cause |main_control| to enter the +endgame, since both of them have `|stop|' as their command code. + +@<Put each...@>= +primitive("end",stop,0);@/ +@!@:end_}{\.{\\end} primitive@> +primitive("dump",stop,1);@/ +@!@:dump_}{\.{\\dump} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +stop:if chr_code=1 then print_esc("dump")@+else print_esc("end"); + +@ We don't want to leave |main_control| immediately when a |stop| command +is sensed, because it may be necessary to invoke an \.{\\output} routine +several times before things really grind to a halt. (The output routine +might even say `\.{\\gdef\\end\{...\}}', to prolong the life of the job.) +Therefore |its_all_over| is |true| only when the current page +and contribution list are empty, and when the last output was not a +``dead cycle.'' + +@<Declare act...@>= +function its_all_over:boolean; {do this when \.{\\end} or \.{\\dump} occurs} +label exit; +begin if privileged then + begin if (page_head=page_tail)and(head=tail)and(dead_cycles=0) then + begin its_all_over:=true; return; + end; + back_input; {we will try to end again after ejecting residual material} + tail_append(new_null_box); + width(tail):=hsize; + tail_append(new_glue(fill_glue)); + tail_append(new_penalty(-@'10000000000));@/ + build_page; {append \.{\\hbox to \\hsize\{\}\\vfill\\penalty-'10000000000}} + end; +its_all_over:=false; +exit:end; + +@* \[47] Building boxes and lists. +The most important parts of |main_control| are concerned with \TeX's +chief mission of box-making. We need to control the activities that put +entries on vlists and hlists, as well as the activities that convert +those lists into boxes. All of the necessary machinery has already been +developed; it remains for us to ``push the buttons'' at the right times. + +@ As an introduction to these routines, let's consider one of the simplest +cases: What happens when `\.{\\hrule}' occurs in vertical mode, or +`\.{\\vrule}' in horizontal mode or math mode? The code in |main_control| +is short, since the |scan_rule_spec| routine already does most of what is +required; thus, there is no need for a special action procedure. + +Note that baselineskip calculations are disabled after a rule in vertical +mode, by setting |prev_depth:=ignore_depth|. + +@<Cases of |main_control| that build...@>= +vmode+hrule,hmode+vrule,mmode+vrule: begin tail_append(scan_rule_spec); + if abs(mode)=vmode then prev_depth:=ignore_depth + else if abs(mode)=hmode then space_factor:=1000; + end; + +@ The processing of things like \.{\\hskip} and \.{\\vskip} is slightly +more complicated. But the code in |main_control| is very short, since +it simply calls on the action routine |append_glue|. Similarly, \.{\\kern} +activates |append_kern|. + +@<Cases of |main_control| that build...@>= +vmode+vskip,hmode+hskip,mmode+hskip,mmode+mskip: append_glue; +any_mode(kern),mmode+mkern: append_kern; + +@ The |hskip| and |vskip| command codes are used for control sequences +like \.{\\hss} and \.{\\vfil} as well as for \.{\\hskip} and \.{\\vskip}. +The difference is in the value of |cur_chr|. + +@d fil_code=0 {identifies \.{\\hfil} and \.{\\vfil}} +@d fill_code=1 {identifies \.{\\hfill} and \.{\\vfill}} +@d ss_code=2 {identifies \.{\\hss} and \.{\\vss}} +@d fil_neg_code=3 {identifies \.{\\hfilneg} and \.{\\vfilneg}} +@d skip_code=4 {identifies \.{\\hskip} and \.{\\vskip}} +@d mskip_code=5 {identifies \.{\\mskip}} + +@<Put each...@>= +primitive("hskip",hskip,skip_code);@/ +@!@:hskip_}{\.{\\hskip} primitive@> +primitive("hfil",hskip,fil_code); +@!@:hfil_}{\.{\\hfil} primitive@> +primitive("hfill",hskip,fill_code);@/ +@!@:hfill_}{\.{\\hfill} primitive@> +primitive("hss",hskip,ss_code); +@!@:hss_}{\.{\\hss} primitive@> +primitive("hfilneg",hskip,fil_neg_code);@/ +@!@:hfil_neg_}{\.{\\hfilneg} primitive@> +primitive("vskip",vskip,skip_code);@/ +@!@:vskip_}{\.{\\vskip} primitive@> +primitive("vfil",vskip,fil_code); +@!@:vfil_}{\.{\\vfil} primitive@> +primitive("vfill",vskip,fill_code);@/ +@!@:vfill_}{\.{\\vfill} primitive@> +primitive("vss",vskip,ss_code); +@!@:vss_}{\.{\\vss} primitive@> +primitive("vfilneg",vskip,fil_neg_code);@/ +@!@:vfil_neg_}{\.{\\vfilneg} primitive@> +primitive("mskip",mskip,mskip_code);@/ +@!@:mskip_}{\.{\\mskip} primitive@> +primitive("kern",kern,explicit); +@!@:kern_}{\.{\\kern} primitive@> +primitive("mkern",mkern,mu_glue);@/ +@!@:mkern_}{\.{\\mkern} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +hskip: case chr_code of + skip_code:print_esc("hskip"); + fil_code:print_esc("hfil"); + fill_code:print_esc("hfill"); + ss_code:print_esc("hss"); + othercases print_esc("hfilneg") + endcases; +vskip: case chr_code of + skip_code:print_esc("vskip"); + fil_code:print_esc("vfil"); + fill_code:print_esc("vfill"); + ss_code:print_esc("vss"); + othercases print_esc("vfilneg") + endcases; +mskip: print_esc("mskip"); +kern: print_esc("kern"); +mkern: print_esc("mkern"); + +@ All the work relating to glue creation has been relegated to the +following subroutine. It does not call |build_page|, because it is +used in at least one place where that would be a mistake. + +@<Declare action...@>= +procedure append_glue; +var s:small_number; {modifier of skip command} +begin s:=cur_chr; +case s of +fil_code: cur_val:=fil_glue; +fill_code: cur_val:=fill_glue; +ss_code: cur_val:=ss_glue; +fil_neg_code: cur_val:=fil_neg_glue; +skip_code: scan_glue(glue_val); +mskip_code: scan_glue(mu_val); +end; {now |cur_val| points to the glue specification} +tail_append(new_glue(cur_val)); +if s>=skip_code then + begin decr(glue_ref_count(cur_val)); + if s>skip_code then subtype(tail):=mu_glue; + end; +end; + +@ @<Declare act...@>= +procedure append_kern; +var s:quarterword; {|subtype| of the kern node} +begin s:=cur_chr; scan_dimen(s=mu_glue,false,false); +tail_append(new_kern(cur_val)); subtype(tail):=s; +end; + +@ Many of the actions related to box-making are triggered by the appearance +of braces in the input. For example, when the user says `\.{\\hbox} +\.{to} \.{100pt\{$\langle\,\hbox{hlist}\,\rangle$\}}' in vertical mode, +the information about the box size (100pt, |exactly|) is put onto |save_stack| +with a level boundary word just above it, and |cur_group:=adjusted_hbox_group|; +\TeX\ enters restricted horizontal mode to process the hlist. The right +brace eventually causes |save_stack| to be restored to its former state, +at which time the information about the box size (100pt, |exactly|) is +available once again; a box is packaged and we leave restricted horizontal +mode, appending the new box to the current list of the enclosing mode +(in this case to the current list of vertical mode), followed by any +vertical adjustments that were removed from the box by |hpack|. + +The next few sections of the program are therefore concerned with the +treatment of left and right curly braces. + +@ If a left brace occurs in the middle of a page or paragraph, it simply +introduces a new level of grouping, and the matching right brace will not have +such a drastic effect. Such grouping affects neither the mode nor the +current list. + +@<Cases of |main_control| that build...@>= +non_math(left_brace): new_save_level(simple_group); +any_mode(begin_group): new_save_level(semi_simple_group); +any_mode(end_group): if cur_group=semi_simple_group then unsave + else off_save; + +@ We have to deal with errors in which braces and such things are not +properly nested. Sometimes the user makes an error of commission by +inserting an extra symbol, but sometimes the user makes an error of omission. +\TeX\ can't always tell one from the other, so it makes a guess and tries +to avoid getting into a loop. + +The |off_save| routine is called when the current group code is wrong. It tries +to insert something into the user's input that will help clean off +the top level. + +@<Declare act...@>= +procedure off_save; +var p:pointer; {inserted token} +begin if cur_group=bottom_level then + @<Drop current token and complain that it was unmatched@> +else begin back_input; p:=get_avail; link(temp_head):=p; + print_err("Missing "); + @<Prepare to insert a token that matches |cur_group|, + and print what it is@>; + print(" inserted"); ins_list(link(temp_head)); + help5("I've inserted something that you may have forgotten.")@/ + ("(See the <inserted text> above.)")@/ + ("With luck, this will get me unwedged. But if you")@/ + ("really didn't forget anything, try typing `2' now; then")@/ + ("my insertion and my current dilemma will both disappear."); + error; + end; +end; + +@ At this point, |link(temp_head)=p|, a pointer to an empty one-word node. + +@<Prepare to insert a token that matches |cur_group|...@>= +case cur_group of +semi_simple_group: begin info(p):=cs_token_flag+frozen_end_group; + print_esc("endgroup"); +@.Missing \\endgroup inserted@> + end; +math_shift_group: begin info(p):=math_shift_token+"$"; print_char("$"); +@.Missing \$ inserted@> + end; +math_left_group: begin info(p):=cs_token_flag+frozen_right; link(p):=get_avail; + p:=link(p); info(p):=other_token+"."; print_esc("right."); +@.Missing \\right\hbox{.} inserted@> +@^null delimiter@> + end; +othercases begin info(p):=right_brace_token+"}"; print_char("}"); +@.Missing \} inserted@> + end +endcases + +@ @<Drop current token and complain that it was unmatched@>= +begin print_err("Extra "); print_cmd_chr(cur_cmd,cur_chr); +@.Extra x@> +help1("Things are pretty mixed up, but I think the worst is over.");@/ +error; +end + +@ The routine for a |right_brace| character branches into many subcases, +since a variety of things may happen, depending on |cur_group|. Some +types of groups are not supposed to be ended by a right brace; error +messages are given in hopes of pinpointing the problem. Most branches +of this routine will be filled in later, when we are ready to understand +them; meanwhile, we must prepare ourselves to deal with such errors. + +@<Cases of |main_control| that build...@>= +any_mode(right_brace): handle_right_brace; + +@ @<Declare the procedure called |handle_right_brace|@>= +procedure handle_right_brace; +var p,@!q:pointer; {for short-term use} +@!d:scaled; {holds |split_max_depth| in |insert_group|} +@!f:integer; {holds |floating_penalty| in |insert_group|} +begin case cur_group of +simple_group: unsave; +bottom_level: begin print_err("Too many }'s"); +@.Too many \}'s@> + help2("You've closed more groups than you opened.")@/ + ("Such booboos are generally harmless, so keep going."); error; + end; +semi_simple_group,math_shift_group,math_left_group: extra_right_brace; +@t\4@>@<Cases of |handle_right_brace| where a |right_brace| triggers + a delayed action@>@; +othercases confusion("rightbrace") +@:this can't happen rightbrace}{\quad rightbrace@> +endcases; +end; + +@ @<Declare act...@>= +procedure extra_right_brace; +begin print_err("Extra }, or forgotten "); +@.Extra \}, or forgotten x@> +case cur_group of +semi_simple_group: print_esc("endgroup"); +math_shift_group: print_char("$"); +math_left_group: print_esc("right"); +end;@/ +help5("I've deleted a group-closing symbol because it seems to be")@/ +("spurious, as in `$x}$'. But perhaps the } is legitimate and")@/ +("you forgot something else, as in `\hbox{$x}'. In such cases")@/ +("the way to recover is to insert both the forgotten and the")@/ +("deleted material, e.g., by typing `I$}'."); error; +incr(align_state); +end; + +@ Here is where we clear the parameters that are supposed to revert to their +default values after every paragraph and when internal vertical mode is entered. + +@<Declare act...@>= +procedure normal_paragraph; +begin if looseness<>0 then eq_word_define(int_base+looseness_code,0); +if hang_indent<>0 then eq_word_define(dimen_base+hang_indent_code,0); +if hang_after<>1 then eq_word_define(int_base+hang_after_code,1); +if par_shape_ptr<>null then eq_define(par_shape_loc,shape_ref,null); +end; + +@ Now let's turn to the question of how \.{\\hbox} is treated. We actually +need to consider also a slightly larger context, since constructions like +`\.{\\setbox3=}\penalty0\.{\\hbox...}' and +`\.{\\leaders}\penalty0\.{\\hbox...}' and +`\.{\\lower3.8pt\\hbox...}' +are supposed to invoke quite +different actions after the box has been packaged. Conversely, +constructions like `\.{\\setbox3=}' can be followed by a variety of +different kinds of boxes, and we would like to encode such things in an +efficient way. + +In other words, there are two problems: To represent the context of a box, +and to represent its type. + +The first problem is solved by putting a ``context code'' on the |save_stack|, +just below the two entries that give the dimensions produced by |scan_spec|. +The context code is either a (signed) shift amount, or it is a large +integer |>=box_flag|, where |box_flag=@t$2^{30}$@>|. Codes |box_flag| through +|box_flag+255| represent `\.{\\setbox0}' through `\.{\\setbox255}'; +codes |box_flag+256| through |box_flag+511| represent `\.{\\global\\setbox0}' +through `\.{\\global\\setbox255}'; +code |box_flag+512| represents `\.{\\shipout}'; and codes |box_flag+513| +through |box_flag+515| represent `\.{\\leaders}', `\.{\\cleaders}', +and `\.{\\xleaders}'. + +The second problem is solved by giving the command code |make_box| to all +control sequences that produce a box, and by using the following |chr_code| +values to distinguish between them: |box_code|, |copy_code|, |last_box_code|, +|vsplit_code|, |vtop_code|, |vtop_code+vmode|, and |vtop_code+hmode|, +where the latter two are used denote \.{\\vbox} and \.{\\hbox}, respectively. + +@d box_flag==@'10000000000 {context code for `\.{\\setbox0}'} +@d ship_out_flag==box_flag+512 {context code for `\.{\\shipout}'} +@d leader_flag==box_flag+513 {context code for `\.{\\leaders}'} +@d box_code=0 {|chr_code| for `\.{\\box}'} +@d copy_code=1 {|chr_code| for `\.{\\copy}'} +@d last_box_code=2 {|chr_code| for `\.{\\lastbox}'} +@d vsplit_code=3 {|chr_code| for `\.{\\vsplit}'} +@d vtop_code=4 {|chr_code| for `\.{\\vtop}'} + +@<Put each...@>= +primitive("moveleft",hmove,1); +@!@:move_left_}{\.{\\moveleft} primitive@> +primitive("moveright",hmove,0);@/ +@!@:move_right_}{\.{\\moveright} primitive@> +primitive("raise",vmove,1); +@!@:raise_}{\.{\\raise} primitive@> +primitive("lower",vmove,0); +@!@:lower_}{\.{\\lower} primitive@> +@# +primitive("box",make_box,box_code); +@!@:box_}{\.{\\box} primitive@> +primitive("copy",make_box,copy_code); +@!@:copy_}{\.{\\copy} primitive@> +primitive("lastbox",make_box,last_box_code); +@!@:last_box_}{\.{\\lastbox} primitive@> +primitive("vsplit",make_box,vsplit_code); +@!@:vsplit_}{\.{\\vsplit} primitive@> +primitive("vtop",make_box,vtop_code);@/ +@!@:vtop_}{\.{\\vtop} primitive@> +primitive("vbox",make_box,vtop_code+vmode); +@!@:vbox_}{\.{\\vbox} primitive@> +primitive("hbox",make_box,vtop_code+hmode);@/ +@!@:hbox_}{\.{\\hbox} primitive@> +primitive("shipout",leader_ship,a_leaders-1); {|ship_out_flag=leader_flag-1|} +@!@:ship_out_}{\.{\\shipout} primitive@> +primitive("leaders",leader_ship,a_leaders); +@!@:leaders_}{\.{\\leaders} primitive@> +primitive("cleaders",leader_ship,c_leaders); +@!@:c_leaders_}{\.{\\cleaders} primitive@> +primitive("xleaders",leader_ship,x_leaders); +@!@:x_leaders_}{\.{\\xleaders} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +hmove: if chr_code=1 then print_esc("moveleft")@+else print_esc("moveright"); +vmove: if chr_code=1 then print_esc("raise")@+else print_esc("lower"); +make_box: case chr_code of + box_code: print_esc("box"); + copy_code: print_esc("copy"); + last_box_code: print_esc("lastbox"); + vsplit_code: print_esc("vsplit"); + vtop_code: print_esc("vtop"); + vtop_code+vmode: print_esc("vbox"); + othercases print_esc("hbox") + endcases; +leader_ship: if chr_code=a_leaders then print_esc("leaders") + else if chr_code=c_leaders then print_esc("cleaders") + else if chr_code=x_leaders then print_esc("xleaders") + else print_esc("shipout"); + +@ Constructions that require a box are started by calling |scan_box| with +a specified context code. The |scan_box| routine verifies +that a |make_box| command comes next and then it calls |begin_box|. + +@<Cases of |main_control| that build...@>= +vmode+hmove,hmode+vmove,mmode+vmove: begin t:=cur_chr; + scan_normal_dimen; + if t=0 then scan_box(cur_val)@+else scan_box(-cur_val); + end; +any_mode(leader_ship): scan_box(leader_flag-a_leaders+cur_chr); +any_mode(make_box): begin_box(0); + +@ The global variable |cur_box| will point to a newly-made box. If the box +is void, we will have |cur_box=null|. Otherwise we will have +|type(cur_box)=hlist_node| or |vlist_node| or |rule_node|; the |rule_node| +case can occur only with leaders. + +@<Glob...@>= +@!cur_box:pointer; {box to be placed into its context} + +@ The |box_end| procedure does the right thing with |cur_box|, if +|box_context| represents the context as explained above. + +@<Declare act...@>= +procedure box_end(@!box_context:integer); +var p:pointer; {|ord_noad| for new box in math mode} +begin if box_context<box_flag then @<Append box |cur_box| to the current list, + shifted by |box_context|@> +else if box_context<ship_out_flag then @<Store \(c)|cur_box| in a box register@> +else if cur_box<>null then + if box_context>ship_out_flag then @<Append a new leader node that + uses |cur_box|@> + else ship_out(cur_box); +end; + +@ The global variable |adjust_tail| will be non-null if and only if the +current box might include adjustments that should be appended to the +current vertical list. + +@<Append box |cur_box| to the current...@>= +begin if cur_box<>null then + begin shift_amount(cur_box):=box_context; + if abs(mode)=vmode then + begin append_to_vlist(cur_box); + if adjust_tail<>null then + begin if adjust_head<>adjust_tail then + begin link(tail):=link(adjust_head); tail:=adjust_tail; + end; + adjust_tail:=null; + end; + if mode>0 then build_page; + end + else begin if abs(mode)=hmode then space_factor:=1000 + else begin p:=new_noad; + math_type(nucleus(p)):=sub_box; + info(nucleus(p)):=cur_box; cur_box:=p; + end; + link(tail):=cur_box; tail:=cur_box; + end; + end; +end + +@ @<Store \(c)|cur_box| in a box register@>= +if box_context<box_flag+256 then + eq_define(box_base-box_flag+box_context,box_ref,cur_box) +else geq_define(box_base-box_flag-256+box_context,box_ref,cur_box) + +@ @<Append a new leader node ...@>= +begin @<Get the next non-blank non-relax...@>; +if ((cur_cmd=hskip)and(abs(mode)<>vmode))or@| + ((cur_cmd=vskip)and(abs(mode)=vmode))or@| + ((cur_cmd=mskip)and(abs(mode)=mmode)) then + begin append_glue; subtype(tail):=box_context-(leader_flag-a_leaders); + leader_ptr(tail):=cur_box; + end +else begin print_err("Leaders not followed by proper glue"); +@.Leaders not followed by...@> + help3("You should say `\leaders <box or rule><hskip or vskip>'.")@/ + ("I found the <box or rule>, but there's no suitable")@/ + ("<hskip or vskip>, so I'm ignoring these leaders."); back_error; + flush_node_list(cur_box); + end; +end + +@ Now that we can see what eventually happens to boxes, we can consider +the first steps in their creation. The |begin_box| routine is called when +|box_context| is a context specification, |cur_chr| specifies the type of +box desired, and |cur_cmd=make_box|. + +@<Declare act...@>= +procedure begin_box(@!box_context:integer); +label exit, done; +var @!p,@!q:pointer; {run through the current list} +@!m:quarterword; {the length of a replacement list} +@!k:halfword; {0 or |vmode| or |hmode|} +@!n:eight_bits; {a box number} +begin case cur_chr of +box_code: begin scan_eight_bit_int; cur_box:=box(cur_val); + box(cur_val):=null; {the box becomes void, at the same level} + end; +copy_code: begin scan_eight_bit_int; cur_box:=copy_node_list(box(cur_val)); + end; +last_box_code: @<If the current list ends with a box node, delete it from + the list and make |cur_box| point to it; otherwise set |cur_box:=null|@>; +vsplit_code: @<Split off part of a vertical box, make |cur_box| point to it@>; +othercases @<Initiate the construction of an hbox or vbox, then |return|@> +endcases;@/ +box_end(box_context); {in simple cases, we use the box immediately} +exit:end; + +@ Note that the condition |not is_char_node(tail)| implies that |head<>tail|, +since |head| is a one-word node. + +@<If the current list ends with a box node, delete it...@>= +begin cur_box:=null; +if abs(mode)=mmode then + begin you_cant; help1("Sorry; this \lastbox will be void."); error; + end +else if (mode=vmode)and(head=tail) then + begin you_cant; + help2("Sorry...I usually can't take things from the current page.")@/ + ("This \lastbox will therefore be void."); error; + end +else begin if not is_char_node(tail) then + if (type(tail)=hlist_node)or(type(tail)=vlist_node) then + @<Remove the last box, unless it's part of a discretionary@>; + end; +end + +@ @<Remove the last box...@>= +begin q:=head; +repeat p:=q; +if not is_char_node(q) then if type(q)=disc_node then + begin for m:=1 to replace_count(q) do p:=link(p); + if p=tail then goto done; + end; +q:=link(p); +until q=tail; +cur_box:=tail; shift_amount(cur_box):=0; +tail:=p; link(p):=null; +done:end + +@ Here we deal with things like `\.{\\vsplit 13 to 100pt}'. + +@<Split off part of a vertical box, make |cur_box| point to it@>= +begin scan_eight_bit_int; n:=cur_val; +if not scan_keyword("to") then +@.to@> + begin print_err("Missing `to' inserted"); +@.Missing `to' inserted@> + help2("I'm working on `\vsplit<box number> to <dimen>';")@/ + ("will look for the <dimen> next."); error; + end; +scan_normal_dimen; +cur_box:=vsplit(n,cur_val); +end + +@ Here is where we enter restricted horizontal mode or internal vertical +mode, in order to make a box. + +@<Initiate the construction of an hbox or vbox, then |return|@>= +begin k:=cur_chr-vtop_code; saved(0):=box_context; +if k=hmode then + if (box_context<box_flag)and(abs(mode)=vmode) then + scan_spec(adjusted_hbox_group,true) + else scan_spec(hbox_group,true) +else begin if k=vmode then scan_spec(vbox_group,true) + else begin scan_spec(vtop_group,true); k:=vmode; + end; + normal_paragraph; + end; +push_nest; mode:=-k; +if k=vmode then + begin prev_depth:=ignore_depth; + if every_vbox<>null then begin_token_list(every_vbox,every_vbox_text); + end +else begin space_factor:=1000; + if every_hbox<>null then begin_token_list(every_hbox,every_hbox_text); + end; +return; +end + +@ @<Declare act...@>= +procedure scan_box(@!box_context:integer); + {the next input should specify a box or perhaps a rule} +begin @<Get the next non-blank non-relax...@>; +if cur_cmd=make_box then begin_box(box_context) +else if (box_context>=leader_flag)and((cur_cmd=hrule)or(cur_cmd=vrule)) then + begin cur_box:=scan_rule_spec; box_end(box_context); + end +else begin@t@>@;@/ + print_err("A <box> was supposed to be here");@/ +@.A <box> was supposed to...@> + help3("I was expecting to see \hbox or \vbox or \copy or \box or")@/ + ("something like that. So you might find something missing in")@/ + ("your output. But keep trying; you can fix this later."); back_error; + end; +end; + +@ When the right brace occurs at the end of an \.{\\hbox} or \.{\\vbox} or +\.{\\vtop} construction, the |package| routine comes into action. We might +also have to finish a paragraph that hasn't ended. + +@<Cases of |handle...@>= +hbox_group: package(0); +adjusted_hbox_group: begin adjust_tail:=adjust_head; package(0); + end; +vbox_group: begin end_graf; package(0); + end; +vtop_group: begin end_graf; package(vtop_code); + end; + +@ @<Declare action...@>= +procedure package(@!c:small_number); +var h:scaled; {height of box} +@!p:pointer; {first node in a box} +@!d:scaled; {max depth} +begin d:=box_max_depth; unsave; save_ptr:=save_ptr-3; +if mode=-hmode then cur_box:=hpack(link(head),saved(2),saved(1)) +else begin cur_box:=vpackage(link(head),saved(2),saved(1),d); + if c=vtop_code then @<Readjust the height and depth of |cur_box|, + for \.{\\vtop}@>; + end; +pop_nest; box_end(saved(0)); +end; + +@ The height of a `\.{\\vtop}' box is inherited from the first item on its list, +if that item is an |hlist_node|, |vlist_node|, or |rule_node|; otherwise +the \.{\\vtop} height is zero. + + +@<Readjust the height...@>= +begin h:=0; p:=list_ptr(cur_box); +if p<>null then if type(p)<=rule_node then h:=height(p); +depth(cur_box):=depth(cur_box)-h+height(cur_box); height(cur_box):=h; +end + +@ A paragraph begins when horizontal-mode material occurs in vertical mode, +or when the paragraph is explicitly started by `\.{\\indent}' or +`\.{\\noindent}'. + +@<Put each...@>= +primitive("indent",start_par,1); +@!@:indent_}{\.{\\indent} primitive@> +primitive("noindent",start_par,0); +@!@:no_indent_}{\.{\\noindent} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +start_par: if chr_code=0 then print_esc("noindent")@+ else print_esc("indent"); + +@ @<Cases of |main_control| that build...@>= +vmode+start_par: new_graf(cur_chr>0); +vmode+letter,vmode+other_char,vmode+char_num,vmode+char_given, + vmode+math_shift,vmode+un_hbox,vmode+vrule, + vmode+accent,vmode+discretionary,vmode+hskip,vmode+valign, + vmode+ex_space,vmode+no_boundary:@t@>@;@/ + begin back_input; new_graf(true); + end; + +@ @<Declare act...@>= +function norm_min(@!h:integer):small_number; +begin if h<=0 then norm_min:=1@+else if h>=63 then norm_min:=63@+ +else norm_min:=h; +end; +@# +procedure new_graf(@!indented:boolean); +begin prev_graf:=0; +if (mode=vmode)or(head<>tail) then + tail_append(new_param_glue(par_skip_code)); +push_nest; mode:=hmode; space_factor:=1000; set_cur_lang; clang:=cur_lang; +prev_graf:=(norm_min(left_hyphen_min)*@'100+norm_min(right_hyphen_min)) + *@'200000+cur_lang; +if indented then + begin tail:=new_null_box; link(head):=tail; width(tail):=par_indent;@+ + end; +if every_par<>null then begin_token_list(every_par,every_par_text); +if nest_ptr=1 then build_page; {put |par_skip| glue on current page} +end; + +@ @<Cases of |main_control| that build...@>= +hmode+start_par,mmode+start_par: indent_in_hmode; + +@ @<Declare act...@>= +procedure indent_in_hmode; +var p,@!q:pointer; +begin if cur_chr>0 then {\.{\\indent}} + begin p:=new_null_box; width(p):=par_indent; + if abs(mode)=hmode then space_factor:=1000 + else begin q:=new_noad; math_type(nucleus(q)):=sub_box; + info(nucleus(q)):=p; p:=q; + end; + tail_append(p); + end; +end; + +@ A paragraph ends when a |par_end| command is sensed, or when we are in +horizontal mode when reaching the right brace of vertical-mode routines +like \.{\\vbox}, \.{\\insert}, or \.{\\output}. + +@<Cases of |main_control| that build...@>= +vmode+par_end: begin normal_paragraph; + if mode>0 then build_page; + end; +hmode+par_end: begin if align_state<0 then off_save; {this tries to + recover from an alignment that didn't end properly} + end_graf; {this takes us to the enclosing mode, if |mode>0|} + if mode=vmode then build_page; + end; +hmode+stop,hmode+vskip,hmode+hrule,hmode+un_vbox,hmode+halign: head_for_vmode; + +@ @<Declare act...@>= +procedure head_for_vmode; +begin if mode<0 then + if cur_cmd<>hrule then off_save + else begin print_err("You can't use `"); + print_esc("hrule"); print("' here except with leaders"); +@.You can't use \\hrule...@> + help2("To put a horizontal rule in an hbox or an alignment,")@/ + ("you should use \leaders or \hrulefill (see The TeXbook)."); + error; + end +else begin back_input; cur_tok:=par_token; back_input; token_type:=inserted; + end; +end; + +@ @<Declare act...@>= +procedure end_graf; +begin if mode=hmode then + begin if head=tail then pop_nest {null paragraphs are ignored} + else line_break(widow_penalty); + normal_paragraph; + error_count:=0; + end; +end; + +@ Insertion and adjustment and mark nodes are constructed by the following +pieces of the program. + +@<Cases of |main_control| that build...@>= +any_mode(insert),hmode+vadjust,mmode+vadjust: begin_insert_or_adjust; +any_mode(mark): make_mark; + +@ @<Forbidden...@>= +vmode+vadjust, + +@ @<Declare act...@>= +procedure begin_insert_or_adjust; +begin if cur_cmd=vadjust then cur_val:=255 +else begin scan_eight_bit_int; + if cur_val=255 then + begin print_err("You can't "); print_esc("insert"); print_int(255); +@.You can't \\insert255@> + help1("I'm changing to \insert0; box 255 is special."); + error; cur_val:=0; + end; + end; +saved(0):=cur_val; incr(save_ptr); +new_save_level(insert_group); scan_left_brace; normal_paragraph; +push_nest; mode:=-vmode; prev_depth:=ignore_depth; +end; + +@ @<Cases of |handle...@>= +insert_group: begin end_graf; q:=split_top_skip; add_glue_ref(q); + d:=split_max_depth; f:=floating_penalty; unsave; decr(save_ptr); + {now |saved(0)| is the insertion number, or 255 for |vadjust|} + p:=vpack(link(head),natural); pop_nest; + if saved(0)<255 then + begin tail_append(get_node(ins_node_size)); + type(tail):=ins_node; subtype(tail):=qi(saved(0)); + height(tail):=height(p)+depth(p); ins_ptr(tail):=list_ptr(p); + split_top_ptr(tail):=q; depth(tail):=d; float_cost(tail):=f; + end + else begin tail_append(get_node(small_node_size)); + type(tail):=adjust_node;@/ + subtype(tail):=0; {the |subtype| is not used} + adjust_ptr(tail):=list_ptr(p); delete_glue_ref(q); + end; + free_node(p,box_node_size); + if nest_ptr=0 then build_page; + end; +output_group: @<Resume the page builder...@>; + +@ @<Declare act...@>= +procedure make_mark; +var p:pointer; {new node} +begin p:=scan_toks(false,true); p:=get_node(small_node_size); +type(p):=mark_node; subtype(p):=0; {the |subtype| is not used} +mark_ptr(p):=def_ref; link(tail):=p; tail:=p; +end; + +@ Penalty nodes get into a list via the |break_penalty| command. +@^penalties@> + +@<Cases of |main_control| that build...@>= +any_mode(break_penalty): append_penalty; + +@ @<Declare action...@>= +procedure append_penalty; +begin scan_int; tail_append(new_penalty(cur_val)); +if mode=vmode then build_page; +end; + +@ The |remove_item| command removes a penalty, kern, or glue node if it +appears at the tail of the current list, using a brute-force linear scan. +Like \.{\\lastbox}, this command is not allowed in vertical mode (except +internal vertical mode), since the current list in vertical mode is sent +to the page builder. But if we happen to be able to implement it in +vertical mode, we do. + +@<Cases of |main_control| that build...@>= +any_mode(remove_item): delete_last; + +@ When |delete_last| is called, |cur_chr| is the |type| of node that +will be deleted, if present. + +@<Declare action...@>= +procedure delete_last; +label exit; +var @!p,@!q:pointer; {run through the current list} +@!m:quarterword; {the length of a replacement list} +begin if (mode=vmode)and(tail=head) then + @<Apologize for inability to do the operation now, + unless \.{\\unskip} follows non-glue@> +else begin if not is_char_node(tail) then if type(tail)=cur_chr then + begin q:=head; + repeat p:=q; + if not is_char_node(q) then if type(q)=disc_node then + begin for m:=1 to replace_count(q) do p:=link(p); + if p=tail then return; + end; + q:=link(p); + until q=tail; + link(p):=null; flush_node_list(tail); tail:=p; + end; + end; +exit:end; + +@ @<Apologize for inability to do the operation...@>= +begin if (cur_chr<>glue_node)or(last_glue<>max_halfword) then + begin you_cant; + help2("Sorry...I usually can't take things from the current page.")@/ + ("Try `I\vskip-\lastskip' instead."); + if cur_chr=kern_node then help_line[0]:= + ("Try `I\kern-\lastkern' instead.") + else if cur_chr<>glue_node then help_line[0]:=@| + ("Perhaps you can make the output routine do it."); + error; + end; +end + +@ @<Put each...@>= +primitive("unpenalty",remove_item,penalty_node);@/ +@!@:un_penalty_}{\.{\\unpenalty} primitive@> +primitive("unkern",remove_item,kern_node);@/ +@!@:un_kern_}{\.{\\unkern} primitive@> +primitive("unskip",remove_item,glue_node);@/ +@!@:un_skip_}{\.{\\unskip} primitive@> +primitive("unhbox",un_hbox,box_code);@/ +@!@:un_hbox_}{\.{\\unhbox} primitive@> +primitive("unhcopy",un_hbox,copy_code);@/ +@!@:un_hcopy_}{\.{\\unhcopy} primitive@> +primitive("unvbox",un_vbox,box_code);@/ +@!@:un_vbox_}{\.{\\unvbox} primitive@> +primitive("unvcopy",un_vbox,copy_code);@/ +@!@:un_vcopy_}{\.{\\unvcopy} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +remove_item: if chr_code=glue_node then print_esc("unskip") + else if chr_code=kern_node then print_esc("unkern") + else print_esc("unpenalty"); +un_hbox: if chr_code=copy_code then print_esc("unhcopy") + else print_esc("unhbox"); +un_vbox: if chr_code=copy_code then print_esc("unvcopy") + else print_esc("unvbox"); + +@ The |un_hbox| and |un_vbox| commands unwrap one of the 256 current boxes. + +@<Cases of |main_control| that build...@>= +vmode+un_vbox,hmode+un_hbox,mmode+un_hbox: unpackage; + +@ @<Declare act...@>= +procedure unpackage; +label exit; +var p:pointer; {the box} +@!c:box_code..copy_code; {should we copy?} +begin c:=cur_chr; scan_eight_bit_int; p:=box(cur_val); +if p=null then return; +if (abs(mode)=mmode)or((abs(mode)=vmode)and(type(p)<>vlist_node))or@| + ((abs(mode)=hmode)and(type(p)<>hlist_node)) then + begin print_err("Incompatible list can't be unboxed"); +@.Incompatible list...@> + help3("Sorry, Pandora. (You sneaky devil.)")@/ + ("I refuse to unbox an \hbox in vertical mode or vice versa.")@/ + ("And I can't open any boxes in math mode.");@/ + error; return; + end; +if c=copy_code then link(tail):=copy_node_list(list_ptr(p)) +else begin link(tail):=list_ptr(p); box(cur_val):=null; + free_node(p,box_node_size); + end; +while link(tail)<>null do tail:=link(tail); +exit:end; + +@ @<Forbidden...@>=vmode+ital_corr, + +@ Italic corrections are converted to kern nodes when the |ital_corr| command +follows a character. In math mode the same effect is achieved by appending +a kern of zero here, since italic corrections are supplied later. + +@<Cases of |main_control| that build...@>= +hmode+ital_corr: append_italic_correction; +mmode+ital_corr: tail_append(new_kern(0)); + +@ @<Declare act...@>= +procedure append_italic_correction; +label exit; +var p:pointer; {|char_node| at the tail of the current list} +@!f:internal_font_number; {the font in the |char_node|} +begin if tail<>head then + begin if is_char_node(tail) then p:=tail + else if type(tail)=ligature_node then p:=lig_char(tail) + else return; + f:=font(p); + tail_append(new_kern(char_italic(f)(char_info(f)(character(p))))); + subtype(tail):=explicit; + end; +exit:end; + +@ Discretionary nodes are easy in the common case `\.{\\-}', but in the +general case we must process three braces full of items. + +@<Put each...@>= +primitive("-",discretionary,1); +@!@:Single-character primitives -}{\quad\.{\\-}@> +primitive("discretionary",discretionary,0); +@!@:discretionary_}{\.{\\discretionary} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +discretionary: if chr_code=1 then + print_esc("-")@+else print_esc("discretionary"); + +@ @<Cases of |main_control| that build...@>= +hmode+discretionary,mmode+discretionary: append_discretionary; + +@ The space factor does not change when we append a discretionary node, +but it starts out as 1000 in the subsidiary lists. + +@<Declare act...@>= +procedure append_discretionary; +var c:integer; {hyphen character} +begin tail_append(new_disc); +if cur_chr=1 then + begin c:=hyphen_char[cur_font]; + if c>=0 then if c<256 then pre_break(tail):=new_character(cur_font,c); + end +else begin incr(save_ptr); saved(-1):=0; new_save_level(disc_group); + scan_left_brace; push_nest; mode:=-hmode; space_factor:=1000; + end; +end; + +@ The three discretionary lists are constructed somewhat as if they were +hboxes. A~subroutine called |build_discretionary| handles the transitions. +(This is sort of fun.) + +@<Cases of |handle...@>= +disc_group: build_discretionary; + +@ @<Declare act...@>= +procedure build_discretionary; +label done,exit; +var p,@!q:pointer; {for link manipulation} +@!n:integer; {length of discretionary list} +begin unsave; +@<Prune the current list, if necessary, until it contains only + |char_node|, |kern_node|, |hlist_node|, |vlist_node|, |rule_node|, + and |ligature_node| items; set |n| to the length of the list, + and set |q| to the list's tail@>; +p:=link(head); pop_nest; +case saved(-1) of +0:pre_break(tail):=p; +1:post_break(tail):=p; +2:@<Attach list |p| to the current list, and record its length; + then finish up and |return|@>; +end; {there are no other cases} +incr(saved(-1)); new_save_level(disc_group); scan_left_brace; +push_nest; mode:=-hmode; space_factor:=1000; +exit:end; + +@ @<Attach list |p| to the current...@>= +begin if (n>0)and(abs(mode)=mmode) then + begin print_err("Illegal math "); print_esc("discretionary"); +@.Illegal math \\disc...@> + help2("Sorry: The third part of a discretionary break must be")@/ + ("empty, in math formulas. I had to delete your third part."); + flush_node_list(p); n:=0; error; + end +else link(tail):=p; +if n<=max_quarterword then replace_count(tail):=n +else begin print_err("Discretionary list is too long"); +@.Discretionary list is too long@> + help2("Wow---I never thought anybody would tweak me here.")@/ + ("You can't seriously need such a huge discretionary list?"); + error; + end; +if n>0 then tail:=q; +decr(save_ptr); return; +end + +@ During this loop, |p=link(q)| and there are |n| items preceding |p|. + +@<Prune the current list, if necessary...@>= +q:=head; p:=link(q); n:=0; +while p<>null do + begin if not is_char_node(p) then if type(p)>rule_node then + if type(p)<>kern_node then if type(p)<>ligature_node then + begin print_err("Improper discretionary list"); +@.Improper discretionary list@> + help1("Discretionary lists must contain only boxes and kerns.");@/ + error; + begin_diagnostic; + print_nl("The following discretionary sublist has been deleted:"); +@.The following...deleted@> + show_box(p); + end_diagnostic(true); + flush_node_list(p); link(q):=null; goto done; + end; + q:=p; p:=link(q); incr(n); + end; +done: + +@ We need only one more thing to complete the horizontal mode routines, namely +the \.{\\accent} primitive. + +@<Cases of |main_control| that build...@>= +hmode+accent: make_accent; + +@ The positioning of accents is straightforward but tedious. Given an accent +of width |a|, designed for characters of height |x| and slant |s|; +and given a character of width |w|, height |h|, and slant |t|: We will shift +the accent down by |x-h|, and we will insert kern nodes that have the effect of +centering the accent over the character and shifting the accent to the +right by $\delta={1\over2}(w-a)+h\cdot t-x\cdot s$. If either character is +absent from the font, we will simply use the other, without shifting. + +@<Declare act...@>= +procedure make_accent; +var s,@!t: real; {amount of slant} +@!p,@!q,@!r:pointer; {character, box, and kern nodes} +@!f:internal_font_number; {relevant font} +@!a,@!h,@!x,@!w,@!delta:scaled; {heights and widths, as explained above} +@!i:four_quarters; {character information} +begin scan_char_num; f:=cur_font; p:=new_character(f,cur_val); +if p<>null then + begin x:=x_height(f); s:=slant(f)/float_constant(65536); +@^real division@> + a:=char_width(f)(char_info(f)(character(p)));@/ + do_assignments;@/ + @<Create a character node |q| for the next character, + but set |q:=null| if problems arise@>; + if q<>null then @<Append the accent with appropriate kerns, + then set |p:=q|@>; + link(tail):=p; tail:=p; space_factor:=1000; + end; +end; + +@ @<Create a character node |q| for the next...@>= +q:=null; f:=cur_font; +if (cur_cmd=letter)or(cur_cmd=other_char)or(cur_cmd=char_given) then + q:=new_character(f,cur_chr) +else if cur_cmd=char_num then + begin scan_char_num; q:=new_character(f,cur_val); + end +else back_input + +@ The kern nodes appended here must be distinguished from other kerns, lest +they be wiped away by the hyphenation algorithm or by a previous line break. + +The two kerns are computed with (machine-dependent) |real| arithmetic, but +their sum is machine-independent; the net effect is machine-independent, +because the user cannot remove these nodes nor access them via \.{\\lastkern}. + +@<Append the accent with appropriate kerns...@>= +begin t:=slant(f)/float_constant(65536); +@^real division@> +i:=char_info(f)(character(q)); +w:=char_width(f)(i); h:=char_height(f)(height_depth(i)); +if h<>x then {the accent must be shifted up or down} + begin p:=hpack(p,natural); shift_amount(p):=x-h; + end; +delta:=round((w-a)/float_constant(2)+h*t-x*s); +@^real multiplication@> +@^real addition@> +r:=new_kern(delta); subtype(r):=acc_kern; link(tail):=r; link(r):=p; +tail:=new_kern(-a-delta); subtype(tail):=acc_kern; link(p):=tail; p:=q; +end + +@ When `\.{\\cr}' or `\.{\\span}' or a tab mark comes through the scanner +into |main_control|, it might be that the user has foolishly inserted +one of them into something that has nothing to do with alignment. But it is +far more likely that a left brace or right brace has been omitted, since +|get_next| takes actions appropriate to alignment only when `\.{\\cr}' +or `\.{\\span}' or tab marks occur with |align_state=0|. The following +program attempts to make an appropriate recovery. + +@<Cases of |main_control| that build...@>= +any_mode(car_ret), any_mode(tab_mark): align_error; +any_mode(no_align): no_align_error; +any_mode(omit): omit_error; + +@ @<Declare act...@>= +procedure align_error; +begin if abs(align_state)>2 then + @<Express consternation over the fact that no alignment is in progress@> +else begin back_input; + if align_state<0 then + begin print_err("Missing { inserted"); +@.Missing \{ inserted@> + incr(align_state); cur_tok:=left_brace_token+"{"; + end + else begin print_err("Missing } inserted"); +@.Missing \} inserted@> + decr(align_state); cur_tok:=right_brace_token+"}"; + end; + help3("I've put in what seems to be necessary to fix")@/ + ("the current column of the current alignment.")@/ + ("Try to go on, since this might almost work."); ins_error; + end; +end; + +@ @<Express consternation...@>= +begin print_err("Misplaced "); print_cmd_chr(cur_cmd,cur_chr); +@.Misplaced \&@> +@.Misplaced \\span@> +@.Misplaced \\cr@> +if cur_tok=tab_token+"&" then + begin help6("I can't figure out why you would want to use a tab mark")@/ + ("here. If you just want an ampersand, the remedy is")@/ + ("simple: Just type `I\&' now. But if some right brace")@/ + ("up above has ended a previous alignment prematurely,")@/ + ("you're probably due for more error messages, and you")@/ + ("might try typing `S' now just to see what is salvageable."); + end +else begin help5("I can't figure out why you would want to use a tab mark")@/ + ("or \cr or \span just now. If something like a right brace")@/ + ("up above has ended a previous alignment prematurely,")@/ + ("you're probably due for more error messages, and you")@/ + ("might try typing `S' now just to see what is salvageable."); + end; +error; +end + +@ The help messages here contain a little white lie, since \.{\\noalign} +and \.{\\omit} are allowed also after `\.{\\noalign\{...\}}'. + +@<Declare act...@>= +procedure no_align_error; +begin print_err("Misplaced "); print_esc("noalign"); +@.Misplaced \\noalign@> +help2("I expect to see \noalign only after the \cr of")@/ + ("an alignment. Proceed, and I'll ignore this case."); error; +end; +procedure omit_error; +begin print_err("Misplaced "); print_esc("omit"); +@.Misplaced \\omit@> +help2("I expect to see \omit only after tab marks or the \cr of")@/ + ("an alignment. Proceed, and I'll ignore this case."); error; +end; + +@ We've now covered most of the abuses of \.{\\halign} and \.{\\valign}. +Let's take a look at what happens when they are used correctly. + +@<Cases of |main_control| that build...@>= +vmode+halign,hmode+valign:init_align; +mmode+halign: if privileged then + if cur_group=math_shift_group then init_align + else off_save; +vmode+endv,hmode+endv: do_endv; + +@ An |align_group| code is supposed to remain on the |save_stack| +during an entire alignment, until |fin_align| removes it. + +A devious user might force an |endv| command to occur just about anywhere; +we must defeat such hacks. + +@<Declare act...@>= +procedure do_endv; +begin base_ptr:=input_ptr; input_stack[base_ptr]:=cur_input; +while (input_stack[base_ptr].index_field<>v_template) and + (input_stack[base_ptr].loc_field=null) and + (input_stack[base_ptr].state_field=token_list) do decr(base_ptr); +if (input_stack[base_ptr].index_field<>v_template) or + (input_stack[base_ptr].loc_field<>null) or + (input_stack[base_ptr].state_field<>token_list) then + fatal_error("(interwoven alignment preambles are not allowed)"); +@.interwoven alignment preambles...@> + if cur_group=align_group then + begin end_graf; + if fin_col then fin_row; + end +else off_save; +end; + +@ @<Cases of |handle_right_brace|...@>= +align_group: begin back_input; cur_tok:=cs_token_flag+frozen_cr; + print_err("Missing "); print_esc("cr"); print(" inserted"); +@.Missing \\cr inserted@> + help1("I'm guessing that you meant to end an alignment here."); + ins_error; + end; + +@ @<Cases of |handle_right_brace|...@>= +no_align_group: begin end_graf; unsave; align_peek; + end; + +@ Finally, \.{\\endcsname} is not supposed to get through to |main_control|. + +@<Cases of |main_control| that build...@>= +any_mode(end_cs_name): cs_error; + +@ @<Declare act...@>= +procedure cs_error; +begin print_err("Extra "); print_esc("endcsname"); +@.Extra \\endcsname@> +help1("I'm ignoring this, since I wasn't doing a \csname."); +error; +end; + +@* \[48] Building math lists. +The routines that \TeX\ uses to create mlists are similar to those we have +just seen for the generation of hlists and vlists. But it is necessary to +make ``noads'' as well as nodes, so the reader should review the +discussion of math mode data structures before trying to make sense out of +the following program. + +Here is a little routine that needs to be done whenever a subformula +is about to be processed. The parameter is a code like |math_group|. + +@<Declare act...@>= +procedure push_math(@!c:group_code); +begin push_nest; mode:=-mmode; incompleat_noad:=null; new_save_level(c); +end; + +@ We get into math mode from horizontal mode when a `\.\$' (i.e., a +|math_shift| character) is scanned. We must check to see whether this +`\.\$' is immediately followed by another, in case display math mode is +called for. + +@<Cases of |main_control| that build...@>= +hmode+math_shift:init_math; + +@ @<Declare act...@>= +procedure init_math; +label reswitch,found,not_found,done; +var w:scaled; {new or partial |pre_display_size|} +@!l:scaled; {new |display_width|} +@!s:scaled; {new |display_indent|} +@!p:pointer; {current node when calculating |pre_display_size|} +@!q:pointer; {glue specification when calculating |pre_display_size|} +@!f:internal_font_number; {font in current |char_node|} +@!n:integer; {scope of paragraph shape specification} +@!v:scaled; {|w| plus possible glue amount} +@!d:scaled; {increment to |v|} +begin get_token; {|get_x_token| would fail on \.{\\ifmmode}\thinspace!} +if (cur_cmd=math_shift)and(mode>0) then @<Go into display math mode@> +else begin back_input; @<Go into ordinary math mode@>; + end; +end; + +@ @<Go into ordinary math mode@>= +begin push_math(math_shift_group); eq_word_define(int_base+cur_fam_code,-1); +if every_math<>null then begin_token_list(every_math,every_math_text); +end + +@ We get into ordinary math mode from display math mode when `\.{\\eqno}' or +`\.{\\leqno}' appears. In such cases |cur_chr| will be 0 or~1, respectively; +the value of |cur_chr| is placed onto |save_stack| for safe keeping. + +@<Cases of |main_control| that build...@>= +mmode+eq_no: if privileged then + if cur_group=math_shift_group then start_eq_no + else off_save; + +@ @<Put each...@>= +primitive("eqno",eq_no,0); +@!@:eq_no_}{\.{\\eqno} primitive@> +primitive("leqno",eq_no,1); +@!@:leq_no_}{\.{\\leqno} primitive@> + +@ When \TeX\ is in display math mode, |cur_group=math_shift_group|, +so it is not necessary for the |start_eq_no| procedure to test for +this condition. + +@<Declare act...@>= +procedure start_eq_no; +begin saved(0):=cur_chr; incr(save_ptr); +@<Go into ordinary math mode@>; +end; + +@ @<Cases of |print_cmd_chr|...@>= +eq_no:if chr_code=1 then print_esc("leqno")@+else print_esc("eqno"); + +@ @<Forbidden...@>=non_math(eq_no), + +@ When we enter display math mode, we need to call |line_break| to +process the partial paragraph that has just been interrupted by the +display. Then we can set the proper values of |display_width| and +|display_indent| and |pre_display_size|. + +@<Go into display math mode@>= +begin if head=tail then {`\.{\\noindent\$\$}' or `\.{\$\${ }\$\$}'} + begin pop_nest; w:=-max_dimen; + end +else begin line_break(display_widow_penalty);@/ + @<Calculate the natural width, |w|, by which the characters of the + final line extend to the right of the reference point, + plus two ems; or set |w:=max_dimen| if the non-blank information + on that line is affected by stretching or shrinking@>; + end; +{now we are in vertical mode, working on the list that will contain the display} +@<Calculate the length, |l|, and the shift amount, |s|, of the display lines@>; +push_math(math_shift_group); mode:=mmode; +eq_word_define(int_base+cur_fam_code,-1);@/ +eq_word_define(dimen_base+pre_display_size_code,w); +eq_word_define(dimen_base+display_width_code,l); +eq_word_define(dimen_base+display_indent_code,s); +if every_display<>null then begin_token_list(every_display,every_display_text); +if nest_ptr=1 then build_page; +end + +@ @<Calculate the natural width, |w|, by which...@>= +v:=shift_amount(just_box)+2*quad(cur_font); w:=-max_dimen; +p:=list_ptr(just_box); +while p<>null do + begin @<Let |d| be the natural width of node |p|; + if the node is ``visible,'' |goto found|; + if the node is glue that stretches or shrinks, set |v:=max_dimen|@>; + if v<max_dimen then v:=v+d; + goto not_found; + found: if v<max_dimen then + begin v:=v+d; w:=v; + end + else begin w:=max_dimen; goto done; + end; + not_found: p:=link(p); + end; +done: + +@ @<Let |d| be the natural width of node |p|...@>= +reswitch: if is_char_node(p) then + begin f:=font(p); d:=char_width(f)(char_info(f)(character(p))); + goto found; + end; +case type(p) of +hlist_node,vlist_node,rule_node: begin d:=width(p); goto found; + end; +ligature_node:@<Make node |p| look like a |char_node|...@>; +kern_node,math_node: d:=width(p); +glue_node:@<Let |d| be the natural width of this glue; if stretching + or shrinking, set |v:=max_dimen|; |goto found| in the case of leaders@>; +whatsit_node: @<Let |d| be the width of the whatsit |p|@>; +othercases d:=0 +endcases + +@ We need to be careful that |w|, |v|, and |d| do not depend on any |glue_set| +values, since such values are subject to system-dependent rounding. +System-dependent numbers are not allowed to infiltrate parameters like +|pre_display_size|, since \TeX82 is supposed to make the same decisions on all +machines. + +@<Let |d| be the natural width of this glue...@>= +begin q:=glue_ptr(p); d:=width(q); +if glue_sign(just_box)=stretching then + begin if (glue_order(just_box)=stretch_order(q))and@| + (stretch(q)<>0) then + v:=max_dimen; + end +else if glue_sign(just_box)=shrinking then + begin if (glue_order(just_box)=shrink_order(q))and@| + (shrink(q)<>0) then + v:=max_dimen; + end; +if subtype(p)>=a_leaders then goto found; +end + +@ A displayed equation is considered to be three lines long, so we +calculate the length and offset of line number |prev_graf+2|. + +@<Calculate the length, |l|, ...@>= +if par_shape_ptr=null then + if (hang_indent<>0)and@| + (((hang_after>=0)and(prev_graf+2>hang_after))or@| + (prev_graf+1<-hang_after)) then + begin l:=hsize-abs(hang_indent); + if hang_indent>0 then s:=hang_indent@+else s:=0; + end + else begin l:=hsize; s:=0; + end +else begin n:=info(par_shape_ptr); + if prev_graf+2>=n then p:=par_shape_ptr+2*n + else p:=par_shape_ptr+2*(prev_graf+2); + s:=mem[p-1].sc; l:=mem[p].sc; + end + +@ Subformulas of math formulas cause a new level of math mode to be entered, +on the semantic nest as well as the save stack. These subformulas arise in +several ways: (1)~A left brace by itself indicates the beginning of a +subformula that will be put into a box, thereby freezing its glue and +preventing line breaks. (2)~A subscript or superscript is treated as a +subformula if it is not a single character; the same applies to +the nucleus of things like \.{\\underline}. (3)~The \.{\\left} primitive +initiates a subformula that will be terminated by a matching \.{\\right}. +The group codes placed on |save_stack| in these three cases are +|math_group|, |math_group|, and |math_left_group|, respectively. + +Here is the code that handles case (1); the other cases are not quite as +trivial, so we shall consider them later. + +@<Cases of |main_control| that build...@>= +mmode+left_brace: begin tail_append(new_noad); + back_input; scan_math(nucleus(tail)); + end; + +@ Recall that the |nucleus|, |subscr|, and |supscr| fields in a noad are +broken down into subfields called |math_type| and either |info| or +|(fam,character)|. The job of |scan_math| is to figure out what to place +in one of these principal fields; it looks at the subformula that +comes next in the input, and places an encoding of that subformula +into a given word of |mem|. + +@d fam_in_range==((cur_fam>=0)and(cur_fam<16)) + +@<Declare act...@>= +procedure scan_math(@!p:pointer); +label restart,reswitch,exit; +var c:integer; {math character code} +begin restart:@<Get the next non-blank non-relax...@>; +reswitch:case cur_cmd of +letter,other_char,char_given: begin c:=ho(math_code(cur_chr)); + if c=@'100000 then + begin @<Treat |cur_chr| as an active character@>; + goto restart; + end; + end; +char_num: begin scan_char_num; cur_chr:=cur_val; cur_cmd:=char_given; + goto reswitch; + end; +math_char_num: begin scan_fifteen_bit_int; c:=cur_val; + end; +math_given: c:=cur_chr; +delim_num: begin scan_twenty_seven_bit_int; c:=cur_val div @'10000; + end; +othercases @<Scan a subformula enclosed in braces and |return|@> +endcases;@/ +math_type(p):=math_char; character(p):=qi(c mod 256); +if (c>=var_code)and fam_in_range then fam(p):=cur_fam +else fam(p):=(c div 256) mod 16; +exit:end; + +@ An active character that is an |outer_call| is allowed here. + +@<Treat |cur_chr|...@>= +begin cur_cs:=cur_chr+active_base; +cur_cmd:=eq_type(cur_cs); cur_chr:=equiv(cur_cs); +x_token; back_input; +end + +@ The pointer |p| is placed on |save_stack| while a complex subformula +is being scanned. + +@<Scan a subformula...@>= +begin back_input; scan_left_brace;@/ +saved(0):=p; incr(save_ptr); push_math(math_group); return; +end + +@ The simplest math formula is, of course, `\.{\${ }\$}', when no noads are +generated. The next simplest cases involve a single character, e.g., +`\.{\$x\$}'. Even though such cases may not seem to be very interesting, +the reader can perhaps understand how happy the author was when `\.{\$x\$}' +was first properly typeset by \TeX. The code in this section was used. +@^Knuth, Donald Ervin@> + +@<Cases of |main_control| that build...@>= +mmode+letter,mmode+other_char,mmode+char_given: + set_math_char(ho(math_code(cur_chr))); +mmode+char_num: begin scan_char_num; cur_chr:=cur_val; + set_math_char(ho(math_code(cur_chr))); + end; +mmode+math_char_num: begin scan_fifteen_bit_int; set_math_char(cur_val); + end; +mmode+math_given: set_math_char(cur_chr); +mmode+delim_num: begin scan_twenty_seven_bit_int; + set_math_char(cur_val div @'10000); + end; + +@ The |set_math_char| procedure creates a new noad appropriate to a given +math code, and appends it to the current mlist. However, if the math code +is sufficiently large, the |cur_chr| is treated as an active character and +nothing is appended. + +@<Declare act...@>= +procedure set_math_char(@!c:integer); +var p:pointer; {the new noad} +begin if c>=@'100000 then + @<Treat |cur_chr|...@> +else begin p:=new_noad; math_type(nucleus(p)):=math_char; + character(nucleus(p)):=qi(c mod 256); + fam(nucleus(p)):=(c div 256) mod 16; + if c>=var_code then + begin if fam_in_range then fam(nucleus(p)):=cur_fam; + type(p):=ord_noad; + end + else type(p):=ord_noad+(c div @'10000); + link(tail):=p; tail:=p; + end; +end; + +@ Primitive math operators like \.{\\mathop} and \.{\\underline} are given +the command code |math_comp|, supplemented by the noad type that they +generate. + +@<Put each...@>= +primitive("mathord",math_comp,ord_noad); +@!@:math_ord_}{\.{\\mathord} primitive@> +primitive("mathop",math_comp,op_noad); +@!@:math_op_}{\.{\\mathop} primitive@> +primitive("mathbin",math_comp,bin_noad); +@!@:math_bin_}{\.{\\mathbin} primitive@> +primitive("mathrel",math_comp,rel_noad); +@!@:math_rel_}{\.{\\mathrel} primitive@> +primitive("mathopen",math_comp,open_noad); +@!@:math_open_}{\.{\\mathopen} primitive@> +primitive("mathclose",math_comp,close_noad); +@!@:math_close_}{\.{\\mathclose} primitive@> +primitive("mathpunct",math_comp,punct_noad); +@!@:math_punct_}{\.{\\mathpunct} primitive@> +primitive("mathinner",math_comp,inner_noad); +@!@:math_inner_}{\.{\\mathinner} primitive@> +primitive("underline",math_comp,under_noad); +@!@:underline_}{\.{\\underline} primitive@> +primitive("overline",math_comp,over_noad);@/ +@!@:overline_}{\.{\\overline} primitive@> +primitive("displaylimits",limit_switch,normal); +@!@:display_limits_}{\.{\\displaylimits} primitive@> +primitive("limits",limit_switch,limits); +@!@:limits_}{\.{\\limits} primitive@> +primitive("nolimits",limit_switch,no_limits); +@!@:no_limits_}{\.{\\nolimits} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +math_comp: case chr_code of + ord_noad: print_esc("mathord"); + op_noad: print_esc("mathop"); + bin_noad: print_esc("mathbin"); + rel_noad: print_esc("mathrel"); + open_noad: print_esc("mathopen"); + close_noad: print_esc("mathclose"); + punct_noad: print_esc("mathpunct"); + inner_noad: print_esc("mathinner"); + under_noad: print_esc("underline"); + othercases print_esc("overline") + endcases; +limit_switch: if chr_code=limits then print_esc("limits") + else if chr_code=no_limits then print_esc("nolimits") + else print_esc("displaylimits"); + +@ @<Cases of |main_control| that build...@>= +mmode+math_comp: begin tail_append(new_noad); + type(tail):=cur_chr; scan_math(nucleus(tail)); + end; +mmode+limit_switch: math_limit_switch; + +@ @<Declare act...@>= +procedure math_limit_switch; +label exit; +begin if head<>tail then if type(tail)=op_noad then + begin subtype(tail):=cur_chr; return; + end; +print_err("Limit controls must follow a math operator"); +@.Limit controls must follow...@> +help1("I'm ignoring this misplaced \limits or \nolimits command."); error; +exit:end; + +@ Delimiter fields of noads are filled in by the |scan_delimiter| routine. +The first parameter of this procedure is the |mem| address where the +delimiter is to be placed; the second tells if this delimiter follows +\.{\\radical} or not. + +@<Declare act...@>= +procedure scan_delimiter(@!p:pointer;@!r:boolean); +begin if r then scan_twenty_seven_bit_int +else begin @<Get the next non-blank non-relax...@>; + case cur_cmd of + letter,other_char: cur_val:=del_code(cur_chr); + delim_num: scan_twenty_seven_bit_int; + othercases cur_val:=-1 + endcases; + end; +if cur_val<0 then @<Report that an invalid delimiter code is being changed + to null; set~|cur_val:=0|@>; +small_fam(p):=(cur_val div @'4000000) mod 16; +small_char(p):=qi((cur_val div @'10000) mod 256); +large_fam(p):=(cur_val div 256) mod 16; +large_char(p):=qi(cur_val mod 256); +end; + +@ @<Report that an invalid delimiter...@>= +begin print_err("Missing delimiter (. inserted)"); +@.Missing delimiter...@> +help6("I was expecting to see something like `(' or `\{' or")@/ + ("`\}' here. If you typed, e.g., `{' instead of `\{', you")@/ + ("should probably delete the `{' by typing `1' now, so that")@/ + ("braces don't get unbalanced. Otherwise just proceed.")@/ + ("Acceptable delimiters are characters whose \delcode is")@/ + ("nonnegative, or you can use `\delimiter <delimiter code>'."); +back_error; cur_val:=0; +end + +@ @<Cases of |main_control| that build...@>= +mmode+radical:math_radical; + +@ @<Declare act...@>= +procedure math_radical; +begin tail_append(get_node(radical_noad_size)); +type(tail):=radical_noad; subtype(tail):=normal; +mem[nucleus(tail)].hh:=empty_field; +mem[subscr(tail)].hh:=empty_field; +mem[supscr(tail)].hh:=empty_field; +scan_delimiter(left_delimiter(tail),true); scan_math(nucleus(tail)); +end; + +@ @<Cases of |main_control| that build...@>= +mmode+accent,mmode+math_accent:math_ac; + +@ @<Declare act...@>= +procedure math_ac; +begin if cur_cmd=accent then + @<Complain that the user should have said \.{\\mathaccent}@>; +tail_append(get_node(accent_noad_size)); +type(tail):=accent_noad; subtype(tail):=normal; +mem[nucleus(tail)].hh:=empty_field; +mem[subscr(tail)].hh:=empty_field; +mem[supscr(tail)].hh:=empty_field; +math_type(accent_chr(tail)):=math_char; +scan_fifteen_bit_int; +character(accent_chr(tail)):=qi(cur_val mod 256); +if (cur_val>=var_code)and fam_in_range then fam(accent_chr(tail)):=cur_fam +else fam(accent_chr(tail)):=(cur_val div 256) mod 16; +scan_math(nucleus(tail)); +end; + +@ @<Complain that the user should have said \.{\\mathaccent}@>= +begin print_err("Please use "); print_esc("mathaccent"); +print(" for accents in math mode"); +@.Please use \\mathaccent...@> +help2("I'm changing \accent to \mathaccent here; wish me luck.")@/ + ("(Accents are not the same in formulas as they are in text.)"); +error; +end + +@ @<Cases of |main_control| that build...@>= +mmode+vcenter: begin scan_spec(vcenter_group,false); normal_paragraph; + push_nest; mode:=-vmode; prev_depth:=ignore_depth; + if every_vbox<>null then begin_token_list(every_vbox,every_vbox_text); + end; + +@ @<Cases of |handle...@>= +vcenter_group: begin end_graf; unsave; save_ptr:=save_ptr-2; + p:=vpack(link(head),saved(1),saved(0)); pop_nest; + tail_append(new_noad); type(tail):=vcenter_noad; + math_type(nucleus(tail)):=sub_box; info(nucleus(tail)):=p; + end; + +@ The routine that inserts a |style_node| holds no surprises. + +@<Put each...@>= +primitive("displaystyle",math_style,display_style); +@!@:display_style_}{\.{\\displaystyle} primitive@> +primitive("textstyle",math_style,text_style); +@!@:text_style_}{\.{\\textstyle} primitive@> +primitive("scriptstyle",math_style,script_style); +@!@:script_style_}{\.{\\scriptstyle} primitive@> +primitive("scriptscriptstyle",math_style,script_script_style); +@!@:script_script_style_}{\.{\\scriptscriptstyle} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +math_style: print_style(chr_code); + +@ @<Cases of |main_control| that build...@>= +mmode+math_style: tail_append(new_style(cur_chr)); +mmode+non_script: begin tail_append(new_glue(zero_glue)); + subtype(tail):=cond_math_glue; + end; +mmode+math_choice: append_choices; + +@ The routine that scans the four mlists of a \.{\\mathchoice} is very +much like the routine that builds discretionary nodes. + +@<Declare act...@>= +procedure append_choices; +begin tail_append(new_choice); incr(save_ptr); saved(-1):=0; +push_math(math_choice_group); scan_left_brace; +end; + +@ @<Cases of |handle_right_brace|...@>= +math_choice_group: build_choices; + +@ @<Declare act...@>= +@t\4@>@<Declare the function called |fin_mlist|@>@t@>@;@/ +procedure build_choices; +label exit; +var p:pointer; {the current mlist} +begin unsave; p:=fin_mlist(null); +case saved(-1) of +0:display_mlist(tail):=p; +1:text_mlist(tail):=p; +2:script_mlist(tail):=p; +3:begin script_script_mlist(tail):=p; decr(save_ptr); return; + end; +end; {there are no other cases} +incr(saved(-1)); push_math(math_choice_group); scan_left_brace; +exit:end; + +@ Subscripts and superscripts are attached to the previous nucleus by the +@^superscripts@>@^subscripts@> +action procedure called |sub_sup|. We use the facts that |sub_mark=sup_mark+1| +and |subscr(p)=supscr(p)+1|. + +@<Cases of |main_control| that build...@>= +mmode+sub_mark,mmode+sup_mark: sub_sup; + +@ @<Declare act...@>= +procedure sub_sup; +var t:small_number; {type of previous sub/superscript} +@!p:pointer; {field to be filled by |scan_math|} +begin t:=empty; p:=null; +if tail<>head then if scripts_allowed(tail) then + begin p:=supscr(tail)+cur_cmd-sup_mark; {|supscr| or |subscr|} + t:=math_type(p); + end; +if (p=null)or(t<>empty) then @<Insert a dummy noad to be sub/superscripted@>; +scan_math(p); +end; + +@ @<Insert a dummy...@>= +begin tail_append(new_noad); +p:=supscr(tail)+cur_cmd-sup_mark; {|supscr| or |subscr|} +if t<>empty then + begin if cur_cmd=sup_mark then + begin print_err("Double superscript"); +@.Double superscript@> + help1("I treat `x^1^2' essentially like `x^1{}^2'."); + end + else begin print_err("Double subscript"); +@.Double subscript@> + help1("I treat `x_1_2' essentially like `x_1{}_2'."); + end; + error; + end; +end + +@ An operation like `\.{\\over}' causes the current mlist to go into a +state of suspended animation: |incompleat_noad| points to a |fraction_noad| +that contains the mlist-so-far as its numerator, while the denominator +is yet to come. Finally when the mlist is finished, the denominator will +go into the incompleat fraction noad, and that noad will become the +whole formula, unless it is surrounded by `\.{\\left}' and `\.{\\right}' +delimiters. + +@d above_code=0 { `\.{\\above}' } +@d over_code=1 { `\.{\\over}' } +@d atop_code=2 { `\.{\\atop}' } +@d delimited_code=3 { `\.{\\abovewithdelims}', etc.} + +@<Put each...@>= +primitive("above",above,above_code);@/ +@!@:above_}{\.{\\above} primitive@> +primitive("over",above,over_code);@/ +@!@:over_}{\.{\\over} primitive@> +primitive("atop",above,atop_code);@/ +@!@:atop_}{\.{\\atop} primitive@> +primitive("abovewithdelims",above,delimited_code+above_code);@/ +@!@:above_with_delims_}{\.{\\abovewithdelims} primitive@> +primitive("overwithdelims",above,delimited_code+over_code);@/ +@!@:over_with_delims_}{\.{\\overwithdelims} primitive@> +primitive("atopwithdelims",above,delimited_code+atop_code); +@!@:atop_with_delims_}{\.{\\atopwithdelims} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +above: case chr_code of + over_code:print_esc("over"); + atop_code:print_esc("atop"); + delimited_code+above_code:print_esc("abovewithdelims"); + delimited_code+over_code:print_esc("overwithdelims"); + delimited_code+atop_code:print_esc("atopwithdelims"); + othercases print_esc("above") + endcases; + +@ @<Cases of |main_control| that build...@>= +mmode+above: math_fraction; + +@ @<Declare act...@>= +procedure math_fraction; +var c:small_number; {the type of generalized fraction we are scanning} +begin c:=cur_chr; +if incompleat_noad<>null then + @<Ignore the fraction operation and complain about this ambiguous case@> +else begin incompleat_noad:=get_node(fraction_noad_size); + type(incompleat_noad):=fraction_noad; + subtype(incompleat_noad):=normal; + math_type(numerator(incompleat_noad)):=sub_mlist; + info(numerator(incompleat_noad)):=link(head); + mem[denominator(incompleat_noad)].hh:=empty_field; + mem[left_delimiter(incompleat_noad)].qqqq:=null_delimiter; + mem[right_delimiter(incompleat_noad)].qqqq:=null_delimiter;@/ + link(head):=null; tail:=head; + @<Use code |c| to distinguish between generalized fractions@>; + end; +end; + +@ @<Use code |c|...@>= +if c>=delimited_code then + begin scan_delimiter(left_delimiter(incompleat_noad),false); + scan_delimiter(right_delimiter(incompleat_noad),false); + end; +case c mod delimited_code of +above_code: begin scan_normal_dimen; + thickness(incompleat_noad):=cur_val; + end; +over_code: thickness(incompleat_noad):=default_code; +atop_code: thickness(incompleat_noad):=0; +end {there are no other cases} + +@ @<Ignore the fraction...@>= +begin if c>=delimited_code then + begin scan_delimiter(garbage,false); scan_delimiter(garbage,false); + end; +if c mod delimited_code=above_code then scan_normal_dimen; +print_err("Ambiguous; you need another { and }"); +@.Ambiguous...@> +help3("I'm ignoring this fraction specification, since I don't")@/ + ("know whether a construction like `x \over y \over z'")@/ + ("means `{x \over y} \over z' or `x \over {y \over z}'."); +error; +end + +@ At the end of a math formula or subformula, the |fin_mlist| routine is +called upon to return a pointer to the newly completed mlist, and to +pop the nest back to the enclosing semantic level. The parameter to +|fin_mlist|, if not null, points to a |right_noad| that ends the +current mlist; this |right_noad| has not yet been appended. + +@<Declare the function called |fin_mlist|@>= +function fin_mlist(@!p:pointer):pointer; +var q:pointer; {the mlist to return} +begin if incompleat_noad<>null then @<Compleat the incompleat noad@> +else begin link(tail):=p; q:=link(head); + end; +pop_nest; fin_mlist:=q; +end; + +@ @<Compleat...@>= +begin math_type(denominator(incompleat_noad)):=sub_mlist; +info(denominator(incompleat_noad)):=link(head); +if p=null then q:=incompleat_noad +else begin q:=info(numerator(incompleat_noad)); + if type(q)<>left_noad then confusion("right"); +@:this can't happen right}{\quad right@> + info(numerator(incompleat_noad)):=link(q); + link(q):=incompleat_noad; link(incompleat_noad):=p; + end; +end + +@ Now at last we're ready to see what happens when a right brace occurs +in a math formula. Two special cases are simplified here: Braces are effectively +removed when they surround a single Ord without sub/superscripts, or when they +surround an accent that is the nucleus of an Ord atom. + +@<Cases of |handle...@>= +math_group: begin unsave; decr(save_ptr);@/ + math_type(saved(0)):=sub_mlist; p:=fin_mlist(null); info(saved(0)):=p; + if p<>null then if link(p)=null then + if type(p)=ord_noad then + begin if math_type(subscr(p))=empty then + if math_type(supscr(p))=empty then + begin mem[saved(0)].hh:=mem[nucleus(p)].hh; + free_node(p,noad_size); + end; + end + else if type(p)=accent_noad then if saved(0)=nucleus(tail) then + if type(tail)=ord_noad then @<Replace the tail of the list by |p|@>; + end; + +@ @<Replace the tail...@>= +begin q:=head; while link(q)<>tail do q:=link(q); +link(q):=p; free_node(tail,noad_size); tail:=p; +end + +@ We have dealt with all constructions of math mode except `\.{\\left}' and +`\.{\\right}', so the picture is completed by the following sections of +the program. + +@<Put each...@>= +primitive("left",left_right,left_noad); +@!@:left_}{\.{\\left} primitive@> +primitive("right",left_right,right_noad); +@!@:right_}{\.{\\right} primitive@> +text(frozen_right):="right"; eqtb[frozen_right]:=eqtb[cur_val]; + +@ @<Cases of |print_cmd_chr|...@>= +left_right: if chr_code=left_noad then print_esc("left") +else print_esc("right"); + +@ @<Cases of |main_control| that build...@>= +mmode+left_right: math_left_right; + +@ @<Declare act...@>= +procedure math_left_right; +var t:small_number; {|left_noad| or |right_noad|} +@!p:pointer; {new noad} +begin t:=cur_chr; +if (t=right_noad)and(cur_group<>math_left_group) then + @<Try to recover from mismatched \.{\\right}@> +else begin p:=new_noad; type(p):=t; + scan_delimiter(delimiter(p),false); + if t=left_noad then + begin push_math(math_left_group); link(head):=p; tail:=p; + end + else begin p:=fin_mlist(p); unsave; {end of |math_left_group|} + tail_append(new_noad); type(tail):=inner_noad; + math_type(nucleus(tail)):=sub_mlist; + info(nucleus(tail)):=p; + end; + end; +end; + +@ @<Try to recover from mismatch...@>= +begin if cur_group=math_shift_group then + begin scan_delimiter(garbage,false); + print_err("Extra "); print_esc("right"); +@.Extra \\right.@> + help1("I'm ignoring a \right that had no matching \left."); + error; + end +else off_save; +end + +@ Here is the only way out of math mode. + +@<Cases of |main_control| that build...@>= +mmode+math_shift: if cur_group=math_shift_group then after_math + else off_save; + +@ @<Declare act...@>= +procedure after_math; +var l:boolean; {`\.{\\leqno}' instead of `\.{\\eqno}'} +@!danger:boolean; {not enough symbol fonts are present} +@!m:integer; {|mmode| or |-mmode|} +@!p:pointer; {the formula} +@!a:pointer; {box containing equation number} +@<Local variables for finishing a displayed formula@>@; +begin danger:=false; +@<Check that the necessary fonts for math symbols are present; + if not, flush the current math lists and set |danger:=true|@>; +m:=mode; l:=false; p:=fin_mlist(null); {this pops the nest} +if mode=-m then {end of equation number} + begin @<Check that another \.\$ follows@>; + cur_mlist:=p; cur_style:=text_style; mlist_penalties:=false; + mlist_to_hlist; a:=hpack(link(temp_head),natural); + unsave; decr(save_ptr); {now |cur_group=math_shift_group|} + if saved(0)=1 then l:=true; + danger:=false; + @<Check that the necessary fonts for math symbols are present; + if not, flush the current math lists and set |danger:=true|@>; + m:=mode; p:=fin_mlist(null); + end +else a:=null; +if m<0 then @<Finish math in text@> +else begin if a=null then @<Check that another \.\$ follows@>; + @<Finish displayed math@>; + end; +end; + +@ @<Check that the necessary fonts...@>= +if (font_params[fam_fnt(2+text_size)]<total_mathsy_params)or@| + (font_params[fam_fnt(2+script_size)]<total_mathsy_params)or@| + (font_params[fam_fnt(2+script_script_size)]<total_mathsy_params) then + begin print_err("Math formula deleted: Insufficient symbol fonts");@/ +@.Math formula deleted...@> + help3("Sorry, but I can't typeset math unless \textfont 2")@/ + ("and \scriptfont 2 and \scriptscriptfont 2 have all")@/ + ("the \fontdimen values needed in math symbol fonts."); + error; flush_math; danger:=true; + end +else if (font_params[fam_fnt(3+text_size)]<total_mathex_params)or@| + (font_params[fam_fnt(3+script_size)]<total_mathex_params)or@| + (font_params[fam_fnt(3+script_script_size)]<total_mathex_params) then + begin print_err("Math formula deleted: Insufficient extension fonts");@/ + help3("Sorry, but I can't typeset math unless \textfont 3")@/ + ("and \scriptfont 3 and \scriptscriptfont 3 have all")@/ + ("the \fontdimen values needed in math extension fonts."); + error; flush_math; danger:=true; + end + +@ The |unsave| is done after everything else here; hence an appearance of +`\.{\\mathsurround}' inside of `\.{\$...\$}' affects the spacing at these +particular \.\$'s. This is consistent with the conventions of +`\.{\$\$...\$\$}', since `\.{\\abovedisplayskip}' inside a display affects the +space above that display. + +@<Finish math in text@>= +begin tail_append(new_math(math_surround,before)); +cur_mlist:=p; cur_style:=text_style; mlist_penalties:=(mode>0); mlist_to_hlist; +link(tail):=link(temp_head); +while link(tail)<>null do tail:=link(tail); +tail_append(new_math(math_surround,after)); +space_factor:=1000; unsave; +end + +@ \TeX\ gets to the following part of the program when the first `\.\$' ending +a display has been scanned. + +@<Check that another \.\$ follows@>= +begin get_x_token; +if cur_cmd<>math_shift then + begin print_err("Display math should end with $$"); +@.Display math...with \$\$@> + help2("The `$' that I just saw supposedly matches a previous `$$'.")@/ + ("So I shall assume that you typed `$$' both times."); + back_error; + end; +end + +@ We have saved the worst for last: The fussiest part of math mode processing +occurs when a displayed formula is being centered and placed with an optional +equation number. + +@<Local variables for finishing...@>= +@!b:pointer; {box containing the equation} +@!w:scaled; {width of the equation} +@!z:scaled; {width of the line} +@!e:scaled; {width of equation number} +@!q:scaled; {width of equation number plus space to separate from equation} +@!d:scaled; {displacement of equation in the line} +@!s:scaled; {move the line right this much} +@!g1,@!g2:small_number; {glue parameter codes for before and after} +@!r:pointer; {kern node used to position the display} +@!t:pointer; {tail of adjustment list} + +@ At this time |p| points to the mlist for the formula; |a| is either +|null| or it points to a box containing the equation number; and we are in +vertical mode (or internal vertical mode). + +@<Finish displayed math@>= +cur_mlist:=p; cur_style:=display_style; mlist_penalties:=false; +mlist_to_hlist; p:=link(temp_head);@/ +adjust_tail:=adjust_head; b:=hpack(p,natural); p:=list_ptr(b); +t:=adjust_tail; adjust_tail:=null;@/ +w:=width(b); z:=display_width; s:=display_indent; +if (a=null)or danger then + begin e:=0; q:=0; + end +else begin e:=width(a); q:=e+math_quad(text_size); + end; +if w+q>z then + @<Squeeze the equation as much as possible; if there is an equation + number that should go on a separate line by itself, + set~|e:=0|@>; +@<Determine the displacement, |d|, of the left edge of the equation, with + respect to the line size |z|, assuming that |l=false|@>; +@<Append the glue or equation number preceding the display@>; +@<Append the display and perhaps also the equation number@>; +@<Append the glue or equation number following the display@>; +resume_after_display + +@ @<Declare act...@>= +procedure resume_after_display; +begin if cur_group<>math_shift_group then confusion("display"); +@:this can't happen display}{\quad display@> +unsave; prev_graf:=prev_graf+3; +push_nest; mode:=hmode; space_factor:=1000; set_cur_lang; clang:=cur_lang; +prev_graf:=(norm_min(left_hyphen_min)*@'100+norm_min(right_hyphen_min)) + *@'200000+cur_lang; +@<Scan an optional space@>; +if nest_ptr=1 then build_page; +end; + +@ The user can force the equation number to go on a separate line +by causing its width to be zero. + +@<Squeeze the equation as much as possible...@>= +begin if (e<>0)and((w-total_shrink[normal]+q<=z)or@| + (total_shrink[fil]<>0)or(total_shrink[fill]<>0)or + (total_shrink[filll]<>0)) then + begin free_node(b,box_node_size); + b:=hpack(p,z-q,exactly); + end +else begin e:=0; + if w>z then + begin free_node(b,box_node_size); + b:=hpack(p,z,exactly); + end; + end; +w:=width(b); +end + +@ We try first to center the display without regard to the existence of +the equation number. If that would make it too close (where ``too close'' +means that the space between display and equation number is less than the +width of the equation number), we either center it in the remaining space +or move it as far from the equation number as possible. The latter alternative +is taken only if the display begins with glue, since we assume that the +user put glue there to control the spacing precisely. + +@<Determine the displacement, |d|, of the left edge of the equation...@>= +d:=half(z-w); +if (e>0)and(d<2*e) then {too close} + begin d:=half(z-w-e); + if p<>null then if not is_char_node(p) then if type(p)=glue_node then d:=0; + end + +@ If the equation number is set on a line by itself, either before or +after the formula, we append an infinite penalty so that no page break will +separate the display from its number; and we use the same size and +displacement for all three potential lines of the display, even though +`\.{\\parshape}' may specify them differently. + +@<Append the glue or equation number preceding the display@>= +tail_append(new_penalty(pre_display_penalty));@/ +if (d+s<=pre_display_size)or l then {not enough clearance} + begin g1:=above_display_skip_code; g2:=below_display_skip_code; + end +else begin g1:=above_display_short_skip_code; + g2:=below_display_short_skip_code; + end; +if l and(e=0) then {it follows that |type(a)=hlist_node|} + begin shift_amount(a):=s; append_to_vlist(a); + tail_append(new_penalty(inf_penalty)); + end +else tail_append(new_param_glue(g1)) + +@ @<Append the display and perhaps also the equation number@>= +if e<>0 then + begin r:=new_kern(z-w-e-d); + if l then + begin link(a):=r; link(r):=b; b:=a; d:=0; + end + else begin link(b):=r; link(r):=a; + end; + b:=hpack(b,natural); + end; +shift_amount(b):=s+d; append_to_vlist(b) + +@ @<Append the glue or equation number following the display@>= +if (a<>null)and(e=0)and not l then + begin tail_append(new_penalty(inf_penalty)); + shift_amount(a):=s+z-width(a); + append_to_vlist(a); + g2:=0; + end; +if t<>adjust_head then {migrating material comes after equation number} + begin link(tail):=link(adjust_head); tail:=t; + end; +tail_append(new_penalty(post_display_penalty)); +if g2>0 then tail_append(new_param_glue(g2)) + +@ When \.{\\halign} appears in a display, the alignment routines operate +essentially as they do in vertical mode. Then the following program is +activated, with |p| and |q| pointing to the beginning and end of the +resulting list, and with |aux_save| holding the |prev_depth| value. + +@<Finish an alignment in a display@>= +begin do_assignments; +if cur_cmd<>math_shift then @<Pontificate about improper alignment in display@> +else @<Check that another \.\$ follows@>; +pop_nest; +tail_append(new_penalty(pre_display_penalty)); +tail_append(new_param_glue(above_display_skip_code)); +link(tail):=p; +if p<>null then tail:=q; +tail_append(new_penalty(post_display_penalty)); +tail_append(new_param_glue(below_display_skip_code)); +prev_depth:=aux_save.sc; resume_after_display; +end + +@ @<Pontificate...@>= +begin print_err("Missing $$ inserted"); +@.Missing {\$\$} inserted@> +help2("Displays can use special alignments (like \eqalignno)")@/ + ("only if nothing but the alignment itself is between $$'s."); +back_error; +end + +@* \[49] Mode-independent processing. +The long |main_control| procedure has now been fully specified, except for +certain activities that are independent of the current mode. These activities +do not change the current vlist or hlist or mlist; if they change anything, +it is the value of a parameter or the meaning of a control sequence. + +Assignments to values in |eqtb| can be global or local. Furthermore, a +control sequence can be defined to be `\.{\\long}' or `\.{\\outer}', and +it might or might not be expanded. The prefixes `\.{\\global}', `\.{\\long}', +and `\.{\\outer}' can occur in any order. Therefore we assign binary numeric +codes, making it possible to accumulate the union of all specified prefixes +by adding the corresponding codes. (\PASCAL's |set| operations could also +have been used.) + +@<Put each...@>= +primitive("long",prefix,1); +@!@:long_}{\.{\\long} primitive@> +primitive("outer",prefix,2); +@!@:outer_}{\.{\\outer} primitive@> +primitive("global",prefix,4); +@!@:global_}{\.{\\global} primitive@> +primitive("def",def,0); +@!@:def_}{\.{\\def} primitive@> +primitive("gdef",def,1); +@!@:gdef_}{\.{\\gdef} primitive@> +primitive("edef",def,2); +@!@:edef_}{\.{\\edef} primitive@> +primitive("xdef",def,3); +@!@:xdef_}{\.{\\xdef} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +prefix: if chr_code=1 then print_esc("long") + else if chr_code=2 then print_esc("outer") + else print_esc("global"); +def: if chr_code=0 then print_esc("def") + else if chr_code=1 then print_esc("gdef") + else if chr_code=2 then print_esc("edef") + else print_esc("xdef"); + +@ Every prefix, and every command code that might or might not be prefixed, +calls the action procedure |prefixed_command|. This routine accumulates +a sequence of prefixes until coming to a non-prefix, then it carries out +the command. + +@<Cases of |main_control| that don't...@>= +any_mode(toks_register), +any_mode(assign_toks), +any_mode(assign_int), +any_mode(assign_dimen), +any_mode(assign_glue), +any_mode(assign_mu_glue), +any_mode(assign_font_dimen), +any_mode(assign_font_int), +any_mode(set_aux), +any_mode(set_prev_graf), +any_mode(set_page_dimen), +any_mode(set_page_int), +any_mode(set_box_dimen), +any_mode(set_shape), +any_mode(def_code), +any_mode(def_family), +any_mode(set_font), +any_mode(def_font), +any_mode(register), +any_mode(advance), +any_mode(multiply), +any_mode(divide), +any_mode(prefix), +any_mode(let), +any_mode(shorthand_def), +any_mode(read_to_cs), +any_mode(def), +any_mode(set_box), +any_mode(hyph_data), +any_mode(set_interaction):prefixed_command; + +@ If the user says, e.g., `\.{\\global\\global}', the redundancy is +silently accepted. + +@<Declare act...@>= +@t\4@>@<Declare subprocedures for |prefixed_command|@>@t@>@;@/ +procedure prefixed_command; +label done,exit; +var a:small_number; {accumulated prefix codes so far} +@!f:internal_font_number; {identifies a font} +@!j:halfword; {index into a \.{\\parshape} specification} +@!k:font_index; {index into |font_info|} +@!p,@!q:pointer; {for temporary short-term use} +@!n:integer; {ditto} +@!e:boolean; {should a definition be expanded? or was \.{\\let} not done?} +begin a:=0; +while cur_cmd=prefix do + begin if not odd(a div cur_chr) then a:=a+cur_chr; + @<Get the next non-blank non-relax...@>; + if cur_cmd<=max_non_prefixed_command then + @<Discard erroneous prefixes and |return|@>; + end; +@<Discard the prefixes \.{\\long} and \.{\\outer} if they are irrelevant@>; +@<Adjust \(f)for the setting of \.{\\globaldefs}@>; +case cur_cmd of +@t\4@>@<Assignments@>@; +othercases confusion("prefix") +@:this can't happen prefix}{\quad prefix@> +endcases; +done: @<Insert a token saved by \.{\\afterassignment}, if any@>; +exit:end; + +@ @<Discard erroneous...@>= +begin print_err("You can't use a prefix with `"); +@.You can't use a prefix with x@> +print_cmd_chr(cur_cmd,cur_chr); print_char("'"); +help1("I'll pretend you didn't say \long or \outer or \global."); +back_error; return; +end + +@ @<Discard the prefixes...@>= +if (cur_cmd<>def)and(a mod 4<>0) then + begin print_err("You can't use `"); print_esc("long"); print("' or `"); + print_esc("outer"); print("' with `"); +@.You can't use \\long...@> + print_cmd_chr(cur_cmd,cur_chr); print_char("'"); + help1("I'll pretend you didn't say \long or \outer here."); + error; + end + +@ The previous routine does not have to adjust |a| so that |a mod 4=0|, +since the following routines test for the \.{\\global} prefix as follows. + +@d global==(a>=4) +@d define(#)==if global then geq_define(#)@+else eq_define(#) +@d word_define(#)==if global then geq_word_define(#)@+else eq_word_define(#) + +@<Adjust \(f)for the setting of \.{\\globaldefs}@>= +if global_defs<>0 then + if global_defs<0 then + begin if global then a:=a-4; + end + else begin if not global then a:=a+4; + end + +@ When a control sequence is to be defined, by \.{\\def} or \.{\\let} or +something similar, the |get_r_token| routine will substitute a special +control sequence for a token that is not redefinable. + +@<Declare subprocedures for |prefixed_command|@>= +procedure get_r_token; +label restart; +begin restart: repeat get_token; +until cur_tok<>space_token; +if (cur_cs=0)or(cur_cs>frozen_control_sequence) then + begin print_err("Missing control sequence inserted"); +@.Missing control...@> + help5("Please don't say `\def cs{...}', say `\def\cs{...}'.")@/ + ("I've inserted an inaccessible control sequence so that your")@/ + ("definition will be completed without mixing me up too badly.")@/ + ("You can recover graciously from this error, if you're")@/ + ("careful; see exercise 27.2 in The TeXbook."); +@:TeXbook}{\sl The \TeX book@> + if cur_cs=0 then back_input; + cur_tok:=cs_token_flag+frozen_protection; ins_error; goto restart; + end; +end; + +@ @<Initialize table entries...@>= +text(frozen_protection):="inaccessible"; + +@ Here's an example of the way many of the following routines operate. +(Unfortunately, they aren't all as simple as this.) + +@<Assignments@>= +set_font: define(cur_font_loc,data,cur_chr); + +@ When a |def| command has been scanned, +|cur_chr| is odd if the definition is supposed to be global, and +|cur_chr>=2| if the definition is supposed to be expanded. + +@<Assignments@>= +def: begin if odd(cur_chr)and not global and(global_defs>=0) then a:=a+4; + e:=(cur_chr>=2); get_r_token; p:=cur_cs; + q:=scan_toks(true,e); define(p,call+(a mod 4),def_ref); + end; + +@ Both \.{\\let} and \.{\\futurelet} share the command code |let|. + +@<Put each...@>= +primitive("let",let,normal);@/ +@!@:let_}{\.{\\let} primitive@> +primitive("futurelet",let,normal+1);@/ +@!@:future_let_}{\.{\\futurelet} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +let: if chr_code<>normal then print_esc("futurelet")@+else print_esc("let"); + +@ @<Assignments@>= +let: begin n:=cur_chr; + get_r_token; p:=cur_cs; + if n=normal then + begin repeat get_token; + until cur_cmd<>spacer; + if cur_tok=other_token+"=" then + begin get_token; + if cur_cmd=spacer then get_token; + end; + end + else begin get_token; q:=cur_tok; get_token; back_input; + cur_tok:=q; back_input; {look ahead, then back up} + end; {note that |back_input| doesn't affect |cur_cmd|, |cur_chr|} + if cur_cmd>=call then add_token_ref(cur_chr); + define(p,cur_cmd,cur_chr); + end; + +@ A \.{\\chardef} creates a control sequence whose |cmd| is |char_given|; +a \.{\\mathchardef} creates a control sequence whose |cmd| is |math_given|; +and the corresponding |chr| is the character code or math code. A \.{\\countdef} +or \.{\\dimendef} or \.{\\skipdef} or \.{\\muskipdef} creates a control +sequence whose |cmd| is |assign_int| or \dots\ or |assign_mu_glue|, and the +corresponding |chr| is the |eqtb| location of the internal register in question. + +@d char_def_code=0 {|shorthand_def| for \.{\\chardef}} +@d math_char_def_code=1 {|shorthand_def| for \.{\\mathchardef}} +@d count_def_code=2 {|shorthand_def| for \.{\\countdef}} +@d dimen_def_code=3 {|shorthand_def| for \.{\\dimendef}} +@d skip_def_code=4 {|shorthand_def| for \.{\\skipdef}} +@d mu_skip_def_code=5 {|shorthand_def| for \.{\\muskipdef}} +@d toks_def_code=6 {|shorthand_def| for \.{\\toksdef}} + +@<Put each...@>= +primitive("chardef",shorthand_def,char_def_code);@/ +@!@:char_def_}{\.{\\chardef} primitive@> +primitive("mathchardef",shorthand_def,math_char_def_code);@/ +@!@:math_char_def_}{\.{\\mathchardef} primitive@> +primitive("countdef",shorthand_def,count_def_code);@/ +@!@:count_def_}{\.{\\countdef} primitive@> +primitive("dimendef",shorthand_def,dimen_def_code);@/ +@!@:dimen_def_}{\.{\\dimendef} primitive@> +primitive("skipdef",shorthand_def,skip_def_code);@/ +@!@:skip_def_}{\.{\\skipdef} primitive@> +primitive("muskipdef",shorthand_def,mu_skip_def_code);@/ +@!@:mu_skip_def_}{\.{\\muskipdef} primitive@> +primitive("toksdef",shorthand_def,toks_def_code);@/ +@!@:toks_def_}{\.{\\toksdef} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +shorthand_def: case chr_code of + char_def_code: print_esc("chardef"); + math_char_def_code: print_esc("mathchardef"); + count_def_code: print_esc("countdef"); + dimen_def_code: print_esc("dimendef"); + skip_def_code: print_esc("skipdef"); + mu_skip_def_code: print_esc("muskipdef"); + othercases print_esc("toksdef") + endcases; +char_given: begin print_esc("char"); print_hex(chr_code); + end; +math_given: begin print_esc("mathchar"); print_hex(chr_code); + end; + +@ We temporarily define |p| to be |relax|, so that an occurrence of |p| +while scanning the definition will simply stop the scanning instead of +producing an ``undefined control sequence'' error or expanding the +previous meaning. This allows, for instance, `\.{\\chardef\\foo=123\\foo}'. + +@<Assignments@>= +shorthand_def: begin n:=cur_chr; get_r_token; p:=cur_cs; define(p,relax,256); + scan_optional_equals; + case n of + char_def_code: begin scan_char_num; define(p,char_given,cur_val); + end; + math_char_def_code: begin scan_fifteen_bit_int; define(p,math_given,cur_val); + end; + othercases begin scan_eight_bit_int; + case n of + count_def_code: define(p,assign_int,count_base+cur_val); + dimen_def_code: define(p,assign_dimen,scaled_base+cur_val); + skip_def_code: define(p,assign_glue,skip_base+cur_val); + mu_skip_def_code: define(p,assign_mu_glue,mu_skip_base+cur_val); + toks_def_code: define(p,assign_toks,toks_base+cur_val); + end; {there are no other cases} + end + endcases; + end; + +@ @<Assignments@>= +read_to_cs: begin scan_int; n:=cur_val; + if not scan_keyword("to") then + begin print_err("Missing `to' inserted"); +@.Missing `to'...@> + help2("You should have said `\read<number> to \cs'.")@/ + ("I'm going to look for the \cs now."); error; + end; + get_r_token; + p:=cur_cs; read_toks(n,p); define(p,call,cur_val); + end; + +@ The token-list parameters, \.{\\output} and \.{\\everypar}, etc., receive +their values in the following way. (For safety's sake, we place an +enclosing pair of braces around an \.{\\output} list.) + +@<Assignments@>= +toks_register,assign_toks: begin q:=cur_cs; + if cur_cmd=toks_register then + begin scan_eight_bit_int; p:=toks_base+cur_val; + end + else p:=cur_chr; {|p=every_par_loc| or |output_routine_loc| or \dots} + scan_optional_equals; + @<Get the next non-blank non-relax non-call token@>; + if cur_cmd<>left_brace then @<If the right-hand side is a token parameter + or token register, finish the assignment and |goto done|@>; + back_input; cur_cs:=q; q:=scan_toks(false,false); + if link(def_ref)=null then {empty list: revert to the default} + begin define(p,undefined_cs,null); free_avail(def_ref); + end + else begin if p=output_routine_loc then {enclose in curlies} + begin link(q):=get_avail; q:=link(q); + info(q):=right_brace_token+"}"; + q:=get_avail; info(q):=left_brace_token+"{"; + link(q):=link(def_ref); link(def_ref):=q; + end; + define(p,call,def_ref); + end; + end; + +@ @<If the right-hand side is a token parameter...@>= +begin if cur_cmd=toks_register then + begin scan_eight_bit_int; cur_cmd:=assign_toks; cur_chr:=toks_base+cur_val; + end; +if cur_cmd=assign_toks then + begin q:=equiv(cur_chr); + if q=null then define(p,undefined_cs,null) + else begin add_token_ref(q); define(p,call,q); + end; + goto done; + end; +end + +@ Similar routines are used to assign values to the numeric parameters. + +@<Assignments@>= +assign_int: begin p:=cur_chr; scan_optional_equals; scan_int; + word_define(p,cur_val); + end; +assign_dimen: begin p:=cur_chr; scan_optional_equals; + scan_normal_dimen; word_define(p,cur_val); + end; +assign_glue,assign_mu_glue: begin p:=cur_chr; n:=cur_cmd; scan_optional_equals; + if n=assign_mu_glue then scan_glue(mu_val)@+else scan_glue(glue_val); + trap_zero_glue; + define(p,glue_ref,cur_val); + end; + +@ When a glue register or parameter becomes zero, it will always point to +|zero_glue| because of the following procedure. (Exception: The tabskip +glue isn't trapped while preambles are being scanned.) + +@<Declare subprocedures for |prefixed_command|@>= +procedure trap_zero_glue; +begin if (width(cur_val)=0)and(stretch(cur_val)=0)and(shrink(cur_val)=0) then + begin add_glue_ref(zero_glue); + delete_glue_ref(cur_val); cur_val:=zero_glue; + end; +end; + +@ The various character code tables are changed by the |def_code| commands, +and the font families are declared by |def_family|. + +@<Put each...@>= +primitive("catcode",def_code,cat_code_base); +@!@:cat_code_}{\.{\\catcode} primitive@> +primitive("mathcode",def_code,math_code_base); +@!@:math_code_}{\.{\\mathcode} primitive@> +primitive("lccode",def_code,lc_code_base); +@!@:lc_code_}{\.{\\lccode} primitive@> +primitive("uccode",def_code,uc_code_base); +@!@:uc_code_}{\.{\\uccode} primitive@> +primitive("sfcode",def_code,sf_code_base); +@!@:sf_code_}{\.{\\sfcode} primitive@> +primitive("delcode",def_code,del_code_base); +@!@:del_code_}{\.{\\delcode} primitive@> +primitive("textfont",def_family,math_font_base); +@!@:text_font_}{\.{\\textfont} primitive@> +primitive("scriptfont",def_family,math_font_base+script_size); +@!@:script_font_}{\.{\\scriptfont} primitive@> +primitive("scriptscriptfont",def_family,math_font_base+script_script_size); +@!@:script_script_font_}{\.{\\scriptscriptfont} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +def_code: if chr_code=cat_code_base then print_esc("catcode") + else if chr_code=math_code_base then print_esc("mathcode") + else if chr_code=lc_code_base then print_esc("lccode") + else if chr_code=uc_code_base then print_esc("uccode") + else if chr_code=sf_code_base then print_esc("sfcode") + else print_esc("delcode"); +def_family: print_size(chr_code-math_font_base); + +@ The different types of code values have different legal ranges; the +following program is careful to check each case properly. + +@<Assignments@>= +def_code: begin @<Let |n| be the largest legal code value, based on |cur_chr|@>; + p:=cur_chr; scan_char_num; p:=p+cur_val; scan_optional_equals; + scan_int; + if ((cur_val<0)and(p<del_code_base))or(cur_val>n) then + begin print_err("Invalid code ("); print_int(cur_val); +@.Invalid code@> + if p<del_code_base then print("), should be in the range 0..") + else print("), should be at most "); + print_int(n); + help1("I'm going to use 0 instead of that illegal code value.");@/ + error; cur_val:=0; + end; + if p<math_code_base then define(p,data,cur_val) + else if p<del_code_base then define(p,data,hi(cur_val)) + else word_define(p,cur_val); + end; + +@ @<Let |n| be the largest...@>= +if cur_chr=cat_code_base then n:=max_char_code +else if cur_chr=math_code_base then n:=@'100000 +else if cur_chr=sf_code_base then n:=@'77777 +else if cur_chr=del_code_base then n:=@'77777777 +else n:=255 + +@ @<Assignments@>= +def_family: begin p:=cur_chr; scan_four_bit_int; p:=p+cur_val; + scan_optional_equals; scan_font_ident; define(p,data,cur_val); + end; + +@ Next we consider changes to \TeX's numeric registers. + +@<Assignments@>= +register,advance,multiply,divide: do_register_command(a); + +@ We use the fact that |register<advance<multiply<divide|. + +@<Declare subprocedures for |prefixed_command|@>= +procedure do_register_command(@!a:small_number); +label found,exit; +var l,@!q,@!r,@!s:pointer; {for list manipulation} +@!p:int_val..mu_val; {type of register involved} +begin q:=cur_cmd; +@<Compute the register location |l| and its type |p|; but |return| if invalid@>; +if q=register then scan_optional_equals +else if scan_keyword("by") then do_nothing; {optional `\.{by}'} +arith_error:=false; +if q<multiply then @<Compute result of |register| or + |advance|, put it in |cur_val|@> +else @<Compute result of |multiply| or |divide|, put it in |cur_val|@>; +if arith_error then + begin print_err("Arithmetic overflow"); +@.Arithmetic overflow@> + help2("I can't carry out that multiplication or division,")@/ + ("since the result is out of range."); + error; return; + end; +if p<glue_val then word_define(l,cur_val) +else begin trap_zero_glue; define(l,glue_ref,cur_val); + end; +exit: end; + +@ Here we use the fact that the consecutive codes |int_val...mu_val| and +|assign_int..assign_mu_glue| correspond to each other nicely. + +@<Compute the register location |l| and its type |p|...@>= +begin if q<>register then + begin get_x_token; + if (cur_cmd>=assign_int)and(cur_cmd<=assign_mu_glue) then + begin l:=cur_chr; p:=cur_cmd-assign_int; goto found; + end; + if cur_cmd<>register then + begin print_err("You can't use `"); print_cmd_chr(cur_cmd,cur_chr); +@.You can't use x after ...@> + print("' after "); print_cmd_chr(q,0); + help1("I'm forgetting what you said and not changing anything."); + error; return; + end; + end; +p:=cur_chr; scan_eight_bit_int; +case p of +int_val: l:=cur_val+count_base; +dimen_val: l:=cur_val+scaled_base; +glue_val: l:=cur_val+skip_base; +mu_val: l:=cur_val+mu_skip_base; +end; {there are no other cases} +end; +found: + +@ @<Compute result of |register| or |advance|...@>= +if p<glue_val then + begin if p=int_val then scan_int@+else scan_normal_dimen; + if q=advance then cur_val:=cur_val+eqtb[l].int; + end +else begin scan_glue(p); + if q=advance then @<Compute the sum of two glue specs@>; + end + +@ @<Compute the sum of two glue specs@>= +begin q:=new_spec(cur_val); r:=equiv(l); +delete_glue_ref(cur_val); +width(q):=width(q)+width(r); +if stretch(q)=0 then stretch_order(q):=normal; +if stretch_order(q)=stretch_order(r) then stretch(q):=stretch(q)+stretch(r) +else if (stretch_order(q)<stretch_order(r))and(stretch(r)<>0) then + begin stretch(q):=stretch(r); stretch_order(q):=stretch_order(r); + end; +if shrink(q)=0 then shrink_order(q):=normal; +if shrink_order(q)=shrink_order(r) then shrink(q):=shrink(q)+shrink(r) +else if (shrink_order(q)<shrink_order(r))and(shrink(r)<>0) then + begin shrink(q):=shrink(r); shrink_order(q):=shrink_order(r); + end; +cur_val:=q; +end + +@ @<Compute result of |multiply| or |divide|...@>= +begin scan_int; +if p<glue_val then + if q=multiply then + if p=int_val then cur_val:=mult_integers(eqtb[l].int,cur_val) + else cur_val:=nx_plus_y(eqtb[l].int,cur_val,0) + else cur_val:=x_over_n(eqtb[l].int,cur_val) +else begin s:=equiv(l); r:=new_spec(s); + if q=multiply then + begin width(r):=nx_plus_y(width(s),cur_val,0); + stretch(r):=nx_plus_y(stretch(s),cur_val,0); + shrink(r):=nx_plus_y(shrink(s),cur_val,0); + end + else begin width(r):=x_over_n(width(s),cur_val); + stretch(r):=x_over_n(stretch(s),cur_val); + shrink(r):=x_over_n(shrink(s),cur_val); + end; + cur_val:=r; + end; +end + +@ The processing of boxes is somewhat different, because we may need +to scan and create an entire box before we actually change the value of the old +one. + +@<Assignments@>= +set_box: begin scan_eight_bit_int; + if global then n:=256+cur_val@+else n:=cur_val; + scan_optional_equals; + if set_box_allowed then scan_box(box_flag+n) + else begin print_err("Improper "); print_esc("setbox"); +@.Improper \\setbox@> + help2("Sorry, \setbox is not allowed after \halign in a display,")@/ + ("or between \accent and an accented character."); error; + end; + end; + +@ The |space_factor| or |prev_depth| settings are changed when a |set_aux| +command is sensed. Similarly, |prev_graf| is changed in the presence of +|set_prev_graf|, and |dead_cycles| or |insert_penalties| in the presence of +|set_page_int|. These definitions are always global. + +When some dimension of a box register is changed, the change isn't exactly +global; but \TeX\ does not look at the \.{\\global} switch. + +@<Assignments@>= +set_aux:alter_aux; +set_prev_graf:alter_prev_graf; +set_page_dimen:alter_page_so_far; +set_page_int:alter_integer; +set_box_dimen:alter_box_dimen; + +@ @<Declare subprocedures for |prefixed_command|@>= +procedure alter_aux; +var c:halfword; {|hmode| or |vmode|} +begin if cur_chr<>abs(mode) then report_illegal_case +else begin c:=cur_chr; scan_optional_equals; + if c=vmode then + begin scan_normal_dimen; prev_depth:=cur_val; + end + else begin scan_int; + if (cur_val<=0)or(cur_val>32767) then + begin print_err("Bad space factor"); +@.Bad space factor@> + help1("I allow only values in the range 1..32767 here."); + int_error(cur_val); + end + else space_factor:=cur_val; + end; + end; +end; + +@ @<Declare subprocedures for |prefixed_command|@>= +procedure alter_prev_graf; +var p:0..nest_size; {index into |nest|} +begin nest[nest_ptr]:=cur_list; p:=nest_ptr; +while abs(nest[p].mode_field)<>vmode do decr(p); +scan_optional_equals; scan_int; +if cur_val<0 then + begin print_err("Bad "); print_esc("prevgraf"); +@.Bad \\prevgraf@> + help1("I allow only nonnegative values here."); + int_error(cur_val); + end +else begin nest[p].pg_field:=cur_val; cur_list:=nest[nest_ptr]; + end; +end; + +@ @<Declare subprocedures for |prefixed_command|@>= +procedure alter_page_so_far; +var c:0..7; {index into |page_so_far|} +begin c:=cur_chr; scan_optional_equals; scan_normal_dimen; +page_so_far[c]:=cur_val; +end; + +@ @<Declare subprocedures for |prefixed_command|@>= +procedure alter_integer; +var c:0..1; {0 for \.{\\deadcycles}, 1 for \.{\\insertpenalties}} +begin c:=cur_chr; scan_optional_equals; scan_int; +if c=0 then dead_cycles:=cur_val +else insert_penalties:=cur_val; +end; + +@ @<Declare subprocedures for |prefixed_command|@>= +procedure alter_box_dimen; +var c:small_number; {|width_offset| or |height_offset| or |depth_offset|} +@!b:eight_bits; {box number} +begin c:=cur_chr; scan_eight_bit_int; b:=cur_val; scan_optional_equals; +scan_normal_dimen; +if box(b)<>null then mem[box(b)+c].sc:=cur_val; +end; + +@ Paragraph shapes are set up in the obvious way. + +@<Assignments@>= +set_shape: begin scan_optional_equals; scan_int; n:=cur_val; + if n<=0 then p:=null + else begin p:=get_node(2*n+1); info(p):=n; + for j:=1 to n do + begin scan_normal_dimen; + mem[p+2*j-1].sc:=cur_val; {indentation} + scan_normal_dimen; + mem[p+2*j].sc:=cur_val; {width} + end; + end; + define(par_shape_loc,shape_ref,p); + end; + +@ Here's something that isn't quite so obvious. It guarantees that +|info(par_shape_ptr)| can hold any positive~|n| for which |get_node(2*n+1)| +doesn't overflow the memory capacity. + +@<Check the ``constant''...@>= +if 2*max_halfword<mem_top-mem_min then bad:=41; + +@ New hyphenation data is loaded by the |hyph_data| command. + +@<Put each...@>= +primitive("hyphenation",hyph_data,0); +@!@:hyphenation_}{\.{\\hyphenation} primitive@> +primitive("patterns",hyph_data,1); +@!@:patterns_}{\.{\\patterns} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +hyph_data: if chr_code=1 then print_esc("patterns") + else print_esc("hyphenation"); + +@ @<Assignments@>= +hyph_data: if cur_chr=1 then + begin @!init new_patterns; goto done;@;@+tini@/ + print_err("Patterns can be loaded only by INITEX"); +@.Patterns can be...@> + help0; error; + repeat get_token; until cur_cmd=right_brace; {flush the patterns} + return; + end + else begin new_hyph_exceptions; goto done; + end; + +@ All of \TeX's parameters are kept in |eqtb| except the font information, +the interaction mode, and the hyphenation tables; these are strictly global. + +@<Assignments@>= +assign_font_dimen: begin find_font_dimen(true); k:=cur_val; + scan_optional_equals; scan_normal_dimen; font_info[k].sc:=cur_val; + end; +assign_font_int: begin n:=cur_chr; scan_font_ident; f:=cur_val; + scan_optional_equals; scan_int; + if n=0 then hyphen_char[f]:=cur_val@+else skew_char[f]:=cur_val; + end; + +@ @<Put each...@>= +primitive("hyphenchar",assign_font_int,0); +@!@:hyphen_char_}{\.{\\hyphenchar} primitive@> +primitive("skewchar",assign_font_int,1); +@!@:skew_char_}{\.{\\skewchar} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +assign_font_int: if chr_code=0 then print_esc("hyphenchar") + else print_esc("skewchar"); + +@ Here is where the information for a new font gets loaded. + +@<Assignments@>= +def_font: new_font(a); + +@ @<Declare subprocedures for |prefixed_command|@>= +procedure new_font(@!a:small_number); +label common_ending; +var u:pointer; {user's font identifier} +@!s:scaled; {stated ``at'' size, or negative of scaled magnification} +@!f:internal_font_number; {runs through existing fonts} +@!t:str_number; {name for the frozen font identifier} +@!old_setting:0..max_selector; {holds |selector| setting} +@!flushable_string:str_number; {string not yet referenced} +begin if job_name=0 then open_log_file; + {avoid confusing \.{texput} with the font name} +@.texput@> +get_r_token; u:=cur_cs; +if u>=hash_base then t:=text(u) +else if u>=single_base then + if u=null_cs then t:="FONT"@+else t:=u-single_base +else begin old_setting:=selector; selector:=new_string; + print("FONT"); print(u-active_base); selector:=old_setting; +@.FONTx@> + str_room(1); t:=make_string; + end; +define(u,set_font,null_font); scan_optional_equals; scan_file_name; +@<Scan the font size specification@>; +@<If this font has already been loaded, set |f| to the internal + font number and |goto common_ending|@>; +f:=read_font_info(u,cur_name,cur_area,s); +common_ending: equiv(u):=f; eqtb[font_id_base+f]:=eqtb[u]; font_id_text(f):=t; +end; + +@ @<Scan the font size specification@>= +name_in_progress:=true; {this keeps |cur_name| from being changed} +if scan_keyword("at") then @<Put the \(p)(positive) `at' size into |s|@> +@.at@> +else if scan_keyword("scaled") then +@.scaled@> + begin scan_int; s:=-cur_val; + if (cur_val<=0)or(cur_val>32768) then + begin print_err("Illegal magnification has been changed to 1000");@/ +@.Illegal magnification...@> + help1("The magnification ratio must be between 1 and 32768."); + int_error(cur_val); s:=-1000; + end; + end +else s:=-1000; +name_in_progress:=false + +@ @<Put the \(p)(positive) `at' size into |s|@>= +begin scan_normal_dimen; s:=cur_val; +if (s<=0)or(s>=@'1000000000) then + begin print_err("Improper `at' size ("); + print_scaled(s); print("pt), replaced by 10pt"); +@.Improper `at' size...@> + help2("I can only handle fonts at positive sizes that are")@/ + ("less than 2048pt, so I've changed what you said to 10pt."); + error; s:=10*unity; + end; +end + +@ When the user gives a new identifier to a font that was previously loaded, +the new name becomes the font identifier of record. Font names `\.{xyz}' and +`\.{XYZ}' are considered to be different. + +@<If this font has already been loaded...@>= +flushable_string:=str_ptr-1; +for f:=font_base+1 to font_ptr do + if str_eq_str(font_name[f],cur_name)and str_eq_str(font_area[f],cur_area) then + begin if cur_name=flushable_string then + begin flush_string; cur_name:=font_name[f]; + end; + if s>0 then + begin if s=font_size[f] then goto common_ending; + end + else if font_size[f]=xn_over_d(font_dsize[f],-s,1000) then + goto common_ending; + end + +@ @<Cases of |print_cmd_chr|...@>= +set_font:begin print("select font "); slow_print(font_name[chr_code]); + if font_size[chr_code]<>font_dsize[chr_code] then + begin print(" at "); print_scaled(font_size[chr_code]); + print("pt"); + end; + end; + +@ @<Put each...@>= +primitive("batchmode",set_interaction,batch_mode); +@!@:batch_mode_}{\.{\\batchmode} primitive@> +primitive("nonstopmode",set_interaction,nonstop_mode); +@!@:nonstop_mode_}{\.{\\nonstopmode} primitive@> +primitive("scrollmode",set_interaction,scroll_mode); +@!@:scroll_mode_}{\.{\\scrollmode} primitive@> +primitive("errorstopmode",set_interaction,error_stop_mode); +@!@:error_stop_mode_}{\.{\\errorstopmode} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +set_interaction: case chr_code of + batch_mode: print_esc("batchmode"); + nonstop_mode: print_esc("nonstopmode"); + scroll_mode: print_esc("scrollmode"); + othercases print_esc("errorstopmode") + endcases; + +@ @<Assignments@>= +set_interaction: new_interaction; + +@ @<Declare subprocedures for |prefixed_command|@>= +procedure new_interaction; +begin print_ln; +interaction:=cur_chr; +@<Initialize the print |selector| based on |interaction|@>; +if log_opened then selector:=selector+2; +end; + +@ The \.{\\afterassignment} command puts a token into the global +variable |after_token|. This global variable is examined just after +every assignment has been performed. + +@<Glob...@>= +@!after_token:halfword; {zero, or a saved token} + +@ @<Set init...@>= +after_token:=0; + +@ @<Cases of |main_control| that don't...@>= +any_mode(after_assignment):begin get_token; after_token:=cur_tok; + end; + +@ @<Insert a token saved by \.{\\afterassignment}, if any@>= +if after_token<>0 then + begin cur_tok:=after_token; back_input; after_token:=0; + end + +@ Here is a procedure that might be called `Get the next non-blank non-relax +non-call non-assignment token'. + +@<Declare act...@>= +procedure do_assignments; +label exit; +begin loop begin @<Get the next non-blank non-relax...@>; + if cur_cmd<=max_non_prefixed_command then return; + set_box_allowed:=false; prefixed_command; set_box_allowed:=true; + end; +exit:end; + +@ @<Cases of |main_control| that don't...@>= +any_mode(after_group):begin get_token; save_for_after(cur_tok); + end; + +@ Files for \.{\\read} are opened and closed by the |in_stream| command. + +@<Put each...@>= +primitive("openin",in_stream,1); +@!@:open_in_}{\.{\\openin} primitive@> +primitive("closein",in_stream,0); +@!@:close_in_}{\.{\\closein} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +in_stream: if chr_code=0 then print_esc("closein") + else print_esc("openin"); + +@ @<Cases of |main_control| that don't...@>= +any_mode(in_stream): open_or_close_in; + +@ @<Declare act...@>= +procedure open_or_close_in; +var c:0..1; {1 for \.{\\openin}, 0 for \.{\\closein}} +@!n:0..15; {stream number} +begin c:=cur_chr; scan_four_bit_int; n:=cur_val; +if read_open[n]<>closed then + begin a_close(read_file[n]); read_open[n]:=closed; + end; +if c<>0 then + begin scan_optional_equals; scan_file_name; + if cur_ext="" then cur_ext:=".tex"; + pack_cur_name; + if a_open_in(read_file[n]) then read_open[n]:=just_open; + end; +end; + +@ The user can issue messages to the terminal, regardless of the +current mode. + +@<Cases of |main_control| that don't...@>= +any_mode(message):issue_message; + +@ @<Put each...@>= +primitive("message",message,0); +@!@:message_}{\.{\\message} primitive@> +primitive("errmessage",message,1); +@!@:err_message_}{\.{\\errmessage} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +message: if chr_code=0 then print_esc("message") + else print_esc("errmessage"); + +@ @<Declare act...@>= +procedure issue_message; +var old_setting:0..max_selector; {holds |selector| setting} +@!c:0..1; {identifies \.{\\message} and \.{\\errmessage}} +@!s:str_number; {the message} +begin c:=cur_chr; link(garbage):=scan_toks(false,true); +old_setting:=selector; selector:=new_string; +token_show(def_ref); selector:=old_setting; +flush_list(def_ref); +str_room(1); s:=make_string; +if c=0 then @<Print string |s| on the terminal@> +else @<Print string |s| as an error message@>; +flush_string; +end; + +@ @<Print string |s| on the terminal@>= +begin if term_offset+length(s)>max_print_line-2 then print_ln +else if (term_offset>0)or(file_offset>0) then print_char(" "); +slow_print(s); update_terminal; +end + +@ If \.{\\errmessage} occurs often in |scroll_mode|, without user-defined +\.{\\errhelp}, we don't want to give a long help message each time. So we +give a verbose explanation only once. + +@<Glob...@>= +@!long_help_seen:boolean; {has the long \.{\\errmessage} help been used?} + +@ @<Set init...@>=long_help_seen:=false; + +@ @<Print string |s| as an error message@>= +begin print_err(""); slow_print(s); +if err_help<>null then use_err_help:=true +else if long_help_seen then help1("(That was another \errmessage.)") +else begin if interaction<error_stop_mode then long_help_seen:=true; + help4("This error message was generated by an \errmessage")@/ + ("command, so I can't give any explicit help.")@/ + ("Pretend that you're Hercule Poirot: Examine all clues,")@/ +@^Poirot, Hercule@> + ("and deduce the truth by order and method."); + end; +error; use_err_help:=false; +end + +@ The |error| routine calls on |give_err_help| if help is requested from +the |err_help| parameter. + +@p procedure give_err_help; +begin token_show(err_help); +end; + +@ The \.{\\uppercase} and \.{\\lowercase} commands are implemented by +building a token list and then changing the cases of the letters in it. + +@<Cases of |main_control| that don't...@>= +any_mode(case_shift):shift_case; + +@ @<Put each...@>= +primitive("lowercase",case_shift,lc_code_base); +@!@:lowercase_}{\.{\\lowercase} primitive@> +primitive("uppercase",case_shift,uc_code_base); +@!@:uppercase_}{\.{\\uppercase} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +case_shift:if chr_code=lc_code_base then print_esc("lowercase") + else print_esc("uppercase"); + +@ @<Declare act...@>= +procedure shift_case; +var b:pointer; {|lc_code_base| or |uc_code_base|} +@!p:pointer; {runs through the token list} +@!t:halfword; {token} +@!c:eight_bits; {character code} +begin b:=cur_chr; p:=scan_toks(false,false); p:=link(def_ref); +while p<>null do + begin @<Change the case of the token in |p|, if a change is appropriate@>; + p:=link(p); + end; +back_list(link(def_ref)); free_avail(def_ref); {omit reference count} +end; + +@ When the case of a |chr_code| changes, we don't change the |cmd|. +We also change active characters, using the fact that +|cs_token_flag+active_base| is a multiple of~256. +@^data structure assumptions@> + +@<Change the case of the token in |p|, if a change is appropriate@>= +t:=info(p); +if t<cs_token_flag+single_base then + begin c:=t mod 256; + if equiv(b+c)<>0 then info(p):=t-c+equiv(b+c); + end + +@ We come finally to the last pieces missing from |main_control|, namely the +`\.{\\show}' commands that are useful when debugging. + +@<Cases of |main_control| that don't...@>= +any_mode(xray): show_whatever; + +@ @d show_code=0 { \.{\\show} } +@d show_box_code=1 { \.{\\showbox} } +@d show_the_code=2 { \.{\\showthe} } +@d show_lists=3 { \.{\\showlists} } + +@<Put each...@>= +primitive("show",xray,show_code); +@!@:show_}{\.{\\show} primitive@> +primitive("showbox",xray,show_box_code); +@!@:show_box_}{\.{\\showbox} primitive@> +primitive("showthe",xray,show_the_code); +@!@:show_the_}{\.{\\showthe} primitive@> +primitive("showlists",xray,show_lists); +@!@:show_lists_}{\.{\\showlists} primitive@> + +@ @<Cases of |print_cmd_chr|...@>= +xray: case chr_code of + show_box_code:print_esc("showbox"); + show_the_code:print_esc("showthe"); + show_lists:print_esc("showlists"); + othercases print_esc("show") + endcases; + +@ @<Declare act...@>= +procedure show_whatever; +label common_ending; +var p:pointer; {tail of a token list to show} +begin case cur_chr of +show_lists: begin begin_diagnostic; show_activities; + end; +show_box_code: @<Show the current contents of a box@>; +show_code: @<Show the current meaning of a token, then |goto common_ending|@>; +othercases @<Show the current value of some parameter or register, + then |goto common_ending|@> +endcases;@/ +@<Complete a potentially long \.{\\show} command@>; +common_ending: if interaction<error_stop_mode then + begin help0; decr(error_count); + end +else if tracing_online>0 then + begin@t@>@;@/ + help3("This isn't an error message; I'm just \showing something.")@/ + ("Type `I\show...' to show more (e.g., \show\cs,")@/ + ("\showthe\count10, \showbox255, \showlists)."); + end +else begin@t@>@;@/ + help5("This isn't an error message; I'm just \showing something.")@/ + ("Type `I\show...' to show more (e.g., \show\cs,")@/ + ("\showthe\count10, \showbox255, \showlists).")@/ + ("And type `I\tracingonline=1\show...' to show boxes and")@/ + ("lists on your terminal as well as in the transcript file."); + end; +error; +end; + +@ @<Show the current meaning of a token...@>= +begin get_token; +if interaction=error_stop_mode then wake_up_terminal; +print_nl("> "); +if cur_cs<>0 then + begin sprint_cs(cur_cs); print_char("="); + end; +print_meaning; goto common_ending; +end + +@ @<Cases of |print_cmd_chr|...@>= +undefined_cs: print("undefined"); +call: print("macro"); +long_call: print_esc("long macro"); +outer_call: print_esc("outer macro"); +long_outer_call: begin print_esc("long"); print_esc("outer macro"); + end; +end_template: print_esc("outer endtemplate"); + +@ @<Show the current contents of a box@>= +begin scan_eight_bit_int; begin_diagnostic; +print_nl("> \box"); print_int(cur_val); print_char("="); +if box(cur_val)=null then print("void") +else show_box(box(cur_val)); +end + +@ @<Show the current value of some parameter...@>= +begin p:=the_toks; +if interaction=error_stop_mode then wake_up_terminal; +print_nl("> "); token_show(temp_head); +flush_list(link(temp_head)); goto common_ending; +end + +@ @<Complete a potentially long \.{\\show} command@>= +end_diagnostic(true); print_err("OK"); +@.OK@> +if selector=term_and_log then if tracing_online<=0 then + begin selector:=term_only; print(" (see the transcript file)"); + selector:=term_and_log; + end + +@* \[50] Dumping and undumping the tables. +After \.{INITEX} has seen a collection of fonts and macros, it +can write all the necessary information on an auxiliary file so +that production versions of \TeX\ are able to initialize their +memory at high speed. The present section of the program takes +care of such output and input. We shall consider simultaneously +the processes of storing and restoring, +so that the inverse relation between them is clear. +@.INITEX@> + +The global variable |format_ident| is a string that is printed right +after the |banner| line when \TeX\ is ready to start. For \.{INITEX} this +string says simply `\.{(INITEX)}'; for other versions of \TeX\ it says, +for example, `\.{(preloaded format=plain 82.11.19)}', showing the year, +month, and day that the format file was created. We have |format_ident=0| +before \TeX's tables are loaded. + +@<Glob...@>= +@!format_ident:str_number; + +@ @<Set init...@>= +format_ident:=0; + +@ @<Initialize table entries...@>= +format_ident:=" (INITEX)"; + +@ @<Declare act...@>= +@!init procedure store_fmt_file; +label found1,found2,done1,done2; +var j,@!k,@!l:integer; {all-purpose indices} +@!p,@!q: pointer; {all-purpose pointers} +@!x: integer; {something to dump} +@!w: four_quarters; {four ASCII codes} +begin @<If dumping is not allowed, abort@>; +@<Create the |format_ident|, open the format file, + and inform the user that dumping has begun@>; +@<Dump constants for consistency check@>; +@<Dump the string pool@>; +@<Dump the dynamic memory@>; +@<Dump the table of equivalents@>; +@<Dump the font information@>; +@<Dump the hyphenation tables@>; +@<Dump a couple more things and the closing check word@>; +@<Close the format file@>; +end; +tini + +@ Corresponding to the procedure that dumps a format file, we have a function +that reads one in. The function returns |false| if the dumped format is +incompatible with the present \TeX\ table sizes, etc. + +@d bad_fmt=6666 {go here if the format file is unacceptable} +@d too_small(#)==begin wake_up_terminal; + wterm_ln('---! Must increase the ',#); +@.Must increase the x@> + goto bad_fmt; + end + +@p @t\4@>@<Declare the function called |open_fmt_file|@>@; +function load_fmt_file:boolean; +label bad_fmt,exit; +var j,@!k:integer; {all-purpose indices} +@!p,@!q: pointer; {all-purpose pointers} +@!x: integer; {something undumped} +@!w: four_quarters; {four ASCII codes} +begin @<Undump constants for consistency check@>; +@<Undump the string pool@>; +@<Undump the dynamic memory@>; +@<Undump the table of equivalents@>; +@<Undump the font information@>; +@<Undump the hyphenation tables@>; +@<Undump a couple more things and the closing check word@>; +load_fmt_file:=true; return; {it worked!} +bad_fmt: wake_up_terminal; + wterm_ln('(Fatal format file error; I''m stymied)'); +@.Fatal format file error@> +load_fmt_file:=false; +exit:end; + +@ The user is not allowed to dump a format file unless |save_ptr=0|. +This condition implies that |cur_level=level_one|, hence +the |xeq_level| array is constant and it need not be dumped. + +@<If dumping is not allowed, abort@>= +if save_ptr<>0 then + begin print_err("You can't dump inside a group"); +@.You can't dump...@> + help1("`{...\dump}' is a no-no."); succumb; + end + +@ Format files consist of |memory_word| items, and we use the following +macros to dump words of different types: + +@d dump_wd(#)==begin fmt_file^:=#; put(fmt_file);@+end +@d dump_int(#)==begin fmt_file^.int:=#; put(fmt_file);@+end +@d dump_hh(#)==begin fmt_file^.hh:=#; put(fmt_file);@+end +@d dump_qqqq(#)==begin fmt_file^.qqqq:=#; put(fmt_file);@+end + +@<Glob...@>= +@!fmt_file:word_file; {for input or output of format information} + +@ The inverse macros are slightly more complicated, since we need to check +the range of the values we are reading in. We say `|undump(a)(b)(x)|' to +read an integer value |x| that is supposed to be in the range |a<=x<=b|. + +@d undump_wd(#)==begin get(fmt_file); #:=fmt_file^;@+end +@d undump_int(#)==begin get(fmt_file); #:=fmt_file^.int;@+end +@d undump_hh(#)==begin get(fmt_file); #:=fmt_file^.hh;@+end +@d undump_qqqq(#)==begin get(fmt_file); #:=fmt_file^.qqqq;@+end +@d undump_end_end(#)==#:=x;@+end +@d undump_end(#)==(x>#) then goto bad_fmt@+else undump_end_end +@d undump(#)==begin undump_int(x); if (x<#) or undump_end +@d undump_size_end_end(#)==too_small(#)@+else undump_end_end +@d undump_size_end(#)==if x># then undump_size_end_end +@d undump_size(#)==begin undump_int(x); + if x<# then goto bad_fmt; undump_size_end + +@ The next few sections of the program should make it clear how we use the +dump/undump macros. + +@<Dump constants for consistency check@>= +dump_int(@$);@/ +dump_int(mem_bot);@/ +dump_int(mem_top);@/ +dump_int(eqtb_size);@/ +dump_int(hash_prime);@/ +dump_int(hyph_size) + +@ Sections of a \.{WEB} program that are ``commented out'' still contribute +strings to the string pool; therefore \.{INITEX} and \TeX\ will have +the same strings. (And it is, of course, a good thing that they do.) +@.WEB@> +@^string pool@> + +@<Undump constants for consistency check@>= +x:=fmt_file^.int; +if x<>@$ then goto bad_fmt; {check that strings are the same} +undump_int(x); +if x<>mem_bot then goto bad_fmt; +undump_int(x); +if x<>mem_top then goto bad_fmt; +undump_int(x); +if x<>eqtb_size then goto bad_fmt; +undump_int(x); +if x<>hash_prime then goto bad_fmt; +undump_int(x); +if x<>hyph_size then goto bad_fmt + +@ @d dump_four_ASCII== + w.b0:=qi(so(str_pool[k])); w.b1:=qi(so(str_pool[k+1])); + w.b2:=qi(so(str_pool[k+2])); w.b3:=qi(so(str_pool[k+3])); + dump_qqqq(w) + +@<Dump the string pool@>= +dump_int(pool_ptr); +dump_int(str_ptr); +for k:=0 to str_ptr do dump_int(str_start[k]); +k:=0; +while k+4<pool_ptr do + begin dump_four_ASCII; k:=k+4; + end; +k:=pool_ptr-4; dump_four_ASCII; +print_ln; print_int(str_ptr); print(" strings of total length "); +print_int(pool_ptr) + +@ @d undump_four_ASCII== + undump_qqqq(w); + str_pool[k]:=si(qo(w.b0)); str_pool[k+1]:=si(qo(w.b1)); + str_pool[k+2]:=si(qo(w.b2)); str_pool[k+3]:=si(qo(w.b3)) + +@<Undump the string pool@>= +undump_size(0)(pool_size)('string pool size')(pool_ptr); +undump_size(0)(max_strings)('max strings')(str_ptr); +for k:=0 to str_ptr do undump(0)(pool_ptr)(str_start[k]); +k:=0; +while k+4<pool_ptr do + begin undump_four_ASCII; k:=k+4; + end; +k:=pool_ptr-4; undump_four_ASCII; +init_str_ptr:=str_ptr; init_pool_ptr:=pool_ptr + +@ By sorting the list of available spaces in the variable-size portion of +|mem|, we are usually able to get by without having to dump very much +of the dynamic memory. + +We recompute |var_used| and |dyn_used|, so that \.{INITEX} dumps valid +information even when it has not been gathering statistics. + +@<Dump the dynamic memory@>= +sort_avail; var_used:=0; +dump_int(lo_mem_max); dump_int(rover); +p:=mem_bot; q:=rover; x:=0; +repeat for k:=p to q+1 do dump_wd(mem[k]); +x:=x+q+2-p; var_used:=var_used+q-p; +p:=q+node_size(q); q:=rlink(q); +until q=rover; +var_used:=var_used+lo_mem_max-p; dyn_used:=mem_end+1-hi_mem_min;@/ +for k:=p to lo_mem_max do dump_wd(mem[k]); +x:=x+lo_mem_max+1-p; +dump_int(hi_mem_min); dump_int(avail); +for k:=hi_mem_min to mem_end do dump_wd(mem[k]); +x:=x+mem_end+1-hi_mem_min; +p:=avail; +while p<>null do + begin decr(dyn_used); p:=link(p); + end; +dump_int(var_used); dump_int(dyn_used); +print_ln; print_int(x); +print(" memory locations dumped; current usage is "); +print_int(var_used); print_char("&"); print_int(dyn_used) + +@ @<Undump the dynamic memory@>= +undump(lo_mem_stat_max+1000)(hi_mem_stat_min-1)(lo_mem_max); +undump(lo_mem_stat_max+1)(lo_mem_max)(rover); +p:=mem_bot; q:=rover; +repeat for k:=p to q+1 do undump_wd(mem[k]); +p:=q+node_size(q); +if (p>lo_mem_max)or((q>=rlink(q))and(rlink(q)<>rover)) then goto bad_fmt; +q:=rlink(q); +until q=rover; +for k:=p to lo_mem_max do undump_wd(mem[k]); +if mem_min<mem_bot-2 then {make more low memory available} + begin p:=llink(rover); q:=mem_min+1; + link(mem_min):=null; info(mem_min):=null; {we don't use the bottom word} + rlink(p):=q; llink(rover):=q;@/ + rlink(q):=rover; llink(q):=p; link(q):=empty_flag; + node_size(q):=mem_bot-q; + end; +undump(lo_mem_max+1)(hi_mem_stat_min)(hi_mem_min); +undump(null)(mem_top)(avail); mem_end:=mem_top; +for k:=hi_mem_min to mem_end do undump_wd(mem[k]); +undump_int(var_used); undump_int(dyn_used) + +@ @<Dump the table of equivalents@>= +@<Dump regions 1 to 4 of |eqtb|@>; +@<Dump regions 5 and 6 of |eqtb|@>; +dump_int(par_loc); dump_int(write_loc);@/ +@<Dump the hash table@> + +@ @<Undump the table of equivalents@>= +@<Undump regions 1 to 6 of |eqtb|@>; +undump(hash_base)(frozen_control_sequence)(par_loc); +par_token:=cs_token_flag+par_loc;@/ +undump(hash_base)(frozen_control_sequence)(write_loc);@/ +@<Undump the hash table@> + +@ The table of equivalents usually contains repeated information, so we dump it +in compressed form: The sequence of $n+2$ values $(n,x_1,\ldots,x_n,m)$ in the +format file represents $n+m$ consecutive entries of |eqtb|, with |m| extra +copies of $x_n$, namely $(x_1,\ldots,x_n,x_n,\ldots,x_n)$. + +@<Dump regions 1 to 4 of |eqtb|@>= +k:=active_base; +repeat j:=k; +while j<int_base-1 do + begin if (equiv(j)=equiv(j+1))and(eq_type(j)=eq_type(j+1))and@| + (eq_level(j)=eq_level(j+1)) then goto found1; + incr(j); + end; +l:=int_base; goto done1; {|j=int_base-1|} +found1: incr(j); l:=j; +while j<int_base-1 do + begin if (equiv(j)<>equiv(j+1))or(eq_type(j)<>eq_type(j+1))or@| + (eq_level(j)<>eq_level(j+1)) then goto done1; + incr(j); + end; +done1:dump_int(l-k); +while k<l do + begin dump_wd(eqtb[k]); incr(k); + end; +k:=j+1; dump_int(k-l); +until k=int_base + +@ @<Dump regions 5 and 6 of |eqtb|@>= +repeat j:=k; +while j<eqtb_size do + begin if eqtb[j].int=eqtb[j+1].int then goto found2; + incr(j); + end; +l:=eqtb_size+1; goto done2; {|j=eqtb_size|} +found2: incr(j); l:=j; +while j<eqtb_size do + begin if eqtb[j].int<>eqtb[j+1].int then goto done2; + incr(j); + end; +done2:dump_int(l-k); +while k<l do + begin dump_wd(eqtb[k]); incr(k); + end; +k:=j+1; dump_int(k-l); +until k>eqtb_size + +@ @<Undump regions 1 to 6 of |eqtb|@>= +k:=active_base; +repeat undump_int(x); +if (x<1)or(k+x>eqtb_size+1) then goto bad_fmt; +for j:=k to k+x-1 do undump_wd(eqtb[j]); +k:=k+x; +undump_int(x); +if (x<0)or(k+x>eqtb_size+1) then goto bad_fmt; +for j:=k to k+x-1 do eqtb[j]:=eqtb[k-1]; +k:=k+x; +until k>eqtb_size + +@ A different scheme is used to compress the hash table, since its lower +region is usually sparse. When |text(p)<>0| for |p<=hash_used|, we output +two words, |p| and |hash[p]|. The hash table is, of course, densely packed +for |p>=hash_used|, so the remaining entries are output in a~block. + +@<Dump the hash table@>= +dump_int(hash_used); cs_count:=frozen_control_sequence-1-hash_used; +for p:=hash_base to hash_used do if text(p)<>0 then + begin dump_int(p); dump_hh(hash[p]); incr(cs_count); + end; +for p:=hash_used+1 to undefined_control_sequence-1 do dump_hh(hash[p]); +dump_int(cs_count);@/ +print_ln; print_int(cs_count); print(" multiletter control sequences") + +@ @<Undump the hash table@>= +undump(hash_base)(frozen_control_sequence)(hash_used); p:=hash_base-1; +repeat undump(p+1)(hash_used)(p); undump_hh(hash[p]); +until p=hash_used; +for p:=hash_used+1 to undefined_control_sequence-1 do undump_hh(hash[p]); +undump_int(cs_count) + +@ @<Dump the font information@>= +dump_int(fmem_ptr); +for k:=0 to fmem_ptr-1 do dump_wd(font_info[k]); +dump_int(font_ptr); +for k:=null_font to font_ptr do + @<Dump the array info for internal font number |k|@>; +print_ln; print_int(fmem_ptr-7); print(" words of font info for "); +print_int(font_ptr-font_base); print(" preloaded font"); +if font_ptr<>font_base+1 then print_char("s") + +@ @<Undump the font information@>= +undump_size(7)(font_mem_size)('font mem size')(fmem_ptr); +for k:=0 to fmem_ptr-1 do undump_wd(font_info[k]); +undump_size(font_base)(font_max)('font max')(font_ptr); +for k:=null_font to font_ptr do + @<Undump the array info for internal font number |k|@> + +@ @<Dump the array info for internal font number |k|@>= +begin dump_qqqq(font_check[k]); +dump_int(font_size[k]); +dump_int(font_dsize[k]); +dump_int(font_params[k]);@/ +dump_int(hyphen_char[k]); +dump_int(skew_char[k]);@/ +dump_int(font_name[k]); +dump_int(font_area[k]);@/ +dump_int(font_bc[k]); +dump_int(font_ec[k]);@/ +dump_int(char_base[k]); +dump_int(width_base[k]); +dump_int(height_base[k]);@/ +dump_int(depth_base[k]); +dump_int(italic_base[k]); +dump_int(lig_kern_base[k]);@/ +dump_int(kern_base[k]); +dump_int(exten_base[k]); +dump_int(param_base[k]);@/ +dump_int(font_glue[k]);@/ +dump_int(bchar_label[k]); +dump_int(font_bchar[k]); +dump_int(font_false_bchar[k]);@/ +print_nl("\font"); print_esc(font_id_text(k)); print_char("="); +print_file_name(font_name[k],font_area[k],""); +if font_size[k]<>font_dsize[k] then + begin print(" at "); print_scaled(font_size[k]); print("pt"); + end; +end + +@ @<Undump the array info for internal font number |k|@>= +begin undump_qqqq(font_check[k]);@/ +undump_int(font_size[k]); +undump_int(font_dsize[k]); +undump(min_halfword)(max_halfword)(font_params[k]);@/ +undump_int(hyphen_char[k]); +undump_int(skew_char[k]);@/ +undump(0)(str_ptr)(font_name[k]); +undump(0)(str_ptr)(font_area[k]);@/ +undump(0)(255)(font_bc[k]); +undump(0)(255)(font_ec[k]);@/ +undump_int(char_base[k]); +undump_int(width_base[k]); +undump_int(height_base[k]);@/ +undump_int(depth_base[k]); +undump_int(italic_base[k]); +undump_int(lig_kern_base[k]);@/ +undump_int(kern_base[k]); +undump_int(exten_base[k]); +undump_int(param_base[k]);@/ +undump(min_halfword)(lo_mem_max)(font_glue[k]);@/ +undump(0)(fmem_ptr-1)(bchar_label[k]); +undump(min_quarterword)(non_char)(font_bchar[k]); +undump(min_quarterword)(non_char)(font_false_bchar[k]); +end + +@ @<Dump the hyphenation tables@>= +dump_int(hyph_count); +for k:=0 to hyph_size do if hyph_word[k]<>0 then + begin dump_int(k); dump_int(hyph_word[k]); dump_int(hyph_list[k]); + end; +print_ln; print_int(hyph_count); print(" hyphenation exception"); +if hyph_count<>1 then print_char("s"); +if trie_not_ready then init_trie; +dump_int(trie_max); +for k:=0 to trie_max do dump_hh(trie[k]); +dump_int(trie_op_ptr); +for k:=1 to trie_op_ptr do + begin dump_int(hyf_distance[k]); + dump_int(hyf_num[k]); + dump_int(hyf_next[k]); + end; +print_nl("Hyphenation trie of length "); print_int(trie_max); +@.Hyphenation trie...@> +print(" has "); print_int(trie_op_ptr); print(" op"); +if trie_op_ptr<>1 then print_char("s"); +print(" out of "); print_int(trie_op_size); +for k:=255 downto 0 do if trie_used[k]>min_quarterword then + begin print_nl(" "); print_int(qo(trie_used[k])); + print(" for language "); print_int(k); + dump_int(k); dump_int(qo(trie_used[k])); + end + +@ Only ``nonempty'' parts of |op_start| need to be restored. + +@<Undump the hyphenation tables@>= +undump(0)(hyph_size)(hyph_count); +for k:=1 to hyph_count do + begin undump(0)(hyph_size)(j); + undump(0)(str_ptr)(hyph_word[j]); + undump(min_halfword)(max_halfword)(hyph_list[j]); + end; +undump_size(0)(trie_size)('trie size')(j); @+init trie_max:=j;@+tini +for k:=0 to j do undump_hh(trie[k]); +undump_size(0)(trie_op_size)('trie op size')(j); @+init trie_op_ptr:=j;@+tini +for k:=1 to j do + begin undump(0)(63)(hyf_distance[k]); {a |small_number|} + undump(0)(63)(hyf_num[k]); + undump(min_quarterword)(max_quarterword)(hyf_next[k]); + end; +init for k:=0 to 255 do trie_used[k]:=min_quarterword;@+tini@;@/ +k:=256; +while j>0 do + begin undump(0)(k-1)(k); undump(1)(j)(x);@+init trie_used[k]:=qi(x);@+tini@;@/ + j:=j-x; op_start[k]:=qo(j); + end; +@!init trie_not_ready:=false @+tini + +@ We have already printed a lot of statistics, so we set |tracing_stats:=0| +to prevent them from appearing again. + +@<Dump a couple more things and the closing check word@>= +dump_int(interaction); dump_int(format_ident); dump_int(69069); +tracing_stats:=0 + +@ @<Undump a couple more things and the closing check word@>= +undump(batch_mode)(error_stop_mode)(interaction); +undump(0)(str_ptr)(format_ident); +undump_int(x); +if (x<>69069)or eof(fmt_file) then goto bad_fmt + +@ @<Create the |format_ident|...@>= +selector:=new_string; +print(" (preloaded format="); print(job_name); print_char(" "); +print_int(year); print_char("."); +print_int(month); print_char("."); print_int(day); print_char(")"); +if interaction=batch_mode then selector:=log_only +else selector:=term_and_log; +str_room(1); +format_ident:=make_string; +pack_job_name(format_extension); +while not w_open_out(fmt_file) do + prompt_file_name("format file name",format_extension); +print_nl("Beginning to dump on file "); +@.Beginning to dump...@> +slow_print(w_make_name_string(fmt_file)); flush_string; +print_nl(""); slow_print(format_ident) + +@ @<Close the format file@>= +w_close(fmt_file) + +@* \[51] The main program. +This is it: the part of \TeX\ that executes all those procedures we have +written. + +Well---almost. Let's leave space for a few more routines that we may +have forgotten. + +@p @<Last-minute procedures@> + +@ We have noted that there are two versions of \TeX82. One, called \.{INITEX}, +@.INITEX@> +has to be run first; it initializes everything from scratch, without +reading a format file, and it has the capability of dumping a format file. +The other one is called `\.{VIRTEX}'; it is a ``virgin'' program that needs +@.VIRTEX@> +to input a format file in order to get started. \.{VIRTEX} typically has +more memory capacity than \.{INITEX}, because it does not need the space +consumed by the auxiliary hyphenation tables and the numerous calls on +|primitive|, etc. + +The \.{VIRTEX} program cannot read a format file instantaneously, of course; +the best implementations therefore allow for production versions of \TeX\ that +not only avoid the loading routine for \PASCAL\ object code, they also have +a format file pre-loaded. This is impossible to do if we stick to standard +\PASCAL; but there is a simple way to fool many systems into avoiding the +initialization, as follows:\quad(1)~We declare a global integer variable +called |ready_already|. The probability is negligible that this +variable holds any particular value like 314159 when \.{VIRTEX} is first +loaded.\quad(2)~After we have read in a format file and initialized +everything, we set |ready_already:=314159|.\quad(3)~Soon \.{VIRTEX} +will print `\.*', waiting for more input; and at this point we +interrupt the program and save its core image in some form that the +operating system can reload speedily.\quad(4)~When that core image is +activated, the program starts again at the beginning; but now +|ready_already=314159| and all the other global variables have +their initial values too. The former chastity has vanished! + +In other words, if we allow ourselves to test the condition +|ready_already=314159|, before |ready_already| has been +assigned a value, we can avoid the lengthy initialization. Dirty tricks +rarely pay off so handsomely. +@^dirty \PASCAL@> +@^system dependencies@> + +On systems that allow such preloading, the standard program called \.{TeX} +should be the one that has \.{plain} format preloaded, since that agrees +with {\sl The \TeX book}. Other versions, e.g., \.{AmSTeX}, should also +@:TeXbook}{\sl The \TeX book@> +@.AmSTeX@> +@.plain@> +be provided for commonly used formats. + +@<Glob...@>= +@!ready_already:integer; {a sacrifice of purity for economy} + +@ Now this is really it: \TeX\ starts and ends here. + +The initial test involving |ready_already| should be deleted if the +\PASCAL\ runtime system is smart enough to detect such a ``mistake.'' +@^system dependencies@> + +@p begin @!{|start_here|} +history:=fatal_error_stop; {in case we quit during initialization} +t_open_out; {open the terminal for output} +if ready_already=314159 then goto start_of_TEX; +@<Check the ``constant'' values...@>@; +if bad>0 then + begin wterm_ln('Ouch---my internal constants have been clobbered!', + '---case ',bad:1); +@.Ouch...clobbered@> + goto final_end; + end; +initialize; {set global variables to their starting values} +@!init if not get_strings_started then goto final_end; +init_prim; {call |primitive| for each primitive} +init_str_ptr:=str_ptr; init_pool_ptr:=pool_ptr; fix_date_and_time; +tini@/ +ready_already:=314159; +start_of_TEX: @<Initialize the output routines@>; +@<Get the first line of input and prepare to start@>; +history:=spotless; {ready to go!} +main_control; {come to life} +final_cleanup; {prepare for death} +end_of_TEX: close_files_and_terminate; +final_end: ready_already:=0; +end. + +@ Here we do whatever is needed to complete \TeX's job gracefully on the +local operating system. The code here might come into play after a fatal +error; it must therefore consist entirely of ``safe'' operations that +cannot produce error messages. For example, it would be a mistake to call +|str_room| or |make_string| at this time, because a call on |overflow| +might lead to an infinite loop. +@^system dependencies@> + +Actually there's one way to get error messages, via |prepare_mag|; +but that can't cause infinite recursion. +@^recursion@> + +This program doesn't bother to close the input files that may still be open. + +@<Last-minute...@>= +procedure close_files_and_terminate; +var k:integer; {all-purpose index} +begin @<Finish the extensions@>; +@!stat if tracing_stats>0 then @<Output statistics about this job@>;@;@+tats@/ +wake_up_terminal; @<Finish the \.{DVI} file@>; +if log_opened then + begin wlog_cr; a_close(log_file); selector:=selector-2; + if selector=term_only then + begin print_nl("Transcript written on "); +@.Transcript written...@> + slow_print(log_name); print_char("."); + end; + end; +end; + +@ The present section goes directly to the log file instead of using +|print| commands, because there's no need for these strings to take +up |str_pool| memory when a non-{\bf stat} version of \TeX\ is being used. + +@<Output statistics...@>= +if log_opened then + begin wlog_ln(' '); + wlog_ln('Here is how much of TeX''s memory',' you used:'); +@.Here is how much...@> + wlog(' ',str_ptr-init_str_ptr:1,' string'); + if str_ptr<>init_str_ptr+1 then wlog('s'); + wlog_ln(' out of ', max_strings-init_str_ptr:1);@/ + wlog_ln(' ',pool_ptr-init_pool_ptr:1,' string characters out of ', + pool_size-init_pool_ptr:1);@/ + wlog_ln(' ',lo_mem_max-mem_min+mem_end-hi_mem_min+2:1,@| + ' words of memory out of ',mem_end+1-mem_min:1);@/ + wlog_ln(' ',cs_count:1,' multiletter control sequences out of ', + hash_size:1);@/ + wlog(' ',fmem_ptr:1,' words of font info for ', + font_ptr-font_base:1,' font'); + if font_ptr<>font_base+1 then wlog('s'); + wlog_ln(', out of ',font_mem_size:1,' for ',font_max-font_base:1);@/ + wlog(' ',hyph_count:1,' hyphenation exception'); + if hyph_count<>1 then wlog('s'); + wlog_ln(' out of ',hyph_size:1);@/ + wlog_ln(' ',max_in_stack:1,'i,',max_nest_stack:1,'n,',@| + max_param_stack:1,'p,',@| + max_buf_stack+1:1,'b,',@| + max_save_stack+6:1,'s stack positions out of ',@| + stack_size:1,'i,', + nest_size:1,'n,', + param_size:1,'p,', + buf_size:1,'b,', + save_size:1,'s'); + end + +@ We get to the |final_cleanup| routine when \.{\\end} or \.{\\dump} has +been scanned and |its_all_over|\kern-2pt. + +@<Last-minute...@>= +procedure final_cleanup; +label exit; +var c:small_number; {0 for \.{\\end}, 1 for \.{\\dump}} +begin c:=cur_chr; +if job_name=0 then open_log_file; +while input_ptr>0 do + if state=token_list then end_token_list@+else end_file_reading; +while open_parens>0 do + begin print(" )"); decr(open_parens); + end; +if cur_level>level_one then + begin print_nl("("); print_esc("end occurred "); + print("inside a group at level "); +@:end_}{\.{(\\end occurred...)}@> + print_int(cur_level-level_one); print_char(")"); + end; +while cond_ptr<>null do + begin print_nl("("); print_esc("end occurred "); + print("when "); print_cmd_chr(if_test,cur_if); + if if_line<>0 then + begin print(" on line "); print_int(if_line); + end; + print(" was incomplete)"); + if_line:=if_line_field(cond_ptr); + cur_if:=subtype(cond_ptr); temp_ptr:=cond_ptr; + cond_ptr:=link(cond_ptr); free_node(temp_ptr,if_node_size); + end; +if history<>spotless then + if ((history=warning_issued)or(interaction<error_stop_mode)) then + if selector=term_and_log then + begin selector:=term_only; + print_nl("(see the transcript file for additional information)"); +@.see the transcript file...@> + selector:=term_and_log; + end; +if c=1 then + begin @!init for c:=top_mark_code to split_bot_mark_code do + if cur_mark[c]<>null then delete_token_ref(cur_mark[c]); + store_fmt_file; return;@+tini@/ + print_nl("(\dump is performed only by INITEX)"); return; +@:dump_}{\.{\\dump...only by INITEX}@> + end; +exit:end; + +@ @<Last-minute...@>= +@!init procedure init_prim; {initialize all the primitives} +begin no_new_control_sequence:=false; +@<Put each...@>; +no_new_control_sequence:=true; +end; +tini + +@ When we begin the following code, \TeX's tables may still contain garbage; +the strings might not even be present. Thus we must proceed cautiously to get +bootstrapped in. + +But when we finish this part of the program, \TeX\ is ready to call on the +|main_control| routine to do its work. + +@<Get the first line...@>= +begin @<Initialize the input routines@>; +if (format_ident=0)or(buffer[loc]="&") then + begin if format_ident<>0 then initialize; {erase preloaded format} + if not open_fmt_file then goto final_end; + if not load_fmt_file then + begin w_close(fmt_file); goto final_end; + end; + w_close(fmt_file); + while (loc<limit)and(buffer[loc]=" ") do incr(loc); + end; +if end_line_char_inactive then decr(limit) +else buffer[limit]:=end_line_char; +fix_date_and_time;@/ +@<Compute the magic offset@>; +@<Initialize the print |selector|...@>; +if (loc<limit)and(cat_code(buffer[loc])<>escape) then start_input; + {\.{\\input} assumed} +end + +@* \[52] Debugging. +Once \TeX\ is working, you should be able to diagnose most errors with +the \.{\\show} commands and other diagnostic features. But for the initial +stages of debugging, and for the revelation of really deep mysteries, you +can compile \TeX\ with a few more aids, including the \PASCAL\ runtime +checks and its debugger. An additional routine called |debug_help| +will also come into play when you type `\.D' after an error message; +|debug_help| also occurs just before a fatal error causes \TeX\ to succumb. +@^debugging@> +@^system dependencies@> + +The interface to |debug_help| is primitive, but it is good enough when used +with a \PASCAL\ debugger that allows you to set breakpoints and to read +variables and change their values. After getting the prompt `\.{debug \#}', you +type either a negative number (this exits |debug_help|), or zero (this +goes to a location where you can set a breakpoint, thereby entering into +dialog with the \PASCAL\ debugger), or a positive number |m| followed by +an argument |n|. The meaning of |m| and |n| will be clear from the +program below. (If |m=13|, there is an additional argument, |l|.) +@.debug \#@> + +@d breakpoint=888 {place where a breakpoint is desirable} + +@<Last-minute...@>= +@!debug procedure debug_help; {routine to display various things} +label breakpoint,exit; +var k,@!l,@!m,@!n:integer; +begin loop begin wake_up_terminal; + print_nl("debug # (-1 to exit):"); update_terminal; +@.debug \#@> + read(term_in,m); + if m<0 then return + else if m=0 then + begin goto breakpoint;@\ {go to every label at least once} + breakpoint: m:=0; @{'BREAKPOINT'@}@\ + end + else begin read(term_in,n); + case m of + @t\4@>@<Numbered cases for |debug_help|@>@; + othercases print("?") + endcases; + end; + end; +exit:end; +gubed + +@ @<Numbered cases...@>= +1: print_word(mem[n]); {display |mem[n]| in all forms} +2: print_int(info(n)); +3: print_int(link(n)); +4: print_word(eqtb[n]); +5: print_word(font_info[n]); +6: print_word(save_stack[n]); +7: show_box(n); + {show a box, abbreviated by |show_box_depth| and |show_box_breadth|} +8: begin breadth_max:=10000; depth_threshold:=pool_size-pool_ptr-10; + show_node_list(n); {show a box in its entirety} + end; +9: show_token_list(n,null,1000); +10: slow_print(n); +11: check_mem(n>0); {check wellformedness; print new busy locations if |n>0|} +12: search_mem(n); {look for pointers to |n|} +13: begin read(term_in,l); print_cmd_chr(n,l); + end; +14: for k:=0 to n do print(buffer[k]); +15: begin font_in_short_display:=null_font; short_display(n); + end; +16: panicking:=not panicking; + +@* \[53] Extensions. +The program above includes a bunch of ``hooks'' that allow further +capabilities to be added without upsetting \TeX's basic structure. +Most of these hooks are concerned with ``whatsit'' nodes, which are +intended to be used for special purposes; whenever a new extension to +\TeX\ involves a new kind of whatsit node, a corresponding change needs +to be made to the routines below that deal with such nodes, +but it will usually be unnecessary to make many changes to the +other parts of this program. + +In order to demonstrate how extensions can be made, we shall treat +`\.{\\write}', `\.{\\openout}', `\.{\\closeout}', `\.{\\immediate}', +`\.{\\special}', and `\.{\\setlanguage}' as if they were extensions. +These commands are actually primitives of \TeX, and they should +appear in all implementations of the system; but let's try to imagine +that they aren't. Then the program below illustrates how a person +could add them. + +Sometimes, of course, an extension will require changes to \TeX\ itself; +no system of hooks could be complete enough for all conceivable extensions. +The features associated with `\.{\\write}' are almost all confined to the +following paragraphs, but there are small parts of the |print_ln| and +|print_char| procedures that were introduced specifically to \.{\\write} +characters. Furthermore one of the token lists recognized by the scanner +is a |write_text|; and there are a few other miscellaneous places where we +have already provided for some aspect of \.{\\write}. The goal of a \TeX\ +extender should be to minimize alterations to the standard parts of the +program, and to avoid them completely if possible. He or she should also +be quite sure that there's no easy way to accomplish the desired goals +with the standard features that \TeX\ already has. ``Think thrice before +extending,'' because that may save a lot of work, and it will also keep +incompatible extensions of \TeX\ from proliferating. +@^system dependencies@> +@^extensions to \TeX@> + +@ First let's consider the format of whatsit nodes that are used to represent +the data associated with \.{\\write} and its relatives. Recall that a whatsit +has |type=whatsit_node|, and the |subtype| is supposed to distinguish +different kinds of whatsits. Each node occupies two or more words; the +exact number is immaterial, as long as it is readily determined from the +|subtype| or other data. + +We shall introduce five |subtype| values here, corresponding to the +control sequences \.{\\openout}, \.{\\write}, \.{\\closeout}, \.{\\special}, and +\.{\\setlanguage}. The second word of I/O whatsits has a |write_stream| field +that identifies the write-stream number (0 to 15, or 16 for out-of-range and +positive, or 17 for out-of-range and negative). +In the case of \.{\\write} and \.{\\special}, there is also a field that +points to the reference count of a token list that should be sent. In the +case of \.{\\openout}, we need three words and three auxiliary subfields +to hold the string numbers for name, area, and extension. + +@d write_node_size=2 {number of words in a write/whatsit node} +@d open_node_size=3 {number of words in an open/whatsit node} +@d open_node=0 {|subtype| in whatsits that represent files to \.{\\openout}} +@d write_node=1 {|subtype| in whatsits that represent things to \.{\\write}} +@d close_node=2 {|subtype| in whatsits that represent streams to \.{\\closeout}} +@d special_node=3 {|subtype| in whatsits that represent \.{\\special} things} +@d language_node=4 {|subtype| in whatsits that change the current language} +@d what_lang(#)==link(#+1) {language number, in the range |0..255|} +@d what_lhm(#)==type(#+1) {minimum left fragment, in the range |1..63|} +@d what_rhm(#)==subtype(#+1) {minimum right fragment, in the range |1..63|} +@d write_tokens(#) == link(#+1) {reference count of token list to write} +@d write_stream(#) == info(#+1) {stream number (0 to 17)} +@d open_name(#) == link(#+1) {string number of file name to open} +@d open_area(#) == info(#+2) {string number of file area for |open_name|} +@d open_ext(#) == link(#+2) {string number of file extension for |open_name|} + +@ The sixteen possible \.{\\write} streams are represented by the |write_file| +array. The |j|th file is open if and only if |write_open[j]=true|. The last +two streams are special; |write_open[16]| represents a stream number +greater than 15, while |write_open[17]| represents a negative stream number, +and both of these variables are always |false|. + +@<Glob...@>= +@!write_file:array[0..15] of alpha_file; +@!write_open:array[0..17] of boolean; + +@ @<Set init...@>= +for k:=0 to 17 do write_open[k]:=false; + +@ Extensions might introduce new command codes; but it's best to use +|extension| with a modifier, whenever possible, so that |main_control| +stays the same. + +@d immediate_code=4 {command modifier for \.{\\immediate}} +@d set_language_code=5 {command modifier for \.{\\setlanguage}} + +@<Put each...@>= +primitive("openout",extension,open_node);@/ +@!@:open_out_}{\.{\\openout} primitive@> +primitive("write",extension,write_node); write_loc:=cur_val;@/ +@!@:write_}{\.{\\write} primitive@> +primitive("closeout",extension,close_node);@/ +@!@:close_out_}{\.{\\closeout} primitive@> +primitive("special",extension,special_node);@/ +@!@:special_}{\.{\\special} primitive@> +primitive("immediate",extension,immediate_code);@/ +@!@:immediate_}{\.{\\immediate} primitive@> +primitive("setlanguage",extension,set_language_code);@/ +@!@:set_language_}{\.{\\setlanguage} primitive@> + +@ The variable |write_loc| just introduced is used to provide an +appropriate error message in case of ``runaway'' write texts. + +@<Glob...@>= +@!write_loc:pointer; {|eqtb| address of \.{\\write}} + +@ @<Cases of |print_cmd_chr|...@>= +extension: case chr_code of + open_node:print_esc("openout"); + write_node:print_esc("write"); + close_node:print_esc("closeout"); + special_node:print_esc("special"); + immediate_code:print_esc("immediate"); + set_language_code:print_esc("setlanguage"); + othercases print("[unknown extension!]") + endcases; + +@ When an |extension| command occurs in |main_control|, in any mode, +the |do_extension| routine is called. + +@<Cases of |main_control| that are for extensions...@>= +any_mode(extension):do_extension; + +@ @<Declare act...@>= +@t\4@>@<Declare procedures needed in |do_extension|@>@; +procedure do_extension; +var i,@!j,@!k:integer; {all-purpose integers} +@!p,@!q,@!r:pointer; {all-purpose pointers} +begin case cur_chr of +open_node:@<Implement \.{\\openout}@>; +write_node:@<Implement \.{\\write}@>; +close_node:@<Implement \.{\\closeout}@>; +special_node:@<Implement \.{\\special}@>; +immediate_code:@<Implement \.{\\immediate}@>; +set_language_code:@<Implement \.{\\setlanguage}@>; +othercases confusion("ext1") +@:this can't happen ext1}{\quad ext1@> +endcases; +end; + +@ Here is a subroutine that creates a whatsit node having a given |subtype| +and a given number of words. It initializes only the first word of the whatsit, +and appends it to the current list. + +@<Declare procedures needed in |do_extension|@>= +procedure new_whatsit(@!s:small_number;@!w:small_number); +var p:pointer; {the new node} +begin p:=get_node(w); type(p):=whatsit_node; subtype(p):=s; +link(tail):=p; tail:=p; +end; + +@ The next subroutine uses |cur_chr| to decide what sort of whatsit is +involved, and also inserts a |write_stream| number. + +@<Declare procedures needed in |do_ext...@>= +procedure new_write_whatsit(@!w:small_number); +begin new_whatsit(cur_chr,w); +if w<>write_node_size then scan_four_bit_int +else begin scan_int; + if cur_val<0 then cur_val:=17 + else if cur_val>15 then cur_val:=16; + end; +write_stream(tail):=cur_val; +end; + +@ @<Implement \.{\\openout}@>= +begin new_write_whatsit(open_node_size); +scan_optional_equals; scan_file_name;@/ +open_name(tail):=cur_name; open_area(tail):=cur_area; open_ext(tail):=cur_ext; +end + +@ When `\.{\\write 12\{...\}}' appears, we scan the token list `\.{\{...\}}' +without expanding its macros; the macros will be expanded later when this +token list is rescanned. + +@<Implement \.{\\write}@>= +begin k:=cur_cs; new_write_whatsit(write_node_size);@/ +cur_cs:=k; p:=scan_toks(false,false); write_tokens(tail):=def_ref; +end + +@ @<Implement \.{\\closeout}@>= +begin new_write_whatsit(write_node_size); write_tokens(tail):=null; +end + +@ When `\.{\\special\{...\}}' appears, we expand the macros in the token +list as in \.{\\xdef} and \.{\\mark}. + +@<Implement \.{\\special}@>= +begin new_whatsit(special_node,write_node_size); write_stream(tail):=null; +p:=scan_toks(false,true); write_tokens(tail):=def_ref; +end + +@ Each new type of node that appears in our data structure must be capable +of being displayed, copied, destroyed, and so on. The routines that we +need for write-oriented whatsits are somewhat like those for mark nodes; +other extensions might, of course, involve more subtlety here. + +@<Basic printing...@>= +procedure print_write_whatsit(@!s:str_number;@!p:pointer); +begin print_esc(s); +if write_stream(p)<16 then print_int(write_stream(p)) +else if write_stream(p)=16 then print_char("*") +@.*\relax@> +else print_char("-"); +end; + +@ @<Display the whatsit...@>= +case subtype(p) of +open_node:begin print_write_whatsit("openout",p); + print_char("="); print_file_name(open_name(p),open_area(p),open_ext(p)); + end; +write_node:begin print_write_whatsit("write",p); + print_mark(write_tokens(p)); + end; +close_node:print_write_whatsit("closeout",p); +special_node:begin print_esc("special"); + print_mark(write_tokens(p)); + end; +language_node:begin print_esc("setlanguage"); + print_int(what_lang(p)); print(" (hyphenmin "); + print_int(what_lhm(p)); print_char(","); + print_int(what_rhm(p)); print_char(")"); + end; +othercases print("whatsit?") +endcases + +@ @<Make a partial copy of the whatsit...@>= +case subtype(p) of +open_node: begin r:=get_node(open_node_size); words:=open_node_size; + end; +write_node,special_node: begin r:=get_node(write_node_size); + add_token_ref(write_tokens(p)); words:=write_node_size; + end; +close_node,language_node: begin r:=get_node(small_node_size); + words:=small_node_size; + end; +othercases confusion("ext2") +@:this can't happen ext2}{\quad ext2@> +endcases + +@ @<Wipe out the whatsit...@>= +begin case subtype(p) of +open_node: free_node(p,open_node_size); +write_node,special_node: begin delete_token_ref(write_tokens(p)); + free_node(p,write_node_size); goto done; + end; +close_node,language_node: free_node(p,small_node_size); +othercases confusion("ext3") +@:this can't happen ext3}{\quad ext3@> +endcases;@/ +goto done; +end + +@ @<Incorporate a whatsit node into a vbox@>=do_nothing + +@ @<Incorporate a whatsit node into an hbox@>=do_nothing + +@ @<Let |d| be the width of the whatsit |p|@>=d:=0 + +@ @d adv_past(#)==@+if subtype(#)=language_node then + begin cur_lang:=what_lang(#); l_hyf:=what_lhm(#); r_hyf:=what_rhm(#);@+end + +@<Advance \(p)past a whatsit node in the \(l)|line_break| loop@>=@+ +adv_past(cur_p) + +@ @<Advance \(p)past a whatsit node in the \(p)pre-hyphenation loop@>=@+ +adv_past(s) + +@ @<Prepare to move whatsit |p| to the current page, then |goto contribute|@>= +goto contribute + +@ @<Process whatsit |p| in |vert_break| loop, |goto not_found|@>= +goto not_found + +@ @<Output the whatsit node |p| in a vlist@>= +out_what(p) + +@ @<Output the whatsit node |p| in an hlist@>= +out_what(p) + +@ After all this preliminary shuffling, we come finally to the routines +that actually send out the requested data. Let's do \.{\\special} first +(it's easier). + +@<Declare procedures needed in |hlist_out|, |vlist_out|@>= +procedure special_out(@!p:pointer); +var old_setting:0..max_selector; {holds print |selector|} +@!k:pool_pointer; {index into |str_pool|} +begin synch_h; synch_v;@/ +old_setting:=selector; selector:=new_string; +show_token_list(link(write_tokens(p)),null,pool_size-pool_ptr); +selector:=old_setting; +str_room(1); +if cur_length<256 then + begin dvi_out(xxx1); dvi_out(cur_length); + end +else begin dvi_out(xxx4); dvi_four(cur_length); + end; +for k:=str_start[str_ptr] to pool_ptr-1 do dvi_out(so(str_pool[k])); +pool_ptr:=str_start[str_ptr]; {erase the string} +end; + +@ To write a token list, we must run it through \TeX's scanner, expanding +macros and \.{\\the} and \.{\\number}, etc. This might cause runaways, +if a delimited macro parameter isn't matched, and runaways would be +extremely confusing since we are calling on \TeX's scanner in the middle +of a \.{\\shipout} command. Therefore we will put a dummy control sequence as +a ``stopper,'' right after the token list. This control sequence is +artificially defined to be \.{\\outer}. +@:end_write_}{\.{\\endwrite}@> + +@<Initialize table...@>= +text(end_write):="endwrite"; eq_level(end_write):=level_one; +eq_type(end_write):=outer_call; equiv(end_write):=null; + +@ @<Declare procedures needed in |hlist_out|, |vlist_out|@>= +procedure write_out(@!p:pointer); +var old_setting:0..max_selector; {holds print |selector|} +@!old_mode:integer; {saved |mode|} +@!j:small_number; {write stream number} +@!q,@!r:pointer; {temporary variables for list manipulation} +begin @<Expand macros in the token list + and make |link(def_ref)| point to the result@>; +old_setting:=selector; j:=write_stream(p); +if write_open[j] then selector:=j +else begin {write to the terminal if file isn't open} + if (j=17)and(selector=term_and_log) then selector:=log_only; + print_nl(""); + end; +token_show(def_ref); print_ln; +flush_list(def_ref); selector:=old_setting; +end; + +@ The final line of this routine is slightly subtle; at least, the author +didn't think about it until getting burnt! There is a used-up token list +@^Knuth, Donald Ervin@> +on the stack, namely the one that contained |end_write_token|. (We +insert this artificial `\.{\\endwrite}' to prevent runaways, as explained +above.) If it were not removed, and if there were numerous writes on a +single page, the stack would overflow. + +@d end_write_token==cs_token_flag+end_write + +@<Expand macros in the token list and...@>= +q:=get_avail; info(q):=right_brace_token+"}";@/ +r:=get_avail; link(q):=r; info(r):=end_write_token; ins_list(q);@/ +begin_token_list(write_tokens(p),write_text);@/ +q:=get_avail; info(q):=left_brace_token+"{"; ins_list(q); +{now we're ready to scan + `\.\{$\langle\,$token list$\,\rangle$\.{\} \\endwrite}'} +old_mode:=mode; mode:=0; + {disable \.{\\prevdepth}, \.{\\spacefactor}, \.{\\lastskip}, \.{\\prevgraf}} +cur_cs:=write_loc; q:=scan_toks(false,true); {expand macros, etc.} +get_token;@+if cur_tok<>end_write_token then + @<Recover from an unbalanced write command@>; +mode:=old_mode; +end_token_list {conserve stack space} + +@ @<Recover from an unbalanced write command@>= +begin print_err("Unbalanced write command"); +@.Unbalanced write...@> +help2("On this page there's a \write with fewer real {'s than }'s.")@/ +("I can't handle that very well; good luck."); error; +repeat get_token; +until cur_tok=end_write_token; +end + +@ The |out_what| procedure takes care of outputting whatsit nodes for +|vlist_out| and |hlist_out|\kern-.3pt. + +@<Declare procedures needed in |hlist_out|, |vlist_out|@>= +procedure out_what(@!p:pointer); +var j:small_number; {write stream number} +begin case subtype(p) of +open_node,write_node,close_node:@<Do some work that has been queued up + for \.{\\write}@>; +special_node:special_out(p); +language_node:do_nothing; +othercases confusion("ext4") +@:this can't happen ext4}{\quad ext4@> +endcases; +end; + +@ We don't implement \.{\\write} inside of leaders. (The reason is that +the number of times a leader box appears might be different in different +implementations, due to machine-dependent rounding in the glue calculations.) +@^leaders@> + +@<Do some work that has been queued up...@>= +if not doing_leaders then + begin j:=write_stream(p); + if subtype(p)=write_node then write_out(p) + else begin if write_open[j] then a_close(write_file[j]); + if subtype(p)=close_node then write_open[j]:=false + else if j<16 then + begin cur_name:=open_name(p); cur_area:=open_area(p); + cur_ext:=open_ext(p); + if cur_ext="" then cur_ext:=".tex"; + pack_cur_name; + while not a_open_out(write_file[j]) do + prompt_file_name("output file name",".tex"); + write_open[j]:=true; + end; + end; + end + +@ The presence of `\.{\\immediate}' causes the |do_extension| procedure +to descend to one level of recursion. Nothing happens unless \.{\\immediate} +is followed by `\.{\\openout}', `\.{\\write}', or `\.{\\closeout}'. +@^recursion@> + +@<Implement \.{\\immediate}@>= +begin get_x_token; +if (cur_cmd=extension)and(cur_chr<=close_node) then + begin p:=tail; do_extension; {append a whatsit node} + out_what(tail); {do the action immediately} + flush_node_list(tail); tail:=p; link(p):=null; + end +else back_input; +end + +@ The \.{\\language} extension is somewhat different. +We need a subroutine that comes into play when a character of +a non-|clang| language is being appended to the current paragraph. + +@<Declare action...@>= +procedure fix_language; +var @!l:ASCII_code; {the new current language} +begin if language<=0 then l:=0 +else if language>255 then l:=0 +else l:=language; +if l<>clang then + begin new_whatsit(language_node,small_node_size); + what_lang(tail):=l; clang:=l;@/ + what_lhm(tail):=norm_min(left_hyphen_min); + what_rhm(tail):=norm_min(right_hyphen_min); + end; +end; + +@ @<Implement \.{\\setlanguage}@>= +if abs(mode)<>hmode then report_illegal_case +else begin new_whatsit(language_node,small_node_size); + scan_int; + if cur_val<=0 then clang:=0 + else if cur_val>255 then clang:=0 + else clang:=cur_val; + what_lang(tail):=clang; + what_lhm(tail):=norm_min(left_hyphen_min); + what_rhm(tail):=norm_min(right_hyphen_min); + end + +@ @<Finish the extensions@>= +for k:=0 to 15 do if write_open[k] then a_close(write_file[k]) + +@* \[54] System-dependent changes. +This section should be replaced, if necessary, by any special +modifications of the program +that are necessary to make \TeX\ work at a particular installation. +It is usually best to design your change file so that all changes to +previous sections preserve the section numbering; then everybody's version +will be consistent with the published program. More extensive changes, +which introduce new sections, can be inserted here; then only the index +itself will get a new section number. +@^system dependencies@> + +@* \[55] Index. +Here is where you can find all uses of each identifier in the program, +with underlined entries pointing to where the identifier was defined. +If the identifier is only one letter long, however, you get to see only +the underlined entries. {\sl All references are to section numbers instead of +page numbers.} + +This index also lists error messages and other aspects of the program +that you might want to look up some day. For example, the entry +for ``system dependencies'' lists all sections that should receive +special attention from people who are installing \TeX\ in a new +operating environment. A list of various things that can't happen appears +under ``this can't happen''. Approximately 40 sections are listed under +``inner loop''; these account for about 60\pct! of \TeX's running time, +exclusive of input and output. |