path: root/systems/knuth/dist/etc/vftovp.web

% This program by D. E. Knuth is not copyrighted and can be used freely.
% Version 1 was implemented in December 1989.
% Version 1.1 fixed problems of strict Pascal (April 1990).
% Version 1.2 fixed various bugs found by Peter Breitenlohner (September 1990).
% Version 1.3 made out_as_fix tell the truth in overflow cases (Dec 2002).
% Version 1.4 reports out-of-range characters (Breitenlohner, Jan 2014),
%  and tests nl>lig_size not 4*lig_size (C. M. Connelly, Melissa O'Neill).

% Here is TeX material that gets inserted after \input webmac
\def\hang{\hangindent 3em\indent\ignorespaces}
\font\ninerm=cmr9
\let\mc=\ninerm % medium caps for names like SAIL
\def\PASCAL{Pascal}

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

\def\title{VF\lowercase{to}VP}
\def\contentspagenumber{101}
\def\topofcontents{\null
  \def\titlepage{F} % include headline on the contents page
  \def\rheader{\mainfont\hfil \contentspagenumber}
  \vfill
  \centerline{\titlefont The {\ttitlefont VFtoVP} processor}
  \vskip 15pt
  \centerline{(Version 1.4, January 2014)}
  \vfill}
\def\botofcontents{\vfill
  \centerline{\hsize 5in\baselineskip9pt
    \vbox{\ninerm\noindent
    The preparation of this program
    was supported in part by the National Science
    Foundation and by the System Development Foundation. `\TeX' is a
    trademark of the American Mathematical Society.}}}
\pageno=\contentspagenumber \advance\pageno by 1

@* Introduction.
The \.{VFtoVP} utility program converts a virtual font (``\.{VF}'') file
and its associated \TeX\ font metric (``\.{TFM}'')
file into an equivalent virtual-property-list (``\.{VPL}'') file. It also
makes a thorough check of the given files, using algorithms that are
essentially the same as those used by
\.{DVI} device drivers and by \TeX. Thus if \TeX\ or a \.{DVI} driver
complains that a \.{TFM} or \.{VF}
file is ``bad,'' this program will pinpoint the source or sources of
badness. A \.{VPL} file output by this program can be edited with
a normal text editor, and the result can be converted back to \.{VF} and \.{TFM}
format using the companion program \.{VPtoVF}.

\indent\.{VFtoVP} is an extended version of the program \.{TFtoPL}, which
is part of the standard \TeX ware library.
The idea of a virtual font was inspired by the work of David R. Fuchs
@^Fuchs, David Raymond@>
who designed a similar set of conventions in 1984 while developing a
device driver for ArborText, Inc. He wrote a somewhat similar program
called \.{AMFtoXPL}.

The |banner| string defined here should be changed whenever \.{VFtoVP}
gets modified.

@d banner=='This is VFtoVP, Version 1.4' {printed when the program starts}

@ This program is written entirely in standard \PASCAL, except that
it occasionally has lower case letters in strings that are output.
Such letters can be converted to upper case if necessary. The input is read
from |vf_file| and |tfm_file|; the output is written on |vpl_file|.
Error messages and
other remarks are written on the |output| file, which the user may
choose to assign to the terminal if the system permits it.
@^system dependencies@>

The term |print| is used instead of |write| when this program writes on
the |output| file, so that all such output can be easily deflected.

@d print(#)==write(#)
@d print_ln(#)==write_ln(#)

@p program VFtoVP(@!vf_file,@!tfm_file,@!vpl_file,@!output);
label @<Labels in the outer block@>@/
const @<Constants in the outer block@>@/
type @<Types in the outer block@>@/
var @<Globals in the outer block@>@/
procedure initialize; {this procedure gets things started properly}
  var @!k:integer; {all-purpose index for initialization}
  begin print_ln(banner);@/
  @<Set initial values@>@/
  end;

@ If the program has to stop prematurely, it goes to the
`|final_end|'.

@d final_end=9999 {label for the end of it all}

@<Labels...@>=final_end;

@ The following parameters can be changed at compile time to extend or
reduce \.{VFtoVP}'s capacity.

@<Constants...@>=
@!tfm_size=30000; {maximum length of |tfm| data, in bytes}
@!vf_size=10000; {maximum length of |vf| data, in bytes}
@!max_fonts=300; {maximum number of local fonts in the |vf| file}
@!lig_size=5000; {maximum length of |lig_kern| program, in words}
@!hash_size=5003; {preferably a prime number, a bit larger than the number
  of character pairs in lig/kern steps}
@!name_length=50; {a file name shouldn't be longer than this}
@!max_stack=50; {maximum depth of \.{DVI} stack in character packets}

@ 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 do_nothing == {empty statement}
@d exit=10 {go here to leave a procedure}
@d not_found=45 {go here when you've found nothing}
@d return==goto exit {terminate a procedure call}
@f return==nil

@<Types...@>=
@!byte=0..255; {unsigned eight-bit quantity}

@* Virtual fonts.  The idea behind \.{VF} files is that a general
interface mechanism is needed to switch between the myriad font
layouts provided by different suppliers of typesetting equipment.
Without such a mechanism, people must go to great lengths writing
inscrutable macros whenever they want to use typesetting conventions
based on one font layout in connection with actual fonts that have
another layout. This puts an extra burden on the typesetting system,
interfering with the other things it needs to do (like kerning,
hyphenation, and ligature formation).

These difficulties go away when we have a ``virtual font,''
i.e., a font that exists in a logical sense but not a physical sense.
A typesetting system like \TeX\ can do its job without knowing where the
actual characters come from; a device driver can then do its job by
letting a \.{VF} file tell what actual characters correspond to the
characters \TeX\ imagined were present. The actual characters
can be shifted and/or magnified and/or combined with other characters
from many different fonts. A virtual font can even make use of characters
from virtual fonts, including itself.

Virtual fonts also allow convenient character substitutions for proofreading
purposes, when fonts designed for one output device are unavailable on another.

@ A \.{VF} file is organized as a stream of 8-bit bytes, using conventions
borrowed from \.{DVI} and \.{PK} files. Thus, a device driver that knows
about \.{DVI} and \.{PK} format will already
contain most of the mechanisms necessary to process \.{VF} files. 
We shall assume that \.{DVI} format is understood; the conventions in the
\.{DVI} documentation (see, for example, {\sl \TeX: The Program}, part 31)
are adopted here to define \.{VF} format.

A preamble
appears at the beginning, followed by a sequence of character definitions,
followed by a postamble. More precisely, the first byte of every \.{VF} file
must be the first byte of the following ``preamble command'':

\yskip\hang|pre| 247 |i[1]| |k[1]| |x[k]| |cs[4]| |ds[4]|.
Here |i| is the identification byte of \.{VF}, currently 202. The string
|x| is merely a comment, usually indicating the source of the \.{VF} file.
Parameters |cs| and |ds| are respectively the check sum and the design size
of the virtual font; they should match the first two words in the header of
the \.{TFM} file, as described below.

\yskip
After the |pre| command, the preamble continues with font definitions;
every font needed to specify ``actual'' characters in later
\\{set\_char} commands is defined here. The font definitions are
exactly the same in \.{VF} files as they are in \.{DVI} files, except
that the scaled size |s| is relative and the design size |d| is absolute:

\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|.

\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\noindent
These font numbers |k| are ``local''; they have no relation to font numbers
defined in the \.{DVI} file that uses this virtual font. The dimension~|s|,
which represents the scaled size of the local font being defined,
is a |fix_word| relative to the design size of the virtual font.
Thus if the local font is to be used at the same size
as the design size of the virtual font itself, |s| will be the
integer value $2^{20}$. The value of |s| must be positive and less than
$2^{24}$ (thus less than 16 when considered as a |fix_word|). 
The dimension~|d| is a |fix_word| in units of printer's points; hence it
is identical to the design size found in the corresponding \.{TFM} file.

@d id_byte=202

@<Glob...@>=
@!vf_file:packed file of byte;

@ The preamble is followed by zero or more character packets, where each
character packet begins with a byte that is $<243$. Character packets have
two formats, one long and one short:

\yskip\hang|long_char| 242 |pl[4]| |cc[4]| |tfm[4]| |dvi[pl]|. This long form
specifies a virtual character in the general case.

\yskip\hang|short_char0..short_char241|
|pl[1]| |cc[1]| |tfm[3]| |dvi[pl]|. This short form specifies a
virtual character in the common case
when |0<=pl<242| and |0<=cc<256| and $0\le|tfm|<2^{24}$.

\yskip\noindent
Here |pl| denotes the packet length following the |tfm| value; |cc| is
the character code; and |tfm| is the character width copied from the
\.{TFM} file for this virtual font. There should be at most one character
packet having any given |cc| code.

The |dvi| bytes are a sequence of complete \.{DVI} commands, properly
nested with respect to |push| and |pop|. All \.{DVI} operations are
permitted except |bop|, |eop|, and commands with opcodes |>=243|.
Font selection commands (|fnt_num0| through |fnt4|) must refer to fonts
defined in the preamble.

Dimensions that appear in the \.{DVI} instructions are analogous to
|fix_word| quantities; i.e., they are integer multiples of $2^{-20}$ times
the design size of the virtual font. For example, if the virtual font
has design size $10\,$pt, the \.{DVI} command to move down $5\,$pt
would be a \\{down} instruction with parameter $2^{19}$. The virtual font
itself might be used at a different size, say $12\,$pt; then that
\\{down} instruction would move down $6\,$pt instead. Each dimension
must be less than $2^{24}$ in absolute value.

Device drivers processing \.{VF} files treat the sequences of |dvi| bytes
as subroutines or macros, implicitly enclosing them with |push| and |pop|.
Each subroutine begins with |w=x=y=z=0|, and with current font~|f| the
number of the first-defined in the preamble (undefined if there's no
such font). After the |dvi| commands have been
performed, the |h| and~|v| position registers of \.{DVI} format and the
current font~|f| are restored to their former values;
then, if the subroutine has been invoked by a \\{set\_char} or \\{set}
command, |h|~is increased by the \.{TFM} width
(properly scaled)---just as if a simple character had been typeset.

@d long_char=242 {\.{VF} command for general character packet}
@d set_char_0=0 {\.{DVI} command to typeset character 0 and move right}
@d set1=128 {typeset a character and move right}
@d set_rule=132 {typeset a rule and move right}
@d put1=133 {typeset a character}
@d put_rule=137 {typeset a rule}
@d nop=138 {no operation}
@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 improper_DVI_for_VF==139,140,243,244,245,246,247,248,249,250,251,252,
    253,254,255

@ The character packets are followed by a trivial postamble, consisting of
one or more bytes all equal to |post| (248). The total number of bytes
in the file should be a multiple of~4.

@* Font metric data.
The idea behind \.{TFM} files is that typesetting routines like \TeX\
need a compact way to store the relevant information about several
dozen fonts, and computer centers need a compact way to store the
relevant information about several hundred fonts. \.{TFM} files are
compact, and most of the information they contain is highly relevant,
so they provide a solution to the problem.

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, and so does \.{VFtoVP}. Note that the bytes
are considered to be unsigned numbers.

@<Glob...@>=
@!tfm_file:packed file of byte;

@ On some systems you may have to do something special to read a
packed file of bytes. For example, the following code didn't work
when it was first tried at Stanford, because packed files have to be
opened with a special switch setting on the \PASCAL\ that was used.
@^system dependencies@>

@<Set init...@>=
reset(tfm_file); reset(vf_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|,
|ne<=256|, 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.

@<Glob...@>=
@!lf,@!lh,@!bc,@!ec,@!nw,@!nh,@!nd,@!ni,@!nl,@!nk,@!ne,@!np:0..@'77777;
  {subfile sizes}

@ The rest of the \.{TFM} file may be regarded as a sequence of ten data
arrays having the informal specification
$$\def\arr$[#1]#2${\&{array} $[#1]$ \&{of} #2}
\vbox{\halign{\hfil\\{#}&$\,:\,$\arr#\hfil\cr
header&|[0..lh-1]stuff|\cr
char\_info&|[bc..ec]char_info_word|\cr
width&|[0..nw-1]fix_word|\cr
height&|[0..nh-1]fix_word|\cr
depth&|[0..nd-1]fix_word|\cr
italic&|[0..ni-1]fix_word|\cr
lig\_kern&|[0..nl-1]lig_kern_command|\cr
kern&|[0..nk-1]fix_word|\cr
exten&|[0..ne-1]extensible_recipe|\cr
param&|[1..np]fix_word|\cr}}$$
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 one of
the |fix_word| values will 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,
and for \.{TFM} files to be used with Xerox printing software it must
contain at least 18 words, allocated as described below. When different
kinds of devices need to be interfaced, it may be necessary to add further
words to the header block.

\yskip\hang|header[0]| is a 32-bit check sum that \TeX\ will copy into the
\.{DVI} output file whenever it uses the font.  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 (7227 \TeX\ points = 254 cm).  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.} Thus, for example,
the value of |param[6]|, one \.{em} or \.{\\quad}, 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.  @^design size@>

\yskip\hang|header[2..11]|, if present, contains 40 bytes that identify
the character coding scheme. The first byte, which must be between 0 and
39, is the number of subsequent ASCII bytes actually relevant in this
string, which is intended to specify what character-code-to-symbol
convention is present in the font.  Examples are \.{ASCII} for standard
ASCII, \.{TeX text} for fonts like \.{cmr10} and \.{cmti9}, \.{TeX math
extension} for \.{cmex10}, \.{XEROX text} for Xerox fonts, \.{GRAPHIC} for
special-purpose non-alphabetic fonts, \.{UNSPECIFIED} for the default case
when there is no information.  Parentheses should not appear in this name.
(Such a string is said to be in {\mc BCPL} format.)
@^coding scheme@>

\yskip\hang|header[12..16]|, if present, contains 20 bytes that name the
font family (e.g., \.{CMR} or \.{HELVETICA}), in {\mc BCPL} format.
This field is also known as the ``font identifier.''
@^family name@>
@^font identifier@>

\yskip\hang|header[17]|, if present, contains a first byte called the
|seven_bit_safe_flag|, then two bytes that are ignored, and a fourth byte
called the |face|. If the value of the fourth byte is less than 18, it has
the following interpretation as a ``weight, slope, and expansion'':  Add 0
or 2 or 4 (for medium or bold or light) to 0 or 1 (for roman or italic) to
0 or 6 or 12 (for regular or condensed or extended).  For example, 13 is
0+1+12, so it represents medium italic extended.  A three-letter code
(e.g., \.{MIE}) can be used for such |face| data.

\yskip\hang|header[18..@twhatever@>]| might also be present; the individual
words are simply called |header[18]|, |header[19]|, etc., at the moment.

@ Next comes the |char_info| array, which contains one |char_info_word|
per character. Each |char_info_word| 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.

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\hang|tag=0| (|no_tag|) means that |remainder| is unused.\par
\hang|tag=1| (|lig_tag|) means that this character has a ligature/kerning
program starting at |lig_kern[remainder]|.\par
\hang|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
\hang|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

@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 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).

Notice that if $a=0$ and $b=1$, the current character is unchanged; if
$a=b$ and $c=1$, the current character is changed but the next character is
unchanged. \.{VFtoVP} will check to see that infinite loops are avoided.

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 have
|256*op_byte+remainder<nl|. If such an instruction is encountered during
normal program execution, it denotes an unconditional halt; no ligature
command is performed.

@d stop_flag=128 {value indicating `\.{STOP}' in a lig/kern program}
@d kern_flag=128 {op code for a kern step}

@ 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.


@ 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 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.

When the character coding scheme is \.{TeX math symbols}, the font is
supposed to have 15 additional parameters called |num1|, |num2|, |num3|,
|denom1|, |denom2|, |sup1|, |sup2|, |sup3|, |sub1|, |sub2|, |supdrop|,
|subdrop|, |delim1|, |delim2|, and |axis_height|, respectively. When the
character coding scheme is \.{TeX math extension}, the font is supposed to
have six additional parameters called |default_rule_thickness| and
|big_op_spacing1| through |big_op_spacing5|.

@ So that is what \.{TFM} files hold. The next question is, ``What about
\.{VPL} files?'' A complete answer to that question appears in the
documentation of the companion program, \.{VPtoVF}, so it will not
be repeated here. Suffice it to say that a \.{VPL} file is an ordinary
\PASCAL\ text file, and that the output of \.{VFtoVP} uses only a
subset of the possible constructions that might appear in a \.{VPL} file.
Furthermore, hardly anybody really wants to look at the formal
definition of \.{VPL} format, because it is almost self-explanatory when
you see an example or two.

@<Glob...@>=
@!vpl_file:text;

@ @<Set init...@>=
rewrite(vpl_file);

@* Unpacking the TFM file.
The first thing \.{VFtoVP} does is read the entire |tfm_file| into an array of
bytes, |tfm[0..(4*lf-1)]|.

@<Types...@>=
@!index=0..tfm_size; {address of a byte in |tfm|}

@ @<Glob...@>=
@!tfm:array [-1000..tfm_size] of byte; {the \.{TFM} input data all goes here}
 {the negative addresses avoid range checks for invalid characters}

@ The input may, of course, be all screwed up and not a \.{TFM} file
at all. So we begin cautiously.

@d abort(#)==begin print_ln(#);
  print_ln('Sorry, but I can''t go on; are you sure this is a TFM?');
  goto final_end;
  end

@<Read the whole \.{TFM} file@>=
read(tfm_file,tfm[0]);
if tfm[0]>127 then abort('The first byte of the input file exceeds 127!');
@.The first byte...@>
if eof(tfm_file) then abort('The input file is only one byte long!');
@.The input...one byte long@>
read(tfm_file,tfm[1]); lf:=tfm[0]*@'400+tfm[1];
if lf=0 then
  abort('The file claims to have length zero, but that''s impossible!');
@.The file claims...@>
if 4*lf-1>tfm_size then abort('The file is bigger than I can handle!');
@.The file is bigger...@>
for tfm_ptr:=2 to 4*lf-1 do
  begin if eof(tfm_file) then
    abort('The file has fewer bytes than it claims!');
@.The file has fewer bytes...@>
  read(tfm_file,tfm[tfm_ptr]);
  end;
if not eof(tfm_file) then
  begin print_ln('There''s some extra junk at the end of the TFM file,');
@.There's some extra junk...@>
  print_ln('but I''ll proceed as if it weren''t there.');
  end

@ After the file has been read successfully, we look at the subfile sizes
to see if they check out.

@d eval_two_bytes(#)==begin if tfm[tfm_ptr]>127 then
    abort('One of the subfile sizes is negative!');
@.One of the subfile sizes...@>
  #:=tfm[tfm_ptr]*@'400+tfm[tfm_ptr+1];
  tfm_ptr:=tfm_ptr+2;
  end

@<Set subfile sizes |lh|, |bc|, \dots, |np|@>=
begin tfm_ptr:=2;@/
eval_two_bytes(lh);
eval_two_bytes(bc);
eval_two_bytes(ec);
eval_two_bytes(nw);
eval_two_bytes(nh);
eval_two_bytes(nd);
eval_two_bytes(ni);
eval_two_bytes(nl);
eval_two_bytes(nk);
eval_two_bytes(ne);
eval_two_bytes(np);
if lh<2 then abort('The header length is only ',lh:1,'!');
@.The header length...@>
if nl>lig_size then
  abort('The lig/kern program is longer than I can handle!');
@.The lig/kern program...@>
if (bc>ec+1)or(ec>255) then abort('The character code range ',
@.The character code range...@>
  bc:1,'..',ec:1,' is illegal!');
if (nw=0)or(nh=0)or(nd=0)or(ni=0) then
  abort('Incomplete subfiles for character dimensions!');
@.Incomplete subfiles...@>
if ne>256 then abort('There are ',ne:1,' extensible recipes!');
@.There are ... recipes@>
if lf<>6+lh+(ec-bc+1)+nw+nh+nd+ni+nl+nk+ne+np then
  abort('Subfile sizes don''t add up to the stated total!');
@.Subfile sizes don't add up...@>
end

@ Once the input data successfully passes these basic checks,
\.{VFtoVP} believes that it is a \.{TFM} file, and the conversion
to \.{VPL} format will take place. Access to the various subfiles
is facilitated by computing the following base addresses. For example,
the |char_info| for character |c| will start in location
|4*(char_base+c)| of the |tfm| array.

@<Globals...@>=
@!char_base,@!width_base,@!height_base,@!depth_base,@!italic_base,
@!lig_kern_base,@!kern_base,@!exten_base,@!param_base:integer;
  {base addresses for the subfiles}

@ @<Compute the base addresses@>=
begin char_base:=6+lh-bc;
width_base:=char_base+ec+1;
height_base:=width_base+nw;
depth_base:=height_base+nh;
italic_base:=depth_base+nd;
lig_kern_base:=italic_base+ni;
kern_base:=lig_kern_base+nl;
exten_base:=kern_base+nk;
param_base:=exten_base+ne-1;
end

@ Of course we want to define macros that suppress the detail of how the
font information is actually encoded. Each word will be referred to by
the |tfm| index of its first byte. For example, if |c| is a character
code between |bc| and |ec|, then |tfm[char_info(c)]| will be the
first byte of its |char_info|, i.e., the |width_index|; furthermore
|width(c)| will point to the |fix_word| for |c|'s width.

@d check_sum=24
@d design_size=check_sum+4
@d scheme=design_size+4
@d family=scheme+40
@d random_word=family+20
@d char_info(#)==4*(char_base+#)
@d width_index(#)==tfm[char_info(#)]
@d nonexistent(#)==((#<bc)or(#>ec)or(width_index(#)=0))
@d height_index(#)==(tfm[char_info(#)+1] div 16)
@d depth_index(#)==(tfm[char_info(#)+1] mod 16)
@d italic_index(#)==(tfm[char_info(#)+2] div 4)
@d tag(#)==(tfm[char_info(#)+2] mod 4)
@d reset_tag(#)==tfm[char_info(#)+2]:=4*italic_index(#)+no_tag
@d remainder(#)==tfm[char_info(#)+3]
@d width(#)==4*(width_base+width_index(#))
@d height(#)==4*(height_base+height_index(#))
@d depth(#)==4*(depth_base+depth_index(#))
@d italic(#)==4*(italic_base+italic_index(#))
@d exten(#)==4*(exten_base+remainder(#))
@d lig_step(#)==4*(lig_kern_base+(#))
@d kern(#)==4*(kern_base+#) {here \#\ is an index, not a character}
@d param(#)==4*(param_base+#) {likewise}

@ One of the things we would like to do is take cognizance of fonts whose
character coding scheme is \.{TeX math symbols} or \.{TeX math extension};
we will set the |font_type| variable to one of the three choices
|vanilla|, |mathsy|, or |mathex|.

@d vanilla=0 {not a special scheme}
@d mathsy=1 {\.{TeX math symbols} scheme}
@d mathex=2 {\.{TeX math extension} scheme}

@<Glob...@>=
@!font_type:vanilla..mathex; {is this font special?}

@* Unpacking the VF file.
Once the \.{TFM} file has been brought into memory, \.{VFtoVP} completes
the input phase by reading the \.{VF} information into another array of bytes.
In this case we don't store all the data; we check the redundant bytes
for consistency with their \.{TFM} counterparts, and we partially decode
the packets.

@<Glob...@>=
@!vf:array[0..vf_size] of byte; {the \.{VF} input data goes here}
@!font_number:array[0..max_fonts] of integer; {local font numbers}
@!font_start,@!font_chars:array[0..max_fonts] of 0..vf_size; {font info}
@!font_ptr:0..max_fonts; {number of local fonts}
@!packet_start,@!packet_end:array[byte] of 0..vf_size;
  {character packet boundaries}
@!packet_found:boolean; {at least one packet has appeared}
@!temp_byte:byte;@+@!count:integer; {registers for simple calculations}
@!real_dsize:real; {the design size, converted to floating point}
@!pl:integer; {packet length}
@!vf_ptr:0..vf_size; {first unused location in |vf|}
@!vf_count:integer; {number of bytes read from |vf_file|}

@ Again we cautiously verify that we've been given decent data.

@d read_vf(#)==read(vf_file,#)
@d vf_abort(#)==
  begin print_ln(#);
  print_ln('Sorry, but I can''t go on; are you sure this is a VF?');
  goto final_end;
  end

@<Read the whole \.{VF} file@>=
read_vf(temp_byte);
if temp_byte<>pre then vf_abort('The first byte isn''t `pre''!');
@.The first byte...@>
@<Read the preamble command@>;
@<Read and store the font definitions and character packets@>;
@<Read and verify the postamble@>

@ @d vf_store(#)==@t@>@;@/
  if vf_ptr+#>=vf_size then vf_abort('The file is bigger than I can handle!');
@.The file is bigger...@>
  for k:=vf_ptr to vf_ptr+#-1 do
    begin if eof(vf_file) then vf_abort('The file ended prematurely!');
@.The file ended prematurely@>
    read_vf(vf[k]);
    end;
  vf_count:=vf_count+#; vf_ptr:=vf_ptr+#

@<Read the preamble command@>=
if eof(vf_file) then vf_abort('The input file is only one byte long!');
@.The input...one byte long@>
read_vf(temp_byte);
if temp_byte<>id_byte then vf_abort('Wrong VF version number in second byte!');
@.Wrong VF version...@>
if eof(vf_file) then vf_abort('The input file is only two bytes long!');
read_vf(temp_byte); {read the length of introductory comment}
vf_count:=11; vf_ptr:=0; vf_store(temp_byte);
for k:=0 to vf_ptr-1 do print(xchr[vf[k]]);
print_ln(' '); count:=0;
for k:=0 to 7 do
  begin if eof(vf_file) then vf_abort('The file ended prematurely!');
@.The file ended prematurely@>
  read_vf(temp_byte);
  if temp_byte=tfm[check_sum+k] then incr(count);
  end;
real_dsize:=(((tfm[design_size]*256+tfm[design_size+1])*256+tfm[design_size+2])
 *256+tfm[design_size+3])/@'4000000;
if count<>8 then
  begin print_ln('Check sum and/or design size mismatch.');
@.Check sum...mismatch@>
  print_ln('Data from TFM file will be assumed correct.');
  end

@ @<Read and store the font definitions and character packets@>=
for k:=0 to 255 do packet_start[k]:=vf_size;
font_ptr:=0; packet_found:=false; font_start[0]:=vf_ptr;
repeat if eof(vf_file) then
  begin print_ln('File ended without a postamble!'); temp_byte:=post;
@.File ended without a postamble@>
  end
else begin read_vf(temp_byte); incr(vf_count);
  if temp_byte<>post then
    if temp_byte>long_char then @<Read and store a font definition@>
    else @<Read and store a character packet@>;
  end;
until temp_byte=post

@ @<Read and verify the postamble@>=
while (temp_byte=post)and not eof(vf_file) do
  begin read_vf(temp_byte); incr(vf_count);
  end;
if not eof(vf_file) then
  begin print_ln('There''s some extra junk at the end of the VF file.');
@.There's some extra junk...@>
  print_ln('I''ll proceed as if it weren''t there.');
  end;
if vf_count mod 4 <> 0 then
  print_ln('VF data not a multiple of 4 bytes')
@.VF data not a multiple of 4 bytes@>

@ @<Read and store a font definition@>=
begin if packet_found or(temp_byte>=pre) then
  vf_abort('Illegal byte ',temp_byte:1,' at beginning of character packet!');
@.Illegal byte...@>
font_number[font_ptr]:=vf_read(temp_byte-fnt_def1+1);
if font_ptr=max_fonts then vf_abort('I can''t handle that many fonts!');
@.I can't handle that many fonts@>
vf_store(14); {|c[4]| |s[4]| |d[4]| |a[1]| |l[1]|}
if vf[vf_ptr-10]>0 then {|s| is negative or exceeds $2^{24}-1$}
  vf_abort('Mapped font size is too big!');
@.Mapped font size...big@>
a:=vf[vf_ptr-2]; l:=vf[vf_ptr-1]; vf_store(a+l); {|n[a+l]|}
@<Print the name of the local font@>;
@<Read the local font's \.{TFM} file and record the characters it contains@>;
incr(font_ptr); font_start[font_ptr]:=vf_ptr; 
end

@ The font area may need to be separated from the font name on some systems.
Here we simply reproduce the font area and font name (with no space
or punctuation between them).
@^system dependencies@>

@<Print the name...@>=
print('MAPFONT ',font_ptr:1,': ');
for k:=font_start[font_ptr]+14 to vf_ptr-1 do print(xchr[vf[k]]);
k:=font_start[font_ptr]+5;
print_ln(' at ',(((vf[k]*256+vf[k+1])*256+vf[k+2])/@'4000000)*real_dsize:2:2,
  'pt')

@ Now we must read in another \.{TFM} file. But this time we needn't be so
careful, because we merely want to discover which characters are present.
The next few sections of the program are copied pretty much verbatim from
\.{DVItype}, so that system-dependent modifications can be copied from existing
software.

It turns out to be convenient to read four bytes at a time, when we are
inputting from the local \.{TFM} files. The input goes into global variables
|b0|, |b1|, |b2|, and |b3|, with |b0| getting the first byte and |b3|
the fourth.

@<Glob...@>=
@!a:integer; {length of the area/directory spec}
@!l:integer; {length of the font name proper}
@!cur_name:packed array[1..name_length] of char; {external name,
  with no lower case letters}
@!b0,@!b1,@!b2,@!b3: byte; {four bytes input at once}
@!font_lh:0..@'77777; {header length of current local font}
@!font_bc,@!font_ec:0..@'77777; {character range of current local font}

@ The |read_tfm_word| procedure sets |b0| through |b3| to the next
four bytes in the current \.{TFM} file.
@^system dependencies@>

@d read_tfm(#)==if eof(tfm_file) then #:=0@+else read(tfm_file,#)

@p procedure read_tfm_word;
begin read_tfm(b0); read_tfm(b1);
read_tfm(b2); read_tfm(b3);
end;

@ We use the |vf| array to store a list of all valid characters in the
local font, beginning at location |font_chars[f]|.

@<Read the local font's \.{TFM} file...@>=
font_chars[font_ptr]:=vf_ptr;
@<Move font name into the |cur_name| string@>;
reset(tfm_file,cur_name);
@^system dependencies@>
if eof(tfm_file) then
  print_ln('---not loaded, TFM file can''t be opened!')
@.TFM file can\'t be opened@>
else  begin font_bc:=0; font_ec:=256; {will cause error if not modified soon}
  read_tfm_word;
  if b2<128 then
    begin font_lh:=b2*256+b3; read_tfm_word;
    if (b0<128) and (b2<128) then
      begin font_bc:=b0*256+b1; font_ec:=b2*256+b3;
      end;
    end;
  if font_bc<=font_ec then
    if font_ec>255 then print_ln('---not loaded, bad TFM file!')
@.bad TFM file@>
    else begin for k:=0 to 3+font_lh do
        begin read_tfm_word;
        if k=4 then @<Check the check sum@>;
        if k=5 then @<Check the design size@>;
        end;
      for k:=font_bc to font_ec do
        begin read_tfm_word;
        if b0>0 then {character |k| exists in the font}
          begin vf[vf_ptr]:=k; incr(vf_ptr);
          if vf_ptr=vf_size then vf_abort('I''m out of VF memory!');
@.I'm out of VF memory@>
          end;
        end;
      end;
  if eof(tfm_file) then
    print_ln('---trouble is brewing, TFM file ended too soon!');
@.trouble is brewing...@>
  end;
incr(vf_ptr) {leave space for character search later}

@ @<Check the check sum@>=
if b0+b1+b2+b3>0 then
  if(b0<>vf[font_start[font_ptr]])or@|
   (b1<>vf[font_start[font_ptr]+1])or@|
   (b2<>vf[font_start[font_ptr]+2])or@|
   (b3<>vf[font_start[font_ptr]+3]) then
    begin print_ln('Check sum in VF file being replaced by TFM check sum');
@.Check sum...replaced...@>
    vf[font_start[font_ptr]]:=b0;
    vf[font_start[font_ptr]+1]:=b1;
    vf[font_start[font_ptr]+2]:=b2;
    vf[font_start[font_ptr]+3]:=b3;
    end

@ @<Check the design size@>=
if(b0<>vf[font_start[font_ptr]+8])or@|
 (b1<>vf[font_start[font_ptr]+9])or@|
 (b2<>vf[font_start[font_ptr]+10])or@|
 (b3<>vf[font_start[font_ptr]+11]) then
  begin print_ln('Design size in VF file being replaced by TFM design size');
@.Design size...replaced...@>
  vf[font_start[font_ptr]+8]:=b0;
  vf[font_start[font_ptr]+9]:=b1;
  vf[font_start[font_ptr]+10]:=b2;
  vf[font_start[font_ptr]+11]:=b3;
  end

@ If no font directory has been specified, \.{DVI}-reading software
is supposed to use the default font directory, which is a
system-dependent place where the standard fonts are kept.
The string variable |default_directory| contains the name of this area.
@^system dependencies@>

@d default_directory_name=='TeXfonts:' {change this to the correct name}
@d default_directory_name_length=9 {change this to the correct length}

@<Glob...@>=
@!default_directory:packed array[1..default_directory_name_length] of char;

@ @<Set init...@>=
default_directory:=default_directory_name;

@ The string |cur_name| is supposed to be set to the external name of the
\.{TFM} file for the current font. This usually means that we need to
prepend the name of the default directory, and
to append the suffix `\.{.TFM}'. Furthermore, we change lower case letters
to upper case, since |cur_name| is a \PASCAL\ string.
@^system dependencies@>

@<Move font name into the |cur_name| string@>=
for k:=1 to name_length do cur_name[k]:=' ';
if a=0 then
  begin for k:=1 to default_directory_name_length do
    cur_name[k]:=default_directory[k];
  r:=default_directory_name_length;
  end
else r:=0;
for k:=font_start[font_ptr]+14 to vf_ptr-1 do
  begin incr(r);
  if r+4>name_length then vf_abort('Font name too long for me!');
@.Font name too long for me@>
  if (vf[k]>="a")and(vf[k]<="z") then
      cur_name[r]:=xchr[vf[k]-@'40]
  else cur_name[r]:=xchr[vf[k]];
  end;
cur_name[r+1]:='.'; cur_name[r+2]:='T'; cur_name[r+3]:='F'; cur_name[r+4]:='M'


@ It's convenient to have a subroutine
that reads a |k|-byte number from |vf_file|.

@d get_vf(#)==if eof(vf_file) then #:=0 @+else read_vf(#)

@p function vf_read(@!k:integer):integer; {actually |1<=k<=4|}
var @!b:byte; {input byte}
@!a:integer; {accumulator}
begin vf_count:=vf_count+k; get_vf(b); a:=b;
if k=4 then if b>=128 then a:=a-256; {4-byte numbers are signed}
while k>1 do
  begin get_vf(b);
  a:=256*a+b; decr(k);
  end;
vf_read:=a;
end;

@ The \.{VF} format supports arbitrary 4-byte character codes,
but \.{VPL} format presently does not.
Therefore we give up if the character code is
not between 0 and~255.

After more experience is gained with present-day \.{VPL} files, the
best way to extend them to arbitrary character codes will become clear;
the extensions to \.{VFtoVP} and \.{VPtoVF} should not be difficult.

@<Read and store a character packet@>=
begin if temp_byte=long_char then
  begin pl:=vf_read(4); c:=vf_read(4); count:=vf_read(4);
    {|pl[4]| |cc[4]| |tfm[4]|}
  end
else begin pl:=temp_byte; c:=vf_read(1); count:=vf_read(3);
    {|pl[1]| |cc[1]| |tfm[3]|}
  end;
if nonexistent(c) then vf_abort('Character ',c:1,' does not exist!');
@.Character c does not exist@>
if packet_start[c]<vf_size then
  print_ln('Discarding earlier packet for character ',c:1);
@.Discarding earlier packet...@>
if count<>tfm_width(c) then
  print_ln('Incorrect TFM width for character ',c:1,' in VF file');
@.Incorrect TFM width...@>
if pl<0 then vf_abort('Negative packet length!');
@.Negative packet length@>
packet_start[c]:=vf_ptr; vf_store(pl); packet_end[c]:=vf_ptr-1;
packet_found:=true;
end

@ The preceding code requires a simple subroutine that evaluates \.{TFM} data.

@p function tfm_width(@!c:byte):integer;
var @!a:integer; {accumulator}
@!k:index; {index into |tfm|}
begin k:=width(c); {we assume that character |c| exists}
a:=tfm[k];
if a>=128 then a:=a-256;
tfm_width:=((256*a+tfm[k+1])*256+tfm[k+2])*256+tfm[k+3];
end;

@* Basic output subroutines.
Let us now define some procedures that will reduce the rest of \.{VFtoVP}'s
work to a triviality.

First of all, it is convenient to have an abbreviation for output to the
\.{VPL} file:

@d out(#)==write(vpl_file,#)

@ In order to stick to standard \PASCAL, we use an |xchr| array to do
appropriate conversion of ASCII codes. Three other little strings are
used to produce |face| codes like \.{MIE}.

@<Glob...@>=
@!ASCII_04,@!ASCII_10,@!ASCII_14: packed array [1..32] of char;
  {strings for output in the user's external character set}
@!xchr:packed array [0..255] of char;
@!MBL_string,@!RI_string,@!RCE_string:packed array [1..3] of char;
  {handy string constants for |face| codes}

@ @<Set init...@>=
ASCII_04:=' !"#$%&''()*+,-./0123456789:;<=>?';@/
ASCII_10:='@@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_';@/
ASCII_14:='`abcdefghijklmnopqrstuvwxyz{|}~?';@/
for k:=0 to 255 do xchr[k]:='?';
for k:=0 to @'37 do
  begin xchr[k+@'40]:=ASCII_04[k+1];
  xchr[k+@'100]:=ASCII_10[k+1];
  xchr[k+@'140]:=ASCII_14[k+1];
  end;
MBL_string:='MBL'; RI_string:='RI '; RCE_string:='RCE';

@ The array |dig| will hold a sequence of digits to be output.

@<Glob...@>=
@!dig:array[0..11] of 0..9;

@ Here, in fact, are two procedures that output |dig[j-1]|$\,\ldots\,$|dig[0]|,
given $j>0$.

@p procedure out_digs(j:integer); {outputs |j| digits}
begin repeat decr(j); out(dig[j]:1);
until j=0;
end;
@#
procedure print_digs(j:integer); {prints |j| digits}
begin repeat decr(j); print(dig[j]:1);
until j=0;
end;

@ The |print_octal| procedure indicates how |print_digs| can be used.
Since this procedure is used only to print character codes, it always
produces three digits.

@p procedure print_octal(c:byte); {prints octal value of |c|}
var j:0..2; {index into |dig|}
begin print(''''); {an apostrophe indicates the octal notation}
for j:=0 to 2 do
  begin dig[j]:=c mod 8; c:=c div 8;
  end;
print_digs(3);
end;

@ A \.{VPL} file has nested parentheses, and we want to format the output
so that its structure is clear. The |level| variable keeps track of the
depth of nesting.

@<Glob...@>=
@!level:0..5;

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

@ Three simple procedures suffice to produce the desired structure in the
output.

@p procedure out_ln; {finishes one line, indents the next}
var l:0..5;
begin write_ln(vpl_file);
for l:=1 to level do out('   ');
end;
@#
procedure left; {outputs a left parenthesis}
begin incr(level); out('(');
end;
@#
procedure right; {outputs a right parenthesis and finishes a line}
begin decr(level); out(')'); out_ln;
end;

@ The value associated with a property can be output in a variety of
ways. For example, we might want to output a {\mc BCPL} string that
begins in |tfm[k]|:

@p procedure out_BCPL(@!k:index); {outputs a string, preceded by a blank space}
var l:0..39; {the number of bytes remaining}
begin out(' '); l:=tfm[k];
while l>0 do
  begin incr(k); decr(l); out(xchr[tfm[k]]);
  end;
end;

@ The property value might also be a sequence of |l| bytes, beginning
in |tfm[k]|, that we would like to output in octal notation.
The following procedure assumes that |l<=4|, but larger values of |l|
could be handled easily by enlarging the |dig| array and increasing
the upper bounds on |b| and |j|.

@p procedure out_octal(@!k,@!l:index); {outputs |l| bytes in octal}
var a:0..@'1777; {accumulator for bits not yet output}
@!b:0..32; {the number of significant bits in |a|}
@!j:0..11; {the number of digits of output}
begin out(' O '); {specify octal format}
a:=0; b:=0; j:=0;
while l>0 do @<Reduce \(1)|l| by one, preserving the invariants@>;
while (a>0)or(j=0) do
  begin dig[j]:=a mod 8; a:=a div 8; incr(j);
  end;
out_digs(j);
end;

@ @<Reduce \(1)|l|...@>=
begin decr(l);
if tfm[k+l]<>0 then
  begin while b>2 do
    begin dig[j]:=a mod 8; a:=a div 8; b:=b-3; incr(j);
    end;
  case b of
  0: a:=tfm[k+l];
  1:a:=a+2*tfm[k+l];
  2:a:=a+4*tfm[k+l];
  end;
  end;
b:=b+8;
end

@ The property value may be a character, which is output in octal
unless it is a letter or a digit.
@^system dependencies@>

@p procedure out_char(@!c:byte); {outputs a character}
begin if font_type>vanilla then
  begin tfm[0]:=c; out_octal(0,1)
  end
else if ((c>="0")and(c<="9"))or@|
   ((c>="A")and(c<="Z"))or@|
   ((c>="a")and(c<="z")) then out(' C ',xchr[c])
else begin tfm[0]:=c; out_octal(0,1);
  end;
end;

@ The property value might be a ``face'' byte, which is output in the
curious code mentioned earlier, provided that it is less than 18.

@p procedure out_face(@!k:index); {outputs a |face|}
var s:0..1; {the slope}
@!b:0..8; {the weight and expansion}
begin if tfm[k]>=18 then out_octal(k,1)
else  begin out(' F ');  {specify face-code format}
  s:=tfm[k] mod 2; b:=tfm[k] div 2;
  out(MBL_string[1+(b mod 3)]);
  out(RI_string[1+s]);
  out(RCE_string[1+(b div 3)]);
  end;
end;

@ And finally, the value might be a |fix_word|, which is output in
decimal notation with just enough decimal places for \.{VPtoVF}
to recover every bit of the given |fix_word|.

All of the numbers involved in the intermediate calculations of
this procedure will be nonnegative and less than $10\cdot2^{24}$.

@p procedure out_fix(@!k:index); {outputs a |fix_word|}
var a:0..@'7777; {accumulator for the integer part}
@!f:integer; {accumulator for the fraction part}
@!j:0..12; {index into |dig|}
@!delta:integer; {amount if allowable inaccuracy}
begin out(' R '); {specify real format}
a:=(tfm[k]*16)+(tfm[k+1] div 16);
f:=((tfm[k+1] mod 16)*@'400+tfm[k+2])*@'400+tfm[k+3];
if a>@'3777 then @<Reduce \(2)negative to positive@>;
@<Output the integer part, |a|, in decimal notation@>;
@<Output the fraction part, $|f|/2^{20}$, in decimal notation@>;
end;

@ The following code outputs at least one digit even if |a=0|.

@<Output the integer...@>=
begin j:=0;
repeat dig[j]:=a mod 10; a:=a div 10; incr(j);
until a=0;
out_digs(j);
end

@ And the following code outputs at least one digit to the right
of the decimal point.

@<Output the fraction...@>=
begin out('.'); f:=10*f+5; delta:=10;
repeat if delta>@'4000000 then f:=f+@'2000000-(delta div 2);
out(f div @'4000000:1); f:=10*(f mod @'4000000); delta:=delta*10;
until f<=delta;
end;

@ @<Reduce \(2)negative to positive@>=
begin out('-'); a:=@'10000-a;
if f>0 then
  begin f:=@'4000000-f; decr(a);
  end;
end

@* Outputting the TFM info.
\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. And when it finds something wrong, it justs
calls the file ``bad,'' without identifying the nature of the problem,
since \.{TFM} files are supposed to be good almost all of the time.

Of course, a bad file shows up every now and again, and that's where
\.{VFtoVP} comes in. This program wants to catch at least as many errors as
\TeX\ does, and to give informative error messages besides.
All of the errors are corrected, so that the \.{VPL} output will
be correct (unless, of course, the \.{TFM} file was so loused up
that no attempt is being made to fathom it).

@ Just before each character is processed, its code is printed in octal
notation. Up to eight such codes appear on a line; so we have a variable
to keep track of how many are currently there. We also keep track of
whether or not any errors have had to be corrected.

@<Glob...@>=
@!chars_on_line:0..8; {the number of characters printed on the current line}
@!perfect:boolean; {was the file free of errors?}

@ @<Set init...@>=
chars_on_line:=0;@/
perfect:=true; {innocent until proved guilty}

@ Error messages are given with the help of the |bad| and |range_error|
and |bad_char| macros:

@d bad(#)==begin perfect:=false; if chars_on_line>0 then print_ln(' ');
  chars_on_line:=0; print_ln('Bad TFM file: ',#);
  end
@.Bad TFM file@>
@d range_error(#)==begin perfect:=false; print_ln(' ');
  print(#,' index for character ');
  print_octal(c); print_ln(' is too large;');
  print_ln('so I reset it to zero.');
  end
@d bad_char_tail(#)==print_octal(#); print_ln('.');
  end
@d bad_char(#)==begin perfect:=false; if chars_on_line>0 then print_ln(' ');
  chars_on_line:=0; print('Bad TFM file: ',#,' nonexistent character ');
  bad_char_tail
@d correct_bad_char_tail(#)==print_octal(tfm[#]); print_ln('.'); tfm[#]:=bc;
  end
@d correct_bad_char(#)== begin perfect:=false;
  if chars_on_line>0 then print_ln(' ');
  chars_on_line:=0; print('Bad TFM file: ',#,' nonexistent character ');
  correct_bad_char_tail

@<Glob...@>=
@!i:0..@'77777; {an index to words of a subfile}
@!c:0..256; {a random character}
@!d:0..3; {byte number in a word}
@!k:index; {a random index}
@!r:0..65535; {a random two-byte value}

@ There are a lot of simple things to do, and they have to be done one
at a time, so we might as well get down to business.  The first things
that \.{VFtoVP} will put into the \.{VPL} file appear in the header part.

@<Do the header@>=
begin font_type:=vanilla;
if lh>=12 then
  begin @<Set the true |font_type|@>;
  if lh>=17 then
    begin @<Output the family name@>;
    if lh>=18 then @<Output the rest of the header@>;
    end;
  @<Output the character coding scheme@>;
  end;
@<Output the design size@>;
@<Output the check sum@>;
@<Output the |seven_bit_safe_flag|@>;
end

@ @<Output the check sum@>=
left; out('CHECKSUM'); out_octal(check_sum,4);
right

@ Incorrect design sizes are changed to 10 points.

@d bad_design(#)==begin bad('Design size ',#,'!');
@.Design size wrong@>
  print_ln('I''ve set it to 10 points.');
  out(' D 10');
  end

@ @<Output the design size@>=
left; out('DESIGNSIZE');
if tfm[design_size]>127 then bad_design('negative')
else if (tfm[design_size]=0)and(tfm[design_size+1]<16) then
  bad_design('too small')
else out_fix(design_size);
right;
out('(COMMENT DESIGNSIZE IS IN POINTS)'); out_ln;
out('(COMMENT OTHER SIZES ARE MULTIPLES OF DESIGNSIZE)'); out_ln
@.DESIGNSIZE IS IN POINTS@>

@ Since we have to check two different {\mc BCPL} strings for validity,
we might as well write a subroutine to make the check.

@p procedure check_BCPL(@!k,@!l:index); {checks a string of length |<l|}
var j:index; {runs through the string}
@!c:byte; {character being checked}
begin if tfm[k]>=l then
  begin bad('String is too long; I''ve shortened it drastically.');
@.String is too long...@>
  tfm[k]:=1;
  end;
for j:=k+1 to k+tfm[k] do
  begin c:=tfm[j];
  if (c="(")or(c=")") then
    begin bad('Parenthesis in string has been changed to slash.');
@.Parenthesis...changed to slash@>
    tfm[j]:="/";
    end
  else if (c<" ")or(c>"~") then
    begin bad('Nonstandard ASCII code has been blotted out.');
@.Nonstandard ASCII code...@>
    tfm[j]:="?";
    end
  else if (c>="a")and(c<="z") then tfm[j]:=c+"A"-"a"; {upper-casify letters}
  end;
end;

@ The |font_type| starts out |vanilla|; possibly we need to reset it.

@<Set the true |font_type|@>=
begin check_BCPL(scheme,40);
if (tfm[scheme]>=11)and@|(tfm[scheme+1]="T")and@|
  (tfm[scheme+2]="E")and@|(tfm[scheme+3]="X")and@|
  (tfm[scheme+4]=" ")and@|(tfm[scheme+5]="M")and@|
  (tfm[scheme+6]="A")and@|(tfm[scheme+7]="T")and@|
  (tfm[scheme+8]="H")and@|(tfm[scheme+9]=" ") then
  begin if (tfm[scheme+10]="S")and(tfm[scheme+11]="Y") then font_type:=mathsy
  else if (tfm[scheme+10]="E")and(tfm[scheme+11]="X") then font_type:=mathex;
  end;
end

@ @<Output the character coding scheme@>=
left; out('CODINGSCHEME');
out_BCPL(scheme);
right

@ @<Output the family name@>=
left; out('FAMILY');
check_BCPL(family,20);
out_BCPL(family);
right

@ @<Output the rest of the header@>=
begin left; out('FACE'); out_face(random_word+3); right;
for i:=18 to lh-1 do
  begin left; out('HEADER D ',i:1);
  out_octal(check_sum+4*i,@,4); right;
  end;
end

@ This program does not check to see if the |seven_bit_safe_flag| has the
correct setting, i.e., if it really reflects the seven-bit-safety of
the \.{TFM} file; the stated value is merely put into the \.{VPL} file.
The \.{VPtoVF} program will store a correct value and give a warning
message if a file falsely claims to be safe.

@<Output the |seven_bit_safe_flag|@>=
if (lh>17) and (tfm[random_word]>127) then
  begin left; out('SEVENBITSAFEFLAG TRUE'); right;
  end

@ The next thing to take care of is the list of parameters.

@<Do the parameters@>=
if np>0 then
  begin left; out('FONTDIMEN'); out_ln;
  for i:=1 to np do @<Check and output the $i$th parameter@>;
  right;
  end;
@<Check to see if |np| is complete for this font type@>;

@ @<Check to see if |np|...@>=
if (font_type=mathsy)and(np<>22) then
  print_ln('Unusual number of fontdimen parameters for a math symbols font (',
@.Unusual number of fontdimen...@>
    np:1,' not 22).')
else if (font_type=mathex)and(np<>13) then
  print_ln('Unusual number of fontdimen parameters for an extension font (',
    np:1,' not 13).')

@ All |fix_word| values except the design size and the first parameter
will be checked to make sure that they are less than 16.0 in magnitude,
using the |check_fix| macro:

@d check_fix_tail(#)==bad(#,' ',i:1,' is too big;');
  print_ln('I have set it to zero.');
  end
@d check_fix(#)==if (tfm[#]>0)and(tfm[#]<255) then
  begin tfm[#]:=0; tfm[(#)+1]:=0; tfm[(#)+2]:=0; tfm[(#)+3]:=0;
  check_fix_tail

@<Check and output the $i$th parameter@>=
begin left;
if i=1 then out('SLANT') {this parameter is not checked}
else  begin check_fix(param(i))('Parameter');@/
@.Parameter n is too big@>
  @<Output the name of parameter $i$@>;
  end;
out_fix(param(i)); right;
end

@ @<Output the name...@>=
if i<=7 then case i of
  2:out('SPACE');@+3:out('STRETCH');@+4:out('SHRINK');
  5:out('XHEIGHT');@+6:out('QUAD');@+7:out('EXTRASPACE')@+end
else if (i<=22)and(font_type=mathsy) then case i of
  8:out('NUM1');@+9:out('NUM2');@+10:out('NUM3');
  11:out('DENOM1');@+12:out('DENOM2');
  13:out('SUP1');@+14:out('SUP2');@+15:out('SUP3');
  16:out('SUB1');@+17:out('SUB2');
  18:out('SUPDROP');@+19:out('SUBDROP');
  20:out('DELIM1');@+21:out('DELIM2');
  22:out('AXISHEIGHT')@+end
else if (i<=13)and(font_type=mathex) then
  if i=8 then out('DEFAULTRULETHICKNESS')
  else out('BIGOPSPACING',i-8:1)
else out('PARAMETER D ',i:1)

@ We need to check the range of all the remaining |fix_word| values,
and to make sure that |width[0]=0|, etc.

@d nonzero_fix(#)==(tfm[#]>0)or(tfm[#+1]>0)or(tfm[#+2]>0)or(tfm[#+3]>0)

@<Check the |fix_word| entries@>=
if nonzero_fix(4*width_base) then bad('width[0] should be zero.');
@.should be zero@>
if nonzero_fix(4*height_base) then bad('height[0] should be zero.');
if nonzero_fix(4*depth_base) then bad('depth[0] should be zero.');
if nonzero_fix(4*italic_base) then bad('italic[0] should be zero.');
for i:=0 to nw-1 do check_fix(4*(width_base+i))('Width');
@.Width n is too big@>
for i:=0 to nh-1 do check_fix(4*(height_base+i))('Height');
@.Height n is too big@>
for i:=0 to nd-1 do check_fix(4*(depth_base+i))('Depth');
@.Depth n is too big@>
for i:=0 to ni-1 do check_fix(4*(italic_base+i))('Italic correction');
@.Italic correction n is too big@>
if nk>0 then for i:=0 to nk-1 do check_fix(kern(i))('Kern');
@.Kern n is too big@>

@ The ligature/kerning program comes next. Before we can put it out in
\.{VPL} format, we need to make a table of ``labels'' that will be inserted
into the program. For each character |c| whose |tag| is |lig_tag| and
whose starting address is |r|, we will store the pair |(c,r)| in the
|label_table| array. If there's a boundary-char program starting at~|r|,
we also store the pair |(256,r)|.
This array is sorted by its second components, using the
simple method of straight insertion.

@<Glob...@>=
@!label_table:array[0..258] of record@t@>@/@!cc:0..256;@!rr:0..lig_size;end;
@!label_ptr: 0..257; {the largest entry in |label_table|}
@!sort_ptr:0..257; {index into |label_table|}
@!boundary_char:0..256; {boundary character, or 256 if none}
@!bchar_label:0..@'77777; {beginning of boundary character program}

@ @<Set init...@>=
boundary_char:=256; bchar_label:=@'77777;@/
label_ptr:=0; label_table[0].rr:=0; {a sentinel appears at the bottom}

@ We'll also identify and remove inaccessible program steps, using the
|activity| array.

@d unreachable=0 {a program step not known to be reachable}
@d pass_through=1 {a program step passed through on initialization}
@d accessible=2 {a program step that can be relevant}

@<Glob...@>=
@!activity:array[0..lig_size] of unreachable..accessible;
@!ai,@!acti:0..lig_size; {indices into |activity|}

@ @<Do the ligatures and kerns@>=
if nl>0 then
  begin for ai:=0 to nl-1 do activity[ai]:=unreachable;
  @<Check for a boundary char@>;
  end;
@<Build the label table@>;
if nl>0 then
  begin left; out('LIGTABLE'); out_ln;@/
  @<Compute the |activity| array@>;
  @<Output and correct the ligature/kern program@>;
  right;
  @<Check for ligature cycles@>;
  end

@ We build the label table even when |nl=0|, because this catches errors
that would not otherwise be detected.

@<Build...@>=
for c:=bc to ec do if tag(c)=lig_tag then
  begin r:=remainder(c);
  if r<nl then
    begin if tfm[lig_step(r)]>stop_flag then
      begin r:=256*tfm[lig_step(r)+2]+tfm[lig_step(r)+3];
      if r<nl then if activity[remainder(c)]=unreachable then
        activity[remainder(c)]:=pass_through;
      end;
    end;
  if r>=nl then
    begin perfect:=false; print_ln(' ');
    print('Ligature/kern starting index for character '); print_octal(c);
    print_ln(' is too large;'); print_ln('so I removed it.'); reset_tag(c);
@.Ligature/kern starting index...@>
    end
  else @<Insert |(c,r)| into |label_table|@>;
  end;
label_table[label_ptr+1].rr:=lig_size; {put ``infinite'' sentinel at the end}

@ @<Insert |(c,r)|...@>=
begin sort_ptr:=label_ptr; {there's a hole at position |sort_ptr+1|}
while label_table[sort_ptr].rr>r do
  begin label_table[sort_ptr+1]:=label_table[sort_ptr];
  decr(sort_ptr); {move the hole}
  end;
label_table[sort_ptr+1].cc:=c;
label_table[sort_ptr+1].rr:=r; {fill the hole}
incr(label_ptr); activity[r]:=accessible;
end

@ @<Check for a bound...@>=
if tfm[lig_step(0)]=255 then
  begin left; out('BOUNDARYCHAR');
  boundary_char:=tfm[lig_step(0)+1]; out_char(boundary_char); right;
  activity[0]:=pass_through;
  end;
if tfm[lig_step(nl-1)]=255 then
  begin r:=256*tfm[lig_step(nl-1)+2]+tfm[lig_step(nl-1)+3];
  if r>=nl then
    begin perfect:=false; print_ln(' ');
    print('Ligature/kern starting index for boundarychar is too large;');
    print_ln('so I removed it.');
@.Ligature/kern starting index...@>
    end
  else begin label_ptr:=1; label_table[1].cc:=256; label_table[1].rr:=r;
    bchar_label:=r; activity[r]:=accessible;
    end;
  activity[nl-1]:=pass_through;
  end

@ @<Compute the |activity| array@>=
for ai:=0 to nl-1 do if activity[ai]=accessible then
  begin r:=tfm[lig_step(ai)];
  if r<stop_flag then
    begin r:=r+ai+1;
    if r>=nl then
      begin bad('Ligature/kern step ',ai:1,' skips too far;');
@.Lig...skips too far@>
      print_ln('I made it stop.'); tfm[lig_step(ai)]:=stop_flag;
      end
    else activity[r]:=accessible;
    end;
  end

@ We ignore |pass_through| items, which don't need to be mentioned in
the \.{VPL} file.

@<Output and correct the ligature...@>=
sort_ptr:=1; {point to the next label that will be needed}
for acti:=0 to nl-1 do if activity[acti]<>pass_through then
  begin i:=acti; @<Take care of commenting out unreachable steps@>;
  @<Output any labels for step $i$@>;
  @<Output step $i$ of the ligature/kern program@>;
  end;
if level=2 then right {the final step was unreachable}

@ @<Output any labels...@>=
while i=label_table[sort_ptr].rr do
  begin left; out('LABEL');
  if label_table[sort_ptr].cc=256 then out(' BOUNDARYCHAR')
  else out_char(label_table[sort_ptr].cc);
  right; incr(sort_ptr);
  end

@ @<Take care of commenting out...@>=
if activity[i]=unreachable then
  begin if level=1 then
    begin left; out('COMMENT THIS PART OF THE PROGRAM IS NEVER USED!'); out_ln;
    end
  end
else if level=2 then right

@ @<Output step $i$...@>=
begin k:=lig_step(i);
if tfm[k]>stop_flag then
  begin if 256*tfm[k+2]+tfm[k+3]>=nl then
    bad('Ligature unconditional stop command address is too big.');
@.Ligature unconditional stop...@>
  end
else if tfm[k+2]>=kern_flag then @<Output a kern step@>
else @<Output a ligature step@>;
if tfm[k]>0 then
  if level=1 then @<Output either \.{SKIP} or \.{STOP}@>;
end

@ The \.{SKIP} command is a bit tricky, because we will be omitting all
inaccessible commands.

@<Output either...@>=
begin if tfm[k]>=stop_flag then out('(STOP)')
else begin count:=0;
  for ai:=i+1 to i+tfm[k] do if activity[ai]=accessible then incr(count);
  out('(SKIP D ',count:1,')'); {possibly $count=0$, so who cares}
  end;
out_ln;
end

@ @<Output a kern step@>=
begin if nonexistent(tfm[k+1]) then if tfm[k+1]<>boundary_char then
  correct_bad_char('Kern step for')(k+1);
@.Kern step for nonexistent...@>
left; out('KRN'); out_char(tfm[k+1]);
r:=256*(tfm[k+2]-kern_flag)+tfm[k+3];
if r>=nk then
  begin bad('Kern index too large.');
@.Kern index too large@>
  out(' R 0.0');
  end
else out_fix(kern(r));
right;
end

@ @<Output a ligature step@>=
begin if nonexistent(tfm[k+1]) then if tfm[k+1]<>boundary_char then
  correct_bad_char('Ligature step for')(k+1);
@.Ligature step for nonexistent...@>
if nonexistent(tfm[k+3]) then
  correct_bad_char('Ligature step produces the')(k+3);
@.Ligature step produces...@>
left; r:=tfm[k+2];
if (r=4)or((r>7)and(r<>11)) then
  begin print_ln('Ligature step with nonstandard code changed to LIG');
  r:=0; tfm[k+2]:=0;
  end;
if r mod 4>1 then out('/');
out('LIG');
if odd(r) then out('/');
while r>3 do
  begin out('>'); r:=r-4;
  end;
out_char(tfm[k+1]); out_char(tfm[k+3]); right;
end

@ The last thing on \.{VFtoVP}'s agenda is to go through the
list of |char_info| and spew out the information about each individual
character.

@<Do the characters@>=
sort_ptr:=0; {this will suppress `\.{STOP}' lines in ligature comments}
for c:=bc to ec do if width_index(c)>0 then
  begin if chars_on_line=8 then
    begin print_ln(' '); chars_on_line:=1;
    end
  else  begin if chars_on_line>0 then print(' ');
    incr(chars_on_line);
    end;
  print_octal(c); {progress report}
  left; out('CHARACTER'); out_char(c); out_ln;
  @<Output the character's width@>;
  if height_index(c)>0 then @<Output the character's height@>;
  if depth_index(c)>0 then @<Output the character's depth@>;
  if italic_index(c)>0 then @<Output the italic correction@>;
  case tag(c) of
  no_tag: do_nothing;
  lig_tag: @<Output the applicable part of the ligature/kern
    program as a comment@>;
  list_tag: @<Output the character link unless there is a problem@>;
  ext_tag: @<Output an extensible character recipe@>;
  end;@/
  if not do_map(c) then goto final_end;
  right;
  end

@ @<Output the character's width@>=
begin left; out('CHARWD');
if width_index(c)>=nw then range_error('Width')
else out_fix(width(c));
right;
end

@ @<Output the character's height@>=
if height_index(c)>=nh then range_error('Height')
@.Height index for char...@>
else  begin left; out('CHARHT'); out_fix(height(c)); right;
  end

@ @<Output the character's depth@>=
if depth_index(c)>=nd then range_error('Depth')
@.Depth index for char@>
else  begin left; out('CHARDP'); out_fix(depth(c)); right;
  end

@ @<Output the italic correction@>=
if italic_index(c)>=ni then range_error('Italic correction')
@.Italic correction index for char...@>
else  begin left; out('CHARIC'); out_fix(italic(c)); right;
  end

@ @<Output the applicable part of the ligature...@>=
begin left; out('COMMENT'); out_ln;@/
i:=remainder(c); r:=lig_step(i);
if tfm[r]>stop_flag then i:=256*tfm[r+2]+tfm[r+3];
repeat @<Output step...@>;
if tfm[k]>=stop_flag then i:=nl
else i:=i+1+tfm[k];
until i>=nl;
right;
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.

@<Output the character link unless there is a problem@>=
begin r:=remainder(c);
if nonexistent(r) then
  begin bad_char('Character list link to')(r); reset_tag(c);
@.Character list link...@>
  end
else  begin while (r<c)and(tag(r)=list_tag) do r:=remainder(r);
  if r=c then
    begin bad('Cycle in a character list!');
@.Cycle in a character list@>
    print('Character '); print_octal(c);
    print_ln(' now ends the list.');
    reset_tag(c);
    end
  else  begin left; out('NEXTLARGER'); out_char(remainder(c));
    right;
    end;
  end;
end

@ @<Output an extensible character recipe@>=
if remainder(c)>=ne then
  begin range_error('Extensible'); reset_tag(c);
@.Extensible index for char@>
  end
else  begin left; out('VARCHAR'); out_ln;
  @<Output the extensible pieces that exist@>;
  right;
  end

@ @<Output the extensible pieces that...@>=
for k:=0 to 3 do if (k=3)or(tfm[exten(c)+k]>0) then
  begin left;
  case k of
  0:out('TOP');@+1:out('MID');@+2:out('BOT');@+3:out('REP')@+end;
  if nonexistent(tfm[exten(c)+k]) then out_char(c)
  else out_char(tfm[exten(c)+k]);
  right;
  end

@ Some of the extensible recipes may not actually be used, but \TeX\ will
complain about them anyway if they refer to nonexistent characters.
Therefore \.{VFtoVP} must check them too.

@<Check the extensible recipes@>=
if ne>0 then for c:=0 to ne-1 do for d:=0 to 3 do
  begin k:=4*(exten_base+c)+d;
  if (tfm[k]>0)or(d=3) then
    begin if nonexistent(tfm[k]) then
      begin bad_char('Extensible recipe involves the')(tfm[k]);
@.Extensible recipe involves...@>
      if d<3 then tfm[k]:=0;
      end;
    end;
  end

@* Checking for ligature loops.
We have programmed almost everything but the most interesting calculation of
all, which has been saved for last as a special treat. \TeX's extended ligature
mechanism allows unwary users to specify sequences of ligature replacements
that never terminate. For example, the pair of commands
$$\.{(/LIG $x$ $y$) (/LIG $y$ $x$)}$$
alternately replaces character $x$ by character $y$ and vice versa. A similar
loop occurs if \.{(LIG/ $z$ $y$)} occurs in the program for $x$ and
 \.{(LIG/ $z$ $x$)} occurs in the program for $y$.

More complicated loops are also possible. For example, suppose the ligature
programs for $x$ and $y$ are
$$\vcenter{\halign{#\hfil\cr
\.{(LABEL $x$)(/LIG/ $z$ $w$)(/LIG/> $w$ $y$)} \dots,\cr
\.{(LABEL $y$)(LIG $w$ $x$)} \dots;\cr}}$$
then the adjacent characters $xz$ change to $xwz$, $xywz$, $xxz$, $xxwz$,
\dots, ad infinitum.

@ To detect such loops, \.{VFtoVP} attempts to evaluate the function
$f(x,y)$ for all character pairs $x$ and~$y$, where $f$ is defined as
follows: If the current character is $x$ and the next character is
$y$, we say the ``cursor'' is between $x$ and $y$; when the cursor
first moves past $y$, the character immediately to its left is
$f(x,y)$. This function is defined if and only if no infinite loop is
generated when the cursor is between $x$ and~$y$.

The function $f(x,y)$ can be defined recursively. It turns out that all pairs
$(x,y)$ belong to one of five classes. The simplest class has $f(x,y)=y$; this
happens if there's no ligature between $x$ and $y$, or in the cases
\.{LIG/>} and \.{/LIG/>>}. Another simple class arises when there's a
\.{LIG} or \.{/LIG>} between $x$ and~$y$, generating the character~$z$;
then $f(x,y)=z$. Otherwise we always have $f(x,y)$ equal to
either $f(x,z)$ or $f(z,y)$ or $f(f(x,z),y)$, where $z$ is the inserted
ligature character.

The first two of these classes can be merged; we can also consider
$(x,y)$ to belong to the simple class when $f(x,y)$ has been evaluated.
For technical reasons we allow $x$ to be 256 (for the boundary character
at the left) or 257 (in cases when an error has been detected).

For each pair $(x,y)$ having a ligature program step, we store
$(x,y)$ in a hash table from which the values $z$ and $class$ can be read.

@d simple=0 {$f(x,y)=z$}
@d left_z=1 {$f(x,y)=f(z,y)$}
@d right_z=2 {$f(x,y)=f(x,z)$}
@d both_z=3 {$f(x,y)=f(f(x,z),y)$}
@d pending=4 {$f(x,y)$ is being evaluated}

@<Glob...@>=
@!hash:array[0..hash_size] of 0..66048; {$256x+y+1$ for $x\le257$ and $y\le255$}
@!class:array[0..hash_size] of simple..pending;
@!lig_z:array[0..hash_size] of 0..257;
@!hash_ptr:0..hash_size; {the number of nonzero entries in |hash|}
@!hash_list:array[0..hash_size] of 0..hash_size; {list of those nonzero entries}
@!h,@!hh:0..hash_size; {indices into the hash table}
@!x_lig_cycle,@!y_lig_cycle:0..256; {problematic ligature pair}

@ @<Check for ligature cycles@>=
hash_ptr:=0; y_lig_cycle:=256;
for hh:=0 to hash_size do hash[hh]:=0; {clear the hash table}
for c:=bc to ec do if tag(c)=lig_tag then
  begin i:=remainder(c);
  if tfm[lig_step(i)]>stop_flag then
    i:=256*tfm[lig_step(i)+2]+tfm[lig_step(i)+3];
  @<Enter data for character $c$ starting at location |i| in the hash table@>;
  end;
if bchar_label<nl then
  begin c:=256; i:=bchar_label;
  @<Enter data for character $c$ starting at location |i| in the hash table@>;
  end;
if hash_ptr=hash_size then
  begin print_ln('Sorry, I haven''t room for so many ligature/kern pairs!');
@.Sorry, I haven't room...@>
  goto final_end;
  end;
for hh:=1 to hash_ptr do
  begin r:=hash_list[hh];
  if class[r]>simple then {make sure $f$ is defined}
     r:=f(r,(hash[r]-1)div 256,(hash[r]-1)mod 256);
  end;
if y_lig_cycle<256 then
  begin  print('Infinite ligature loop starting with ');
@.Infinite ligature loop...@>
  if x_lig_cycle=256 then print('boundary')@+else print_octal(x_lig_cycle);
  print(' and '); print_octal(y_lig_cycle); print_ln('!');
  out('(INFINITE LIGATURE LOOP MUST BE BROKEN!)'); goto final_end;
  end

@ @<Enter data for character $c$...@>=
repeat hash_input; k:=tfm[lig_step(i)];
if k>=stop_flag then i:=nl
else i:=i+1+k;
until i>=nl

@ We use an ``ordered hash table'' with linear probing, because such a table
is efficient when the lookup of a random key tends to be unsuccessful.

@p procedure hash_input; {enter data for character |c| and command |i|}
label exit;
var @!cc:simple..both_z; {class of data being entered}
@!zz:0..255; {function value or ligature character being entered}
@!y:0..255; {the character after the cursor}
@!key:integer; {value to be stored in |hash|}
@!t:integer; {temporary register for swapping}
begin if hash_ptr=hash_size then return;
@<Compute the command parameters |y|, |cc|, and |zz|@>;
key:=256*c+y+1; h:=(1009*key) mod hash_size;
while hash[h]>0 do
  begin if hash[h]<=key then
    begin if hash[h]=key then return; {unused ligature command}
    t:=hash[h]; hash[h]:=key; key:=t; {do ordered-hash-table insertion}
    t:=class[h]; class[h]:=cc; cc:=t; {namely, do a swap}
    t:=lig_z[h]; lig_z[h]:=zz; zz:=t;
    end;
  if h>0 then decr(h)@+else h:=hash_size;
  end;
hash[h]:=key; class[h]:=cc; lig_z[h]:=zz;
incr(hash_ptr); hash_list[hash_ptr]:=h;
exit:end;

@ We must store kern commands as well as ligature commands, because the former
might make the latter inapplicable.

@<Compute the command param...@>=
k:=lig_step(i); y:=tfm[k+1]; t:=tfm[k+2]; cc:=simple; zz:=tfm[k+3];
if t>=kern_flag then zz:=y
else begin case t of
  0,6:do_nothing; {\.{LIG},\.{/LIG>}}
  5,11:zz:=y; {\.{LIG/>}, \.{/LIG/>>}}
  1,7:cc:=left_z; {\.{LIG/}, \.{/LIG/>}}
  2:cc:=right_z; {\.{/LIG}}
  3:cc:=both_z; {\.{/LIG/}}
  end; {there are no other cases}
  end

@ Evaluation of $f(x,y)$ is handled by two mutually recursive procedures.
Kind of a neat algorithm, generalizing a depth-first search.

@p function f(@!h,@!x,@!y:index):index; forward;@t\2@>
  {compute $f$ for arguments known to be in |hash[h]|}
function eval(@!x,@!y:index):index; {compute $f(x,y)$ with hashtable lookup}
var @!key:integer; {value sought in hash table}
begin key:=256*x+y+1; h:=(1009*key) mod hash_size;
while hash[h]>key do
  if h>0 then decr(h)@+else h:=hash_size;
if hash[h]<key then eval:=y {not in ordered hash table}
else eval:=f(h,x,y);
end;

@ Pascal's beastly convention for |forward| declarations prevents us from
saying |function f(h,x,y:index):index| here.

@p function f;
begin case class[h] of
simple: do_nothing;
left_z: begin class[h]:=pending; lig_z[h]:=eval(lig_z[h],y); class[h]:=simple;
  end;
right_z: begin class[h]:=pending; lig_z[h]:=eval(x,lig_z[h]); class[h]:=simple;
  end;
both_z: begin class[h]:=pending; lig_z[h]:=eval(eval(x,lig_z[h]),y);
  class[h]:=simple;
  end;
pending: begin x_lig_cycle:=x; y_lig_cycle:=y; lig_z[h]:=257; class[h]:=simple;
  end; {the value 257 will break all cycles, since it's not in |hash|}
end; {there are no other cases}
f:=lig_z[h];
end;

@* Outputting the VF info.
The routines we've used for output from the |tfm| array have counterparts
for output from |vf|. One difference is that the string outputs from |vf|
need to be checked for balanced parentheses. The |string_balance| routine
tests the string of length~|l| that starts at location~|k|.

@p function string_balance(@!k,@!l:integer):boolean;
label not_found,exit;
var @!j,@!bal:integer;
begin if l>0 then if vf[k]=" " then goto not_found;
  {a leading blank is considered unbalanced}
bal:=0;
for j:=k to k+l-1 do
  begin if (vf[j]<" ")or(vf[j]>=127) then goto not_found;
  if vf[j]="(" then incr(bal)
  else if vf[j]=")" then
    if bal=0 then goto not_found else decr(bal);
  end;
if bal>0 then goto not_found;
string_balance:=true; return;
not_found:string_balance:=false;
exit:end;

@ @d bad_vf(#)==begin perfect:=false; if chars_on_line>0 then print_ln(' ');
  chars_on_line:=0; print_ln('Bad VF file: ',#);
  end
@.Bad VF file@>

@<Do the virtual font title@>=
if string_balance(0,font_start[0]) then
  begin left; out('VTITLE ');
  for k:=0 to font_start[0]-1 do out(xchr[vf[k]]);
  right;
  end
else bad_vf('Title is not a balanced ASCII string')
@.Title is not balanced@>

@ We can re-use some code by moving |fix_word| data to |tfm|, using the
fact that the design size has already been output.

@p procedure out_as_fix(@!x:integer);
var @!k:1..3;
begin if abs(x)>=@'100000000 then
  begin bad_vf('Oversize dimension has been reset to zero.');
@.Oversize dimension...@>
  x:=0;
  end;
if x>=0 then tfm[design_size]:=0
else begin tfm[design_size]:=255; x:=x+@'100000000;
  end;
for k:=3 downto 1 do
  begin tfm[design_size+k]:=x mod 256; x:=x div 256;
  end;
out_fix(design_size);
end;

@ @<Do the local fonts@>=
for f:=0 to font_ptr-1 do
  begin left; out('MAPFONT D ',f:1); out_ln;
  @<Output the font area and name@>;
  for k:=0 to 11 do tfm[k]:=vf[font_start[f]+k];
  if tfm[0]+tfm[1]+tfm[2]+tfm[3]>0 then
    begin left; out('FONTCHECKSUM'); out_octal(0,4); right;
    end;
  left; out('FONTAT'); out_fix(4); right;
  left; out('FONTDSIZE'); out_fix(8); right; right;
  end

@ @<Output the font area and name@>=
a:=vf[font_start[f]+12]; l:=vf[font_start[f]+13];
if a>0 then
  if not string_balance(font_start[f]+14,a) then
    bad_vf('Improper font area will be ignored')
@.Improper font area@>
  else begin left; out('FONTAREA ');
    for k:=font_start[f]+14 to font_start[f]+a+13 do out(xchr[vf[k]]);
    right;
    end;
if (l=0)or not string_balance(font_start[f]+14+a,l) then
  bad_vf('Improper font name will be ignored')
@.Improper font name@>
else begin left; out('FONTNAME ');
  for k:=font_start[f]+14+a to font_start[f]+a+l+13 do out(xchr[vf[k]]);
  right;
  end

@ Now we get to the interesting part of \.{VF} output, where \.{DVI}
commands are translated into symbolic form. The \.{VPL} language is a subset
of \.{DVI}, so we sometimes need to output semantic equivalents of
the commands instead of producing a literal translation. This causes a
small but tolerable loss of efficiency. We need to simulate the stack
used by \.{DVI}-reading software.

@<Glob...@>=
@!top:0..max_stack; {\.{DVI} stack pointer}
@!wstack,@!xstack,@!ystack,@!zstack:array[0..max_stack] of integer;
 {stacked values of \.{DVI} registers |w|, |x|, |y|, |z|}
@!vf_limit:0..vf_size; {the current packet ends here}
@!o:byte; {the current opcode}

@ @<Do the packet for character |c|@>=
if packet_start[c]=vf_size then
  bad_vf('Missing packet for character ',c:1)
@.Missing packet@>
else begin left; out('MAP'); out_ln;
  top:=0; wstack[0]:=0; xstack[0]:=0; ystack[0]:=0; zstack[0]:=0;
  vf_ptr:=packet_start[c]; vf_limit:=packet_end[c]+1; f:=0;
  while vf_ptr<vf_limit do
    begin o:=vf[vf_ptr]; incr(vf_ptr);
    case o of
    @<Cases of \.{DVI} instructions that can appear in character packets@>@;
    improper_DVI_for_VF: bad_vf('Illegal DVI code ',o:1,' will be ignored');
    end; {there are no other cases}
    end;
  if top>0 then
    begin bad_vf('More pushes than pops!');
@.More pushes than pops@>
    repeat out('(POP)'); decr(top);@+until top=0;
    end;
  right;
  end

@ A procedure called |get_bytes| helps fetch the parameters of \.{DVI} commands.

@p function get_bytes(@!k:integer;@!signed:boolean):integer;
var @!a:integer; {accumulator}
begin if vf_ptr+k>vf_limit then
  begin bad_vf('Packet ended prematurely'); k:=vf_limit-vf_ptr;
  end;
a:=vf[vf_ptr];
if (k=4) or signed then
  if a>=128 then a:=a-256;
incr(vf_ptr);
while k>1 do
  begin a:=a*256+vf[vf_ptr]; incr(vf_ptr); decr(k);
  end;
get_bytes:=a;
end;

@ Let's look at the simplest cases first, in order to get some experience.

@d four_cases(#)==#,#+1,#+2,#+3
@d eight_cases(#)==four_cases(#),four_cases(#+4)
@d sixteen_cases(#)==eight_cases(#),eight_cases(#+8)
@d thirty_two_cases(#)==sixteen_cases(#),sixteen_cases(#+16)
@d sixty_four_cases(#)==thirty_two_cases(#),thirty_two_cases(#+32)

@<Cases...@>=
nop:do_nothing;
push:begin if top=max_stack then
    begin print_ln('Stack overflow!'); goto final_end;
@.Stack overflow@>
    end;
  incr(top); wstack[top]:=wstack[top-1]; xstack[top]:=xstack[top-1];
  ystack[top]:=ystack[top-1]; zstack[top]:=zstack[top-1]; out('(PUSH)');
  out_ln;
  end;                            
pop:if top=0 then bad_vf('More pops than pushes!')
@.More pops than pushes@>
  else begin decr(top); out('(POP)'); out_ln;
    end;
set_rule,put_rule:begin if o=put_rule then out('(PUSH)');
  left; out('SETRULE'); out_as_fix(get_bytes(4,true));
  out_as_fix(get_bytes(4,true));
  if o=put_rule then out(')(POP');
  right;
  end;

@ Horizontal and vertical motions become \.{RIGHT} and \.{DOWN} in \.{VPL}
lingo.

@<Cases...@>=
four_cases(right1):begin out('(MOVERIGHT');
  out_as_fix(get_bytes(o-right1+1,true));
  out(')'); out_ln;@+end;
w0,four_cases(w1):begin if o<>w0 then wstack[top]:=get_bytes(o-w1+1,true);
  out('(MOVERIGHT'); out_as_fix(wstack[top]); out(')'); out_ln;@+end;
x0,four_cases(x1):begin if o<>x0 then xstack[top]:=get_bytes(o-x1+1,true);
  out('(MOVERIGHT'); out_as_fix(xstack[top]); out(')'); out_ln;@+end;
four_cases(down1):begin out('(MOVEDOWN'); out_as_fix(get_bytes(o-down1+1,true));
  out(')'); out_ln;@+end;
y0,four_cases(y1):begin if o<>y0 then ystack[top]:=get_bytes(o-y1+1,true);
  out('(MOVEDOWN'); out_as_fix(ystack[top]); out(')'); out_ln;@+end;
z0,four_cases(z1):begin if o<>z0 then zstack[top]:=get_bytes(o-z1+1,true);
  out('(MOVEDOWN'); out_as_fix(zstack[top]); out(')'); out_ln;@+end;

@ Variable |f| always refers to the current font. If |f=font_ptr|, it's
a font that hasn't been defined (so its characters will be ignored).

@<Cases...@>=
sixty_four_cases(fnt_num_0),four_cases(fnt1):begin f:=0;
  if o>=fnt1 then font_number[font_ptr]:=get_bytes(o-fnt1+1,false)
  else font_number[font_ptr]:=o-fnt_num_0;
  while font_number[f]<>font_number[font_ptr] do incr(f);
  if f=font_ptr then bad_vf('Undeclared font selected')
@.Undeclared font selected@>
  else begin out('(SELECTFONT D ',f:1,')'); out_ln;
    end;
  end;

@ Before we typeset a character we make sure that it exists.

@<Cases...@>=
sixty_four_cases(set_char_0),sixty_four_cases(set_char_0+64),
 four_cases(set1),four_cases(put1):begin if o>=set1 then
    if o>=put1 then k:=get_bytes(o-put1+1,false)
    else k:=get_bytes(o-set1+1,false)
  else k:=o;
  c:=k;
  if (k<0)or(k>255) then
    bad_vf('Character ',k:1,' is out of range and will be ignored')
  else if f=font_ptr then
    bad_vf('Character ',c:1,' in undeclared font will be ignored')
@.Character...will be ignored@>
  else begin vf[font_start[f+1]-1]:=c; {store |c| in the ``hole'' we left}
    k:=font_chars[f];@+while vf[k]<>c do incr(k);
    if k=font_start[f+1]-1 then
      bad_vf('Character ',c:1,' in font ',f:1,' will be ignored')
    else begin if o>=put1 then out('(PUSH)');
      left; out('SETCHAR'); out_char(c);
      if o>=put1 then out(')(POP');
      right;
      end;
    end;
  end;

@ The ``special'' commands are the only ones remaining to be dealt with.
We use a hexadecimal
output in the general case, if a simple string would be inadequate.

@d out_hex(#)==begin a:=#;
    if a<10 then out(a:1)
    else out(xchr[a-10+"A"]);
    end

@<Cases...@>=
four_cases(xxx1):begin k:=get_bytes(o-xxx1+1,false);
  if k<0 then bad_vf('String of negative length!')
  else begin left;
    if k+vf_ptr>vf_limit then
      begin bad_vf('Special command truncated to packet length');
      k:=vf_limit-vf_ptr;
      end;
    if (k>64)or not string_balance(vf_ptr,k) then
      begin out('SPECIALHEX ');
      while k>0 do
        begin if k mod 32=0 then out_ln
        else if k mod 4=0 then out(' ');
        out_hex(vf[vf_ptr] div 16); out_hex(vf[vf_ptr] mod 16);
        incr(vf_ptr); decr(k);
        end;
      end
    else begin out('SPECIAL ');
      while k>0 do
        begin out(xchr[vf[vf_ptr]]); incr(vf_ptr); decr(k);
        end;
      end;
    right;
    end;
  end;

@* The main program.
The routines sketched out so far need to be packaged into separate procedures,
on some systems, since some \PASCAL\ compilers place a strict limit on the
size of a routine. The packaging is done here in an attempt to avoid some
system-dependent changes.

First come the |vf_input| and |organize| procedures, which read the input data
and get ready for subsequent events. If something goes wrong, the routines
return |false|.

@p function vf_input:boolean;
label final_end, exit;
var vf_ptr:0..vf_size; {an index into |vf|}
@!k:integer; {all-purpose index}
@!c:integer; {character code}
begin @<Read the whole \.{VF} file@>;
vf_input:=true; return;
final_end: vf_input:=false;
exit: end;
@#
function organize:boolean;
label final_end, exit;
var tfm_ptr:index; {an index into |tfm|}
begin @<Read the whole \.{TFM} file@>;
@<Set subfile sizes |lh|, |bc|, \dots, |np|@>;
@<Compute the base addresses@>;
organize:=vf_input; return;
final_end: organize:=false;
exit: end;

@ Next we do the simple things.

@p procedure do_simple_things;
var i:0..@'77777; {an index to words of a subfile}
@!f:0..vf_size; {local font number}
@!k:integer; {all-purpose index}
begin @<Do the virtual font title@>;
@<Do the header@>;
@<Do the parameters@>;
@<Do the local fonts@>;
@<Check the |fix_word| entries@>;
end;

@ And then there's a routine for individual characters.

@p function do_map(@!c:byte):boolean;
label final_end,exit;
var @!k:integer;
@!f:0..vf_size; {current font number}
begin @<Do the packet for character |c|@>;
do_map:=true; return;
final_end: do_map:=false;
exit:end;
@#
function do_characters:boolean;
label final_end, exit;
var @!c:byte; {character being done}
@!k:index; {a random index}
@!ai:0..lig_size; {index into |activity|}
begin @<Do the characters@>;@/
do_characters:=true; return;
final_end: do_characters:=false;
exit:end;

@ Here is where \.{VFtoVP} begins and ends.
@p begin initialize;@/
if not organize then goto final_end;
do_simple_things;@/
@<Do the ligatures and kerns@>;
@<Check the extensible recipes@>;
if not do_characters then goto final_end;
print_ln('.');@/
if level<>0 then print_ln('This program isn''t working!');
@.This program isn't working@>
if not perfect then
  begin out('(COMMENT THE TFM AND/OR VF FILE WAS BAD, ');
  out('SO THE DATA HAS BEEN CHANGED!)');
  write_ln(vpl_file);
  end;
@.THE TFM AND/OR VF FILE WAS BAD...@>
final_end:end.

@* System-dependent changes.
This section should be replaced, if necessary, by changes to the program
that are necessary to make \.{VFtoVP} 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 printed 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@>

@* Index.
Pointers to error messages appear here together with the section numbers
where each ident\-i\-fier is used.