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+% This program is not copyrighted and can be used freely.
+% PKtype.web
+%
+% PKtype verifies the correctness of a PK file.
+%
+% Preliminary 0.0 version: May, 1985
+% First release, 0.9 version: 8 May 1985
+% Updated to reflect new pk format, 2.0 version: 25 July 1985
+% Updated again for new pk format, 2.1 version: 15 August 1985
+% Docmentation updated, 2.2 version: 17 November 1987
+%
+% slight editing to correspond with MFware report -- don, 21 October 89
+% additional editing suggested by P Breitenlohner -- don, 18 November 89
+% Corrected two typos -- 21 December 96 (don)
+% More typos -- 23 April 20 (tgr/karl)
+
+\def\versiondate{23 April 2020}
+%
+\def\hang{\hangindent 3em\noindent\ignorespaces}
+\font\ninerm=cmr9
+\font\logo=logo10 % font used for the METAFONT logo
+\def\MF{{\logo META}\-{\logo FONT}}
+\def\PASCAL{Pascal}
+\def\tamu{Texas A\char38 M}
+\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{PKtype}
+\def\contentspagenumber{0}
+\def\topofcontents{\null
+ \def\titlepage{F} % include headline on the contents page
+ \def\rheader{\mainfont\hfil \contentspagenumber}
+ \vfill
+ \centerline{\titlefont The {\ttitlefont PKtype} processor}
+ \vskip 15pt
+ \centerline{(Version 2.3, \versiondate)}
+ \vfill}
+\def\botofcontents{\vfill
+ \centerline{\hsize 5in\baselineskip9pt
+ \vbox{\ninerm\noindent
+ The preparation of this report
+ was supported in part by the National Science
+ Foundation under grants IST-8201926 and MCS-8300984,
+ and by the System Development Foundation. `\TeX' is a
+ trademark of the American Mathematical Society.}}}
+\pageno=\contentspagenumber \advance\pageno by 1
+
+@* Introduction.
+This program reads a \.{PK} file, verifies that it is in the correct
+format, and writes it in textual format.
+
+@ The |banner| string defined here should be changed whenever \.{PKtype}
+gets modified.
+
+@d banner=='This is PKtype, Version 2.3' {printed when the program starts}
+
+@ This program is written in standard \PASCAL, except where it is necessary
+to use extensions; for example, \.{PKtype} must read files whose names
+are dynamically specified, and that would be impossible in pure \PASCAL.
+
+@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
+
+@ Both the input and output come from binary files. On line interaction
+is handled through \PASCAL's standard |input| and |output| files. Two macros
+are used to write to the type file, so this output can easily be redirected.
+
+@d print_ln(#)==write_ln(output,#)
+@d print(#)==write(output,#)
+@d t_print_ln(#)==write_ln(typ_file,#)
+@d t_print(#)==write(typ_file,#)
+
+@p program PKtype(@!input,@!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 i:integer; {loop index for initializations}
+ 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;
+
+@ These constants determine the maximum length of a file name and the length
+of the terminal line, as well as the widest character that can be translated.
+@^system dependencies@>
+
+@<Constants...@>=
+@!name_length=80; {maximum length of a file name}
+@!terminal_line_length=132; {maximum length of an input line}
+
+@ 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}
+
+@ It is possible that a malformed packed file (heaven forbid!) or some other
+error might be detected by this program. Such errors might occur in a deeply
+nested procedure, so the procedure called |jump_out| has been added to transfer
+to the very end of the program with an error message.
+
+@d abort(#)==begin print_ln(' ',#); t_print_ln(' ',#); jump_out; end
+
+@p procedure jump_out;
+begin goto final_end;
+end;
+
+@* The character set.
+Like all programs written with the \.{WEB} system, \.{PKtype} can be
+used with any character set. But it uses ASCII code internally, because
+the programming for portable input-output is easier when a fixed internal
+code is used.
+
+The next few sections of \.{PKtype} have therefore been copied from the
+analogous ones in the \.{WEB} system routines. They have been considerably
+simplified, since \.{PKtype} need not deal with the controversial
+ASCII codes less than @'40 or greater than @'176.
+
+@<Types...@>=
+@!ASCII_code=" ".."~"; {a subrange of the integers}
+
+@ The original \PASCAL\ compiler was designed in the late 60s, when six-bit
+character sets were common, so it did not make provision for lower case
+letters. Nowadays, of course, we need to deal with both upper and lower case
+alphabets in a convenient way, especially in a program like \.{PKtype}.
+So we shall assume that the \PASCAL\ system being used for \.{PKtype}
+has a character set containing at least the standard visible characters
+of ASCII code (|"!"| through |"~"|).
+
+Some \PASCAL\ compilers use the original name |char| for the data type
+associated with the characters in text files, 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 in the
+output file. 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=127 {ordinal number of the largest element of |text_char|}
+
+@<Types...@>=
+@!text_file=packed file of text_char;
+
+@ The \.{PKtype} 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.
+
+@<Globals...@>=
+@!xord: array [text_char] of ASCII_code;
+ {specifies conversion of input characters}
+@!xchr: array [0..255] of text_char;
+ {specifies conversion of output characters}
+
+@ Under our assumption that the visible characters of standard ASCII are
+all present, the following assignment statements initialize the
+|xchr| array properly, without needing any system-dependent changes.
+
+@<Set init...@>=
+for i:=0 to @'37 do xchr[i]:='?';
+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]:='~';
+for i:=@'177 to 255 do xchr[i]:='?';
+
+@ The following system-independent code makes the |xord| array contain a
+suitable inverse to the information in |xchr|.
+
+@<Set init...@>=
+for i:=first_text_char to last_text_char do xord[chr(i)]:=@'40;
+for i:=" " to "~" do xord[xchr[i]]:=i;
+
+@* Packed file format.
+The packed file format is a compact representation of the data contained in a
+\.{GF} file. The information content is the same, but packed (\.{PK}) files
+are almost always less than half the size of their \.{GF} counterparts. They
+are also easier to convert into a raster representation because they do not
+have a profusion of \\{paint}, \\{skip}, and \\{new\_row} commands to be
+separately interpreted. In addition, the \.{PK} format expressly forbids
+\&{special} commands within a character. The minimum bounding box for each
+character is explicit in the format, and does not need to be scanned for as in
+the \.{GF} format. Finally, the width and escapement values are combined with
+the raster information into character ``packets'', making it simpler in many
+cases to process a character.
+
+A \.{PK} file is organized as a stream of 8-bit bytes. At times, these bytes
+might be split into 4-bit nybbles or single bits, or combined into multiple
+byte parameters. When bytes are split into smaller pieces, the `first' piece
+is always the most significant of the byte. For instance, the first bit of
+a byte is the bit with value 128; the first nybble can be found by dividing
+a byte by 16. Similarly, when bytes are combined into multiple byte
+parameters, the first byte is the most significant of the parameter. If the
+parameter is signed, it is represented by two's-complement notation.
+
+The set of possible eight-bit values is separated into two sets, those that
+introduce a character definition, and those that do not. The values that
+introduce a character definition range from 0 to 239; byte values
+above 239 are interpreted as commands. Bytes that introduce character
+definitions are called flag bytes, and various fields within the byte indicate
+various things about how the character definition is encoded. Command bytes
+have zero or more parameters, and can never appear within a character
+definition or between parameters of another command, where they would be
+interpreted as data.
+
+A \.{PK} file consists of a preamble, followed by a sequence of one or more
+character definitions, followed by a postamble. The preamble command must
+be the first byte in the file, followed immediately by its parameters.
+Any number of character definitions may follow, and any command but the
+preamble command and the postamble command may occur between character
+definitions. The very last command in the file must be the postamble.
+
+@ The packed file format is intended to be easy to read and interpret by
+device drivers. The small size of the file reduces the input/output overhead
+each time a font is loaded. For those drivers that load and save each font
+file into memory, the small size also helps reduce the memory requirements.
+The length of each character packet is specified, allowing the character raster
+data to be loaded into memory by simply counting bytes, rather than
+interpreting each command; then, each character can be interpreted on a demand
+basis. This also makes it possible for a driver to skip a particular
+character quickly if it knows that the character is unused.
+
+@ First, the command bytes will be presented; then the format of the
+character definitions will be defined. Eight of the possible sixteen
+commands (values 240 through 255) are currently defined; the others are
+reserved for future extensions. The commands are listed below. Each command
+is specified by its symbolic name (e.g., \\{pk\_no\_op}), its opcode byte,
+and any parameters. The parameters are followed by a bracketed number
+telling how many bytes they occupy, with the number preceded by a plus sign if
+it is a signed quantity. (Four byte quantities are always signed, however.)
+
+\yskip\hang|pk_xxx1| 240 |k[1]| |x[k]|. This command is undefined in general;
+it functions as a $(k+2)$-byte \\{no\_op} unless special \.{PK}-reading
+programs are being used. \MF\ generates \\{xxx} commands when encountering
+a \&{special} string. It is recommended that |x| be a string having the form
+of a keyword followed by possible parameters relevant to that keyword.
+
+\yskip\hang\\{pk\_xxx2} 241 |k[2]| |x[k]|. Like |pk_xxx1|, but |0<=k<65536|.
+
+\yskip\hang\\{pk\_xxx3} 242 |k[3]| |x[k]|. Like |pk_xxx1|, but
+|0<=k<@t$2^{24}$@>|. \MF\ uses this when sending a \&{special} string whose
+length exceeds~255.
+
+\yskip\hang\\{pk\_xxx4} 243 |k[4]| |x[k]|. Like |pk_xxx1|, but |k| can be
+ridiculously large; |k| mustn't be negative.
+
+\yskip\hang|pk_yyy| 244 |y[4]|. This command is undefined in general; it
+functions as a five-byte \\{no\_op} unless special \.{PK} reading programs
+are being used. \MF\ puts |scaled| numbers into |yyy|'s, as a result of
+\&{numspecial} commands; the intent is to provide numeric parameters to
+\\{xxx} commands that immediately precede.
+
+\yskip\hang|pk_post| 245. Beginning of the postamble. This command is
+followed by enough |pk_no_op| commands to make the file a multiple
+of four bytes long. Zero through three bytes are usual, but any number
+is allowed.
+This should make the file easy to read on machines that pack four bytes to
+a word.
+
+\yskip\hang|pk_no_op| 246. No operation, do nothing. Any number of
+|pk_no_op|'s may appear between \.{PK} commands, but a |pk_no_op| cannot be
+inserted between a command and its parameters, between two parameters, or
+inside a character definition.
+
+\yskip\hang|pk_pre| 247 |i[1]| |k[1]| |x[k]| |ds[4]| |cs[4]| |hppp[4]|
+|vppp[4]|. Preamble command. Here, |i| is the identification byte of the
+file, currently equal to 89. The string |x| is merely a comment, usually
+indicating the source of the \.{PK} file. The parameters |ds| and |cs| are
+the design size of the file in $1/2^{20}$ points, and the checksum of the
+file, respectively. The checksum should match the \.{TFM} file and the
+\.{GF} files for this font. Parameters |hppp| and |vppp| are the ratios
+of pixels per point, horizontally and vertically, multiplied by $2^{16}$; they
+can be used to correlate the font with specific device resolutions,
+magnifications, and ``at sizes''. Usually, the name of the \.{PK} file is
+formed by concatenating the font name (e.g., cmr10) with the resolution at
+which the font is prepared in pixels per inch multiplied by the magnification
+factor, and the letters \.{pk}. For instance, cmr10 at 300 dots per inch
+should be named \.{cmr10.300pk}; at one thousand dots per inch and magstephalf,
+it should be named \.{cmr10.1095pk}.
+
+@ We put a few of the above opcodes into definitions for symbolic use by
+this program.
+
+@d pk_id = 89 {the version of \.{PK} file described}
+@d pk_xxx1 = 240 {\&{special} commands}
+@d pk_yyy = 244 {\&{numspecial} commands}
+@d pk_post = 245 {postamble}
+@d pk_no_op = 246 {no operation}
+@d pk_pre = 247 {preamble}
+@d pk_undefined == 248, 249, 250, 251, 252, 253, 254, 255
+
+@ The \.{PK} format has two conflicting goals: to pack character raster and
+size information as compactly as possible, while retaining ease of translation
+into raster and other forms. A suitable compromise was found in the use of
+run-encoding of the raster information. Instead of packing the individual
+bits of the character, we instead count the number of consecutive `black' or
+`white' pixels in a horizontal raster row, and then encode this number. Run
+counts are found for each row from left to right, traversing rows from the
+top to bottom. This is essentially the way the \.{GF} format works.
+Instead of presenting each row individually, however, we concatenate all
+of the horizontal raster rows into one long string of pixels, and encode this
+row. With knowledge of the width of the bit-map, the original character glyph
+can easily be reconstructed. In addition, we do not need special commands to
+mark the end of one row and the beginning of the next.
+
+Next, we place the burden of finding the minimum bounding box on the part
+of the font generator, since the characters will usually be used much more
+often than they are generated. The minimum bounding box is the smallest
+rectangle that encloses all `black' pixels of a character. We also
+eliminate the need for a special end of character marker, by supplying
+exactly as many bits as are required to fill the minimum bounding box, from
+which the end of the character is implicit.
+
+Let us next consider the distribution of the run counts. Analysis of several
+dozen pixel files at 300 dots per inch yields a distribution peaking at four,
+falling off slowly until ten, then a bit more steeply until twenty, and then
+asymptotically approaching the horizontal. Thus, the great majority of our
+run counts will fit in a four-bit nybble. The eight-bit byte is attractive for
+our run-counts, as it is the standard on many systems; however, the wasted four
+bits in the majority of cases seem a high price to pay. Another possibility
+is to use a Huffman-type encoding scheme with a variable number of bits for
+each run-count; this was rejected because of the overhead in fetching and
+examining individual bits in the file. Thus, the character raster definitions
+in the \.{PK} file format are based on the four-bit nybble.
+
+@ An analysis of typical pixel files yielded another interesting statistic:
+Fully 37\char`\%\
+of the raster rows were duplicates of the previous row. Thus, the \.{PK}
+format allows the specification of repeat counts, which indicate how many times
+a horizontal raster row is to be repeated. These repeated rows are taken out
+of the character glyph before individual rows are concatenated into the long
+string of pixels.
+
+For elegance, we disallow a run count of zero. The case of a null raster
+description should be gleaned from the character width and height being equal
+to zero, and no raster data should be read. No other zero counts are ever
+necessary. Also, in the absence of repeat counts, the repeat value is set to
+be zero (only the original row is sent.) If a repeat count is seen, it takes
+effect on the current row. The current row is defined as the row on which the
+first pixel of the next run count will lie. The repeat count is set back to
+zero when the last pixel in the current row is seen, and the row is sent out.
+
+This poses a problem for entirely black and entirely white rows, however. Let
+us say that the current row ends with four white pixels, and then we have five
+entirely empty rows, followed by a black pixel at the beginning of the next
+row, and the character width is ten pixels. We would like to use a repeat
+count, but there is no legal place to put it. If we put it before the white
+run count, it will apply to the current row. If we put it after, it applies
+to the row with the black pixel at the beginning. Thus, entirely white or
+entirely black repeated rows are always packed as large run counts (in this
+case, a white run count of 54) rather than repeat counts.
+
+@ Now we turn our attention to the actual packing of the run counts and
+repeat counts into nybbles. There are only sixteen possible nybble values.
+We need to indicate run counts and repeat counts. Since the run counts are
+much more common, we will devote the majority of the nybble values to them.
+We therefore indicate a repeat count by a nybble of 14 followed by a packed
+number, where a packed number will be explained later. Since the repeat
+count value of one is so common, we indicate a repeat one command by a single
+nybble of 15. A 14 followed by the packed number 1 is still legal for a
+repeat one count. The run counts are coded directly as packed
+numbers.
+
+For packed numbers, therefore, we have the nybble values 0 through 13. We
+need to represent the positive integers up to, say, $2^{31}-1$. We would
+like the more common smaller numbers to take only one or two nybbles, and
+the infrequent large numbers to take three or more. We could therefore
+allocate one nybble value to indicate a large run count taking three or more
+nybbles. We do this with the value 0.
+
+@ We are left with the values 1 through 13. We can allocate some of these, say
+|dyn_f|, to be one-nybble run counts.
+These will work for the run counts |1..dyn_f|. For subsequent run
+counts, we will use a nybble greater than |dyn_f|, followed by a second nybble,
+whose value can run from 0 through 15. Thus, the two-nybble values will
+run from |dyn_f+1..(13-dyn_f)*16+dyn_f|. We have our definition of large run
+count values now, being all counts greater than |(13-dyn_f)*16+dyn_f|.
+
+We can analyze our several dozen pixel files and determine an optimal value of
+|dyn_f|, and use this value for all of the characters. Unfortunately, values
+of |dyn_f| that pack small characters well tend to pack the large characters
+poorly, and values that pack large characters well are not efficient for the
+smaller characters. Thus, we choose the optimal |dyn_f| on a character basis,
+picking the value that will pack each individual character in the smallest
+number of nybbles. Legal values of |dyn_f| run from 0 (with no one-nybble run
+counts) to 13 (with no two-nybble run counts).
+
+@ Our only remaining task in the coding of packed numbers is the large run
+counts. We use a scheme suggested by D.~E.~Knuth
+@^Knuth, Donald Ervin@>
+that simply and elegantly represents arbitrarily large values. The
+general scheme to represent an integer |i| is to write its hexadecimal
+representation, with leading zeros removed. Then we count the number of
+digits, and prepend one less than that many zeros before the hexadecimal
+representation. Thus, the values from one to fifteen occupy one nybble;
+the values sixteen through 255 occupy three, the values 256 through 4095
+require five, etc.
+
+For our purposes, however, we have already represented the numbers one
+through |(13-dyn_f)*16+dyn_f|. In addition, the one-nybble values have
+already been taken by our other commands, which means that only the values
+from sixteen up are available to us for long run counts. Thus, we simply
+normalize our long run counts, by subtracting |(13-dyn_f)*16+dyn_f+1| and
+adding 16, and then we represent the result according to the scheme above.
+
+@ The final algorithm for decoding the run counts based on the above scheme
+looks like this, assuming that a procedure called \\{get\_nyb} is available
+to get the next nybble from the file, and assuming that the global
+|repeat_count| indicates whether a row needs to be repeated. Note that this
+routine is recursive, but since a repeat count can never directly follow
+another repeat count, it can only be recursive to one level.
+
+@<Packed number procedure@>=
+function pk_packed_num : integer ;
+var i, @!j : integer ;
+begin
+ i := get_nyb ;
+ if i = 0 then begin
+ repeat j := get_nyb ; incr(i) ; until j <> 0 ;
+ while i > 0 do begin j := j * 16 + get_nyb ; decr(i) ; end ;
+ pk_packed_num := j - 15 + (13-dyn_f)*16 + dyn_f ;
+ end else if i <= dyn_f then
+ pk_packed_num := i
+ else if i < 14 then
+ pk_packed_num := (i-dyn_f-1)*16+get_nyb+dyn_f+1
+ else begin
+ if repeat_count <> 0 then abort('Second repeat count for this row!') ;
+@.Second repeat count...@>
+ repeat_count := 1; {prevent recursion more than one level}
+ if i = 14 then repeat_count := pk_packed_num;
+ send_out(true, repeat_count) ;
+ pk_packed_num := pk_packed_num ;
+ end ;
+end ;
+
+@ For low resolution fonts, or characters with `gray' areas, run encoding can
+often make the character many times larger. Therefore, for those characters
+that cannot be encoded efficiently with run counts, the \.{PK} format allows
+bit-mapping of the characters. This is indicated by a |dyn_f| value of
+14. The bits are packed tightly, by concatenating all of the horizontal raster
+rows into one long string, and then packing this string eight bits to a byte.
+The number of bytes required can be calculated by |(width*height+7) div 8|.
+This format should only be used when packing the character by run counts takes
+more bytes than this, although, of course, it is legal for any character.
+Any extra bits in the last byte should be set to zero.
+
+@ At this point, we are ready to introduce the format for a character
+descriptor. It consists of three parts: a flag byte, a character preamble,
+and the raster data. The most significant four bits of the flag byte
+yield the |dyn_f| value for that character. (Notice that only values of
+0 through 14 are legal for |dyn_f|, with 14 indicating a bit mapped character;
+thus, the flag bytes do not conflict with the command bytes, whose upper nybble
+is always 15.) The next bit (with weight 8) indicates whether the first run
+count is a black count or a white count, with a one indicating a black count.
+For bit-mapped characters, this bit should be set to a zero. The next bit
+(with weight 4) indicates whether certain later parameters (referred to as size
+parameters) are given in one-byte or two-byte quantities, with a one indicating
+that they are in two-byte quantities. The last two bits are concatenated on to
+the beginning of the packet-length parameter in the character preamble,
+which will be explained below.
+
+However, if the last three bits of the flag byte are all set (normally
+indicating that the size parameters are two-byte values and that a 3 should be
+prepended to the length parameter), then a long format of the character
+preamble should be used instead of one of the short forms.
+
+Therefore, there are three formats for the character preamble; the one that
+is used depends on the least significant three bits of the flag byte. If the
+least significant three bits are in the range zero through three, the short
+format is used. If they are in the range four through six, the extended short
+format is used. Otherwise, if the least significant bits are all set, then
+the long form of the character preamble is used. The preamble formats are
+explained below.
+
+\yskip\hang Short form: |flag[1]| |pl[1]| |cc[1]| |tfm[3]| |dm[1]| |w[1]|
+|h[1]| |hoff[+1]| |voff[+1]|.
+If this format of the character preamble is used, the above
+parameters must all fit in the indicated number of bytes, signed or unsigned
+as indicated. Almost all of the standard \TeX\ font characters fit; the few
+exceptions are fonts such as \.{cminch}.
+
+\yskip\hang Extended short form: |flag[1]| |pl[2]| |cc[1]| |tfm[3]| |dm[2]|
+|w[2]| |h[2]| |hoff[+2]| |voff[+2]|. Larger characters use this extended
+format.
+
+\yskip\hang Long form: |flag[1]| |pl[4]| |cc[4]| |tfm[4]| |dx[4]| |dy[4]|
+|w[4]| |h[4]| |hoff[4]| |voff[4]|. This is the general format that
+allows all of the
+parameters of the \.{GF} file format, including vertical escapement.
+\vskip\baselineskip
+The |flag| parameter is the flag byte. The parameter |pl| (packet length)
+contains the offset
+of the byte following this character descriptor, with respect to the beginning
+of the |tfm| width parameter. This is given so a \.{PK} reading program can,
+once it has read the flag byte, packet length, and character code (|cc|), skip
+over the character by simply reading this many more bytes. For the two short
+forms of the character preamble, the last two bits of the flag byte should be
+considered the two most-significant bits of the packet length. For the short
+format, the true packet length might be calculated as |(flag mod 4)*256+pl|;
+for the short extended format, it might be calculated as
+|(flag mod 4)*65536+pl|.
+
+The |w| parameter is the width and the |h| parameter is the height in pixels
+of the minimum bounding box. The |dx| and |dy| parameters are the horizontal
+and vertical escapements, respectively. In the short formats, |dy| is assumed
+to be zero and |dm| is |dx| but in pixels;
+in the long format, |dx| and |dy| are both
+in pixels multiplied by $2^{16}$. The |hoff| is the horizontal offset from the
+upper left pixel to the reference pixel; the |voff| is the vertical offset.
+They are both given in pixels, with right and down being positive. The
+reference pixel is the pixel that occupies the unit square in \MF; the
+\MF\ reference point is the lower left hand corner of this pixel. (See the
+example below.)
+
+@ \TeX\ requires all characters that have the same character codes
+modulo 256 to have also the same |tfm| widths and escapement values. The \.{PK}
+format does not itself make this a requirement, but in order for the font to
+work correctly with the \TeX\ software, this constraint should be observed.
+(The standard version of \TeX\ cannot output character codes greater
+than 255, but extended versions do exist.)
+
+Following the character preamble is the raster information for the
+character, packed by run counts or by bits, as indicated by the flag byte.
+If the character is packed by run counts and the required number of nybbles
+is odd, then the last byte of the raster description should have a zero
+for its least significant nybble.
+
+@ As an illustration of the \.{PK} format, the character \char4\ from the font
+amr10 at 300 dots per inch will be encoded. This character was chosen
+because it illustrates some
+of the borderline cases. The raster for the character looks like this (the
+row numbers are chosen for convenience, and are not \MF's row numbers.)
+
+\vskip\baselineskip
+{\def\smbox{\vrule height 7pt width 7pt depth 0pt \hskip 3pt}%
+\catcode`\*=\active \let*=\smbox
+\centerline{\vbox{\baselineskip=10pt
+\halign{\hfil#\quad&&\hfil#\hfil\cr
+0& & &*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*\cr
+1& & &*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*\cr
+2& & &*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*\cr
+3& & &*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*\cr
+4& & &*&*& & & & & & & & & & & & & & & & &*&*\cr
+5& & &*&*& & & & & & & & & & & & & & & & &*&*\cr
+6& & &*&*& & & & & & & & & & & & & & & & &*&*\cr
+7\cr
+8\cr
+9& & & & &*&*& & & & & & & & & & & & &*&*& & \cr
+10& & & & &*&*& & & & & & & & & & & & &*&*& & \cr
+11& & & & &*&*& & & & & & & & & & & & &*&*& & \cr
+12& & & & &*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*& & \cr
+13& & & & &*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*& & \cr
+14& & & & &*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*& & \cr
+15& & & & &*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*& & \cr
+16& & & & &*&*& & & & & & & & & & & & &*&*& & \cr
+17& & & & &*&*& & & & & & & & & & & & &*&*& & \cr
+18& & & & &*&*& & & & & & & & & & & & &*&*& & \cr
+19\cr
+20\cr
+21\cr
+22& & &*&*& & & & & & & & & & & & & & & & &*&*\cr
+23& & &*&*& & & & & & & & & & & & & & & & &*&*\cr
+24& & &*&*& & & & & & & & & & & & & & & & &*&*\cr
+25& & &*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*\cr
+26& & &*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*\cr
+27& & &*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*\cr
+28&+& &*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*&*\cr
+&\hphantom{*}&\hphantom{*}\cr
+}}}}
+The width of the minimum bounding box for this character is 20; its height
+is 29. The `+' represents the reference pixel; notice how it lies outside the
+minimum bounding box. The |hoff| value is $-2$, and the |voff| is~28.
+
+The first task is to calculate the run counts and repeat counts. The repeat
+counts are placed at the first transition (black to white or white to black)
+in a row, and are enclosed in brackets. White counts are enclosed in
+parentheses. It is relatively easy to generate the counts list:
+\vskip\baselineskip
+\centerline{82 [2] (16) 2 (42) [2] 2 (12) 2 (4) [3]}
+\centerline{16 (4) [2] 2 (12) 2 (62) [2] 2 (16) 82}
+\vskip\baselineskip
+Note that any duplicated rows that are not all white or all black are removed
+before the run counts are calculated. The rows thus removed are rows 5, 6,
+10, 11, 13, 14, 15, 17, 18, 23, and 24.
+
+@ The next step in the encoding of this character is to calculate the optimal
+value of |dyn_f|. The details of how this calculation is done are not
+important here; suffice it to say that there is a simple algorithm that can
+determine the best value of |dyn_f| in one pass over the count list. For this
+character, the optimal value turns out to be 8 (atypically low). Thus, all
+count values less than or equal to 8 are packed in one nybble; those from
+nine to $(13-8)*16+8$ or 88 are packed in two nybbles. The run encoded values
+now become (in hex, separated according to the above list):
+\vskip\baselineskip
+\centerline{\tt D9 E2 97 2 B1 E2 2 93 2 4 E3}
+\centerline{\tt 97 4 E2 2 93 2 C5 E2 2 97 D9}
+\vskip\baselineskip\noindent
+which comes to 36 nybbles, or 18 bytes. This is shorter than the 73 bytes
+required for the bit map, so we use the run count packing.
+
+@ The short form of the character preamble is used because all of the
+parameters fit in their respective lengths. The packet length is therefore
+18 bytes for the raster, plus
+eight bytes for the character preamble parameters following the character
+code, or 26. The |tfm| width for this character is 640796, or {\tt 9C71C} in
+hexadecimal. The horizontal escapement is 25 pixels. The flag byte is
+88 hex, indicating the short preamble, the black first count, and the
+|dyn_f| value of 8. The final total character packet, in hexadecimal, is:
+\vskip\baselineskip
+$$\vbox{\halign{\hfil #\quad&&{\tt #\ }\cr
+Flag byte&88\cr
+Packet length&1A\cr
+Character code&04\cr
+|tfm| width&09&C7&1C\cr
+Horizontal escapement (pixels)&19\cr
+Width of bit map&14\cr
+Height of bit map&1D\cr
+Horizontal offset (signed)&FE\cr
+Vertical offset&1C\cr
+Raster data&D9&E2&97\cr
+&2B&1E&22\cr
+&93&24&E3\cr
+&97&4E&22\cr
+&93&2C&5E\cr
+&22&97&D9\cr}}$$
+
+@* Input and output.
+There are two types of files that this program must deal with---standard
+text files and files of bytes (packed files.)
+For our purposes, we shall consider an eight-bit byte to consist of the
+values |0..255|. If your system does not pack these values to a byte, it is
+no major difficulty; you must only insure that the input function
+|pk_byte| can read packed bytes.
+
+@<Types...@>=
+@!eight_bits=0..255; {packed file byte}
+@!byte_file=packed file of eight_bits ; {for packed file words}
+@^system dependencies@>
+
+@ @<Glob...@>=
+@!pk_file:byte_file; {where the input comes from}
+@!typ_file:text_file; {where the final output goes}
+@^system dependencies@>
+
+@ To prepare these files for input and output, we |reset| and |rewrite| them.
+An extension of \PASCAL\ is needed, since we want to associate files
+with external names that are specified dynamically (i.e., not
+known at compile time). The following code assumes that `|reset(f,s)|'
+does this, when |f| is a file variable and |s| is a string variable that
+specifies the file name. If |eof(f)| is true immediately after
+|reset(f,s)| has acted, we assume that no file named |s| is accessible.
+@^system dependencies@>
+
+@p procedure open_pk_file; {prepares the input for reading}
+begin reset(pk_file,pk_name);
+pk_loc := 0 ;
+end;
+@#
+procedure open_typ_file; {prepares to write text data to the |typ_file|}
+begin rewrite(typ_file,typ_name);
+end;
+
+@ We need a place to store the names of the input and output file, as well
+as a byte counter for the output file.
+
+@<Glob...@>=
+@!pk_name,@!typ_name:packed array[1..name_length] of char; {name of input
+ and output files}
+@!pk_loc:integer; {how many bytes have we read?}
+
+@ We also need a function that will get a single byte from the \.{pk} file.
+
+@p function pk_byte : eight_bits ;
+var temp : eight_bits ;
+begin
+ temp := pk_file^ ;
+ get(pk_file) ;
+ incr(pk_loc) ;
+ pk_byte := temp ;
+end ;
+
+@ Now we are ready to open the files.
+
+@<Open files@>=
+open_pk_file ;
+open_typ_file ;
+t_print_ln(banner) ;
+t_print('Input file: ') ;
+i := 1 ;
+while pk_name[i] <> ' ' do begin
+ t_print(pk_name[i]) ; incr(i) ;
+end ;
+t_print_ln(' ')
+
+@ As we are reading the packed file, we often need to fetch 16 and 32 bit
+quantities. Here we have two procedures to do this.
+
+@p function get_16 : integer ;
+var a : integer ;
+begin a := pk_byte ; get_16 := a * 256 + pk_byte ; end ;
+@#
+function get_32 : integer ;
+var a : integer ;
+begin a := get_16 ; if a > 32767 then a := a - 65536 ;
+get_32 := a * 65536 + get_16 ; end ;
+
+@ We still need the |term_pos| variable.
+
+@<Glob...@>=
+@!term_pos : integer ; {current terminal position}
+
+@ Now we read and check the preamble of the \.{PK} file. In the preamble, we
+find the |hppp|, |design_size|, |checksum|.
+
+@<Read preamble@>=
+if pk_byte <> pk_pre then abort('Bad PK file: pre command missing!') ;
+@.pre command missing@>
+if pk_byte <> pk_id then abort('Wrong version of PK file!') ;
+@.Wrong version of PK file@>
+j := pk_byte ;
+t_print('''') ;
+for i := 1 to j do t_print(xchr[pk_byte]) ;
+t_print_ln('''') ;
+design_size := get_32 ;
+t_print_ln('Design size = ',design_size:1) ;
+checksum := get_32 ;
+t_print_ln('Checksum = ',checksum:1) ;
+hppp := get_32 ; vppp := get_32 ;
+t_print('Resolution: horizontal = ',hppp:1,' vertical = ',vppp:1) ;
+magnification := round(hppp * 72.27 / 65536) ;
+t_print_ln(' (',magnification:1,' dpi)') ;
+if hppp <> vppp then print_ln('Warning: aspect ratio not 1:1!')
+
+@ Of course, we need to define the above variables.
+
+@<Glob...@>=
+@!magnification : integer ; {resolution at which pixel file is prepared}
+@!design_size : integer ; {design size in FIXes}
+@!checksum : integer ; {checksum of pixel file}
+@!hppp, @!vppp : integer ; {horizontal and vertical points per inch}
+
+@* Character unpacking.
+Here we simply unpack the character, writing the information we glean to the
+|typ_file|.
+
+@<Unpack and write character@>=
+t_print((pk_loc-1):1,': Flag byte = ',flag_byte:1) ;
+dyn_f := flag_byte div 16 ;
+flag_byte := flag_byte mod 16 ;
+turn_on := flag_byte >= 8 ;
+if turn_on then flag_byte := flag_byte - 8 ;
+if flag_byte = 7 then
+ @<Read long character preamble@>
+else if flag_byte > 3 then
+ @<Read extended short character preamble@>
+else
+ @<Read short character preamble@> ;
+t_print_ln(' Character = ',car:1,' Packet length = ',
+ packet_length:1) ;
+t_print_ln(' Dynamic packing variable = ',dyn_f:1) ;
+t_print(' TFM width = ',tfm_width:1,' dx = ',dx:1) ;
+if dy <> 0 then t_print_ln(' dy = ',dy:1) else t_print_ln(' ') ;
+t_print_ln(' Height = ',height:1,' Width = ',width:1,' X-offset = ',
+ x_off:1, ' Y-offset = ',y_off:1) ;
+@<Read and translate raster description@> ;
+if end_of_packet <> pk_loc then abort('Bad PK file: Bad packet length!')
+@.Bad packet length@>
+
+@ We need a whole lot of globals used but not defined up there.
+
+@<Glob...@>=
+@!i, @!j : integer ; {index pointers}
+@!flag_byte : integer ; {the byte that introduces the character definition}
+@!end_of_packet : integer ; {where we expect the end of the packet to be}
+@!width, @!height : integer ; {width and height of character}
+@!x_off, @!y_off : integer ; {x and y offsets of character}
+@!tfm_width : integer ; {character tfm width}
+@!tfms : array [0..255] of integer ; {character tfm widths}
+@!dx, @!dy : integer ; {escapement values}
+@!dxs, @!dys : array [0..255] of integer ; {escapement values}
+@!status : array[0..255] of boolean ; {has the character been seen?}
+@!dyn_f : integer ; {dynamic packing variable}
+@!car : integer ; {the character we are reading}
+@!packet_length : integer ; {the length of the character packet}
+
+@ Now, the preamble reading modules. First, we have the general case: the
+long character preamble format.
+
+@<Read long character preamble@>=
+begin
+ packet_length := get_32 ; car := get_32 ;
+ end_of_packet := packet_length + pk_loc ;
+ packet_length := packet_length + 9 ;
+ tfm_width := get_32 ;
+ dx := get_32 ; dy := get_32 ;
+ width := get_32 ;
+ height := get_32 ;
+ x_off := get_32 ; y_off := get_32 ;
+end
+
+@ This module reads the character preamble with double byte parameters.
+
+@<Read extended short character preamble@>=
+begin
+ packet_length := (flag_byte - 4) * 65536 + get_16 ;
+ car := pk_byte ;
+ end_of_packet := packet_length + pk_loc ;
+ packet_length := packet_length + 4 ;
+ i := pk_byte ;
+ tfm_width := i * 65536 + get_16 ;
+ dx := get_16 * 65536 ;
+ dy := 0 ;
+ width := get_16 ;
+ height := get_16 ;
+ x_off := get_16 ; y_off := get_16 ;
+ if x_off > 32767 then x_off := x_off - 65536 ;
+ if y_off > 32767 then y_off := y_off - 65536 ;
+end
+
+@ Here we read the most common character preamble, that with single byte
+parameters.
+
+@<Read short character preamble@>=
+begin
+ packet_length := flag_byte * 256 + pk_byte ;
+ car := pk_byte ;
+ end_of_packet := packet_length + pk_loc ;
+ packet_length := packet_length + 3 ;
+ i := pk_byte ;
+ tfm_width := i * 65536 + get_16 ;
+ dx := pk_byte * 65536 ;
+ dy := 0 ;
+ width := pk_byte ;
+ height := pk_byte ;
+ x_off := pk_byte ; y_off := pk_byte ;
+ if x_off > 127 then x_off := x_off - 256 ;
+ if y_off > 127 then y_off := y_off - 256 ;
+end
+
+@ Now we have the most important part of the program, where we actually
+interpret the commands in the raster description. First of all, we need
+a procedure to get a single nybble from the file, as well as one to get
+a single bit.
+
+@p function get_nyb : integer ;
+var temp : eight_bits ;
+begin
+ if bit_weight = 0 then begin
+ input_byte := pk_byte ;
+ bit_weight := 16 ;
+ end ;
+ temp := input_byte div bit_weight ;
+ input_byte := input_byte - temp * bit_weight ;
+ bit_weight := bit_weight div 16 ;
+ get_nyb := temp ;
+end ;
+@#
+function get_bit : boolean ;
+var temp : boolean ;
+begin
+ bit_weight := bit_weight div 2 ;
+ if bit_weight = 0 then begin
+ input_byte := pk_byte ;
+ bit_weight := 128 ;
+ end ;
+ temp := input_byte >= bit_weight ;
+ if temp then
+ input_byte := input_byte - bit_weight ;
+ get_bit := temp ;
+end ;
+
+@ We also need a function to write output to the screen. We put as many
+counts on a line as possible, to reduce the volume of output. Each count
+will appear as a number, with white counts enclosed by parentheses and repeat
+counts by brackets.
+
+@p procedure send_out(@!repeat_count: boolean ; @!value : integer ) ;
+var i, len : integer ;
+begin
+ i := 10 ; len := 1 ;
+ while value >= i do begin incr(len) ; i := i * 10 ; end ;
+ if repeat_count or not turn_on then len := len + 2 ;
+ if term_pos + len > 78 then begin
+ term_pos := len + 2 ; t_print_ln(' ') ; t_print(' ') ;
+ end else term_pos := term_pos + len ;
+ if repeat_count then t_print('[', value:1, ']')
+ else if turn_on then t_print(value:1)
+ else t_print('(', value:1, ')') ;
+end ;
+@<Packed number procedure@>
+
+@ Now, the globals to help communication between these procedures.
+
+@<Glob...@>=
+@!input_byte : eight_bits ; {the byte we are currently decimating}
+@!bit_weight : eight_bits ; {weight of the current bit}
+@!nybble : eight_bits ; {the current nybble}
+
+@ And the main procedure.
+
+@<Read and translate raster description@>=
+bit_weight := 0 ;
+if dyn_f = 14 then
+ @<Get raster by bits@>
+else @<Create normally packed raster@>
+
+@ If |dyn_f=14|, then we need to get the raster representation
+one bit at a time.
+
+@<Get raster by bits@>=
+begin
+for i := 1 to height do begin
+ t_print(' ') ;
+ for j := 1 to width do
+ if get_bit then t_print('*')
+ else t_print('.') ;
+ t_print_ln(' ') ;
+end;
+end
+
+@ Otherwise, we translate the bit counts into the raster rows. |count|
+contains the number of bits of the current color, and |turn_on| indicates
+whether or not they should be black. |rows_left| contains the number of
+rows to be sent.
+
+@<Create normally packed raster@>=
+begin
+term_pos := 2 ;
+t_print(' ') ;
+rows_left := height ;
+h_bit := width ;
+repeat_count := 0 ;
+while rows_left > 0 do begin
+ count := pk_packed_num ;
+ send_out(false, count) ;
+ if count >= h_bit then begin
+ rows_left := rows_left - repeat_count - 1 ;
+ repeat_count := 0 ;
+ count := count - h_bit ;
+ h_bit := width ;
+ rows_left := rows_left - count div width ;
+ count := count mod width ;
+ end ;
+ h_bit := h_bit - count ;
+ turn_on := not turn_on ;
+end ;
+t_print_ln(' ') ;
+if (rows_left <> 0) or (h_bit <> width) then
+ abort('Bad PK file: More bits than required!');
+@.More bits than required@>
+end
+
+@ We need to declare the repeat flag, bit counter, and color flag here.
+
+@<Glob...@>=
+@!repeat_count : integer ; {how many times to repeat the next row?}
+@!rows_left : integer ; {how many rows left?}
+@!turn_on : boolean ; {are we black here?}
+@!h_bit : integer ; {what is our horizontal position?}
+@!count : integer ; {how many bits of current color left?}
+
+@ If any specials are found, we write them out here.
+
+@d four_cases(#)==#,#+1,#+2,#+3
+
+@p procedure skip_specials ;
+var @!i, @!j: integer ;
+begin
+ repeat
+ flag_byte := pk_byte ;
+ if flag_byte >= 240 then
+ case flag_byte of
+ four_cases(pk_xxx1):
+begin
+ t_print((pk_loc-1):1,': Special: ''') ;
+ i := 0 ;
+ for j := pk_xxx1 to flag_byte do i := 256 * i + pk_byte ;
+ for j := 1 to i do t_print(xchr[pk_byte]) ;
+ t_print_ln('''') ;
+end ;
+ pk_yyy : t_print_ln((pk_loc-1):1,': Num special: ',get_32:1) ;
+ pk_post : t_print_ln((pk_loc-1):1,': Postamble') ;
+ pk_no_op : t_print_ln((pk_loc-1):1,': No op') ;
+ pk_pre, pk_undefined : abort('Unexpected ', flag_byte:1,'!') ;
+@.Unexpected bbb@>
+ endcases ;
+ until (flag_byte < 240) or (flag_byte = pk_post) ;
+end ;
+
+@* Terminal communication.
+We must get the file names and determine whether input is to be in
+hexadecimal or binary. To do this, we use the standard input path
+name. We need a procedure to flush the input buffer. For most systems,
+this will be an empty statement. For other systems, a |print_ln| will
+provide a quick fix. We also need a routine to get a line of input from
+the terminal. On some systems, a simple |read_ln| will do. Finally,
+a macro to print a string to the first blank is required.
+
+@d flush_buffer == begin end
+@d get_line(#) == if eoln(input) then read_ln(input) ;
+ i := 1 ;
+ while not (eoln(input) or eof(input)) do begin
+ #[i] := input^ ;
+ incr(i) ;
+ get(input) ;
+ end ;
+ #[i] := ' '
+
+@ @p procedure dialog ;
+var i : integer ; {index variable}
+buffer : packed array [1..name_length] of char; {input buffer}
+begin
+ for i := 1 to name_length do begin
+ typ_name[i] := ' ' ;
+ pk_name[i] := ' ' ;
+ end;
+ print('Input file name: ') ;
+ flush_buffer ;
+ get_line(pk_name) ;
+ print('Output file name: ') ;
+ flush_buffer ;
+ get_line(typ_name) ;
+end ;
+
+@* The main program.
+Now that we have all the pieces written, let us put them together.
+
+@p begin
+initialize ;
+dialog ;
+@<Open files@> ;
+@<Read preamble@> ;
+skip_specials ;
+while flag_byte <> pk_post do begin
+ @<Unpack and write character@> ;
+ skip_specials ;
+end ;
+j := 0 ;
+while not eof(pk_file) do begin
+ i := pk_byte ;
+ if i <> pk_no_op then abort('Bad byte at end of file: ',i:1) ;
+@.Bad byte at end of file@>
+ t_print_ln((pk_loc-1):1,': No op') ;
+ incr(j) ;
+end ;
+t_print_ln(pk_loc:1,' bytes read from packed file.');
+final_end :
+end .
+
+@* System-dependent changes.
+This section should be replaced, if necessary, by changes to the program
+that are necessary to make \.{PKtype} work at a particular installation.
+Any additional routines should be inserted here.
+@^system dependencies@>
+
+@* Index.
+Pointers to error messages appear here together with the section numbers
+where each ident\-i\-fier is used.