% This file is part of CWEB.
% This program by Silvio Levy and Donald E. Knuth
% is based on a program by Knuth.
% It is distributed WITHOUT ANY WARRANTY, express or implied.
% Version 4.9 --- May 2023

% Copyright (C) 1987,1990,1993,2000 Silvio Levy and Donald E. Knuth

% Permission is granted to make and distribute verbatim copies of this
% document provided that the copyright notice and this permission notice
% are preserved on all copies.

% Permission is granted to copy and distribute modified versions of this
% document under the conditions for verbatim copying, provided that the
% entire resulting derived work is given a different name and distributed
% under the terms of a permission notice identical to this one.

% Amendments to 'ctangle.w' resulting in this updated version were created
% by numerous collaborators over the course of many years.

% Please send comments, suggestions, etc. to tex-k@@tug.org.

% Here is TeX material that gets inserted after \input cwebmac
\def\hang{\hangindent 3em\indent\ignorespaces}
\def\pb{$\.|\ldots\.|$} % C brackets (|...|)
\def\v{\char'174} % vertical (|) in typewriter font
\mathchardef\RA="3221 % right arrow
\mathchardef\BA="3224 % double arrow

\def\title{CTANGLE (Version 4.9)}
\def\topofcontents{\null\vfill
  \centerline{\titlefont The {\ttitlefont CTANGLE} processor}
  \vskip 15pt
  \centerline{(Version 4.9)}
  \vfill}
\def\botofcontents{\vfill
\noindent
Copyright \copyright\ 1987, 1990, 1993, 2000 Silvio Levy and Donald E. Knuth
\bigskip\noindent
Permission is granted to make and distribute verbatim copies of this
document provided that the copyright notice and this permission notice
are preserved on all copies.

\smallskip\noindent
Permission is granted to copy and distribute modified versions of this
document under the conditions for verbatim copying, provided that the
entire resulting derived work is given a different name and distributed
under the terms of a permission notice identical to this one.
}
\pageno=\contentspagenumber \advance\pageno by 1
\let\maybe=\iftrue

@** Introduction.
This is the \.{CTANGLE} program by Silvio Levy and Donald E. Knuth,
based on \.{TANGLE} by Knuth.
We are thankful to
Nelson Beebe, Hans-Hermann Bode (to whom the \CPLUSPLUS/ adaptation is due),
Klaus Guntermann, Norman Ramsey, Tomas Rokicki, Joachim Schnitter,
Joachim Schrod, Lee Wittenberg, and others who have contributed improvements.

The ``banner line'' defined here should be changed whenever \.{CTANGLE}
is modified.

@d banner "This is CTANGLE (Version 4.9)"

@c
@<Include files@>@/
@h
@<Common code for \.{CWEAVE} and \.{CTANGLE}@>@/
@<Typedef declarations@>@/
@<Private variables@>@/
@<Predeclaration of procedures@>

@ \.{CTANGLE} has a fairly straightforward outline.  It operates in
two phases: First it reads the source file, saving the \CEE/ code in
compressed form; then it shuffles and outputs the code.

Please read the documentation for \.{COMMON}, the set of routines common
to \.{CTANGLE} and \.{CWEAVE}, before proceeding further.

@c
int main (
int ac,
char **av)
{
  argc=ac; argv=av;
  program=ctangle;
  @<Set initial values@>@;
  common_init();
  if (show_banner) puts(banner); /* print a ``banner line'' */
  phase_one(); /* read all the user's text and compress it into |tok_mem| */
  phase_two(); /* output the contents of the compressed tables */
  return wrap_up(); /* and exit gracefully */
}

@ The next few sections contain stuff from the file |"common.w"| that must
be included in both |"ctangle.w"| and |"cweave.w"|. It appears in
file |"common.h"|, which is also included in |"common.w"| to propagate
possible changes from this \.{COMMON} interface consistently.

@i common.h

@* Data structures exclusive to {\tt CTANGLE}.
We've already seen that the |byte_mem| array holds the names of identifiers,
strings, and sections;
the |tok_mem| array holds the replacement texts
for sections. Allocation is sequential, since things are deleted only
during Phase II, and only in a last-in-first-out manner.

A \&{text} variable is a structure containing a pointer into
|tok_mem|, which tells where the corresponding text starts, and an
integer |text_link|, which, as we shall see later, is used to connect
pieces of text that have the same name.  All the \&{text}s are stored in
the array |text_info|, and we use a \&{text\_pointer} variable to refer
to them.

The first position of |tok_mem| that is unoccupied by
replacement text is called |tok_ptr|, and the first unused location of
|text_info| is called |text_ptr|.  Thus we usually have the identity
|text_ptr->tok_start==tok_ptr|.

@<Typed...@>=
typedef struct {
  eight_bits *tok_start; /* pointer into |tok_mem| */
  sixteen_bits text_link; /* relates replacement texts */
} text;
typedef text *text_pointer;

@ @d max_texts 4000 /* number of replacement texts, must be less than 10240 */
@d max_toks 270000 /* number of bytes in compressed \CEE/ code */
@<Private...@>=
static text text_info[max_texts];
static text_pointer text_info_end=text_info+max_texts-1;
static text_pointer text_ptr; /* first unused position in |text_info| */
static eight_bits tok_mem[max_toks];
static eight_bits *tok_mem_end=tok_mem+max_toks-1;
static eight_bits *tok_ptr; /* first unused position in |tok_mem| */

@ @<Set init...@>=
text_info->tok_start=tok_ptr=tok_mem;
text_ptr=text_info+1; text_ptr->tok_start=tok_mem;
  /* this makes replacement text 0 of length zero */

@ If |p| is a pointer to a section name, |p->equiv| is a pointer to its
replacement text, an element of the array |text_info|.

@d equiv equiv_or_xref /* info corresponding to names */

@ @<Set init...@>=
init_node(name_dir); /* the undefined section has no replacement text */

@ Here's the procedure that decides whether a name of length |l|
starting at position |first| equals the identifier pointed to by |p|:

@c
boolean names_match(
name_pointer p, /* points to the proposed match */
const char *first, /* position of first character of string */
size_t l, /* length of identifier */
eight_bits t) /* not used by \.{CTANGLE} */
{@+(void)t;@/
  return length(p)==l && strncmp(first,p->byte_start,l)==0;
}

@ The common lookup routine |id_lookup| refers to a separate routine
|init_node| when the data structure grows.

@c
void
init_node(
name_pointer node)
{
    node->equiv=(void *)text_info;
}

@* Tokens.
Replacement texts, which represent \CEE/ code in a compressed format,
appear in |tok_mem| as mentioned above. The codes in
these texts are called `tokens'; some tokens occupy two consecutive
eight-bit byte positions, and the others take just one byte.

If $p$ points to a replacement text, |p->tok_start| is the |tok_mem| position
of the first eight-bit code of that text. If |p->text_link==0|,
this is the replacement text for a macro, otherwise it is the replacement
text for a section. In the latter case |p->text_link| is either equal to
|section_flag|, which means that there is no further text for this section, or
|p->text_link| points to a continuation of this replacement text; such
links are created when several sections have \CEE/ texts with the same
name, and they also tie together all the \CEE/ texts of unnamed sections.
The replacement text pointer for the first unnamed section appears in
|text_info->text_link|, and the most recent such pointer is |last_unnamed|.

@d macro 0
@d section_flag max_texts /* final |text_link| in section replacement texts */

@<Private...@>=
static text_pointer last_unnamed; /* most recent replacement text of unnamed section */

@ @<Set init...@>= last_unnamed=text_info; text_info->text_link=macro;

@ If the first byte of a token is less than |0200|, the token occupies a
single byte. Otherwise we make a sixteen-bit token by combining two consecutive
bytes |a| and |b|. If |0200<=a<0250|, then |(a-0200)@t${}\times2^8$@>+b|
points to an identifier; if |0250<=a<0320|, then
|(a-0250)@t${}\times2^8$@>+b| points to a section name
(or, if it has the special value |output_defs_flag|,
to the area where the preprocessor definitions are stored); and if
|0320<=a<0400|, then |(a-0320)@t${}\times2^8$@>+b| is the number of the section
in which the current replacement text appears.

Codes less than |0200| are 7-bit |char| codes that represent themselves.
Some of the 7-bit codes will not be present, however, so we can
use them for special purposes. The following symbolic names are used:

\yskip \hang |string| denotes the beginning or end of a string
or a verbatim construction.

\hang |constant| denotes a numerical constant.

\hang |join| denotes the concatenation of adjacent items with no space
or line breaks allowed between them (the \.{@@\&} operation of \.{CWEB}).
@^ASCII code dependencies@>

@d string 02 /* takes the place of ASCII \.{STX} */
@d constant 03 /* takes the place of ASCII \.{ETX} */
@d join 0177 /* takes the place of ASCII \.{DEL} */
@d output_defs_flag (2*024000-1) /* |024000==(0250-0200)*0400| */

@ The following procedure is used to enter a two-byte value into
|tok_mem| when a replacement text is being generated.

@c
static void
store_two_bytes(
sixteen_bits x)
{
  if (tok_ptr+2>tok_mem_end) overflow("token");
  *tok_ptr++=x>>8; /* store high byte */
  *tok_ptr++=x&0377; /* store low byte */
}

@ @<Predecl...@>=@+static void store_two_bytes(sixteen_bits);

@** Stacks for output.  The output process uses a stack to keep track
of what is going on at different ``levels'' as the sections are being
written out.  Entries on this stack have four parts:

\yskip\hang |byte_field| is the |tok_mem| location from which the next
token on a particular level will be read;

\hang |name_field| points to the name corresponding to a particular level;

\hang |repl_field| points to the replacement text currently being read
at a particular level;

\hang |section_field| is the section number, or zero if this is a macro.

\yskip\noindent The current values of these four quantities are referred to
quite frequently, so they are stored in an extra slot at the very end of the
|stack| array.  We call the current values |cur_byte|, |cur_name|, |cur_repl|,
and |cur_section|.

The global variable |stack_ptr| tells how many levels of output are
currently in progress. The end of all output occurs when the stack is
empty, i.e., when |stack_ptr==stack|.

@<Typed...@>=
typedef struct {
  eight_bits *byte_field; /* present location within replacement text */
  name_pointer name_field; /* |byte_start| index for text being output */
  text_pointer repl_field; /* |tok_start| index for text being output */
  sixteen_bits section_field; /* section number or zero if not a section */
} output_state;
typedef output_state *stack_pointer;

@ @d stack_size 50 /* number of simultaneous levels of macro expansion */
@d cur_state stack[stack_size+1] /* |cur_byte|, |cur_name|, |cur_repl|,
  and |cur_section| */
@d cur_byte cur_state.byte_field /* location of next output byte in |tok_mem|*/
@d cur_name cur_state.name_field /* pointer to current name being expanded */
@d cur_repl cur_state.repl_field /* pointer to current replacement text */
@d cur_section cur_state.section_field /* current section number being expanded */
@d cur_end (cur_repl+1)->tok_start /* current ending location in |tok_mem| */

@<Private...@>=
static output_state stack[stack_size+2]; /* info for non-current levels */
static stack_pointer stack_end=stack+stack_size; /* end of |stack| */
static stack_pointer stack_ptr; /* first unused location in the output state stack */

@ To get the output process started, we will perform the following
initialization steps. We may assume that |text_info->text_link| is nonzero,
since it points to the \CEE/ text in the first unnamed section that generates
code; if there are no such sections, there is nothing to output, and an
error message will have been generated before we do any of the initialization.

@<Initialize the output stacks@>=
stack_ptr=stack+1; cur_name=name_dir; cur_repl=text_info->text_link+text_info;
cur_byte=cur_repl->tok_start; cur_section=0;

@ When the replacement text for name |p| is to be inserted into the output,
the following subroutine is called to save the old level of output and get
the new one going.

We assume that the \CEE/ compiler can copy structures.
@^system dependencies@>

@c
static void
push_level( /* suspends the current level */
name_pointer p)
{
  if (stack_ptr==stack_end) overflow("stack");
  *stack_ptr=cur_state;
  stack_ptr++;
  if (p!=NULL) { /* |p==NULL| means we are in |output_defs| */
    cur_name=p; cur_repl=(text_pointer)p->equiv;
    cur_byte=cur_repl->tok_start; cur_section=0;
  }
}

@ @<Predecl...@>=
static void push_level(name_pointer);@/
static void pop_level(boolean);

@ When we come to the end of a replacement text, the |pop_level| subroutine
does the right thing: It either moves to the continuation of this replacement
text or returns the state to the most recently stacked level.

@c
static void
pop_level( /* do this when |cur_byte| reaches |cur_end| */
boolean flag) /* |flag==false| means we are in |output_defs| */
{
  if (flag && cur_repl->text_link<section_flag) { /* link to a continuation */
    cur_repl=cur_repl->text_link+text_info; /* stay on the same level */
    cur_byte=cur_repl->tok_start; return;
  }
  stack_ptr--; /* go down to the previous level */
  if (stack_ptr>stack) cur_state=*stack_ptr;@^system dependencies@>
}

@ The heart of the output procedure is the function |get_output|,
which produces the next token of output and sends it on to the lower-level
function |out_char|. The main purpose of |get_output| is to handle the
necessary stacking and unstacking. It sends the value |section_number|
if the next output begins or ends the replacement text of some section,
in which case |cur_val| is that section's number (if beginning) or the
negative of that value (if ending). (A section number of 0 indicates
not the beginning or ending of a section, but a \#\&{line} command.)
And it sends the value |identifier|
if the next output is an identifier, in which case
|cur_val| points to that identifier name.

@d section_number 0201 /* code returned by |get_output| for section numbers */
@d identifier 0202 /* code returned by |get_output| for identifiers */

@<Private...@>=
static int cur_val; /* additional information corresponding to output token */

@ If |get_output| finds that no more output remains, it returns with
|stack_ptr==stack|.
@^high-bit character handling@>

@c
static void
get_output(void) /* sends next token to |out_char| */
{
  sixteen_bits a; /* value of current byte */
  restart: if (stack_ptr==stack) return;
  if (cur_byte==cur_end) {
    cur_val=-((int)cur_section); /* cast needed because of sign extension */
    pop_level(true);
    if (cur_val==0) goto restart;
    out_char(section_number); return;
  }
  a=*cur_byte++;
  if (out_state==verbatim && a!=string && a!=constant && a!='\n')
    C_putc(a); /* a high-bit character can occur in a string */
  else if (a<0200) out_char(a); /* one-byte token */
  else {
    a=(a-0200)*0400+*cur_byte++;
    switch (a/024000) { /* |024000==(0250-0200)*0400| */
      case 0: cur_val=(int)a; out_char(identifier); break;
      case 1: if (a==output_defs_flag) output_defs();
        else @<Expand section |a-024000|, |goto restart|@>@;
        break;
      default: cur_val=(int)a-050000;
        if (cur_val>0) cur_section=(sixteen_bits)cur_val;
        out_char(section_number);
    }
  }
}

@ @<Predecl...@>=@+static void get_output(void);

@ The user may have forgotten to give any \CEE/ text for a section name,
or the \CEE/ text may have been associated with a different name by mistake.

@<Expand section |a-...@>=
{
  a-=024000;
  if ((a+name_dir)->equiv!=(void *)text_info) push_level(a+name_dir);
  else if (a!=0) {
    fputs("\n! Not present: <",stdout);
    print_section_name(a+name_dir); err_print(">");
@.Not present: <section name>@>
  }
  goto restart;
}

@* Producing the output.
The |get_output| routine above handles most of the complexity of output
generation, but there are two further considerations that have a nontrivial
effect on \.{CTANGLE}'s algorithms.

@ First,
we want to make sure that the output has spaces and line breaks in
the right places (e.g., not in the middle of a string or a constant or an
identifier, not at a `\.{@@\&}' position
where quantities are being joined together, and certainly after an \.=
because the \CEE/ compiler thinks \.{=-} is ambiguous).

The output process can be in one of following states:

\yskip\hang |num_or_id| means that the last item in the buffer is a number or
identifier, hence a blank space or line break must be inserted if the next
item is also a number or identifier.

\yskip\hang |unbreakable| means that the last item in the buffer was followed
by the \.{@@\&} operation that inhibits spaces between it and the next item.

\yskip\hang |verbatim| means we're copying only character tokens, and
that they are to be output exactly as stored.  This is the case during
strings, verbatim constructions and numerical constants.

\yskip\hang |post_slash| means we've just output a slash.

\yskip\hang |normal| means none of the above.

\yskip\noindent Furthermore, if the variable |protect| is |true|, newlines
are preceded by a `\.\\'.

@d normal 0 /* non-unusual state */
@d num_or_id 1 /* state associated with numbers and identifiers */
@d post_slash 2 /* state following a \./ */
@d unbreakable 3 /* state associated with \.{@@\&} */
@d verbatim 4 /* state in the middle of a string */

@<Private...@>=
static eight_bits out_state; /* current status of partial output */
static boolean protect; /* should newline characters be quoted? */

@ Here is a routine that is invoked when we want to output the current line.
During the output process, |cur_line| equals the number of the next line
to be output.

@c
static void
flush_buffer(void) /* writes one line to output file */
{
  C_putc('\n');
  if (cur_line % 100 == 0 && show_progress) {
    putchar('.');
    if (cur_line % 500 == 0) printf("%d",cur_line);
    update_terminal(); /* progress report */
  }
  cur_line++;
}

@ @<Predecl...@>=@+static void flush_buffer(void);

@ Second, we have modified the original \.{TANGLE} so that it will write output
on multiple files.
If a section name is introduced in at least one place by \.{@@(}
instead of \.{@@<}, we treat it as the name of a file.
All these special sections are saved on a stack, |output_files|.
We write them out after we've done the unnamed section.

@d max_files 256
@<Private...@>=
static name_pointer output_files[max_files];
static name_pointer *cur_out_file, *end_output_files, *an_output_file;
static char cur_section_name_char; /* is it |'<'| or |'('| */
static char output_file_name[longest_name+1]; /* name of the file */

@ We make |end_output_files| point just beyond the end of
|output_files|. The stack pointer
|cur_out_file| starts out there. Every time we see a new file, we
decrement |cur_out_file| and then write it in.
@<Set initial...@>=
cur_out_file=end_output_files=output_files+max_files;

@ @<If it's not there, add |cur_section_name| to the output file stack, or
complain we're out of room@>=
{
  for (an_output_file=cur_out_file;
        an_output_file<end_output_files; an_output_file++)
            if (*an_output_file==cur_section_name) break;
  if (an_output_file==end_output_files) {
    if (cur_out_file>output_files)
        *--cur_out_file=cur_section_name;
    else overflow("output files");
  }
}

@* The big output switch.  Here then is the routine that does the
output.

@c
static void
phase_two (void) {
  phase=2;
  web_file_open=false;
  cur_line=1;
  @<Initialize the output stacks@>@;
  @<Output macro definitions if appropriate@>@;
  if (text_info->text_link==macro && cur_out_file==end_output_files) {
    fputs("\n! No program text was specified.",stdout); mark_harmless();
@.No program text...@>
  }
  else {
    if (show_progress) {
      printf(cur_out_file==end_output_files ? @|
        "\nWriting the output file (%s):" : @|
        "\nWriting the output files: (%s)",C_file_name);
@.Writing the output...@>
      update_terminal();
    }
    if (text_info->text_link!=macro) {
      while (stack_ptr>stack) get_output();
      flush_buffer();
    }
    @<Write all the named output files@>@;
    if (show_happiness) {
      if (show_progress) new_line();
      fputs("Done.",stdout);
    }
  }
}

@ @<Predecl...@>=@+static void phase_two(void);

@ To write the named output files, we proceed as for the unnamed
section.
The only subtlety is that we have to open each one.

@<Write all the named output files@>=
for (an_output_file=end_output_files; an_output_file>cur_out_file;) {
    an_output_file--;
    sprint_section_name(output_file_name,*an_output_file);
    fclose(C_file);
    if ((C_file=fopen(output_file_name,"wb"))==NULL)
      fatal("! Cannot open output file ",output_file_name);
@.Cannot open output file@>
    if (show_progress) { printf("\n(%s)",output_file_name); update_terminal(); }
    cur_line=1;
    stack_ptr=stack+1;
    cur_name=*an_output_file;
    cur_repl=(text_pointer)cur_name->equiv;
    cur_byte=cur_repl->tok_start;
    while (stack_ptr > stack) get_output();
    flush_buffer();
}

@ If a \.{@@h} was not encountered in the input,
we go through the list of replacement texts and copy the ones
that refer to macros, preceded by the \.{\#define} preprocessor command.

@<Output macro definitions if appropriate@>=
  if (!output_defs_seen)
    output_defs();

@ @<Private...@>=
static boolean output_defs_seen=false;

@ @<Predecl...@>=
static void output_defs(void);@/
static void out_char(eight_bits);

@ @d macro_end (cur_text+1)->tok_start /* end of |macro| replacement text */
@#
@d C_printf(c,a) fprintf(C_file,c,a)
@d C_putc(c) fputc((int)(c),C_file) /* isn't \CEE/ wonderfully consistent? */

@c
static void
output_defs(void)
{
  sixteen_bits a;
  push_level(NULL);
  for (cur_text=text_info+1; cur_text<text_ptr; cur_text++)
    if (cur_text->text_link==macro) { /* |cur_text| is the text for a |macro| */
      cur_byte=cur_text->tok_start;
      C_printf("%s","#define ");
      out_state=normal;
      protect=true; /* newlines should be preceded by |'\\'| */
      while (cur_byte<macro_end) {
        a=*cur_byte++;
        if (cur_byte==macro_end && a=='\n') break; /* disregard a final newline */
        if (out_state==verbatim && a!=string && a!=constant && a!='\n')
          C_putc(a); /* a high-bit character can occur in a string */
@^high-bit character handling@>
        else if (a<0200) out_char(a); /* one-byte token */
        else {
          a=(a-0200)*0400+*cur_byte++;
          if (a<024000) { /* |024000==(0250-0200)*0400| */
            cur_val=(int)a; out_char(identifier);
          }
          else if (a<050000) confusion("macro defs have strange char");
          else {
            cur_val=(int)a-050000; cur_section=(sixteen_bits)cur_val;
            out_char(section_number);
          }
      /* no other cases */
        }
      }
      protect=false;
      flush_buffer();
    }
  pop_level(false);
}

@ A many-way switch is used to send the output.  Note that this function
is not called if |out_state==verbatim|, except perhaps with arguments
|'\n'| (protect the newline), |string| (end the string), or |constant|
(end the constant).

@c
static void
out_char(
eight_bits cur_char)
{
  char *j; /* pointer into |byte_mem| */
restart:
    switch (cur_char) {
      case '\n': if (protect && out_state!=verbatim) C_putc(' ');
        if (protect || out_state==verbatim) C_putc('\\');
        flush_buffer(); if (out_state!=verbatim) out_state=normal; break;
      @/@t\4@>@<Case of an identifier@>@;
      @/@t\4@>@<Case of a section number@>@;
      @/@t\4@>@<Cases like \.{!=}@>@;
      case '=': case '>': C_putc(cur_char);@+C_putc(' ');
        out_state=normal; break;
      case join: out_state=unbreakable; break;
      case constant: if (out_state==verbatim) {
          out_state=num_or_id; break;
        }
        if(out_state==num_or_id) C_putc(' '); out_state=verbatim; break;
      case string: if (out_state==verbatim) out_state=normal;
        else out_state=verbatim; break;
      case '/': C_putc('/'); out_state=post_slash; break;
      case '*': if (out_state==post_slash) C_putc(' ');
        @=/* fall through */@>@;
      default: C_putc(cur_char); out_state=normal; break;
    }
}

@ @<Cases like \.{!=}@>=@t\1\quad@>
case plus_plus: C_putc('+');@+C_putc('+'); out_state=normal; break;
case minus_minus: C_putc('-');@+C_putc('-'); out_state=normal; break;
case minus_gt: C_putc('-');@+C_putc('>'); out_state=normal; break;
case gt_gt: C_putc('>');@+C_putc('>'); out_state=normal; break;
case eq_eq: C_putc('=');@+C_putc('='); out_state=normal; break;
case lt_lt: C_putc('<');@+C_putc('<'); out_state=normal; break;
case gt_eq: C_putc('>');@+C_putc('='); out_state=normal; break;
case lt_eq: C_putc('<');@+C_putc('='); out_state=normal; break;
case non_eq: C_putc('!');@+C_putc('='); out_state=normal; break;
case and_and: C_putc('&');@+C_putc('&'); out_state=normal; break;
case or_or: C_putc('|');@+C_putc('|'); out_state=normal; break;
case dot_dot_dot: C_putc('.');@+C_putc('.');@+C_putc('.'); out_state=normal;
    break;
case colon_colon: C_putc(':');@+C_putc(':'); out_state=normal; break;
case period_ast: C_putc('.');@+C_putc('*'); out_state=normal; break;
case minus_gt_ast: C_putc('-');@+C_putc('>');@+C_putc('*'); out_state=normal;
    break;

@ When an identifier is output to the \CEE/ file, characters in the range
128--255 (|0200|--|0377|) must be changed into something else, so the \CEE/
compiler won't complain.  By default, \.{CTANGLE} converts the
character with code $16 x+y$ to the three characters `\.X$xy$', but
a different transliteration table can be specified.  Thus a German
might want {\it gr\"un\/} to appear as a still readable \.{gruen}.
This makes debugging a lot less confusing.

@d translit_length 10

@<Private...@>=
static char translit[0200][translit_length];

@ @<Set init...@>=
{ int i;
  for (i=0;i<0200;i++)
     snprintf(translit[i],translit_length,"X%02X",(unsigned int)(0200+i));
}

@ @<Case of an identifier@>=@t\1\quad@>
case identifier:
  if (out_state==num_or_id) C_putc(' ');
  for (j=(cur_val+name_dir)->byte_start;
       j<(cur_val+name_dir+1)->byte_start; j++)
    if ((eight_bits)(*j)<0200) C_putc(*j);
@^high-bit character handling@>
    else C_printf("%s",translit[(eight_bits)(*j)-0200]);
  out_state=num_or_id; break;

@ @<Case of a sec...@>=@t\1\quad@>
case section_number:
  if (cur_val>0) C_printf("/*%d:*/",cur_val);
  else if(cur_val<0) C_printf("/*:%d*/",-cur_val);
  else if (protect) {
    cur_byte +=4; /* skip line number and file name */
    cur_char = (eight_bits)'\n';
    goto restart;
  } else {
    sixteen_bits a;
    a=*cur_byte++ *0400;
    a+=*cur_byte++; /* gets the line number */
    C_printf("\n#line %d \"",(int)a);
@:line}{\.{\#line}@>
    cur_val=(int)(*cur_byte++-0200)*0400;
    cur_val+=*cur_byte++; /* points to the file name */
    for (j=(cur_val+name_dir)->byte_start;
         j<(cur_val+name_dir+1)->byte_start; j++) {
      if (*j=='\\' || *j=='"') C_putc('\\');
      C_putc(*j);
    }
    C_putc('"');@+C_putc('\n');
  }
  break;

@** Introduction to the input phase.
We have now seen that \.{CTANGLE} will be able to output the full
\CEE/ program, if we can only get that program into the byte memory in
the proper format. The input process is something like the output process
in reverse, since we compress the text as we read it in and we expand it
as we write it out.

There are three main input routines. The most interesting is the one that gets
the next token of a \CEE/ text; the other two are used to scan rapidly past
\TEX/ text in the \.{CWEB} source code. One of the latter routines will jump to
the next token that starts with `\.{@@}', and the other skips to the end
of a \CEE/ comment.

@ Control codes in \.{CWEB} begin with `\.{@@}', and the next character
identifies the code. Some of these are of interest only to \.{CWEAVE},
so \.{CTANGLE} ignores them; the others are converted by \.{CTANGLE} into
internal code numbers by the |ccode| table below. The ordering
of these internal code numbers has been chosen to simplify the program logic;
larger numbers are given to the control codes that denote more significant
milestones.

@d ignore 00 /* control code of no interest to \.{CTANGLE} */
@d ord 0302 /* control code for `\.{@@'}' */
@d control_text 0303 /* control code for `\.{@@t}', `\.{@@\^}', etc. */
@d translit_code 0304 /* control code for `\.{@@l}' */
@d output_defs_code 0305 /* control code for `\.{@@h}' */
@d format_code 0306 /* control code for `\.{@@f}' */
@d definition 0307 /* control code for `\.{@@d}' */
@d begin_C 0310 /* control code for `\.{@@c}' */
@d section_name 0311 /* control code for `\.{@@<}' */
@d new_section 0312 /* control code for `\.{@@\ }' and `\.{@@*}' */

@<Private...@>=
static eight_bits ccode[256]; /* meaning of a char following \.{@@} */

@ @<Set ini...@>= {
  int c; /* must be |int| so the |for| loop will end */
  for (c=0; c<256; c++) ccode[c]=ignore;
}
ccode[' ']=ccode['\t']=ccode['\n']=ccode['\v']=ccode['\r']=ccode['\f']
  =ccode['*']=new_section;
ccode['@@']=(eight_bits)'@@'; ccode['=']=string;
ccode['d']=ccode['D']=definition;
ccode['f']=ccode['F']=ccode['s']=ccode['S']=format_code;
ccode['c']=ccode['C']=ccode['p']=ccode['P']=begin_C;
ccode['^']=ccode[':']=ccode['.']=ccode['t']=ccode['T']=
ccode['q']=ccode['Q']=control_text;
ccode['h']=ccode['H']=output_defs_code;
ccode['l']=ccode['L']=translit_code;
ccode['&']=join;
ccode['<']=ccode['(']=section_name;
ccode['\'']=ord;

@ The |skip_ahead| procedure reads through the input at fairly high speed
until finding the next non-ignorable control code, which it returns.

@c
static eight_bits
skip_ahead(void) /* skip to next control code */
{
  eight_bits c; /* control code found */
  while (true) {
    if (loc>limit && (get_line()==false)) return new_section;
    *(limit+1)='@@';
    while (*loc!='@@') loc++;
    if (loc<=limit) {
      loc++; c=ccode[(eight_bits)*loc]; loc++;
      if (c!=ignore || *(loc-1)=='>') return c;
    }
  }
}

@ @<Predecl...@>=
static eight_bits skip_ahead(void);@/
static boolean skip_comment(boolean);

@ The |skip_comment| procedure reads through the input at somewhat high
speed in order to pass over comments, which \.{CTANGLE} does not transmit
to the output. If the comment is introduced by \.{/*}, |skip_comment|
proceeds until finding the end-comment token \.{*/} or a newline; in the
latter case |skip_comment| will be called again by |get_next|, since the
comment is not finished.  This is done so that each newline in the
\CEE/ part of a section is copied to the output; otherwise the \#\&{line}
commands inserted into the \CEE/ file by the output routines become useless.
On the other hand, if the comment is introduced by \.{//} (i.e., if it
is a \CPLUSPLUS/ ``short comment''), it always is simply delimited by the next
newline. The boolean argument |is_long_comment| distinguishes between
the two types of comments.

If |skip_comment| comes to the end of the section, it prints an error message.
No comment, long or short, is allowed to contain `\.{@@\ }' or `\.{@@*}'.

@<Private...@>=
static boolean comment_continues=false; /* are we scanning a comment? */

@ @c
static boolean skip_comment( /* skips over comments */
boolean is_long_comment)
{
  char c; /* current character */
  while (true) {
    if (loc>limit) {
      if (is_long_comment) {
        if (get_line()) return comment_continues=true;
        else {
          err_print("! Input ended in mid-comment");
@.Input ended in mid-comment@>
          return comment_continues=false;
        }
      }
      else return comment_continues=false;
    }
    c=*(loc++);
    if (is_long_comment && c=='*' && *loc=='/') {
      loc++; return comment_continues=false;
    }
    if (c=='@@') {
      if (ccode[(eight_bits)*loc]==new_section) {
        err_print("! Section name ended in mid-comment"); loc--;
@.Section name ended in mid-comment@>
        return comment_continues=false;
      }
      else loc++;
    }
  }
}

@* Inputting the next token.

@<Private...@>=
static name_pointer cur_section_name; /* name of section just scanned */
static boolean no_where; /* suppress |print_where|? */

@ As one might expect, |get_next| consists mostly of a big switch
that branches to the various special cases that can arise.

@c
static eight_bits
get_next(void) /* produces the next input token */
{
  static boolean preprocessing=false;
  eight_bits c; /* the current character */
  while (true) {
    if (loc>limit) {
      if (preprocessing && *(limit-1)!='\\') preprocessing=false;
      if (get_line()==false) return new_section;
      else if (print_where && !no_where) {
          print_where=false;
          @<Insert the line number into |tok_mem|@>@;
        }
        else return (eight_bits)'\n';
    }
    c=(eight_bits)*loc;
    if (comment_continues || (c=='/' && (*(loc+1)=='*' || *(loc+1)=='/'))) {
      if (skip_comment(comment_continues||*(loc+1)=='*')) return '\n';
          /* scan to end of comment or newline */
      else continue;
    }
    loc++;
    if (xisdigit(c) || c=='.') @<Get a constant@>@;
    else if (c=='\'' || c=='"'@|
           || ((c=='L' || c=='u' || c=='U')&&(*loc=='\'' || *loc=='"'))@|
           || ((c=='u' && *loc=='8')&&(*(loc+1)=='\'' || *(loc+1)=='"')))
        @<Get a string@>@;
    else if (isalpha((int)c) || isxalpha(c) || ishigh(c))
      @<Get an identifier@>@;
    else if (c=='@@') @<Get control code and possible section name@>@;
    else if (xisspace(c)) {
        if (!preprocessing || loc>limit) continue;
          /* we don't want a blank after a final backslash */
        else return (eight_bits)' ';
          /* ignore spaces and tabs, unless |preprocessing| */
    }
    else if (c=='#' && loc==buffer+1) preprocessing=true;
    mistake: @<Compress two-symbol operator@>@;
    return c;
  }
}

@ @<Predecl...@>=@+static eight_bits get_next(void);

@ The following code assigns values to the combinations \.{++},
\.{--}, \.{->}, \.{>=}, \.{<=}, \.{==}, \.{<<}, \.{>>}, \.{!=}, %\.{||}
\.{\v\v} and~\.{\&\&}, and to the \CPLUSPLUS/
combinations \.{...}, \.{::}, \.{.*} and \.{->*}.
The compound assignment operators (e.g., \.{+=}) are
treated as separate tokens.

@<Compress tw...@>=
switch(c) {
  case '+': if (*loc=='+') compress(plus_plus); break;
  case '-': if (*loc=='-') {@+compress(minus_minus);@+}
            else if (*loc=='>') {
              if (*(loc+1)=='*') {loc++;@+compress(minus_gt_ast);}
              else compress(minus_gt);
            } break;
  case '.': if (*loc=='*') {@+compress(period_ast);@+}
            else if (*loc=='.' && *(loc+1)=='.') {
              loc++;@+compress(dot_dot_dot);
            } break;
  case ':': if (*loc==':') compress(colon_colon); break;
  case '=': if (*loc=='=') compress(eq_eq); break;
  case '>': if (*loc=='=') {@+compress(gt_eq);@+}
    else if (*loc=='>') compress(gt_gt); break;
  case '<': if (*loc=='=') {@+compress(lt_eq);@+}
    else if (*loc=='<') compress(lt_lt); break;
  case '&': if (*loc=='&') compress(and_and); break;
  case '|': if (*loc=='|') compress(or_or); break;
  case '!': if (*loc=='=') compress(non_eq); break;
}

@ @<Get an identifier@>= {
  id_first=--loc;
  do
    ++loc;
  while (isalpha((int)*loc) || isdigit((int)*loc) @|
      || isxalpha(*loc) || ishigh(*loc));
  id_loc=loc; return identifier;
}

@ @<Get a constant@>= {
  boolean hex_flag = false; /* are we reading a hexadecimal literal? */
  id_first=loc-1;
  if (*id_first=='.' && !xisdigit(*loc)) goto mistake; /* not a constant */
  if (*id_first=='0') {
    if (*loc=='x' || *loc=='X') { /* hex constant */
      hex_flag = true;
      loc++; while (xisxdigit(*loc) || *loc=='\'') loc++;
    }
    else if (*loc=='b' || *loc=='B') { /* binary constant */
      loc++; while (*loc=='0' || *loc=='1' || *loc=='\'') loc++; goto found;
    }
  }
  while (xisdigit(*loc) || *loc=='\'') loc++;
  if (*loc=='.') {
    loc++;
    while ((hex_flag && xisxdigit(*loc)) || xisdigit(*loc) || *loc=='\'') loc++;
  }
  if (*loc=='e' || *loc=='E') { /* float constant */
    if (*++loc=='+' || *loc=='-') loc++;
    while (xisdigit(*loc) || *loc=='\'') loc++;
  }
  else if (hex_flag && (*loc=='p' || *loc=='P')) { /* hex float constant */
    if (*++loc=='+' || *loc=='-') loc++;
    while (xisxdigit(*loc) || *loc=='\'') loc++;
  }
found: while (*loc=='u' || *loc=='U' || *loc=='l' || *loc=='L'
            || *loc=='f' || *loc=='F') loc++;
  id_loc=loc;
  return constant;
}

@ \CEE/ strings and character constants, delimited by double and single
quotes, respectively, can contain newlines or instances of their own
delimiters if they are protected by a backslash.  We follow this
convention, but do not allow the string to be longer than |longest_name|.

@<Get a string@>= {
  char delim = (char)c; /* what started the string */
  id_first = section_text+1;
  id_loc = section_text; *++id_loc=delim;
  if (delim=='L' || delim=='u' || delim=='U') { /* wide character constant */
    if (delim=='u' && *loc=='8') *++id_loc=*loc++;
    delim=*loc++; *++id_loc=delim;
  }
  while (true) {
    if (loc>=limit) {
      if(*(limit-1)!='\\') {
        err_print("! String didn't end"); loc=limit; break;
@.String didn't end@>
      }
      if(get_line()==false) {
        err_print("! Input ended in middle of string"); loc=buffer; break;
@.Input ended in middle of string@>
      }
      else if (++id_loc<=section_text_end) *id_loc='\n'; /* will print as
      \.{"\\\\\\n"} */
    }
    if ((c=(eight_bits)*loc++)==delim) {
      if (++id_loc<=section_text_end) *id_loc=(char)c;
      break;
    }
    if (c=='\\') {
      if (loc>=limit) continue;
      if (++id_loc<=section_text_end) *id_loc = '\\';
      c=(eight_bits)*loc++;
    }
    if (++id_loc<=section_text_end) *id_loc=(char)c;
  }
  if (id_loc>=section_text_end) {
    fputs("\n! String too long: ",stdout);
@.String too long@>
    term_write(section_text+1,25);
    err_print("...");
  }
  id_loc++;
  return string;
}

@ After an \.{@@} sign has been scanned, the next character tells us
whether there is more work to do.

@<Get control code and possible section name@>=
switch(c=ccode[(eight_bits)*loc++]) {
  case ignore: continue;
  case translit_code: err_print("! Use @@l in limbo only"); continue;
@.Use @@l in limbo...@>
  case control_text: while ((c=skip_ahead())=='@@');
    /* only \.{@@@@} and \.{@@>} are expected */
    if (*(loc-1)!='>')
      err_print("! Double @@ should be used in control text");
@.Double @@ should be used...@>
    continue;
  case section_name:
    cur_section_name_char=*(loc-1);
    @<Scan the section name and make |cur_section_name| point to it@>@;
  case string: @<Scan a verbatim string@>@;
  case ord: @<Scan an ASCII constant@>@;
  default: return c;
}

@ After scanning a valid ASCII constant that follows
\.{@@'}, this code plows ahead until it finds the next single quote.
(Special care is taken if the quote is part of the constant.)
Anything after a valid ASCII constant is ignored;
thus, \.{@@'\\nopq'} gives the same result as \.{@@'\\n'}.

@<Scan an ASCII constant@>=
  id_first=loc;
  if (*loc=='\\')
    if (*++loc=='\'') loc++;
  while (*loc!='\'') {
    if (*loc=='@@') {
      if (*(loc+1)!='@@')
        err_print("! Double @@ should be used in ASCII constant");
@.Double @@ should be used...@>
      else loc++;
    }
    loc++;
    if (loc>limit) {
        err_print("! String didn't end"); loc=limit-1; break;
@.String didn't end@>
    }
  }
  loc++;
  return ord;

@ @<Scan the section name...@>= {
  char *k=section_text; /* pointer into |section_text| */
  @<Put section name into |section_text|@>@;
  if (k-section_text>3 && strncmp(k-2,"...",3)==0)
    cur_section_name=section_lookup(section_text+1,k-3,true);
      /* |true| means it's a prefix */
  else cur_section_name=section_lookup(section_text+1,k,false);
      /* |false| means it's not */
  if (cur_section_name_char=='(')
    @<If it's not there, add |cur_section_name| to the output file stack, or
          complain we're out of room@>@;
  return section_name;
}

@ Section names are placed into the |section_text| array with consecutive spaces,
tabs, and carriage-returns replaced by single spaces. There will be no
spaces at the beginning or the end. (We set |section_text[0]=' '| to facilitate
this, since the |section_lookup| routine uses |section_text[1]| as the first
character of the name.)

@<Set init...@>=section_text[0]=' ';

@ @<Put section name...@>=
while (true) {
  if (loc>limit && get_line()==false) {
    err_print("! Input ended in section name");
@.Input ended in section name@>
    loc=buffer+1; break;
  }
  c=(eight_bits)*loc;
  @<If end of name or erroneous nesting, |break|@>@;
  loc++; if (k<section_text_end) k++;
  if (xisspace(c)) {
    c=(eight_bits)' '; if (*(k-1)==' ') k--;
  }
*k=(char)c;
}
if (k>=section_text_end) {
  fputs("\n! Section name too long: ",stdout);
@.Section name too long@>
  term_write(section_text+1,25);
  printf("..."); mark_harmless();
}
if (*k==' ' && k>section_text) k--;

@ @<If end of name or erroneous nesting,...@>=
if (c=='@@') {
  c=(eight_bits)*(loc+1);
  if (c=='>') {
    loc+=2; break;
  }
  if (ccode[(eight_bits)c]==new_section) {
    err_print("! Section name didn't end"); break;
@.Section name didn't end@>
  }
  if (ccode[(eight_bits)c]==section_name) {
    err_print("! Nesting of section names not allowed"); break;
@.Nesting of section names...@>
  }
  *(++k)='@@'; loc++; /* now |c==*loc| again */
}

@ At the present point in the program we
have |*(loc-1)==string|; we set |id_first| to the beginning
of the string itself, and |id_loc| to its ending-plus-one location in the
buffer.  We also set |loc| to the position just after the ending delimiter.

@<Scan a verbatim string@>=
id_first=loc++; *(limit+1)='@@'; *(limit+2)='>';
while (*loc!='@@' || *(loc+1)!='>') loc++;
if (loc>=limit) err_print("! Verbatim string didn't end");
@.Verbatim string didn't end@>
id_loc=loc; loc+=2;
return string;

@* Scanning a macro definition.
The rules for generating the replacement texts corresponding to macros and
\CEE/ texts of a section are almost identical; the only differences are that

\yskip \item{a)}Section names are not allowed in macros;
in fact, the appearance of a section name terminates such macros and denotes
the name of the current section.

\item{b)}The symbols \.{@@d} and \.{@@f} and \.{@@c} are not allowed after
section names, while they terminate macro definitions.

\item{c)}Spaces are inserted after right parentheses in macros, because the
ANSI \CEE/ preprocessor sometimes requires it.

\yskip Therefore there is a single procedure |scan_repl| whose parameter
|t| specifies either |macro| or |section_name|. After |scan_repl| has
acted, |cur_text| will point to the replacement text just generated, and
|next_control| will contain the control code that terminated the activity.

@d app_repl(c) {
  if (tok_ptr==tok_mem_end) overflow("token");
  else *(tok_ptr++)=(eight_bits)c;
}

@<Private...@>=
static text_pointer cur_text; /* replacement text formed by |scan_repl| */
static eight_bits next_control;

@ @c
static void
scan_repl( /* creates a replacement text */
eight_bits t)
{
  sixteen_bits a; /* the current token */
  if (t==section_name) @<Insert the line number into |tok_mem|@>@;
  while (true) switch (a=get_next()) {
      @/@t\4@>@<In cases that |a| is a non-|char| token (|identifier|,
        |section_name|, etc.), either process it and change |a| to a byte
        that should be stored, or |continue| if |a| should be ignored,
        or |goto done| if |a| signals the end of this replacement text@>@;
      case ')': app_repl(a);
        if (t==macro) app_repl(' ');
        break;
      default: app_repl(a); /* store |a| in |tok_mem| */
    }
  done: next_control=(eight_bits) a;
  if (text_ptr>text_info_end) overflow("text");
  cur_text=text_ptr; (++text_ptr)->tok_start=tok_ptr;
}

@ @<Predecl...@>=@+static void scan_repl(eight_bits);

@ Here is the code for the line number: first a |sixteen_bits| equal
to |0150000|; then the numeric line number; then a pointer to the
file name.

@d store_id(a) a=id_lookup(id_first,id_loc,'\0')-name_dir;@/
  app_repl((a / 0400)+0200);
  app_repl(a % 0400)

@<Insert the line...@>=
{
  eight_bits a; /* shadow variable |a| */
  store_two_bytes(0150000);
  if (changing && include_depth==change_depth) { /* correction made Feb 2017 */
    id_first=change_file_name;
     store_two_bytes((sixteen_bits)change_line);
  }@+else {
    id_first=cur_file_name;
    store_two_bytes((sixteen_bits)cur_line);
  }
  id_loc=id_first+strlen(id_first);
  store_id(a);
}

@ @<In cases that |a| is...@>=@t\1\quad@>
case identifier: store_id(a);
  if (*buffer=='#' && @| (
      ( id_loc-id_first==5 && strncmp("endif",id_first,5)==0 ) || @|
      ( id_loc-id_first==4 && strncmp("else",id_first,4)==0 ) || @|
      ( id_loc-id_first==4 && strncmp("elif",id_first,4)==0 ) ) )
      /* Avoid preprocessor calamities */
    print_where=true;
  break;
case section_name: if (t!=section_name) goto done;
  else {
    @<Was an `\.{@@}' missed here?@>@;
    a=cur_section_name-name_dir;
    app_repl((a / 0400)+0250);
    app_repl(a % 0400);
    @<Insert the line number into |tok_mem|@>@;
  }
  break;
case output_defs_code: if (t!=section_name) err_print("! Misplaced @@h");
@.Misplaced @@h@>
  else {
    output_defs_seen=true;
    a=output_defs_flag;
    app_repl((a / 0400)+0200);
    app_repl(a % 0400);
    @<Insert the line number into |tok_mem|@>@;
  }
  break;
case constant: case string:
  @<Copy a string or verbatim construction or numerical constant@>@;
  break;
case ord:
  @<Copy an ASCII constant@>@;
  break;
case definition: case format_code: case begin_C: if (t!=section_name) goto done;
  else {
    err_print("! @@d, @@f and @@c are ignored in C text"); continue;
@.@@d, @@f and @@c are ignored in C text@>
  }
case new_section: goto done;

@ @<Was an `\.{@@}'...@>= {
  char *try_loc=loc;
  while (*try_loc==' ' && try_loc<limit) try_loc++;
  if (*try_loc=='+' && try_loc<limit) try_loc++;
  while (*try_loc==' ' && try_loc<limit) try_loc++;
  if (*try_loc=='=') err_print ("! Missing `@@ ' before a named section");
@.Missing `@@ '...@>
  /* user who isn't defining a section should put newline after the name,
     as explained in the manual */
}

@ By default, \.{CTANGLE} purges single-quote characters from \CPLUSPLUS/-style
literals, e.g., \.{1'000'000}, so that you can use this notation also in \CEE/
code. The \.{+k} switch will `keep' the single quotes in the output.

@d keep_digit_separators flags['k']

@<Copy a string...@>=
  app_repl(a); /* |string| or |constant| */
  while (id_first < id_loc) { /* simplify \.{@@@@} pairs */
    if (*id_first=='@@') {
      if (*(id_first+1)=='@@') id_first++;
      else err_print("! Double @@ should be used in string");
@.Double @@ should be used...@>
    }
    else if (a==constant && *id_first=='\'' && !keep_digit_separators)
      id_first++;
    app_repl(*id_first++);
  }
  app_repl(a);

@ This section should be rewritten on machines that don't use ASCII
code internally.
@^ASCII code dependencies@>

@<Copy an ASCII constant@>= {
  int c=(int)((eight_bits) *id_first);
  if (c=='\\') {
    c=(int)((eight_bits) *++id_first);
    if (c>='0' && c<='7') {
      c-='0';
      if (*(id_first+1)>='0' && *(id_first+1)<='7') {
        c=8*c+*(++id_first) - '0';
        if (*(id_first+1)>='0' && *(id_first+1)<='7' && c<32)
          c=8*c+*(++id_first)- '0';
      }
    }
    else switch (c) {
    case 't':c='\t';@+break;
    case 'n':c='\n';@+break;
    case 'b':c='\b';@+break;
    case 'f':c='\f';@+break;
    case 'v':c='\v';@+break;
    case 'r':c='\r';@+break;
    case 'a':c='\7';@+break;
    case '?':c='?';@+break;
    case 'x':
      if (xisdigit(*(id_first+1))) c=(int)(*(++id_first)-'0');
      else if (xisxdigit(*(id_first+1))) {
        ++id_first;
        c=toupper((int)*id_first)-'A'+10;
      }
      if (xisdigit(*(id_first+1))) c=16*c+(int)(*(++id_first)-'0');
      else if (xisxdigit(*(id_first+1))) {
        ++id_first;
        c=16*c+toupper((int)*id_first)-(int)'A'+10;
      }
      break;
    case '\\':c='\\';@+break;
    case '\'':c='\'';@+break;
    case '\"':c='\"';@+break;
    default: err_print("! Unrecognized escape sequence");
@.Unrecognized escape sequence@>
    }
  }@/
  /* at this point |c| should have been converted to its ASCII code number */
  app_repl(constant);
  if (c>=100) app_repl((int)'0'+c/100);
  if (c>=10) app_repl((int)'0'+(c/10)%10);
  app_repl((int)'0'+c%10);
  app_repl(constant);
}

@* Scanning a section.
The |scan_section| procedure starts when `\.{@@\ }' or `\.{@@*}' has been
sensed in the input, and it proceeds until the end of that section.  It
uses |section_count| to keep track of the current section number; with luck,
\.{CWEAVE} and \.{CTANGLE} will both assign the same numbers to sections.

The body of |scan_section| is a loop where we look for control codes
that are significant to \.{CTANGLE}: those
that delimit a definition, the \CEE/ part of a module, or a new module.

@c
static void
scan_section(void)
{
  name_pointer p; /* section name for the current section */
  text_pointer q; /* text for the current section */
  sixteen_bits a; /* token for left-hand side of definition */
  section_count++; @+ no_where=true;
  if (*(loc-1)=='*' && show_progress) { /* starred section */
    printf("*%d",(int)section_count); update_terminal();
  }
  next_control=ignore;
  while (true) {
    @<Skip ahead until |next_control| corresponds to \.{@@d}, \.{@@<},
      \.{@@\ } or the like@>@;
    if (next_control == definition) { /* \.{@@d} */
        @<Scan a definition@>@;
        continue;
    }
    if (next_control == begin_C) { /* \.{@@c} or \.{@@p} */
      p=name_dir; break;
    }
    if (next_control == section_name) { /* \.{@@<} or \.{@@(} */
      p=cur_section_name;
      @<If section is not being defined, |continue| @>@;
      break;
    }
    return; /* \.{@@\ } or \.{@@*} */
  }
  no_where=print_where=false;
  @<Scan the \CEE/ part of the current section@>@;
}

@ @<Predecl...@>=@+static void scan_section(void);

@ At the top of this loop, if |next_control==section_name|, the
section name has already been scanned (see |@<Get control code
and...@>|).  Thus, if we encounter |next_control==section_name| in the
skip-ahead process, we should likewise scan the section name, so later
processing will be the same in both cases.

@<Skip ahead until |next_control| ...@>=
while (next_control<definition)
      /* |definition| is the lowest of the ``significant'' codes */
  if((next_control=skip_ahead())==section_name){
    loc-=2; next_control=get_next();
  }

@ @<Scan a definition@>=
while ((next_control=get_next())=='\n'); /* allow newline before definition */
if (next_control!=identifier) {
  err_print("! Definition flushed, must start with identifier");
@.Definition flushed...@>
  continue;
}
store_id(a); /* append the lhs */
if (*loc!='(') { /* identifier must be separated from replacement text */
  app_repl(string); app_repl(' '); app_repl(string);
}
scan_repl(macro);
cur_text->text_link=macro;

@ If the section name is not followed by \.{=} or \.{+=}, no \CEE/
code is forthcoming: the section is being cited, not being
defined.  This use is illegal after the definition part of the
current section has started, except inside a comment, but
\.{CTANGLE} does not enforce this rule; it simply ignores the offending
section name and everything following it, up to the next significant
control code.

@<If section is not being defined, |continue| @>=
while ((next_control=get_next())=='+'); /* allow optional \.{+=} */
if (next_control!='=' && next_control!=eq_eq)
  continue;

@ @<Scan the \CEE/...@>=
@<Insert the section number into |tok_mem|@>@;
scan_repl(section_name); /* now |cur_text| points to the replacement text */
@<Update the data structure so that the replacement text is accessible@>@;

@ @<Insert the section number...@>=
store_two_bytes((sixteen_bits)(0150000+section_count));
  /* |0150000==0320*0400| */

@ @<Update the data...@>=
if (p==name_dir||p==NULL) { /* unnamed section, or bad section name */
  last_unnamed->text_link=cur_text-text_info; last_unnamed=cur_text;
}
else if (p->equiv==(void *)text_info) p->equiv=(void *)cur_text;
  /* first section of this name */
else {
  q=(text_pointer)p->equiv;
  while (q->text_link<section_flag)
    q=q->text_link+text_info; /* find end of list */
  q->text_link=cur_text-text_info;
}
cur_text->text_link=section_flag;
  /* mark this replacement text as a nonmacro */

@ @c
static void
phase_one(void) {
  phase=1;
  section_count=0;
  reset_input();
  skip_limbo();
  while (!input_has_ended) scan_section();
  check_complete();
}

@ @<Predec...@>=@+static void phase_one(void);

@ Only a small subset of the control codes is legal in limbo, so limbo
processing is straightforward.

@c
static void
skip_limbo(void)
{
  while (true) {
    if (loc>limit && get_line()==false) return;
    *(limit+1)='@@';
    while (*loc!='@@') loc++;
    if (loc++<=limit) {
      char c=*loc++;
      switch (ccode[(eight_bits)c]) {
        case new_section: return;
        case translit_code: @<Read in transliteration of a character@>@; break;
        case format_code: case '@@': break;
        case control_text: if (c=='q' || c=='Q') {
          while ((c=(char)skip_ahead())=='@@');
          if (*(loc-1)!='>')
            err_print("! Double @@ should be used in control text");
@.Double @@ should be used...@>
          break;
          } @=/* otherwise fall through */@>@;
        default: err_print("! Double @@ should be used in limbo");
@.Double @@ should be used...@>
      }
    }
  }
}

@ @<Predecl...@>=@+static void skip_limbo(void);

@ @<Read in transliteration of a character@>=
  while(xisspace(*loc)&&loc<limit) loc++;
  loc+=3;
  if (loc>limit || !xisxdigit(*(loc-3)) || !xisxdigit(*(loc-2)) @|
         || (*(loc-3)>='0' && *(loc-3)<='7') || !xisspace(*(loc-1)))
    err_print("! Improper hex number following @@l");
@.Improper hex number...@>
  else {
    unsigned int i;
    char *beg;
    sscanf(loc-3,"%x",&i);
    while(xisspace(*loc)&&loc<limit) loc++;
    beg=loc;
    while(loc<limit&&(xisalpha(*loc)||xisdigit(*loc)||isxalpha(*loc))) loc++;
    if (loc-beg>=translit_length)
      err_print("! Replacement string in @@l too long");
@.Replacement string in @@l...@>
    else{
      strncpy(translit[i-0200],beg,(size_t)(loc-beg));
      translit[i-0200][loc-beg]='\0';
    }
  }

@ Because on some systems the difference between two pointers is a |ptrdiff_t|
but not an |int|, we use \.{\%td} to print these quantities.

@c
void
print_stats(void) {
  puts("\nMemory usage statistics:");
  printf("%td names (out of %ld)\n",@^system dependencies@>
          (ptrdiff_t)(name_ptr-name_dir),(long)max_names);
  printf("%td replacement texts (out of %ld)\n",
          (ptrdiff_t)(text_ptr-text_info),(long)max_texts);
  printf("%td bytes (out of %ld)\n",
          (ptrdiff_t)(byte_ptr-byte_mem),(long)max_bytes);
  printf("%td tokens (out of %ld)\n",
          (ptrdiff_t)(tok_ptr-tok_mem),(long)max_toks);
}

@** Index.
Here is a cross-reference table for \.{CTANGLE}.
All sections in which an identifier is
used are listed with that identifier, except that reserved words are
indexed only when they appear in format definitions, and the appearances
of identifiers in section names are not indexed. Underlined entries
correspond to where the identifier was declared. Error messages and
a few other things like ``ASCII code dependencies'' are indexed here too.