syntax.c 75 KB
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/* GNU Emacs routines to deal with syntax tables; also word and list parsing.
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   Copyright (C) 1985, 87, 93, 94, 95, 1997 Free Software Foundation, Inc.
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This file is part of GNU Emacs.

GNU Emacs is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs; see the file COPYING.  If not, write to
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the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */
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#include <config.h>
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#include <ctype.h>
#include "lisp.h"
#include "commands.h"
#include "buffer.h"
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#include "charset.h"
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/* Make syntax table lookup grant data in gl_state.  */
#define SYNTAX_ENTRY_VIA_PROPERTY

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#include "syntax.h"
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#include "intervals.h"

/* We use these constants in place for comment-style and
   string-ender-char to distinguish  comments/strings started by
   comment_fence and string_fence codes.  */

#define ST_COMMENT_STYLE (256 + 1)
#define ST_STRING_STYLE (256 + 2)
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#include "category.h"
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Lisp_Object Qsyntax_table_p, Qsyntax_table, Qscan_error;
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int words_include_escapes;
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int parse_sexp_lookup_properties;
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/* Used as a temporary in SYNTAX_ENTRY and other macros in syntax.h,
   if not compiled with GCC.  No need to mark it, since it is used
   only very temporarily.  */
Lisp_Object syntax_temp;

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/* This is the internal form of the parse state used in parse-partial-sexp.  */

struct lisp_parse_state
  {
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    int depth;		/* Depth at end of parsing.  */
    int instring;	/* -1 if not within string, else desired terminator.  */
    int incomment;	/* Nonzero if within a comment at end of parsing.  */
    int comstyle;	/* comment style a=0, or b=1, or ST_COMMENT_STYLE.  */
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    int quoted;		/* Nonzero if just after an escape char at end of parsing */
    int thislevelstart;	/* Char number of most recent start-of-expression at current level */
    int prevlevelstart; /* Char number of start of containing expression */
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    int location;	/* Char number at which parsing stopped.  */
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    int mindepth;	/* Minimum depth seen while scanning.  */
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    int comstr_start;	/* Position just after last comment/string starter.  */
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  };

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/* These variables are a cache for finding the start of a defun.
   find_start_pos is the place for which the defun start was found.
   find_start_value is the defun start position found for it.
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   find_start_value_byte is the corresponding byte position.
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   find_start_buffer is the buffer it was found in.
   find_start_begv is the BEGV value when it was found.
   find_start_modiff is the value of MODIFF when it was found.  */

static int find_start_pos;
static int find_start_value;
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static int find_start_value_byte;
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static struct buffer *find_start_buffer;
static int find_start_begv;
static int find_start_modiff;
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static int find_defun_start P_ ((int, int));
static int back_comment P_ ((int, int, int, int, int *, int *));
static int char_quoted P_ ((int, int));
static Lisp_Object skip_chars P_ ((int, int, Lisp_Object, Lisp_Object));
static Lisp_Object scan_lists P_ ((int, int, int, int));
static void scan_sexps_forward P_ ((struct lisp_parse_state *,
				    int, int, int, int,
				    int, Lisp_Object, int));
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struct gl_state_s gl_state;		/* Global state of syntax parser.  */

INTERVAL interval_of ();
#define INTERVALS_AT_ONCE 10		/* 1 + max-number of intervals
					   to scan to property-change.  */

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/* Update gl_state to an appropriate interval which contains CHARPOS.  The
   sign of COUNT give the relative position of CHARPOS wrt the previously
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   valid interval.  If INIT, only [be]_property fields of gl_state are
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   valid at start, the rest is filled basing on OBJECT.
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   `gl_state.*_i' are the intervals, and CHARPOS is further in the search
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   direction than the intervals - or in an interval.  We update the
   current syntax-table basing on the property of this interval, and
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   update the interval to start further than CHARPOS - or be
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   NULL_INTERVAL.  We also update lim_property to be the next value of
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   charpos to call this subroutine again - or be before/after the
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   start/end of OBJECT.  */

void
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update_syntax_table (charpos, count, init, object)
     int charpos, count, init;
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     Lisp_Object object;
{
  Lisp_Object tmp_table;
  int cnt = 0, doing_extra = 0, invalidate = 1;
  INTERVAL i, oldi;

  if (init)
    {
      gl_state.start = gl_state.b_property;
      gl_state.stop = gl_state.e_property;
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      gl_state.forward_i = interval_of (charpos, object);
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      i = gl_state.backward_i = gl_state.forward_i;
      gl_state.left_ok = gl_state.right_ok = 1;
      invalidate = 0;
      if (NULL_INTERVAL_P (i))
	return;
      gl_state.b_property = i->position - 1;
      gl_state.e_property = INTERVAL_LAST_POS (i);
      goto update;
    }
  oldi = i = count > 0 ? gl_state.forward_i : gl_state.backward_i;

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  /* We are guarantied to be called with CHARPOS either in i,
     or further off.  */
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  if (NULL_INTERVAL_P (i))
    error ("Error in syntax_table logic for to-the-end intervals");
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  else if (charpos < i->position)		/* Move left.  */
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    {
      if (count > 0)
	error ("Error in syntax_table logic for intervals <-.");
      /* Update the interval.  */
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      i = update_interval (i, charpos);
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      if (oldi->position != INTERVAL_LAST_POS (i))
	{
	  invalidate = 0;
	  gl_state.right_ok = 1;	/* Invalidate the other end.  */
	  gl_state.forward_i = i;
	  gl_state.e_property = INTERVAL_LAST_POS (i);
	}
    } 
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  else if (charpos >= INTERVAL_LAST_POS (i)) /* Move right.  */
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    {
      if (count < 0)
	error ("Error in syntax_table logic for intervals ->.");
      /* Update the interval.  */
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      i = update_interval (i, charpos);
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      if (i->position != INTERVAL_LAST_POS (oldi))
	{
	  invalidate = 0;
	  gl_state.left_ok = 1;		/* Invalidate the other end.  */
	  gl_state.backward_i = i;
	  gl_state.b_property = i->position - 1;
	}
    }
  else if (count > 0 ? gl_state.right_ok : gl_state.left_ok)
    {
      /* We do not need to recalculate tmp_table.  */
      tmp_table = gl_state.old_prop;
    }

  update:
  tmp_table = textget (i->plist, Qsyntax_table);

  if (invalidate)
    invalidate = !EQ (tmp_table, gl_state.old_prop); /* Need to invalidate? */
      
  if (invalidate)			/* Did not get to adjacent interval.  */
    {					/* with the same table => */
					/* invalidate the old range.  */
      if (count > 0)
	{
	  gl_state.backward_i = i;
	  gl_state.left_ok = 1;		/* Invalidate the other end.  */
	  gl_state.b_property = i->position - 1;
	} 
      else 
	{
	  gl_state.forward_i = i;	
	  gl_state.right_ok = 1;	/* Invalidate the other end.  */
	  gl_state.e_property = INTERVAL_LAST_POS (i);
	}
    }
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  gl_state.current_syntax_table = tmp_table;
  gl_state.old_prop = tmp_table;
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  if (EQ (Fsyntax_table_p (tmp_table), Qt))
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    {
      gl_state.use_global = 0;
    } 
  else if (CONSP (tmp_table))
    {
      gl_state.use_global = 1;
      gl_state.global_code = tmp_table;
    }
  else 
    {
      gl_state.use_global = 0;
      gl_state.current_syntax_table = current_buffer->syntax_table;
    }

  while (!NULL_INTERVAL_P (i))
    {
      if (cnt && !EQ (tmp_table, textget (i->plist, Qsyntax_table)))
	{
	  if (count > 0)
	    gl_state.right_ok = 0;
	  else 
	    gl_state.left_ok = 0;
	  break;	  
	}
      else if (cnt == INTERVALS_AT_ONCE) 
	{
	  if (count > 0)
	    gl_state.right_ok = 1;
	  else 
	    gl_state.left_ok = 1;
	  break;
	}
      cnt++;
      i = count > 0 ? next_interval (i) : previous_interval (i);
    }
  if (NULL_INTERVAL_P (i)) 
    {					/* This property goes to the end.  */
      if (count > 0)
	gl_state.e_property = gl_state.stop;
      else
	gl_state.b_property = gl_state.start;
    } 
  else 
    {
      if (count > 0) 
	{
	  gl_state.e_property = i->position;
	  gl_state.forward_i = i;
	}
      else 
	{
	  gl_state.b_property = i->position + LENGTH (i) - 1;
	  gl_state.backward_i = i;
	}
    }    
}

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/* Returns TRUE if char at CHARPOS is quoted.
   Global syntax-table data should be set up already to be good at CHARPOS
   or after.  On return global syntax data is good for lookup at CHARPOS. */
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static int
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char_quoted (charpos, bytepos)
     register int charpos, bytepos;
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{
  register enum syntaxcode code;
  register int beg = BEGV;
  register int quoted = 0;
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  int orig = charpos;

  DEC_BOTH (charpos, bytepos);
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  while (bytepos >= beg)
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    {
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      UPDATE_SYNTAX_TABLE_BACKWARD (charpos);
      code = SYNTAX (FETCH_CHAR (bytepos));
      if (! (code == Scharquote || code == Sescape))
	break;

      DEC_BOTH (charpos, bytepos);
      quoted = !quoted;
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    }
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  UPDATE_SYNTAX_TABLE (orig);
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  return quoted;
}
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/* Return the bytepos one character after BYTEPOS.
   We assume that BYTEPOS is not at the end of the buffer.  */

INLINE int
inc_bytepos (bytepos)
     int bytepos;
{
  INC_POS (bytepos);
  return bytepos;
}

/* Return the bytepos one character before BYTEPOS.
   We assume that BYTEPOS is not at the start of the buffer.  */

INLINE int
dec_bytepos (bytepos)
     int bytepos;
{
  DEC_POS (bytepos);
  return bytepos;
}
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/* Find a defun-start that is the last one before POS (or nearly the last).
   We record what we find, so that another call in the same area
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   can return the same value right away.  

   There is no promise at which position the global syntax data is
   valid on return from the subroutine, so the caller should explicitly
   update the global data.  */
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static int
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find_defun_start (pos, pos_byte)
     int pos, pos_byte;
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{
  int tem;
  int shortage;
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  int opoint = PT, opoint_byte = PT_BYTE;
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  /* Use previous finding, if it's valid and applies to this inquiry.  */
  if (current_buffer == find_start_buffer
      /* Reuse the defun-start even if POS is a little farther on.
	 POS might be in the next defun, but that's ok.
	 Our value may not be the best possible, but will still be usable.  */
      && pos <= find_start_pos + 1000
      && pos >= find_start_value
      && BEGV == find_start_begv
      && MODIFF == find_start_modiff)
    return find_start_value;

  /* Back up to start of line.  */
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  scan_newline (pos, pos_byte, BEGV, BEGV_BYTE, -1, 1);
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  /* We optimize syntax-table lookup for rare updates.  Thus we accept
     only those `^\s(' which are good in global _and_ text-property
     syntax-tables.  */
  gl_state.current_syntax_table = current_buffer->syntax_table;
  gl_state.use_global = 0;
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  while (PT > BEGV)
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    {
      /* Open-paren at start of line means we found our defun-start.  */
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      if (SYNTAX (FETCH_CHAR (PT_BYTE)) == Sopen)
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	{
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	  SETUP_SYNTAX_TABLE (PT + 1, -1);	/* Try again... */
	  if (SYNTAX (FETCH_CHAR (PT_BYTE)) == Sopen)
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	    break;
	  /* Now fallback to the default value.  */
	  gl_state.current_syntax_table = current_buffer->syntax_table;
	  gl_state.use_global = 0;
	}
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      /* Move to beg of previous line.  */
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      scan_newline (PT, PT_BYTE, BEGV, BEGV_BYTE, -2, 1);
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    }

  /* Record what we found, for the next try.  */
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  find_start_value = PT;
  find_start_value_byte = PT_BYTE;
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  find_start_buffer = current_buffer;
  find_start_modiff = MODIFF;
  find_start_begv = BEGV;
  find_start_pos = pos;

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  TEMP_SET_PT_BOTH (opoint, opoint_byte);

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  return find_start_value;
}

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/* Checks whether charpos FROM is at the end of a comment.
   FROM_BYTE is the bytepos corresponding to FROM.
   Do not move back before STOP.

   Return a positive value if we find a comment ending at FROM/FROM_BYTE;
   return -1 otherwise.

   If successful, store the charpos of the comment's beginning
   into *CHARPOS_PTR, and the bytepos into *BYTEPOS_PTR.
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   Global syntax data remains valid for backward search starting at
   the returned value (or at FROM, if the search was not successful).  */
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static int
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back_comment (from, from_byte, stop, comstyle, charpos_ptr, bytepos_ptr)
     int from, from_byte, stop;
     int comstyle;
     int *charpos_ptr, *bytepos_ptr;
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{
  /* Look back, counting the parity of string-quotes,
     and recording the comment-starters seen.
     When we reach a safe place, assume that's not in a string;
     then step the main scan to the earliest comment-starter seen
     an even number of string quotes away from the safe place.

     OFROM[I] is position of the earliest comment-starter seen
     which is I+2X quotes from the comment-end.
     PARITY is current parity of quotes from the comment end.  */
  int parity = 0;
  int my_stringend = 0;
  int string_lossage = 0;
  int comment_end = from;
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  int comment_end_byte = from_byte;
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  int comstart_pos = 0;
  int comstart_parity = 0;
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  int comstart_byte;
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  int scanstart = from - 1;
  register enum syntaxcode code;
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  int c;
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  /* At beginning of range to scan, we're outside of strings;
     that determines quote parity to the comment-end.  */
  while (from != stop)
    {
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      int temp_byte;

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      /* Move back and examine a character.  */
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      DEC_BOTH (from, from_byte);
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      UPDATE_SYNTAX_TABLE_BACKWARD (from);

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      c = FETCH_CHAR (from_byte);
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      code = SYNTAX (c);

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      /* If this char is the second of a 2-char comment end sequence,
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	 back up and give the pair the appropriate syntax.  */
      if (from > stop && SYNTAX_COMEND_SECOND (c)
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	  && (temp_byte = dec_bytepos (from_byte),
	      SYNTAX_COMEND_FIRST (FETCH_CHAR (temp_byte))))
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	{
	  code = Sendcomment;
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	  DEC_BOTH (from, from_byte);
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	  /* This is apparently the best we can do: */
	  UPDATE_SYNTAX_TABLE_BACKWARD (from);
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	  c = FETCH_CHAR (from_byte);
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	}
			
      /* If this char starts a 2-char comment start sequence,
	 treat it like a 1-char comment starter.  */
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      if (from < scanstart && SYNTAX_COMSTART_FIRST (c)
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	  && (temp_byte = inc_bytepos (from_byte),
	      (SYNTAX_COMSTART_SECOND (FETCH_CHAR (temp_byte))
	       && comstyle == SYNTAX_COMMENT_STYLE (FETCH_CHAR (temp_byte)))))
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	code = Scomment;
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      /* Ignore escaped characters, except comment-enders.  */
      if (code != Sendcomment && char_quoted (from, from_byte))
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	continue;

      /* Track parity of quotes.  */
      if (code == Sstring)
	{
	  parity ^= 1;
	  if (my_stringend == 0)
	    my_stringend = c;
	  /* If we have two kinds of string delimiters.
	     There's no way to grok this scanning backwards.  */
	  else if (my_stringend != c)
	    string_lossage = 1;
	}

      if (code == Sstring_fence || code == Scomment_fence)
	{
	  parity ^= 1;
	  if (my_stringend == 0)
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	    my_stringend
	      = code == Sstring_fence ? ST_STRING_STYLE : ST_COMMENT_STYLE;
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	  /* If we have two kinds of string delimiters.
	     There's no way to grok this scanning backwards.  */
	  else if (my_stringend != (code == Sstring_fence 
				    ? ST_STRING_STYLE : ST_COMMENT_STYLE))
	    string_lossage = 1;
	}

      /* Record comment-starters according to that
	 quote-parity to the comment-end.  */
      if (code == Scomment)
	{
	  comstart_parity = parity;
	  comstart_pos = from;
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	  comstart_byte = from_byte;
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	}

      /* If we find another earlier comment-ender,
	 any comment-starts earlier than that don't count
	 (because they go with the earlier comment-ender).  */
      if (code == Sendcomment
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	  && SYNTAX_COMMENT_STYLE (FETCH_CHAR (from_byte)) == comstyle)
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	break;

      /* Assume a defun-start point is outside of strings.  */
      if (code == Sopen
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	  && (from == stop
	      || (temp_byte = dec_bytepos (from_byte),
		  FETCH_CHAR (temp_byte) == '\n')))
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	break;
    }

  if (comstart_pos == 0)
    {
      from = comment_end;
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      from_byte = comment_end_byte;
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      UPDATE_SYNTAX_TABLE_FORWARD (comment_end - 1);
    }
  /* If the earliest comment starter
     is followed by uniform paired string quotes or none,
     we know it can't be inside a string
     since if it were then the comment ender would be inside one.
     So it does start a comment.  Skip back to it.  */
  else if (comstart_parity == 0 && !string_lossage) 
    {
      from = comstart_pos;
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      from_byte = comstart_byte;
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      /* Globals are correct now.  */
    }
  else
    {
      /* We had two kinds of string delimiters mixed up
	 together.  Decode this going forwards.
	 Scan fwd from the previous comment ender
	 to the one in question; this records where we
	 last passed a comment starter.  */
      struct lisp_parse_state state;
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      scan_sexps_forward (&state,
			  find_defun_start (comment_end, comment_end_byte),
			  find_start_value_byte,
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			  comment_end - 1, -10000, 0, Qnil, 0);
      if (state.incomment)
	{
	  /* scan_sexps_forward changed the direction of search in
	     global variables, so we need to update it completely.  */
	  
	  from = state.comstr_start;
	}
      else
	{
	  from = comment_end;	  
	}
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      from_byte = CHAR_TO_BYTE (from);
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      UPDATE_SYNTAX_TABLE_FORWARD (from - 1);
    }
    
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  *charpos_ptr = from;
  *bytepos_ptr = from_byte;

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  return from;
}

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DEFUN ("syntax-table-p", Fsyntax_table_p, Ssyntax_table_p, 1, 1, 0,
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  "Return t if OBJECT is a syntax table.\n\
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Currently, any char-table counts as a syntax table.")
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  (object)
     Lisp_Object object;
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{
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  if (CHAR_TABLE_P (object)
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      && EQ (XCHAR_TABLE (object)->purpose, Qsyntax_table))
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    return Qt;
  return Qnil;
}

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static void
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check_syntax_table (obj)
     Lisp_Object obj;
{
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  if (!(CHAR_TABLE_P (obj)
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	&& EQ (XCHAR_TABLE (obj)->purpose, Qsyntax_table)))
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    wrong_type_argument (Qsyntax_table_p, obj);
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}   

DEFUN ("syntax-table", Fsyntax_table, Ssyntax_table, 0, 0, 0,
  "Return the current syntax table.\n\
This is the one specified by the current buffer.")
  ()
{
  return current_buffer->syntax_table;
}

DEFUN ("standard-syntax-table", Fstandard_syntax_table,
   Sstandard_syntax_table, 0, 0, 0,
  "Return the standard syntax table.\n\
This is the one used for new buffers.")
  ()
{
  return Vstandard_syntax_table;
}

DEFUN ("copy-syntax-table", Fcopy_syntax_table, Scopy_syntax_table, 0, 1, 0,
  "Construct a new syntax table and return it.\n\
It is a copy of the TABLE, which defaults to the standard syntax table.")
  (table)
     Lisp_Object table;
{
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  Lisp_Object copy;

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  if (!NILP (table))
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    check_syntax_table (table);
  else
    table = Vstandard_syntax_table;

  copy = Fcopy_sequence (table);
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  /* Only the standard syntax table should have a default element.
     Other syntax tables should inherit from parents instead.  */
  XCHAR_TABLE (copy)->defalt = Qnil;

  /* Copied syntax tables should all have parents.
     If we copied one with no parent, such as the standard syntax table,
     use the standard syntax table as the copy's parent.  */
  if (NILP (XCHAR_TABLE (copy)->parent))
    Fset_char_table_parent (copy, Vstandard_syntax_table);
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  return copy;
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}

DEFUN ("set-syntax-table", Fset_syntax_table, Sset_syntax_table, 1, 1, 0,
  "Select a new syntax table for the current buffer.\n\
One argument, a syntax table.")
  (table)
     Lisp_Object table;
{
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  check_syntax_table (table);
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  current_buffer->syntax_table = table;
  /* Indicate that this buffer now has a specified syntax table.  */
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  current_buffer->local_var_flags
    |= XFASTINT (buffer_local_flags.syntax_table);
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  return table;
}

/* Convert a letter which signifies a syntax code
 into the code it signifies.
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 This is used by modify-syntax-entry, and other things.  */
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unsigned char syntax_spec_code[0400] =
  { 0377, 0377, 0377, 0377, 0377, 0377, 0377, 0377,
    0377, 0377, 0377, 0377, 0377, 0377, 0377, 0377,
    0377, 0377, 0377, 0377, 0377, 0377, 0377, 0377,
    0377, 0377, 0377, 0377, 0377, 0377, 0377, 0377,
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    (char) Swhitespace, (char) Scomment_fence, (char) Sstring, 0377,
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        (char) Smath, 0377, 0377, (char) Squote,
    (char) Sopen, (char) Sclose, 0377, 0377,
	0377, (char) Swhitespace, (char) Spunct, (char) Scharquote,
    0377, 0377, 0377, 0377, 0377, 0377, 0377, 0377,
    0377, 0377, 0377, 0377,
	(char) Scomment, 0377, (char) Sendcomment, 0377,
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    (char) Sinherit, 0377, 0377, 0377, 0377, 0377, 0377, 0377,   /* @, A ... */
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    0377, 0377, 0377, 0377, 0377, 0377, 0377, 0377,
    0377, 0377, 0377, 0377, 0377, 0377, 0377, (char) Sword,
    0377, 0377, 0377, 0377, (char) Sescape, 0377, 0377, (char) Ssymbol,
    0377, 0377, 0377, 0377, 0377, 0377, 0377, 0377,   /* `, a, ... */
    0377, 0377, 0377, 0377, 0377, 0377, 0377, 0377,
    0377, 0377, 0377, 0377, 0377, 0377, 0377, (char) Sword,
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    0377, 0377, 0377, 0377, (char) Sstring_fence, 0377, 0377, 0377
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  };

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/* Indexed by syntax code, give the letter that describes it.  */
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char syntax_code_spec[16] =
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  {
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    ' ', '.', 'w', '_', '(', ')', '\'', '\"', '$', '\\', '/', '<', '>', '@',
    '!', '|'
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  };
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/* Indexed by syntax code, give the object (cons of syntax code and
   nil) to be stored in syntax table.  Since these objects can be
   shared among syntax tables, we generate them in advance.  By
   sharing objects, the function `describe-syntax' can give a more
   compact listing.  */
static Lisp_Object Vsyntax_code_object;

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/* Look up the value for CHARACTER in syntax table TABLE's parent
   and its parents.  SYNTAX_ENTRY calls this, when TABLE itself has nil
   for CHARACTER.  It's actually used only when not compiled with GCC.  */

Lisp_Object
syntax_parent_lookup (table, character)
     Lisp_Object table;
     int character;
{
  Lisp_Object value;

  while (1)
    {
      table = XCHAR_TABLE (table)->parent;
      if (NILP (table))
	return Qnil;

      value = XCHAR_TABLE (table)->contents[character];
      if (!NILP (value))
	return value;
    }
}

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DEFUN ("char-syntax", Fchar_syntax, Schar_syntax, 1, 1, 0,
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  "Return the syntax code of CHARACTER, described by a character.\n\
For example, if CHARACTER is a word constituent,\n\
the character `w' is returned.\n\
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The characters that correspond to various syntax codes\n\
are listed in the documentation of `modify-syntax-entry'.")
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  (character)
     Lisp_Object character;
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{
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  int char_int;
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  gl_state.current_syntax_table = current_buffer->syntax_table;

  gl_state.use_global = 0;
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  CHECK_NUMBER (character, 0);
  char_int = XINT (character);
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  return make_number (syntax_code_spec[(int) SYNTAX (char_int)]);
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}

DEFUN ("matching-paren", Fmatching_paren, Smatching_paren, 1, 1, 0,
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  "Return the matching parenthesis of CHARACTER, or nil if none.")
  (character)
     Lisp_Object character;
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{
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  int char_int, code;
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  gl_state.current_syntax_table = current_buffer->syntax_table;
  gl_state.use_global = 0;
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  CHECK_NUMBER (character, 0);
  char_int = XINT (character);
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  code = SYNTAX (char_int);
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  if (code == Sopen || code == Sclose)
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    return SYNTAX_MATCH (char_int);
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  return Qnil;
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}

/* This comment supplies the doc string for modify-syntax-entry,
   for make-docfile to see.  We cannot put this in the real DEFUN
   due to limits in the Unix cpp.

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DEFUN ("modify-syntax-entry", foo, bar, 2, 3, 0,
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  "Set syntax for character CHAR according to string S.\n\
The syntax is changed only for table TABLE, which defaults to\n\
 the current buffer's syntax table.\n\
The first character of S should be one of the following:\n\
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  Space or -  whitespace syntax.    w   word constituent.\n\
  _           symbol constituent.   .   punctuation.\n\
  (           open-parenthesis.     )   close-parenthesis.\n\
  \"           string quote.         \\   escape.\n\
  $           paired delimiter.     '   expression quote or prefix operator.\n\
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  <           comment starter.      >   comment ender.\n\
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  /           character-quote.      @   inherit from `standard-syntax-table'.\n\
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\n\
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Only single-character comment start and end sequences are represented thus.\n\
Two-character sequences are represented as described below.\n\
The second character of S is the matching parenthesis,\n\
 used only if the first character is `(' or `)'.\n\
Any additional characters are flags.\n\
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Defined flags are the characters 1, 2, 3, 4, b, and p.\n\
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 1 means CHAR is the start of a two-char comment start sequence.\n\
 2 means CHAR is the second character of such a sequence.\n\
 3 means CHAR is the start of a two-char comment end sequence.\n\
 4 means CHAR is the second character of such a sequence.\n\
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\n\
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There can be up to two orthogonal comment sequences.  This is to support\n\
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language modes such as C++.  By default, all comment sequences are of style\n\
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a, but you can set the comment sequence style to b (on the second character\n\
of a comment-start, or the first character of a comment-end sequence) using\n\
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this flag:\n\
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 b means CHAR is part of comment sequence b.\n\
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\n\
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 p means CHAR is a prefix character for `backward-prefix-chars';\n\
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   such characters are treated as whitespace when they occur\n\
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   between expressions.")
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  (char, s, table)
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*/

DEFUN ("modify-syntax-entry", Fmodify_syntax_entry, Smodify_syntax_entry, 2, 3, 
  /* I really don't know why this is interactive
     help-form should at least be made useful whilst reading the second arg
   */
  "cSet syntax for character: \nsSet syntax for %s to: ",
  0 /* See immediately above */)
  (c, newentry, syntax_table)
     Lisp_Object c, newentry, syntax_table;
{
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  register unsigned char *p;
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  register enum syntaxcode code;
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  int val;
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  Lisp_Object match;
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  CHECK_NUMBER (c, 0);
  CHECK_STRING (newentry, 1);
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  if (NILP (syntax_table))
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    syntax_table = current_buffer->syntax_table;
  else
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    check_syntax_table (syntax_table);
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  p = XSTRING (newentry)->data;
  code = (enum syntaxcode) syntax_spec_code[*p++];
  if (((int) code & 0377) == 0377)
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    error ("invalid syntax description letter: %c", p[-1]);
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  if (code == Sinherit)
    {
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      SET_RAW_SYNTAX_ENTRY (syntax_table, XINT (c), Qnil);
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      return Qnil;
    }

  if (*p)
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    {
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      int len;
      int character = STRING_CHAR_AND_LENGTH (p, XSTRING (newentry)->size - 1,
					      len);
      XSETINT (match, character);
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      if (XFASTINT (match) == ' ')
	match = Qnil;
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      p += len;
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    }
  else
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    match = Qnil;
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  val = (int) code;
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  while (*p)
    switch (*p++)
      {
      case '1':
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	val |= 1 << 16;
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	break;

      case '2':
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	val |= 1 << 17;
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	break;

      case '3':
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	val |= 1 << 18;
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	break;

      case '4':
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	val |= 1 << 19;
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	break;

      case 'p':
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	val |= 1 << 20;
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	break;
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      case 'b':
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	val |= 1 << 21;
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	break;
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      }
	
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  if (val < XVECTOR (Vsyntax_code_object)->size && NILP (match))
    newentry = XVECTOR (Vsyntax_code_object)->contents[val];
  else
    /* Since we can't use a shared object, let's make a new one.  */
    newentry = Fcons (make_number (val), match);
    
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  SET_RAW_SYNTAX_ENTRY (syntax_table, XINT (c), newentry);
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  return Qnil;
}

/* Dump syntax table to buffer in human-readable format */

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static void
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describe_syntax (value)
    Lisp_Object value;
{
  register enum syntaxcode code;
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  char desc, match, start1, start2, end1, end2, prefix, comstyle;
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  char str[2];
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  Lisp_Object first, match_lisp;
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  Findent_to (make_number (16), make_number (1));

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  if (NILP (value))
    {
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      insert_string ("default\n");
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      return;
    }

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  if (CHAR_TABLE_P (value))
    {
      insert_string ("deeper char-table ...\n");
      return;
    }

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  if (!CONSP (value))
    {
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      insert_string ("invalid\n");
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      return;
    }

  first = XCONS (value)->car;
  match_lisp = XCONS (value)->cdr;

  if (!INTEGERP (first) || !(NILP (match_lisp) || INTEGERP (match_lisp)))
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    {
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      insert_string ("invalid\n");
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      return;
    }

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  code = (enum syntaxcode) (XINT (first) & 0377);
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  start1 = (XINT (first) >> 16) & 1;
  start2 = (XINT (first) >> 17) & 1;
  end1 = (XINT (first) >> 18) & 1;
  end2 = (XINT (first) >> 19) & 1;
  prefix = (XINT (first) >> 20) & 1;
  comstyle = (XINT (first) >> 21) & 1;
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  if ((int) code < 0 || (int) code >= (int) Smax)
    {
      insert_string ("invalid");
      return;
    }
  desc = syntax_code_spec[(int) code];

  str[0] = desc, str[1] = 0;
  insert (str, 1);

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  if (NILP (match_lisp))
    insert (" ", 1);
  else
    insert_char (XINT (match_lisp));
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  if (start1)
    insert ("1", 1);
  if (start2)
    insert ("2", 1);

  if (end1)
    insert ("3", 1);
  if (end2)
    insert ("4", 1);

  if (prefix)
    insert ("p", 1);
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  if (comstyle)
    insert ("b", 1);
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  insert_string ("\twhich means: ");

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  switch (SWITCH_ENUM_CAST (code))
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    {
    case Swhitespace:
      insert_string ("whitespace"); break;
    case Spunct:
      insert_string ("punctuation"); break;
    case Sword:
      insert_string ("word"); break;
    case Ssymbol:
      insert_string ("symbol"); break;
    case Sopen:
      insert_string ("open"); break;
    case Sclose:
      insert_string ("close"); break;
    case Squote:
      insert_string ("quote"); break;
    case Sstring:
      insert_string ("string"); break;
    case Smath:
      insert_string ("math"); break;
    case Sescape:
      insert_string ("escape"); break;
    case Scharquote:
      insert_string ("charquote"); break;
    case Scomment:
      insert_string ("comment"); break;
    case Sendcomment:
      insert_string ("endcomment"); break;
    default:
      insert_string ("invalid");
      return;
    }

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  if (!NILP (match_lisp))
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    {
      insert_string (", matches ");
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      insert_char (XINT (match_lisp));
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    }

  if (start1)
    insert_string (",\n\t  is the first character of a comment-start sequence");
  if (start2)
    insert_string (",\n\t  is the second character of a comment-start sequence");

  if (end1)
    insert_string (",\n\t  is the first character of a comment-end sequence");
  if (end2)
    insert_string (",\n\t  is the second character of a comment-end sequence");
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  if (comstyle)
    insert_string (" (comment style b)");

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  if (prefix)
    insert_string (",\n\t  is a prefix character for `backward-prefix-chars'");

  insert_string ("\n");
}

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static Lisp_Object
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describe_syntax_1 (vector)
     Lisp_Object vector;
{
  struct buffer *old = current_buffer;
  set_buffer_internal (XBUFFER (Vstandard_output));
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  describe_vector (vector, Qnil, describe_syntax, 0, Qnil, Qnil, (int *) 0, 0);
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  while (! NILP (XCHAR_TABLE (vector)->parent))
    {
      vector = XCHAR_TABLE (vector)->parent;
      insert_string ("\nThe parent syntax table is:");
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      describe_vector (vector, Qnil, describe_syntax, 0, Qnil, Qnil,
		       (int *) 0, 0);
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    }
	
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  call0 (intern ("help-mode"));
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  set_buffer_internal (old);
  return Qnil;
}

DEFUN ("describe-syntax", Fdescribe_syntax, Sdescribe_syntax, 0, 0, "",
  "Describe the syntax specifications in the syntax table.\n\
The descriptions are inserted in a buffer, which is then displayed.")
  ()
{
  internal_with_output_to_temp_buffer
     ("*Help*", describe_syntax_1, current_buffer->syntax_table);

  return Qnil;
}

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int parse_sexp_ignore_comments;

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/* Return the position across COUNT words from FROM.
   If that many words cannot be found before the end of the buffer, return 0.
   COUNT negative means scan backward and stop at word beginning.  */

scan_words (from, count)
     register int from, count;
{
  register int beg = BEGV;
  register int end = ZV;
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  register int from_byte = CHAR_TO_BYTE (from);
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  register enum syntaxcode code;
  int ch0, ch1;
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  immediate_quit = 1;
  QUIT;

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  SETUP_SYNTAX_TABLE (from, count);

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  while (count > 0)
    {
      while (1)
	{
	  if (from == end)
	    {
	      immediate_quit = 0;
	      return 0;
	    }
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	  UPDATE_SYNTAX_TABLE_FORWARD (from);
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	  ch0 = FETCH_CHAR (from_byte);
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	  code = SYNTAX (ch0);
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	  INC_BOTH (from, from_byte);
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	  if (words_include_escapes
	      && (code == Sescape || code == Scharquote))
	    break;
	  if (code == Sword)
	    break;
	}
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      /* Now CH0 is a character which begins a word and FROM is the
         position of the next character.  */
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      while (1)
	{
	  if (from == end) break;
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	  UPDATE_SYNTAX_TABLE_FORWARD (from);
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	  ch1 = FETCH_CHAR (from_byte);
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	  code = SYNTAX (ch1);
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	  if (!(words_include_escapes
		&& (code == Sescape || code == Scharquote)))
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	    if (code != Sword || WORD_BOUNDARY_P (ch0, ch1))
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	      break;
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	  INC_BOTH (from, from_byte);
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	  ch0 = ch1;
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	}
      count--;
    }
  while (count < 0)
    {
      while (1)
	{
	  if (from == beg)
	    {
	      immediate_quit = 0;
	      return 0;
	    }
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	  DEC_BOTH (from, from_byte);
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	  UPDATE_SYNTAX_TABLE_BACKWARD (from);
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	  ch1 = FETCH_CHAR (from_byte);
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	  code = SYNTAX (ch1);
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	  if (words_include_escapes
	      && (code == Sescape || code == Scharquote))
	    break;
	  if (code == Sword)
	    break;
	}
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      /* Now CH1 is a character which ends a word and FROM is the
         position of it.  */
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      while (1)
	{
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	  int temp_byte;

	  if (from == beg)
	    break;
	  temp_byte = dec_bytepos (from_byte);
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	  UPDATE_SYNTAX_TABLE_BACKWARD (from);
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	  ch0 = FETCH_CHAR (temp_byte);
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	  code = SYNTAX (ch0);
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	  if (!(words_include_escapes
		&& (code == Sescape || code == Scharquote)))
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	    if (code != Sword || WORD_BOUNDARY_P (ch0, ch1))
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	      break;
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	  DEC_BOTH (from, from_byte);
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	  ch1 = ch0;
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	}
      count++;
    }

  immediate_quit = 0;

  return from;
}

DEFUN ("forward-word", Fforward_word, Sforward_word, 1, 1, "p",
  "Move point forward ARG words (backward if ARG is negative).\n\
Normally returns t.\n\
If an edge of the buffer is reached, point is left there\n\
and nil is returned.")
  (count)
     Lisp_Object count;
{
  int val;
  CHECK_NUMBER (count, 0);

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  if (!(val = scan_words (PT, XINT (count))))
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    {
      SET_PT (XINT (count) > 0 ? ZV : BEGV);
      return Qnil;
    }
  SET_PT (val);
  return Qt;
}

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Lisp_Object skip_chars ();

DEFUN ("skip-chars-forward", Fskip_chars_forward, Sskip_chars_forward, 1, 2, 0,
  "Move point forward, stopping before a char not in STRING, or at pos LIM.\n\
STRING is like the inside of a `[...]' in a regular expression\n\
except that `]' is never special and `\\' quotes `^', `-' or `\\'.\n\
Thus, with arg \"a-zA-Z\", this skips letters stopping before first nonletter.\n\
With arg \"^a-zA-Z\", skips nonletters stopping before first letter.\n\
Returns the distance traveled, either zero or positive.")
  (string, lim)
     Lisp_Object string, lim;
{
  return skip_chars (1, 0, string, lim);
}

DEFUN ("skip-chars-backward", Fskip_chars_backward, Sskip_chars_backward, 1, 2, 0,
  "Move point backward, stopping after a char not in STRING, or at pos LIM.\n\
See `skip-chars-forward' for details.\n\
Returns the distance traveled, either zero or negative.")
  (string, lim)
     Lisp_Object string, lim;
{
  return skip_chars (0, 0, string, lim);
}

DEFUN ("skip-syntax-forward", Fskip_syntax_forward, Sskip_syntax_forward, 1, 2, 0,
  "Move point forward across chars in specified syntax classes.\n\
SYNTAX is a string of syntax code characters.\n\
Stop before a char whose syntax is not in SYNTAX, or at position LIM.\n\
If SYNTAX starts with ^, skip characters whose syntax is NOT in SYNTAX.\n\
This function returns the distance traveled, either zero or positive.")
  (syntax, lim)
     Lisp_Object syntax, lim;
{
  return skip_chars (1, 1, syntax, lim);
}

DEFUN ("skip-syntax-backward", Fskip_syntax_backward, Sskip_syntax_backward, 1, 2, 0,
  "Move point backward across chars in specified syntax classes.\n\
SYNTAX is a string of syntax code characters.\n\
Stop on reaching a char whose syntax is not in SYNTAX, or at position LIM.\n\
If SYNTAX starts with ^, skip characters whose syntax is NOT in SYNTAX.\n\
This function returns the distance traveled, either zero or negative.")
  (syntax, lim)
     Lisp_Object syntax, lim;
{
  return skip_chars (0, 1, syntax, lim);
}

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static Lisp_Object
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skip_chars (forwardp, syntaxp, string, lim)
     int forwardp, syntaxp;
     Lisp_Object string, lim;
{
  register unsigned char *p, *pend;
  register unsigned int c;
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  register int ch;