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/* Random utility Lisp functions.
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   Copyright (C) 1985, 86, 87, 93, 94, 95 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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/* Note on some machines this defines `vector' as a typedef,
   so make sure we don't use that name in this file.  */
#undef vector
#define vector *****

#include "lisp.h"
#include "commands.h"
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#include "charset.h"
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#include "buffer.h"
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#include "keyboard.h"
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#include "intervals.h"
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#include "frame.h"
#include "window.h"
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#ifndef NULL
#define NULL (void *)0
#endif

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/* Nonzero enables use of dialog boxes for questions
   asked by mouse commands.  */
int use_dialog_box;

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extern Lisp_Object Flookup_key ();

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extern int minibuffer_auto_raise;
extern Lisp_Object minibuf_window;

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Lisp_Object Qstring_lessp, Qprovide, Qrequire;
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Lisp_Object Qyes_or_no_p_history;
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Lisp_Object Qcursor_in_echo_area;
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static int internal_equal ();
57

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DEFUN ("identity", Fidentity, Sidentity, 1, 1, 0,
  "Return the argument unchanged.")
  (arg)
     Lisp_Object arg;
{
  return arg;
}

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extern long get_random ();
extern void seed_random ();
extern long time ();

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DEFUN ("random", Frandom, Srandom, 0, 1, 0,
  "Return a pseudo-random number.\n\
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All integers representable in Lisp are equally likely.\n\
  On most systems, this is 28 bits' worth.\n\
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With positive integer argument N, return random number in interval [0,N).\n\
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With argument t, set the random number seed from the current time and pid.")
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  (n)
     Lisp_Object n;
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{
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  EMACS_INT val;
  Lisp_Object lispy_val;
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  unsigned long denominator;
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  if (EQ (n, Qt))
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    seed_random (getpid () + time (NULL));
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  if (NATNUMP (n) && XFASTINT (n) != 0)
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    {
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      /* Try to take our random number from the higher bits of VAL,
	 not the lower, since (says Gentzel) the low bits of `random'
	 are less random than the higher ones.  We do this by using the
	 quotient rather than the remainder.  At the high end of the RNG
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	 it's possible to get a quotient larger than n; discarding
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	 these values eliminates the bias that would otherwise appear
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	 when using a large n.  */
      denominator = ((unsigned long)1 << VALBITS) / XFASTINT (n);
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      do
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	val = get_random () / denominator;
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      while (val >= XFASTINT (n));
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    }
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  else
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    val = get_random ();
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  XSETINT (lispy_val, val);
  return lispy_val;
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}

/* Random data-structure functions */

DEFUN ("length", Flength, Slength, 1, 1, 0,
  "Return the length of vector, list or string SEQUENCE.\n\
A byte-code function object is also allowed.")
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  (sequence)
     register Lisp_Object sequence;
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{
  register Lisp_Object tail, val;
  register int i;

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  if (STRINGP (sequence))
    XSETFASTINT (val, XSTRING (sequence)->size);
  else if (VECTORP (sequence))
    XSETFASTINT (val, XVECTOR (sequence)->size);
  else if (CHAR_TABLE_P (sequence))
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    XSETFASTINT (val, CHAR_TABLE_ORDINARY_SLOTS);
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  else if (BOOL_VECTOR_P (sequence))
    XSETFASTINT (val, XBOOL_VECTOR (sequence)->size);
  else if (COMPILEDP (sequence))
    XSETFASTINT (val, XVECTOR (sequence)->size & PSEUDOVECTOR_SIZE_MASK);
  else if (CONSP (sequence))
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    {
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      for (i = 0, tail = sequence; !NILP (tail); i++)
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	{
	  QUIT;
	  tail = Fcdr (tail);
	}

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      XSETFASTINT (val, i);
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    }
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  else if (NILP (sequence))
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    XSETFASTINT (val, 0);
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  else
    {
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      sequence = wrong_type_argument (Qsequencep, sequence);
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      goto retry;
    }
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  return val;
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}

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/* This does not check for quits.  That is safe
   since it must terminate.  */

DEFUN ("safe-length", Fsafe_length, Ssafe_length, 1, 1, 0,
  "Return the length of a list, but avoid error or infinite loop.\n\
This function never gets an error.  If LIST is not really a list,\n\
it returns 0.  If LIST is circular, it returns a finite value\n\
which is at least the number of distinct elements.")
 (list)
     Lisp_Object list;
{
  Lisp_Object tail, halftail, length;
  int len = 0;

  /* halftail is used to detect circular lists.  */
  halftail = list;
  for (tail = list; CONSP (tail); tail = XCONS (tail)->cdr)
    {
      if (EQ (tail, halftail) && len != 0)
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	break;
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      len++;
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      if ((len & 1) == 0)
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	halftail = XCONS (halftail)->cdr;
    }

  XSETINT (length, len);
  return length;
}

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DEFUN ("string-equal", Fstring_equal, Sstring_equal, 2, 2, 0,
  "T if two strings have identical contents.\n\
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Case is significant, but text properties are ignored.\n\
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Symbols are also allowed; their print names are used instead.")
  (s1, s2)
     register Lisp_Object s1, s2;
{
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  if (SYMBOLP (s1))
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    XSETSTRING (s1, XSYMBOL (s1)->name);
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  if (SYMBOLP (s2))
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    XSETSTRING (s2, XSYMBOL (s2)->name);
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  CHECK_STRING (s1, 0);
  CHECK_STRING (s2, 1);

  if (XSTRING (s1)->size != XSTRING (s2)->size ||
      bcmp (XSTRING (s1)->data, XSTRING (s2)->data, XSTRING (s1)->size))
    return Qnil;
  return Qt;
}

DEFUN ("string-lessp", Fstring_lessp, Sstring_lessp, 2, 2, 0,
  "T if first arg string is less than second in lexicographic order.\n\
Case is significant.\n\
Symbols are also allowed; their print names are used instead.")
  (s1, s2)
     register Lisp_Object s1, s2;
{
  register int i;
  register unsigned char *p1, *p2;
  register int end;

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  if (SYMBOLP (s1))
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    XSETSTRING (s1, XSYMBOL (s1)->name);
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  if (SYMBOLP (s2))
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    XSETSTRING (s2, XSYMBOL (s2)->name);
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  CHECK_STRING (s1, 0);
  CHECK_STRING (s2, 1);

  p1 = XSTRING (s1)->data;
  p2 = XSTRING (s2)->data;
  end = XSTRING (s1)->size;
  if (end > XSTRING (s2)->size)
    end = XSTRING (s2)->size;

  for (i = 0; i < end; i++)
    {
      if (p1[i] != p2[i])
	return p1[i] < p2[i] ? Qt : Qnil;
    }
  return i < XSTRING (s2)->size ? Qt : Qnil;
}

static Lisp_Object concat ();

/* ARGSUSED */
Lisp_Object
concat2 (s1, s2)
     Lisp_Object s1, s2;
{
#ifdef NO_ARG_ARRAY
  Lisp_Object args[2];
  args[0] = s1;
  args[1] = s2;
  return concat (2, args, Lisp_String, 0);
#else
  return concat (2, &s1, Lisp_String, 0);
#endif /* NO_ARG_ARRAY */
}

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/* ARGSUSED */
Lisp_Object
concat3 (s1, s2, s3)
     Lisp_Object s1, s2, s3;
{
#ifdef NO_ARG_ARRAY
  Lisp_Object args[3];
  args[0] = s1;
  args[1] = s2;
  args[2] = s3;
  return concat (3, args, Lisp_String, 0);
#else
  return concat (3, &s1, Lisp_String, 0);
#endif /* NO_ARG_ARRAY */
}

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DEFUN ("append", Fappend, Sappend, 0, MANY, 0,
  "Concatenate all the arguments and make the result a list.\n\
The result is a list whose elements are the elements of all the arguments.\n\
Each argument may be a list, vector or string.\n\
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The last argument is not copied, just used as the tail of the new list.")
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  (nargs, args)
     int nargs;
     Lisp_Object *args;
{
  return concat (nargs, args, Lisp_Cons, 1);
}

DEFUN ("concat", Fconcat, Sconcat, 0, MANY, 0,
  "Concatenate all the arguments and make the result a string.\n\
The result is a string whose elements are the elements of all the arguments.\n\
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Each argument may be a string or a list or vector of characters (integers).\n\
\n\
Do not use individual integers as arguments!\n\
The behavior of `concat' in that case will be changed later!\n\
If your program passes an integer as an argument to `concat',\n\
you should change it right away not to do so.")
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  (nargs, args)
     int nargs;
     Lisp_Object *args;
{
  return concat (nargs, args, Lisp_String, 0);
}

DEFUN ("vconcat", Fvconcat, Svconcat, 0, MANY, 0,
  "Concatenate all the arguments and make the result a vector.\n\
The result is a vector whose elements are the elements of all the arguments.\n\
Each argument may be a list, vector or string.")
  (nargs, args)
     int nargs;
     Lisp_Object *args;
{
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  return concat (nargs, args, Lisp_Vectorlike, 0);
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}

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/* Retrun a copy of a sub char table ARG.  The elements except for a
   nested sub char table are not copied.  */
static Lisp_Object
copy_sub_char_table (arg)
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     Lisp_Object arg;
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{
  Lisp_Object copy = make_sub_char_table (XCHAR_TABLE (arg)->defalt);
  int i;

  /* Copy all the contents.  */
  bcopy (XCHAR_TABLE (arg)->contents, XCHAR_TABLE (copy)->contents,
	 SUB_CHAR_TABLE_ORDINARY_SLOTS * sizeof (Lisp_Object));
  /* Recursively copy any sub char-tables in the ordinary slots.  */
  for (i = 32; i < SUB_CHAR_TABLE_ORDINARY_SLOTS; i++)
    if (SUB_CHAR_TABLE_P (XCHAR_TABLE (arg)->contents[i]))
      XCHAR_TABLE (copy)->contents[i]
	= copy_sub_char_table (XCHAR_TABLE (copy)->contents[i]);

  return copy;
}


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DEFUN ("copy-sequence", Fcopy_sequence, Scopy_sequence, 1, 1, 0,
  "Return a copy of a list, vector or string.\n\
The elements of a list or vector are not copied; they are shared\n\
with the original.")
  (arg)
     Lisp_Object arg;
{
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  if (NILP (arg)) return arg;
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  if (CHAR_TABLE_P (arg))
    {
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      int i;
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      Lisp_Object copy;

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      copy = Fmake_char_table (XCHAR_TABLE (arg)->purpose, Qnil);
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      /* Copy all the slots, including the extra ones.  */
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      bcopy (XVECTOR (arg)->contents, XVECTOR (copy)->contents,
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	     ((XCHAR_TABLE (arg)->size & PSEUDOVECTOR_SIZE_MASK)
	      * sizeof (Lisp_Object)));
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      /* Recursively copy any sub char tables in the ordinary slots
         for multibyte characters.  */
      for (i = CHAR_TABLE_SINGLE_BYTE_SLOTS;
	   i < CHAR_TABLE_ORDINARY_SLOTS; i++)
	if (SUB_CHAR_TABLE_P (XCHAR_TABLE (arg)->contents[i]))
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	  XCHAR_TABLE (copy)->contents[i]
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	    = copy_sub_char_table (XCHAR_TABLE (copy)->contents[i]);
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      return copy;
    }

  if (BOOL_VECTOR_P (arg))
    {
      Lisp_Object val;
      int size_in_chars
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	= (XBOOL_VECTOR (arg)->size + BITS_PER_CHAR - 1) / BITS_PER_CHAR;
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      val = Fmake_bool_vector (Flength (arg), Qnil);
      bcopy (XBOOL_VECTOR (arg)->data, XBOOL_VECTOR (val)->data,
	     size_in_chars);
      return val;
    }

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  if (!CONSP (arg) && !VECTORP (arg) && !STRINGP (arg))
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    arg = wrong_type_argument (Qsequencep, arg);
  return concat (1, &arg, CONSP (arg) ? Lisp_Cons : XTYPE (arg), 0);
}

static Lisp_Object
concat (nargs, args, target_type, last_special)
     int nargs;
     Lisp_Object *args;
     enum Lisp_Type target_type;
     int last_special;
{
  Lisp_Object val;
  Lisp_Object len;
  register Lisp_Object tail;
  register Lisp_Object this;
  int toindex;
  register int leni;
  register int argnum;
  Lisp_Object last_tail;
  Lisp_Object prev;

  /* In append, the last arg isn't treated like the others */
  if (last_special && nargs > 0)
    {
      nargs--;
      last_tail = args[nargs];
    }
  else
    last_tail = Qnil;

  for (argnum = 0; argnum < nargs; argnum++)
    {
      this = args[argnum];
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      if (!(CONSP (this) || NILP (this) || VECTORP (this) || STRINGP (this)
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	    || COMPILEDP (this) || BOOL_VECTOR_P (this)))
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	{
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	  if (INTEGERP (this))
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            args[argnum] = Fnumber_to_string (this);
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	  else
	    args[argnum] = wrong_type_argument (Qsequencep, this);
	}
    }

  for (argnum = 0, leni = 0; argnum < nargs; argnum++)
    {
      this = args[argnum];
      len = Flength (this);
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      if (VECTORP (this) && target_type == Lisp_String)
	{
	  /* We must pay attention to a multibyte character which
             takes more than one byte in string.  */
	  int i;
	  Lisp_Object ch;

	  for (i = 0; i < XFASTINT (len); i++)
	    {
	      ch = XVECTOR (this)->contents[i];
	      if (! INTEGERP (ch))
		wrong_type_argument (Qintegerp, ch);
	      leni += Fchar_bytes (ch);
	    }
	}
      else
	leni += XFASTINT (len);
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    }

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  XSETFASTINT (len, leni);
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  if (target_type == Lisp_Cons)
    val = Fmake_list (len, Qnil);
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  else if (target_type == Lisp_Vectorlike)
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    val = Fmake_vector (len, Qnil);
  else
    val = Fmake_string (len, len);

  /* In append, if all but last arg are nil, return last arg */
  if (target_type == Lisp_Cons && EQ (val, Qnil))
    return last_tail;

  if (CONSP (val))
    tail = val, toindex = -1;		/* -1 in toindex is flag we are making a list */
  else
    toindex = 0;

  prev = Qnil;

  for (argnum = 0; argnum < nargs; argnum++)
    {
      Lisp_Object thislen;
      int thisleni;
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      register unsigned int thisindex = 0;
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      this = args[argnum];
      if (!CONSP (this))
	thislen = Flength (this), thisleni = XINT (thislen);

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      if (STRINGP (this) && STRINGP (val)
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	  && ! NULL_INTERVAL_P (XSTRING (this)->intervals))
	{
	  copy_text_properties (make_number (0), thislen, this,
				make_number (toindex), val, Qnil);
	}

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      while (1)
	{
	  register Lisp_Object elt;

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	  /* Fetch next element of `this' arg into `elt', or break if
             `this' is exhausted. */
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	  if (NILP (this)) break;
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	  if (CONSP (this))
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	    elt = XCONS (this)->car, this = XCONS (this)->cdr;
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	  else
	    {
	      if (thisindex >= thisleni) break;
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	      if (STRINGP (this))
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		XSETFASTINT (elt, XSTRING (this)->data[thisindex++]);
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	      else if (BOOL_VECTOR_P (this))
		{
		  int size_in_chars
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		    = ((XBOOL_VECTOR (this)->size + BITS_PER_CHAR - 1)
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		       / BITS_PER_CHAR);
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		  int byte;
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		  byte = XBOOL_VECTOR (val)->data[thisindex / BITS_PER_CHAR];
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		  if (byte & (1 << (thisindex % BITS_PER_CHAR)))
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		    elt = Qt;
		  else
		    elt = Qnil;
		}
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	      else
		elt = XVECTOR (this)->contents[thisindex++];
	    }

	  /* Store into result */
	  if (toindex < 0)
	    {
	      XCONS (tail)->car = elt;
	      prev = tail;
	      tail = XCONS (tail)->cdr;
	    }
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	  else if (VECTORP (val))
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	    XVECTOR (val)->contents[toindex++] = elt;
	  else
	    {
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	      while (!INTEGERP (elt))
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		elt = wrong_type_argument (Qintegerp, elt);
	      {
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		int c = XINT (elt);
		unsigned char work[4], *str;
		int i = CHAR_STRING (c, work, str);

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#ifdef MASSC_REGISTER_BUG
		/* Even removing all "register"s doesn't disable this bug!
		   Nothing simpler than this seems to work. */
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		unsigned char *p = & XSTRING (val)->data[toindex];
		bcopy (str, p, i);
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#else
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		bcopy (str, & XSTRING (val)->data[toindex], i);
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#endif
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		toindex += i;
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	      }
	    }
	}
    }
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  if (!NILP (prev))
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    XCONS (prev)->cdr = last_tail;

  return val;  
}

DEFUN ("copy-alist", Fcopy_alist, Scopy_alist, 1, 1, 0,
  "Return a copy of ALIST.\n\
This is an alist which represents the same mapping from objects to objects,\n\
but does not share the alist structure with ALIST.\n\
The objects mapped (cars and cdrs of elements of the alist)\n\
are shared, however.\n\
Elements of ALIST that are not conses are also shared.")
  (alist)
     Lisp_Object alist;
{
  register Lisp_Object tem;

  CHECK_LIST (alist, 0);
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  if (NILP (alist))
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    return alist;
  alist = concat (1, &alist, Lisp_Cons, 0);
  for (tem = alist; CONSP (tem); tem = XCONS (tem)->cdr)
    {
      register Lisp_Object car;
      car = XCONS (tem)->car;

      if (CONSP (car))
	XCONS (tem)->car = Fcons (XCONS (car)->car, XCONS (car)->cdr);
    }
  return alist;
}

DEFUN ("substring", Fsubstring, Ssubstring, 2, 3, 0,
  "Return a substring of STRING, starting at index FROM and ending before TO.\n\
TO may be nil or omitted; then the substring runs to the end of STRING.\n\
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If FROM or TO is negative, it counts from the end.\n\
\n\
This function allows vectors as well as strings.")
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  (string, from, to)
     Lisp_Object string;
     register Lisp_Object from, to;
{
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  Lisp_Object res;
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  int size;

  if (! (STRINGP (string) || VECTORP (string)))
    wrong_type_argument (Qarrayp, string);
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  CHECK_NUMBER (from, 1);
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  if (STRINGP (string))
    size = XSTRING (string)->size;
  else
    size = XVECTOR (string)->size;

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  if (NILP (to))
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    XSETINT (to, size);
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  else
    CHECK_NUMBER (to, 2);

  if (XINT (from) < 0)
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    XSETINT (from, XINT (from) + size);
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  if (XINT (to) < 0)
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    XSETINT (to, XINT (to) + size);
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  if (!(0 <= XINT (from) && XINT (from) <= XINT (to)
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        && XINT (to) <= size))
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    args_out_of_range_3 (string, from, to);

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  if (STRINGP (string))
    {
      res = make_string (XSTRING (string)->data + XINT (from),
			 XINT (to) - XINT (from));
      copy_text_properties (from, to, string, make_number (0), res, Qnil);
    }
  else
    res = Fvector (XINT (to) - XINT (from),
		   XVECTOR (string)->contents + XINT (from));
		   
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  return res;
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}

DEFUN ("nthcdr", Fnthcdr, Snthcdr, 2, 2, 0,
  "Take cdr N times on LIST, returns the result.")
  (n, list)
     Lisp_Object n;
     register Lisp_Object list;
{
  register int i, num;
  CHECK_NUMBER (n, 0);
  num = XINT (n);
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  for (i = 0; i < num && !NILP (list); i++)
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    {
      QUIT;
      list = Fcdr (list);
    }
  return list;
}

DEFUN ("nth", Fnth, Snth, 2, 2, 0,
  "Return the Nth element of LIST.\n\
N counts from zero.  If LIST is not that long, nil is returned.")
  (n, list)
     Lisp_Object n, list;
{
  return Fcar (Fnthcdr (n, list));
}

DEFUN ("elt", Felt, Selt, 2, 2, 0,
  "Return element of SEQUENCE at index N.")
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  (sequence, n)
     register Lisp_Object sequence, n;
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{
  CHECK_NUMBER (n, 0);
  while (1)
    {
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      if (CONSP (sequence) || NILP (sequence))
	return Fcar (Fnthcdr (n, sequence));
      else if (STRINGP (sequence) || VECTORP (sequence)
	       || BOOL_VECTOR_P (sequence) || CHAR_TABLE_P (sequence))
	return Faref (sequence, n);
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      else
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	sequence = wrong_type_argument (Qsequencep, sequence);
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    }
}

DEFUN ("member", Fmember, Smember, 2, 2, 0,
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  "Return non-nil if ELT is an element of LIST.  Comparison done with `equal'.\n\
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The value is actually the tail of LIST whose car is ELT.")
  (elt, list)
     register Lisp_Object elt;
     Lisp_Object list;
{
  register Lisp_Object tail;
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  for (tail = list; !NILP (tail); tail = XCONS (tail)->cdr)
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    {
      register Lisp_Object tem;
      tem = Fcar (tail);
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      if (! NILP (Fequal (elt, tem)))
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	return tail;
      QUIT;
    }
  return Qnil;
}

DEFUN ("memq", Fmemq, Smemq, 2, 2, 0,
  "Return non-nil if ELT is an element of LIST.  Comparison done with EQ.\n\
The value is actually the tail of LIST whose car is ELT.")
  (elt, list)
     register Lisp_Object elt;
     Lisp_Object list;
{
  register Lisp_Object tail;
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  for (tail = list; !NILP (tail); tail = XCONS (tail)->cdr)
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    {
      register Lisp_Object tem;
      tem = Fcar (tail);
      if (EQ (elt, tem)) return tail;
      QUIT;
    }
  return Qnil;
}

DEFUN ("assq", Fassq, Sassq, 2, 2, 0,
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  "Return non-nil if KEY is `eq' to the car of an element of LIST.\n\
The value is actually the element of LIST whose car is KEY.\n\
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Elements of LIST that are not conses are ignored.")
  (key, list)
     register Lisp_Object key;
     Lisp_Object list;
{
  register Lisp_Object tail;
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  for (tail = list; !NILP (tail); tail = XCONS (tail)->cdr)
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    {
      register Lisp_Object elt, tem;
      elt = Fcar (tail);
      if (!CONSP (elt)) continue;
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      tem = XCONS (elt)->car;
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      if (EQ (key, tem)) return elt;
      QUIT;
    }
  return Qnil;
}

/* Like Fassq but never report an error and do not allow quits.
   Use only on lists known never to be circular.  */

Lisp_Object
assq_no_quit (key, list)
     register Lisp_Object key;
     Lisp_Object list;
{
  register Lisp_Object tail;
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  for (tail = list; CONSP (tail); tail = XCONS (tail)->cdr)
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    {
      register Lisp_Object elt, tem;
      elt = Fcar (tail);
      if (!CONSP (elt)) continue;
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      tem = XCONS (elt)->car;
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      if (EQ (key, tem)) return elt;
    }
  return Qnil;
}

DEFUN ("assoc", Fassoc, Sassoc, 2, 2, 0,
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  "Return non-nil if KEY is `equal' to the car of an element of LIST.\n\
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The value is actually the element of LIST whose car equals KEY.")
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  (key, list)
     register Lisp_Object key;
     Lisp_Object list;
{
  register Lisp_Object tail;
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  for (tail = list; !NILP (tail); tail = XCONS (tail)->cdr)
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    {
      register Lisp_Object elt, tem;
      elt = Fcar (tail);
      if (!CONSP (elt)) continue;
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      tem = Fequal (XCONS (elt)->car, key);
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      if (!NILP (tem)) return elt;
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      QUIT;
    }
  return Qnil;
}

DEFUN ("rassq", Frassq, Srassq, 2, 2, 0,
  "Return non-nil if ELT is `eq' to the cdr of an element of LIST.\n\
The value is actually the element of LIST whose cdr is ELT.")
  (key, list)
     register Lisp_Object key;
     Lisp_Object list;
{
  register Lisp_Object tail;
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  for (tail = list; !NILP (tail); tail = XCONS (tail)->cdr)
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    {
      register Lisp_Object elt, tem;
      elt = Fcar (tail);
      if (!CONSP (elt)) continue;
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      tem = XCONS (elt)->cdr;
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      if (EQ (key, tem)) return elt;
      QUIT;
    }
  return Qnil;
}
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DEFUN ("rassoc", Frassoc, Srassoc, 2, 2, 0,
  "Return non-nil if KEY is `equal' to the cdr of an element of LIST.\n\
The value is actually the element of LIST whose cdr equals KEY.")
  (key, list)
     register Lisp_Object key;
     Lisp_Object list;
{
  register Lisp_Object tail;
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  for (tail = list; !NILP (tail); tail = XCONS (tail)->cdr)
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    {
      register Lisp_Object elt, tem;
      elt = Fcar (tail);
      if (!CONSP (elt)) continue;
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      tem = Fequal (XCONS (elt)->cdr, key);
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      if (!NILP (tem)) return elt;
      QUIT;
    }
  return Qnil;
}
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DEFUN ("delq", Fdelq, Sdelq, 2, 2, 0,
  "Delete by side effect any occurrences of ELT as a member of LIST.\n\
The modified LIST is returned.  Comparison is done with `eq'.\n\
If the first member of LIST is ELT, there is no way to remove it by side effect;\n\
therefore, write `(setq foo (delq element foo))'\n\
to be sure of changing the value of `foo'.")
  (elt, list)
     register Lisp_Object elt;
     Lisp_Object list;
{
  register Lisp_Object tail, prev;
  register Lisp_Object tem;

  tail = list;
  prev = Qnil;
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  while (!NILP (tail))
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    {
      tem = Fcar (tail);
      if (EQ (elt, tem))
	{
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	  if (NILP (prev))
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	    list = XCONS (tail)->cdr;
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	  else
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	    Fsetcdr (prev, XCONS (tail)->cdr);
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	}
      else
	prev = tail;
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      tail = XCONS (tail)->cdr;
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      QUIT;
    }
  return list;
}

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DEFUN ("delete", Fdelete, Sdelete, 2, 2, 0,
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  "Delete by side effect any occurrences of ELT as a member of LIST.\n\
The modified LIST is returned.  Comparison is done with `equal'.\n\
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If the first member of LIST is ELT, deleting it is not a side effect;\n\
it is simply using a different list.\n\
Therefore, write `(setq foo (delete element foo))'\n\
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to be sure of changing the value of `foo'.")
  (elt, list)
     register Lisp_Object elt;
     Lisp_Object list;
{
  register Lisp_Object tail, prev;
  register Lisp_Object tem;

  tail = list;
  prev = Qnil;
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  while (!NILP (tail))
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    {
      tem = Fcar (tail);
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      if (! NILP (Fequal (elt, tem)))
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	{
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	  if (NILP (prev))
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	    list = XCONS (tail)->cdr;
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	  else
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	    Fsetcdr (prev, XCONS (tail)->cdr);
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	}
      else
	prev = tail;
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      tail = XCONS (tail)->cdr;
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      QUIT;
    }
  return list;
}

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DEFUN ("nreverse", Fnreverse, Snreverse, 1, 1, 0,
  "Reverse LIST by modifying cdr pointers.\n\
Returns the beginning of the reversed list.")
  (list)
     Lisp_Object list;
{
  register Lisp_Object prev, tail, next;

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  if (NILP (list)) return list;
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  prev = Qnil;
  tail = list;
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  while (!NILP (tail))
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    {
      QUIT;
      next = Fcdr (tail);
      Fsetcdr (tail, prev);
      prev = tail;
      tail = next;
    }
  return prev;
}

DEFUN ("reverse", Freverse, Sreverse, 1, 1, 0,
  "Reverse LIST, copying.  Returns the beginning of the reversed list.\n\
See also the function `nreverse', which is used more often.")
  (list)
     Lisp_Object list;
{
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  Lisp_Object new;
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  for (new = Qnil; CONSP (list); list = XCONS (list)->cdr)
    new = Fcons (XCONS (list)->car, new);
  if (!NILP (list))
    wrong_type_argument (Qconsp, list);
  return new;
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}

Lisp_Object merge ();

DEFUN ("sort", Fsort, Ssort, 2, 2, 0,
  "Sort LIST, stably, comparing elements using PREDICATE.\n\
Returns the sorted list.  LIST is modified by side effects.\n\
PREDICATE is called with two elements of LIST, and should return T\n\
if the first element is \"less\" than the second.")
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  (list, predicate)
     Lisp_Object list, predicate;
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{
  Lisp_Object front, back;
  register Lisp_Object len, tem;
  struct gcpro gcpro1, gcpro2;
  register int length;

  front = list;
  len = Flength (list);
  length = XINT (len);
  if (length < 2)
    return list;

  XSETINT (len, (length / 2) - 1);
  tem = Fnthcdr (len, list);
  back = Fcdr (tem);
  Fsetcdr (tem, Qnil);

  GCPRO2 (front, back);
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  front = Fsort (front, predicate);
  back = Fsort (back, predicate);
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  UNGCPRO;
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  return merge (front, back, predicate);
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}

Lisp_Object
merge (org_l1, org_l2, pred)
     Lisp_Object org_l1, org_l2;
     Lisp_Object pred;
{
  Lisp_Object value;
  register Lisp_Object tail;
  Lisp_Object tem;
  register Lisp_Object l1, l2;
  struct gcpro gcpro1, gcpro2, gcpro3, gcpro4;

  l1 = org_l1;
  l2 = org_l2;
  tail = Qnil;
  value = Qnil;

  /* It is sufficient to protect org_l1 and org_l2.
     When l1 and l2 are updated, we copy the new values
     back into the org_ vars.  */
  GCPRO4 (org_l1, org_l2, pred, value);

  while (1)
    {
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      if (NILP (l1))
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	{
	  UNGCPRO;
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	  if (NILP (tail))
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	    return l2;
	  Fsetcdr (tail, l2);
	  return value;
	}
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      if (NILP (l2))
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	{
	  UNGCPRO;
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	  if (NILP (tail))
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	    return l1;
	  Fsetcdr (tail, l1);
	  return value;
	}
      tem = call2 (pred, Fcar (l2), Fcar (l1));
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      if (NILP (tem))
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	{
	  tem = l1;
	  l1 = Fcdr (l1);
	  org_l1 = l1;
	}
      else
	{
	  tem = l2;
	  l2 = Fcdr (l2);
	  org_l2 = l2;
	}
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      if (NILP (tail))
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	value = tem;
      else
	Fsetcdr (tail, tem);
      tail = tem;
    }
}

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DEFUN ("plist-get", Fplist_get, Splist_get, 2, 2, 0,
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  "Extract a value from a property list.\n\
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PLIST is a property list, which is a list of the form\n\
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\(PROP1 VALUE1 PROP2 VALUE2...).  This function returns the value\n\
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corresponding to the given PROP, or nil if PROP is not\n\
one of the properties on the list.")
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  (plist, prop)
     Lisp_Object plist;
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     register Lisp_Object prop;
{
  register Lisp_Object tail;
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  for (tail = plist; !NILP (tail); tail = Fcdr (XCONS (tail)->cdr))
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    {
      register Lisp_Object tem;
      tem = Fcar (tail);
      if (EQ (prop, tem))
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	return Fcar (XCONS (tail)->cdr);
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    }
  return Qnil;
}

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DEFUN ("get", Fget, Sget, 2, 2, 0,
  "Return the value of SYMBOL's PROPNAME property.\n\
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This is the last value stored with `(put SYMBOL PROPNAME VALUE)'.")
  (symbol, propname)
     Lisp_Object symbol, propname;
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{
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  CHECK_SYMBOL (symbol, 0);
  return Fplist_get (XSYMBOL (symbol)->plist, propname);
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}

DEFUN ("plist-put", Fplist_put, Splist_put, 3, 3, 0,
  "Change value in PLIST of PROP to VAL.\n\
PLIST is a property list, which is a list of the form\n\
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\(PROP1 VALUE1 PROP2 VALUE2 ...).  PROP is a symbol and VAL is any object.\n\
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If PROP is already a property on the list, its value is set to VAL,\n\
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otherwise the new PROP VAL pair is added.  The new plist is returned;\n\
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use `(setq x (plist-put x prop val))' to be sure to use the new value.\n\
The PLIST is modified by side effects.")
  (plist, prop, val)
    Lisp_Object plist;
    register Lisp_Object prop;
    Lisp_Object val;
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{
  register Lisp_Object tail, prev;
  Lisp_Object newcell;
  prev = Qnil;
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  for (tail = plist; CONSP (tail) && CONSP (XCONS (tail)->cdr);
       tail = XCONS (XCONS (tail)->cdr)->cdr)
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    {
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      if (EQ (prop, XCONS (tail)->car))
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	{
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	  Fsetcar (XCONS (tail)->cdr, val);
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	  return plist;
	}
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      prev = tail;
    }
  newcell = Fcons (prop, Fcons (val, Qnil));
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  if (NILP (prev))
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    return newcell;
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  else
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    Fsetcdr (XCONS (prev)->cdr, newcell);
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  return plist;
}

DEFUN ("put", Fput, Sput, 3, 3, 0,
  "Store SYMBOL's PROPNAME property with value VALUE.\n\
It can be retrieved with `(get SYMBOL PROPNAME)'.")
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  (symbol, propname, value)
     Lisp_Object symbol, propname, value;
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{
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  CHECK_SYMBOL (symbol, 0);
  XSYMBOL (symbol)->plist
    = Fplist_put (XSYMBOL (symbol)->plist, propname, value);
  return value;
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}

DEFUN ("equal", Fequal, Sequal, 2, 2, 0,
  "T if two Lisp objects have similar structure and contents.\n\
They must have the same data type.\n\
Conses are compared by comparing the cars and the cdrs.\n\
Vectors and strings are compared element by element.\n\
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Numbers are compared by value, but integers cannot equal floats.\n\
 (Use `=' if you want integers and floats to be able to be equal.)\n\
Symbols must match exactly.")
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  (o1, o2)
     register Lisp_Object o1, o2;
{
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  return internal_equal (o1, o2, 0) ? Qt : Qnil;
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}

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static int
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internal_equal (o1, o2, depth)
     register Lisp_Object o1, o2;
     int depth;
{
  if (depth > 200)
    error ("Stack overflow in equal");
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 tail_recurse:
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  QUIT;
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  if (EQ (o1, o2))
    return 1;
  if (XTYPE (o1) != XTYPE (o2))
    return 0;

  switch (XTYPE (o1))
    {
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#ifdef LISP_FLOAT_TYPE
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    case Lisp_Float:
      return (extract_float (o1) == extract_float (o2));