msort.c

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/* msort -- an alternative to qsort, with an identical interface.
   Copyright (C) 1992 Free Software Foundation, Inc.
   Written by Mike Haertel, September 1988.

This file is part of the GNU C Library.

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

The GNU C Library 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
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.  */

#include <ansidecl.h>
#include <stdlib.h>
#include <string.h>

#define MEMCPY(dst, src, s)			\
  ((s) == sizeof (int)				\
   ? (*(int *) (dst) = *(int *) (src), (dst))	\
   : memcpy (dst, src, s))

static void
DEFUN(msort_with_tmp, (b, n, s, cmp, t),
      PTR b AND size_t n AND size_t s AND __compar_fn_t cmp AND char *t)
{
  char *tmp;
  char *b1, *b2;
  size_t n1, n2;

  if (n <= 1)
    return;

  n1 = n / 2;
  n2 = n - n1;
  b1 = b;
  b2 = (char *) b + (n1 * s);

  msort_with_tmp (b1, n1, s, cmp, t);
  msort_with_tmp (b2, n2, s, cmp, t);

  tmp = t;

  while (n1 > 0 && n2 > 0)
    {
      if ((*cmp) (b1, b2) <= 0)
	{
	  MEMCPY (tmp, b1, s);
	  b1 += s;
	  --n1;
	}
      else
	{
	  MEMCPY (tmp, b2, s);
	  b2 += s;
	  --n2;
	}
      tmp += s;
    }
  if (n1 > 0)
    memcpy (tmp, b1, n1 * s);
  memcpy (b, t, (n - n2) * s);
}

void
DEFUN(qsort, (b, n, s, cmp),
      PTR b AND size_t n AND size_t s AND __compar_fn_t cmp)
{
  CONST size_t size = n * s;

  if (size < 1024)
    /* The temporary array is small, so put it on the stack.  */
    msort_with_tmp (b, n, s, cmp, __alloca (size));
  else
    {
      /* It's somewhat large, so malloc it.  */
      int save = errno;
      char *tmp = malloc (size);
      if (tmp == NULL)
	{
	  /* Couldn't get space, so use the slower algorithm
	     that doesn't need a temporary array.  */
	  extern void EXFUN(_quicksort, (PTR __base,
					 size_t __nmemb, size_t __size,
					 __compar_fn_t __compar));
	  _quicksort (b, n, s, cmp);
	}
      else
	{
	  msort_with_tmp (b, n, s, cmp, tmp);
	  free (tmp);
	}
      errno = save;
    }
}