stdlib/msort.c

   1 /* An alternative to qsort, with an identical interface.
   2    This file is part of the GNU C Library.
   3    Copyright (C) 1992, 1995, 1996, 1997, 1999 Free Software Foundation, Inc.
   4    Written by Mike Haertel, September 1988.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Library General Public License as
   8    published by the Free Software Foundation; either version 2 of the
   9    License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Library General Public License for more details.
  15
  16    You should have received a copy of the GNU Library General Public
  17    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  18    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 #include <alloca.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <memcopy.h>
  25 #include <errno.h>
  26
  27 static void msort_with_tmp (void *b, size_t n, size_t s,
  28                             __compar_fn_t cmp, char *t);
  29
  30 static void
  31 msort_with_tmp (void *b, size_t n, size_t s, __compar_fn_t cmp,
  32                 char *t)
  33 {
  34   char *tmp;
  35   char *b1, *b2;
  36   size_t n1, n2;
  37
  38   if (n <= 1)
  39     return;
  40
  41   n1 = n / 2;
  42   n2 = n - n1;
  43   b1 = b;
  44   b2 = (char *) b + (n1 * s);
  45
  46   msort_with_tmp (b1, n1, s, cmp, t);
  47   msort_with_tmp (b2, n2, s, cmp, t);
  48
  49   tmp = t;
  50
  51   if (s == OPSIZ && (b1 - (char *) 0) % OPSIZ == 0)
  52     /* We are operating on aligned words.  Use direct word stores.  */
  53     while (n1 > 0 && n2 > 0)
  54       {
  55         if ((*cmp) (b1, b2) <= 0)
  56           {
  57             --n1;
  58             *((op_t *) tmp)++ = *((op_t *) b1)++;
  59           }
  60         else
  61           {
  62             --n2;
  63             *((op_t *) tmp)++ = *((op_t *) b2)++;
  64           }
  65       }
  66   else
  67     while (n1 > 0 && n2 > 0)
  68       {
  69         if ((*cmp) (b1, b2) <= 0)
  70           {
  71             tmp = (char *) __mempcpy (tmp, b1, s);
  72             b1 += s;
  73             --n1;
  74           }
  75         else
  76           {
  77             tmp = (char *) __mempcpy (tmp, b2, s);
  78             b2 += s;
  79             --n2;
  80           }
  81       }
  82   if (n1 > 0)
  83     memcpy (tmp, b1, n1 * s);
  84   memcpy (b, t, (n - n2) * s);
  85 }
  86
  87 void
  88 qsort (void *b, size_t n, size_t s, __compar_fn_t cmp)
  89 {
  90   const size_t size = n * s;
  91
  92   if (size < 1024)
  93     /* The temporary array is small, so put it on the stack.  */
  94     msort_with_tmp (b, n, s, cmp, __alloca (size));
  95   else
  96     {
  97       /* It's somewhat large, so malloc it.  */
  98       int save = errno;
  99       char *tmp = malloc (size);
 100       if (tmp == NULL)
 101         {
 102           /* Couldn't get space, so use the slower algorithm
 103              that doesn't need a temporary array.  */
 104           _quicksort (b, n, s, cmp);
 105         }
 106       else
 107         {
 108           msort_with_tmp (b, n, s, cmp, tmp);
 109           free (tmp);
 110         }
 111       __set_errno (save);
 112     }
 113 }