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, 1995-1997, 1999, 2000, 2001 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 Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the 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    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <alloca.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <unistd.h>
  25 #include <memcopy.h>
  26 #include <errno.h>
  27
  28 static void msort_with_tmp (void *b, size_t n, size_t s,
  29                             __compar_fn_t cmp, char *t);
  30
  31 static void
  32 msort_with_tmp (void *b, size_t n, size_t s, __compar_fn_t cmp,
  33                 char *t)
  34 {
  35   char *tmp;
  36   char *b1, *b2;
  37   size_t n1, n2;
  38
  39   if (n <= 1)
  40     return;
  41
  42   n1 = n / 2;
  43   n2 = n - n1;
  44   b1 = b;
  45   b2 = (char *) b + (n1 * s);
  46
  47   msort_with_tmp (b1, n1, s, cmp, t);
  48   msort_with_tmp (b2, n2, s, cmp, t);
  49
  50   tmp = t;
  51
  52   if (s == OPSIZ && (b1 - (char *) 0) % OPSIZ == 0)
  53     /* We are operating on aligned words.  Use direct word stores.  */
  54     while (n1 > 0 && n2 > 0)
  55       {
  56         if ((*cmp) (b1, b2) <= 0)
  57           {
  58             --n1;
  59             *((op_t *) tmp)++ = *((op_t *) b1)++;
  60           }
  61         else
  62           {
  63             --n2;
  64             *((op_t *) tmp)++ = *((op_t *) b2)++;
  65           }
  66       }
  67   else
  68     while (n1 > 0 && n2 > 0)
  69       {
  70         if ((*cmp) (b1, b2) <= 0)
  71           {
  72             tmp = (char *) __mempcpy (tmp, b1, s);
  73             b1 += s;
  74             --n1;
  75           }
  76         else
  77           {
  78             tmp = (char *) __mempcpy (tmp, b2, s);
  79             b2 += s;
  80             --n2;
  81           }
  82       }
  83   if (n1 > 0)
  84     memcpy (tmp, b1, n1 * s);
  85   memcpy (b, t, (n - n2) * s);
  86 }
  87
  88 void
  89 qsort (void *b, size_t n, size_t s, __compar_fn_t cmp)
  90 {
  91   const size_t size = n * s;
  92
  93   if (size < 1024)
  94     {
  95       void *buf = __alloca (size);
  96
  97       /* The temporary array is small, so put it on the stack.  */
  98       msort_with_tmp (b, n, s, cmp, buf);
  99     }
 100   else
 101     {
 102       /* We should avoid allocating too much memory since this might
 103          have to be backed up by swap space.  */
 104       static long int phys_pages;
 105       static int pagesize;
 106
 107       if (phys_pages == 0)
 108         {
 109           phys_pages = __sysconf (_SC_PHYS_PAGES);
 110
 111           if (phys_pages == -1)
 112             /* Error while determining the memory size.  So let's
 113                assume there is enough memory.  Otherwise the
 114                implementer should provide a complete implementation of
 115                the `sysconf' function.  */
 116             phys_pages = (long int) (~0ul >> 1);
 117
 118           /* The following determines that we will never use more than
 119              a quarter of the physical memory.  */
 120           phys_pages /= 4;
 121
 122           pagesize = __sysconf (_SC_PAGESIZE);
 123         }
 124
 125       /* Just a comment here.  We cannot compute
 126            phys_pages * pagesize
 127            and compare the needed amount of memory against this value.
 128            The problem is that some systems might have more physical
 129            memory then can be represented with a `size_t' value (when
 130            measured in bytes.  */
 131
 132       /* If the memory requirements are too high don't allocate memory.  */
 133       if (size / pagesize > phys_pages)
 134         _quicksort (b, n, s, cmp);
 135       else
 136         {
 137           /* It's somewhat large, so malloc it.  */
 138           int save = errno;
 139           char *tmp = malloc (size);
 140           if (tmp == NULL)
 141             {
 142               /* Couldn't get space, so use the slower algorithm
 143                  that doesn't need a temporary array.  */
 144               __set_errno (save);
 145               _quicksort (b, n, s, cmp);
 146             }
 147           else
 148             {
 149               __set_errno (save);
 150               msort_with_tmp (b, n, s, cmp, tmp);
 151               free (tmp);
 152             }
 153         }
 154     }
 155 }