summary refs log tree commit diff
path: root/stdlib/msort.c
blob: d174edd3b7f7e04c498e96eee485069bfbefa790 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
/* An alternative to qsort, with an identical interface.
   This file is part of the GNU C Library.
   Copyright (C) 1992, 1995-1997, 1999, 2000 Free Software Foundation, Inc.
   Written by Mike Haertel, September 1988.

   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., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <alloca.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <memcopy.h>
#include <errno.h>

static void msort_with_tmp (void *b, size_t n, size_t s,
			    __compar_fn_t cmp, char *t);

static void
msort_with_tmp (void *b, size_t n, size_t s, __compar_fn_t cmp,
		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;

  if (s == OPSIZ && (b1 - (char *) 0) % OPSIZ == 0)
    /* We are operating on aligned words.  Use direct word stores.  */
    while (n1 > 0 && n2 > 0)
      {
	if ((*cmp) (b1, b2) <= 0)
	  {
	    --n1;
	    *((op_t *) tmp)++ = *((op_t *) b1)++;
	  }
	else
	  {
	    --n2;
	    *((op_t *) tmp)++ = *((op_t *) b2)++;
	  }
      }
  else
    while (n1 > 0 && n2 > 0)
      {
	if ((*cmp) (b1, b2) <= 0)
	  {
	    tmp = (char *) __mempcpy (tmp, b1, s);
	    b1 += s;
	    --n1;
	  }
	else
	  {
	    tmp = (char *) __mempcpy (tmp, b2, s);
	    b2 += s;
	    --n2;
	  }
      }
  if (n1 > 0)
    memcpy (tmp, b1, n1 * s);
  memcpy (b, t, (n - n2) * s);
}

void
qsort (void *b, size_t n, size_t s, __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
    {
      /* We should avoid allocating too much memory since this might
	 have to be backed up by swap space.  */
      static long int phys_pages;
      static int pagesize;

      if (phys_pages == 0)
	{
	  phys_pages = __sysconf (_SC_PHYS_PAGES);

	  if (phys_pages == -1)
	    /* Error while determining the memory size.  So let's
	       assume there is enough memory.  Otherwise the
	       implementer should provide a complete implementation of
	       the `sysconf' function.  */
	    phys_pages = (long int) (~0ul >> 1);

	  /* The following determines that we will never use more than
	     a quarter of the physical memory.  */
	  phys_pages /= 4;

	  pagesize = __sysconf (_SC_PAGESIZE);
	}

      /* Just a comment here.  We cannot compute
	   phys_pages * pagesize
	   and compare the needed amount of memory against this value.
	   The problem is that some systems might have more physical
	   memory then can be represented with a `size_t' value (when
	   measured in bytes.  */

      /* If the memory requirements are too high don't allocate memory.  */
      if (size / pagesize > phys_pages)
	_quicksort (b, n, s, cmp);
      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.  */
	      __set_errno (save);
	      _quicksort (b, n, s, cmp);
	    }
	  else
	    {
	      __set_errno (save);
	      msort_with_tmp (b, n, s, cmp, tmp);
	      free (tmp);
	    }
	}
    }
}