libiberty/sort.c

   1 /* Sorting algorithms.
   2    Copyright (C) 2000 Free Software Foundation, Inc.
   3    Contributed by Mark Mitchell <mark@codesourcery.com>.
   4
   5 This file is part of GNU CC.
   6
   7 GNU CC is free software; you can redistribute it and/or modify it
   8 under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2, or (at your option)
  10 any later version.
  11
  12 GNU CC is distributed in the hope that it will be useful, but
  13 WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15 General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GNU CC; see the file COPYING.  If not, write to
  19 the Free Software Foundation, 59 Temple Place - Suite 330,
  20 Boston, MA 02111-1307, USA.  */
  21
  22 #ifdef HAVE_CONFIG_H
  23 #include "config.h"
  24 #endif
  25 #include "libiberty.h"
  26 #include "sort.h"
  27 #ifdef HAVE_LIMITS_H
  28 #include <limits.h>
  29 #endif
  30 #ifdef HAVE_SYS_PARAM_H
  31 #include <sys/param.h>
  32 #endif
  33 #ifdef HAVE_STDLIB_H
  34 #include <stdlib.h>
  35 #endif
  36 #ifdef HAVE_STRING_H
  37 #include <string.h>
  38 #endif
  39
  40 #ifndef UCHAR_MAX
  41 #define UCHAR_MAX ((unsigned char)(-1))
  42 #endif
  43
  44 /* POINTERS and WORK are both arrays of N pointers.  When this
  45    function returns POINTERS will be sorted in ascending order.  */
  46
  47 void sort_pointers (n, pointers, work)
  48      size_t n;
  49      void **pointers;
  50      void **work;
  51 {
  52   /* The type of a single digit.  This can be any unsigned integral
  53      type.  When changing this, DIGIT_MAX should be changed as
  54      well.  */
  55   typedef unsigned char digit_t;
  56
  57   /* The maximum value a single digit can have.  */
  58 #define DIGIT_MAX (UCHAR_MAX + 1)
  59
  60   /* The Ith entry is the number of elements in *POINTERSP that have I
  61      in the digit on which we are currently sorting.  */
  62   unsigned int count[DIGIT_MAX];
  63   /* Nonzero if we are running on a big-endian machine.  */
  64   int big_endian_p;
  65   size_t i;
  66   size_t j;
  67
  68   /* The algorithm used here is radix sort which takes time linear in
  69      the number of elements in the array.  */
  70
  71   /* The algorithm here depends on being able to swap the two arrays
  72      an even number of times.  */
  73   if ((sizeof (void *) / sizeof (digit_t)) % 2 != 0)
  74     abort ();
  75
  76   /* Figure out the endianness of the machine.  */
  77   for (i = 0, j = 0; i < sizeof (size_t); ++i)
  78     {
  79       j *= (UCHAR_MAX + 1);
  80       j += i;
  81     }
  82   big_endian_p = (((char *)&j)[0] == 0);
  83
  84   /* Move through the pointer values from least significant to most
  85      significant digits.  */
  86   for (i = 0; i < sizeof (void *) / sizeof (digit_t); ++i)
  87     {
  88       digit_t *digit;
  89       digit_t *bias;
  90       digit_t *top;
  91       unsigned int *countp;
  92       void **pointerp;
  93
  94       /* The offset from the start of the pointer will depend on the
  95          endianness of the machine.  */
  96       if (big_endian_p)
  97         j = sizeof (void *) / sizeof (digit_t) - i;
  98       else
  99         j = i;
 100
 101       /* Now, perform a stable sort on this digit.  We use counting
 102          sort.  */
 103       memset (count, 0, DIGIT_MAX * sizeof (unsigned int));
 104
 105       /* Compute the address of the appropriate digit in the first and
 106          one-past-the-end elements of the array.  On a little-endian
 107          machine, the least-significant digit is closest to the front.  */
 108       bias = ((digit_t *) pointers) + j;
 109       top = ((digit_t *) (pointers + n)) + j;
 110
 111       /* Count how many there are of each value.  At the end of this
 112          loop, COUNT[K] will contain the number of pointers whose Ith
 113          digit is K.  */
 114       for (digit = bias;
 115            digit < top;
 116            digit += sizeof (void *) / sizeof (digit_t))
 117         ++count[*digit];
 118
 119       /* Now, make COUNT[K] contain the number of pointers whose Ith
 120          digit is less than or equal to K.  */
 121       for (countp = count + 1; countp < count + DIGIT_MAX; ++countp)
 122         *countp += countp[-1];
 123
 124       /* Now, drop the pointers into their correct locations.  */
 125       for (pointerp = pointers + n - 1; pointerp >= pointers; --pointerp)
 126         work[--count[((digit_t *) pointerp)[j]]] = *pointerp;
 127
 128       /* Swap WORK and POINTERS so that POINTERS contains the sorted
 129          array.  */
 130       pointerp = pointers;
 131       pointers = work;
 132       work = pointerp;
 133     }
 134 }
 135
 136 /* Everything below here is a unit test for the routines in this
 137    file.  */
 138
 139 #ifdef UNIT_TEST
 140
 141 #include <stdio.h>
 142
 143 void *xmalloc (n)
 144      size_t n;
 145 {
 146   return malloc (n);
 147 }
 148
 149 int main (int argc, char **argv)
 150 {
 151   int k;
 152   int result;
 153   size_t i;
 154   void **pointers;
 155   void **work;
 156
 157   if (argc > 1)
 158     k = atoi (argv[1]);
 159   else
 160     k = 10;
 161
 162   pointers = xmalloc (k * sizeof (void *));
 163   work = xmalloc (k * sizeof (void *));
 164
 165   for (i = 0; i < k; ++i)
 166     {
 167       pointers[i] = (void *) random ();
 168       printf ("%x\n", pointers[i]);
 169     }
 170
 171   sort_pointers (k, pointers, work);
 172
 173   printf ("\nSorted\n\n");
 174
 175   result = 0;
 176
 177   for (i = 0; i < k; ++i)
 178     {
 179       printf ("%x\n", pointers[i]);
 180       if (i > 0 && (char*) pointers[i] < (char*) pointers[i - 1])
 181         result = 1;
 182     }
 183
 184   free (pointers);
 185   free (work);
 186
 187   return result;
 188 }
 189
 190 #endif