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 #include <limits.h>
  28 #ifdef HAVE_STDLIB_H
  29 #include <stdlib.h>
  30 #endif
  31 #ifdef HAVE_STRING_H
  32 #include <string.h>
  33 #endif
  34
  35 #ifndef UCHAR_MAX
  36 #define UCHAR_MAX ((unsigned char)(-1))
  37 #endif
  38
  39 /* POINTERS and WORK are both arrays of N pointers.  When this
  40    function returns POINTERS will be sorted in ascending order.  */
  41
  42 void sort_pointers (n, pointers, work)
  43      size_t n;
  44      void **pointers;
  45      void **work;
  46 {
  47   /* The type of a single digit.  This can be any unsigned integral
  48      type.  When changing this, DIGIT_MAX should be changed as
  49      well.  */
  50   typedef unsigned char digit_t;
  51
  52   /* The maximum value a single digit can have.  */
  53 #define DIGIT_MAX (UCHAR_MAX + 1)
  54
  55   /* The Ith entry is the number of elements in *POINTERSP that have I
  56      in the digit on which we are currently sorting.  */
  57   unsigned int count[DIGIT_MAX];
  58   /* Nonzero if we are running on a big-endian machine.  */
  59   int big_endian_p;
  60   size_t i;
  61   size_t j;
  62
  63   /* The algorithm used here is radix sort which takes time linear in
  64      the number of elements in the array.  */
  65
  66   /* The algorithm here depends on being able to swap the two arrays
  67      an even number of times.  */
  68   if ((sizeof (void *) / sizeof (digit_t)) % 2 != 0)
  69     abort ();
  70
  71   /* Figure out the endianness of the machine.  */
  72   for (i = 0, j = 0; i < sizeof (size_t); ++i)
  73     {
  74       j *= (UCHAR_MAX + 1);
  75       j += i;
  76     }
  77   big_endian_p = (((char *)&j)[0] == 0);
  78
  79   /* Move through the pointer values from least significant to most
  80      significant digits.  */
  81   for (i = 0; i < sizeof (void *) / sizeof (digit_t); ++i)
  82     {
  83       digit_t *digit;
  84       digit_t *bias;
  85       digit_t *top;
  86       unsigned int *countp;
  87       void **pointerp;
  88
  89       /* The offset from the start of the pointer will depend on the
  90          endianness of the machine.  */
  91       if (big_endian_p)
  92         j = sizeof (void *) / sizeof (digit_t) - i;
  93       else
  94         j = i;
  95
  96       /* Now, perform a stable sort on this digit.  We use counting
  97          sort.  */
  98       memset (count, 0, DIGIT_MAX * sizeof (unsigned int));
  99
 100       /* Compute the address of the appropriate digit in the first and
 101          one-past-the-end elements of the array.  On a little-endian
 102          machine, the least-significant digit is closest to the front.  */
 103       bias = ((digit_t *) pointers) + j;
 104       top = ((digit_t *) (pointers + n)) + j;
 105
 106       /* Count how many there are of each value.  At the end of this
 107          loop, COUNT[K] will contain the number of pointers whose Ith
 108          digit is K.  */
 109       for (digit = bias;
 110            digit < top;
 111            digit += sizeof (void *) / sizeof (digit_t))
 112         ++count[*digit];
 113
 114       /* Now, make COUNT[K] contain the number of pointers whose Ith
 115          digit is less than or equal to K.  */
 116       for (countp = count + 1; countp < count + DIGIT_MAX; ++countp)
 117         *countp += countp[-1];
 118
 119       /* Now, drop the pointers into their correct locations.  */
 120       for (pointerp = pointers + n - 1; pointerp >= pointers; --pointerp)
 121         work[--count[((digit_t *) pointerp)[j]]] = *pointerp;
 122
 123       /* Swap WORK and POINTERS so that POINTERS contains the sorted
 124          array.  */
 125       pointerp = pointers;
 126       pointers = work;
 127       work = pointerp;
 128     }
 129 }
 130
 131 /* Everything below here is a unit test for the routines in this
 132    file.  */
 133
 134 #ifdef UNIT_TEST
 135
 136 #include <stdio.h>
 137
 138 void *xmalloc (n)
 139      size_t n;
 140 {
 141   return malloc (n);
 142 }
 143
 144 int main (int argc, char **argv)
 145 {
 146   int k;
 147   int result;
 148   size_t i;
 149   void **pointers;
 150   void **work;
 151
 152   if (argc > 1)
 153     k = atoi (argv[1]);
 154   else
 155     k = 10;
 156
 157   pointers = xmalloc (k * sizeof (void *));
 158   work = xmalloc (k * sizeof (void *));
 159
 160   for (i = 0; i < k; ++i)
 161     {
 162       pointers[i] = (void *) random ();
 163       printf ("%x\n", pointers[i]);
 164     }
 165
 166   sort_pointers (k, pointers, work);
 167
 168   printf ("\nSorted\n\n");
 169
 170   result = 0;
 171
 172   for (i = 0; i < k; ++i)
 173     {
 174       printf ("%x\n", pointers[i]);
 175       if (i > 0 && (char*) pointers[i] < (char*) pointers[i - 1])
 176         result = 1;
 177     }
 178
 179   free (pointers);
 180   free (work);
 181
 182   return result;
 183 }
 184
 185 #endif