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