libiberty/sort.c

   1 /* Sorting algorithms.
   2    Copyright (C) 2000-2018 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, 51 Franklin Street - Fifth Floor,
  20 Boston, MA 02110-1301, 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 (size_t n, void **pointers, void **work)
  48 {
  49   /* The type of a single digit.  This can be any unsigned integral
  50      type.  When changing this, DIGIT_MAX should be changed as
  51      well.  */
  52   typedef unsigned char digit_t;
  53
  54   /* The maximum value a single digit can have.  */
  55 #define DIGIT_MAX (UCHAR_MAX + 1)
  56
  57   /* The Ith entry is the number of elements in *POINTERSP that have I
  58      in the digit on which we are currently sorting.  */
  59   unsigned int count[DIGIT_MAX];
  60   /* Nonzero if we are running on a big-endian machine.  */
  61   int big_endian_p;
  62   size_t i;
  63   size_t j;
  64
  65   /* The algorithm used here is radix sort which takes time linear in
  66      the number of elements in the array.  */
  67
  68   /* The algorithm here depends on being able to swap the two arrays
  69      an even number of times.  */
  70   if ((sizeof (void *) / sizeof (digit_t)) % 2 != 0)
  71     abort ();
  72
  73   /* Figure out the endianness of the machine.  */
  74   for (i = 0, j = 0; i < sizeof (size_t); ++i)
  75     {
  76       j *= (UCHAR_MAX + 1);
  77       j += i;
  78     }
  79   big_endian_p = (((char *)&j)[0] == 0);
  80
  81   /* Move through the pointer values from least significant to most
  82      significant digits.  */
  83   for (i = 0; i < sizeof (void *) / sizeof (digit_t); ++i)
  84     {
  85       digit_t *digit;
  86       digit_t *bias;
  87       digit_t *top;
  88       unsigned int *countp;
  89       void **pointerp;
  90
  91       /* The offset from the start of the pointer will depend on the
  92          endianness of the machine.  */
  93       if (big_endian_p)
  94         j = sizeof (void *) / sizeof (digit_t) - i;
  95       else
  96         j = i;
  97
  98       /* Now, perform a stable sort on this digit.  We use counting
  99          sort.  */
 100       memset (count, 0, DIGIT_MAX * sizeof (unsigned int));
 101
 102       /* Compute the address of the appropriate digit in the first and
 103          one-past-the-end elements of the array.  On a little-endian
 104          machine, the least-significant digit is closest to the front.  */
 105       bias = ((digit_t *) pointers) + j;
 106       top = ((digit_t *) (pointers + n)) + j;
 107
 108       /* Count how many there are of each value.  At the end of this
 109          loop, COUNT[K] will contain the number of pointers whose Ith
 110          digit is K.  */
 111       for (digit = bias;
 112            digit < top;
 113            digit += sizeof (void *) / sizeof (digit_t))
 114         ++count[*digit];
 115
 116       /* Now, make COUNT[K] contain the number of pointers whose Ith
 117          digit is less than or equal to K.  */
 118       for (countp = count + 1; countp < count + DIGIT_MAX; ++countp)
 119         *countp += countp[-1];
 120
 121       /* Now, drop the pointers into their correct locations.  */
 122       for (pointerp = pointers + n - 1; pointerp >= pointers; --pointerp)
 123         work[--count[((digit_t *) pointerp)[j]]] = *pointerp;
 124
 125       /* Swap WORK and POINTERS so that POINTERS contains the sorted
 126          array.  */
 127       pointerp = pointers;
 128       pointers = work;
 129       work = pointerp;
 130     }
 131 }
 132
 133 /* Everything below here is a unit test for the routines in this
 134    file.  */
 135
 136 #ifdef UNIT_TEST
 137
 138 #include <stdio.h>
 139
 140 void *xmalloc (size_t n)
 141 {
 142   return malloc (n);
 143 }
 144
 145 int main (int argc, char **argv)
 146 {
 147   int k;
 148   int result;
 149   size_t i;
 150   void **pointers;
 151   void **work;
 152
 153   if (argc > 1)
 154     k = atoi (argv[1]);
 155   else
 156     k = 10;
 157
 158   pointers = XNEWVEC (void*, k);
 159   work = XNEWVEC (void*, k);
 160
 161   for (i = 0; i < k; ++i)
 162     {
 163       pointers[i] = (void *) random ();
 164       printf ("%x\n", pointers[i]);
 165     }
 166
 167   sort_pointers (k, pointers, work);
 168
 169   printf ("\nSorted\n\n");
 170
 171   result = 0;
 172
 173   for (i = 0; i < k; ++i)
 174     {
 175       printf ("%x\n", pointers[i]);
 176       if (i > 0 && (char*) pointers[i] < (char*) pointers[i - 1])
 177         result = 1;
 178     }
 179
 180   free (pointers);
 181   free (work);
 182
 183   return result;
 184 }
 185
 186 #endif