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  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, 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
  187.