1/* Sorting algorithms.
2   Copyright (C) 2000 Free Software Foundation, Inc.
3   Contributed by Mark Mitchell <mark@codesourcery.com>.
4
5This file is part of GNU CC.
6
7GNU CC is free software; you can redistribute it and/or modify it
8under the terms of the GNU General Public License as published by
9the Free Software Foundation; either version 2, or (at your option)
10any later version.
11
12GNU CC is distributed in the hope that it will be useful, but
13WITHOUT ANY WARRANTY; without even the implied warranty of
14MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
15General Public License for more details.
16
17You should have received a copy of the GNU General Public License
18along with GNU CC; see the file COPYING.  If not, write to
19the Free Software Foundation, 51 Franklin Street - Fifth Floor,
20Boston, 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
47void 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
140void *xmalloc (size_t n)
141{
142  return malloc (n);
143}
144
145int 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