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