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comparison lib-src/qsort.c @ 0:376386a54a3c r19-14

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Import from CVS: tag r19-14
author cvs
date Mon, 13 Aug 2007 08:45:50 +0200
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1 /* Plug-compatible replacement for UNIX qsort.
2 Copyright (C) 1989 Free Software Foundation, Inc.
3 Written by Douglas C. Schmidt (schmidt@ics.uci.edu)
4
5 This file is part of GNU CC.
6
7 GNU QSORT is free software; you can redistribute it and/or modify
8 it 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 QSORT is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
16
17 You should have received a copy of the GNU General Public License
18 along with GNU QSORT; see the file COPYING. If not, write to
19 the Free the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
20 Boston, MA 02111-1307, USA. */
21
22 /* Synched up with: FSF 19.28. */
23
24 #ifdef sparc
25 #include <alloca.h>
26 #endif
27
28 /* Invoke the comparison function, returns either 0, < 0, or > 0. */
29 #define CMP(A,B) ((*cmp)((A),(B)))
30
31 /* Byte-wise swap two items of size SIZE. */
32 #define SWAP(A,B,SIZE) do {int sz = (SIZE); char *a = (A); char *b = (B); \
33 do { char _temp = *a;*a++ = *b;*b++ = _temp;} while (--sz);} while (0)
34
35 /* Copy SIZE bytes from item B to item A. */
36 #define COPY(A,B,SIZE) {int sz = (SIZE); do { *(A)++ = *(B)++; } while (--sz); }
37
38 /* This should be replaced by a standard ANSI macro. */
39 #define BYTES_PER_WORD 8
40
41 /* The next 4 #defines implement a very fast in-line stack abstraction. */
42 #define STACK_SIZE (BYTES_PER_WORD * sizeof (long))
43 #define PUSH(LOW,HIGH) do {top->lo = LOW;top++->hi = HIGH;} while (0)
44 #define POP(LOW,HIGH) do {LOW = (--top)->lo;HIGH = top->hi;} while (0)
45 #define STACK_NOT_EMPTY (stack < top)
46
47 /* Discontinue quicksort algorithm when partition gets below this size.
48 This particular magic number was chosen to work best on a Sun 4/260. */
49 #define MAX_THRESH 4
50
51 /* Stack node declarations used to store unfulfilled partition obligations. */
52 typedef struct
53 {
54 char *lo;
55 char *hi;
56 } stack_node;
57
58 /* Order size using quicksort. This implementation incorporates
59 four optimizations discussed in Sedgewick:
60
61 1. Non-recursive, using an explicit stack of pointer that store the
62 next array partition to sort. To save time, this maximum amount
63 of space required to store an array of MAX_INT is allocated on the
64 stack. Assuming a 32-bit integer, this needs only 32 *
65 sizeof (stack_node) == 136 bits. Pretty cheap, actually.
66
67 2. Chose the pivot element using a median-of-three decision tree.
68 This reduces the probability of selecting a bad pivot value and
69 eliminates certain extraneous comparisons.
70
71 3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving
72 insertion sort to order the MAX_THRESH items within each partition.
73 This is a big win, since insertion sort is faster for small, mostly
74 sorted array segments.
75
76 4. The larger of the two sub-partitions is always pushed onto the
77 stack first, with the algorithm then concentrating on the
78 smaller partition. This *guarantees* no more than log (n)
79 stack size is needed (actually O(1) in this case)! */
80
81 int
82 qsort (base_ptr, total_elems, size, cmp)
83 char *base_ptr;
84 int total_elems;
85 int size;
86 int (*cmp)();
87 {
88 /* Allocating SIZE bytes for a pivot buffer facilitates a better
89 algorithm below since we can do comparisons directly on the pivot. */
90 char *pivot_buffer = (char *) alloca (size);
91 int max_thresh = MAX_THRESH * size;
92
93 if (total_elems > MAX_THRESH)
94 {
95 char *lo = base_ptr;
96 char *hi = lo + size * (total_elems - 1);
97 stack_node stack[STACK_SIZE]; /* Largest size needed for 32-bit int!!! */
98 stack_node *top = stack + 1;
99
100 while (STACK_NOT_EMPTY)
101 {
102 char *left_ptr;
103 char *right_ptr;
104 {
105 char *pivot = pivot_buffer;
106 {
107 /* Select median value from among LO, MID, and HI. Rearrange
108 LO and HI so the three values are sorted. This lowers the
109 probability of picking a pathological pivot value and
110 skips a comparison for both the LEFT_PTR and RIGHT_PTR. */
111
112 char *mid = lo + size * ((hi - lo) / size >> 1);
113
114 if (CMP (mid, lo) < 0)
115 SWAP (mid, lo, size);
116 if (CMP (hi, mid) < 0)
117 SWAP (mid, hi, size);
118 else
119 goto jump_over;
120 if (CMP (mid, lo) < 0)
121 SWAP (mid, lo, size);
122 jump_over:
123 COPY (pivot, mid, size);
124 pivot = pivot_buffer;
125 }
126 left_ptr = lo + size;
127 right_ptr = hi - size;
128
129 /* Here's the famous ``collapse the walls'' section of quicksort.
130 Gotta like those tight inner loops! They are the main reason
131 that this algorithm runs much faster than others. */
132 do
133 {
134 while (CMP (left_ptr, pivot) < 0)
135 left_ptr += size;
136
137 while (CMP (pivot, right_ptr) < 0)
138 right_ptr -= size;
139
140 if (left_ptr < right_ptr)
141 {
142 SWAP (left_ptr, right_ptr, size);
143 left_ptr += size;
144 right_ptr -= size;
145 }
146 else if (left_ptr == right_ptr)
147 {
148 left_ptr += size;
149 right_ptr -= size;
150 break;
151 }
152 }
153 while (left_ptr <= right_ptr);
154
155 }
156
157 /* Set up pointers for next iteration. First determine whether
158 left and right partitions are below the threshold size. If so,
159 ignore one or both. Otherwise, push the larger partition's
160 bounds on the stack and continue sorting the smaller one. */
161
162 if ((right_ptr - lo) <= max_thresh)
163 {
164 if ((hi - left_ptr) <= max_thresh) /* Ignore both small partitions. */
165 POP (lo, hi);
166 else /* Ignore small left partition. */
167 lo = left_ptr;
168 }
169 else if ((hi - left_ptr) <= max_thresh) /* Ignore small right partition. */
170 hi = right_ptr;
171 else if ((right_ptr - lo) > (hi - left_ptr)) /* Push larger left partition indices. */
172 {
173 PUSH (lo, right_ptr);
174 lo = left_ptr;
175 }
176 else /* Push larger right partition indices. */
177 {
178 PUSH (left_ptr, hi);
179 hi = right_ptr;
180 }
181 }
182 }
183
184 /* Once the BASE_PTR array is partially sorted by quicksort the rest
185 is completely sorted using insertion sort, since this is efficient
186 for partitions below MAX_THRESH size. BASE_PTR points to the beginning
187 of the array to sort, and END_PTR points at the very last element in
188 the array (*not* one beyond it!). */
189
190 #define MIN(X,Y) ((X) < (Y) ? (X) : (Y))
191
192 {
193 char *end_ptr = base_ptr + size * (total_elems - 1);
194 char *run_ptr;
195 char *tmp_ptr = base_ptr;
196 char *thresh = MIN (end_ptr, base_ptr + max_thresh);
197
198 /* Find smallest element in first threshold and place it at the
199 array's beginning. This is the smallest array element,
200 and the operation speeds up insertion sort's inner loop. */
201
202 for (run_ptr = tmp_ptr + size; run_ptr <= thresh; run_ptr += size)
203 if (CMP (run_ptr, tmp_ptr) < 0)
204 tmp_ptr = run_ptr;
205
206 if (tmp_ptr != base_ptr)
207 SWAP (tmp_ptr, base_ptr, size);
208
209 /* Insertion sort, running from left-hand-side up to `right-hand-side.'
210 Pretty much straight out of the original GNU qsort routine. */
211
212 for (run_ptr = base_ptr + size; (tmp_ptr = run_ptr += size) <= end_ptr; )
213 {
214
215 while (CMP (run_ptr, tmp_ptr -= size) < 0)
216 ;
217
218 if ((tmp_ptr += size) != run_ptr)
219 {
220 char *trav;
221
222 for (trav = run_ptr + size; --trav >= run_ptr;)
223 {
224 char c = *trav;
225 char *hi, *lo;
226
227 for (hi = lo = trav; (lo -= size) >= tmp_ptr; hi = lo)
228 *hi = *lo;
229 *hi = c;
230 }
231 }
232
233 }
234 }
235 return 1;
236 }
237