2 * Copyright (c) 1991, 1993
3 * The Regents of the University of California. All rights reserved.
5 * This code is derived from software contributed to Berkeley by
6 * Ronnie Kon at Mindcraft Inc., Kevin Lew and Elmer Yglesias.
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
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16 * 3. Neither the name of the University nor the names of its contributors
17 * may be used to endorse or promote products derived from this software
18 * without specific prior written permission.
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
38 * Swap two areas of size number of bytes. Although qsort(3) permits random
39 * blocks of memory to be sorted, sorting pointers is almost certainly the
40 * common case (and, were it not, could easily be made so). Regardless, it
41 * isn't worth optimizing; the SWAP's get sped up by the cache, and pointer
42 * arithmetic gets lost in the time required for comparison function calls.
44 #define SWAP(a, b, count, size, tmp) { \
53 /* Copy one block of size size to another. */
54 #define COPY(a, b, count, size, tmp1, tmp2) { \
64 * Build the list into a heap, where a heap is defined such that for
65 * the records K1 ... KN, Kj/2 >= Kj for 1 <= j/2 <= j <= N.
67 * There two cases. If j == nmemb, select largest of Ki and Kj. If
68 * j < nmemb, select largest of Ki, Kj and Kj+1.
70 #define CREATE(initval, nmemb, par_i, child_i, par, child, size, count, tmp) { \
71 for (par_i = initval; (child_i = par_i * 2) <= nmemb; \
73 child = base + child_i * size; \
74 if (child_i < nmemb && compar(child, child + size) < 0) { \
78 par = base + par_i * size; \
79 if (compar(child, par) <= 0) \
81 SWAP(par, child, count, size, tmp); \
86 * Select the top of the heap and 'heapify'. Since by far the most expensive
87 * action is the call to the compar function, a considerable optimization
88 * in the average case can be achieved due to the fact that k, the displaced
89 * elememt, is ususally quite small, so it would be preferable to first
90 * heapify, always maintaining the invariant that the larger child is copied
91 * over its parent's record.
93 * Then, starting from the *bottom* of the heap, finding k's correct place,
94 * again maintianing the invariant. As a result of the invariant no element
95 * is 'lost' when k is assigned its correct place in the heap.
97 * The time savings from this optimization are on the order of 15-20% for the
98 * average case. See Knuth, Vol. 3, page 158, problem 18.
100 * XXX Don't break the #define SELECT line, below. Reiser cpp gets upset.
102 #define SELECT(par_i, child_i, nmemb, par, child, size, k, count, tmp1, tmp2) { \
103 for (par_i = 1; (child_i = par_i * 2) <= nmemb; par_i = child_i) { \
104 child = base + child_i * size; \
105 if (child_i < nmemb && compar(child, child + size) < 0) { \
109 par = base + par_i * size; \
110 COPY(par, child, count, size, tmp1, tmp2); \
114 par_i = child_i / 2; \
115 child = base + child_i * size; \
116 par = base + par_i * size; \
117 if (child_i == 1 || compar(k, par) < 0) { \
118 COPY(child, k, count, size, tmp1, tmp2); \
121 COPY(child, par, count, size, tmp1, tmp2); \
126 * Heapsort -- Knuth, Vol. 3, page 145. Runs in O (N lg N), both average
127 * and worst. While heapsort is faster than the worst case of quicksort,
128 * the BSD quicksort does median selection so that the chance of finding
129 * a data set that will trigger the worst case is nonexistent. Heapsort's
130 * only advantage over quicksort is that it requires little additional memory.
133 heapsort(vbase, nmemb, size, compar)
136 int (*compar)(const void *, const void *);
139 char tmp, *tmp1, *tmp2;
140 char *base, *k, *p, *t;
150 if ((k = malloc(size)) == NULL)
154 * Items are numbered from 1 to nmemb, so offset from size bytes
155 * below the starting address.
157 base = (char *)vbase - size;
159 for (l = nmemb / 2 + 1; --l;)
160 CREATE(l, nmemb, i, j, t, p, size, cnt, tmp);
163 * For each element of the heap, save the largest element into its
164 * final slot, save the displaced element (k), then recreate the
168 COPY(k, base + nmemb * size, cnt, size, tmp1, tmp2);
169 COPY(base + nmemb * size, base + size, cnt, size, tmp1, tmp2);
171 SELECT(i, j, nmemb, t, p, size, k, cnt, tmp1, tmp2);