2 * SPDX-License-Identifier: BSD-3-Clause
4 * Copyright (c) 1991, 1993
5 * The Regents of the University of California. All rights reserved.
6 * Copyright (c) 2014 David T. Chisnall
9 * This code is derived from software contributed to Berkeley by
10 * Ronnie Kon at Mindcraft Inc., Kevin Lew and Elmer Yglesias.
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13 * modification, are permitted provided that the following conditions
15 * 1. Redistributions of source code must retain the above copyright
16 * notice, this list of conditions and the following disclaimer.
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20 * 3. Neither the name of the University nor the names of its contributors
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37 #if defined(LIBC_SCCS) && !defined(lint)
38 static char sccsid[] = "@(#)heapsort.c 8.1 (Berkeley) 6/4/93";
39 #endif /* LIBC_SCCS and not lint */
44 #ifdef I_AM_HEAPSORT_B
45 #include "block_abi.h"
46 #define COMPAR(x, y) CALL_BLOCK(compar, x, y)
47 typedef DECLARE_BLOCK(int, heapsort_block, const void *, const void *);
49 #define COMPAR(x, y) compar(x, y)
53 * Swap two areas of size number of bytes. Although qsort(3) permits random
54 * blocks of memory to be sorted, sorting pointers is almost certainly the
55 * common case (and, were it not, could easily be made so). Regardless, it
56 * isn't worth optimizing; the SWAP's get sped up by the cache, and pointer
57 * arithmetic gets lost in the time required for comparison function calls.
59 #define SWAP(a, b, count, size, tmp) { \
68 /* Copy one block of size size to another. */
69 #define COPY(a, b, count, size, tmp1, tmp2) { \
79 * Build the list into a heap, where a heap is defined such that for
80 * the records K1 ... KN, Kj/2 >= Kj for 1 <= j/2 <= j <= N.
82 * There two cases. If j == nmemb, select largest of Ki and Kj. If
83 * j < nmemb, select largest of Ki, Kj and Kj+1.
85 #define CREATE(initval, nmemb, par_i, child_i, par, child, size, count, tmp) { \
86 for (par_i = initval; (child_i = par_i * 2) <= nmemb; \
88 child = base + child_i * size; \
89 if (child_i < nmemb && COMPAR(child, child + size) < 0) { \
93 par = base + par_i * size; \
94 if (COMPAR(child, par) <= 0) \
96 SWAP(par, child, count, size, tmp); \
101 * Select the top of the heap and 'heapify'. Since by far the most expensive
102 * action is the call to the compar function, a considerable optimization
103 * in the average case can be achieved due to the fact that k, the displaced
104 * elememt, is usually quite small, so it would be preferable to first
105 * heapify, always maintaining the invariant that the larger child is copied
106 * over its parent's record.
108 * Then, starting from the *bottom* of the heap, finding k's correct place,
109 * again maintianing the invariant. As a result of the invariant no element
110 * is 'lost' when k is assigned its correct place in the heap.
112 * The time savings from this optimization are on the order of 15-20% for the
113 * average case. See Knuth, Vol. 3, page 158, problem 18.
115 * XXX Don't break the #define SELECT line, below. Reiser cpp gets upset.
117 #define SELECT(par_i, child_i, nmemb, par, child, size, k, count, tmp1, tmp2) { \
118 for (par_i = 1; (child_i = par_i * 2) <= nmemb; par_i = child_i) { \
119 child = base + child_i * size; \
120 if (child_i < nmemb && COMPAR(child, child + size) < 0) { \
124 par = base + par_i * size; \
125 COPY(par, child, count, size, tmp1, tmp2); \
129 par_i = child_i / 2; \
130 child = base + child_i * size; \
131 par = base + par_i * size; \
132 if (child_i == 1 || COMPAR(k, par) < 0) { \
133 COPY(child, k, count, size, tmp1, tmp2); \
136 COPY(child, par, count, size, tmp1, tmp2); \
140 #ifdef I_AM_HEAPSORT_B
141 int heapsort_b(void *, size_t, size_t, heapsort_block);
143 int heapsort(void *, size_t, size_t,
144 int (*)(const void *, const void *));
147 * Heapsort -- Knuth, Vol. 3, page 145. Runs in O (N lg N), both average
148 * and worst. While heapsort is faster than the worst case of quicksort,
149 * the BSD quicksort does median selection so that the chance of finding
150 * a data set that will trigger the worst case is nonexistent. Heapsort's
151 * only advantage over quicksort is that it requires little additional memory.
153 #ifdef I_AM_HEAPSORT_B
155 heapsort_b(void *vbase, size_t nmemb, size_t size, heapsort_block compar)
158 heapsort(void *vbase, size_t nmemb, size_t size,
159 int (*compar)(const void *, const void *))
163 char tmp, *tmp1, *tmp2;
164 char *base, *k, *p, *t;
174 if ((k = malloc(size)) == NULL)
178 * Items are numbered from 1 to nmemb, so offset from size bytes
179 * below the starting address.
181 base = (char *)vbase - size;
183 for (l = nmemb / 2 + 1; --l;)
184 CREATE(l, nmemb, i, j, t, p, size, cnt, tmp);
187 * For each element of the heap, save the largest element into its
188 * final slot, save the displaced element (k), then recreate the
192 COPY(k, base + nmemb * size, cnt, size, tmp1, tmp2);
193 COPY(base + nmemb * size, base + size, cnt, size, tmp1, tmp2);
195 SELECT(i, j, nmemb, t, p, size, k, cnt, tmp1, tmp2);