heapsort.c revision 288005
1/*- 2 * Copyright (c) 1991, 1993 3 * The Regents of the University of California. All rights reserved. 4 * Copyright (c) 2014 David T. Chisnall 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to Berkeley by 8 * Ronnie Kon at Mindcraft Inc., Kevin Lew and Elmer Yglesias. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. Neither the name of the University nor the names of its contributors 19 * may be used to endorse or promote products derived from this software 20 * without specific prior written permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35#if defined(LIBC_SCCS) && !defined(lint) 36static char sccsid[] = "@(#)heapsort.c 8.1 (Berkeley) 6/4/93"; 37#endif /* LIBC_SCCS and not lint */ 38#include <sys/cdefs.h> 39__FBSDID("$FreeBSD: head/lib/libc/stdlib/heapsort.c 288005 2015-09-20 03:53:08Z rodrigc $"); 40 41#include <errno.h> 42#include <stddef.h> 43#include <stdlib.h> 44 45#ifdef I_AM_HEAPSORT_B 46#include "block_abi.h" 47#define COMPAR(x, y) CALL_BLOCK(compar, x, y) 48typedef DECLARE_BLOCK(int, heapsort_block, const void *, const void *); 49#else 50#define COMPAR(x, y) compar(x, y) 51#endif 52 53/* 54 * Swap two areas of size number of bytes. Although qsort(3) permits random 55 * blocks of memory to be sorted, sorting pointers is almost certainly the 56 * common case (and, were it not, could easily be made so). Regardless, it 57 * isn't worth optimizing; the SWAP's get sped up by the cache, and pointer 58 * arithmetic gets lost in the time required for comparison function calls. 59 */ 60#define SWAP(a, b, count, size, tmp) { \ 61 count = size; \ 62 do { \ 63 tmp = *a; \ 64 *a++ = *b; \ 65 *b++ = tmp; \ 66 } while (--count); \ 67} 68 69/* Copy one block of size size to another. */ 70#define COPY(a, b, count, size, tmp1, tmp2) { \ 71 count = size; \ 72 tmp1 = a; \ 73 tmp2 = b; \ 74 do { \ 75 *tmp1++ = *tmp2++; \ 76 } while (--count); \ 77} 78 79/* 80 * Build the list into a heap, where a heap is defined such that for 81 * the records K1 ... KN, Kj/2 >= Kj for 1 <= j/2 <= j <= N. 82 * 83 * There two cases. If j == nmemb, select largest of Ki and Kj. If 84 * j < nmemb, select largest of Ki, Kj and Kj+1. 85 */ 86#define CREATE(initval, nmemb, par_i, child_i, par, child, size, count, tmp) { \ 87 for (par_i = initval; (child_i = par_i * 2) <= nmemb; \ 88 par_i = child_i) { \ 89 child = base + child_i * size; \ 90 if (child_i < nmemb && COMPAR(child, child + size) < 0) { \ 91 child += size; \ 92 ++child_i; \ 93 } \ 94 par = base + par_i * size; \ 95 if (COMPAR(child, par) <= 0) \ 96 break; \ 97 SWAP(par, child, count, size, tmp); \ 98 } \ 99} 100 101/* 102 * Select the top of the heap and 'heapify'. Since by far the most expensive 103 * action is the call to the compar function, a considerable optimization 104 * in the average case can be achieved due to the fact that k, the displaced 105 * elememt, is ususally quite small, so it would be preferable to first 106 * heapify, always maintaining the invariant that the larger child is copied 107 * over its parent's record. 108 * 109 * Then, starting from the *bottom* of the heap, finding k's correct place, 110 * again maintianing the invariant. As a result of the invariant no element 111 * is 'lost' when k is assigned its correct place in the heap. 112 * 113 * The time savings from this optimization are on the order of 15-20% for the 114 * average case. See Knuth, Vol. 3, page 158, problem 18. 115 * 116 * XXX Don't break the #define SELECT line, below. Reiser cpp gets upset. 117 */ 118#define SELECT(par_i, child_i, nmemb, par, child, size, k, count, tmp1, tmp2) { \ 119 for (par_i = 1; (child_i = par_i * 2) <= nmemb; par_i = child_i) { \ 120 child = base + child_i * size; \ 121 if (child_i < nmemb && COMPAR(child, child + size) < 0) { \ 122 child += size; \ 123 ++child_i; \ 124 } \ 125 par = base + par_i * size; \ 126 COPY(par, child, count, size, tmp1, tmp2); \ 127 } \ 128 for (;;) { \ 129 child_i = par_i; \ 130 par_i = child_i / 2; \ 131 child = base + child_i * size; \ 132 par = base + par_i * size; \ 133 if (child_i == 1 || COMPAR(k, par) < 0) { \ 134 COPY(child, k, count, size, tmp1, tmp2); \ 135 break; \ 136 } \ 137 COPY(child, par, count, size, tmp1, tmp2); \ 138 } \ 139} 140 141#ifdef I_AM_HEAPSORT_B 142int heapsort_b(void *vbase, size_t nmemb, size_t size, heapsort_block compar); 143#else 144int heapsort(void *vbase, size_t nmemb, size_t size, 145 int (*compar)(const void *, const void *)); 146#endif 147/* 148 * Heapsort -- Knuth, Vol. 3, page 145. Runs in O (N lg N), both average 149 * and worst. While heapsort is faster than the worst case of quicksort, 150 * the BSD quicksort does median selection so that the chance of finding 151 * a data set that will trigger the worst case is nonexistent. Heapsort's 152 * only advantage over quicksort is that it requires little additional memory. 153 */ 154#ifdef I_AM_HEAPSORT_B 155int 156heapsort_b(void *vbase, size_t nmemb, size_t size, heapsort_block compar) 157#else 158int 159heapsort(void *vbase, size_t nmemb, size_t size, 160 int (*compar)(const void *, const void *)) 161#endif 162{ 163 size_t cnt, i, j, l; 164 char tmp, *tmp1, *tmp2; 165 char *base, *k, *p, *t; 166 167 if (nmemb <= 1) 168 return (0); 169 170 if (!size) { 171 errno = EINVAL; 172 return (-1); 173 } 174 175 if ((k = malloc(size)) == NULL) 176 return (-1); 177 178 /* 179 * Items are numbered from 1 to nmemb, so offset from size bytes 180 * below the starting address. 181 */ 182 base = (char *)vbase - size; 183 184 for (l = nmemb / 2 + 1; --l;) 185 CREATE(l, nmemb, i, j, t, p, size, cnt, tmp); 186 187 /* 188 * For each element of the heap, save the largest element into its 189 * final slot, save the displaced element (k), then recreate the 190 * heap. 191 */ 192 while (nmemb > 1) { 193 COPY(k, base + nmemb * size, cnt, size, tmp1, tmp2); 194 COPY(base + nmemb * size, base + size, cnt, size, tmp1, tmp2); 195 --nmemb; 196 SELECT(i, j, nmemb, t, p, size, k, cnt, tmp1, tmp2); 197 } 198 free(k); 199 return (0); 200} 201