1 /* $OpenBSD: heapsort.c,v 1.11 2017/05/20 12:48:56 millert Exp $ */ 2 /*- 3 * Copyright (c) 1991, 1993 4 * The Regents of the University of California. All rights reserved. 5 * 6 * This code is derived from software contributed to Berkeley by 7 * Ronnie Kon at Mindcraft Inc., Kevin Lew and Elmer Yglesias. 8 * 9 * Redistribution and use in source and binary forms, with or without 10 * modification, are permitted provided that the following conditions 11 * are met: 12 * 1. Redistributions of source code must retain the above copyright 13 * notice, this list of conditions and the following disclaimer. 14 * 2. Redistributions in binary form must reproduce the above copyright 15 * notice, this list of conditions and the following disclaimer in the 16 * documentation and/or other materials provided with the distribution. 17 * 3. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 */ 33 34 #include <sys/types.h> 35 #include <errno.h> 36 #include <stdlib.h> 37 38 /* 39 * Swap two areas of size number of bytes. Although qsort(3) permits random 40 * blocks of memory to be sorted, sorting pointers is almost certainly the 41 * common case (and, were it not, could easily be made so). Regardless, it 42 * isn't worth optimizing; the SWAP's get sped up by the cache, and pointer 43 * arithmetic gets lost in the time required for comparison function calls. 44 */ 45 #define SWAP(a, b, count, size, tmp) { \ 46 count = size; \ 47 do { \ 48 tmp = *a; \ 49 *a++ = *b; \ 50 *b++ = tmp; \ 51 } while (--count); \ 52 } 53 54 /* Copy one block of size size to another. */ 55 #define COPY(a, b, count, size, tmp1, tmp2) { \ 56 count = size; \ 57 tmp1 = a; \ 58 tmp2 = b; \ 59 do { \ 60 *tmp1++ = *tmp2++; \ 61 } while (--count); \ 62 } 63 64 /* 65 * Build the list into a heap, where a heap is defined such that for 66 * the records K1 ... KN, Kj/2 >= Kj for 1 <= j/2 <= j <= N. 67 * 68 * There are two cases. If j == nmemb, select largest of Ki and Kj. If 69 * j < nmemb, select largest of Ki, Kj and Kj+1. 70 */ 71 #define CREATE(initval, nmemb, par_i, child_i, par, child, size, count, tmp) { \ 72 for (par_i = initval; (child_i = par_i * 2) <= nmemb; \ 73 par_i = child_i) { \ 74 child = base + child_i * size; \ 75 if (child_i < nmemb && compar(child, child + size) < 0) { \ 76 child += size; \ 77 ++child_i; \ 78 } \ 79 par = base + par_i * size; \ 80 if (compar(child, par) <= 0) \ 81 break; \ 82 SWAP(par, child, count, size, tmp); \ 83 } \ 84 } 85 86 /* 87 * Select the top of the heap and 'heapify'. Since by far the most expensive 88 * action is the call to the compar function, a considerable optimization 89 * in the average case can be achieved due to the fact that k, the displaced 90 * element, is usually quite small, so it would be preferable to first 91 * heapify, always maintaining the invariant that the larger child is copied 92 * over its parent's record. 93 * 94 * Then, starting from the *bottom* of the heap, finding k's correct place, 95 * again maintaining the invariant. As a result of the invariant no element 96 * is 'lost' when k is assigned its correct place in the heap. 97 * 98 * The time savings from this optimization are on the order of 15-20% for the 99 * average case. See Knuth, Vol. 3, page 158, problem 18. 100 * 101 * XXX Don't break the #define SELECT line, below. Reiser cpp gets upset. 102 */ 103 #define SELECT(par_i, child_i, nmemb, par, child, size, k, count, tmp1, tmp2) { \ 104 for (par_i = 1; (child_i = par_i * 2) <= nmemb; par_i = child_i) { \ 105 child = base + child_i * size; \ 106 if (child_i < nmemb && compar(child, child + size) < 0) { \ 107 child += size; \ 108 ++child_i; \ 109 } \ 110 par = base + par_i * size; \ 111 COPY(par, child, count, size, tmp1, tmp2); \ 112 } \ 113 for (;;) { \ 114 child_i = par_i; \ 115 par_i = child_i / 2; \ 116 child = base + child_i * size; \ 117 par = base + par_i * size; \ 118 if (child_i == 1 || compar(k, par) < 0) { \ 119 COPY(child, k, count, size, tmp1, tmp2); \ 120 break; \ 121 } \ 122 COPY(child, par, count, size, tmp1, tmp2); \ 123 } \ 124 } 125 126 /* 127 * Heapsort -- Knuth, Vol. 3, page 145. Runs in O (N lg N), both average 128 * and worst. While heapsort is faster than the worst case of quicksort, 129 * the BSD quicksort does median selection so that the chance of finding 130 * a data set that will trigger the worst case is nonexistent. Heapsort's 131 * only advantage over quicksort is that it requires little additional memory. 132 */ 133 int 134 heapsort(void *vbase, size_t nmemb, size_t size, 135 int (*compar)(const void *, const void *)) 136 { 137 size_t cnt, i, j, l; 138 char tmp, *tmp1, *tmp2; 139 char *base, *k, *p, *t; 140 141 if (nmemb <= 1) 142 return (0); 143 144 if (!size) { 145 errno = EINVAL; 146 return (-1); 147 } 148 149 if ((k = malloc(size)) == NULL) 150 return (-1); 151 152 /* 153 * Items are numbered from 1 to nmemb, so offset from size bytes 154 * below the starting address. 155 */ 156 base = (char *)vbase - size; 157 158 for (l = nmemb / 2 + 1; --l;) 159 CREATE(l, nmemb, i, j, t, p, size, cnt, tmp); 160 161 /* 162 * For each element of the heap, save the largest element into its 163 * final slot, save the displaced element (k), then recreate the 164 * heap. 165 */ 166 while (nmemb > 1) { 167 COPY(k, base + nmemb * size, cnt, size, tmp1, tmp2); 168 COPY(base + nmemb * size, base + size, cnt, size, tmp1, tmp2); 169 --nmemb; 170 SELECT(i, j, nmemb, t, p, size, k, cnt, tmp1, tmp2); 171 } 172 free(k); 173 return (0); 174 } 175 DEF_WEAK(heapsort); 176