stdlib/heapsort.c

   1 /*
   2  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
   7  *
   8  * This file contains Original Code and/or Modifications of Original Code
   9  * as defined in and that are subject to the Apple Public Source License
  10  * Version 2.0 (the 'License'). You may not use this file except in
  11  * compliance with the License. Please obtain a copy of the License at
  12  * http://www.opensource.apple.com/apsl/ and read it before using this
  13  * file.
  14  *
  15  * The Original Code and all software distributed under the License are
  16  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  17  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  18  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  20  * Please see the License for the specific language governing rights and
  21  * limitations under the License.
  22  *
  23  * @APPLE_LICENSE_HEADER_END@
  24  */
  25 /*
  26  * Copyright (c) 1991, 1993
  27  *      The Regents of the University of California.  All rights reserved.
  28  *
  29  * This code is derived from software contributed to Berkeley by
  30  * Ronnie Kon at Mindcraft Inc., Kevin Lew and Elmer Yglesias.
  31  *
  32  * Redistribution and use in source and binary forms, with or without
  33  * modification, are permitted provided that the following conditions
  34  * are met:
  35  * 1. Redistributions of source code must retain the above copyright
  36  *    notice, this list of conditions and the following disclaimer.
  37  * 2. Redistributions in binary form must reproduce the above copyright
  38  *    notice, this list of conditions and the following disclaimer in the
  39  *    documentation and/or other materials provided with the distribution.
  40  * 3. All advertising materials mentioning features or use of this software
  41  *    must display the following acknowledgement:
  42  *      This product includes software developed by the University of
  43  *      California, Berkeley and its contributors.
  44  * 4. Neither the name of the University nor the names of its contributors
  45  *    may be used to endorse or promote products derived from this software
  46  *    without specific prior written permission.
  47  *
  48  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  49  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  50  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  51  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  52  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  53  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  54  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  55  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  56  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  57  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  58  * SUCH DAMAGE.
  59  */
  60
  61
  62 #include <sys/types.h>
  63 #include <errno.h>
  64 #include <stdlib.h>
  65 #include <stddef.h>
  66
  67 /*
  68  * Swap two areas of size number of bytes.  Although qsort(3) permits random
  69  * blocks of memory to be sorted, sorting pointers is almost certainly the
  70  * common case (and, were it not, could easily be made so).  Regardless, it
  71  * isn't worth optimizing; the SWAP's get sped up by the cache, and pointer
  72  * arithmetic gets lost in the time required for comparison function calls.
  73  */
  74 #define SWAP(a, b, count, size, tmp) { \
  75         count = size; \
  76         do { \
  77                 tmp = *a; \
  78                 *a++ = *b; \
  79                 *b++ = tmp; \
  80         } while (--count); \
  81 }
  82
  83 /* Copy one block of size size to another. */
  84 #define COPY(a, b, count, size, tmp1, tmp2) { \
  85         count = size; \
  86         tmp1 = a; \
  87         tmp2 = b; \
  88         do { \
  89                 *tmp1++ = *tmp2++; \
  90         } while (--count); \
  91 }
  92
  93 /*
  94  * Build the list into a heap, where a heap is defined such that for
  95  * the records K1 ... KN, Kj/2 >= Kj for 1 <= j/2 <= j <= N.
  96  *
  97  * There two cases.  If j == nmemb, select largest of Ki and Kj.  If
  98  * j < nmemb, select largest of Ki, Kj and Kj+1.
  99  */
 100 #define CREATE(initval, nmemb, par_i, child_i, par, child, size, count, tmp) { \
 101         for (par_i = initval; (child_i = par_i * 2) <= nmemb; \
 102             par_i = child_i) { \
 103                 child = base + child_i * size; \
 104                 if (child_i < nmemb && compar(child, child + size) < 0) { \
 105                         child += size; \
 106                         ++child_i; \
 107                 } \
 108                 par = base + par_i * size; \
 109                 if (compar(child, par) <= 0) \
 110                         break; \
 111                 SWAP(par, child, count, size, tmp); \
 112         } \
 113 }
 114
 115 /*
 116  * Select the top of the heap and 'heapify'.  Since by far the most expensive
 117  * action is the call to the compar function, a considerable optimization
 118  * in the average case can be achieved due to the fact that k, the displaced
 119  * elememt, is ususally quite small, so it would be preferable to first
 120  * heapify, always maintaining the invariant that the larger child is copied
 121  * over its parent's record.
 122  *
 123  * Then, starting from the *bottom* of the heap, finding k's correct place,
 124  * again maintianing the invariant.  As a result of the invariant no element
 125  * is 'lost' when k is assigned its correct place in the heap.
 126  *
 127  * The time savings from this optimization are on the order of 15-20% for the
 128  * average case. See Knuth, Vol. 3, page 158, problem 18.
 129  *
 130  * XXX Don't break the #define SELECT line, below.  Reiser cpp gets upset.
 131  */
 132 #define SELECT(par_i, child_i, nmemb, par, child, size, k, count, tmp1, tmp2) { \
 133         for (par_i = 1; (child_i = par_i * 2) <= nmemb; par_i = child_i) { \
 134                 child = base + child_i * size; \
 135                 if (child_i < nmemb && compar(child, child + size) < 0) { \
 136                         child += size; \
 137                         ++child_i; \
 138                 } \
 139                 par = base + par_i * size; \
 140                 COPY(par, child, count, size, tmp1, tmp2); \
 141         } \
 142         for (;;) { \
 143                 child_i = par_i; \
 144                 par_i = child_i / 2; \
 145                 child = base + child_i * size; \
 146                 par = base + par_i * size; \
 147                 if (child_i == 1 || compar(k, par) < 0) { \
 148                         COPY(child, k, count, size, tmp1, tmp2); \
 149                         break; \
 150                 } \
 151                 COPY(child, par, count, size, tmp1, tmp2); \
 152         } \
 153 }
 154
 155 /*
 156  * Heapsort -- Knuth, Vol. 3, page 145.  Runs in O (N lg N), both average
 157  * and worst.  While heapsort is faster than the worst case of quicksort,
 158  * the BSD quicksort does median selection so that the chance of finding
 159  * a data set that will trigger the worst case is nonexistent.  Heapsort's
 160  * only advantage over quicksort is that it requires little additional memory.
 161  */
 162 int
 163 heapsort(vbase, nmemb, size, compar)
 164         void *vbase;
 165         size_t nmemb, size;
 166         int (*compar) __P((const void *, const void *));
 167 {
 168         register int cnt, i, j, l;
 169         register char tmp, *tmp1, *tmp2;
 170         char *base, *k, *p, *t;
 171
 172         if (nmemb <= 1)
 173                 return (0);
 174
 175         if (!size) {
 176                 errno = EINVAL;
 177                 return (-1);
 178         }
 179
 180         if ((k = malloc(size)) == NULL)
 181                 return (-1);
 182
 183         /*
 184          * Items are numbered from 1 to nmemb, so offset from size bytes
 185          * below the starting address.
 186          */
 187         base = (char *)vbase - size;
 188
 189         for (l = nmemb / 2 + 1; --l;)
 190                 CREATE(l, nmemb, i, j, t, p, size, cnt, tmp);
 191
 192         /*
 193          * For each element of the heap, save the largest element into its
 194          * final slot, save the displaced element (k), then recreate the
 195          * heap.
 196          */
 197         while (nmemb > 1) {
 198                 COPY(k, base + nmemb * size, cnt, size, tmp1, tmp2);
 199                 COPY(base + nmemb * size, base + size, cnt, size, tmp1, tmp2);
 200                 --nmemb;
 201                 SELECT(i, j, nmemb, t, p, size, k, cnt, tmp1, tmp2);
 202         }
 203         free(k);
 204         return (0);
 205 }