stdlib/heapsort_r-fbsd.c

   1 /*-
   2  * Copyright (c) 1991, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * This code is derived from software contributed to Berkeley by
   6  * Ronnie Kon at Mindcraft Inc., Kevin Lew and Elmer Yglesias.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  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
  15  *    documentation and/or other materials provided with the distribution.
  16  * 4. 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.
  19  *
  20  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  32
  33 #if defined(LIBC_SCCS) && !defined(lint)
  34 static char sccsid[] = "@(#)heapsort.c  8.1 (Berkeley) 6/4/93";
  35 #endif /* LIBC_SCCS and not lint */
  36 #include <sys/cdefs.h>
  37 __FBSDID("$FreeBSD: src/lib/libc/stdlib/heapsort.c,v 1.6 2008/01/13 02:11:10 das Exp $");
  38
  39 #include <errno.h>
  40 #include <stddef.h>
  41 #include <stdlib.h>
  42
  43 /*
  44  * Swap two areas of size number of bytes.  Although qsort(3) permits random
  45  * blocks of memory to be sorted, sorting pointers is almost certainly the
  46  * common case (and, were it not, could easily be made so).  Regardless, it
  47  * isn't worth optimizing; the SWAP's get sped up by the cache, and pointer
  48  * arithmetic gets lost in the time required for comparison function calls.
  49  */
  50 #define SWAP(a, b, count, size, tmp) { \
  51         count = size; \
  52         do { \
  53                 tmp = *a; \
  54                 *a++ = *b; \
  55                 *b++ = tmp; \
  56         } while (--count); \
  57 }
  58
  59 /* Copy one block of size size to another. */
  60 #define COPY(a, b, count, size, tmp1, tmp2) { \
  61         count = size; \
  62         tmp1 = a; \
  63         tmp2 = b; \
  64         do { \
  65                 *tmp1++ = *tmp2++; \
  66         } while (--count); \
  67 }
  68
  69 /*
  70  * Build the list into a heap, where a heap is defined such that for
  71  * the records K1 ... KN, Kj/2 >= Kj for 1 <= j/2 <= j <= N.
  72  *
  73  * There two cases.  If j == nmemb, select largest of Ki and Kj.  If
  74  * j < nmemb, select largest of Ki, Kj and Kj+1.
  75  */
  76 #define CREATE(initval, nmemb, par_i, child_i, par, child, size, count, tmp) { \
  77         for (par_i = initval; (child_i = par_i * 2) <= nmemb; \
  78             par_i = child_i) { \
  79                 child = base + child_i * size; \
  80                 if (child_i < nmemb && compar(thunk, child, child + size) < 0) { \
  81                         child += size; \
  82                         ++child_i; \
  83                 } \
  84                 par = base + par_i * size; \
  85                 if (compar(thunk, child, par) <= 0) \
  86                         break; \
  87                 SWAP(par, child, count, size, tmp); \
  88         } \
  89 }
  90
  91 /*
  92  * Select the top of the heap and 'heapify'.  Since by far the most expensive
  93  * action is the call to the compar function, a considerable optimization
  94  * in the average case can be achieved due to the fact that k, the displaced
  95  * elememt, is ususally quite small, so it would be preferable to first
  96  * heapify, always maintaining the invariant that the larger child is copied
  97  * over its parent's record.
  98  *
  99  * Then, starting from the *bottom* of the heap, finding k's correct place,
 100  * again maintianing the invariant.  As a result of the invariant no element
 101  * is 'lost' when k is assigned its correct place in the heap.
 102  *
 103  * The time savings from this optimization are on the order of 15-20% for the
 104  * average case. See Knuth, Vol. 3, page 158, problem 18.
 105  *
 106  * XXX Don't break the #define SELECT line, below.  Reiser cpp gets upset.
 107  */
 108 #define SELECT(par_i, child_i, nmemb, par, child, size, k, count, tmp1, tmp2) { \
 109         for (par_i = 1; (child_i = par_i * 2) <= nmemb; par_i = child_i) { \
 110                 child = base + child_i * size; \
 111                 if (child_i < nmemb && compar(thunk, child, child + size) < 0) { \
 112                         child += size; \
 113                         ++child_i; \
 114                 } \
 115                 par = base + par_i * size; \
 116                 COPY(par, child, count, size, tmp1, tmp2); \
 117         } \
 118         for (;;) { \
 119                 child_i = par_i; \
 120                 par_i = child_i / 2; \
 121                 child = base + child_i * size; \
 122                 par = base + par_i * size; \
 123                 if (child_i == 1 || compar(thunk, k, par) < 0) { \
 124                         COPY(child, k, count, size, tmp1, tmp2); \
 125                         break; \
 126                 } \
 127                 COPY(child, par, count, size, tmp1, tmp2); \
 128         } \
 129 }
 130
 131 /*
 132  * Heapsort -- Knuth, Vol. 3, page 145.  Runs in O (N lg N), both average
 133  * and worst.  While heapsort is faster than the worst case of quicksort,
 134  * the BSD quicksort does median selection so that the chance of finding
 135  * a data set that will trigger the worst case is nonexistent.  Heapsort's
 136  * only advantage over quicksort is that it requires little additional memory.
 137  */
 138 __private_extern__ int
 139 __heapsort_r(vbase, nmemb, size, thunk, compar)
 140         void *vbase;
 141         size_t nmemb, size;
 142         void *thunk;
 143         int (*compar)(void *, const void *, const void *);
 144 {
 145         size_t cnt, i, j, l;
 146         char tmp, *tmp1, *tmp2;
 147         char *base, *k, *p, *t;
 148
 149         if (nmemb <= 1)
 150                 return (0);
 151
 152         if (!size) {
 153                 errno = EINVAL;
 154                 return (-1);
 155         }
 156
 157         if ((k = malloc(size)) == NULL)
 158                 return (-1);
 159
 160         /*
 161          * Items are numbered from 1 to nmemb, so offset from size bytes
 162          * below the starting address.
 163          */
 164         base = (char *)vbase - size;
 165
 166         for (l = nmemb / 2 + 1; --l;)
 167                 CREATE(l, nmemb, i, j, t, p, size, cnt, tmp);
 168
 169         /*
 170          * For each element of the heap, save the largest element into its
 171          * final slot, save the displaced element (k), then recreate the
 172          * heap.
 173          */
 174         while (nmemb > 1) {
 175                 COPY(k, base + nmemb * size, cnt, size, tmp1, tmp2);
 176                 COPY(base + nmemb * size, base + size, cnt, size, tmp1, tmp2);
 177                 --nmemb;
 178                 SELECT(i, j, nmemb, t, p, size, k, cnt, tmp1, tmp2);
 179         }
 180         free(k);
 181         return (0);
 182 }