190 lines
6.4 KiB
C
190 lines
6.4 KiB
C
/* $NetBSD: heapsort.c,v 1.6 1995/12/28 08:52:20 thorpej Exp $ */
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/*-
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* Copyright (c) 1991, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* Ronnie Kon at Mindcraft Inc., Kevin Lew and Elmer Yglesias.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#if defined(LIBC_SCCS) && !defined(lint)
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#if 0
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static char sccsid[] = "from: @(#)heapsort.c 8.1 (Berkeley) 6/4/93";
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#else
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static char *rcsid = "$NetBSD: heapsort.c,v 1.6 1995/12/28 08:52:20 thorpej Exp $";
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#endif
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#endif /* LIBC_SCCS and not lint */
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#include <sys/types.h>
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#include <errno.h>
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#include <stdlib.h>
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/*
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* Swap two areas of size number of bytes. Although qsort(3) permits random
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* blocks of memory to be sorted, sorting pointers is almost certainly the
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* common case (and, were it not, could easily be made so). Regardless, it
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* isn't worth optimizing; the SWAP's get sped up by the cache, and pointer
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* arithmetic gets lost in the time required for comparison function calls.
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*/
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#define SWAP(a, b, count, size, tmp) { \
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count = size; \
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do { \
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tmp = *a; \
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*a++ = *b; \
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*b++ = tmp; \
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} while (--count); \
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}
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/* Copy one block of size size to another. */
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#define COPY(a, b, count, size, tmp1, tmp2) { \
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count = size; \
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tmp1 = a; \
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tmp2 = b; \
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do { \
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*tmp1++ = *tmp2++; \
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} while (--count); \
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}
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/*
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* Build the list into a heap, where a heap is defined such that for
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* the records K1 ... KN, Kj/2 >= Kj for 1 <= j/2 <= j <= N.
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*
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* There two cases. If j == nmemb, select largest of Ki and Kj. If
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* j < nmemb, select largest of Ki, Kj and Kj+1.
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*/
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#define CREATE(initval, nmemb, par_i, child_i, par, child, size, count, tmp) { \
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for (par_i = initval; (child_i = par_i * 2) <= nmemb; \
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par_i = child_i) { \
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child = base + child_i * size; \
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if (child_i < nmemb && compar(child, child + size) < 0) { \
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child += size; \
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++child_i; \
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} \
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par = base + par_i * size; \
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if (compar(child, par) <= 0) \
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break; \
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SWAP(par, child, count, size, tmp); \
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} \
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}
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/*
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* Select the top of the heap and 'heapify'. Since by far the most expensive
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* action is the call to the compar function, a considerable optimization
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* in the average case can be achieved due to the fact that k, the displaced
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* elememt, is ususally quite small, so it would be preferable to first
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* heapify, always maintaining the invariant that the larger child is copied
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* over its parent's record.
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*
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* Then, starting from the *bottom* of the heap, finding k's correct place,
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* again maintianing the invariant. As a result of the invariant no element
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* is 'lost' when k is assigned its correct place in the heap.
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*
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* The time savings from this optimization are on the order of 15-20% for the
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* average case. See Knuth, Vol. 3, page 158, problem 18.
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*
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* XXX Don't break the #define SELECT line, below. Reiser cpp gets upset.
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*/
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#define SELECT(par_i, child_i, nmemb, par, child, size, k, count, tmp1, tmp2) { \
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for (par_i = 1; (child_i = par_i * 2) <= nmemb; par_i = child_i) { \
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child = base + child_i * size; \
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if (child_i < nmemb && compar(child, child + size) < 0) { \
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child += size; \
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++child_i; \
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} \
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par = base + par_i * size; \
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COPY(par, child, count, size, tmp1, tmp2); \
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} \
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for (;;) { \
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child_i = par_i; \
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par_i = child_i / 2; \
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child = base + child_i * size; \
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par = base + par_i * size; \
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if (child_i == 1 || compar(k, par) < 0) { \
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COPY(child, k, count, size, tmp1, tmp2); \
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break; \
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} \
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COPY(child, par, count, size, tmp1, tmp2); \
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} \
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}
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/*
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* Heapsort -- Knuth, Vol. 3, page 145. Runs in O (N lg N), both average
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* and worst. While heapsort is faster than the worst case of quicksort,
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* the BSD quicksort does median selection so that the chance of finding
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* a data set that will trigger the worst case is nonexistent. Heapsort's
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* only advantage over quicksort is that it requires little additional memory.
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*/
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int
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heapsort(vbase, nmemb, size, compar)
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void *vbase;
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size_t nmemb, size;
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int (*compar) __P((const void *, const void *));
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{
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register int cnt, i, j, l;
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register char tmp, *tmp1, *tmp2;
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char *base, *k, *p, *t;
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if (nmemb <= 1)
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return (0);
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if (!size) {
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errno = EINVAL;
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return (-1);
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}
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if ((k = malloc(size)) == NULL)
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return (-1);
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/*
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* Items are numbered from 1 to nmemb, so offset from size bytes
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* below the starting address.
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*/
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base = (char *)vbase - size;
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for (l = nmemb / 2 + 1; --l;)
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CREATE(l, nmemb, i, j, t, p, size, cnt, tmp);
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/*
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* For each element of the heap, save the largest element into its
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* final slot, save the displaced element (k), then recreate the
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* heap.
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*/
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while (nmemb > 1) {
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COPY(k, base + nmemb * size, cnt, size, tmp1, tmp2);
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COPY(base + nmemb * size, base + size, cnt, size, tmp1, tmp2);
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--nmemb;
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SELECT(i, j, nmemb, t, p, size, k, cnt, tmp1, tmp2);
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}
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free(k);
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return (0);
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}
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