NetBSD/lib/libc/stdlib/heapsort.c

127 lines
4.3 KiB
C

/*-
* Copyright (c) 1991 The Regents of the University of California.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#if defined(LIBC_SCCS) && !defined(lint)
/*static char *sccsid = "from: @(#)heapsort.c 5.1 (Berkeley) 6/4/91";*/
static char *rcsid = "$Id: heapsort.c,v 1.3 1993/08/26 00:48:00 jtc Exp $";
#endif /* LIBC_SCCS and not lint */
#include <sys/cdefs.h>
#include <sys/types.h>
#include <errno.h>
#include <stdlib.h>
/*
* Swap two areas of size number of bytes. Although qsort(3) permits random
* blocks of memory to be sorted, sorting pointers is almost certainly the
* common case (and, were it not, could easily be made so). Regardless, it
* isn't worth optimizing; the SWAP's get sped up by the cache, and pointer
* arithmetic gets lost in the time required for comparison function calls.
*/
#define SWAP(a, b) { \
cnt = size; \
do { \
ch = *a; \
*a++ = *b; \
*b++ = ch; \
} while (--cnt); \
}
/*
* Build the list into a heap, where a heap is defined such that for
* the records K1 ... KN, Kj/2 >= Kj for 1 <= j/2 <= j <= N.
*
* There two cases. If j == nmemb, select largest of Ki and Kj. If
* j < nmemb, select largest of Ki, Kj and Kj+1.
*
* The initial value depends on if we're building the initial heap or
* reconstructing it after saving a value.
*/
#define HEAP(initval) { \
for (i = initval; (j = i * 2) <= nmemb; i = j) { \
p = (char *)bot + j * size; \
if (j < nmemb && compar(p, p + size) < 0) { \
p += size; \
++j; \
} \
t = (char *)bot + i * size; \
if (compar(p, t) <= 0) \
break; \
SWAP(t, p); \
} \
}
/*
* Heapsort -- Knuth, Vol. 3, page 145. Runs in O (N lg N), both average
* and worst. While heapsort is faster than the worst case of quicksort,
* the BSD quicksort does median selection so that the chance of finding
* a data set that will trigger the worst case is nonexistent. Heapsort's
* only advantage over quicksort is that it requires no additional memory.
*/
heapsort(bot, nmemb, size, compar)
register void *bot;
register size_t nmemb, size;
int (*compar) __P((const void *, const void *));
{
register char *p, *t, ch;
register int cnt, i, j, l;
if (nmemb <= 1)
return (0);
if (!size) {
errno = EINVAL;
return (-1);
}
/*
* Items are numbered from 1 to nmemb, so offset from size bytes
* below the starting address.
*/
bot -= size;
for (l = nmemb / 2 + 1; --l;)
HEAP(l);
/*
* For each element of the heap, save the largest element into its
* final slot, then recreate the heap.
*/
while (nmemb > 1) {
p = (char *)bot + size;
t = (char *)bot + nmemb * size;
SWAP(p, t);
--nmemb;
HEAP(1);
}
return (0);
}