/* $OpenBSD: heapsort.c,v 1.11 2017/05/20 12:48:56 millert Exp $ */
/*-
* Copyright (c) 1991, 1993
* The Regents of the University of California. All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Ronnie Kon at Mindcraft Inc., Kevin Lew and Elmer Yglesias.
*
* 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. 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.
*/
#include <errno.h>
#include <stddef.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, count, size, tmp) { \
count = size; \
do { \
tmp = *a; \
*a++ = *b; \
*b++ = tmp; \
} while (--count); \
}
/* Copy one block of size size to another. */
#define COPY(a, b, count, size, tmp1, tmp2) { \
count = size; \
tmp1 = a; \
tmp2 = b; \
do { \
*tmp1++ = *tmp2++; \
} while (--count); \
}
/*
* 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 are two cases. If j == nmemb, select largest of Ki and Kj. If
* j < nmemb, select largest of Ki, Kj and Kj+1.
*/
#define CREATE(initval, nmemb, par_i, child_i, par, child, size, count, tmp) { \
for (par_i = initval; (child_i = par_i * 2) <= nmemb; \
par_i = child_i) { \
child = base + child_i * size; \
if (child_i < nmemb && compar(child, child + size) < 0) { \
child += size; \
++child_i; \
} \
par = base + par_i * size; \
if (compar(child, par) <= 0) \
break; \
SWAP(par, child, count, size, tmp); \
} \
}
/*
* Select the top of the heap and 'heapify'. Since by far the most expensive
* action is the call to the compar function, a considerable optimization
* in the average case can be achieved due to the fact that k, the displaced
* element, is usually quite small, so it would be preferable to first
* heapify, always maintaining the invariant that the larger child is copied
* over its parent's record.
*
* Then, starting from the *bottom* of the heap, finding k's correct place,
* again maintaining the invariant. As a result of the invariant no element
* is 'lost' when k is assigned its correct place in the heap.
*
* The time savings from this optimization are on the order of 15-20% for the
* average case. See Knuth, Vol. 3, page 158, problem 18.
*
* XXX Don't break the #define SELECT line, below. Reiser cpp gets upset.
*/
#define SELECT(par_i, child_i, nmemb, par, child, size, k, count, tmp1, tmp2) { \
for (par_i = 1; (child_i = par_i * 2) <= nmemb; par_i = child_i) { \
child = base + child_i * size; \
if (child_i < nmemb && compar(child, child + size) < 0) { \
child += size; \
++child_i; \
} \
par = base + par_i * size; \
COPY(par, child, count, size, tmp1, tmp2); \
} \
for (;;) { \
child_i = par_i; \
par_i = child_i / 2; \
child = base + child_i * size; \
par = base + par_i * size; \
if (child_i == 1 || compar(k, par) < 0) { \
COPY(child, k, count, size, tmp1, tmp2); \
break; \
} \
COPY(child, par, count, size, tmp1, tmp2); \
} \
}
/*
* 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 little additional memory.
*/
int
heapsort(void *vbase, size_t nmemb, size_t size,
int (*compar)(const void *, const void *))
{
size_t cnt, i, j, l;
char tmp, *tmp1, *tmp2;
char *base, *k, *p, *t;
if (nmemb <= 1)
return (0);
if (!size) {
errno = EINVAL;
return (-1);
}
if ((k = malloc(size)) == NULL)
return (-1);
/*
* Items are numbered from 1 to nmemb, so offset from size bytes
* below the starting address.
*/
base = (char *)vbase - size;
for (l = nmemb / 2 + 1; --l;)
CREATE(l, nmemb, i, j, t, p, size, cnt, tmp);
/*
* For each element of the heap, save the largest element into its
* final slot, save the displaced element (k), then recreate the
* heap.
*/
while (nmemb > 1) {
COPY(k, base + nmemb * size, cnt, size, tmp1, tmp2);
COPY(base + nmemb * size, base + size, cnt, size, tmp1, tmp2);
--nmemb;
SELECT(i, j, nmemb, t, p, size, k, cnt, tmp1, tmp2);
}
free(k);
return (0);
}
