+/*-
+ * 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[] = "@(#)heapsort.c 5.1 (Berkeley) 6/4/91";
+#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);
+}