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  #pragma clang diagnostic push
 34  #pragma clang diagnostic ignored "-Wstrict-prototypes"
 35  
 36  #if defined(LIBC_SCCS) && !defined(lint)
 37  static char sccsid[] = "@(#)heapsort.c	8.1 (Berkeley) 6/4/93";
 38  #endif /* LIBC_SCCS and not lint */
 39  #include <sys/cdefs.h>
 40  __FBSDID("$FreeBSD: src/lib/libc/stdlib/heapsort.c,v 1.6 2008/01/13 02:11:10 das Exp $");
 41  
 42  #include <errno.h>
 43  #include <stddef.h>
 44  #include <stdlib.h>
 45  
 46  /*
 47   * Swap two areas of size number of bytes.  Although qsort(3) permits random
 48   * blocks of memory to be sorted, sorting pointers is almost certainly the
 49   * common case (and, were it not, could easily be made so).  Regardless, it
 50   * isn't worth optimizing; the SWAP's get sped up by the cache, and pointer
 51   * arithmetic gets lost in the time required for comparison function calls.
 52   */
 53  #define	SWAP(a, b, count, size, tmp) { \
 54  	count = size; \
 55  	do { \
 56  		tmp = *a; \
 57  		*a++ = *b; \
 58  		*b++ = tmp; \
 59  	} while (--count); \
 60  }
 61  
 62  /* Copy one block of size size to another. */
 63  #define COPY(a, b, count, size, tmp1, tmp2) { \
 64  	count = size; \
 65  	tmp1 = a; \
 66  	tmp2 = b; \
 67  	do { \
 68  		*tmp1++ = *tmp2++; \
 69  	} while (--count); \
 70  }
 71  
 72  /*
 73   * Build the list into a heap, where a heap is defined such that for
 74   * the records K1 ... KN, Kj/2 >= Kj for 1 <= j/2 <= j <= N.
 75   *
 76   * There two cases.  If j == nmemb, select largest of Ki and Kj.  If
 77   * j < nmemb, select largest of Ki, Kj and Kj+1.
 78   */
 79  #define CREATE(initval, nmemb, par_i, child_i, par, child, size, count, tmp) { \
 80  	for (par_i = initval; (child_i = par_i * 2) <= nmemb; \
 81  	    par_i = child_i) { \
 82  		child = base + child_i * size; \
 83  		if (child_i < nmemb && compar(child, child + size) < 0) { \
 84  			child += size; \
 85  			++child_i; \
 86  		} \
 87  		par = base + par_i * size; \
 88  		if (compar(child, par) <= 0) \
 89  			break; \
 90  		SWAP(par, child, count, size, tmp); \
 91  	} \
 92  }
 93  
 94  /*
 95   * Select the top of the heap and 'heapify'.  Since by far the most expensive
 96   * action is the call to the compar function, a considerable optimization
 97   * in the average case can be achieved due to the fact that k, the displaced
 98   * elememt, is ususally quite small, so it would be preferable to first
 99   * heapify, always maintaining the invariant that the larger child is copied
100   * over its parent's record.
101   *
102   * Then, starting from the *bottom* of the heap, finding k's correct place,
103   * again maintianing the invariant.  As a result of the invariant no element
104   * is 'lost' when k is assigned its correct place in the heap.
105   *
106   * The time savings from this optimization are on the order of 15-20% for the
107   * average case. See Knuth, Vol. 3, page 158, problem 18.
108   *
109   * XXX Don't break the #define SELECT line, below.  Reiser cpp gets upset.
110   */
111  #define SELECT(par_i, child_i, nmemb, par, child, size, k, count, tmp1, tmp2) { \
112  	for (par_i = 1; (child_i = par_i * 2) <= nmemb; par_i = child_i) { \
113  		child = base + child_i * size; \
114  		if (child_i < nmemb && compar(child, child + size) < 0) { \
115  			child += size; \
116  			++child_i; \
117  		} \
118  		par = base + par_i * size; \
119  		COPY(par, child, count, size, tmp1, tmp2); \
120  	} \
121  	for (;;) { \
122  		child_i = par_i; \
123  		par_i = child_i / 2; \
124  		child = base + child_i * size; \
125  		par = base + par_i * size; \
126  		if (child_i == 1 || compar(k, par) < 0) { \
127  			COPY(child, k, count, size, tmp1, tmp2); \
128  			break; \
129  		} \
130  		COPY(child, par, count, size, tmp1, tmp2); \
131  	} \
132  }
133  
134  /*
135   * Heapsort -- Knuth, Vol. 3, page 145.  Runs in O (N lg N), both average
136   * and worst.  While heapsort is faster than the worst case of quicksort,
137   * the BSD quicksort does median selection so that the chance of finding
138   * a data set that will trigger the worst case is nonexistent.  Heapsort's
139   * only advantage over quicksort is that it requires little additional memory.
140   */
141  int
142  heapsort(vbase, nmemb, size, compar)
143  	void *vbase;
144  	size_t nmemb, size;
145  	int (*compar)(const void *, const void *);
146  {
147  	size_t cnt, i, j, l;
148  	char tmp, *tmp1, *tmp2;
149  	char *base, *k, *p, *t;
150  
151  	if (nmemb <= 1)
152  		return (0);
153  
154  	if (!size) {
155  		errno = EINVAL;
156  		return (-1);
157  	}
158  
159  	if ((k = malloc(size)) == NULL)
160  		return (-1);
161  
162  	/*
163  	 * Items are numbered from 1 to nmemb, so offset from size bytes
164  	 * below the starting address.
165  	 */
166  	base = (char *)vbase - size;
167  
168  	for (l = nmemb / 2 + 1; --l;)
169  		CREATE(l, nmemb, i, j, t, p, size, cnt, tmp);
170  
171  	/*
172  	 * For each element of the heap, save the largest element into its
173  	 * final slot, save the displaced element (k), then recreate the
174  	 * heap.
175  	 */
176  	while (nmemb > 1) {
177  		COPY(k, base + nmemb * size, cnt, size, tmp1, tmp2);
178  		COPY(base + nmemb * size, base + size, cnt, size, tmp1, tmp2);
179  		--nmemb;
180  		SELECT(i, j, nmemb, t, p, size, k, cnt, tmp1, tmp2);
181  	}
182  	free(k);
183  	return (0);
184  }
185  #pragma clang diagnostic pop