1/*	$NetBSD: bsearch.c,v 1.15 2012/03/04 20:01:45 christos Exp $	*/
2
3/*
4 * Copyright (c) 1990, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of the University nor the names of its contributors
16 *    may be used to endorse or promote products derived from this software
17 *    without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * SUCH DAMAGE.
30 */
31
32#include <sys/cdefs.h>
33#if defined(LIBC_SCCS) && !defined(lint)
34#if 0
35static char sccsid[] = "@(#)bsearch.c	8.1 (Berkeley) 6/4/93";
36#else
37__RCSID("$NetBSD: bsearch.c,v 1.15 2012/03/04 20:01:45 christos Exp $");
38#endif
39#endif /* LIBC_SCCS and not lint */
40
41#include <assert.h>
42#include <errno.h>
43#include <stdlib.h>
44
45/*
46 * Perform a binary search.
47 *
48 * The code below is a bit sneaky.  After a comparison fails, we
49 * divide the work in half by moving either left or right. If lim
50 * is odd, moving left simply involves halving lim: e.g., when lim
51 * is 5 we look at item 2, so we change lim to 2 so that we will
52 * look at items 0 & 1.  If lim is even, the same applies.  If lim
53 * is odd, moving right again involes halving lim, this time moving
54 * the base up one item past p: e.g., when lim is 5 we change base
55 * to item 3 and make lim 2 so that we will look at items 3 and 4.
56 * If lim is even, however, we have to shrink it by one before
57 * halving: e.g., when lim is 4, we still looked at item 2, so we
58 * have to make lim 3, then halve, obtaining 1, so that we will only
59 * look at item 3.
60 */
61void *
62bsearch(const void *key, const void *base0, size_t nmemb, size_t size,
63    int (*compar)(const void *, const void *))
64{
65	const char *base = base0;
66	size_t lim;
67	int cmp;
68	const void *p;
69
70	_DIAGASSERT(key != NULL);
71	_DIAGASSERT(base0 != NULL || nmemb == 0);
72	_DIAGASSERT(compar != NULL);
73
74	for (lim = nmemb; lim != 0; lim >>= 1) {
75		p = base + (lim >> 1) * size;
76		cmp = (*compar)(key, p);
77		if (cmp == 0)
78			return __UNCONST(p);
79		if (cmp > 0) {	/* key > p: move right */
80			base = (const char *)p + size;
81			lim--;
82		}		/* else move left */
83	}
84	return (NULL);
85}
86