1/*	$OpenBSD: bsearch.c,v 1.9 2021/12/02 20:58:01 cheloha Exp $ */
2/*
3 * Copyright (c) 1990 Regents of the University of California.
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 *    notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 *    notice, this list of conditions and the following disclaimer in the
13 *    documentation and/or other materials provided with the distribution.
14 * 3. Neither the name of the University nor the names of its contributors
15 *    may be used to endorse or promote products derived from this software
16 *    without specific prior written permission.
17 *
18 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 * SUCH DAMAGE.
29 */
30
31#include <stdlib.h>
32
33/*
34 * Perform a binary search.
35 *
36 * The code below is a bit sneaky.  After a comparison fails, we
37 * divide the work in half by moving either left or right. If lim
38 * is odd, moving left simply involves halving lim: e.g., when lim
39 * is 5 we look at item 2, so we change lim to 2 so that we will
40 * look at items 0 & 1.  If lim is even, the same applies.  If lim
41 * is odd, moving right again involves halving lim, this time moving
42 * the base up one item past p: e.g., when lim is 5 we change base
43 * to item 3 and make lim 2 so that we will look at items 3 and 4.
44 * If lim is even, however, we have to shrink it by one before
45 * halving: e.g., when lim is 4, we still looked at item 2, so we
46 * have to make lim 3, then halve, obtaining 1, so that we will only
47 * look at item 3.
48 */
49void *
50bsearch(const void *key, const void *base0, size_t nmemb, size_t size,
51    int (*compar)(const void *, const void *))
52{
53	const char *base = base0;
54	const void *p;
55	size_t lim;
56	int cmp;
57
58	for (lim = nmemb; lim != 0; lim >>= 1) {
59		p = base + (lim >> 1) * size;
60		cmp = (*compar)(key, p);
61		if (cmp == 0)
62			return ((void *)p);
63		if (cmp > 0) {	/* key > p: move right */
64			base = (char *)p + size;
65			lim--;
66		} /* else move left */
67	}
68	return (NULL);
69}
70