bsearch.c revision 331722 
1/*-
2 * Copyright (c) 1990, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 * 4. Neither the name of the University nor the names of its contributors
14 *    may be used to endorse or promote products derived from this software
15 *    without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 */
29
30#if defined(LIBC_SCCS) && !defined(lint)
31static char sccsid[] = "@(#)bsearch.c	8.1 (Berkeley) 6/4/93";
32#endif /* LIBC_SCCS and not lint */
33#include <sys/cdefs.h>
34__FBSDID("$FreeBSD: stable/11/sys/libkern/bsearch.c 331722 2018-03-29 02:50:57Z eadler $");
35
36#include <sys/param.h>
37#include <sys/libkern.h>
38
39/*
40 * Perform a binary search.
41 *
42 * The code below is a bit sneaky.  After a comparison fails, we
43 * divide the work in half by moving either left or right. If lim
44 * is odd, moving left simply involves halving lim: e.g., when lim
45 * is 5 we look at item 2, so we change lim to 2 so that we will
46 * look at items 0 & 1.  If lim is even, the same applies.  If lim
47 * is odd, moving right again involes halving lim, this time moving
48 * the base up one item past p: e.g., when lim is 5 we change base
49 * to item 3 and make lim 2 so that we will look at items 3 and 4.
50 * If lim is even, however, we have to shrink it by one before
51 * halving: e.g., when lim is 4, we still looked at item 2, so we
52 * have to make lim 3, then halve, obtaining 1, so that we will only
53 * look at item 3.
54 */
55void *
56bsearch(key, base0, nmemb, size, compar)
57	const void *key;
58	const void *base0;
59	size_t nmemb;
60	size_t size;
61	int (*compar)(const void *, const void *);
62{
63	const char *base = base0;
64	size_t lim;
65	int cmp;
66	const void *p;
67
68	for (lim = nmemb; lim != 0; lim >>= 1) {
69		p = base + (lim >> 1) * size;
70		cmp = (*compar)(key, p);
71		if (cmp == 0)
72			return ((void *)(uintptr_t)p);
73		if (cmp > 0) {	/* key > p: move right */
74			base = (const char *)p + size;
75			lim--;
76		}		/* else move left */
77	}
78	return (NULL);
79}
80