bsearch.c revision 83289 
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 * 3. All advertising materials mentioning features or use of this software
14 *    must display the following acknowledgement:
15 *	This product includes software developed by the University of
16 *	California, Berkeley and its contributors.
17 * 4. Neither the name of the University nor the names of its contributors
18 *    may be used to endorse or promote products derived from this software
19 *    without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 *
33 * $FreeBSD: head/sys/libkern/bsearch.c 83289 2001-09-10 10:33:46Z peter $
34 */
35
36#if defined(LIBC_SCCS) && !defined(lint)
37static char sccsid[] = "@(#)bsearch.c	8.1 (Berkeley) 6/4/93";
38#endif /* LIBC_SCCS and not lint */
39
40#include <sys/param.h>
41#include <machine/ansi.h>
42#include <sys/libkern.h>
43
44/*
45 * Perform a binary search.
46 *
47 * The code below is a bit sneaky.  After a comparison fails, we
48 * divide the work in half by moving either left or right. If lim
49 * is odd, moving left simply involves halving lim: e.g., when lim
50 * is 5 we look at item 2, so we change lim to 2 so that we will
51 * look at items 0 & 1.  If lim is even, the same applies.  If lim
52 * is odd, moving right again involes halving lim, this time moving
53 * the base up one item past p: e.g., when lim is 5 we change base
54 * to item 3 and make lim 2 so that we will look at items 3 and 4.
55 * If lim is even, however, we have to shrink it by one before
56 * halving: e.g., when lim is 4, we still looked at item 2, so we
57 * have to make lim 3, then halve, obtaining 1, so that we will only
58 * look at item 3.
59 */
60void *
61bsearch(key, base0, nmemb, size, compar)
62	register const void *key;
63	const void *base0;
64	size_t nmemb;
65	register size_t size;
66	register int (*compar) __P((const void *, const void *));
67{
68	register const char *base = base0;
69	register size_t lim;
70	register int cmp;
71	register const void *p;
72
73	for (lim = nmemb; lim != 0; lim >>= 1) {
74		p = base + (lim >> 1) * size;
75		cmp = (*compar)(key, p);
76		if (cmp == 0)
77			return ((void *)(uintptr_t)p);
78		if (cmp > 0) {	/* key > p: move right */
79			base = (const char *)p + size;
80			lim--;
81		}		/* else move left */
82	}
83	return (NULL);
84}
85