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
35 static 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 */
61 void *
bsearch(const void * key,const void * base0,size_t nmemb,size_t size,int (* compar)(const void *,const void *))62 bsearch(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