1 /* $OpenBSD: bsearch.h,v 1.2 2022/10/07 02:58:01 jsg 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 #ifndef _LINUX_BSEARCH_H
32 #define _LINUX_BSEARCH_H
33
34 #include <sys/param.h>
35
36 /*
37 * Perform a binary search.
38 *
39 * The code below is a bit sneaky. After a comparison fails, we
40 * divide the work in half by moving either left or right. If lim
41 * is odd, moving left simply involves halving lim: e.g., when lim
42 * is 5 we look at item 2, so we change lim to 2 so that we will
43 * look at items 0 & 1. If lim is even, the same applies. If lim
44 * is odd, moving right again involves halving lim, this time moving
45 * the base up one item past p: e.g., when lim is 5 we change base
46 * to item 3 and make lim 2 so that we will look at items 3 and 4.
47 * If lim is even, however, we have to shrink it by one before
48 * halving: e.g., when lim is 4, we still looked at item 2, so we
49 * have to make lim 3, then halve, obtaining 1, so that we will only
50 * look at item 3.
51 */
52 static inline void *
bsearch(const void * key,const void * base0,size_t nmemb,size_t size,int (* compar)(const void *,const void *))53 bsearch(const void *key, const void *base0, size_t nmemb, size_t size,
54 int (*compar)(const void *, const void *))
55 {
56 const char *base = base0;
57 const void *p;
58 size_t lim;
59 int cmp;
60
61 for (lim = nmemb; lim != 0; lim >>= 1) {
62 p = base + (lim >> 1) * size;
63 cmp = (*compar)(key, p);
64 if (cmp == 0)
65 return ((void *)p);
66 if (cmp > 0) { /* key > p: move right */
67 base = (char *)p + size;
68 lim--;
69 } /* else move left */
70 }
71 return (NULL);
72 }
73
74 #endif
75