FreeBSD/Linux Kernel Cross Reference
sys/libkern/bsearch.c
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)
31 static char sccsid[] = "@(#)bsearch.c 8.1 (Berkeley) 6/4/93";
32 #endif /* LIBC_SCCS and not lint */
33 #include <sys/cdefs.h>
34 __FBSDID("$FreeBSD$");
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 */
55 void *
56 bsearch(key, base0, nmemb, size, compar)
57 register const void *key;
58 const void *base0;
59 size_t nmemb;
60 register size_t size;
61 register int (*compar)(const void *, const void *);
62 {
63 register const char *base = base0;
64 register size_t lim;
65 register int cmp;
66 register 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 }
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