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