1 /*
2 * Copyright (c) 1990 Regents of the University of California.
3 * 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. 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 #include <stdlib.h>
31
32 /*
33 * Perform a binary search.
34 *
35 * The code below is a bit sneaky. After a comparison fails, we
36 * divide the work in half by moving either left or right. If lim
37 * is odd, moving left simply involves halving lim: e.g., when lim
38 * is 5 we look at item 2, so we change lim to 2 so that we will
39 * look at items 0 & 1. If lim is even, the same applies. If lim
40 * is odd, moving right again involes halving lim, this time moving
41 * the base up one item past p: e.g., when lim is 5 we change base
42 * to item 3 and make lim 2 so that we will look at items 3 and 4.
43 * If lim is even, however, we have to shrink it by one before
44 * halving: e.g., when lim is 4, we still looked at item 2, so we
45 * have to make lim 3, then halve, obtaining 1, so that we will only
46 * look at item 3.
47 */
48 void *
bsearch(const void * key,const void * base0,size_t nmemb,size_t size,int (* compar)(const void *,const void *))49 bsearch(const void *key, const void *base0, size_t nmemb, size_t size,
50 int (*compar)(const void *, const void *))
51 {
52 const char *base = base0;
53 int lim, cmp;
54 const void *p;
55
56 for (lim = nmemb; lim != 0; lim >>= 1) {
57 p = base + (lim >> 1) * size;
58 cmp = (*compar)(key, p);
59 if (cmp > 0) { /* key > p: move right */
60 base = (char *)p + size;
61 lim--;
62 } else if (cmp == 0) {
63 return ((void *)p);
64 } /* else move left */
65 }
66 return (NULL);
67 }
68