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c6da642e DD |
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. [rescinded 22 July 1999] | |
14 | * 4. 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 | #include "config.h" | |
32 | #include "ansidecl.h" | |
33 | #include <sys/types.h> /* size_t */ | |
34 | #include <stdio.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 involes 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 | void * | |
53 | bsearch(key, base0, nmemb, size, compar) | |
54 | register void *key; | |
55 | void *base0; | |
56 | size_t nmemb; | |
57 | register size_t size; | |
58 | register int (*compar)(); | |
59 | { | |
60 | register char *base = base0; | |
61 | register int lim, cmp; | |
62 | register void *p; | |
63 | ||
64 | for (lim = nmemb; lim != 0; lim >>= 1) { | |
65 | p = base + (lim >> 1) * size; | |
66 | cmp = (*compar)(key, p); | |
67 | if (cmp == 0) | |
68 | return (p); | |
69 | if (cmp > 0) { /* key > p: move right */ | |
70 | base = (char *)p + size; | |
71 | lim--; | |
72 | } /* else move left */ | |
73 | } | |
74 | return (NULL); | |
75 | } |