2001-05-28 Philip Blundell <philb@gnu.org>
[binutils.git] / libiberty / bsearch.c
blob6a8ee33341d672e0976cd8224624519004fd1c95
1 /*
2 * Copyright (c) 1990 Regents of the University of California.
3 * All rights reserved.
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 [rescinded 22 July 1999]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.
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.
31 #include "config.h"
32 #include "ansidecl.h"
33 #include <sys/types.h> /* size_t */
34 #include <stdio.h>
37 * Perform a binary search.
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.
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)();
60 register char *base = base0;
61 register int lim, cmp;
62 register void *p;
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 */
74 return (NULL);