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 [rescinded 22 July 1999]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 /*
32
33 @deftypefn Supplemental void* bsearch (const void *@var{key}, @
34 const void *@var{base}, size_t @var{nmemb}, size_t @var{size}, @
35 int (*@var{compar})(const void *, const void *))
36
37 Performs a search over an array of @var{nmemb} elements pointed to by
38 @var{base} for a member that matches the object pointed to by @var{key}.
39 The size of each member is specified by @var{size}. The array contents
40 should be sorted in ascending order according to the @var{compar}
41 comparison function. This routine should take two arguments pointing to
42 the @var{key} and to an array member, in that order, and should return an
43 integer less than, equal to, or greater than zero if the @var{key} object
44 is respectively less than, matching, or greater than the array member.
45
46 @end deftypefn
47
48 */
49
50 #include "config.h"
51 #include "ansidecl.h"
52 #include <sys/types.h> /* size_t */
53 #include <stdio.h>
54
55 /*
56 * Perform a binary search.
57 *
58 * The code below is a bit sneaky. After a comparison fails, we
59 * divide the work in half by moving either left or right. If lim
60 * is odd, moving left simply involves halving lim: e.g., when lim
61 * is 5 we look at item 2, so we change lim to 2 so that we will
62 * look at items 0 & 1. If lim is even, the same applies. If lim
63 * is odd, moving right again involes halving lim, this time moving
64 * the base up one item past p: e.g., when lim is 5 we change base
65 * to item 3 and make lim 2 so that we will look at items 3 and 4.
66 * If lim is even, however, we have to shrink it by one before
67 * halving: e.g., when lim is 4, we still looked at item 2, so we
68 * have to make lim 3, then halve, obtaining 1, so that we will only
69 * look at item 3.
70 */
71 void *
72 bsearch (const void *key, const void *base0,
73 size_t nmemb, size_t size,
74 int (*compar)(const void *, const void *))
75 {
76 const char *base = (const char *) base0;
77 int lim, cmp;
78 const void *p;
79
80 for (lim = nmemb; lim != 0; lim >>= 1) {
81 p = base + (lim >> 1) * size;
82 cmp = (*compar)(key, p);
83 if (cmp == 0)
84 return (void *)p;
85 if (cmp > 0) { /* key > p: move right */
86 base = (const char *)p + size;
87 lim--;
88 } /* else move left */
89 }
90 return (NULL);
91 }