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 [rescinded 22 July 1999]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