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 [rescinded 22 July 1999]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_r (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 *, void *), void *@var{arg})
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 three arguments: the first
42 two point to the @var{key} and to an array member, and the last is passed
43 down unchanged from @code{bsearch_r}'s last argument. It should return an
44 integer less than, equal to, or greater than zero if the @var{key} object
45 is respectively less than, matching, or greater than the array member.
46
47 @end deftypefn
48
49 */
50
51 #include "config.h"
52 #include "ansidecl.h"
53 #include <sys/types.h> /* size_t */
54 #include <stdio.h>
55
56 /*
57 * Perform a binary search.
58 *
59 * The code below is a bit sneaky. After a comparison fails, we
60 * divide the work in half by moving either left or right. If lim
61 * is odd, moving left simply involves halving lim: e.g., when lim
62 * is 5 we look at item 2, so we change lim to 2 so that we will
63 * look at items 0 & 1. If lim is even, the same applies. If lim
64 * is odd, moving right again involes halving lim, this time moving
65 * the base up one item past p: e.g., when lim is 5 we change base
66 * to item 3 and make lim 2 so that we will look at items 3 and 4.
67 * If lim is even, however, we have to shrink it by one before
68 * halving: e.g., when lim is 4, we still looked at item 2, so we
69 * have to make lim 3, then halve, obtaining 1, so that we will only
70 * look at item 3.
71 */
72 void *
bsearch_r(const void * key,const void * base0,size_t nmemb,size_t size,int (* compar)(const void *,const void *,void *),void * arg)73 bsearch_r (const void *key, const void *base0,
74 size_t nmemb, size_t size,
75 int (*compar)(const void *, const void *, void *),
76 void *arg)
77 {
78 const char *base = (const char *) base0;
79 int lim, cmp;
80 const void *p;
81
82 for (lim = nmemb; lim != 0; lim >>= 1) {
83 p = base + (lim >> 1) * size;
84 cmp = (*compar)(key, p, arg);
85 if (cmp == 0)
86 return (void *)p;
87 if (cmp > 0) { /* key > p: move right */
88 base = (const char *)p + size;
89 lim--;
90 } /* else move left */
91 }
92 return (NULL);
93 }
94