1 /*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1990, 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of the University nor the names of its contributors
16 * may be used to endorse or promote products derived from this software
17 * without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * SUCH DAMAGE.
30 */
31
32 #include <stddef.h>
33 #include <stdlib.h>
34
35 #ifdef I_AM_BSEARCH_B
36 #include "block_abi.h"
37 #define COMPAR(x,y) CALL_BLOCK(compar, x, y)
38 typedef DECLARE_BLOCK(int, compar_block, const void *, const void *);
39 #else
40 #define COMPAR(x,y) compar(x, y)
41 #endif
42
43 /*
44 * Perform a binary search.
45 *
46 * The code below is a bit sneaky. After a comparison fails, we
47 * divide the work in half by moving either left or right. If lim
48 * is odd, moving left simply involves halving lim: e.g., when lim
49 * is 5 we look at item 2, so we change lim to 2 so that we will
50 * look at items 0 & 1. If lim is even, the same applies. If lim
51 * is odd, moving right again involves halving lim, this time moving
52 * the base up one item past p: e.g., when lim is 5 we change base
53 * to item 3 and make lim 2 so that we will look at items 3 and 4.
54 * If lim is even, however, we have to shrink it by one before
55 * halving: e.g., when lim is 4, we still looked at item 2, so we
56 * have to make lim 3, then halve, obtaining 1, so that we will only
57 * look at item 3.
58 */
59 #ifdef I_AM_BSEARCH_B
60 void *
bsearch_b(const void * key,const void * base0,size_t nmemb,size_t size,compar_block compar)61 bsearch_b(const void *key, const void *base0, size_t nmemb, size_t size,
62 compar_block compar)
63 #else
64 void *
65 bsearch(const void *key, const void *base0, size_t nmemb, size_t size,
66 int (*compar)(const void *, const void *))
67 #endif
68 {
69 const char *base = base0;
70 size_t lim;
71 int cmp;
72 const void *p;
73
74 for (lim = nmemb; lim != 0; lim >>= 1) {
75 p = base + (lim >> 1) * size;
76 cmp = COMPAR(key, p);
77 if (cmp == 0)
78 return ((void *)p);
79 if (cmp > 0) { /* key > p: move right */
80 base = (char *)p + size;
81 lim--;
82 } /* else move left */
83 }
84 return (NULL);
85 }
86