bsearch.c revision 302408 
1/*
2 * Copyright (c) 1990, 1993
3 *	The Regents of the University of California.  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. Neither the name of the University nor the names of its contributors
14 *    may be used to endorse or promote products derived from this software
15 *    without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 */
29
30#if defined(LIBC_SCCS) && !defined(lint)
31static char sccsid[] = "@(#)bsearch.c	8.1 (Berkeley) 6/4/93";
32#endif /* LIBC_SCCS and not lint */
33#include <sys/cdefs.h>
34__FBSDID("$FreeBSD: stable/11/lib/libc/stdlib/bsearch.c 288030 2015-09-20 20:24:28Z rodrigc $");
35
36#include <stddef.h>
37#include <stdlib.h>
38
39#ifdef	I_AM_BSEARCH_B
40#include "block_abi.h"
41#define	COMPAR(x,y)	CALL_BLOCK(compar, x, y)
42#else
43#define	COMPAR(x,y)	compar(x, y)
44#endif
45
46/*
47 * Perform a binary search.
48 *
49 * The code below is a bit sneaky.  After a comparison fails, we
50 * divide the work in half by moving either left or right. If lim
51 * is odd, moving left simply involves halving lim: e.g., when lim
52 * is 5 we look at item 2, so we change lim to 2 so that we will
53 * look at items 0 & 1.  If lim is even, the same applies.  If lim
54 * is odd, moving right again involes halving lim, this time moving
55 * the base up one item past p: e.g., when lim is 5 we change base
56 * to item 3 and make lim 2 so that we will look at items 3 and 4.
57 * If lim is even, however, we have to shrink it by one before
58 * halving: e.g., when lim is 4, we still looked at item 2, so we
59 * have to make lim 3, then halve, obtaining 1, so that we will only
60 * look at item 3.
61 */
62#ifdef I_AM_BSEARCH_B
63void *
64bsearch_b(const void *key, const void *base0, size_t nmemb, size_t size,
65    DECLARE_BLOCK(int, compar, const void *, const void *))
66#else
67void *
68bsearch(const void *key, const void *base0, size_t nmemb, size_t size,
69    int (*compar)(const void *, const void *))
70#endif
71{
72	const char *base = base0;
73	size_t lim;
74	int cmp;
75	const void *p;
76
77	for (lim = nmemb; lim != 0; lim >>= 1) {
78		p = base + (lim >> 1) * size;
79		cmp = COMPAR(key, p);
80		if (cmp == 0)
81			return ((void *)p);
82		if (cmp > 0) {	/* key > p: move right */
83			base = (char *)p + size;
84			lim--;
85		}		/* else move left */
86	}
87	return (NULL);
88}
89