bsearch.c revision 330897 
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#if defined(LIBC_SCCS) && !defined(lint)
33static char sccsid[] = "@(#)bsearch.c	8.1 (Berkeley) 6/4/93";
34#endif /* LIBC_SCCS and not lint */
35#include <sys/cdefs.h>
36__FBSDID("$FreeBSD: stable/11/lib/libc/stdlib/bsearch.c 330897 2018-03-14 03:19:51Z eadler $");
37
38#include <stddef.h>
39#include <stdlib.h>
40
41#ifdef	I_AM_BSEARCH_B
42#include "block_abi.h"
43#define	COMPAR(x,y)	CALL_BLOCK(compar, x, y)
44#else
45#define	COMPAR(x,y)	compar(x, y)
46#endif
47
48/*
49 * Perform a binary search.
50 *
51 * The code below is a bit sneaky.  After a comparison fails, we
52 * divide the work in half by moving either left or right. If lim
53 * is odd, moving left simply involves halving lim: e.g., when lim
54 * is 5 we look at item 2, so we change lim to 2 so that we will
55 * look at items 0 & 1.  If lim is even, the same applies.  If lim
56 * is odd, moving right again involes halving lim, this time moving
57 * the base up one item past p: e.g., when lim is 5 we change base
58 * to item 3 and make lim 2 so that we will look at items 3 and 4.
59 * If lim is even, however, we have to shrink it by one before
60 * halving: e.g., when lim is 4, we still looked at item 2, so we
61 * have to make lim 3, then halve, obtaining 1, so that we will only
62 * look at item 3.
63 */
64#ifdef I_AM_BSEARCH_B
65void *
66bsearch_b(const void *key, const void *base0, size_t nmemb, size_t size,
67    DECLARE_BLOCK(int, compar, const void *, const void *))
68#else
69void *
70bsearch(const void *key, const void *base0, size_t nmemb, size_t size,
71    int (*compar)(const void *, const void *))
72#endif
73{
74	const char *base = base0;
75	size_t lim;
76	int cmp;
77	const void *p;
78
79	for (lim = nmemb; lim != 0; lim >>= 1) {
80		p = base + (lim >> 1) * size;
81		cmp = COMPAR(key, p);
82		if (cmp == 0)
83			return ((void *)p);
84		if (cmp > 0) {	/* key > p: move right */
85			base = (char *)p + size;
86			lim--;
87		}		/* else move left */
88	}
89	return (NULL);
90}
91