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  * 4. 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  * © Portions copyright (c) 2005-2006  Nokia Corporation.  All rights reserved.

    29  */

    30 

    31 #if defined(LIBC_SCCS) && !defined(lint)

    32 static char sccsid[] = "@(#)bsearch.c	8.1 (Berkeley) 6/4/93";

    33 #endif /* LIBC_SCCS and not lint */

    34 #include <sys/cdefs.h>

    35 __FBSDID("$FreeBSD: src/lib/libc/stdlib/bsearch.c,v 1.3 2002/03/21 22:48:41 obrien Exp $");

    36 

    37 #include <stddef.h>

    38 #include <stdlib.h>

    39 

    40 /*

    41  * Perform a binary search.

    42  *

    43  * The code below is a bit sneaky.  After a comparison fails, we

    44  * divide the work in half by moving either left or right. If lim

    45  * is odd, moving left simply involves halving lim: e.g., when lim

    46  * is 5 we look at item 2, so we change lim to 2 so that we will

    47  * look at items 0 & 1.  If lim is even, the same applies.  If lim

    48  * is odd, moving right again involes halving lim, this time moving

    49  * the base up one item past p: e.g., when lim is 5 we change base

    50  * to item 3 and make lim 2 so that we will look at items 3 and 4.

    51  * If lim is even, however, we have to shrink it by one before

    52  * halving: e.g., when lim is 4, we still looked at item 2, so we

    53  * have to make lim 3, then halve, obtaining 1, so that we will only

    54  * look at item 3.

    55  */

    56 

    57 EXPORT_C

    58 void *

    59 bsearch(key, base0, nmemb, size, compar)

    60 	const void *key;

    61 	const void *base0;

    62 	size_t nmemb;

    63 	size_t size;

    64 	int (*compar)(const void *, const void *);

    65 {

    66 	const char *base = base0;

    67 	size_t lim;

    68 	int cmp;

    69 	const void *p;

    70 

    71 	for (lim = nmemb; lim != 0; lim >>= 1) {

    72 		p = base + (lim >> 1) * size;

    73 		cmp = (*compar)(key, p);

    74 		if (cmp == 0)

    75 			return ((void *)p);

    76 		if (cmp > 0) {	/* key > p: move right */

    77 			base = (char *)p + size;

    78 			lim--;

    79 		}		/* else move left */

    80 	}

    81 	return (NULL);

    82 }