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bsearch.c revision 1.10 
      1 /*	$NetBSD: bsearch.c,v 1.10 1999/09/16 11:45:33 lukem Exp $	*/
      2 
      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. All advertising materials mentioning features or use of this software
     16  *    must display the following acknowledgement:
     17  *	This product includes software developed by the University of
     18  *	California, Berkeley and its contributors.
     19  * 4. Neither the name of the University nor the names of its contributors
     20  *    may be used to endorse or promote products derived from this software
     21  *    without specific prior written permission.
     22  *
     23  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     24  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     25  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     26  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     27  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     28  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     29  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     30  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     31  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     32  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     33  * SUCH DAMAGE.
     34  */
     35 
     36 #include <sys/cdefs.h>
     37 #if defined(LIBC_SCCS) && !defined(lint)
     38 #if 0
     39 static char sccsid[] = "@(#)bsearch.c	8.1 (Berkeley) 6/4/93";
     40 #else
     41 __RCSID("$NetBSD: bsearch.c,v 1.10 1999/09/16 11:45:33 lukem Exp $");
     42 #endif
     43 #endif /* LIBC_SCCS and not lint */
     44 
     45 #include <assert.h>
     46 #include <errno.h>
     47 #include <stdlib.h>
     48 
     49 /*
     50  * Perform a binary search.
     51  *
     52  * The code below is a bit sneaky.  After a comparison fails, we
     53  * divide the work in half by moving either left or right. If lim
     54  * is odd, moving left simply involves halving lim: e.g., when lim
     55  * is 5 we look at item 2, so we change lim to 2 so that we will
     56  * look at items 0 & 1.  If lim is even, the same applies.  If lim
     57  * is odd, moving right again involes halving lim, this time moving
     58  * the base up one item past p: e.g., when lim is 5 we change base
     59  * to item 3 and make lim 2 so that we will look at items 3 and 4.
     60  * If lim is even, however, we have to shrink it by one before
     61  * halving: e.g., when lim is 4, we still looked at item 2, so we
     62  * have to make lim 3, then halve, obtaining 1, so that we will only
     63  * look at item 3.
     64  */
     65 void *
     66 bsearch(key, base0, nmemb, size, compar)
     67 	const void *key;
     68 	const void *base0;
     69 	size_t nmemb;
     70 	size_t size;
     71 	int (*compar) __P((const void *, const void *));
     72 {
     73 	const char *base = base0;
     74 	size_t lim;
     75 	int cmp;
     76 	const void *p;
     77 
     78 	_DIAGASSERT(key != NULL);
     79 	_DIAGASSERT(base0 != NULL);
     80 	_DIAGASSERT(compar != NULL);
     81 #ifdef _DIAGNOSTIC
     82 	if (key == NULL || base0 == NULL || compar == NULL) {
     83 		errno = EFAULT;
     84 		return (NULL);
     85 	}
     86 #endif
     87 
     88 	for (lim = nmemb; lim != 0; lim >>= 1) {
     89 		p = base + (lim >> 1) * size;
     90 		cmp = (*compar)(key, p);
     91 		if (cmp == 0)
     92 			/* LINTED interface spec */
     93 			return ((void *)p);
     94 		if (cmp > 0) {	/* key > p: move right */
     95 			/* LINTED we don't touch base */
     96 			base = (char *)p + size;
     97 			lim--;
     98 		}		/* else move left */
     99 	}
    100 	return (NULL);
    101 }
    102