1 /* $NetBSD: bsearch.c,v 1.13 2005/11/29 03:12:00 christos 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. 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 <sys/cdefs.h> 33 #if defined(LIBC_SCCS) && !defined(lint) 34 #if 0 35 static char sccsid[] = "@(#)bsearch.c 8.1 (Berkeley) 6/4/93"; 36 #else 37 __RCSID("$NetBSD: bsearch.c,v 1.13 2005/11/29 03:12:00 christos Exp $"); 38 #endif 39 #endif /* LIBC_SCCS and not lint */ 40 41 #include <assert.h> 42 #include <errno.h> 43 #include <stdlib.h> 44 45 /* 46 * Perform a binary search. 47 * 48 * The code below is a bit sneaky. After a comparison fails, we 49 * divide the work in half by moving either left or right. If lim 50 * is odd, moving left simply involves halving lim: e.g., when lim 51 * is 5 we look at item 2, so we change lim to 2 so that we will 52 * look at items 0 & 1. If lim is even, the same applies. If lim 53 * is odd, moving right again involes halving lim, this time moving 54 * the base up one item past p: e.g., when lim is 5 we change base 55 * to item 3 and make lim 2 so that we will look at items 3 and 4. 56 * If lim is even, however, we have to shrink it by one before 57 * halving: e.g., when lim is 4, we still looked at item 2, so we 58 * have to make lim 3, then halve, obtaining 1, so that we will only 59 * look at item 3. 60 */ 61 void * 62 bsearch(key, base0, nmemb, size, compar) 63 const void *key; 64 const void *base0; 65 size_t nmemb; 66 size_t size; 67 int (*compar) __P((const void *, const void *)); 68 { 69 const char *base = base0; 70 size_t lim; 71 int cmp; 72 const void *p; 73 74 _DIAGASSERT(key != NULL); 75 _DIAGASSERT(base0 != NULL); 76 _DIAGASSERT(compar != NULL); 77 78 for (lim = nmemb; lim != 0; lim >>= 1) { 79 p = base + (lim >> 1) * size; 80 cmp = (*compar)(key, p); 81 if (cmp == 0) 82 return __UNCONST(p); 83 if (cmp > 0) { /* key > p: move right */ 84 base = (const char *)p + size; 85 lim--; 86 } /* else move left */ 87 } 88 return (NULL); 89 } 90