1 /* $NetBSD: bsearch.c,v 1.6 1997/07/13 20:16:38 christos Exp $ */ 2 3 /* 4 * Copyright (c) 1990 Regents of the University of California. 5 * 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 = "from: @(#)bsearch.c 5.4 (Berkeley) 2/23/91"; 40 #else 41 __RCSID("$NetBSD: bsearch.c,v 1.6 1997/07/13 20:16:38 christos Exp $"); 42 #endif 43 #endif /* LIBC_SCCS and not lint */ 44 45 #include <stdlib.h> 46 47 /* 48 * Perform a binary search. 49 * 50 * The code below is a bit sneaky. After a comparison fails, we 51 * divide the work in half by moving either left or right. If lim 52 * is odd, moving left simply involves halving lim: e.g., when lim 53 * is 5 we look at item 2, so we change lim to 2 so that we will 54 * look at items 0 & 1. If lim is even, the same applies. If lim 55 * is odd, moving right again involes halving lim, this time moving 56 * the base up one item past p: e.g., when lim is 5 we change base 57 * to item 3 and make lim 2 so that we will look at items 3 and 4. 58 * If lim is even, however, we have to shrink it by one before 59 * halving: e.g., when lim is 4, we still looked at item 2, so we 60 * have to make lim 3, then halve, obtaining 1, so that we will only 61 * look at item 3. 62 */ 63 void * 64 bsearch(key, base0, nmemb, size, compar) 65 register const void *key; 66 const void *base0; 67 size_t nmemb; 68 register size_t size; 69 register int (*compar) __P((const void *, const void *)); 70 { 71 register const char *base = base0; 72 register int lim, cmp; 73 register const void *p; 74 75 for (lim = nmemb; lim != 0; lim >>= 1) { 76 p = base + (lim >> 1) * size; 77 cmp = (*compar)(key, p); 78 if (cmp == 0) 79 return ((void *)p); 80 if (cmp > 0) { /* key > p: move right */ 81 base = (char *)p + size; 82 lim--; 83 } /* else move left */ 84 } 85 return (NULL); 86 } 87