1 /* $NetBSD: bsearch.c,v 1.5 1995/12/28 08:52:10 thorpej 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 #if defined(LIBC_SCCS) && !defined(lint) 37 #if 0 38 static char *sccsid = "from: @(#)bsearch.c 5.4 (Berkeley) 2/23/91"; 39 #else 40 static char *rcsid = "$NetBSD: bsearch.c,v 1.5 1995/12/28 08:52:10 thorpej Exp $"; 41 #endif 42 #endif /* LIBC_SCCS and not lint */ 43 44 #include <stdlib.h> 45 46 /* 47 * Perform a binary search. 48 * 49 * The code below is a bit sneaky. After a comparison fails, we 50 * divide the work in half by moving either left or right. If lim 51 * is odd, moving left simply involves halving lim: e.g., when lim 52 * is 5 we look at item 2, so we change lim to 2 so that we will 53 * look at items 0 & 1. If lim is even, the same applies. If lim 54 * is odd, moving right again involes halving lim, this time moving 55 * the base up one item past p: e.g., when lim is 5 we change base 56 * to item 3 and make lim 2 so that we will look at items 3 and 4. 57 * If lim is even, however, we have to shrink it by one before 58 * halving: e.g., when lim is 4, we still looked at item 2, so we 59 * have to make lim 3, then halve, obtaining 1, so that we will only 60 * look at item 3. 61 */ 62 void * 63 bsearch(key, base0, nmemb, size, compar) 64 register const void *key; 65 const void *base0; 66 size_t nmemb; 67 register size_t size; 68 register int (*compar) __P((const void *, const void *)); 69 { 70 register const char *base = base0; 71 register int lim, cmp; 72 register const void *p; 73 74 for (lim = nmemb; lim != 0; lim >>= 1) { 75 p = base + (lim >> 1) * size; 76 cmp = (*compar)(key, p); 77 if (cmp == 0) 78 return ((void *)p); 79 if (cmp > 0) { /* key > p: move right */ 80 base = (char *)p + size; 81 lim--; 82 } /* else move left */ 83 } 84 return (NULL); 85 } 86