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 * 29 * @(#)bsearch.c 8.1 (Berkeley) 6/4/93 30 * $FreeBSD: src/sys/libkern/bsearch.c,v 1.8 2005/01/07 00:24:32 imp Exp $ 31 * $DragonFly: src/sys/libkern/bsearch.c,v 1.1 2007/11/18 17:53:02 pavalos Exp $ 32 */ 33 34 #include <sys/param.h> 35 #include <sys/libkern.h> 36 37 /* 38 * Perform a binary search. 39 * 40 * The code below is a bit sneaky. After a comparison fails, we 41 * divide the work in half by moving either left or right. If lim 42 * is odd, moving left simply involves halving lim: e.g., when lim 43 * is 5 we look at item 2, so we change lim to 2 so that we will 44 * look at items 0 & 1. If lim is even, the same applies. If lim 45 * is odd, moving right again involes halving lim, this time moving 46 * the base up one item past p: e.g., when lim is 5 we change base 47 * to item 3 and make lim 2 so that we will look at items 3 and 4. 48 * If lim is even, however, we have to shrink it by one before 49 * halving: e.g., when lim is 4, we still looked at item 2, so we 50 * have to make lim 3, then halve, obtaining 1, so that we will only 51 * look at item 3. 52 */ 53 void * 54 bsearch(const void *key, const void *base0, size_t nmemb, size_t size, 55 int (*compar)(const void *, const void *)) 56 { 57 const char *base = base0; 58 size_t lim; 59 int cmp; 60 const void *p; 61 62 for (lim = nmemb; lim != 0; lim >>= 1) { 63 p = base + (lim >> 1) * size; 64 cmp = (*compar)(key, p); 65 if (cmp == 0) 66 return ((void *)(uintptr_t)p); 67 if (cmp > 0) { /* key > p: move right */ 68 base = (const char *)p + size; 69 lim--; 70 } /* else move left */ 71 } 72 return (NULL); 73 } 74