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 * 3. All advertising materials mentioning features or use of this software 14 * must display the following acknowledgement: 15 * This product includes software developed by the University of 16 * California, Berkeley and its contributors. 17 * 4. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 * 33 * @(#)bsearch.c 8.1 (Berkeley) 6/4/93 34 * $DragonFly: src/lib/libc/stdlib/bsearch.c,v 1.5 2005/11/20 12:37:48 swildner Exp $ 35 */ 36 37 #include <stddef.h> 38 #include <stdlib.h> 39 40 /* 41 * Perform a binary search. 42 * 43 * The code below is a bit sneaky. After a comparison fails, we 44 * divide the work in half by moving either left or right. If lim 45 * is odd, moving left simply involves halving lim: e.g., when lim 46 * is 5 we look at item 2, so we change lim to 2 so that we will 47 * look at items 0 & 1. If lim is even, the same applies. If lim 48 * is odd, moving right again involes halving lim, this time moving 49 * the base up one item past p: e.g., when lim is 5 we change base 50 * to item 3 and make lim 2 so that we will look at items 3 and 4. 51 * If lim is even, however, we have to shrink it by one before 52 * halving: e.g., when lim is 4, we still looked at item 2, so we 53 * have to make lim 3, then halve, obtaining 1, so that we will only 54 * look at item 3. 55 */ 56 void * 57 bsearch(const void *key, const void *base0, size_t nmemb, size_t size, 58 int (*compar)(const void *, const void *)) 59 { 60 const char *base = base0; 61 size_t lim; 62 int cmp; 63 const void *p; 64 65 for (lim = nmemb; lim != 0; lim >>= 1) { 66 p = base + (lim >> 1) * size; 67 cmp = (*compar)(key, p); 68 if (cmp == 0) 69 return ((void *)p); 70 if (cmp > 0) { /* key > p: move right */ 71 base = (char *)p + size; 72 lim--; 73 } /* else move left */ 74 } 75 return (NULL); 76 } 77