1 /* $OpenBSD: bsearch.c,v 1.9 2021/12/02 20:58:01 cheloha Exp $ */ 2 /* 3 * Copyright (c) 1990 Regents of the University of California. 4 * All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 3. Neither the name of the University nor the names of its contributors 15 * may be used to endorse or promote products derived from this software 16 * without specific prior written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28 * SUCH DAMAGE. 29 */ 30 31 #include <stdlib.h> 32 33 /* 34 * Perform a binary search. 35 * 36 * The code below is a bit sneaky. After a comparison fails, we 37 * divide the work in half by moving either left or right. If lim 38 * is odd, moving left simply involves halving lim: e.g., when lim 39 * is 5 we look at item 2, so we change lim to 2 so that we will 40 * look at items 0 & 1. If lim is even, the same applies. If lim 41 * is odd, moving right again involves halving lim, this time moving 42 * the base up one item past p: e.g., when lim is 5 we change base 43 * to item 3 and make lim 2 so that we will look at items 3 and 4. 44 * If lim is even, however, we have to shrink it by one before 45 * halving: e.g., when lim is 4, we still looked at item 2, so we 46 * have to make lim 3, then halve, obtaining 1, so that we will only 47 * look at item 3. 48 */ 49 void * 50 bsearch(const void *key, const void *base0, size_t nmemb, size_t size, 51 int (*compar)(const void *, const void *)) 52 { 53 const char *base = base0; 54 const void *p; 55 size_t lim; 56 int cmp; 57 58 for (lim = nmemb; lim != 0; lim >>= 1) { 59 p = base + (lim >> 1) * size; 60 cmp = (*compar)(key, p); 61 if (cmp == 0) 62 return ((void *)p); 63 if (cmp > 0) { /* key > p: move right */ 64 base = (char *)p + size; 65 lim--; 66 } /* else move left */ 67 } 68 return (NULL); 69 } 70