1 /* 2 * Copyright (c) 1990 Regents of the University of California. 3 * 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. 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 30 #if defined(LIBC_SCCS) && !defined(lint) 31 static char *rcsid = "$OpenBSD: bsearch.c,v 1.4 2003/06/02 20:18:37 millert Exp $"; 32 #endif /* LIBC_SCCS and not lint */ 33 34 #include <stdlib.h> 35 36 /* 37 * Perform a binary search. 38 * 39 * The code below is a bit sneaky. After a comparison fails, we 40 * divide the work in half by moving either left or right. If lim 41 * is odd, moving left simply involves halving lim: e.g., when lim 42 * is 5 we look at item 2, so we change lim to 2 so that we will 43 * look at items 0 & 1. If lim is even, the same applies. If lim 44 * is odd, moving right again involes halving lim, this time moving 45 * the base up one item past p: e.g., when lim is 5 we change base 46 * to item 3 and make lim 2 so that we will look at items 3 and 4. 47 * If lim is even, however, we have to shrink it by one before 48 * halving: e.g., when lim is 4, we still looked at item 2, so we 49 * have to make lim 3, then halve, obtaining 1, so that we will only 50 * look at item 3. 51 */ 52 void * 53 bsearch(key, base0, nmemb, size, compar) 54 register const void *key; 55 const void *base0; 56 size_t nmemb; 57 register size_t size; 58 register int (*compar)(const void *, const void *); 59 { 60 register const char *base = base0; 61 register int lim, cmp; 62 register const void *p; 63 64 for (lim = nmemb; lim != 0; lim >>= 1) { 65 p = base + (lim >> 1) * size; 66 cmp = (*compar)(key, p); 67 if (cmp == 0) 68 return ((void *)p); 69 if (cmp > 0) { /* key > p: move right */ 70 base = (char *)p + size; 71 lim--; 72 } /* else move left */ 73 } 74 return (NULL); 75 } 76