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 #include <stdlib.h> 31 32 /* 33 * Perform a binary search. 34 * 35 * The code below is a bit sneaky. After a comparison fails, we 36 * divide the work in half by moving either left or right. If lim 37 * is odd, moving left simply involves halving lim: e.g., when lim 38 * is 5 we look at item 2, so we change lim to 2 so that we will 39 * look at items 0 & 1. If lim is even, the same applies. If lim 40 * is odd, moving right again involes halving lim, this time moving 41 * the base up one item past p: e.g., when lim is 5 we change base 42 * to item 3 and make lim 2 so that we will look at items 3 and 4. 43 * If lim is even, however, we have to shrink it by one before 44 * halving: e.g., when lim is 4, we still looked at item 2, so we 45 * have to make lim 3, then halve, obtaining 1, so that we will only 46 * look at item 3. 47 */ 48 void * 49 bsearch(const void *key, const void *base0, size_t nmemb, size_t size, 50 int (*compar)(const void *, const void *)) 51 { 52 const char *base = base0; 53 int lim, cmp; 54 const void *p; 55 56 for (lim = nmemb; lim != 0; lim >>= 1) { 57 p = base + (lim >> 1) * size; 58 cmp = (*compar)(key, p); 59 if (cmp > 0) { /* key > p: move right */ 60 base = (char *)p + size; 61 lim--; 62 } else if (cmp == 0) { 63 return ((void *)p); 64 } /* else move left */ 65 } 66 return (NULL); 67 } 68
