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 34 #include "config.h" 35 36 #if defined(LIBC_SCCS) && !defined(lint) 37 static const char sccsid[] = "@(#)bsearch.c 8.1 (Berkeley) 6/4/93"; 38 #endif /* LIBC_SCCS and not lint */ 39 40 #include <stddef.h> 41 #include <stdlib.h> 42 43 #include "port.h" 44 45 /* 46 * Perform a binary search. 47 * 48 * The code below is a bit sneaky. After a comparison fails, we 49 * divide the work in half by moving either left or right. If lim 50 * is odd, moving left simply involves halving lim: e.g., when lim 51 * is 5 we look at item 2, so we change lim to 2 so that we will 52 * look at items 0 & 1. If lim is even, the same applies. If lim 53 * is odd, moving right again involes halving lim, this time moving 54 * the base up one item past p: e.g., when lim is 5 we change base 55 * to item 3 and make lim 2 so that we will look at items 3 and 4. 56 * If lim is even, however, we have to shrink it by one before 57 * halving: e.g., when lim is 4, we still looked at item 2, so we 58 * have to make lim 3, then halve, obtaining 1, so that we will only 59 * look at item 3. 60 * 61 * PUBLIC: #ifndef HAVE_BSEARCH 62 * PUBLIC: void *bsearch __P((const void *, const void *, size_t, 63 * PUBLIC: size_t, int (*)(const void *, const void *))); 64 * PUBLIC: #endif 65 */ 66 void * 67 bsearch(register const void *key, const void *base0, size_t nmemb, register size_t size, register int (*compar) (const void *, const void *)) 68 { 69 register const char *base = base0; 70 register size_t lim; 71 register int cmp; 72 register const void *p; 73 74 for (lim = nmemb; lim != 0; lim >>= 1) { 75 p = base + (lim >> 1) * size; 76 cmp = (*compar)(key, p); 77 if (cmp == 0) 78 return ((void *)p); 79 if (cmp > 0) { /* key > p: move right */ 80 base = (char *)p + size; 81 lim--; 82 } /* else move left */ 83 } 84 return (NULL); 85 } 86