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