1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 1990, 1993 5 * The Regents of the University of California. All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. Neither the name of the University nor the names of its contributors 16 * may be used to endorse or promote products derived from this software 17 * without specific prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29 * SUCH DAMAGE. 30 */ 31 32 #include <sys/cdefs.h> 33 #include <sys/param.h> 34 #include <sys/libkern.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 involves 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(const void *key, const void *base0, size_t nmemb, size_t size, 54 int (*compar)(const void *, const void *)) 55 { 56 const char *base = base0; 57 size_t lim; 58 int cmp; 59 const void *p; 60 61 for (lim = nmemb; lim != 0; lim >>= 1) { 62 p = base + (lim >> 1) * size; 63 cmp = (*compar)(key, p); 64 if (cmp == 0) 65 return ((void *)(uintptr_t)p); 66 if (cmp > 0) { /* key > p: move right */ 67 base = (const char *)p + size; 68 lim--; 69 } /* else move left */ 70 } 71 return (NULL); 72 } 73