bsearch.c revision 92905
11573Srgrimes/* 21573Srgrimes * Copyright (c) 1990, 1993 31573Srgrimes * The Regents of the University of California. All rights reserved. 41573Srgrimes * 51573Srgrimes * Redistribution and use in source and binary forms, with or without 61573Srgrimes * modification, are permitted provided that the following conditions 71573Srgrimes * are met: 81573Srgrimes * 1. Redistributions of source code must retain the above copyright 91573Srgrimes * notice, this list of conditions and the following disclaimer. 101573Srgrimes * 2. Redistributions in binary form must reproduce the above copyright 111573Srgrimes * notice, this list of conditions and the following disclaimer in the 121573Srgrimes * documentation and/or other materials provided with the distribution. 131573Srgrimes * 3. All advertising materials mentioning features or use of this software 141573Srgrimes * must display the following acknowledgement: 151573Srgrimes * This product includes software developed by the University of 161573Srgrimes * California, Berkeley and its contributors. 171573Srgrimes * 4. Neither the name of the University nor the names of its contributors 181573Srgrimes * may be used to endorse or promote products derived from this software 191573Srgrimes * without specific prior written permission. 201573Srgrimes * 211573Srgrimes * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 221573Srgrimes * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 231573Srgrimes * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 241573Srgrimes * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 251573Srgrimes * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 261573Srgrimes * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 271573Srgrimes * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 281573Srgrimes * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 291573Srgrimes * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 301573Srgrimes * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 311573Srgrimes * SUCH DAMAGE. 321573Srgrimes */ 331573Srgrimes 341573Srgrimes#if defined(LIBC_SCCS) && !defined(lint) 351573Srgrimesstatic char sccsid[] = "@(#)bsearch.c 8.1 (Berkeley) 6/4/93"; 361573Srgrimes#endif /* LIBC_SCCS and not lint */ 3792889Sobrien#include <sys/cdefs.h> 3892889Sobrien__FBSDID("$FreeBSD: head/lib/libc/stdlib/bsearch.c 92905 2002-03-21 22:49:10Z obrien $"); 391573Srgrimes 401573Srgrimes#include <stddef.h> 411573Srgrimes#include <stdlib.h> 421573Srgrimes 431573Srgrimes/* 441573Srgrimes * Perform a binary search. 451573Srgrimes * 461573Srgrimes * The code below is a bit sneaky. After a comparison fails, we 471573Srgrimes * divide the work in half by moving either left or right. If lim 481573Srgrimes * is odd, moving left simply involves halving lim: e.g., when lim 491573Srgrimes * is 5 we look at item 2, so we change lim to 2 so that we will 501573Srgrimes * look at items 0 & 1. If lim is even, the same applies. If lim 511573Srgrimes * is odd, moving right again involes halving lim, this time moving 521573Srgrimes * the base up one item past p: e.g., when lim is 5 we change base 531573Srgrimes * to item 3 and make lim 2 so that we will look at items 3 and 4. 541573Srgrimes * If lim is even, however, we have to shrink it by one before 551573Srgrimes * halving: e.g., when lim is 4, we still looked at item 2, so we 561573Srgrimes * have to make lim 3, then halve, obtaining 1, so that we will only 571573Srgrimes * look at item 3. 581573Srgrimes */ 591573Srgrimesvoid * 601573Srgrimesbsearch(key, base0, nmemb, size, compar) 6192889Sobrien const void *key; 621573Srgrimes const void *base0; 631573Srgrimes size_t nmemb; 6492889Sobrien size_t size; 6592905Sobrien int (*compar)(const void *, const void *); 661573Srgrimes{ 6792889Sobrien const char *base = base0; 6892889Sobrien size_t lim; 6992889Sobrien int cmp; 7092889Sobrien const void *p; 711573Srgrimes 721573Srgrimes for (lim = nmemb; lim != 0; lim >>= 1) { 731573Srgrimes p = base + (lim >> 1) * size; 741573Srgrimes cmp = (*compar)(key, p); 751573Srgrimes if (cmp == 0) 761573Srgrimes return ((void *)p); 771573Srgrimes if (cmp > 0) { /* key > p: move right */ 781573Srgrimes base = (char *)p + size; 791573Srgrimes lim--; 801573Srgrimes } /* else move left */ 811573Srgrimes } 821573Srgrimes return (NULL); 831573Srgrimes} 84