177298Sobrien/* 277298Sobrien * Copyright (c) 1990 Regents of the University of California. 377298Sobrien * All rights reserved. 477298Sobrien * 577298Sobrien * Redistribution and use in source and binary forms, with or without 677298Sobrien * modification, are permitted provided that the following conditions 777298Sobrien * are met: 877298Sobrien * 1. Redistributions of source code must retain the above copyright 977298Sobrien * notice, this list of conditions and the following disclaimer. 1077298Sobrien * 2. Redistributions in binary form must reproduce the above copyright 1177298Sobrien * notice, this list of conditions and the following disclaimer in the 1277298Sobrien * documentation and/or other materials provided with the distribution. 1377298Sobrien * 3. [rescinded 22 July 1999] 1477298Sobrien * 4. Neither the name of the University nor the names of its contributors 1577298Sobrien * may be used to endorse or promote products derived from this software 1677298Sobrien * without specific prior written permission. 1777298Sobrien * 1877298Sobrien * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 1977298Sobrien * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 2077298Sobrien * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 2177298Sobrien * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 2277298Sobrien * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 2377298Sobrien * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 2477298Sobrien * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 2577298Sobrien * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 2677298Sobrien * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 2777298Sobrien * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 2877298Sobrien * SUCH DAMAGE. 2977298Sobrien */ 3077298Sobrien 3189857Sobrien/* 3289857Sobrien 3389857Sobrien@deftypefn Supplemental void* bsearch (const void *@var{key}, const void *@var{base}, size_t @var{nmemb}, size_t @var{size}, int (*@var{compar})(const void *, const void *)) 3489857Sobrien 3589857SobrienPerforms a search over an array of @var{nmemb} elements pointed to by 3689857Sobrien@var{base} for a member that matches the object pointed to by @var{key}. 3789857SobrienThe size of each member is specified by @var{size}. The array contents 3889857Sobrienshould be sorted in ascending order according to the @var{compar} 3989857Sobriencomparison function. This routine should take two arguments pointing to 4089857Sobrienthe @var{key} and to an array member, in that order, and should return an 4189857Sobrieninteger less than, equal to, or greater than zero if the @var{key} object 4289857Sobrienis respectively less than, matching, or greater than the array member. 4389857Sobrien 4489857Sobrien@end deftypefn 4589857Sobrien 4689857Sobrien*/ 4789857Sobrien 4877298Sobrien#include "config.h" 4977298Sobrien#include "ansidecl.h" 5077298Sobrien#include <sys/types.h> /* size_t */ 5177298Sobrien#include <stdio.h> 5277298Sobrien 5377298Sobrien/* 5477298Sobrien * Perform a binary search. 5577298Sobrien * 5677298Sobrien * The code below is a bit sneaky. After a comparison fails, we 5777298Sobrien * divide the work in half by moving either left or right. If lim 5877298Sobrien * is odd, moving left simply involves halving lim: e.g., when lim 5977298Sobrien * is 5 we look at item 2, so we change lim to 2 so that we will 6077298Sobrien * look at items 0 & 1. If lim is even, the same applies. If lim 6177298Sobrien * is odd, moving right again involes halving lim, this time moving 6277298Sobrien * the base up one item past p: e.g., when lim is 5 we change base 6377298Sobrien * to item 3 and make lim 2 so that we will look at items 3 and 4. 6477298Sobrien * If lim is even, however, we have to shrink it by one before 6577298Sobrien * halving: e.g., when lim is 4, we still looked at item 2, so we 6677298Sobrien * have to make lim 3, then halve, obtaining 1, so that we will only 6777298Sobrien * look at item 3. 6877298Sobrien */ 6977298Sobrienvoid * 70218822Sdimbsearch (register const void *key, const void *base0, 71218822Sdim size_t nmemb, register size_t size, 72218822Sdim register int (*compar)(const void *, const void *)) 7377298Sobrien{ 74218822Sdim register const char *base = (const char *) base0; 7577298Sobrien register int lim, cmp; 76218822Sdim register const void *p; 7777298Sobrien 7877298Sobrien for (lim = nmemb; lim != 0; lim >>= 1) { 7977298Sobrien p = base + (lim >> 1) * size; 8077298Sobrien cmp = (*compar)(key, p); 8177298Sobrien if (cmp == 0) 82218822Sdim return (void *)p; 8377298Sobrien if (cmp > 0) { /* key > p: move right */ 84218822Sdim base = (const char *)p + size; 8577298Sobrien lim--; 8677298Sobrien } /* else move left */ 8777298Sobrien } 8877298Sobrien return (NULL); 8977298Sobrien} 90