/* * Copyright (c) 1990 Regents of the University of California. * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. [rescinded 22 July 1999] * 4. Neither the name of the University nor the names of its contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ /* @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 *)) Performs a search over an array of @var{nmemb} elements pointed to by @var{base} for a member that matches the object pointed to by @var{key}. The size of each member is specified by @var{size}. The array contents should be sorted in ascending order according to the @var{compar} comparison function. This routine should take two arguments pointing to the @var{key} and to an array member, in that order, and should return an integer less than, equal to, or greater than zero if the @var{key} object is respectively less than, matching, or greater than the array member. @end deftypefn */ #include "config.h" #include "ansidecl.h" #include <sys/types.h> /* size_t */ #include <stdio.h> /* * Perform a binary search. * * The code below is a bit sneaky. After a comparison fails, we * divide the work in half by moving either left or right. If lim * is odd, moving left simply involves halving lim: e.g., when lim * is 5 we look at item 2, so we change lim to 2 so that we will * look at items 0 & 1. If lim is even, the same applies. If lim * is odd, moving right again involes halving lim, this time moving * the base up one item past p: e.g., when lim is 5 we change base * to item 3 and make lim 2 so that we will look at items 3 and 4. * If lim is even, however, we have to shrink it by one before * halving: e.g., when lim is 4, we still looked at item 2, so we * have to make lim 3, then halve, obtaining 1, so that we will only * look at item 3. */ void * bsearch(key, base0, nmemb, size, compar) register void *key; void *base0; size_t nmemb; register size_t size; register int (*compar)(); { register char *base = base0; register int lim, cmp; register void *p; for (lim = nmemb; lim != 0; lim >>= 1) { p = base + (lim >> 1) * size; cmp = (*compar)(key, p); if (cmp == 0) return (p); if (cmp > 0) { /* key > p: move right */ base = (char *)p + size; lim--; } /* else move left */ } return (NULL); }