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/* $OpenBSD: bsearch.c,v 1.9 2021/12/02 20:58:01 cheloha Exp $ */
/*
* 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. 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.
*/
#include <stdlib.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 involves 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(const void *key, const void *base0, size_t nmemb, size_t size,
int (*compar)(const void *, const void *))
{
const char *base = base0;
const void *p;
size_t lim;
int cmp;
for (lim = nmemb; lim != 0; lim >>= 1) {
p = base + (lim >> 1) * size;
cmp = (*compar)(key, p);
if (cmp == 0)
return ((void *)p);
if (cmp > 0) { /* key > p: move right */
base = (char *)p + size;
lim--;
} /* else move left */
}
return (NULL);
}
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