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bac427a Feb 3, 2011
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/*
* 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 [rescinded 22 July 1999]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 (register const void *key, const void *base0,
size_t nmemb, register size_t size,
register int (*compar)(const void *, const void *))
{
register const char *base = (const char *) base0;
register int lim, cmp;
register const void *p;
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 = (const char *)p + size;
lim--;
} /* else move left */
}
return (NULL);
}