92 lines
3.7 KiB
C
92 lines
3.7 KiB
C
|
/*
|
||
|
|
* 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 [rescinded 22 July 1999]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 (const void *key, const void *base0,
|
||
|
|
size_t nmemb, size_t size,
|
||
|
|
int (*compar)(const void *, const void *))
|
||
|
|
{
|
||
|
|
const char *base = (const char *) base0;
|
||
|
|
int lim, cmp;
|
||
|
|
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);
|
||
|
|
}
|