Subversion Repositories or1k

/*

 * 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 [rescinded 22 July 1999]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.

 */

#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);

}