FreeBSD/Linux Kernel Cross Reference
sys/libkern/bsearch.c

     /*-
      * Copyright (c) 1990, 1993
      *      The 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.
     *
     * @(#)bsearch.c        8.1 (Berkeley) 6/4/93
     * $FreeBSD: src/sys/libkern/bsearch.c,v 1.8 2005/01/07 00:24:32 imp Exp $
     * $DragonFly: src/sys/libkern/bsearch.c,v 1.1 2007/11/18 17:53:02 pavalos Exp $
     */
    
    #include <sys/param.h>
    #include <sys/libkern.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 *
    kbsearch(const void *key, const void *base0, size_t nmemb, size_t size,
            int (*compar)(const void *, const void *))
    {
            const char *base = base0;
            size_t lim;
            int 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 *)(uintptr_t)p);
                    if (cmp > 0) {  /* key > p: move right */
                            base = (const char *)p + size;
                            lim--;
                    }               /* else move left */
            }
            return (NULL);
    }

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