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

     /*
      * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
      *
      * @APPLE_LICENSE_HEADER_START@
      * 
      * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
      * 
      * This file contains Original Code and/or Modifications of Original Code
      * as defined in and that are subject to the Apple Public Source License
     * Version 2.0 (the 'License'). You may not use this file except in
     * compliance with the License. Please obtain a copy of the License at
     * http://www.opensource.apple.com/apsl/ and read it before using this
     * file.
     * 
     * The Original Code and all software distributed under the License are
     * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
     * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
     * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
     * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
     * Please see the License for the specific language governing rights and
     * limitations under the License.
     * 
     * @APPLE_LICENSE_HEADER_END@
     */
    /*
     * 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. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by the University of
     *      California, Berkeley and its contributors.
     * 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.
     */
    
    #if defined(LIBC_SCCS) && !defined(lint)
    static char sccsid[] = "@(#)bsearch.c   8.1 (Berkeley) 6/4/93";
    #endif /* LIBC_SCCS and not lint */
    
    #include <libsa/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 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.
     */
    __private_extern__
    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 = base0;
            register size_t lim;
            register int 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 = (char *)p + size;
                           lim--;
                   }               /* else move left */
           }
           return (NULL);
   }

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