The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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

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    1 /*
    2  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
    3  *
    4  * @APPLE_LICENSE_HEADER_START@
    5  * 
    6  * The contents of this file constitute Original Code as defined in and
    7  * are subject to the Apple Public Source License Version 1.1 (the
    8  * "License").  You may not use this file except in compliance with the
    9  * License.  Please obtain a copy of the License at
   10  * http://www.apple.com/publicsource and read it before using this file.
   11  * 
   12  * This Original Code and all software distributed under the License are
   13  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
   14  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
   15  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
   16  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
   17  * License for the specific language governing rights and limitations
   18  * under the License.
   19  * 
   20  * @APPLE_LICENSE_HEADER_END@
   21  */
   22 /*
   23  * Copyright (c) 1990, 1993
   24  *      The Regents of the University of California.  All rights reserved.
   25  *
   26  * Redistribution and use in source and binary forms, with or without
   27  * modification, are permitted provided that the following conditions
   28  * are met:
   29  * 1. Redistributions of source code must retain the above copyright
   30  *    notice, this list of conditions and the following disclaimer.
   31  * 2. Redistributions in binary form must reproduce the above copyright
   32  *    notice, this list of conditions and the following disclaimer in the
   33  *    documentation and/or other materials provided with the distribution.
   34  * 3. All advertising materials mentioning features or use of this software
   35  *    must display the following acknowledgement:
   36  *      This product includes software developed by the University of
   37  *      California, Berkeley and its contributors.
   38  * 4. Neither the name of the University nor the names of its contributors
   39  *    may be used to endorse or promote products derived from this software
   40  *    without specific prior written permission.
   41  *
   42  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   43  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   44  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   45  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   46  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   47  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   48  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   49  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   50  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   51  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   52  * SUCH DAMAGE.
   53  */
   54 
   55 #if defined(LIBC_SCCS) && !defined(lint)
   56 static char sccsid[] = "@(#)bsearch.c   8.1 (Berkeley) 6/4/93";
   57 #endif /* LIBC_SCCS and not lint */
   58 
   59 #include <libsa/stdlib.h>
   60 
   61 /*
   62  * Perform a binary search.
   63  *
   64  * The code below is a bit sneaky.  After a comparison fails, we
   65  * divide the work in half by moving either left or right. If lim
   66  * is odd, moving left simply involves halving lim: e.g., when lim
   67  * is 5 we look at item 2, so we change lim to 2 so that we will
   68  * look at items 0 & 1.  If lim is even, the same applies.  If lim
   69  * is odd, moving right again involes halving lim, this time moving
   70  * the base up one item past p: e.g., when lim is 5 we change base
   71  * to item 3 and make lim 2 so that we will look at items 3 and 4.
   72  * If lim is even, however, we have to shrink it by one before
   73  * halving: e.g., when lim is 4, we still looked at item 2, so we
   74  * have to make lim 3, then halve, obtaining 1, so that we will only
   75  * look at item 3.
   76  */
   77 __private_extern__
   78 void * bsearch(
   79         register const void *key,
   80         const void *base0,
   81         size_t nmemb,
   82         register size_t size,
   83         register int (*compar)(const void *, const void *)) {
   84 
   85         register const char *base = base0;
   86         register size_t lim;
   87         register int cmp;
   88         register const void *p;
   89 
   90         for (lim = nmemb; lim != 0; lim >>= 1) {
   91                 p = base + (lim >> 1) * size;
   92                 cmp = (*compar)(key, p);
   93                 if (cmp == 0)
   94                         return ((void *)p);
   95                 if (cmp > 0) {  /* key > p: move right */
   96                         base = (char *)p + size;
   97                         lim--;
   98                 }               /* else move left */
   99         }
  100         return (NULL);
  101 }

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