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_OSREFERENCE_LICENSE_HEADER_START@
    5  * 
    6  * This file contains Original Code and/or Modifications of Original Code
    7  * as defined in and that are subject to the Apple Public Source License
    8  * Version 2.0 (the 'License'). You may not use this file except in
    9  * compliance with the License. The rights granted to you under the License
   10  * may not be used to create, or enable the creation or redistribution of,
   11  * unlawful or unlicensed copies of an Apple operating system, or to
   12  * circumvent, violate, or enable the circumvention or violation of, any
   13  * terms of an Apple operating system software license agreement.
   14  * 
   15  * Please obtain a copy of the License at
   16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
   17  * 
   18  * The Original Code and all software distributed under the License are
   19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
   20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
   21  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
   22  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
   23  * Please see the License for the specific language governing rights and
   24  * limitations under the License.
   25  * 
   26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
   27  */
   28 /*
   29  * Copyright (c) 1990, 1993
   30  *      The Regents of the University of California.  All rights reserved.
   31  *
   32  * Redistribution and use in source and binary forms, with or without
   33  * modification, are permitted provided that the following conditions
   34  * are met:
   35  * 1. Redistributions of source code must retain the above copyright
   36  *    notice, this list of conditions and the following disclaimer.
   37  * 2. Redistributions in binary form must reproduce the above copyright
   38  *    notice, this list of conditions and the following disclaimer in the
   39  *    documentation and/or other materials provided with the distribution.
   40  * 3. All advertising materials mentioning features or use of this software
   41  *    must display the following acknowledgement:
   42  *      This product includes software developed by the University of
   43  *      California, Berkeley and its contributors.
   44  * 4. Neither the name of the University nor the names of its contributors
   45  *    may be used to endorse or promote products derived from this software
   46  *    without specific prior written permission.
   47  *
   48  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   49  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   50  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   51  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   52  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   53  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   54  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   55  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   56  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   57  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   58  * SUCH DAMAGE.
   59  */
   60 
   61 #if defined(LIBC_SCCS) && !defined(lint)
   62 static char sccsid[] = "@(#)bsearch.c   8.1 (Berkeley) 6/4/93";
   63 #endif /* LIBC_SCCS and not lint */
   64 
   65 #include <libsa/stdlib.h>
   66 
   67 /*
   68  * Perform a binary search.
   69  *
   70  * The code below is a bit sneaky.  After a comparison fails, we
   71  * divide the work in half by moving either left or right. If lim
   72  * is odd, moving left simply involves halving lim: e.g., when lim
   73  * is 5 we look at item 2, so we change lim to 2 so that we will
   74  * look at items 0 & 1.  If lim is even, the same applies.  If lim
   75  * is odd, moving right again involes halving lim, this time moving
   76  * the base up one item past p: e.g., when lim is 5 we change base
   77  * to item 3 and make lim 2 so that we will look at items 3 and 4.
   78  * If lim is even, however, we have to shrink it by one before
   79  * halving: e.g., when lim is 4, we still looked at item 2, so we
   80  * have to make lim 3, then halve, obtaining 1, so that we will only
   81  * look at item 3.
   82  */
   83 __private_extern__
   84 const void * bsearch(
   85         register const void *key,
   86         const void *base0,
   87         size_t nmemb,
   88         register size_t size,
   89         register int (*compar)(const void *, const void *)) {
   90 
   91         register const char *base = base0;
   92         register size_t lim;
   93         register int cmp;
   94         register const void *p;
   95 
   96         for (lim = nmemb; lim != 0; lim >>= 1) {
   97                 p = base + (lim >> 1) * size;
   98                 cmp = (*compar)(key, p);
   99                 if (cmp == 0)
  100                         return p;
  101                 if (cmp > 0) {  /* key > p: move right */
  102                         base = (const char *)p + size;
  103                         lim--;
  104                 }               /* else move left */
  105         }
  106         return (NULL);
  107 }

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