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/libkern/bsearch.c

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    1 /*
    2  * Copyright (c) 1990, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  * 3. All advertising materials mentioning features or use of this software
   14  *    must display the following acknowledgement:
   15  *      This product includes software developed by the University of
   16  *      California, Berkeley and its contributors.
   17  * 4. Neither the name of the University nor the names of its contributors
   18  *    may be used to endorse or promote products derived from this software
   19  *    without specific prior written permission.
   20  *
   21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   31  * SUCH DAMAGE.
   32  *
   33  * $FreeBSD: src/sys/libkern/bsearch.c,v 1.5 2002/04/11 06:53:40 mike Exp $
   34  */
   35 
   36 #if defined(LIBC_SCCS) && !defined(lint)
   37 static char sccsid[] = "@(#)bsearch.c   8.1 (Berkeley) 6/4/93";
   38 #endif /* LIBC_SCCS and not lint */
   39 
   40 #include <sys/param.h>
   41 #include <sys/libkern.h>
   42 
   43 /*
   44  * Perform a binary search.
   45  *
   46  * The code below is a bit sneaky.  After a comparison fails, we
   47  * divide the work in half by moving either left or right. If lim
   48  * is odd, moving left simply involves halving lim: e.g., when lim
   49  * is 5 we look at item 2, so we change lim to 2 so that we will
   50  * look at items 0 & 1.  If lim is even, the same applies.  If lim
   51  * is odd, moving right again involes halving lim, this time moving
   52  * the base up one item past p: e.g., when lim is 5 we change base
   53  * to item 3 and make lim 2 so that we will look at items 3 and 4.
   54  * If lim is even, however, we have to shrink it by one before
   55  * halving: e.g., when lim is 4, we still looked at item 2, so we
   56  * have to make lim 3, then halve, obtaining 1, so that we will only
   57  * look at item 3.
   58  */
   59 void *
   60 bsearch(key, base0, nmemb, size, compar)
   61         register const void *key;
   62         const void *base0;
   63         size_t nmemb;
   64         register size_t size;
   65         register int (*compar)(const void *, const void *);
   66 {
   67         register const char *base = base0;
   68         register size_t lim;
   69         register int cmp;
   70         register const void *p;
   71 
   72         for (lim = nmemb; lim != 0; lim >>= 1) {
   73                 p = base + (lim >> 1) * size;
   74                 cmp = (*compar)(key, p);
   75                 if (cmp == 0)
   76                         return ((void *)(uintptr_t)p);
   77                 if (cmp > 0) {  /* key > p: move right */
   78                         base = (const char *)p + size;
   79                         lim--;
   80                 }               /* else move left */
   81         }
   82         return (NULL);
   83 }

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