bsearch.c - vx32 - Local 9vx git repository for patches.
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       ---
       bsearch.c (3156B)
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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 
           34 #include <stddef.h>
           35 #include <stdlib.h>
           36 
           37 /*
           38  * Perform a binary search.
           39  *
           40  * The code below is a bit sneaky.  After a comparison fails, we
           41  * divide the work in half by moving either left or right. If lim
           42  * is odd, moving left simply involves halving lim: e.g., when lim
           43  * is 5 we look at item 2, so we change lim to 2 so that we will
           44  * look at items 0 & 1.  If lim is even, the same applies.  If lim
           45  * is odd, moving right again involes halving lim, this time moving
           46  * the base up one item past p: e.g., when lim is 5 we change base
           47  * to item 3 and make lim 2 so that we will look at items 3 and 4.
           48  * If lim is even, however, we have to shrink it by one before
           49  * halving: e.g., when lim is 4, we still looked at item 2, so we
           50  * have to make lim 3, then halve, obtaining 1, so that we will only
           51  * look at item 3.
           52  */
           53 void *
           54 bsearch(key, base0, nmemb, size, compar)
           55         const void *key;
           56         const void *base0;
           57         size_t nmemb;
           58         size_t size;
           59         int (*compar)(const void *, const void *);
           60 {
           61         const char *base = base0;
           62         size_t lim;
           63         int cmp;
           64         const void *p;
           65 
           66         for (lim = nmemb; lim != 0; lim >>= 1) {
           67                 p = base + (lim >> 1) * size;
           68                 cmp = (*compar)(key, p);
           69                 if (cmp == 0)
           70                         return ((void *)p);
           71                 if (cmp > 0) {        /* key > p: move right */
           72                         base = (char *)p + size;
           73                         lim--;
           74                 }                /* else move left */
           75         }
           76         return (NULL);
           77 }