stdlib/FreeBSD/bsearch.c

   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  * 4. Neither the name of the University nor the names of its contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  */
  29
  30 #if defined(LIBC_SCCS) && !defined(lint)
  31 static char sccsid[] = "@(#)bsearch.c   8.1 (Berkeley) 6/4/93";
  32 #endif /* LIBC_SCCS and not lint */
  33 #include <sys/cdefs.h>
  34 __FBSDID("$FreeBSD: src/lib/libc/stdlib/bsearch.c,v 1.4 2007/01/09 00:28:09 imp Exp $");
  35
  36 #include <stddef.h>
  37 #include <stdlib.h>
  38
  39 /*
  40  * Perform a binary search.
  41  *
  42  * The code below is a bit sneaky.  After a comparison fails, we
  43  * divide the work in half by moving either left or right. If lim
  44  * is odd, moving left simply involves halving lim: e.g., when lim
  45  * is 5 we look at item 2, so we change lim to 2 so that we will
  46  * look at items 0 & 1.  If lim is even, the same applies.  If lim
  47  * is odd, moving right again involes halving lim, this time moving
  48  * the base up one item past p: e.g., when lim is 5 we change base
  49  * to item 3 and make lim 2 so that we will look at items 3 and 4.
  50  * If lim is even, however, we have to shrink it by one before
  51  * halving: e.g., when lim is 4, we still looked at item 2, so we
  52  * have to make lim 3, then halve, obtaining 1, so that we will only
  53  * look at item 3.
  54  */
  55 void *
  56 bsearch(key, base0, nmemb, size, compar)
  57         const void *key;
  58         const void *base0;
  59         size_t nmemb;
  60         size_t size;
  61         int (*compar)(const void *, const void *);
  62 {
  63         const char *base = base0;
  64         size_t lim;
  65         int cmp;
  66         const void *p;
  67
  68         for (lim = nmemb; lim != 0; lim >>= 1) {
  69                 p = base + (lim >> 1) * size;
  70                 cmp = (*compar)(key, p);
  71                 if (cmp == 0)
  72                         return ((void *)p);
  73                 if (cmp > 0) {  /* key > p: move right */
  74                         base = (char *)p + size;
  75                         lim--;
  76                 }               /* else move left */
  77         }
  78         return (NULL);
  79 }
  80
  81 #ifdef __BLOCKS__
  82 void *
  83 bsearch_b(key, base0, nmemb, size, compar)
  84         const void *key;
  85         const void *base0;
  86         size_t nmemb;
  87         size_t size;
  88         int (^compar)(const void *, const void *);
  89 {
  90         const char *base = base0;
  91         size_t lim;
  92         int cmp;
  93         const void *p;
  94
  95         for (lim = nmemb; lim != 0; lim >>= 1) {
  96                 p = base + (lim >> 1) * size;
  97                 cmp = compar(key, p);
  98                 if (cmp == 0)
  99                         return ((void *)p);
 100                 if (cmp > 0) {  /* key > p: move right */
 101                         base = (char *)p + size;
 102                         lim--;
 103                 }               /* else move left */
 104         }
 105         return (NULL);
 106 }
 107 #endif /* __BLOCKS__ */