external/bsd/nvi/dist/clib/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  * 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 "config.h"
  35
  36 #if defined(LIBC_SCCS) && !defined(lint)
  37 static const char sccsid[] = "@(#)bsearch.c     8.1 (Berkeley) 6/4/93";
  38 #endif /* LIBC_SCCS and not lint */
  39 #else
  40 __RCSID("$NetBSD: bsearch.c,v 1.2 2014/01/26 21:43:45 christos Exp $");
  41 #endif
  42
  43 #include <stddef.h>
  44 #include <stdlib.h>
  45
  46 #include "port.h"
  47
  48 /*
  49  * Perform a binary search.
  50  *
  51  * The code below is a bit sneaky.  After a comparison fails, we
  52  * divide the work in half by moving either left or right. If lim
  53  * is odd, moving left simply involves halving lim: e.g., when lim
  54  * is 5 we look at item 2, so we change lim to 2 so that we will
  55  * look at items 0 & 1.  If lim is even, the same applies.  If lim
  56  * is odd, moving right again involes halving lim, this time moving
  57  * the base up one item past p: e.g., when lim is 5 we change base
  58  * to item 3 and make lim 2 so that we will look at items 3 and 4.
  59  * If lim is even, however, we have to shrink it by one before
  60  * halving: e.g., when lim is 4, we still looked at item 2, so we
  61  * have to make lim 3, then halve, obtaining 1, so that we will only
  62  * look at item 3.
  63  *
  64  * PUBLIC: #ifndef HAVE_BSEARCH
  65  * PUBLIC: void *bsearch __P((const void *, const void *, size_t,
  66  * PUBLIC:    size_t, int (*)(const void *, const void *)));
  67  * PUBLIC: #endif
  68  */
  69 void *
  70 bsearch(register const void *key, const void *base0, size_t nmemb, register size_t size, register int (*compar) (const void *, const void *))
  71 {
  72         register const char *base = base0;
  73         register size_t lim;
  74         register int cmp;
  75         register const void *p;
  76
  77         for (lim = nmemb; lim != 0; lim >>= 1) {
  78                 p = base + (lim >> 1) * size;
  79                 cmp = (*compar)(key, p);
  80                 if (cmp == 0)
  81                         return ((void *)p);
  82                 if (cmp > 0) {  /* key > p: move right */
  83                         base = (char *)p + size;
  84                         lim--;
  85                 }               /* else move left */
  86         }
  87         return (NULL);
  88 }