dist/nvi/clib/bsearch.c

   1 /*      $NetBSD$ */
   2
   3 /*
   4  * Copyright (c) 1990, 1993
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. All advertising materials mentioning features or use of this software
  16  *    must display the following acknowledgement:
  17  *      This product includes software developed by the University of
  18  *      California, Berkeley and its contributors.
  19  * 4. Neither the name of the University nor the names of its contributors
  20  *    may be used to endorse or promote products derived from this software
  21  *    without specific prior written permission.
  22  *
  23  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  24  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  25  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  26  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  27  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  28  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  29  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  30  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  31  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  32  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  33  * SUCH DAMAGE.
  34  */
  35
  36 #include "config.h"
  37
  38 #if defined(LIBC_SCCS) && !defined(lint)
  39 static const char sccsid[] = "@(#)bsearch.c     8.1 (Berkeley) 6/4/93";
  40 #endif /* LIBC_SCCS and not lint */
  41
  42 #include <stddef.h>
  43 #include <stdlib.h>
  44
  45 #include "port.h"
  46
  47 /*
  48  * Perform a binary search.
  49  *
  50  * The code below is a bit sneaky.  After a comparison fails, we
  51  * divide the work in half by moving either left or right. If lim
  52  * is odd, moving left simply involves halving lim: e.g., when lim
  53  * is 5 we look at item 2, so we change lim to 2 so that we will
  54  * look at items 0 & 1.  If lim is even, the same applies.  If lim
  55  * is odd, moving right again involes halving lim, this time moving
  56  * the base up one item past p: e.g., when lim is 5 we change base
  57  * to item 3 and make lim 2 so that we will look at items 3 and 4.
  58  * If lim is even, however, we have to shrink it by one before
  59  * halving: e.g., when lim is 4, we still looked at item 2, so we
  60  * have to make lim 3, then halve, obtaining 1, so that we will only
  61  * look at item 3.
  62  *
  63  * PUBLIC: #ifndef HAVE_BSEARCH
  64  * PUBLIC: void *bsearch __P((const void *, const void *, size_t,
  65  * PUBLIC:    size_t, int (*)(const void *, const void *)));
  66  * PUBLIC: #endif
  67  */
  68 void *
  69 bsearch(register const void *key, const void *base0, size_t nmemb, register size_t size, register int (*compar) (const void *, const void *))
  70 {
  71         register const char *base = base0;
  72         register size_t lim;
  73         register int cmp;
  74         register const void *p;
  75
  76         for (lim = nmemb; lim != 0; lim >>= 1) {
  77                 p = base + (lim >> 1) * size;
  78                 cmp = (*compar)(key, p);
  79                 if (cmp == 0)
  80                         return ((void *)p);
  81                 if (cmp > 0) {  /* key > p: move right */
  82                         base = (char *)p + size;
  83                         lim--;
  84                 }               /* else move left */
  85         }
  86         return (NULL);
  87 }