libsa/bsearch.c

   1 /*
   2  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * The contents of this file constitute Original Code as defined in and
   7  * are subject to the Apple Public Source License Version 1.1 (the
   8  * "License").  You may not use this file except in compliance with the
   9  * License.  Please obtain a copy of the License at
  10  * http://www.apple.com/publicsource and read it before using this file.
  11  *
  12  * This Original Code and all software distributed under the License are
  13  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  14  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  15  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  16  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
  17  * License for the specific language governing rights and limitations
  18  * under the License.
  19  *
  20  * @APPLE_LICENSE_HEADER_END@
  21  */
  22 /*
  23  * Copyright (c) 1990, 1993
  24  *      The Regents of the University of California.  All rights reserved.
  25  *
  26  * Redistribution and use in source and binary forms, with or without
  27  * modification, are permitted provided that the following conditions
  28  * are met:
  29  * 1. Redistributions of source code must retain the above copyright
  30  *    notice, this list of conditions and the following disclaimer.
  31  * 2. Redistributions in binary form must reproduce the above copyright
  32  *    notice, this list of conditions and the following disclaimer in the
  33  *    documentation and/or other materials provided with the distribution.
  34  * 3. All advertising materials mentioning features or use of this software
  35  *    must display the following acknowledgement:
  36  *      This product includes software developed by the University of
  37  *      California, Berkeley and its contributors.
  38  * 4. Neither the name of the University nor the names of its contributors
  39  *    may be used to endorse or promote products derived from this software
  40  *    without specific prior written permission.
  41  *
  42  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  43  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  44  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  45  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  46  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  47  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  48  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  49  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  50  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  51  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  52  * SUCH DAMAGE.
  53  */
  54
  55 #if defined(LIBC_SCCS) && !defined(lint)
  56 static char sccsid[] = "@(#)bsearch.c   8.1 (Berkeley) 6/4/93";
  57 #endif /* LIBC_SCCS and not lint */
  58
  59 #include <libsa/stdlib.h>
  60
  61 /*
  62  * Perform a binary search.
  63  *
  64  * The code below is a bit sneaky.  After a comparison fails, we
  65  * divide the work in half by moving either left or right. If lim
  66  * is odd, moving left simply involves halving lim: e.g., when lim
  67  * is 5 we look at item 2, so we change lim to 2 so that we will
  68  * look at items 0 & 1.  If lim is even, the same applies.  If lim
  69  * is odd, moving right again involes halving lim, this time moving
  70  * the base up one item past p: e.g., when lim is 5 we change base
  71  * to item 3 and make lim 2 so that we will look at items 3 and 4.
  72  * If lim is even, however, we have to shrink it by one before
  73  * halving: e.g., when lim is 4, we still looked at item 2, so we
  74  * have to make lim 3, then halve, obtaining 1, so that we will only
  75  * look at item 3.
  76  */
  77 __private_extern__
  78 void * bsearch(
  79         register const void *key,
  80         const void *base0,
  81         size_t nmemb,
  82         register size_t size,
  83         register int (*compar)(const void *, const void *)) {
  84
  85         register const char *base = base0;
  86         register size_t lim;
  87         register int cmp;
  88         register const void *p;
  89
  90         for (lim = nmemb; lim != 0; lim >>= 1) {
  91                 p = base + (lim >> 1) * size;
  92                 cmp = (*compar)(key, p);
  93                 if (cmp == 0)
  94                         return ((void *)p);
  95                 if (cmp > 0) {  /* key > p: move right */
  96                         base = (char *)p + size;
  97                         lim--;
  98                 }               /* else move left */
  99         }
 100         return (NULL);
 101 }