libsa/bsearch.c

   1 /*
   2  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
   7  *
   8  * This file contains Original Code and/or Modifications of Original Code
   9  * as defined in and that are subject to the Apple Public Source License
  10  * Version 2.0 (the 'License'). You may not use this file except in
  11  * compliance with the License. Please obtain a copy of the License at
  12  * http://www.opensource.apple.com/apsl/ and read it before using this
  13  * file.
  14  *
  15  * The Original Code and all software distributed under the License are
  16  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  17  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  18  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  20  * Please see the License for the specific language governing rights and
  21  * limitations under the License.
  22  *
  23  * @APPLE_LICENSE_HEADER_END@
  24  */
  25 /*
  26  * Copyright (c) 1990, 1993
  27  *      The Regents of the University of California.  All rights reserved.
  28  *
  29  * Redistribution and use in source and binary forms, with or without
  30  * modification, are permitted provided that the following conditions
  31  * are met:
  32  * 1. Redistributions of source code must retain the above copyright
  33  *    notice, this list of conditions and the following disclaimer.
  34  * 2. Redistributions in binary form must reproduce the above copyright
  35  *    notice, this list of conditions and the following disclaimer in the
  36  *    documentation and/or other materials provided with the distribution.
  37  * 3. All advertising materials mentioning features or use of this software
  38  *    must display the following acknowledgement:
  39  *      This product includes software developed by the University of
  40  *      California, Berkeley and its contributors.
  41  * 4. Neither the name of the University nor the names of its contributors
  42  *    may be used to endorse or promote products derived from this software
  43  *    without specific prior written permission.
  44  *
  45  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  46  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  47  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  48  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  49  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  50  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  51  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  52  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  53  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  54  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  55  * SUCH DAMAGE.
  56  */
  57
  58 #if defined(LIBC_SCCS) && !defined(lint)
  59 static char sccsid[] = "@(#)bsearch.c   8.1 (Berkeley) 6/4/93";
  60 #endif /* LIBC_SCCS and not lint */
  61
  62 #include <libsa/stdlib.h>
  63
  64 /*
  65  * Perform a binary search.
  66  *
  67  * The code below is a bit sneaky.  After a comparison fails, we
  68  * divide the work in half by moving either left or right. If lim
  69  * is odd, moving left simply involves halving lim: e.g., when lim
  70  * is 5 we look at item 2, so we change lim to 2 so that we will
  71  * look at items 0 & 1.  If lim is even, the same applies.  If lim
  72  * is odd, moving right again involes halving lim, this time moving
  73  * the base up one item past p: e.g., when lim is 5 we change base
  74  * to item 3 and make lim 2 so that we will look at items 3 and 4.
  75  * If lim is even, however, we have to shrink it by one before
  76  * halving: e.g., when lim is 4, we still looked at item 2, so we
  77  * have to make lim 3, then halve, obtaining 1, so that we will only
  78  * look at item 3.
  79  */
  80 __private_extern__
  81 void * bsearch(
  82         register const void *key,
  83         const void *base0,
  84         size_t nmemb,
  85         register size_t size,
  86         register int (*compar)(const void *, const void *)) {
  87
  88         register const char *base = base0;
  89         register size_t lim;
  90         register int cmp;
  91         register const void *p;
  92
  93         for (lim = nmemb; lim != 0; lim >>= 1) {
  94                 p = base + (lim >> 1) * size;
  95                 cmp = (*compar)(key, p);
  96                 if (cmp == 0)
  97                         return ((void *)p);
  98                 if (cmp > 0) {  /* key > p: move right */
  99                         base = (char *)p + size;
 100                         lim--;
 101                 }               /* else move left */
 102         }
 103         return (NULL);
 104 }