libsa/bsearch.c

   1 /*
   2  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. The rights granted to you under the License
  10  * may not be used to create, or enable the creation or redistribution of,
  11  * unlawful or unlicensed copies of an Apple operating system, or to
  12  * circumvent, violate, or enable the circumvention or violation of, any
  13  * terms of an Apple operating system software license agreement.
  14  *
  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
  19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  21  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  23  * Please see the License for the specific language governing rights and
  24  * limitations under the License.
  25  *
  26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  27  */
  28 /*
  29  * Copyright (c) 1990, 1993
  30  *      The Regents of the University of California.  All rights reserved.
  31  *
  32  * Redistribution and use in source and binary forms, with or without
  33  * modification, are permitted provided that the following conditions
  34  * are met:
  35  * 1. Redistributions of source code must retain the above copyright
  36  *    notice, this list of conditions and the following disclaimer.
  37  * 2. Redistributions in binary form must reproduce the above copyright
  38  *    notice, this list of conditions and the following disclaimer in the
  39  *    documentation and/or other materials provided with the distribution.
  40  * 3. All advertising materials mentioning features or use of this software
  41  *    must display the following acknowledgement:
  42  *      This product includes software developed by the University of
  43  *      California, Berkeley and its contributors.
  44  * 4. Neither the name of the University nor the names of its contributors
  45  *    may be used to endorse or promote products derived from this software
  46  *    without specific prior written permission.
  47  *
  48  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  49  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  50  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  51  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  52  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  53  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  54  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  55  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  56  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  57  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  58  * SUCH DAMAGE.
  59  */
  60
  61 #if defined(LIBC_SCCS) && !defined(lint)
  62 static char sccsid[] = "@(#)bsearch.c   8.1 (Berkeley) 6/4/93";
  63 #endif /* LIBC_SCCS and not lint */
  64
  65 #include <libsa/stdlib.h>
  66
  67 /*
  68  * Perform a binary search.
  69  *
  70  * The code below is a bit sneaky.  After a comparison fails, we
  71  * divide the work in half by moving either left or right. If lim
  72  * is odd, moving left simply involves halving lim: e.g., when lim
  73  * is 5 we look at item 2, so we change lim to 2 so that we will
  74  * look at items 0 & 1.  If lim is even, the same applies.  If lim
  75  * is odd, moving right again involes halving lim, this time moving
  76  * the base up one item past p: e.g., when lim is 5 we change base
  77  * to item 3 and make lim 2 so that we will look at items 3 and 4.
  78  * If lim is even, however, we have to shrink it by one before
  79  * halving: e.g., when lim is 4, we still looked at item 2, so we
  80  * have to make lim 3, then halve, obtaining 1, so that we will only
  81  * look at item 3.
  82  */
  83 __private_extern__
  84 const void * bsearch(
  85         register const void *key,
  86         const void *base0,
  87         size_t nmemb,
  88         register size_t size,
  89         register int (*compar)(const void *, const void *)) {
  90
  91         register const char *base = base0;
  92         register size_t lim;
  93         register int cmp;
  94         register const void *p;
  95
  96         for (lim = nmemb; lim != 0; lim >>= 1) {
  97                 p = base + (lim >> 1) * size;
  98                 cmp = (*compar)(key, p);
  99                 if (cmp == 0)
 100                         return p;
 101                 if (cmp > 0) {  /* key > p: move right */
 102                         base = (const char *)p + size;
 103                         lim--;
 104                 }               /* else move left */
 105         }
 106         return (NULL);
 107 }