LXR darwin-xnu/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)
  56static 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__
  78void * 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}
 102