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cell-binutils  2.17cvs20070401
bsearch.c
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00001 /*
00002  * Copyright (c) 1990 Regents of the University of California.
00003  * All rights reserved.
00004  *
00005  * Redistribution and use in source and binary forms, with or without
00006  * modification, are permitted provided that the following conditions
00007  * are met:
00008  * 1. Redistributions of source code must retain the above copyright
00009  *    notice, this list of conditions and the following disclaimer.
00010  * 2. Redistributions in binary form must reproduce the above copyright
00011  *    notice, this list of conditions and the following disclaimer in the
00012  *    documentation and/or other materials provided with the distribution.
00013  * 3. [rescinded 22 July 1999]
00014  * 4. Neither the name of the University nor the names of its contributors
00015  *    may be used to endorse or promote products derived from this software
00016  *    without specific prior written permission.
00017  *
00018  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
00019  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
00020  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
00021  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
00022  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
00023  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
00024  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
00025  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
00026  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
00027  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
00028  * SUCH DAMAGE.
00029  */
00030 
00031 /*
00032 
00033 @deftypefn Supplemental void* bsearch (const void *@var{key}, const void *@var{base}, size_t @var{nmemb}, size_t @var{size}, int (*@var{compar})(const void *, const void *))
00034 
00035 Performs a search over an array of @var{nmemb} elements pointed to by
00036 @var{base} for a member that matches the object pointed to by @var{key}.
00037 The size of each member is specified by @var{size}.  The array contents
00038 should be sorted in ascending order according to the @var{compar}
00039 comparison function.  This routine should take two arguments pointing to
00040 the @var{key} and to an array member, in that order, and should return an
00041 integer less than, equal to, or greater than zero if the @var{key} object
00042 is respectively less than, matching, or greater than the array member.
00043 
00044 @end deftypefn
00045 
00046 */
00047 
00048 #include "config.h"
00049 #include "ansidecl.h"
00050 #include <sys/types.h>             /* size_t */
00051 #include <stdio.h>
00052 
00053 /*
00054  * Perform a binary search.
00055  *
00056  * The code below is a bit sneaky.  After a comparison fails, we
00057  * divide the work in half by moving either left or right. If lim
00058  * is odd, moving left simply involves halving lim: e.g., when lim
00059  * is 5 we look at item 2, so we change lim to 2 so that we will
00060  * look at items 0 & 1.  If lim is even, the same applies.  If lim
00061  * is odd, moving right again involes halving lim, this time moving
00062  * the base up one item past p: e.g., when lim is 5 we change base
00063  * to item 3 and make lim 2 so that we will look at items 3 and 4.
00064  * If lim is even, however, we have to shrink it by one before
00065  * halving: e.g., when lim is 4, we still looked at item 2, so we
00066  * have to make lim 3, then halve, obtaining 1, so that we will only
00067  * look at item 3.
00068  */
00069 void *
00070 bsearch (register const void *key, const void *base0,
00071          size_t nmemb, register size_t size,
00072          register int (*compar)(const void *, const void *))
00073 {
00074        register const char *base = (const char *) base0;
00075        register int lim, cmp;
00076        register const void *p;
00077 
00078        for (lim = nmemb; lim != 0; lim >>= 1) {
00079               p = base + (lim >> 1) * size;
00080               cmp = (*compar)(key, p);
00081               if (cmp == 0)
00082                      return (void *)p;
00083               if (cmp > 0) {       /* key > p: move right */
00084                      base = (const char *)p + size;
00085                      lim--;
00086               } /* else move left */
00087        }
00088        return (NULL);
00089 }