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[/] [openrisc/] [trunk/] [gnu-dev/] [or1k-gcc/] [libiberty/] [bsearch.c] - Blame information for rev 736

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1 736 jeremybenn
/*
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 * Copyright (c) 1990 Regents of the University of California.
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 * All rights reserved.
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 *
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 * Redistribution and use in source and binary forms, with or without
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 * modification, are permitted provided that the following conditions
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 * are met:
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 * 1. Redistributions of source code must retain the above copyright
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 *    notice, this list of conditions and the following disclaimer.
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 * 2. Redistributions in binary form must reproduce the above copyright
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 *    notice, this list of conditions and the following disclaimer in the
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 *    documentation and/or other materials provided with the distribution.
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 * 3. [rescinded 22 July 1999]
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 * 4. Neither the name of the University nor the names of its contributors
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 *    may be used to endorse or promote products derived from this software
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 *    without specific prior written permission.
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 *
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 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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 * SUCH DAMAGE.
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 */
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/*
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@deftypefn Supplemental void* bsearch (const void *@var{key}, @
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  const void *@var{base}, size_t @var{nmemb}, size_t @var{size}, @
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  int (*@var{compar})(const void *, const void *))
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Performs a search over an array of @var{nmemb} elements pointed to by
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@var{base} for a member that matches the object pointed to by @var{key}.
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The size of each member is specified by @var{size}.  The array contents
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should be sorted in ascending order according to the @var{compar}
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comparison function.  This routine should take two arguments pointing to
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the @var{key} and to an array member, in that order, and should return an
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integer less than, equal to, or greater than zero if the @var{key} object
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is respectively less than, matching, or greater than the array member.
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@end deftypefn
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*/
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#include "config.h"
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#include "ansidecl.h"
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#include <sys/types.h>          /* size_t */
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#include <stdio.h>
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/*
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 * Perform a binary search.
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 *
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 * The code below is a bit sneaky.  After a comparison fails, we
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 * divide the work in half by moving either left or right. If lim
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 * is odd, moving left simply involves halving lim: e.g., when lim
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 * is 5 we look at item 2, so we change lim to 2 so that we will
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 * look at items 0 & 1.  If lim is even, the same applies.  If lim
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 * is odd, moving right again involes halving lim, this time moving
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 * the base up one item past p: e.g., when lim is 5 we change base
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 * to item 3 and make lim 2 so that we will look at items 3 and 4.
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 * If lim is even, however, we have to shrink it by one before
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 * halving: e.g., when lim is 4, we still looked at item 2, so we
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 * have to make lim 3, then halve, obtaining 1, so that we will only
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 * look at item 3.
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 */
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void *
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bsearch (register const void *key, const void *base0,
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         size_t nmemb, register size_t size,
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         register int (*compar)(const void *, const void *))
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{
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        register const char *base = (const char *) base0;
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        register int lim, cmp;
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        register const void *p;
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        for (lim = nmemb; lim != 0; lim >>= 1) {
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                p = base + (lim >> 1) * size;
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                cmp = (*compar)(key, p);
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                if (cmp == 0)
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                        return (void *)p;
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                if (cmp > 0) {   /* key > p: move right */
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                        base = (const char *)p + size;
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                        lim--;
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                } /* else move left */
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        }
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        return (NULL);
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}

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