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76 lines
2.9 KiB
C
76 lines
2.9 KiB
C
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/*
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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 [rescinded 22 July 1999]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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#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(key, base0, nmemb, size, compar)
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register void *key;
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void *base0;
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size_t nmemb;
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register size_t size;
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register int (*compar)();
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{
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register char *base = base0;
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register int lim, cmp;
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register 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 (p);
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if (cmp > 0) { /* key > p: move right */
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base = (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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