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/* $OpenBSD: bsearch.c,v 1.8 2016/10/22 19:19:34 tb Exp $ */ |
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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. 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 <stdlib.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 involves 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(const void *key, const void *base0, size_t nmemb, size_t size, |
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int (*compar)(const void *, const void *)) |
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{ |
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const char *base = base0; |
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int lim, cmp; |
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const void *p; |
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✓✓ |
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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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✓✓ |
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if (cmp == 0) |
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return ((void *)p); |
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✓✓ |
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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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} |