70 lines
2.1 KiB
C
70 lines
2.1 KiB
C
/*
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* Copyright (c) 2012, 2016 Jonas 'Sortie' Termansen.
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*
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* stdlib/bsearch.c
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* Binary search.
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*/
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#include <stdint.h>
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#include <stdlib.h>
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/*
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* Semantics of binary search:
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*
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* bsearch(key, base, 0, size, compare) may return NULL.
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*
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* If 0 <= i < nmemb
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* and ptr = base + size * i
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* and compare(key, ptr) = 0 then
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* bsearch(key, base, nmemb, size, compare) may return ptr.
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*
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* If 0 <= i < nmemb
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* and ptr = base + size * i
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* and compare(key, ptr) < 0 then
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* bsearch(key, base, nmemb, size, compare) may return
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* bsearch(key, base, i, size, compare).
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*
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* If 0 <= i < nmemb
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* and ptr = base + size * i
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* and compare(key, ptr) > 0 then
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* bsearch(key, base, nmemb, size, compare) may return
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* bsearch(key, base + size * (i + 1), nemb - (i + 1), size, compare).
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*/
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void* bsearch(const void* key,
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const void* base_ptr,
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size_t nmemb,
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size_t size,
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int (*compare)(const void*, const void*))
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{
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const unsigned char* base = (const unsigned char*) base_ptr;
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while ( nmemb )
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{
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size_t i = nmemb / 2;
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const unsigned char* candidate = base + i * size;
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int rel = compare(key, candidate);
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if ( rel < 0 ) /* key smaller than candidate */
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nmemb = i;
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else if ( 0 < rel ) /* key greater than candidate */
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{
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base = candidate + size;
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nmemb -= i + 1;
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}
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else /* key equal to candidate */
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return (void*) candidate;
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}
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return NULL;
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}
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