92 lines
2.4 KiB
C
92 lines
2.4 KiB
C
/*
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* bsearch.c
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* Original Author: G. Haley
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* Rewritten by: G. Noer
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*
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* Searches an array of nmemb members, the initial member of which is pointed
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* to by base, for a member that matches the object pointed to by key. The
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* contents of the array shall be in ascending order according to a comparison
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* function pointed to by compar. The function shall return an integer less
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* than, equal to or greater than zero if the first argument is considered to be
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* respectively less than, equal to or greater than the second. Returns a
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* pointer to the matching member of the array, or a null pointer if no match
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* is found.
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*/
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/*
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FUNCTION
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<<bsearch>>---binary search
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INDEX
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bsearch
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SYNOPSIS
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#include <stdlib.h>
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void *bsearch(const void *<[key]>, const void *<[base]>,
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size_t <[nmemb]>, size_t <[size]>,
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int (*<[compar]>)(const void *, const void *));
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DESCRIPTION
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<<bsearch>> searches an array beginning at <[base]> for any element
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that matches <[key]>, using binary search. <[nmemb]> is the element
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count of the array; <[size]> is the size of each element.
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The array must be sorted in ascending order with respect to the
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comparison function <[compar]> (which you supply as the last argument of
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<<bsearch>>).
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You must define the comparison function <<(*<[compar]>)>> to have two
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arguments; its result must be negative if the first argument is
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less than the second, zero if the two arguments match, and
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positive if the first argument is greater than the second (where
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``less than'' and ``greater than'' refer to whatever arbitrary
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ordering is appropriate).
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RETURNS
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Returns a pointer to an element of <[array]> that matches <[key]>. If
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more than one matching element is available, the result may point to
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any of them.
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PORTABILITY
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<<bsearch>> is ANSI.
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No supporting OS subroutines are required.
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*/
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#include <stdlib.h>
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void *
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bsearch (const void *key,
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const void *base,
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size_t nmemb,
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size_t size,
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int (*compar) (const void *, const void *))
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{
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void *current;
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size_t lower = 0;
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size_t upper = nmemb;
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size_t index;
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int result;
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if (nmemb == 0 || size == 0)
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return NULL;
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while (lower < upper)
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{
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index = (lower + upper) / 2;
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current = (void *) (((char *) base) + (index * size));
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result = compar (key, current);
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if (result < 0)
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upper = index;
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else if (result > 0)
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lower = index + 1;
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else
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return current;
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}
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return NULL;
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}
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