140 lines
6.3 KiB
C
140 lines
6.3 KiB
C
/****************************************************************************
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* libs/libc/stdlib/lib_bsearch.c
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*
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* Copyright (c) 1990, 1993
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* The Regents of the University of California. 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. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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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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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <stdlib.h>
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#include <assert.h>
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: bsearch
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*
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* Description:
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* The bsearch() function will search an array of nel objects, the initial
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* element of which is pointed to by 'base', for an element that matches
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* the object pointed to by 'key'. The size of each element in the array
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* is specified by 'width'. If the nel argument has the value zero, the
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* comparison function pointed to by 'compar' will not be called and no
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* match will be found.
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*
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* The comparison function pointed to by 'compar' will be called with two
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* arguments that point to the 'key' object and to an array element, in
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* that order.
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*
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* The application will ensure that the comparison function pointed to by
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* 'compar 'does not alter the contents of the array. The implementation
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* may reorder elements of the array between calls to the comparison
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* function, but will not alter the contents of any individual element.
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*
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* The implementation will ensure that the first argument is always a
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* pointer to the 'key'.
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*
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* When the same objects (consisting of width bytes, irrespective of their
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* current positions in the array) are passed more than once to the
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* comparison function, the results will be consistent with one another.
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* That is, the same object will always compare the same way with the key.
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*
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* The application will ensure that the function returns an integer less
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* than, equal to, or greater than 0 if the key object is considered,
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* respectively, to be less than, to match, or to be greater than the
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* array element. The application will ensure that the array consists of
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* all the elements that compare less than, all the elements that compare
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* equal to, and all the elements that compare greater than the key
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* object, in that order.
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*
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* (Based on description from OpenGroup.org).
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*
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* Returned Value:
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* The bsearch() function will return a pointer to a matching member of
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* the array, or a null pointer if no match is found. If two or more
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* members compare equal, which member is returned is unspecified.
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*
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* Notes from the NetBSD version:
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* The code below is a bit sneaky. After a comparison fails, we divide
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* the work in half by moving either left or right. If 'lim' is odd,
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* moving left simply involves halving 'lim': e.g., when 'lim' is 5 we
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* look at item 2, so we change 'lim' to 2 so that we will look at items
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* 0 & 1. If 'lim' is even, the same applies. If 'lim' is odd, moving
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* right again involes halving 'lim', this time moving the base up one
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* item past 'middle': e.g., when 'lim' is 5 we change base to item 3 and
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* make 'lim' 2 so that we will look at items 3 and 4. If 'lim' is
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* even, however, we have to shrink it by one before halving: e.g.,
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* when 'lim' is 4, we still looked at item 2, so we have to make 'lim'
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* 3, then halve, obtaining 1, so that we will only look at item 3.
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*
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****************************************************************************/
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FAR void *bsearch(FAR const void *key, FAR const void *base, size_t nel,
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size_t width, CODE int (*compar)(FAR const void *,
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FAR const void *))
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{
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FAR const void *middle; /* Current entry being tested */
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FAR const char *lower; /* The lower limit of the search region */
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size_t lim; /* The number of elements in the region */
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int cmp; /* Boolean comparison result */
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DEBUGASSERT(key != NULL);
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DEBUGASSERT(base != NULL || nel == 0);
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DEBUGASSERT(compar != NULL);
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for (lim = nel, lower = (const char *)base; lim != 0; lim >>= 1)
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{
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middle = lower + (lim >> 1) * width;
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cmp = (*compar)(key, middle);
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if (cmp == 0)
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{
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return (FAR void *)middle;
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}
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if (cmp > 0)
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{
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/* key > middle: move right (else move left) */
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lower = (FAR const char *)middle + width;
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lim--;
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}
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}
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return NULL;
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}
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