123 lines
3.2 KiB
C
123 lines
3.2 KiB
C
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/***
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*bsearch.c - do a binary search
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*
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* Copyright (c) Microsoft Corporation. All rights reserved.
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*
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*Purpose:
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* defines bsearch() - do a binary search an an array
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*
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*******************************************************************************/
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#include <cruntime.h>
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#include <stdlib.h>
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#include <search.h>
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#include <internal.h>
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#if defined (_M_CEE)
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#define __fileDECL __clrcall
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#else /* defined (_M_CEE) */
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#define __fileDECL __cdecl
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#endif /* defined (_M_CEE) */
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/***
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*char *bsearch() - do a binary search on an array
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*
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*Purpose:
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* Does a binary search of a sorted array for a key.
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*
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*Entry:
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* const char *key - key to search for
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* const char *base - base of sorted array to search
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* unsigned int num - number of elements in array
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* unsigned int width - number of bytes per element
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* int (*compare)() - pointer to function that compares two array
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* elements, returning neg when #1 < #2, pos when #1 > #2, and
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* 0 when they are equal. Function is passed pointers to two
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* array elements.
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*
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*Exit:
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* if key is found:
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* returns pointer to occurrence of key in array
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* if key is not found:
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* returns NULL
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*
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*Exceptions:
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* Input parameters are validated. Refer to the validation section of the function.
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*
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*******************************************************************************/
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#ifdef __USE_CONTEXT
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#define __COMPARE(context, p1, p2) (*compare)(context, p1, p2)
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#else /* __USE_CONTEXT */
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#define __COMPARE(context, p1, p2) (*compare)(p1, p2)
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#endif /* __USE_CONTEXT */
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#if !defined (_M_CEE)
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_CRTIMP
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#endif /* !defined (_M_CEE) */
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SECURITYSAFECRITICAL_ATTRIBUTE
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#ifdef __USE_CONTEXT
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void * __fileDECL bsearch_s (
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const void *key,
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const void *base,
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size_t num,
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size_t width,
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int (__fileDECL *compare)(void *, const void *, const void *),
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void *context
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)
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#else /* __USE_CONTEXT */
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void * __fileDECL bsearch (
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const void *key,
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const void *base,
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size_t num,
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size_t width,
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int (__fileDECL *compare)(const void *, const void *)
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)
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#endif /* __USE_CONTEXT */
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{
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char *lo = (char *)base;
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char *hi = (char *)base + (num - 1) * width;
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char *mid;
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size_t half;
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int result;
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/* validation section */
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_VALIDATE_RETURN(base != NULL || num == 0, EINVAL, NULL);
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_VALIDATE_RETURN(width > 0, EINVAL, NULL);
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_VALIDATE_RETURN(compare != NULL, EINVAL, NULL);
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/*
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We allow a NULL key here because it breaks some older code and because we do not dereference
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this ourselves so we can't be sure that it's a problem for the comparison function
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*/
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while (lo <= hi)
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{
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if ((half = num / 2) != 0)
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{
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mid = lo + (num & 1 ? half : (half - 1)) * width;
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if (!(result = __COMPARE(context, key, mid)))
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return(mid);
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else if (result < 0)
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{
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hi = mid - width;
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num = num & 1 ? half : half-1;
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}
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else
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{
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lo = mid + width;
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num = half;
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}
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}
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else if (num)
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return (__COMPARE(context, key, lo) ? NULL : lo);
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else
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break;
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}
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return NULL;
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}
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#undef __fileDECL
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#undef __COMPARE
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