memcmp.c

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/***************************************************************************//**
 @file memcmp.c
 
 @brief Defines the memcmp function
*******************************************************************************/
#include <string.h>
 
/*******************************************************************************
 memcmp
*//**
 @brief Compares the first n characters of s1 and s2
 @param *s1 The first object to be compared
 @param *s2 The second object to be compared
 @param n The number of characters to compare
 
 The memcmp function compares the first n characters of the object pointed to
 by s1 to the first n characters of the object pointed to by s2.
 
 @note The contents of "holes" used as padding for purposes of alignment
 within structure objects are indeterminate. Strings shorter than
 their allocated space and unions may also cause problems in
 comparison.
 
 @note If n is 0 then valid objects are considered equal
 
 @note The returned value will never be greater than UCHAR_MAX and never
 less than CHAR_MIN
 
 @note If the comparison will cause a memory read that wraps then the
 comparison will not take place
 
 @return Integer indicating if s1 is greater than, equal to, or less than s2
 @retval >0 s1 is greater than s2 or no comparison could be made
 @retval 0 s1 is equal to s2
 @retval <0 s1 is less than s2
*******************************************************************************/
int
memcmp(const void *s1, const void *s2, size_t n)
{
 const unsigned char *pStr1 = s1;
 const unsigned char *pStr2 = s2;
 int ret = 0;
 
 if ( !s1 ||
 !s2 ||
 /* Check for wrapping while comparing */
 ((((unsigned long) -1) - ((unsigned long) s1)) < n) ||
 ((((unsigned long) -1) - ((unsigned long) s2)) < n))
 {
 return 1;
 }
 
 while (n-- > 0)
 {
 if (*(pStr1++) - *(pStr2++))
 {
 ret = *(--pStr1) - *(--pStr2);
 break;
 }
 }
 
 return ret;
}