memmove.c

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 Copyright (c) 2017 Walt Elam
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/***************************************************************************//**
 @file memmove.c
 
 @brief Defines the memmove function
*******************************************************************************/
#include <string.h>
 
/*******************************************************************************
 memmove
*//**
 @brief Copies n characters from s2 into s1
 @param *s1 The destination location to which to copy characters
 @param *s2 The source location from which to copy characters
 @param n The number of characters to copy
 
 The memmove function copies n characters from the object pointed to by s2
 into the object pointed to by s1. Copying takes place as if the n characters
 from the object pointed to by s2 are first copied into a temporary array of
 n characters that does not overlap the objects pointed to by s1 and s2, and
 then the n characters from the temporary array are copied into the object
 pointed to by s1.
 
 @warn If copying is attempted such that a memory read/write will wrap, the
 copy will not take place.
 
 @return The value of s1
*******************************************************************************/
void *
memmove(void *s1, const void *s2, size_t n)
{
 char *pDst = s1;
 const char *pSrc = s2;
 
 if ( !s1 ||
 !s2 ||
 /* Check for wrapping while copying */
 ((((unsigned long) -1) - ((unsigned long) s1)) < n) ||
 ((((unsigned long) -1) - ((unsigned long) s2)) < n))
 {
 return s1;
 }
 
 /* Copy forward or backward to handle object overlap */
 if (pDst < pSrc)
 {
 while (0 < n--)
 {
 *(pDst++) = *(pSrc++);
 }
 }
 else
 {
 pDst += n;
 pSrc += n;
 
 while (0 < n--)
 {
 *(--pDst) = *(--pSrc);
 }
 }
 
 return s1;
}