deliberately overlapping memcpy implementation
@param dst destination buffer
@param back how many bytes back we start (the initial size of the overlapping window), must be > 0
@param cnt number of bytes to copy, must be >= 0
cnt > back is valid, this will copy the bytes we just copied,
thus creating a repeating pattern with a period length of back.
deliberately overlapping memcpy implementation @param dst destination buffer @param back how many bytes back we start (the initial size of the overlapping window), must be > 0 @param cnt number of bytes to copy, must be >= 0
cnt > back is valid, this will copy the bytes we just copied, thus creating a repeating pattern with a period length of back.