Function fill_via_chunks 

pub(crate) fn fill_via_chunks<T: Observable>(
    src: &[T],
    dest: &mut [u8],
) -> (usize, usize)

Fill dest from src

Returns (n, byte_len). src[..n] is consumed, dest[..byte_len] is filled. src[n..] and dest[byte_len..] are left unaltered.