Function checksum 

pub fn checksum<T>(data: &[u8]) -> T
where
    T: Default + From<u8> + Copy,
    Wrapping<T>: Add<Output = Wrapping<T>>,

Type agonostic wrapping checksum function. We typically only use the u32 version, as u16 and u8 values are the same, with the top bytes masked off.