Macro impl_backends 

macro_rules! impl_backends {
    (
        enc_name = $enc_name:ident,
        dec_name = $dec_name:ident,
        key_size = $key_size:ty,
        keys_ty = $keys_ty:ty,
        par_size = $par_size:ty,
        expand_keys = $expand_keys:expr,
        inv_keys = $inv_keys:expr,
        encrypt = $encrypt:expr,
        encrypt_par = $encrypt_par:expr,
        decrypt = $decrypt:expr,
        decrypt_par = $decrypt_par:expr,
) => { ... };
}