The new functions of U64x4 and U64x8 are not consistent:

This is U64x4 .

     pub fn new(x0: u64, x1: u64, x2: u64, x3: u64) -> Self {
         Self {
             value: [x0, x1, x2, x3],
         }
     }

     pub fn from_u32(x: [u32; 8]) -> Self {
         Self {
             value: [
                 (u64::from(x[1]) << 32) + u64::from(x[0]),
                 (u64::