code: func (xxh XXHZero) Sum(b []byte) []byte {
  	h32 := xxh.Sum32()
  	return append(b, byte(h32), byte(h32>>8), byte(h32>>16), byte(h32>>24))
  }
docs: // Sum appends the current hash to b and returns the resulting slice.
  // It does not change the underlying hash state.