func (s *Xor64Source) Seed(seed int64) {
	if seed == 0 {
		seed = seed0
	}
	*s = Xor64Source(seed)
}
func (s *Xor64Source) Seed(seed int64) {
	if seed == 0 {
		seed = seed0
	}
	*s = Xor64Source(seed)
}
// Seed uses the given value to initialize the generator. If this value is 0, a
// pre-defined seed is used instead, since the xorshift algorithm requires at
// least one bit of the internal state to be set.