func xor64(x uint64) uint64 {
	x ^= x << 13
	x ^= x >> 7
	x ^= x << 17
	return x
}
func xor64(x uint64) uint64 {
	x ^= x << 13
	x ^= x >> 7
	x ^= x << 17
	return x
}
func xor64 ( x uint64 ) uint64 { x ^= x << 13 x ^= x >> 7 x ^= x << 17 return x }
// xor64 generates the next value of a pseudo-random sequence given a current
// state x.
xor64 generates the next value of a pseudo - random sequence given a current state x .