code: func Intn(n int) int {
  	if n <= 0 {
  		panic("fastrand: argument to Intn is <= 0: " + strconv.Itoa(n))
  	}
  	// NOTE: since n is at most math.MaxUint64/2, max is minimized when:
  	//    n = math.MaxUint64/4 + 1 -> max = math.MaxUint64 - math.MaxUint64/4
  	// This gives an expected 1.333 tries before choosing a value < max.
  	return int(Uint64n(uint64(n)))
  }
docs: // Intn returns a uniform random int in [0,n). It panics if n <= 0.