func alike(a, b float64) bool {
	switch {
	case IsNaN(a) && IsNaN(b):
		return true
	case a == b:
		return Signbit(a) == Signbit(b)
	}
	return false
}

func TestNaN(t *testing.T) {
	f64 := NaN()
	if f64 == f64 {
		t.Fatalf("NaN() returns %g, expected NaN", f64)
	}
	f32 := float32(f64)
	if f32 == f32 {
		t.Fatalf("float32(NaN()) is %g, expected NaN", f32)
	}