out := new(Nat)
	out.Mod(x, m)
	expected := natFromBytes([]byte{0x04, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x09})
	if out.Equal(expected) != 1 {
		t.Errorf("%+v != %+v", out, expected)
	}
}

func TestModSub(t *testing.T) {
	m := modulusFromBytes([]byte{13})
	x := &Nat{[]uint{6}}
	y := &Nat{[]uint{7}}
	x.Sub(y, m)
	expected := &Nat{[]uint{12}}
	if x.Equal(expected) != 1 {
		t.Errorf("%+v != %+v", x, expected)