r = addMul64(r, a, b)
	r = addMul64(r, a, b)
	r = addMul64(r, a, b)
	if r.lo != 16888498990613035 || r.hi != 640 {
		t.Errorf("wrong answer: %d + %d*(2**64)", r.lo, r.hi)
	}
}

func TestSetBytesRoundTrip(t *testing.T) {
	f1 := func(in [32]byte, fe Element) bool {
		fe.SetBytes(in[:])

		// Mask the most significant bit as it's ignored by SetBytes. (Now