x := a - q
	// If x underflowed, then x >= 2¹⁶ - q > 2¹⁵, so the top bit is set.
	x += (x >> 15) * q
	return fieldElement(x)
}

func fieldAdd(a, b fieldElement) fieldElement {
	x := uint16(a + b)
	return fieldReduceOnce(x)
}

func fieldSub(a, b fieldElement) fieldElement {
	x := uint16(a - b + q)
	return fieldReduceOnce(x)
}

const (

	}
}

func TestFieldSub(t *testing.T) {
	for a := fieldElement(0); a < q; a++ {
		for b := fieldElement(0); b < q; b++ {
			got := fieldSub(a, b)
			exp := (a - b + q) % q
			if got != exp {
				t.Fatalf("%d - %d = %d, expected %d", a, b, got, exp)
			}
		}
	}
}

func TestFieldMul(t *testing.T) {
	for a := fieldElement(0); a < q; a++ {
		for b := fieldElement(0); b < q; b++ {
			got := fieldMul(a, b)