func (z *Int) Rsh(x *Int, s uint) *Int {
	x.doinit()
	z.doinit()
	C._mpz_div_2exp(&z.i[0], &x.i[0], C.ulong(s))
	return z
}

// Exp sets z = x^y % m and returns z.
// If m == nil, Exp sets z = x^y.
func (z *Int) Exp(x, y, m *Int) *Int {
	m.doinit()
	x.doinit()
	y.doinit()
	z.doinit()
	if m == nil {
		C.mpz_pow_ui(&z.i[0], &x.i[0], C.mpz_get_ui(&y.i[0]))
	} else {