Function gcd

test/unittest/modint_test.cpp:10–13

using ll = long long;

ll gcd(ll a, ll b) {
    if (b == 0) return a;
    return gcd(b, a % b);
}

static_assert(internal::is_modint<static_modint<1>>::value, "");
static_assert(internal::is_modint<static_modint<998244353>>::value, "");