快速幂模板

int f(int a, int b) {
    int ans = 1;
    int base = a;
    while (b)
    {
        if (b & 1)ans = base * ans;
        base = base * base;
        b >>= 1;
    }
    return ans;
}

取余版本：

int f(int a, int b, int c) {
    int ans = 1;
    int base = a % c;
    while (b)
    {
        if (b & 1)ans = (base * ans) % c;
        base = (base * base) % c;
        b >>= 1;
    }
    return ans;
}