快速幂代码实现

qmi(int a , int b , int mod) // 求 a ^ b % mod;
{
    int res = 1;
    while(b)
    {
        if(b & 1)
        {
            res = (long long)res * a % mod;
        }
        b >>= 1;
        a = (long long)a * a % mod;
    }
    return res;
}