rt，求问矩阵快速幂如何减小常数？以下面这份代码为例：

typedef long long ll;
class Matrix {
public:
    std::vector<std::vector<ll>> data;
    int n;
	Matrix() : n(0) { data.clear(); }
    Matrix(int z) : n(z) { data.resize(n, std::vector<ll>(n, 0)); }
    ll& at(int row, int col) {
		return data[row - 1][col - 1];
	}
    ll& _at(int row, int col) { return data[row][col]; }
    Matrix operator*(Matrix& B) const {
	    Matrix C(n);
	    for (int i = 0; i < n; ++i)
		    for (int j = 0; j < n; ++j)
			    for (int k = 0; k < n; ++k)
				    C._at(i, j) = (C._at(i, j) + (data[i][k] * B._at(k, j)) % mod) % mod;
	    return C;
	}
    void print() const {
	    for (const auto& row : data) {
		    for (const auto& elem : row) {
			    std::cout << elem << " ";
			}
		    std::cout << std::endl;
		}
	}
} in, op, op2;
Matrix power(Matrix z, ll exp) {
    Matrix ret(z.n), base = z;
    for (int i = 0; i < z.n; ++i)
	    ret._at(i, i) = 1;
    for (; exp; exp >>= 1)
		(exp & 1) && (ret = ret * base, 0),
	    base = base * base;
    return ret;
}