代码

// what is matter? never mind.
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#define idx(i, j) ((i) * n + (j))
void matrix_multiply(int n, const double *A, const double *B, double *C) {
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			for (int k = 0; k < n; k++) {
				C[idx(i, k)] += A[idx(i, j)] * B[idx(j, k)];
			}
		}
	}
}

评测结果