gf2_matrix_times
square[n] = gf2_matrix_times(mat, mat[n]);
zeros[0][n] = gf2_matrix_times(op, n);
zeros[1][n] = gf2_matrix_times(op, n << 8);
zeros[2][n] = gf2_matrix_times(op, n << 16);
zeros[3][n] = gf2_matrix_times(op, n << 24);