注意：在c++类中使用循环时，需要确保循环变量索引不要是该类的数据成员，
如果循环变量索引是该类的数据成员，会导致循环被自动unroll展开。

一、类成员变量作为for循环索引，for循环被展开案例
template <typename T0, typename T1, typename T2, typename T3, int N>
class foo_class {
private:
pe_mac<T0, T1, T2> mac;
public:
T0 areg;
T0 breg;
T2 mreg;
T1 preg;
T0 shift[N];
int k; // Class Member
T0 shift_output;
void exec(T1 *pcout, T0 *dataOut, T1 pcin, T3 coeff, T0 data, int col)
{
Function_label0:;
#pragma HLS inline off
SRL:for (k = N-1; k >= 0; --k) {
#pragma HLS unroll // Loop will fail UNROLL
if (k > 0)
shift[k] = shift[k-1];
else
shift[k] = data;
}
*dataOut = shift_output;
shift_output = shift[N-1];
}
*pcout = mac.exec1(shift[4*col], coeff, pcin);
};

二、代码修正
上述代码将不会按照vivado hls的指令进行响应，所以，应该重新写该代码，修改方式是
从类中将索引变量k移除，将k放在函数中，成为局部变量。
template <typename T0, typename T1, typename T2, typename T3, int N>
class foo_class {
private:
pe_mac<T0, T1, T2> mac;
public:
T0 areg;
T0 breg;
T2 mreg;
T1 preg;
T0 shift[N];
T0 shift_output;
void exec(T1 *pcout, T0 *dataOut, T1 pcin, T3 coeff, T0 data, int col)
{
Function_label0:;
int k; // Local variable
#pragma HLS inline off
SRL:for (k = N-1; k >= 0; --k) {
#pragma HLS unroll // Loop will unroll
if (k > 0)
shift[k] = shift[k-1];
else
shift[k] = data;
}
*dataOut = shift_output;
shift_output = shift[N-1];
}
*pcout = mac.exec1(shift[4*col], coeff, pcin);
};