为何计算数组移动L2范数的代码运行时间差异近5倍？

我实现了一段计算两个数组移动L2范数的C++代码：

func_lstl2(const int &nx, const float x[],const int &ny, const float y[], int &shift, double &lstl2)
{    

    int maxshift = 200;
    int len_z = maxshift * 2;
    int len_work = len_z + ny;
    //initialize array work and array z
    double *z = new double[len_z]; float *work = new float[len_work];
    for (int i = 0; i < len_z; i++)
        z[i] = 0;
    for (int i = 0; i < len_work; i++)
        work[i] = 0;
    for (int i = 0; i < ny; i++)
        work[i + maxshift] = y[i];
    // do moving least square residue calculation
    float temp;
    for (int i = 0; i < len_z; i++)
    {
        for (int j = 0; j < nx; j++)
        {
            temp = x[j] - work[i + j];
            z[i] += temp * temp;
        }
    }
    // find the best fit value
    lstl2 = 1E30;
    shift = 0;
    for (int i = 0; i < len_z; i++)
    {
        if (z[i] < lstl2)
        {
            lstl2 = z[i];
            shift = i - maxshift;
        }
    }

    //end of program
    delete[] z;
    delete[] work;
}

我测试了两组长度均为2000的数组，调用代码如下：

int shift; double lstl2;
func_lstl2(2000,z1,2000,z2,shift,lstl2) ;
func_lstl2(2000,x1,2000,x2,shift,lstl2) ;

奇怪的是，处理z数组耗时0.0032346秒，处理x数组却耗时0.0140903秒，运行时间差了近5倍。我找不到问题所在，恳请帮忙排查。相关数组文件已提供。

内容的提问来源于stack exchange，提问作者YS_Jin