关于<和>

 __kernel void DotProduct (__global float* a, __global float* b, __global float* c, int iNumElements){    // find position in global arrays    int iGID = get_global_id(0);    // bound check (equivalent to the limit on a 'for' loop for standard/serial C code    if (iGID >= iNumElements)    {           return;     }    // process /*  int iInOffset = iGID << 2;    c[iGID] = a[iInOffset] * b[iInOffset]                + a[iInOffset + 1] * b[iInOffset + 1]               + a[iInOffset + 2] * b[iInOffset + 2]               + a[iInOffset + 3] * b[iInOffset + 3];*/    int iInOffset = iGID * 4;    c[iGID] = a[iInOffset] * b[iInOffset]                + a[iInOffset + 1] * b[iInOffset + 1]               + a[iInOffset + 2] * b[iInOffset + 2]               + a[iInOffset + 3] * b[iInOffset + 3];}

<<2  向左移2位，就是乘4.

>>除4.。。。。。