def cDiff():
    """
    Return the kernel source of cDiff.
    """
    R = """
        KERNEL void cDiff(  GLOBAL_MEM    const    int            *order2,
                                               GLOBAL_MEM     const   float2     *indata,
                                               GLOBAL_MEM                  float2     *outdata)
        {
        const unsigned int gid =  get_global_id(0); 
        const unsigned int ind = order2[gid];
        outdata[gid]=indata[ind]- indata[gid];
        };
        """
    return R
