__kernel void
twice(__constant int *data_count,
      __global int *input_data)
      //      __global int *output_data)
{
    long count = (long)data_count[0];
    for (int i = 0; i<count; i++) {
        // output_data[i] = 2*input_data[i];
        input_data[i] *= 2;
    }

}