//blocks
  for (k = 0; k < grid_size; k++)
    {
      //fill in subgrid with block k
      for (i = block_size * (k/block_size); i < block_size * (k/block_size)
         + block_size; i++)
    {
      for (j =  block_size * (k % block_size); j < block_size * (k % block_size)
         + block_size; j++)
        {
          subgrid[(i%block_size)*block_size + j%block_size] = &grid[i][j];
        }
    }


      return_value = func(subgrid) && return_value;
    }