message: Avoid divisions when the divisor is a power of two.
diff: @@ -183,11 +183,11 @@ void MakeBlockMap(int rows, int cols, int depth, int kernel_rows,
  const int smallc =
  round_down_pot(cols >> num_blocks_of_cols_log2, kernel_cols);
  const int missr =
  - round_up_pot(rows - (smallr << num_blocks_of_rows_log2), kernel_rows) /
  - kernel_rows;
  + round_up_pot(rows - (smallr << num_blocks_of_rows_log2), kernel_rows) >>
  + floor_log2(kernel_rows);
  const int missc =
  - round_up_pot(cols - (smallc << num_blocks_of_cols_log2), kernel_cols) /
  - kernel_cols;
  + round_up_pot(cols - (smallc << num_blocks_of_cols_log2), kernel_cols) >>
  + floor_log2(kernel_cols);
  block_map->dims[Side::kLhs] = rows;
  block_map->dims[Side::kRhs] = cols;
  