cube__invert Subroutine

   pure subroutine cube__invert(self)
      implicit none
      class(cube_t), intent(inout) :: self
      integer :: i
      integer(int64) :: mask

      if (.not. self%is_switched_to_bmp) then
         call self%switch_bmp()
      end if

      mask = not(shiftl(1_int64, 32) -1)
      self%bmp%b(0) = iand(not(self%bmp%b(0)), mask)

      do concurrent (i = 1:BMP_SIZE-1)
         self%bmp%b(i) = not(self%bmp%b(i))
      end do

      if (.not. allocated(self%sps)) then
         self%sps = [segment_t(BMP_SIZE_BIT, UTF8_CODE_MAX)]
      else
         call invert_segment_list(self%sps)
      end if

      self%single_flag = self%num() == 1
   end subroutine cube__invert