cube_t__equal Function

   pure function cube_t__equal(a, b) result(ret)
      use :: forgex_segment_m, only: segment_t, merge_segments, sort_segment_by_min
      implicit none
      type(cube_t), intent(in) :: a, b

      type(segment_t), allocatable :: a_sps(:), b_sps(:)
      logical :: ret, candi

      integer :: i

      ret = .false.

      if (a%is_switched_to_bmp .neqv. b%is_switched_to_bmp) return
      if (.not. all(a%ascii%a(:) == b%ascii%a(:))) return

      if (allocated(a%bmp) .and. allocated(b%bmp)) then
         if (any(a%bmp%b(:) /= b%bmp%b(:))) return
      end if


      if (allocated(a%sps) .and. allocated(b%sps)) then
         a_sps = a%sps
         b_sps = b%sps
         call sort_segment_by_min(a_sps)
         call merge_segments(a_sps)
         call sort_segment_by_min(b_sps)
         call merge_segments(b_sps)

         if (size(a_sps, dim=1) == size(b_sps, dim=1)) then
            candi = .true. 
            do i = 1, size(a_sps, dim=1)
               candi = candi .and. a_sps(i) == b_sps(i)
            end do
            ret = candi
            return

         end if
      end if

      ret = .true.

   end function cube_t__equal