eulerian_obj_AddUpGhostCells_x Subroutine

    impure subroutine eulerian_obj_AddUpGhostCells_x(this)
      !> Adds up ghostcells in the x direction
      ! with non-blocking mpi directives.
      implicit none
      class(eulerian_obj_base), intent(inout) :: this                          !! An Eulerian object
      ! Work variables
      integer :: Ng(3)
      integer :: sendL(3),sendR(3)
      type(MPI_STATUS)  :: statuses(4)
      type(MPI_REQUEST) :: requests(4)
      integer :: ierr
      real(wp),allocatable :: buffR_r(:,:,:),buffL_r(:,:,:)
      integer, allocatable :: buffR_i(:,:,:),buffL_i(:,:,:)
      integer :: i,j,k,ii,jj,kk

      associate (lo => this%block%lo, hi => this%block%hi,   &
                 ngc=> this%block%ngc, mpi => this%parallel, &
                 gc_slab_r => this%block%gc_slab_r,          &
                 gc_slab_i => this%block%gc_slab_i)

        ! Number of grid points (including ghostcells)
        Ng=hi-lo+1+2*ngc

        ! 2D exceptions
        if (Ng(1)-2*ngc.le.ngc) then
          select type (this)
          type is (eulerian_obj_r)
            do i=1,ngc
              this%cell(hi(1),:,:) = this%cell(hi(1),:,:) + this%cell(hi(1)+i,:,:)
              this%cell(lo(1),:,:) = this%cell(lo(1),:,:) + this%cell(lo(1)-i,:,:)
            end do
          type is (eulerian_obj_i)
            do i=1,ngc
              this%cell(hi(1),:,:) = this%cell(hi(1),:,:) + this%cell(hi(1)+i,:,:)
              this%cell(lo(1),:,:) = this%cell(lo(1),:,:) + this%cell(lo(1)-i,:,:)
            end do
          end select

          return
        end if

        ! Address of first element in buffer
        sendL(1)=lo(1)-ngc  ; sendL(2)=lo(2)-ngc  ; sendL(3)=lo(3)-ngc
        sendR(1)=hi(1)+1    ; sendR(2)=lo(2)-ngc  ; sendR(3)=lo(3)-ngc

        select type (this)
        type is (eulerian_obj_r)
          ! Allocate receive buffers
          allocate(buffR_r(ngc,Ng(2),Ng(3)))
          allocate(buffL_r(ngc,Ng(2),Ng(3)))

          ! Post receives from Left and right ranks
          call MPI_IRECV( buffL_r(1,1,1), ngc*Ng(2)*Ng(3), mpi%REAL_WP, &
            mpi%rank%L(1)-1, 0, mpi%comm%g, requests(1), ierr)
          call MPI_IRECV( buffR_r(1,1,1), ngc*Ng(2)*Ng(3), mpi%REAL_WP, &
            mpi%rank%R(1)-1, 0, mpi%comm%g, requests(2), ierr)
          ! Send buffers to left and right ranks
          call MPI_ISEND( this%cell(sendR(1),sendR(2),sendR(3)), 1, gc_slab_r(1), &
            mpi%rank%R(1)-1, 0, mpi%comm%g, requests(4), ierr)
          call MPI_ISEND( this%cell(sendL(1),sendL(2),sendL(3)), 1, gc_slab_r(1), &
            mpi%rank%L(1)-1, 0, mpi%comm%g, requests(3), ierr)
        type is (eulerian_obj_i)
          ! Allocate receive buffers
          allocate(buffR_i(ngc,Ng(2),Ng(3)))
          allocate(buffL_i(ngc,Ng(2),Ng(3)))
          ! Post receives from Left and right ranks
          call MPI_IRECV( buffL_i(1,1,1), ngc*Ng(2)*Ng(3), mpi%INTEGER, &
            mpi%rank%L(1)-1, 0, mpi%comm%g, requests(1), ierr)
          call MPI_IRECV( buffR_i(1,1,1), ngc*Ng(2)*Ng(3), mpi%INTEGER, &
            mpi%rank%R(1)-1, 0, mpi%comm%g, requests(2), ierr)
          ! Send buffers to left and right ranks
          call MPI_ISEND( this%cell(sendR(1),sendR(2),sendR(3)), 1, gc_slab_i(1), &
            mpi%rank%R(1)-1, 0, mpi%comm%g, requests(4), ierr)
          call MPI_ISEND( this%cell(sendL(1),sendL(2),sendL(3)), 1, gc_slab_i(1), &
            mpi%rank%L(1)-1, 0, mpi%comm%g, requests(3), ierr)
        end select

        ! Synchronize
        call MPI_WAITALL( 4, requests, statuses, ierr )

        select type(this)
        type is (eulerian_obj_r)
          ! Add left buffer to left ghostcells
          if (mpi%rank%L(1)-1.ne.MPI_PROC_NULL) then
            do k=lo(3)-ngc,hi(3)+ngc
              do j=lo(2)-ngc,hi(2)+ngc
                do i=lo(1),lo(1)+ngc-1
                  ii=i-(lo(1)      )+1
                  jj=j-(lo(2)-ngc  )+1
                  kk=k-(lo(3)-ngc  )+1
                  this%cell(i,j,k)=this%cell(i,j,k) + buffL_r(ii,jj,kk)
                end do
              end do
            end do
          end if
          ! Add right buffer to right ghostcells
          if (mpi%rank%R(1)-1.ne.MPI_PROC_NULL) then
            do k=lo(3)-ngc,hi(3)+ngc
              do j=lo(2)-ngc,hi(2)+ngc
                do i=hi(1)-ngc+1,hi(1)
                  ii=i-(hi(1)-ngc+1)+1
                  jj=j-(lo(2)-ngc  )+1
                  kk=k-(lo(3)-ngc  )+1
                  this%cell(i,j,k)=this%cell(i,j,k) + buffR_r(ii,jj,kk)
                end do
              end do
            end do
          end if
          deallocate(buffL_r,buffR_r)
        type is (eulerian_obj_i)
          ! Add left buffer to left ghostcells
          if (mpi%rank%L(1)-1.ne.MPI_PROC_NULL) then
            do k=lo(3)-ngc,hi(3)+ngc
              do j=lo(2)-ngc,hi(2)+ngc
                do i=lo(1),lo(1)+ngc-1
                  ii=i-(lo(1)      )+1
                  jj=j-(lo(2)-ngc  )+1
                  kk=k-(lo(3)-ngc  )+1
                  this%cell(i,j,k)=this%cell(i,j,k) + buffL_i(ii,jj,kk)
                end do
              end do
            end do
          end if
          ! Add right buffer to right ghostcells
          if (mpi%rank%R(1)-1.ne.MPI_PROC_NULL) then
            do k=lo(3)-ngc,hi(3)+ngc
              do j=lo(2)-ngc,hi(2)+ngc
                do i=hi(1)-ngc+1,hi(1)
                  ii=i-(hi(1)-ngc+1)+1
                  jj=j-(lo(2)-ngc  )+1
                  kk=k-(lo(3)-ngc  )+1
                  this%cell(i,j,k)=this%cell(i,j,k) + buffR_i(ii,jj,kk)
                end do
              end do
            end do
          end if
          deallocate(buffL_i,buffR_i)
        end select

      end associate

      return
    end subroutine eulerian_obj_AddUpGhostCells_x