CODEWITHSUNDEEP
optimizationparallel-processingfortrangfortranpure-virtual
Charles
Charles

Reputation: 987

Pure Fortran subroutine via dynamic slicing

I recently read (here) that pure subroutines can allow better parallization optimizations. Assuming this is true, is there a way that I can make the following routine pure?

 subroutine diff_stag(operator,dfdh,f,T,dir,pad,gt)
   implicit none
   procedure(stencils_stag) :: operator
   type(realField),intent(inout) :: dfdh
   type(realField),intent(in) :: f
   type(triDiag),intent(in) :: T
   integer,intent(in) :: dir,pad,gt
   integer :: i,j,k
   select case (dir)
   case (1)
   !$OMP PARALLEL DO SHARED(T,f,gt)
   do k=1+pad,f%s(3)-pad; do j=1+pad,f%s(2)-pad
     call operator(dfdh%f(:,j,k),f%f(:,j,k),T,f%s(dir),dfdh%s(dir),gt)
   enddo; enddo
   !$OMP END PARALLEL DO
   case (2)
   !$OMP PARALLEL DO SHARED(T,f,gt)
   do k=1+pad,f%s(3)-pad; do i=1+pad,f%s(1)-pad
     call operator(dfdh%f(i,:,k),f%f(i,:,k),T,f%s(dir),dfdh%s(dir),gt)
   enddo; enddo
   !$OMP END PARALLEL DO
   case (3)
   !$OMP PARALLEL DO SHARED(T,f,gt)
   do j=1+pad,f%s(2)-pad; do i=1+pad,f%s(1)-pad
     call operator(dfdh%f(i,j,:),f%f(i,j,:),T,f%s(dir),dfdh%s(dir),gt)
   enddo; enddo
   !$OMP END PARALLEL DO
   case default
   stop 'Error: dir must = 1,2,3 in delGen_T in ops_del.f90.'
   end select
 end subroutine

The problem, I believe, is that the select case introduces a side effect, which is unallowed.

Is there a way that I can slice the fields f%f(i,j,k) and dfdh%f(i,j,k) so that the select case is not needed?

Any help is greatly appreciated!

Upvotes: 0

Views: 111

Answers (1)

IanH
IanH

Reputation: 21431

The given subroutine cannot be made pure, as it contains a STOP statement.

Beyond that, whether the subroutine could be made pure would depend on whether the operator subroutine was pure (or could be made pure), and perhaps whether the derived types had pointer components.

I don't think "dynamic slicing" is relevant.

Upvotes: 3

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