Using Coarrays to Parallelize Legacy Fortran Applications: Strategy and Case Study

Listing 8

Optimized collective sum routine.

subroutine vector_co_sum_parallel(vector)

 real(rkind), intent(inout)  :: vector(:)[*]

 real(rkind), allocatable  :: temp(:)

 integer image, step

 allocate (temp, mold = vector)

 step = 2

 do while (step/2 <= num_images())

  sync all

  if (this_image() + step/2 <= num_images()) then

   temp = vector + vector[this_image() + step/2]

  else

   temp = vector

  end if

  sync all

  vector = temp

  step = step * 2

 end do

 sync all

 if (this_image()/ = 1) vector = vector1

 sync all

end subroutine