dp_radix_sort Module Subroutine

   module subroutine dp_radix_sort(array, work, reverse)
      use iso_c_binding, only: c_loc, c_f_pointer
      real(kind=dp), dimension(:), intent(inout), target :: array
      real(kind=dp), dimension(:), intent(inout), target, optional :: work
      logical, intent(in), optional :: reverse
      integer(kind=int_index) :: i, N, pos, rev_pos
      integer(kind=int64), dimension(:), pointer :: arri64
      integer(kind=int64), dimension(:), pointer :: buffer
      real(kind=dp) :: item
      logical :: use_internal_buffer
      N = size(array, kind=int_index)
      if (present(work)) then
         if (size(work, kind=int_index) < N) then
            error stop "sp_radix_sort: work array is too small."
         end if
         use_internal_buffer = .false.
         call c_f_pointer(c_loc(work), buffer, [N])
      else
         use_internal_buffer = .true.
         allocate (buffer(N))
      end if
      call c_f_pointer(c_loc(array), arri64, [N])
      call radix_sort_u64_helper(N, arri64, buffer)
      if (arri64(1) >= 0 .and. arri64(N) < 0) then
         pos = 1
         rev_pos = N
         do while (arri64(rev_pos) < 0)
            buffer(pos) = arri64(rev_pos)
            pos = pos + 1
            rev_pos = rev_pos - 1
         end do
         buffer(pos:N) = arri64(1:rev_pos)
         arri64(:) = buffer(:)
      end if
      if (pic_optional(reverse, .false.)) then
         do i = 1, N/2
            item = array(i)
            array(i) = array(N - i + 1)
            array(N - i + 1) = item
         end do
      end if
      if (use_internal_buffer) then
         deallocate (buffer)
      end if
   end subroutine dp_radix_sort