anchor.diff:      use linear_interpolator_mod, only: nearest_index_sorted
       use logging_mod, only: log_output_unit
       use stop_mod, only: generic_stop
  -    use iso_c_binding, only: c_ptr
  +    use iso_c_binding, only: c_ptr, c_null_ptr, c_loc, c_f_pointer
       implicit none
  -
  -    real(dp), parameter :: cx = 2.7_dp, cy = 3.05_dp
  -        !! Parameters for test case
   
       type grid_spacetime_interpolator_type
           !! Interpolation of multi-gridded time-series.
  
positive.code:         time = start_time + 5.0_dp
          call gsi%interpolate(time, tx, ty, tv)
          do k = 1, ng
              if(all(abs(tv(:,k) - k*(time + cx * x0 + cy * y0)) < errtol)) then
                  print*, 'PASS'
              else
                  print*, 'FAIL', abs(tv(:,k) - k*(time + cx * x0 + cy * y0))
              end if
          end do
  
  
negative.code:         time = start_time + 5.0_dp
          call gsi%interpolate(time, tx, ty, tv)
          do k = 1, ng
              if(all(abs(tv(:,k) - k*(time + cxy(1) * tx + cxy(2) * ty)) < errtol)) then
                  print*, 'PASS'
              else
                  print*, 'FAIL', abs(tv(:,k) - k*(time + cxy(1) * tx + cxy(2) * ty))
              end if
          end do
  
  