input:
  CCTK_INT input_array_time_levels[N_input_arrays];

"internal" (?):
  CCTK_POINTER per_point_status;
        pointing to CCTK_INT[N_interp_points]
  CCTK_INT     error_point_status;
        minus number of points with non-zero per_point_status

output:
  CCTK_INT local_interpolator_status;