Fixed a bug in distribcell offsets logic (#3424)

include/openmc/cell.h

@@ -226,6 +226,8 @@ public:
   void set_temperature(
     double T, int32_t instance = -1, bool set_contained = false);
 
+  int32_t n_instances() const;
+
   //! Set the rotation matrix of a cell instance
   //! \param[in] rot The rotation matrix of length 3 or 9
   void set_rotation(const vector<double>& rot);
@@ -312,12 +314,11 @@ public:
   //----------------------------------------------------------------------------
   // Data members
 
-  int32_t id_;              //!< Unique ID
-  std::string name_;        //!< User-defined name
-  Fill type_;               //!< Material, universe, or lattice
-  int32_t universe_;        //!< Universe # this cell is in
-  int32_t fill_;            //!< Universe # filling this cell
-  int32_t n_instances_ {0}; //!< Number of instances of this cell
+  int32_t id_;       //!< Unique ID
+  std::string name_; //!< User-defined name
+  Fill type_;        //!< Material, universe, or lattice
+  int32_t universe_; //!< Universe # this cell is in
+  int32_t fill_;     //!< Universe # filling this cell
 
   //! \brief Index corresponding to this cell in distribcell arrays
   int distribcell_index_ {C_NONE};

include/openmc/geometry_aux.h

@@ -15,8 +15,6 @@
 namespace openmc {
 
 namespace model {
-extern std::unordered_map<int32_t, std::unordered_map<int32_t, int32_t>>
-  universe_cell_counts;
 extern std::unordered_map<int32_t, int32_t> universe_level_counts;
 } // namespace model
 
@@ -80,15 +78,13 @@ void prepare_distribcell(
   const std::vector<int32_t>* user_distribcells = nullptr);
 
 //==============================================================================
-//! Recursively search through the geometry and count cell instances.
+//! Recursively search through the geometry and count universe instances.
 //!
-//! This function will update the Cell::n_instances value for each cell in the
-//! geometry.
-//! \param univ_indx The index of the universe to begin searching from (probably
-//!   the root universe).
+//! This function will update Universe.n_instances_ for each
+//! universe in the geometry.
 //==============================================================================
 
-void count_cell_instances(int32_t univ_indx);
+void count_universe_instances();
 
 //==============================================================================
 //! Recursively search through universes and count universe instances.

include/openmc/lattice.h

@@ -76,7 +76,7 @@ public:
   }
 
   //! Populate the distribcell offset tables.
-  int32_t fill_offset_table(int32_t offset, int32_t target_univ_id, int map,
+  int32_t fill_offset_table(int32_t target_univ_id, int map,
     std::unordered_map<int32_t, int32_t>& univ_count_memo);
 
   //! \brief Check lattice indices.

include/openmc/universe.h

@@ -29,6 +29,7 @@ class Universe {
 public:
   int32_t id_;            //!< Unique ID
   vector<int32_t> cells_; //!< Cells within this universe
+  int32_t n_instances_;   //!< Number of instances of this universe
 
   //! \brief Write universe information to an HDF5 group.
   //! \param group_id An HDF5 group id.