Implement cell instance filter

include/openmc/tallies/filter_cell_instance.h

@@ -0,0 +1,92 @@
+#ifndef OPENMC_TALLIES_FILTER_CELL_INSTANCE_H
+#define OPENMC_TALLIES_FILTER_CELL_INSTANCE_H
+
+#include <cstdint>
+#include <functional> // for hash
+#include <unordered_map>
+#include <vector>
+
+#include <gsl/gsl>
+
+#include "openmc/tallies/filter.h"
+
+//==============================================================================
+//! Define an instance of a particular cell
+//==============================================================================
+
+namespace openmc {
+struct CellInstance {
+  //! Check for equality
+  bool operator==(const CellInstance& other) const
+  { return index_cell == other.index_cell && instance == other.instance; }
+
+  gsl::index index_cell;
+  gsl::index instance;
+};
+} // namespace openmc
+
+namespace std {
+template<>
+struct hash<openmc::CellInstance> {
+  // Taken from https://stackoverflow.com/a/17017281
+  std::size_t operator()(const openmc::CellInstance& k) const
+  {
+    std::size_t res = 17;
+    res = 31 * res + std::hash<gsl::index>()(k.index_cell);
+    res = 31 * res + std::hash<gsl::index>()(k.instance);
+    return res;
+  }
+};
+} // namespace std
+
+
+namespace openmc {
+
+//==============================================================================
+//! Specifies cell instances that tally events reside in.
+//==============================================================================
+
+class CellInstanceFilter : public Filter {
+public:
+  //----------------------------------------------------------------------------
+  // Constructors, destructors
+
+  //CellInstanceFilter() = default;
+  //CellInstanceFilter(gsl::span<CellInstance> instances);
+  ~CellInstanceFilter() = default;
+
+  //----------------------------------------------------------------------------
+  // Methods
+
+  std::string type() const override {return "cellinstance";}
+
+  void from_xml(pugi::xml_node node) override;
+
+  void get_all_bins(const Particle* p, int estimator, FilterMatch& match)
+  const override;
+
+  void to_statepoint(hid_t filter_group) const override;
+
+  std::string text_label(int bin) const override;
+
+  //----------------------------------------------------------------------------
+  // Accessors
+
+  const std::vector<CellInstance>& cell_instances() const { return cell_instances_; }
+
+  void set_cell_instances(gsl::span<CellInstance> instances);
+
+private:
+  //----------------------------------------------------------------------------
+  // Data members
+
+  //! The indices of the cells binned by this filter.
+  std::vector<CellInstance> cell_instances_;
+
+  //! A map from cell/instance indices to filter bin indices.
+  std::unordered_map<CellInstance, gsl::index> map_;
+};
+
+} // namespace openmc
+
+#endif // OPENMC_TALLIES_FILTER_CELL_INSTANCE_H