From 64e93c930c1fe45f6784f7a09edf5fc0eb499ace Mon Sep 17 00:00:00 2001
From: Patrick Shriwise <pshriwise@gmail.com>
Date: Wed, 18 Aug 2021 08:52:10 -0500
Subject: [PATCH] Moving the compute_instance method to the ParentCellStack and
 adding some documentation there.

---
 include/openmc/cell.h | 26 +++++++++++++++++---------
 src/cell.cpp          | 12 +++++++-----
 2 files changed, 24 insertions(+), 14 deletions(-)

diff --git a/include/openmc/cell.h b/include/openmc/cell.h
index 0e3e4b5df..6cce58f7a 100644
--- a/include/openmc/cell.h
+++ b/include/openmc/cell.h
@@ -321,27 +321,42 @@ struct ParentCell {
   gsl::index lattice_index;
 };
 
+struct ParentCellHash {
+  std::size_t operator()(const ParentCell& p) const
+  {
+    return 4096*p.cell_index + p.lattice_index;
+  }
+};
+
 struct ParentCellStack {
 
+  //! push method that adds to the parent_cells visited cells for this search universe
   void push(int32_t search_universe, const ParentCell& pc) {
     parent_cells_.push_back(pc);
     // add parent cell to the set of cells we've visited for this search universe
     visited_cells_[search_universe].insert(pc);
   }
 
+  //! removes the last parent_cell and clears the visited cells for the popped cell's universe
   void pop() {
     visited_cells_[this->current_univ()].clear();
     parent_cells_.pop_back();
   }
 
-  bool visited(int32_t univ_idx, const ParentCell& parent_cell) {
-    return visited_cells_[univ_idx].count(parent_cell) != 0;
+  //! checks whether or not the parent cell has been visited already for this search universe
+  bool visited(int32_t search_universe, const ParentCell& parent_cell) {
+    return visited_cells_[search_universe].count(parent_cell) != 0;
   }
 
+  //! return the next universe to search for a parent cell
   int32_t current_univ() const { return model::cells[parent_cells_.back().cell_index]->universe_; }
 
+  //! indicates whether nor not parent cells are present on the stack
   bool empty() const { return parent_cells_.empty(); }
 
+  //! compute an instance for the provided distribcell index
+  int32_t compute_instance(int32_t distribcell_index) const;
+
   // Accessors
   std::vector<ParentCell>& parent_cells() { return parent_cells_; }
   const std::vector<ParentCell>& parent_cells() const { return parent_cells_; }
@@ -351,13 +366,6 @@ struct ParentCellStack {
   std::unordered_map<int32_t, std::set<ParentCell>> visited_cells_;
 };
 
-struct ParentCellHash {
-  std::size_t operator()(const ParentCell& p) const
-  {
-    return 4096*p.cell_index + p.lattice_index;
-  }
-};
-
 //==============================================================================
 //! Define an instance of a particular cell
 //==============================================================================
diff --git a/src/cell.cpp b/src/cell.cpp
index 60e7f89f3..9bfe2be31 100644
--- a/src/cell.cpp
+++ b/src/cell.cpp
@@ -1266,7 +1266,7 @@ Cell::find_parent_cells(vector<ParentCell>& parent_cells, int32_t instance) cons
     }
 
     // if we're at the top of the geometry and the instance matches, we're done
-    if (univ_idx == model::root_universe && this->compute_instance(stack.parent_cells()) == instance) break;
+    if (univ_idx == model::root_universe && stack.compute_instance(this->distribcell_index_) == instance) break;
 
     // if there was no match on the current cell's universe, report an error
     if (univ_idx == this->universe_) {
@@ -1286,15 +1286,17 @@ Cell::find_parent_cells(vector<ParentCell>& parent_cells, int32_t instance) cons
   return stack.parent_cells();
 }
 
-int32_t Cell::compute_instance(const vector<ParentCell>& parent_cells) const {
+int32_t
+ParentCellStack::compute_instance(int32_t distribcell_index) const
+{
   int32_t instance = 0;
-  for (const auto& parent_cell : parent_cells) {
+  for (const auto& parent_cell : this->parent_cells_) {
     auto& cell = model::cells[parent_cell.cell_index];
     if (cell->type_ == Fill::UNIVERSE) {
-      instance += cell->offset_[this->distribcell_index_];
+      instance += cell->offset_[distribcell_index];
     } else if (cell->type_ == Fill::LATTICE) {
       auto& lattice = model::lattices[cell->fill_];
-      instance += lattice->offset(this->distribcell_index_, parent_cell.lattice_index);
+      instance += lattice->offset(distribcell_index, parent_cell.lattice_index);
     }
   }
   return instance;