voloctree: split mapped octant list build loop to make it more readable

The split separates the loop in a first loop to find the first overlapping
rank of the reference mesh and the first overlapping octant of the mapped
mesh. A second loop fill the octant lists starting from data retrieved in
the previous one. This version of the algorithm should be safe, avoiding
evaluation of morton number of non-existing octants and giving empty lists
if no overlap occurs.

src/voloctree/voloctree_mapper.cpp

@@ -1232,41 +1232,52 @@ bool VolOctreeMapper::_recoverPartition()
     std::map<int, std::vector<Octant>> list_octant;
     std::map<int, std::vector<long>> list_id;
     std::map<int, std::vector<long>> list_globalId;
-    uint32_t idx = 0;
-    for (int reference_rank : toreference_rank[m_rank]) {
+
+    // Initialize idx position in mapped tree to the first mapped
+    // octant inside the overlapping region
+    std::vector<int>::iterator overlap_ref_rank_end_it = toreference_rank[m_rank].end();
+    std::vector<int>::iterator first_overlap_rank_it = overlap_ref_rank_end_it;
+    uint32_t first_overlap_map_idx = 0;
+    for (std::vector<int>::iterator ref_rank_it = toreference_rank[m_rank].begin(); ref_rank_it != overlap_ref_rank_end_it; ++ref_rank_it) {
+        first_overlap_map_idx = 0;
+        int reference_rank = *ref_rank_it;
         uint64_t reference_first_morton = partitionFDReference[reference_rank];
-        uint64_t reference_last_morton = partitionLDReference[reference_rank];
-        // Initialize idx position in mapped tree to the first mapped
-        // octant inside the overlapping region
-        uint64_t morton = mappedPatch->getTree().getLastDescMorton(idx);
+        uint64_t morton = mappedPatch->getTree().getLastDescMorton(first_overlap_map_idx);
         while (morton < reference_first_morton) {
-            idx++;
-            if (idx == mappedPatch->getTree().getNumOctants()) {
+            first_overlap_map_idx++;
+            if (first_overlap_map_idx == mappedPatch->getTree().getNumOctants()) {
                 break;
             }
-            morton = mappedPatch->getTree().getLastDescMorton(idx);
+            morton = mappedPatch->getTree().getLastDescMorton(first_overlap_map_idx);
         }
-        if (idx == mappedPatch->getTree().getNumOctants()) {
-            continue;
-        }
-        // Fill partitioning info structure with mapped octants in the
-        // overlapping region
-        morton = mappedPatch->getTree().getMorton(idx);
-        while (morton < reference_last_morton) {
-            Octant oct = *mappedPatch->getTree().getOctant(idx);
-            list_octant[reference_rank].push_back(oct);
-            VolOctree::OctantInfo octantIfo(idx, true);
-            long id = mappedPatch->getOctantId(octantIfo);
-            list_id[reference_rank].push_back(id);
-            long globalId = mappedPatch->getTree().getGlobalIdx(idx);
-            list_globalId[reference_rank].push_back(globalId);
-            m_partitionIR.list_sent_octantIR.emplace_back(oct, id, globalId, reference_rank);
-            idx++;
-            if (idx == mappedPatch->getTree().getNumOctants()) {
-                --idx;
-                break;
+        first_overlap_rank_it = ref_rank_it;
+    }
+
+    // Fill partitioning info structure with mapped octants in the
+    // overlapping region
+    if (first_overlap_map_idx < mappedPatch->getTree().getNumOctants() ) {
+        uint32_t idx = first_overlap_map_idx;
+        bool exitLoop = false;
+        for (std::vector<int>::iterator ref_rank_it = first_overlap_rank_it; ref_rank_it != overlap_ref_rank_end_it && !exitLoop; ++ref_rank_it) {
+            int reference_rank = *ref_rank_it;
+            uint64_t reference_last_morton = partitionLDReference[reference_rank];
+            uint64_t morton = mappedPatch->getTree().getMorton(idx);
+            while (morton < reference_last_morton) {
+                Octant oct = *mappedPatch->getTree().getOctant(idx);
+                list_octant[reference_rank].push_back(oct);
+                VolOctree::OctantInfo octantIfo(idx, true);
+                long id = mappedPatch->getOctantId(octantIfo);
+                list_id[reference_rank].push_back(id);
+                long globalId = mappedPatch->getTree().getGlobalIdx(idx);
+                list_globalId[reference_rank].push_back(globalId);
+                m_partitionIR.list_sent_octantIR.emplace_back(oct, id, globalId, reference_rank);
+                idx++;
+                if (idx == mappedPatch->getTree().getNumOctants()) {
+                    exitLoop = true;
+                    break;
+                }
+                morton = mappedPatch->getTree().getMorton(idx);
             }
-            morton = mappedPatch->getTree().getMorton(idx);
         }
     }