1 files changed, 15 insertions, 14 deletions
diff --git a/src/Persistent_cohomology/include/gudhi/Persistent_cohomology.h b/src/Persistent_cohomology/include/gudhi/Persistent_cohomology.h
index 3875afc6..2d6a85c1 100644
--- a/src/Persistent_cohomology/include/gudhi/Persistent_cohomology.h
+++ b/src/Persistent_cohomology/include/gudhi/Persistent_cohomology.h
@@ -431,13 +431,14 @@ class Persistent_cohomology {
       std::map<Simplex_key, Arith_element> & map_a_ds, Simplex_handle sigma,
       int dim_sigma) {
     // traverses the boundary of sigma, keeps track of the annotation vectors,
-    // with multiplicity.
-#if 0
-    std::vector<std::pair<Column *, int>> annotations_in_boundary;
-#else
-    static std::vector<std::pair<Column *, int>> annotations_in_boundary;
-    annotations_in_boundary.clear();
-#endif
+    // with multiplicity. We used to sum the coefficients directly in
+    // annotations_in_boundary by using a map, we now do it later.
+    typedef std::pair<Column *, int> annotation_t;
+    std::vector<annotation_t> annotations_in_boundary;
+    /* A small speed boost is possible with the following non-thread-safe:
+       static std::vector<std::pair<Column *, int>> annotations_in_boundary;
+       annotations_in_boundary.clear();
+    */
     int sign = 1 - 2 * (dim_sigma % 2);  // \in {-1,1} provides the sign in the
                                          // alternate sum in the boundary.
     Simplex_key key;
@@ -454,18 +455,18 @@ class Persistent_cohomology {
       }
       sign = -sign;
     }
-    std::sort(annotations_in_boundary.begin(),annotations_in_boundary.end(),[](auto&a,auto&b){return a.first<b.first;});
+    // Place identical annotations consecutively so we can easily sum their multiplicities.
+    std::sort(annotations_in_boundary.begin(), annotations_in_boundary.end(),
+	[](annotation_t& a, annotation_t& b) { return a.first < b.first; });
+
     // Sum the annotations with multiplicity, using a map<key,coeff>
     // to represent a sparse vector.
     std::pair<typename std::map<Simplex_key, Arith_element>::iterator, bool> result_insert_a_ds;
 
-    auto ann_it = annotations_in_boundary.begin();
-    while (ann_it != annotations_in_boundary.end()) {
-      auto col = ann_it->first;
+    for (auto ann_it = annotations_in_boundary.begin(); ann_it != annotations_in_boundary.end(); /**/) {
+      Column* col = ann_it->first;
       int coef = ann_it->second;
-      for (;;) {
-	if (++ann_it == annotations_in_boundary.end() || ann_it->first != col)
-	  break;
+      while (++ann_it != annotations_in_boundary.end() && ann_it->first == col) {
 	coef += ann_it->second;
       }
       // The following test is just a heuristic, it is not required, and it is fine that is misses p == 0.