Add a comment for assert that explains null_key mechanism

git-svn-id: svn+ssh://scm.gforge.inria.fr/svnroot/gudhi/branches/3billions_simplices_fix@1484 636b058d-ea47-450e-bf9e-a15bfbe3eedb

Former-commit-id: 12246383db2c71ce36d03e5702180605459e6fe3

1 files changed, 1 insertions, 0 deletions

diff --git a/src/Persistent_cohomology/include/gudhi/Persistent_cohomology.h b/src/Persistent_cohomology/include/gudhi/Persistent_cohomology.h
index d3da812e..b31df6a4 100644
--- a/src/Persistent_cohomology/include/gudhi/Persistent_cohomology.h
+++ b/src/Persistent_cohomology/include/gudhi/Persistent_cohomology.h
@@ -109,6 +109,7 @@ class Persistent_cohomology {
         column_pool_(),  // memory pools for the CAM
         cell_pool_() {
     if (cpx_->num_simplices() > std::numeric_limits<Simplex_key>::max()) {
+      // num_simplices must be strictly lower than the limit, because a value is reserved for null_key.
       throw std::out_of_range ("The number of simplices is more than Simplex_key type numeric limit.");
     }
     Simplex_key idx_fil = 0;