From: Timo Heister <timo.heister@gmail.com>
Date: Mon, 17 Feb 2020 04:10:10 +0000 (-0500)
Subject: Fix overflow in tria.n_global_active_cells()
X-Git-Tag: v9.2.0-rc1~513^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9b4c1ed4b5960a7238edcbed804b1bf02df2034d;p=dealii.git

Fix overflow in tria.n_global_active_cells()

for large computations.
---

diff --git a/source/distributed/tria_base.cc b/source/distributed/tria_base.cc
index 87b76f80da..189be2a997 100644
--- a/source/distributed/tria_base.cc
+++ b/source/distributed/tria_base.cc
@@ -217,9 +217,12 @@ namespace parallel
         if (cell->subdomain_id() == my_subdomain)
           ++number_cache.n_locally_owned_active_cells;
 
+    // Potentially cast to a 64 bit type before accumulating to avoid overflow:
     number_cache.n_global_active_cells =
-      Utilities::MPI::sum(number_cache.n_locally_owned_active_cells,
+      Utilities::MPI::sum(static_cast<types::global_dof_index>(
+                            number_cache.n_locally_owned_active_cells),
                           this->mpi_communicator);
+
     number_cache.n_global_levels =
       Utilities::MPI::max(this->n_levels(), this->mpi_communicator);
   }