From: Martin Kronbichler <kronbichler@lnm.mw.tum.de>
Date: Sat, 10 Nov 2018 21:23:32 +0000 (+0100)
Subject: Avoid negative index offsets.
X-Git-Tag: v9.1.0-rc1~566^2~1
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b2494e7c79a3d975b9a6692571e040d026a6919c;p=dealii.git

Avoid negative index offsets.
---

diff --git a/include/deal.II/matrix_free/dof_info.templates.h b/include/deal.II/matrix_free/dof_info.templates.h
index a3400b2b50..2987edf8cd 100644
--- a/include/deal.II/matrix_free/dof_info.templates.h
+++ b/include/deal.II/matrix_free/dof_info.templates.h
@@ -817,8 +817,11 @@ namespace internal
                       dof_indices[j * ndofs + 1] - dof_indices[j * ndofs];
                   for (unsigned int k = 0; k < ndofs; ++k)
                     for (unsigned int j = 0; j < n_comp; ++j)
-                      if (dof_indices[j * ndofs + k] !=
-                          dof_indices[j * ndofs] + k * offsets[j])
+                      // the first if case is to avoid negative offsets
+                      // (invalid)
+                      if (dof_indices[j * ndofs + 1] < dof_indices[j * ndofs] ||
+                          dof_indices[j * ndofs + k] !=
+                            dof_indices[j * ndofs] + k * offsets[j])
                         {
                           indices_are_interleaved_and_mixed = 0;
                           break;