From: Martin Kronbichler <kronbichler@lnm.mw.tum.de>
Date: Tue, 20 Aug 2019 19:13:16 +0000 (+0200)
Subject: Avoid superfluous zero + add-into in tensor contraction
X-Git-Tag: v9.2.0-rc1~1202^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F8609%2Fhead;p=dealii.git

Avoid superfluous zero + add-into in tensor contraction
---

diff --git a/include/deal.II/base/tensor_accessors.h b/include/deal.II/base/tensor_accessors.h
index b08d048709..a82c4027ed 100644
--- a/include/deal.II/base/tensor_accessors.h
+++ b/include/deal.II/base/tensor_accessors.h
@@ -714,12 +714,22 @@ namespace TensorAccessors
       {
         // Some auto-differentiable numbers need explicit
         // zero initialization.
-        T1 result = dealii::internal::NumberType<T1>::value(0.0);
-        for (unsigned int i = 0; i < dim; ++i)
-          result +=
-            Contract2<no_contr - 1, dim>::template contract2<T1>(left[i],
-                                                                 right[i]);
-        return result;
+        if (dim == 0)
+          {
+            T1 result = dealii::internal::NumberType<T1>::value(0.0);
+            return result;
+          }
+        else
+          {
+            T1 result =
+              Contract2<no_contr - 1, dim>::template contract2<T1>(left[0],
+                                                                   right[0]);
+            for (unsigned int i = 1; i < dim; ++i)
+              result +=
+                Contract2<no_contr - 1, dim>::template contract2<T1>(left[i],
+                                                                     right[i]);
+            return result;
+          }
       }
     };