Simplify implementation of method UGGridGeometry::affine

The old implementation constructed a GeometryType object and asked
that whether it was a simplex.  Apparently this inlined badly.
The new implementation queries the UG-internal data structures
directly, which leads to a measurable performance gain.

CHANGELOG.md

@@ -30,6 +30,8 @@ SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
 
 - The method `UGGridGeometry::integrationElement` has been simplified, and is faster now.
 
+- The method `UGGridGeometry::affine` has been reimplemented, and is much faster now.
+
 ## Python
 
 - Improve pickling support (GridViews and some GridFunction objects can now be pickled).

dune/grid/uggrid/uggridgeometry.hh

@@ -49,7 +49,15 @@ namespace Dune {
     GeometryType type () const;
 
     //! returns true if type is simplex, false otherwise
-    bool affine() const { return type().isSimplex(); }
+    bool affine() const
+    {
+      if constexpr (mydim==0 || mydim==1)  // Vertices and edges are always affine
+        return true;
+      else if constexpr (mydim==2)
+        return UG_NS<coorddim>::Tag(target_)==UG::D2::TRIANGLE;
+      else
+        return UG_NS<coorddim>::Tag(target_)==UG::D3::TETRAHEDRON;
+    }
 
     //! return the number of corners of this element.
     int corners () const {