Merge pull request #1039 from atgeirr/fix-compile-maxabs-unsigned

Avoid ambiguous calls to abs with unsigned integers.

opm/core/linalg/ParallelIstlInformation.hpp

@@ -590,17 +590,32 @@ private:
     namespace detail
     {
         /// \brief Computes the maximum of the absolute values of two values.
-    template<typename T>
+        template<typename T, typename Enable = void>
         struct MaxAbsFunctor
         {
-        typedef T result_type;
+            using result_type = T;
-
+            result_type operator()(const T& t1,
-        result_type operator()(const T& t1, const T& t2)
+                                   const T& t2)
             {
                 return std::max(std::abs(t1), std::abs(t2));
             }
         };
+
+        // Specialization for unsigned integers. They need their own
+        // version since abs(x) is ambiguous (as well as somewhat
+        // meaningless).
+        template<typename T>
+        struct MaxAbsFunctor<T, typename std::enable_if<std::is_unsigned<T>::value>::type>
+        {
+            using result_type = T;
+            result_type operator()(const T& t1,
+                                   const T& t2)
+            {
+                return std::max(t1, t2);
             }
+        };
+    }
+
     /// \brief Create a functor for computing a global L infinity norm
     ///
     /// To be used with ParallelISTLInformation::computeReduction.

tests/test_parallelistlinformation.cpp

@@ -33,6 +33,7 @@
 #include <functional>
 #ifdef HAVE_DUNE_ISTL
 
+
 template<typename T>
 void runSumMaxMinTest(const T offset)
 {
@@ -60,7 +61,9 @@ void runSumMaxMinTest(const T offset)
     BOOST_CHECK(std::get<1>(values)==std::max(N+offset-1, std::get<1>(oldvalues)));
     BOOST_CHECK(std::get<2>(values)==std::min(offset, std::get<2>(oldvalues)));
     BOOST_CHECK(std::get<3>(values)==((end-1)*end*(2*end-1)-(start-1)*start*(2*start-1))/6+std::get<3>(oldvalues));
-    BOOST_CHECK(std::get<4>(values)==std::max(std::abs(offset),std::abs(N+offset-1)));
+    // Must avoid std::abs() directly to prevent ambiguity with unsigned integers.
+    Opm::Reduction::detail::MaxAbsFunctor<T> maxabsfunc;
+    BOOST_CHECK(std::get<4>(values)==maxabsfunc(offset, N+offset-1));
 }
 
 BOOST_AUTO_TEST_CASE(tupleReductionTestInt)