Simplify isnan detection with C++11 library.

CMakeLists.txt

@@ -328,15 +328,14 @@ SET(CMAKE_MINSIZEREL_POSTFIX "" CACHE STRING "add a postfix, usually empty on wi
 
 # isnan might not be real symbol, so can't check using function_exists
 check_cxx_source_compiles(
-    "#include <cmath>
-    int main() { return isnan(0.0);} "
-    HAVE_ISNAN)
-
-check_cxx_source_compiles(
-    "#include <cmath>
+    "#include <cstdlib>
     int main() { return std::isnan(0.0);} "
     HAVE_STD_ISNAN)
 
+if (NOT ${HAVE_STD_ISNAN})
+  message(FATAL_ERROR "Your compiler lacks C++11 std::isnan, please update it")
+endif()
+
 if(CMAKE_COMPILER_IS_GNUCXX)
     set(WARNING_FLAGS_CXX "-Wall")
     set(WARNING_FLAGS_C   "-Wall")

simgear/math/SGMisc.hxx

@@ -153,17 +153,7 @@ public:
   /// Use with care: allways code that you do not need to use that!
   static bool isNaN(const T& v)
   {
-#ifdef HAVE_STD_ISNAN
     return std::isnan(v);
-#elif defined HAVE_ISNAN
-    return (isnan(v) != 0);
-#else
-    // Use that every compare involving a NaN returns false
-    // But be careful, some usual compiler switches like for example
-    // -fast-math from gcc might optimize that expression to v != v which
-    // behaves exactly like the opposite ...
-    return !(v == v);
-#endif
   }
 };
 

simgear/simgear_config_cmake.h.in

@@ -9,7 +9,7 @@
 #cmakedefine HAVE_FTIME
 #cmakedefine HAVE_RINT
 #cmakedefine HAVE_TIMEGM
-#cmakedefine HAVE_ISNAN
+
 #cmakedefine HAVE_STD_ISNAN
 #cmakedefine HAVE_WINDOWS_H
 #cmakedefine HAVE_MKDTEMP