+#if defined (__FreeBSD__)
+# if __FreeBSD_version < 500000
+ extern "C" {
+ inline int isnan(double r) { return !(r <= 0 || r >= 0); }
+ }
+# endif
+#endif
+
+#if defined (__CYGWIN__)
+# include <ieeefp.h> // isnan
+#endif
+
+#if defined(__MINGW32__)
+# define isnan(x) _isnan(x)