complex (arg): Use std::signbit only when available.

2010-02-22  Paolo Carlini  <paolo.carlini@oracle.com>

	* include/tr1_impl/complex (arg): Use std::signbit only when
	available.

From-SVN: r156972

libstdc++-v3/ChangeLog

 2010-02-22  Paolo Carlini  <paolo.carlini@oracle.com>
 
+	* include/tr1_impl/complex (arg): Use std::signbit only when
+	available.
+
+2010-02-22  Paolo Carlini  <paolo.carlini@oracle.com>
+
 	* include/bits/functional_hash.h (hash<string>, hash<wstring>,
 	hash<u16string>, hash<u32string>, hash<error_code>): Move, per
 	DR 1182 to...

libstdc++-v3/include/tr1_impl/complex

@@ -311,8 +311,12 @@ _GLIBCXX_BEGIN_NAMESPACE_TR1
     arg(_Tp __x)
     {
       typedef typename __gnu_cxx::__promote<_Tp>::__type __type;
+#if (_GLIBCXX_USE_C99_MATH && !_GLIBCXX_USE_C99_FP_MACROS_DYNAMIC)
       return std::signbit(__x) ? __type(3.1415926535897932384626433832795029L)
 	                       : __type();
+#else
+      return std::arg(std::complex<__type>(__x));
+#endif
     }
 
   template<typename _Tp>