atan2f
float atan2f(float, float);
extern float atan2f(float, float);
using ::atan2f;
extern float atan2f(float, float);
inline float atan2(float __X, float __Y) { return atan2f(__X, __Y); }
return (atan2f(F_IM(z), F_RE(z)));
F_IM(ans) = atan2f(y, x);