// is_signed

template <class _Tp, bool = is_integral<_Tp>::value>
struct ___is_signed : public integral_constant<bool, _Tp(-1) < _Tp(0)> {};

template <class _Tp>
struct ___is_signed<_Tp, false> : public true_type {};  // floating point

template <class _Tp, bool = is_arithmetic<_Tp>::value>
struct __is_signed : public ___is_signed<_Tp> {};

template <class _Tp> struct __is_signed<_Tp, false> : public false_type {};

template <class _Tp> struct is_signed : public __is_signed<_Tp> {};