inline _GLIBCXX_CONSTEXPR long double
  abs(long double __x)
  { return __builtin_fabsl(__x); }
#endif

  template<typename _Tp>
    inline _GLIBCXX_CONSTEXPR
    typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value,
                                    double>::__type
    abs(_Tp __x)
    { return __builtin_fabs(__x); }

  using ::acos;

#ifndef __CORRECT_ISO_CPP_MATH_H_PROTO1
  inline _GLIBCXX_CONSTEXPR float
  acos(float __x)