std_cmath.h

gcc-you can use this code to learn something about gcc, and inquire further into linux,

  frexp(float __x, int* __exp) { return ::frexp(__x, __exp); }
#endif

#if _GLIBCPP_HAVE_FREXPL
  inline long double 
  frexp(long double __x, int* __exp) { return ::frexpl(__x, __exp); }
#else
  inline long double 
  frexp(long double __x, int* __exp) 
  { return ::frexp(static_cast<double>(__x), __exp); }
#endif

  using ::ldexp;

#if _GLIBCPP_HAVE_LDEXPF
  inline float 
  ldexp(float __x, int __exp) { return __gnu_cxx::__c99_binding::ldexpf(__x, __exp); }
#else
  inline float 
  ldexp(float __x, int __exp)
  { return ::ldexp(static_cast<double>(__x), __exp); }
#endif

#if _GLIBCPP_HAVE_LDEXPL
  inline long double 
  ldexp(long double __x, int __exp) { return ::ldexpl(__x, __exp); }
#else
  inline long double 
  ldexp(long double __x, int __exp) 
  { return ::ldexp(static_cast<double>(__x), __exp); }
#endif

  using ::log;

#if _GLIBCPP_HAVE_LOGF
  inline float 
  log(float __x) { return __gnu_cxx::__c99_binding::logf(__x); }
#else
  inline float log(float __x)
  { return ::log(static_cast<double>(__x)); }
#endif

#if _GLIBCPP_HAVE_LOGL
  inline long double 
  log(long double __x) { return ::logl(__x); }
#else
  inline long double 
  log(long double __x) { return ::log(static_cast<double>(__x)); }
#endif

  using ::log10;

#if _GLIBCPP_HAVE_LOG10F
  inline float 
  log10(float __x) { return __gnu_cxx::__c99_binding::log10f(__x); }
#else
  inline float 
  log10(float __x) { return ::log10(static_cast<double>(__x)); }
#endif

#if _GLIBCPP_HAVE_LOG10L
  inline long double 
  log10(long double __x) { return ::log10l(__x); }
#else
  inline long double 
  log10(long double __x) { return ::log10(static_cast<double>(__x)); }
#endif

  using ::modf;

#if _GLIBCPP_HAVE_MODFF
  inline float 
  modf(float __x, float* __iptr) { return __gnu_cxx::__c99_binding::modff(__x, __iptr); }
#else
  inline float 
  modf(float __x, float* __iptr)
  {
    double __tmp;
    double __res = ::modf(static_cast<double>(__x), &__tmp);
    *__iptr = static_cast<float>(__tmp);
    return __res;
  }
#endif

#if _GLIBCPP_HAVE_MODFL
  inline long double 
  modf(long double __x, long double* __iptr) { return ::modfl(__x, __iptr); }
#else
  inline long double 
  modf(long double __x, long double* __iptr) 
  { 
    double __tmp;
    double __res = ::modf(static_cast<double>(__x), &__tmp);
    * __iptr = static_cast<long double>(__tmp);
    return __res;
  }
#endif

  template<typename _Tp>
    inline _Tp
    __pow_helper(_Tp __x, int __n)
    {
      return __n < 0
        ? _Tp(1)/__cmath_power(__x, -__n)
        : __cmath_power(__x, __n);
    }

  using ::pow;

#if _GLIBCPP_HAVE_POWF
  inline float 
  pow(float __x, float __y) { return __gnu_cxx::__c99_binding::powf(__x, __y); }
#else
  inline float 
  pow(float __x, float __y)
  { return ::pow(static_cast<double>(__x), static_cast<double>(__y)); }
#endif

#if _GLIBCPP_HAVE_POWL
  inline long double 
  pow(long double __x, long double __y) { return ::powl(__x, __y); }
#else
  inline long double 
  pow(long double __x, long double __y) 
  { return ::pow(static_cast<double>(__x), static_cast<double>(__y)); }
#endif

  inline double 
  pow(double __x, int __i)
  { return __pow_helper(__x, __i); }

  inline float 
  pow(float __x, int __n)
  { return __pow_helper(__x, __n); }

  inline long double 
  pow(long double __x, int __n)
  { return __pow_helper(__x, __n); }

  using ::sin;

  inline float
  sin(float __x)
  { return __builtin_sinf(__x); }

  inline long double
  sin(long double __x)
  { return __builtin_sinl(__x); }

  using ::sinh;

#if _GLIBCPP_HAVE_SINHF
  inline float 
  sinh(float __x) { return __gnu_cxx::__c99_binding::sinhf(__x); }
#else
  inline float 
  sinh(float __x) { return ::sinh(static_cast<double>(__x)); }
#endif

#if _GLIBCPP_HAVE_SINHL
  inline long double 
  sinh(long double __x) { return ::sinhl(__x); }
#else
  inline long double 
  sinh(long double __x) { return ::sinh(static_cast<double>(__x)); }
#endif

  using ::sqrt;

  inline float
  sqrt(float __x)
  { return __builtin_sqrtf(__x); }

  inline long double
  sqrt(long double __x)
  { return __builtin_sqrtl(__x); }

  using ::tan;

#if _GLIBCPP_HAVE_TANF
  inline float 
  tan(float __x) { return __gnu_cxx::__c99_binding::tanf(__x); }
#else
  inline float 
  tan(float __x) { return ::tan(static_cast<double>(__x)); }
#endif

#if _GLIBCPP_HAVE_TANL
  inline long double 
  tan(long double __x) { return ::tanl(__x); }
#else
  inline long double 
  tan(long double __x) { return ::tan(static_cast<double>(__x)); }
#endif

  using ::tanh;

#if _GLIBCPP_HAVE_TANHF
  inline float 
  tanh(float __x) { return __gnu_cxx::__c99_binding::tanhf(__x); }
#else
  inline float 
  tanh(float __x) { return ::tanh(static_cast<double>(__x)); }
#endif

#if _GLIBCPP_HAVE_TANHL
  inline long double 
  tanh(long double __x) { return ::tanhl(__x); }
#else
  inline long double 
  tanh(long double __x) { return ::tanh(static_cast<double>(__x)); }
#endif
} 


#if _GLIBCPP_USE_C99
#if !_GLIBCPP_USE_C99_FP_MACROS_DYNAMIC
// These are possible macros imported from C99-land. For strict
// conformance, remove possible C99-injected names from the global
// namespace, and sequester them in the __gnu_cxx extension namespace. 
namespace __gnu_cxx
{
  template<typename _Tp>
    int 
    __capture_fpclassify(_Tp __f) { return fpclassify(__f); }

  template<typename _Tp>
    int 
    __capture_isfinite(_Tp __f) { return isfinite(__f); }

  template<typename _Tp>
    int 
    __capture_isinf(_Tp __f) { return isinf(__f); }

  template<typename _Tp>
    int 
    __capture_isnan(_Tp __f) { return isnan(__f); }

  template<typename _Tp>
    int 
    __capture_isnormal(_Tp __f) { return isnormal(__f); }

  template<typename _Tp>
    int 
    __capture_signbit(_Tp __f) { return signbit(__f); }

  template<typename _Tp>
    int 
    __capture_isgreater(_Tp __f1, _Tp __f2)
    { return isgreater(__f1, __f2); }

  template<typename _Tp>
     int 
     __capture_isgreaterequal(_Tp __f1, _Tp __f2) 
     { return isgreaterequal(__f1, __f2); }

  template<typename _Tp>
     int 
     __capture_isless(_Tp __f1, _Tp __f2) { return isless(__f1, __f2); }

  template<typename _Tp>
     int 
     __capture_islessequal(_Tp __f1, _Tp __f2) 
     { return islessequal(__f1, __f2); }

  template<typename _Tp>
     int 
     __capture_islessgreater(_Tp __f1, _Tp __f2) 
     { return islessgreater(__f1, __f2); }

  template<typename _Tp>
     int 
     __capture_isunordered(_Tp __f1, _Tp __f2) 
     { return isunordered(__f1, __f2); }
} 
#endif /* _GLIBCPP_USE_C99_FP_MACROS_DYNAMIC */
#endif

#undef fpclassify
#undef isfinite
#undef isinf
#undef isnan
#undef isnormal
#undef signbit
#undef isgreater
#undef isgreaterequal
#undef isless
#undef islessequal
#undef islessgreater
#undef isunordered

#if _GLIBCPP_USE_C99
#if !_GLIBCPP_USE_C99_FP_MACROS_DYNAMIC
namespace __gnu_cxx
{
  template<typename _Tp>
    int
    fpclassify(_Tp __f) { return __capture_fpclassify(__f); }

  template<typename _Tp>
    int
    isfinite(_Tp __f) { return __capture_isfinite(__f); }

  template<typename _Tp>
    int 
    isinf(_Tp __f) { return __capture_isinf(__f); }

  template<typename _Tp>
    int 
    isnan(_Tp __f) { return __capture_isnan(__f); }

  template<typename _Tp>
    int 
    isnormal(_Tp __f) { return __capture_isnormal(__f); }

  template<typename _Tp>
    int 
    signbit(_Tp __f) { return __capture_signbit(__f); }

  template<typename _Tp>
    int 
    isgreater(_Tp __f1, _Tp __f2) { return __capture_isgreater(__f1, __f2); }

  template<typename _Tp>
    int 
    isgreaterequal(_Tp __f1, _Tp __f2) 
    { return __capture_isgreaterequal(__f1, __f2); }

  template<typename _Tp>
    int 
    isless(_Tp __f1, _Tp __f2) { return __capture_isless(__f1, __f2); }

  template<typename _Tp>
    int 
    islessequal(_Tp __f1, _Tp __f2) 
    { return __capture_islessequal(__f1, __f2); }

  template<typename _Tp>
    int 
    islessgreater(_Tp __f1, _Tp __f2) 
    { return __capture_islessgreater(__f1, __f2); }

  template<typename _Tp>
    int 
    isunordered(_Tp __f1, _Tp __f2) 
    { return __capture_isunordered(__f1, __f2); }
}

namespace std
{
  using __gnu_cxx::fpclassify;
  using __gnu_cxx::isfinite;
  using __gnu_cxx::isinf;
  using __gnu_cxx::isnan;
  using __gnu_cxx::isnormal;
  using __gnu_cxx::signbit;
  using __gnu_cxx::isgreater;
  using __gnu_cxx::isgreaterequal;
  using __gnu_cxx::isless;
  using __gnu_cxx::islessequal;
  using __gnu_cxx::islessgreater;
  using __gnu_cxx::isunordered;
}
#endif /* _GLIBCPP_USE_C99_FP_MACROS_DYNAMIC */
#endif
  
#ifdef _GLIBCPP_NO_TEMPLATE_EXPORT
#  define export
#  include <bits/cmath.tcc>
#endif

#endif