ACE中对于不同类型数据的最大值最小值管理ACE_Numeric_Limits

对于不同类型的变量，这里定义了其最大最小值来提供给ACE_Utils等使用

template <typename T> struct ACE_Numeric_Limits;


// ------------------------------------------
// Special cases.
template<>
struct ACE_Export ACE_Numeric_Limits<char>
{
  static char min (void) { return CHAR_MIN; }
  static char max (void) { return CHAR_MAX; }
};

// ------------------------------------------
// Signed integers.

template<>
struct ACE_Export ACE_Numeric_Limits<signed char>
{
  static signed char min (void) { return SCHAR_MIN; }
  static signed char max (void) { return SCHAR_MAX; }
};

template<>
struct ACE_Export ACE_Numeric_Limits<signed short>
{
  static signed short min (void) { return SHRT_MIN; }
  static signed short max (void) { return SHRT_MAX; }
};

template<>
struct ACE_Export ACE_Numeric_Limits<signed int>
{
  static signed int min (void) { return INT_MIN; }
  static signed int max (void) { return INT_MAX; }
};

template<>
struct ACE_Export ACE_Numeric_Limits<signed long>
{
  static signed long min (void) { return LONG_MIN; }
  static signed long max (void) { return LONG_MAX; }
};

template<>
struct ACE_Export ACE_Numeric_Limits<signed long long>
{
#if defined (LLONG_MIN)
#  define ACE_LLONG_MIN LLONG_MIN
#elif defined (LONG_LONG_MIN)
#  define ACE_LLONG_MIN LONG_LONG_MIN
#elif defined (LONGLONG_MIN)
#  define ACE_LLONG_MIN LONGLONG_MIN
#else
#  error Unable to determine minimum signed long long value.
#endif  /* LLONG_MIN */

#if defined (LLONG_MAX)
#  define ACE_LLONG_MAX LLONG_MAX
#elif defined (LONG_LONG_MAX)
#  define ACE_LLONG_MAX LONG_LONG_MAX
#elif defined (LONGLONG_MAX)
#  define ACE_LLONG_MAX LONGLONG_MAX
#else
#  error Unable to determine maximum signed long long value.
#endif  /* LLONG_MAX */

  static signed long long min (void) { return ACE_LLONG_MIN; }
  static signed long long max (void) { return ACE_LLONG_MAX; }
};

// ------------------------------------------
// Unsigned integers
template<>
struct ACE_Export ACE_Numeric_Limits<unsigned char>
{
  static unsigned char min (void) { return 0; }
  static unsigned char max (void) { return UCHAR_MAX; }
};

template<>
struct ACE_Export ACE_Numeric_Limits<unsigned short>
{
  static unsigned short min (void) { return 0; }
  static unsigned short max (void) { return USHRT_MAX; }
};

template<>
struct ACE_Export ACE_Numeric_Limits<unsigned int>
{
  static unsigned int min (void) { return 0; }
  static unsigned int max (void) { return UINT_MAX; }
};

template<>
struct ACE_Export ACE_Numeric_Limits<unsigned long>
{
  static unsigned long min (void) { return 0; }
  static unsigned long max (void) { return ULONG_MAX; }
};

template<>
struct ACE_Export ACE_Numeric_Limits<unsigned long long>
{
  static unsigned long long min (void) { return 0; }
  static unsigned long long max (void)
  {
# if defined (ULLONG_MAX)
    return ULLONG_MAX;
# elif defined (ULONGLONG_MAX)
    return ULONGLONG_MAX;
# else
#  error Unable to determine maximum unsigned long long value.
# endif  /* ULLONG_MAX */
  }
};

// ------------------------------------------
// Floating point types

template<>
struct ACE_Export ACE_Numeric_Limits<float>
{
  static float min (void) { return FLT_MIN; }
  static float max (void) { return FLT_MAX; }
};

template<>
struct ACE_Export ACE_Numeric_Limits<double>
{
  static double min (void) { return DBL_MIN; }
  static double max (void) { return DBL_MAX; }
};

template<>
struct ACE_Export ACE_Numeric_Limits<long double>
{
  static long double min (void) { return LDBL_MIN; }
  static long double max (void) { return LDBL_MAX; }
};

#else

// std::numeric_limits<> has all of the necessary specializations.
// Just wrap it.

template <typename T>
struct ACE_Numeric_Limits
{
  static T min (void) { return std::numeric_limits<T>::min (); }
  static T max (void) { return std::numeric_limits<T>::max (); }
};

# if (defined (ACE_WIN64) && defined (_MSC_VER) && _MSC_VER <= 1310) 
    || defined (ACE_LACKS_NUMERIC_LIMITS_64_BIT_TYPES)
// The Microsoft Platform SDK does not provide std::numeric_limits<>
// specializations for 64 bit integers so we need to explicitly provide
// ACE_Numeric_Limits<> specializations to compensate for this
// deficiency.
//
// Unfortunately there is no way to tell if the platform SDK is being
// used so we specialize for the ACE_WIN64 + MSVC++ 7.1 case, which is
// the configuration that exhibits this problem.  It also happens to
// be a fairly isolated configuration since 64-bit support in MSVC++
// 7.1 was not very good to begin with.
template<>
struct ACE_Numeric_Limits<LONGLONG>
{
  static LONGLONG min (void) { return _I64_MIN; }
  static LONGLONG max (void) { return _I64_MAX; }
};

template<>
struct ACE_Numeric_Limits<ULONGLONG>
{
  static ULONGLONG min (void) { return 0; }
  static ULONGLONG max (void) { return _UI64_MAX; }
};
# endif  /* ACE_WIN64 && _MSC_VER <= 1310 */