std_limits.h

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

// The template and inlines for the -*- C++ -*- numeric_limits classes.

// Copyright (C) 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 2, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

// Note: this is not a conforming implementation.
// Written by Gabriel Dos Reis <[e-mail]>

//
// ISO 14882:1998
// 18.2.1
//

/** @file limits
 *  This is a Standard C++ Library header.  You should @c #include this header
 *  in your programs, rather than any of the "st[dl]_*.h" implementation files.
 */

#ifndef _CPP_NUMERIC_LIMITS
#define _CPP_NUMERIC_LIMITS 1

#pragma GCC system_header

#include <bits/c++config.h>

//
// The numeric_limits<> traits document implementation-defined aspects
// of fundamental arithmetic data types (integers and floating points).
// From Standard C++ point of view, there are 13 such types:
//   * integers
//         bool						        (1)
//         char, signed char, unsigned char			(3)
//         short, unsigned short				(2)
//         int, unsigned					(2)
//         long, unsigned long					(2)
//
//   * floating points
//         float						(1)
//         double						(1)
//         long double						(1)
//
// GNU C++ undertstands (where supported by the host C-library)
//   * integer
//         long long, unsigned long long			(2)
//
// which brings us to 15 fundamental arithmetic data types in GNU C++.
//
//
// Since a numeric_limits<> is a bit tricky to get right, we rely on
// an interface composed of macros which should be defined in config/os
// or config/cpu when they differ from the generic (read arbitrary)
// definitions given here.
//

// These values can be overridden in the target configuration file.
// The default values are appropriate for many 32-bit targets.

// GCC only intrinsicly supports modulo integral types.  The only remaining
// integral exceptional values is division by zero.  Only targets that do not
// signal division by zero in some "hard to ignore" way should use false.
#ifndef __glibcpp_integral_traps
# define __glibcpp_integral_traps true
#endif

// float
//

// Default values.  Should be overriden in configuration files if necessary.

#ifndef __glibcpp_float_has_denorm_loss
#  define __glibcpp_float_has_denorm_loss false
#endif
#ifndef __glibcpp_float_traps
#  define __glibcpp_float_traps false
#endif
#ifndef __glibcpp_float_tinyness_before
#  define __glibcpp_float_tinyness_before false
#endif

// double

// Default values.  Should be overriden in configuration files if necessary.

#ifndef __glibcpp_double_has_denorm_loss
#  define __glibcpp_double_has_denorm_loss false
#endif
#ifndef __glibcpp_double_traps
#  define __glibcpp_double_traps false
#endif
#ifndef __glibcpp_double_tinyness_before
#  define __glibcpp_double_tinyness_before false
#endif

// long double

// Default values.  Should be overriden in configuration files if necessary.

#ifndef __glibcpp_long_double_has_denorm_loss
#  define __glibcpp_long_double_has_denorm_loss false
#endif
#ifndef __glibcpp_long_double_traps
#  define __glibcpp_long_double_traps false
#endif
#ifndef __glibcpp_long_double_tinyness_before
#  define __glibcpp_long_double_tinyness_before false
#endif

// You should not need to define any macros below this point.

#define __glibcpp_signed(T)	((T)(-1) < 0)

#define __glibcpp_min(T) \
  (__glibcpp_signed (T) ? (T)1 << __glibcpp_digits (T) : (T)0)

#define __glibcpp_max(T) \
  (__glibcpp_signed (T) ? ((T)1 << __glibcpp_digits (T)) - 1 : ~(T)0)

#define __glibcpp_digits(T) \
  (sizeof(T) * __CHAR_BIT__ - __glibcpp_signed (T))

// The fraction 643/2136 approximates log10(2) to 7 significant digits.
#define __glibcpp_digits10(T) \
  (__glibcpp_digits (T) * 643 / 2136)


namespace std
{
  enum float_round_style
  {
    round_indeterminate       = -1,
    round_toward_zero         = 0,
    round_to_nearest          = 1,
    round_toward_infinity     = 2,
    round_toward_neg_infinity = 3
  };

  enum float_denorm_style
  {
    denorm_indeterminate = -1,
    denorm_absent        = 0,
    denorm_present       = 1
  };

  //
  // The primary class traits
  //
  struct __numeric_limits_base
  {
    static const bool is_specialized = false;

    static const int digits = 0;
    static const int digits10 = 0;
    static const bool is_signed = false;
    static const bool is_integer = false;
    static const bool is_exact = false;
    static const int radix = 0;

    static const int min_exponent = 0;
    static const int min_exponent10 = 0;
    static const int max_exponent = 0;
    static const int max_exponent10 = 0;

    static const bool has_infinity = false;
    static const bool has_quiet_NaN = false;
    static const bool has_signaling_NaN = false;
    static const float_denorm_style has_denorm = denorm_absent;
    static const bool has_denorm_loss = false;

    static const bool is_iec559 = false;
    static const bool is_bounded = false;
    static const bool is_modulo = false;

    static const bool traps = false;
    static const bool tinyness_before = false;
    static const float_round_style round_style = round_toward_zero;
  };

  template<typename _Tp>
    struct numeric_limits : public __numeric_limits_base
    {
      static _Tp min() throw() { return static_cast<_Tp>(0); }
      static _Tp max() throw() { return static_cast<_Tp>(0); }
      static _Tp epsilon() throw() { return static_cast<_Tp>(0); }
      static _Tp round_error() throw() { return static_cast<_Tp>(0); }
      static _Tp infinity() throw()  { return static_cast<_Tp>(0); }
      static _Tp quiet_NaN() throw() { return static_cast<_Tp>(0); }
      static _Tp signaling_NaN() throw() { return static_cast<_Tp>(0); }
      static _Tp denorm_min() throw() { return static_cast<_Tp>(0); }
    };

  // Now there follow 15 explicit specializations.  Yes, 15.  Make sure
  // you get the count right.
  template<>
    struct numeric_limits<bool>
    {
      static const bool is_specialized = true;

      static bool min() throw()
      { return false; }
      static bool max() throw()
      { return true; }

      static const int digits = 1;
      static const int digits10 = 0;
      static const bool is_signed = false;
      static const bool is_integer = true;
      static const bool is_exact = true;
      static const int radix = 2;
      static bool epsilon() throw()
      { return false; }
      static bool round_error() throw()
      { return false; }

      static const int min_exponent = 0;
      static const int min_exponent10 = 0;
      static const int max_exponent = 0;
      static const int max_exponent10 = 0;

      static const bool has_infinity = false;
      static const bool has_quiet_NaN = false;
      static const bool has_signaling_NaN = false;
      static const float_denorm_style has_denorm = denorm_absent;
      static const bool has_denorm_loss = false;

      static bool infinity() throw()
      { return false; }
      static bool quiet_NaN() throw()
      { return false; }
      static bool signaling_NaN() throw()
      { return false; }
      static bool denorm_min() throw()
      { return false; }

      static const bool is_iec559 = false;
      static const bool is_bounded = true;
      static const bool is_modulo = false;

      // It is not clear what it means for a boolean type to trap.
      // This is a DR on the LWG issue list.  Here, I use integer
      // promotion semantics.
      static const bool traps = __glibcpp_integral_traps;
      static const bool tinyness_before = false;
      static const float_round_style round_style = round_toward_zero;
    };

  template<>
    struct numeric_limits<char>
    {
      static const bool is_specialized = true;

      static char min() throw()
      { return __glibcpp_min(char); }
      static char max() throw()
      { return __glibcpp_max(char); }

      static const int digits = __glibcpp_digits (char);
      static const int digits10 = __glibcpp_digits10 (char);
      static const bool is_signed = __glibcpp_signed (char);
      static const bool is_integer = true;
      static const bool is_exact = true;
      static const int radix = 2;
      static char epsilon() throw()
      { return 0; }
      static char round_error() throw()
      { return 0; }

      static const int min_exponent = 0;
      static const int min_exponent10 = 0;
      static const int max_exponent = 0;
      static const int max_exponent10 = 0;

      static const bool has_infinity = false;
      static const bool has_quiet_NaN = false;
      static const bool has_signaling_NaN = false;
      static const float_denorm_style has_denorm = denorm_absent;
      static const bool has_denorm_loss = false;

      static char infinity() throw()
      { return char(); }
      static char quiet_NaN() throw()
      { return char(); }
      static char signaling_NaN() throw()
      { return char(); }
      static char denorm_min() throw()
      { return static_cast<char>(0); }

      static const bool is_iec559 = false;
      static const bool is_bounded = true;
      static const bool is_modulo = true;

      static const bool traps = __glibcpp_integral_traps;
      static const bool tinyness_before = false;
      static const float_round_style round_style = round_toward_zero;
    };

  template<>
    struct numeric_limits<signed char>
    {
      static const bool is_specialized = true;

      static signed char min() throw()
      { return -__SCHAR_MAX__ - 1; }
      static signed char max() throw()
      { return __SCHAR_MAX__; }

      static const int digits = __glibcpp_digits (signed char);
      static const int digits10 = __glibcpp_digits10 (signed char);
      static const bool is_signed = true;
      static const bool is_integer = true;
      static const bool is_exact = true;
      static const int radix = 2;
      static signed char epsilon() throw()
      { return 0; }
      static signed char round_error() throw()
      { return 0; }

      static const int min_exponent = 0;
      static const int min_exponent10 = 0;
      static const int max_exponent = 0;
      static const int max_exponent10 = 0;

      static const bool has_infinity = false;
      static const bool has_quiet_NaN = false;
      static const bool has_signaling_NaN = false;
      static const float_denorm_style has_denorm = denorm_absent;
      static const bool has_denorm_loss = false;

      static signed char infinity() throw()