Chris@16: // (C) Copyright David Abrahams 2001, Howard Hinnant 2001.
Chris@16: //
Chris@16: // Distributed under the Boost Software License, Version 1.0. (See
Chris@16: // accompanying file LICENSE_1_0.txt or copy at
Chris@16: // http://www.boost.org/LICENSE_1_0.txt)
Chris@16: //
Chris@16: // Template class numeric_traits<Number> --
Chris@16: //
Chris@16: //    Supplies:
Chris@16: //
Chris@16: //      typedef difference_type -- a type used to represent the difference
Chris@16: //      between any two values of Number.
Chris@16: //
Chris@16: //    Support:
Chris@16: //      1. Not all specializations are supplied
Chris@16: //
Chris@16: //      2. Use of specializations that are not supplied will cause a
Chris@16: //      compile-time error
Chris@16: //
Chris@16: //      3. Users are free to specialize numeric_traits for any type.
Chris@16: //
Chris@16: //      4. Right now, specializations are only supplied for integer types.
Chris@16: //
Chris@16: //      5. On implementations which do not supply compile-time constants in
Chris@16: //      std::numeric_limits<>, only specializations for built-in integer types
Chris@16: //      are supplied.
Chris@16: //
Chris@16: //      6. Handling of numbers whose range of representation is at least as
Chris@16: //      great as boost::intmax_t can cause some differences to be
Chris@16: //      unrepresentable in difference_type:
Chris@16: //
Chris@16: //        Number    difference_type
Chris@16: //        ------    ---------------
Chris@16: //        signed    Number
Chris@16: //        unsigned  intmax_t
Chris@16: //
Chris@16: // template <class Number> typename numeric_traits<Number>::difference_type
Chris@16: // numeric_distance(Number x, Number y)
Chris@16: //    computes (y - x), attempting to avoid overflows.
Chris@16: //
Chris@16: 
Chris@16: // See http://www.boost.org for most recent version including documentation.
Chris@16: 
Chris@16: // Revision History
Chris@16: // 11 Feb 2001 - Use BOOST_STATIC_CONSTANT (David Abrahams)
Chris@16: // 11 Feb 2001 - Rolled back ineffective Borland-specific code
Chris@16: //               (David Abrahams)
Chris@16: // 10 Feb 2001 - Rolled in supposed Borland fixes from John Maddock, but
Chris@16: //               not seeing any improvement yet (David Abrahams)
Chris@16: // 06 Feb 2001 - Factored if_true out into boost/detail/select_type.hpp
Chris@16: //               (David Abrahams)
Chris@16: // 23 Jan 2001 - Fixed logic of difference_type selection, which was
Chris@16: //               completely wack. In the process, added digit_traits<>
Chris@16: //               to compute the number of digits in intmax_t even when
Chris@16: //               not supplied by numeric_limits<>. (David Abrahams)
Chris@16: // 21 Jan 2001 - Created (David Abrahams)
Chris@16: 
Chris@16: #ifndef BOOST_NUMERIC_TRAITS_HPP_DWA20001901
Chris@16: # define BOOST_NUMERIC_TRAITS_HPP_DWA20001901
Chris@16: 
Chris@16: # include <boost/config.hpp>
Chris@16: # include <boost/cstdint.hpp>
Chris@16: # include <boost/static_assert.hpp>
Chris@16: # include <boost/type_traits.hpp>
Chris@16: # include <boost/detail/select_type.hpp>
Chris@16: # include <boost/limits.hpp>
Chris@16: 
Chris@16: namespace boost { namespace detail {
Chris@16: 
Chris@16:   // Template class is_signed -- determine whether a numeric type is signed
Chris@16:   // Requires that T is constructable from the literals -1 and 0.  Compile-time
Chris@16:   // error results if that requirement is not met (and thus signedness is not
Chris@16:   // likely to have meaning for that type).
Chris@16:   template <class Number>
Chris@16:   struct is_signed
Chris@16:   {
Chris@101: #if defined(BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS)
Chris@16:     BOOST_STATIC_CONSTANT(bool, value = (Number(-1) < Number(0)));
Chris@16: #else
Chris@16:     BOOST_STATIC_CONSTANT(bool, value = std::numeric_limits<Number>::is_signed);
Chris@16: #endif
Chris@16:   };
Chris@16: 
Chris@16: # ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
Chris@16:   // digit_traits - compute the number of digits in a built-in integer
Chris@16:   // type. Needed for implementations on which numeric_limits is not specialized
Chris@16:   // for intmax_t (e.g. VC6).
Chris@16:   template <bool is_specialized> struct digit_traits_select;
Chris@16: 
Chris@16:   // numeric_limits is specialized; just select that version of digits
Chris@16:   template <> struct digit_traits_select<true>
Chris@16:   {
Chris@16:       template <class T> struct traits
Chris@16:       {
Chris@16:           BOOST_STATIC_CONSTANT(int, digits = std::numeric_limits<T>::digits);
Chris@16:       };
Chris@16:   };
Chris@16: 
Chris@16:   // numeric_limits is not specialized; compute digits from sizeof(T)
Chris@16:   template <> struct digit_traits_select<false>
Chris@16:   {
Chris@16:       template <class T> struct traits
Chris@16:       {
Chris@16:           BOOST_STATIC_CONSTANT(int, digits = (
Chris@16:               sizeof(T) * std::numeric_limits<unsigned char>::digits
Chris@16:               - (is_signed<T>::value ? 1 : 0))
Chris@16:               );
Chris@16:       };
Chris@16:   };
Chris@16: 
Chris@16:   // here's the "usable" template
Chris@16:   template <class T> struct digit_traits
Chris@16:   {
Chris@16:       typedef digit_traits_select<
Chris@16:                 ::std::numeric_limits<T>::is_specialized> selector;
Chris@16:       typedef typename selector::template traits<T> traits;
Chris@16:       BOOST_STATIC_CONSTANT(int, digits = traits::digits);
Chris@16:   };
Chris@16: #endif
Chris@16: 
Chris@16:   // Template class integer_traits<Integer> -- traits of various integer types
Chris@16:   // This should probably be rolled into boost::integer_traits one day, but I
Chris@16:   // need it to work without <limits>
Chris@16:   template <class Integer>
Chris@16:   struct integer_traits
Chris@16:   {
Chris@16: # ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
Chris@16:    private:
Chris@16:       typedef Integer integer_type;
Chris@16:       typedef std::numeric_limits<integer_type> x;
Chris@16:    public:
Chris@16:       typedef typename
Chris@16:       if_true<(int(x::is_signed)
Chris@16:               && (!int(x::is_bounded)
Chris@16:                  // digits is the number of no-sign bits
Chris@16:                   || (int(x::digits) + 1 >= digit_traits<boost::intmax_t>::digits)))>::template then<
Chris@16:         Integer,
Chris@16:           
Chris@16:       typename if_true<(int(x::digits) + 1 < digit_traits<signed int>::digits)>::template then<
Chris@16:         signed int,
Chris@16: 
Chris@16:       typename if_true<(int(x::digits) + 1 < digit_traits<signed long>::digits)>::template then<
Chris@16:         signed long,
Chris@16: 
Chris@16:    // else
Chris@16:         intmax_t
Chris@16:       >::type>::type>::type difference_type;
Chris@16: #else
Chris@16:       BOOST_STATIC_ASSERT(boost::is_integral<Integer>::value);
Chris@16: 
Chris@16:       typedef typename
Chris@16:       if_true<(sizeof(Integer) >= sizeof(intmax_t))>::template then<
Chris@16:                
Chris@16:         typename if_true<(is_signed<Integer>::value)>::template then<
Chris@16:           Integer,
Chris@16:           intmax_t
Chris@16:         >::type,
Chris@16: 
Chris@16:         typename if_true<(sizeof(Integer) < sizeof(std::ptrdiff_t))>::template then<
Chris@16:           std::ptrdiff_t,
Chris@16:           intmax_t
Chris@16:         >::type
Chris@16:       >::type difference_type;
Chris@16: # endif
Chris@16:   };
Chris@16: 
Chris@16:   // Right now, only supports integers, but should be expanded.
Chris@16:   template <class Number>
Chris@16:   struct numeric_traits
Chris@16:   {
Chris@16:       typedef typename integer_traits<Number>::difference_type difference_type;
Chris@16:   };
Chris@16: 
Chris@16:   template <class Number>
Chris@16:   typename numeric_traits<Number>::difference_type numeric_distance(Number x, Number y)
Chris@16:   {
Chris@16:       typedef typename numeric_traits<Number>::difference_type difference_type;
Chris@16:       return difference_type(y) - difference_type(x);
Chris@16:   }
Chris@16: }}
Chris@16: 
Chris@16: #endif // BOOST_NUMERIC_TRAITS_HPP_DWA20001901