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