192 lines
6.6 KiB
C++
192 lines
6.6 KiB
C++
// (C) Copyright David Abrahams 2001, Howard Hinnant 2001.
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//
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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// Template class numeric_traits<Number> --
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//
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// Supplies:
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//
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// typedef difference_type -- a type used to represent the difference
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// between any two values of Number.
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//
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// Support:
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// 1. Not all specializations are supplied
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//
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// 2. Use of specializations that are not supplied will cause a
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// compile-time error
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//
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// 3. Users are free to specialize numeric_traits for any type.
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//
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// 4. Right now, specializations are only supplied for integer types.
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//
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// 5. On implementations which do not supply compile-time constants in
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// std::numeric_limits<>, only specializations for built-in integer types
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// are supplied.
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//
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// 6. Handling of numbers whose range of representation is at least as
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// great as boost::intmax_t can cause some differences to be
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// unrepresentable in difference_type:
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//
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// Number difference_type
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// ------ ---------------
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// signed Number
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// unsigned intmax_t
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//
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// template <class Number> typename numeric_traits<Number>::difference_type
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// numeric_distance(Number x, Number y)
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// computes (y - x), attempting to avoid overflows.
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//
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// See http://www.boost.org for most recent version including documentation.
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// Revision History
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// 11 Feb 2001 - Use BOOST_STATIC_CONSTANT (David Abrahams)
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// 11 Feb 2001 - Rolled back ineffective Borland-specific code
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// (David Abrahams)
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// 10 Feb 2001 - Rolled in supposed Borland fixes from John Maddock, but
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// not seeing any improvement yet (David Abrahams)
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// 06 Feb 2001 - Factored if_true out into boost/detail/select_type.hpp
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// (David Abrahams)
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// 23 Jan 2001 - Fixed logic of difference_type selection, which was
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// completely wack. In the process, added digit_traits<>
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// to compute the number of digits in intmax_t even when
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// not supplied by numeric_limits<>. (David Abrahams)
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// 21 Jan 2001 - Created (David Abrahams)
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#ifndef BOOST_NUMERIC_TRAITS_HPP_DWA20001901
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# define BOOST_NUMERIC_TRAITS_HPP_DWA20001901
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# include <boost/config.hpp>
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# include <boost/cstdint.hpp>
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# include <boost/static_assert.hpp>
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# include <boost/type_traits.hpp>
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# include <boost/detail/select_type.hpp>
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# include <boost/limits.hpp>
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namespace boost { namespace detail {
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// Template class is_signed -- determine whether a numeric type is signed
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// Requires that T is constructable from the literals -1 and 0. Compile-time
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// error results if that requirement is not met (and thus signedness is not
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// likely to have meaning for that type).
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template <class Number>
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struct is_signed
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{
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#if defined(BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS) || defined(BOOST_MSVC) && BOOST_MSVC <= 1300
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BOOST_STATIC_CONSTANT(bool, value = (Number(-1) < Number(0)));
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#else
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BOOST_STATIC_CONSTANT(bool, value = std::numeric_limits<Number>::is_signed);
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#endif
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};
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# ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
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// digit_traits - compute the number of digits in a built-in integer
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// type. Needed for implementations on which numeric_limits is not specialized
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// for intmax_t (e.g. VC6).
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template <bool is_specialized> struct digit_traits_select;
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// numeric_limits is specialized; just select that version of digits
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template <> struct digit_traits_select<true>
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{
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template <class T> struct traits
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{
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BOOST_STATIC_CONSTANT(int, digits = std::numeric_limits<T>::digits);
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};
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};
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// numeric_limits is not specialized; compute digits from sizeof(T)
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template <> struct digit_traits_select<false>
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{
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template <class T> struct traits
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{
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BOOST_STATIC_CONSTANT(int, digits = (
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sizeof(T) * std::numeric_limits<unsigned char>::digits
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- (is_signed<T>::value ? 1 : 0))
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);
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};
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};
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// here's the "usable" template
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template <class T> struct digit_traits
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{
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typedef digit_traits_select<
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::std::numeric_limits<T>::is_specialized> selector;
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typedef typename selector::template traits<T> traits;
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BOOST_STATIC_CONSTANT(int, digits = traits::digits);
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};
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#endif
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// Template class integer_traits<Integer> -- traits of various integer types
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// This should probably be rolled into boost::integer_traits one day, but I
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// need it to work without <limits>
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template <class Integer>
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struct integer_traits
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{
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# ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
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private:
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typedef Integer integer_type;
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typedef std::numeric_limits<integer_type> x;
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# if defined(BOOST_MSVC) && BOOST_MSVC <= 1300
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// for some reason, MSVC asserts when it shouldn't unless we make these
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// local definitions
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BOOST_STATIC_CONSTANT(bool, is_integer = x::is_integer);
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BOOST_STATIC_CONSTANT(bool, is_specialized = x::is_specialized);
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BOOST_STATIC_ASSERT(is_integer);
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BOOST_STATIC_ASSERT(is_specialized);
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# endif
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public:
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typedef typename
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if_true<(int(x::is_signed)
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&& (!int(x::is_bounded)
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// digits is the number of no-sign bits
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|| (int(x::digits) + 1 >= digit_traits<boost::intmax_t>::digits)))>::template then<
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Integer,
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typename if_true<(int(x::digits) + 1 < digit_traits<signed int>::digits)>::template then<
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signed int,
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typename if_true<(int(x::digits) + 1 < digit_traits<signed long>::digits)>::template then<
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signed long,
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// else
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intmax_t
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>::type>::type>::type difference_type;
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#else
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BOOST_STATIC_ASSERT(boost::is_integral<Integer>::value);
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typedef typename
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if_true<(sizeof(Integer) >= sizeof(intmax_t))>::template then<
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typename if_true<(is_signed<Integer>::value)>::template then<
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Integer,
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intmax_t
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>::type,
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typename if_true<(sizeof(Integer) < sizeof(std::ptrdiff_t))>::template then<
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std::ptrdiff_t,
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intmax_t
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>::type
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>::type difference_type;
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# endif
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};
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// Right now, only supports integers, but should be expanded.
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template <class Number>
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struct numeric_traits
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{
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typedef typename integer_traits<Number>::difference_type difference_type;
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};
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template <class Number>
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typename numeric_traits<Number>::difference_type numeric_distance(Number x, Number y)
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{
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typedef typename numeric_traits<Number>::difference_type difference_type;
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return difference_type(y) - difference_type(x);
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}
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}}
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#endif // BOOST_NUMERIC_TRAITS_HPP_DWA20001901
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