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include/boost/iterator/counting_iterator.hpp
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include/boost/iterator/counting_iterator.hpp
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// Copyright David Abrahams 2003.
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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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#ifndef BOOST_ITERATOR_COUNTING_ITERATOR_DWA200348_HPP
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#define BOOST_ITERATOR_COUNTING_ITERATOR_DWA200348_HPP
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#include <limits>
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#include <type_traits>
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#include <boost/config.hpp>
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#include <boost/core/use_default.hpp>
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#include <boost/detail/numeric_traits.hpp>
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#include <boost/iterator/iterator_adaptor.hpp>
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#include <boost/iterator/iterator_categories.hpp>
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#include <boost/iterator/detail/if_default.hpp>
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#include <boost/iterator/detail/eval_if_default.hpp>
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#include <boost/iterator/detail/type_traits/type_identity.hpp>
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namespace boost {
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namespace iterators {
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template<
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typename Incrementable,
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typename CategoryOrTraversal,
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typename Difference
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>
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class counting_iterator;
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namespace detail {
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// Try to detect numeric types at compile time in ways compatible
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// with the limitations of the compiler and library.
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template< typename T >
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struct is_numeric :
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public std::integral_constant< bool, std::numeric_limits< T >::is_specialized >
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{};
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template<>
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struct is_numeric< long long > :
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public std::true_type
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{};
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template<>
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struct is_numeric< unsigned long long > :
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public std::true_type
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{};
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#if defined(BOOST_HAS_INT128)
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template<>
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struct is_numeric< boost::int128_type > :
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public std::true_type
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{};
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template<>
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struct is_numeric< boost::uint128_type > :
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public std::true_type
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{};
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#endif
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// Some compilers fail to have a numeric_limits specialization
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template<>
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struct is_numeric< wchar_t > :
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public std::true_type
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{};
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template< typename T >
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struct numeric_difference
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{
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using type = typename boost::detail::numeric_traits< T >::difference_type;
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};
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#if defined(BOOST_HAS_INT128)
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// std::numeric_limits, which is used by numeric_traits, is not specialized for __int128 in some standard libraries
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template<>
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struct numeric_difference< boost::int128_type >
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{
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using type = boost::int128_type;
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};
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template<>
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struct numeric_difference< boost::uint128_type >
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{
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using type = boost::int128_type;
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};
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#endif
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template< typename Incrementable, typename CategoryOrTraversal, typename Difference, bool IsNumeric = is_numeric< Incrementable >::value >
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struct counting_iterator_types
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{
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using traversal = detail::eval_if_default_t<
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CategoryOrTraversal,
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iterator_traversal< Incrementable >
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>;
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using difference = detail::eval_if_default_t<
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Difference,
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iterator_difference< Incrementable >
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>;
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};
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template< typename Incrementable, typename CategoryOrTraversal, typename Difference >
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struct counting_iterator_types< Incrementable, CategoryOrTraversal, Difference, true >
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{
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using traversal = detail::if_default_t<
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CategoryOrTraversal,
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random_access_traversal_tag
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>;
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using difference = detail::eval_if_default_t<
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Difference,
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numeric_difference< Incrementable >
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>;
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};
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template< typename Incrementable, typename CategoryOrTraversal, typename Difference >
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struct counting_iterator_base
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{
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using iterator_types = counting_iterator_types< Incrementable, CategoryOrTraversal, Difference >;
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using type = iterator_adaptor<
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counting_iterator< Incrementable, CategoryOrTraversal, Difference >, // self
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Incrementable, // Base
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#ifndef BOOST_ITERATOR_REF_CONSTNESS_KILLS_WRITABILITY
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const // MSVC won't strip this. Instead we enable Thomas'
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// criterion (see boost/iterator/detail/facade_iterator_category.hpp)
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#endif
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Incrementable, // Value
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typename iterator_types::traversal,
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Incrementable const&, // reference
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typename iterator_types::difference
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>;
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};
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// A distance calculation policy for wrapped iterators
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template< typename Difference, typename Incrementable1, typename Incrementable2 >
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struct iterator_distance
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{
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static Difference distance(Incrementable1 x, Incrementable2 y)
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{
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return y - x;
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}
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};
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// A distance calculation policy for wrapped numbers
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template< typename Difference, typename Incrementable1, typename Incrementable2 >
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struct number_distance
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{
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static Difference distance(Incrementable1 x, Incrementable2 y)
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{
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return boost::detail::numeric_distance(x, y);
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}
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};
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} // namespace detail
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template<
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typename Incrementable,
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typename CategoryOrTraversal = use_default,
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typename Difference = use_default
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>
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class counting_iterator :
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public detail::counting_iterator_base< Incrementable, CategoryOrTraversal, Difference >::type
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{
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friend class iterator_core_access;
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private:
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using super_t = typename detail::counting_iterator_base<
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Incrementable, CategoryOrTraversal, Difference
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>::type;
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public:
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using reference = typename super_t::reference;
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using difference_type = typename super_t::difference_type;
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counting_iterator() = default;
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counting_iterator(counting_iterator const&) = default;
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counting_iterator& operator=(counting_iterator const&) = default;
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counting_iterator(Incrementable x) :
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super_t(x)
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{
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}
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private:
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reference dereference() const
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{
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return this->base_reference();
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}
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template< typename OtherIncrementable >
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difference_type
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distance_to(counting_iterator< OtherIncrementable, CategoryOrTraversal, Difference > const& y) const
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{
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using distance_traits = typename std::conditional<
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detail::is_numeric< Incrementable >::value,
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detail::number_distance< difference_type, Incrementable, OtherIncrementable >,
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detail::iterator_distance< difference_type, Incrementable, OtherIncrementable >
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>::type;
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return distance_traits::distance(this->base(), y.base());
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}
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};
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// Manufacture a counting iterator for an arbitrary incrementable type
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template< typename Incrementable >
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inline counting_iterator< Incrementable > make_counting_iterator(Incrementable x)
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{
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return counting_iterator< Incrementable >(x);
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}
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} // namespace iterators
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using iterators::counting_iterator;
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using iterators::make_counting_iterator;
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} // namespace boost
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#endif // BOOST_ITERATOR_COUNTING_ITERATOR_DWA200348_HPP
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