// Copyright (c) 2018 Sergei Fedorov
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// Copyright (c) 2019-2020 Antony Polukhin
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_PFR_DETAIL_MAKE_INTEGER_SEQUENCE_HPP
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#define BOOST_PFR_DETAIL_MAKE_INTEGER_SEQUENCE_HPP
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#pragma once
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#include <boost/pfr/detail/config.hpp>
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#include <type_traits>
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#include <utility>
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#include <cstddef>
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namespace boost { namespace pfr { namespace detail {
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#if BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE == 0
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#ifdef __has_builtin
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# if __has_builtin(__make_integer_seq)
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# define BOOST_PFR_USE_MAKE_INTEGER_SEQ_BUILTIN
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# endif
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#endif
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#ifdef BOOST_PFR_USE_MAKE_INTEGER_SEQ_BUILTIN
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using std::integer_sequence;
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// Clang unable to use namespace qualified std::integer_sequence in __make_integer_seq.
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template <typename T, T N>
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using make_integer_sequence = __make_integer_seq<integer_sequence, T, N>;
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#undef BOOST_PFR_USE_MAKE_INTEGER_SEQ_BUILTIN
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#else
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template <typename T, typename U>
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struct join_sequences;
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template <typename T, T... A, T... B>
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struct join_sequences<std::integer_sequence<T, A...>, std::integer_sequence<T, B...>> {
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using type = std::integer_sequence<T, A..., B...>;
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};
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template <typename T, T Min, T Max>
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struct build_sequence_impl {
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static_assert(Min < Max, "Start of range must be less than its end");
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static constexpr T size = Max - Min;
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using type = typename join_sequences<
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typename build_sequence_impl<T, Min, Min + size / 2>::type,
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typename build_sequence_impl<T, Min + size / 2 + 1, Max>::type
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>::type;
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};
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template <typename T, T V>
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struct build_sequence_impl<T, V, V> {
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using type = std::integer_sequence<T, V>;
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};
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template <typename T, std::size_t N>
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struct make_integer_sequence_impl : build_sequence_impl<T, 0, N - 1> {};
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template <typename T>
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struct make_integer_sequence_impl<T, 0> {
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using type = std::integer_sequence<T>;
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};
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template <typename T, T N>
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using make_integer_sequence = typename make_integer_sequence_impl<T, N>::type;
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#endif // !defined BOOST_PFR_USE_MAKE_INTEGER_SEQ_BUILTIN
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#else // BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE == 1
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template <typename T, T N>
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using make_integer_sequence = std::make_integer_sequence<T, N>;
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#endif // BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE == 1
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template <std::size_t N>
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using make_index_sequence = make_integer_sequence<std::size_t, N>;
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template <typename... T>
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using index_sequence_for = make_index_sequence<sizeof...(T)>;
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}}} // namespace boost::pfr::detail
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#endif
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