/*=============================================================================
    Copyright (c) 2015 Agustin K-ballo Berge
    Copyright (c) 2015 Kohei Takahashi

    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)
==============================================================================*/

#ifndef BOOST_FUSION_SUPPORT_DETAIL_INDEX_SEQUENCE_06232015_1038
#define BOOST_FUSION_SUPPORT_DETAIL_INDEX_SEQUENCE_06232015_1038

#include <boost/fusion/support/config.hpp>
#include <cstddef>

// GCC5 has O(logN) implementation, see https://gcc.gnu.org/PR66059 .
#if (defined(__cpp_lib_integer_sequence) && __cpp_lib_integer_sequence >= 201304) \
 || (defined(BOOST_LIBSTDCXX_VERSION) \
     && BOOST_LIBSTDCXX_VERSION >= 500000 && __cplusplus >= 201402)
#include <utility>
#define BOOST_FUSION_STDLIB_HAS_INTEGER_SEQUENCE
#endif

namespace boost {
namespace fusion {
namespace detail {
#ifdef BOOST_FUSION_STDLIB_HAS_INTEGER_SEQUENCE
// Use aliasing templates without checking availability, the compiler should work.
template <std::size_t ...Ints>
using index_sequence = std::index_sequence<Ints...>;

template <std::size_t N>
struct make_index_sequence
{
    using type = std::make_index_sequence<N>;
};
#else
template <std::size_t ...Ints>
struct index_sequence
{
    typedef std::size_t value_type;

    BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
    static std::size_t
    size() BOOST_NOEXCEPT
    { return sizeof...(Ints); }

    // non standard extension
    typedef index_sequence type;
};

template <typename Left, typename Right>
struct _make_index_sequence_join;

template <std::size_t... Left, std::size_t... Right>
struct _make_index_sequence_join<
    index_sequence<Left...>, index_sequence<Right...>
> : index_sequence<Left..., (sizeof...(Left) + Right)...>
{};

template <std::size_t N>
struct make_index_sequence
    : _make_index_sequence_join<
      typename make_index_sequence<N / 2>::type
    , typename make_index_sequence<N - N / 2>::type
    >
{};

template <>
struct make_index_sequence<1>
    : index_sequence<0>
{};

template <>
struct make_index_sequence<0>
    : index_sequence<>
{};
#endif
}
}
}

#endif
