indexsequence.h

/*  This file is part of the Vc library. {{{
Copyright © 2014-2015 Matthias Kretz <kretz@kde.org>

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
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      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.
    * Neither the names of contributing organizations nor the
      names of its contributors may be used to endorse or promote products
      derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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}}}*/

#ifndef VC_COMMON_INDEXSEQUENCE_H_
#define VC_COMMON_INDEXSEQUENCE_H_

#include <Vc/global.h>

namespace Vc_VERSIONED_NAMESPACE
{
template <std::size_t... I> struct index_sequence
{
    static constexpr std::size_t size() noexcept { return sizeof...(I); }
};

template <std::size_t N> struct make_index_sequence_impl {
    template <std::size_t Offset, std::size_t... Ns>
    static index_sequence<Ns..., (Ns + Offset)...> join(std::false_type,
                                                        index_sequence<Ns...>);
    template <std::size_t Offset, std::size_t... Ns>
    static index_sequence<Ns..., Offset - 1, (Ns + Offset)...> join(
        std::true_type, index_sequence<Ns...>);

    using is_odd = std::integral_constant<bool, N & 1>;
    using half = typename make_index_sequence_impl<N / 2>::type;
    using type = decltype(join<(N + 1) / 2>(is_odd(), half()));
};
template <> struct make_index_sequence_impl<0> {
    using type = index_sequence<>;
};
template <> struct make_index_sequence_impl<1> {
    using type = index_sequence<0>;
};
template <> struct make_index_sequence_impl<2> {
    using type = index_sequence<0, 1>;
};

template <std::size_t N>
using make_index_sequence = typename make_index_sequence_impl<N>::type;
}

#endif  // VC_COMMON_INDEXSEQUENCE_H_

// vim: foldmethod=marker