Vc/common/indexsequence.h

0001 /*  This file is part of the Vc library. {{{
0002 Copyright © 2014-2015 Matthias Kretz <kretz@kde.org>
0003
0004 Redistribution and use in source and binary forms, with or without
0005 modification, are permitted provided that the following conditions are met:
0006     * Redistributions of source code must retain the above copyright
0007       notice, this list of conditions and the following disclaimer.
0008     * Redistributions in binary form must reproduce the above copyright
0009       notice, this list of conditions and the following disclaimer in the
0010       documentation and/or other materials provided with the distribution.
0011     * Neither the names of contributing organizations nor the
0012       names of its contributors may be used to endorse or promote products
0013       derived from this software without specific prior written permission.
0014
0015 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
0016 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
0017 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
0018 DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE FOR ANY
0019 DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
0020 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
0021 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
0022 ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
0023 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
0024 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
0025
0026 }}}*/
0027
0028 #ifndef VC_COMMON_INDEXSEQUENCE_H_
0029 #define VC_COMMON_INDEXSEQUENCE_H_
0030
0031 #include "../global.h"
0032
0033 namespace Vc_VERSIONED_NAMESPACE
0034 {
0035 /** \internal
0036  * Helper class for a sequence of size_t values from 0 to N. This type will be included in
0037  * C++14.
0038  */
0039 template <std::size_t... I> struct index_sequence
0040 {
0041     static constexpr std::size_t size() noexcept { return sizeof...(I); }
0042 };
0043
0044 /** \internal
0045  * This struct builds an index_sequence type from a given upper bound \p N.
0046  * It does so recursively via concatenation of to index sequences of length N/2.
0047  */
0048 template <std::size_t N> struct make_index_sequence_impl {
0049     template <std::size_t Offset, std::size_t... Ns>
0050     static index_sequence<Ns..., (Ns + Offset)...> join(std::false_type,
0051                                                         index_sequence<Ns...>);
0052     template <std::size_t Offset, std::size_t... Ns>
0053     static index_sequence<Ns..., Offset - 1, (Ns + Offset)...> join(
0054         std::true_type, index_sequence<Ns...>);
0055
0056     using is_odd = std::integral_constant<bool, N & 1>;
0057     using half = typename make_index_sequence_impl<N / 2>::type;
0058     using type = decltype(join<(N + 1) / 2>(is_odd(), half()));
0059 };
0060 template <> struct make_index_sequence_impl<0> {
0061     using type = index_sequence<>;
0062 };
0063 template <> struct make_index_sequence_impl<1> {
0064     using type = index_sequence<0>;
0065 };
0066 template <> struct make_index_sequence_impl<2> {
0067     using type = index_sequence<0, 1>;
0068 };
0069
0070 /** \internal
0071  * Creates an index_sequence type for the upper bound \p N.
0072  */
0073 template <std::size_t N>
0074 using make_index_sequence = typename make_index_sequence_impl<N>::type;
0075 }
0076
0077 #endif  // VC_COMMON_INDEXSEQUENCE_H_
0078
0079 // vim: foldmethod=marker