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https://gitlab.kitware.com/vtk/vtk-m
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5773ea3e13
Currently, VTK-m is using C++11. However, it is often useful to use features in the `std` namespace that are defined for C++14 or later. We can provide our own versions (sometimes), but it is preferable to use the version provided by the compiler if available. There were already some examples of defining portable versions of C++14 and C++17 classes in a `vtkmstd` namespace, but these were sprinkled around the source code. There is now a top level `vtkmstd` directory and in it are header files that provide portable versions of these future C++ classes. In each case, preprocessor macros are used to select which version of the class to use.
70 lines
1.8 KiB
C++
70 lines
1.8 KiB
C++
//============================================================================
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// Copyright (c) Kitware, Inc.
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// All rights reserved.
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// See LICENSE.txt for details.
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//
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// This software is distributed WITHOUT ANY WARRANTY; without even
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// the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
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// PURPOSE. See the above copyright notice for more information.
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//============================================================================
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#ifndef vtk_m_std_aligned_union_h
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#define vtk_m_std_aligned_union_h
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#include <vtkm/internal/Configure.h>
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#include <type_traits>
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#if defined(VTKM_USING_GLIBCXX_4)
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#include <algorithm>
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namespace vtkmstd
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{
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template <std::size_t... Xs>
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struct max_size;
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template <std::size_t X>
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struct max_size<X>
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{
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static constexpr std::size_t value = X;
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};
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template <std::size_t X0, std::size_t... Xs>
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struct max_size<X0, Xs...>
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{
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static constexpr std::size_t other_value = max_size<Xs...>::value;
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static constexpr std::size_t value = (other_value > X0) ? other_value : X0;
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};
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// This is to get around an apparent bug in GCC 4.8 where alianas(x) does not
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// seem to work when x is a constexpr. See
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// https://stackoverflow.com/questions/29879609/g-complains-constexpr-function-is-not-a-constant-expression
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template <std::size_t Alignment, std::size_t Size>
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struct aligned_data_block
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{
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alignas(Alignment) char _s[Size];
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};
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template <std::size_t Len, class... Types>
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struct aligned_union
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{
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static constexpr std::size_t alignment_value = vtkmstd::max_size<alignof(Types)...>::value;
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using type =
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vtkmstd::aligned_data_block<alignment_value, vtkmstd::max_size<Len, sizeof(Types)...>::value>;
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};
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} // namespace vtkmstd
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#else // NOT VTKM_USING_GLIBCXX_4
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namespace vtkmstd
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{
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using std::aligned_union;
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} // namespace vtkmstd
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#endif // NOT VTKM_USING_GLIBCXX_4
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#endif //vtk_m_std_aligned_union_h
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