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37 * \brief Declares MultiDimArray.
39 * \author Christian Blau <cblau@gwdg.de>
40 * \ingroup module_math
41 * \ingroup module_mdspan
45 #ifndef GMX_MATH_MULTIDIMARRAY_H_
46 #define GMX_MATH_MULTIDIMARRAY_H_
48 #include "gromacs/mdspan/mdspan.h"
49 #include "gromacs/utility/arrayref.h"
56 //! Same as std::void_t from C++17
60 template<typename T, typename = void>
61 struct is_resizable : std::false_type
66 struct is_resizable<T, void_t<decltype(std::declval<T>().resize(size_t()))>> : std::true_type
70 //! Type has a resize member function callable with size_t argument
72 constexpr bool is_resizable_v = is_resizable<T>::value;
75 /*! \libinternal \brief
76 * Multidimensional array that manages its own memory.
78 * \note No bounds checking when accessing memory
80 * \note That the view holds a valid pointer to the data is a class invariant.
82 * The Container type that stores the data may be resizable (std::vector or similar)
83 * or static (std::array or similar). Copy and move assignment routines as well as
84 * swapping are designed to yield good performances in both cases, notably
85 * foregoing the copy-swap idiom due to the bad performance in swapping std::array.
87 * This class avoids throwing exeptions, apart from the ones that might be thrown
88 * from the containers during resizing an allocation. (bad_malloc from std::vector
89 * is a likely candidate)
92 * Holds as many elements as required by a multidimensional view.
93 * \tparam TContainer Data type container for the data to be stored
94 * as MultiDimArray with random element access and
95 * value_type, refence and const_reference exposed
96 * \tparam Extents An extents class describing the array dimensions
97 * as used in module_mdspan
98 * \tparam LayoutPolicy The data layout as in module_mdspan describes
99 * translation of indices to memory offset.
100 * Defaults to right aligned, so that the right-most index
101 * is contiguous in memory.
103 template<class TContainer, class Extents, class LayoutPolicy = layout_right>
107 //! the type of values that are stored
108 using value_type = typename TContainer::value_type;
109 //! reference type to the stored values
110 using reference = typename TContainer::reference;
111 //! const reference type to the stored values
112 using const_reference = typename TContainer::const_reference;
113 //! the view used to access the data
114 using view_type = basic_mdspan<value_type, Extents, LayoutPolicy>;
115 //! const view on the data
116 using const_view_type = basic_mdspan<const value_type, Extents, LayoutPolicy>;
117 /*! \brief Iterator type for contiguous iteration over the stored data.
118 * Used, e.g., in free begin and end functions
120 using iterator = typename ArrayRef<value_type>::iterator;
121 /*! \brief Const iterator type for contiguous iteration over the stored data.
122 * used, e.g., in free begin and end functions
124 using const_iterator = const typename ArrayRef<const value_type>::const_iterator;
126 static_assert(detail::is_resizable_v<TContainer> == (Extents::rank_dynamic() > 0),
127 "Resizable container (e.g. std::vector) requires at least one dynamic rank. "
128 "Non-resizable container (e.g. std::array) requires zero dynamic ranks.");
131 * Allocate dynamic array data and set view with the dynamic extents.
133 * \param[in] dynamicExtent A parameter pack that describes the dynamic
134 * size of the array. Empty if purely static.
136 * \tparam IndexType Parameter pack type holding the dynamic
137 * extents of the multidimensional array
139 template<class... IndexType, typename T = TContainer, typename = typename std::enable_if_t<detail::is_resizable_v<T>>>
140 MultiDimArray(IndexType... dynamicExtent)
142 resize(dynamicExtent...);
145 * Construction from fixed sized arrays if the array size is static and
146 * layout policy allows compile time determination of the container size.
148 * Enables the expected initialization
149 * MultiDimArray<std::array<float, 9>, extents<3,3>> arr = {{1,2...}}
150 * \tparam T Template parameter for activation via SFINAE.
152 // SFINAE required because std::vector::size isn't constexpr and is_constexpr doesn't exist.
153 template<typename T = TContainer, typename = typename std::enable_if_t<!detail::is_resizable_v<T>>>
154 constexpr MultiDimArray(const TContainer& data = {}) noexcept : data_(data), view_(data_.data())
156 static_assert(TContainer().size() == typename view_type::mapping_type().required_span_size(),
157 "Non-resizable container type size must match static MultiDimArray size.");
160 constexpr MultiDimArray(const MultiDimArray& o) :
162 view_(data_.data(), o.view_.extents())
166 MultiDimArray(MultiDimArray&& o) noexcept :
167 data_(std::move(o.data_)),
168 view_(data_.data(), o.view_.extents())
172 MultiDimArray& operator=(const MultiDimArray& o)
175 view_ = view_type(data_.data(), o.view_.extents());
179 MultiDimArray& operator=(MultiDimArray&& o) noexcept
181 data_ = std::move(o.data_);
182 view_ = view_type(data_.data(), o.view_.extents());
185 //! Swaps content with other
186 void swap(MultiDimArray& o)
189 swap(data_, o.data_);
190 // swap(view_, o.view_) also swaps the pointer to the data and thus does not work
191 // instead, restore the view as class invariant after the data swapping operation
192 o.view_ = view_type(o.data_.data(), view_.extents());
193 view_ = view_type(data_.data(), o.view_.extents());
196 * Resize the dynamic extents of the array if any and set container size
199 * Invalidates data and views of this array.
201 * \param[in] dynamicExtent A parameter pack that describes the dynamic
202 * size of the array. Empty if purely static.
203 * \tparam IndexType Parameter pack type holding the dynamic
204 * extents of the multidimensional array
206 template<class... IndexType>
207 void resize(IndexType... dynamicExtent)
209 // use a mapping object to determine the required span size;
210 layout_right::mapping<Extents> map{ Extents{ dynamicExtent... } };
211 data_.resize(map.required_span_size());
212 // to construct a valid view on the data, the container has to be resized before
213 // the assignment, so that data_.data() is valid
214 view_ = view_type(data_.data(), dynamicExtent...);
216 /*! \brief Data access via multidimensional indices.
217 * This allows referencing rank R array elements as array(x_0,x_1,x_2, .., x_R)
219 * \param[in] index multidimensional indices as parameter pack
220 * the number of parameters must match the rank of the array.
222 * \returns reference to array element
224 template<class... IndexType>
225 reference operator()(IndexType... index) noexcept
227 return view_(index...);
229 /*! \brief Const data access via multidimensional indices.
230 * This allows referencing rank R array elements as array(x_0,x_1,x_2, .., x_R)
232 * \param[in] index multidimensional indices as parameter pack
233 * the number of parameters must match the rank of the array.
235 * \returns const reference to array element
237 template<class... IndexType>
238 constexpr const_reference operator()(IndexType... index) const noexcept
240 return view_(index...);
242 /*! \brief Contiguous access to the data.
243 * \returns ArrayRef to stored data.
245 ArrayRef<value_type> toArrayRef() { return { data_.data(), data_.data() + data_.size() }; }
246 /*! \brief Contiguous const access to the data.
247 * \returns ArrayRef to stored data.
249 constexpr ArrayRef<const value_type> toArrayRef() const
251 return { data_.data(), data_.data() + data_.size() };
253 /*! \brief Return the extent.
254 * \param[in] k dimension to query for extent
255 * \returns extent along specified dimension
257 constexpr typename view_type::index_type extent(int k) const noexcept
259 return view_.extent(k);
261 //! Conversion to multidimensional view on the data
262 constexpr view_type asView() noexcept { return view_; }
263 //! Conversion to const multidimensional view on the data
264 constexpr const_view_type asConstView() const noexcept
266 return { data_.data(), view_.mapping() };
270 //! The contiguous data that is equipped with multidimensional indexing in this class
272 //! Multidimensional view into data_.
276 //! Free MultiDimArray begin function addressing its contiguous memory.
277 template<class TContainer, class Extents>
278 constexpr typename MultiDimArray<TContainer, Extents>::const_iterator
279 begin(const MultiDimArray<TContainer, Extents>& multiDimArray)
281 return multiDimArray.toArrayRef().begin();
284 //! Free MultiDimArray begin function addressing its contiguous memory.
285 template<class TContainer, class Extents>
286 constexpr typename MultiDimArray<TContainer, Extents>::iterator begin(MultiDimArray<TContainer, Extents>& multiDimArray)
288 return multiDimArray.toArrayRef().begin();
291 //! Free MultiDimArray end function addressing its contiguous memory.
292 template<class TContainer, class Extents>
293 constexpr typename MultiDimArray<TContainer, Extents>::const_iterator
294 end(const MultiDimArray<TContainer, Extents>& multiDimArray)
296 return multiDimArray.toArrayRef().end();
299 //! Free MultiDimArray end function addressing its contiguous memory.
300 template<class TContainer, class Extents>
301 constexpr typename MultiDimArray<TContainer, Extents>::iterator end(MultiDimArray<TContainer, Extents>& multiDimArray)
303 return multiDimArray.toArrayRef().end();
307 template<class TContainer, class Extents>
308 void swap(MultiDimArray<TContainer, Extents>& a, MultiDimArray<TContainer, Extents>& b) noexcept
315 #endif // GMX_MATH_MULTIDIMARRAY_H_