src/gromacs/math/arrayrefwithpadding.h

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  35 /*! \file
  36  * \brief Declares gmx::ArrayRefWithPadding that refers to memory whose
  37  * size includes padding for SIMD operations.
  38  *
  39  * \author Mark Abraham <mark.j.abraham@gmail.com>
  40  *
  41  * \inpublicapi
  42  * \ingroup module_math
  43  */
  44 #ifndef GMX_MATH_ARRAYREFWITHPADDING_H
  45 #define GMX_MATH_ARRAYREFWITHPADDING_H
  46
  47 #include <cstddef>
  48
  49 #include "gromacs/utility/arrayref.h"
  50 #include "gromacs/utility/basedefinitions.h"
  51 #include "gromacs/utility/gmxassert.h"
  52
  53 namespace gmx
  54 {
  55
  56 /*! \brief Interface to a C array of T (or part of a std container of
  57  * T), that includes padding that is suitable for the kinds of SIMD
  58  * operations GROMACS uses.
  59  *
  60  * High level code e.g. in the force calculation routines need to hold
  61  * a non-owning view of memory and be able to create ArrayRef objects
  62  * that view padded or unpadded memory, suitable for the various
  63  * component routines. This class implements that non-owning view,
  64  * and the only available functionality refers to its size, and the
  65  * methods to create such ArrayRef objects.
  66  *
  67  * \copydoc ArrayRef
  68  * \inlibraryapi
  69  * \ingroup module_math
  70  */
  71 template <typename T>
  72 class ArrayRefWithPadding
  73 {
  74     public:
  75         //! Type of values stored in the reference.
  76         using value_type = T;
  77         //! Type for representing size of the reference.
  78         using size_type = index;
  79         //! Const pointer to an element.
  80         using const_pointer = const T*;
  81         //! Const iterator type to an element.
  82         using const_iterator = const T*;
  83         //! Pointer to an element.
  84         using pointer = T*;
  85         //! Iterator type to an element.
  86         using iterator = T*;
  87
  88         /*! \brief
  89          * Constructs an empty reference.
  90          */
  91         ArrayRefWithPadding()
  92             : begin_(nullptr), end_(nullptr), paddedEnd_(nullptr) {}
  93         /*! \brief
  94          * Constructs a reference to a particular range.
  95          *
  96          * \param[in] begin        Pointer to the beginning of a range.
  97          * \param[in] end          Pointer to the end of a range without padding.
  98          * \param[in] paddedEnd    Pointer to the end of a range including padding.
  99          *
 100          * Passed pointers must remain valid for the lifetime of this object.
 101          */
 102         ArrayRefWithPadding(pointer begin, pointer end, pointer paddedEnd)
 103             : begin_(begin), end_(end), paddedEnd_(paddedEnd)
 104         {
 105             GMX_ASSERT(end >= begin, "Invalid range");
 106             GMX_ASSERT(paddedEnd >= end, "Invalid range");
 107         }
 108         //! Copy constructor
 109         ArrayRefWithPadding(const ArrayRefWithPadding &o)
 110             : begin_(o.begin_), end_(o.end_), paddedEnd_(o.paddedEnd_) {}
 111         //! Move constructor
 112         ArrayRefWithPadding(ArrayRefWithPadding &&o) noexcept
 113             : begin_(std::move(o.begin_)), end_(std::move(o.end_)), paddedEnd_(std::move(o.paddedEnd_)) {}
 114         //! Convenience overload constructor to make an ArrayRefWithPadding<const T> from a non-const one.
 115         template<typename U,
 116                  typename = std::enable_if_t<
 117                          std::is_same<value_type,
 118                                       const typename std::remove_reference_t<U>::value_type>::value> >
 119         ArrayRefWithPadding(U &&o)
 120         {
 121             auto constArrayRefWithPadding = o.constArrayRefWithPadding();
 122             this->swap(constArrayRefWithPadding);
 123         }
 124         //! Copy assignment operator
 125         ArrayRefWithPadding &operator=(ArrayRefWithPadding const &o)
 126         {
 127             if (&o != this)
 128             {
 129                 begin_     = o.begin_;
 130                 end_       = o.end_;
 131                 paddedEnd_ = o.paddedEnd_;
 132             }
 133             return *this;
 134         }
 135         //! Move assignment operator
 136         ArrayRefWithPadding &operator=(ArrayRefWithPadding &&o) noexcept
 137         {
 138             if (&o != this)
 139             {
 140                 begin_     = std::move(o.begin_);
 141                 end_       = std::move(o.end_);
 142                 paddedEnd_ = std::move(o.paddedEnd_);
 143             }
 144             return *this;
 145         }
 146
 147         //! Return the size of the view, i.e with the padding.
 148         size_type size() const { return paddedEnd_ - begin_; }
 149         //! Whether the reference refers to no memory.
 150         bool empty() const { return begin_ == end_; }
 151
 152         //! Returns an ArrayRef of elements that does not include the padding region.
 153         ArrayRef<T> unpaddedArrayRef()
 154         {
 155             return {begin_, end_};
 156         }
 157         //! Returns an ArrayRef of const elements that does not include the padding region.
 158         ArrayRef<const T> unpaddedConstArrayRef() const
 159         {
 160             return {begin_, end_};
 161         }
 162         //! Returns an ArrayRef of elements that does include the padding region.
 163         ArrayRef<T> paddedArrayRef()
 164         {
 165             return {begin_, paddedEnd_};
 166         }
 167         //! Returns an ArrayRef of const elements that does include the padding region.
 168         ArrayRef<const T> paddedConstArrayRef() const
 169         {
 170             return {begin_, paddedEnd_};
 171         }
 172         //! Returns an identical ArrayRefWithPadding that refers to const elements.
 173         ArrayRefWithPadding<const T> constArrayRefWithPadding() const
 174         {
 175             return {begin_, end_, paddedEnd_};
 176         }
 177         /*! \brief
 178          * Swaps referenced memory with the other object.
 179          *
 180          * The actual memory areas are not modified, only the references are
 181          * swapped.
 182          */
 183         void swap(ArrayRefWithPadding<T> &other)
 184         {
 185             std::swap(begin_, other.begin_);
 186             std::swap(end_, other.end_);
 187             std::swap(paddedEnd_, other.paddedEnd_);
 188         }
 189
 190     private:
 191         pointer begin_;
 192         pointer end_;
 193         pointer paddedEnd_;
 194 };
 195
 196 } // namespace gmx
 197
 198 #endif