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      1 // This file is part of Eigen, a lightweight C++ template library
      2 // for linear algebra.
      3 //
      4 // Copyright (C) 2012 Gael Guennebaud <gael.guennebaud (at) inria.fr>
      5 //
      6 // This Source Code Form is subject to the terms of the Mozilla
      7 // Public License v. 2.0. If a copy of the MPL was not distributed
      8 // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
      9 
     10 #ifndef EIGEN_REF_H
     11 #define EIGEN_REF_H
     12 
     13 namespace Eigen {
     14 
     15 template<typename Derived> class RefBase;
     16 template<typename PlainObjectType, int Options = 0,
     17          typename StrideType = typename internal::conditional<PlainObjectType::IsVectorAtCompileTime,InnerStride<1>,OuterStride<> >::type > class Ref;
     18 
     19 /** \class Ref
     20   * \ingroup Core_Module
     21   *
     22   * \brief A matrix or vector expression mapping an existing expressions
     23   *
     24   * \tparam PlainObjectType the equivalent matrix type of the mapped data
     25   * \tparam Options specifies whether the pointer is \c #Aligned, or \c #Unaligned.
     26   *                The default is \c #Unaligned.
     27   * \tparam StrideType optionally specifies strides. By default, Ref implies a contiguous storage along the inner dimension (inner stride==1),
     28   *                   but accept a variable outer stride (leading dimension).
     29   *                   This can be overridden by specifying strides.
     30   *                   The type passed here must be a specialization of the Stride template, see examples below.
     31   *
     32   * This class permits to write non template functions taking Eigen's object as parameters while limiting the number of copies.
     33   * A Ref<> object can represent either a const expression or a l-value:
     34   * \code
     35   * // in-out argument:
     36   * void foo1(Ref<VectorXf> x);
     37   *
     38   * // read-only const argument:
     39   * void foo2(const Ref<const VectorXf>& x);
     40   * \endcode
     41   *
     42   * In the in-out case, the input argument must satisfies the constraints of the actual Ref<> type, otherwise a compilation issue will be triggered.
     43   * By default, a Ref<VectorXf> can reference any dense vector expression of float having a contiguous memory layout.
     44   * Likewise, a Ref<MatrixXf> can reference any column major dense matrix expression of float whose column's elements are contiguously stored with
     45   * the possibility to have a constant space inbetween each column, i.e.: the inner stride mmust be equal to 1, but the outer-stride (or leading dimension),
     46   * can be greater than the number of rows.
     47   *
     48   * In the const case, if the input expression does not match the above requirement, then it is evaluated into a temporary before being passed to the function.
     49   * Here are some examples:
     50   * \code
     51   * MatrixXf A;
     52   * VectorXf a;
     53   * foo1(a.head());             // OK
     54   * foo1(A.col());              // OK
     55   * foo1(A.row());              // compilation error because here innerstride!=1
     56   * foo2(A.row());              // The row is copied into a contiguous temporary
     57   * foo2(2*a);                  // The expression is evaluated into a temporary
     58   * foo2(A.col().segment(2,4)); // No temporary
     59   * \endcode
     60   *
     61   * The range of inputs that can be referenced without temporary can be enlarged using the last two template parameter.
     62   * Here is an example accepting an innerstride!=1:
     63   * \code
     64   * // in-out argument:
     65   * void foo3(Ref<VectorXf,0,InnerStride<> > x);
     66   * foo3(A.row());              // OK
     67   * \endcode
     68   * The downside here is that the function foo3 might be significantly slower than foo1 because it won't be able to exploit vectorization, and will involved more
     69   * expensive address computations even if the input is contiguously stored in memory. To overcome this issue, one might propose to overloads internally calling a
     70   * template function, e.g.:
     71   * \code
     72   * // in the .h:
     73   * void foo(const Ref<MatrixXf>& A);
     74   * void foo(const Ref<MatrixXf,0,Stride<> >& A);
     75   *
     76   * // in the .cpp:
     77   * template<typename TypeOfA> void foo_impl(const TypeOfA& A) {
     78   *     ... // crazy code goes here
     79   * }
     80   * void foo(const Ref<MatrixXf>& A) { foo_impl(A); }
     81   * void foo(const Ref<MatrixXf,0,Stride<> >& A) { foo_impl(A); }
     82   * \endcode
     83   *
     84   *
     85   * \sa PlainObjectBase::Map(), \ref TopicStorageOrders
     86   */
     87 
     88 namespace internal {
     89 
     90 template<typename _PlainObjectType, int _Options, typename _StrideType>
     91 struct traits<Ref<_PlainObjectType, _Options, _StrideType> >
     92   : public traits<Map<_PlainObjectType, _Options, _StrideType> >
     93 {
     94   typedef _PlainObjectType PlainObjectType;
     95   typedef _StrideType StrideType;
     96   enum {
     97     Options = _Options,
     98     Flags = traits<Map<_PlainObjectType, _Options, _StrideType> >::Flags | NestByRefBit
     99   };
    100 
    101   template<typename Derived> struct match {
    102     enum {
    103       HasDirectAccess = internal::has_direct_access<Derived>::ret,
    104       StorageOrderMatch = PlainObjectType::IsVectorAtCompileTime || Derived::IsVectorAtCompileTime || ((PlainObjectType::Flags&RowMajorBit)==(Derived::Flags&RowMajorBit)),
    105       InnerStrideMatch = int(StrideType::InnerStrideAtCompileTime)==int(Dynamic)
    106                       || int(StrideType::InnerStrideAtCompileTime)==int(Derived::InnerStrideAtCompileTime)
    107                       || (int(StrideType::InnerStrideAtCompileTime)==0 && int(Derived::InnerStrideAtCompileTime)==1),
    108       OuterStrideMatch = Derived::IsVectorAtCompileTime
    109                       || int(StrideType::OuterStrideAtCompileTime)==int(Dynamic) || int(StrideType::OuterStrideAtCompileTime)==int(Derived::OuterStrideAtCompileTime),
    110       AlignmentMatch = (_Options!=Aligned) || ((PlainObjectType::Flags&AlignedBit)==0) || ((traits<Derived>::Flags&AlignedBit)==AlignedBit),
    111       ScalarTypeMatch = internal::is_same<typename PlainObjectType::Scalar, typename Derived::Scalar>::value,
    112       MatchAtCompileTime = HasDirectAccess && StorageOrderMatch && InnerStrideMatch && OuterStrideMatch && AlignmentMatch && ScalarTypeMatch
    113     };
    114     typedef typename internal::conditional<MatchAtCompileTime,internal::true_type,internal::false_type>::type type;
    115   };
    116 
    117 };
    118 
    119 template<typename Derived>
    120 struct traits<RefBase<Derived> > : public traits<Derived> {};
    121 
    122 }
    123 
    124 template<typename Derived> class RefBase
    125  : public MapBase<Derived>
    126 {
    127   typedef typename internal::traits<Derived>::PlainObjectType PlainObjectType;
    128   typedef typename internal::traits<Derived>::StrideType StrideType;
    129 
    130 public:
    131 
    132   typedef MapBase<Derived> Base;
    133   EIGEN_DENSE_PUBLIC_INTERFACE(RefBase)
    134 
    135   inline Index innerStride() const
    136   {
    137     return StrideType::InnerStrideAtCompileTime != 0 ? m_stride.inner() : 1;
    138   }
    139 
    140   inline Index outerStride() const
    141   {
    142     return StrideType::OuterStrideAtCompileTime != 0 ? m_stride.outer()
    143          : IsVectorAtCompileTime ? this->size()
    144          : int(Flags)&RowMajorBit ? this->cols()
    145          : this->rows();
    146   }
    147 
    148   RefBase()
    149     : Base(0,RowsAtCompileTime==Dynamic?0:RowsAtCompileTime,ColsAtCompileTime==Dynamic?0:ColsAtCompileTime),
    150       // Stride<> does not allow default ctor for Dynamic strides, so let' initialize it with dummy values:
    151       m_stride(StrideType::OuterStrideAtCompileTime==Dynamic?0:StrideType::OuterStrideAtCompileTime,
    152                StrideType::InnerStrideAtCompileTime==Dynamic?0:StrideType::InnerStrideAtCompileTime)
    153   {}
    154 
    155   EIGEN_INHERIT_ASSIGNMENT_OPERATORS(RefBase)
    156 
    157 protected:
    158 
    159   typedef Stride<StrideType::OuterStrideAtCompileTime,StrideType::InnerStrideAtCompileTime> StrideBase;
    160 
    161   template<typename Expression>
    162   void construct(Expression& expr)
    163   {
    164     if(PlainObjectType::RowsAtCompileTime==1)
    165     {
    166       eigen_assert(expr.rows()==1 || expr.cols()==1);
    167       ::new (static_cast<Base*>(this)) Base(expr.data(), 1, expr.size());
    168     }
    169     else if(PlainObjectType::ColsAtCompileTime==1)
    170     {
    171       eigen_assert(expr.rows()==1 || expr.cols()==1);
    172       ::new (static_cast<Base*>(this)) Base(expr.data(), expr.size(), 1);
    173     }
    174     else
    175       ::new (static_cast<Base*>(this)) Base(expr.data(), expr.rows(), expr.cols());
    176 
    177     if(Expression::IsVectorAtCompileTime && (!PlainObjectType::IsVectorAtCompileTime) && ((Expression::Flags&RowMajorBit)!=(PlainObjectType::Flags&RowMajorBit)))
    178       ::new (&m_stride) StrideBase(expr.innerStride(), StrideType::InnerStrideAtCompileTime==0?0:1);
    179     else
    180       ::new (&m_stride) StrideBase(StrideType::OuterStrideAtCompileTime==0?0:expr.outerStride(),
    181                                    StrideType::InnerStrideAtCompileTime==0?0:expr.innerStride());
    182   }
    183 
    184   StrideBase m_stride;
    185 };
    186 
    187 
    188 template<typename PlainObjectType, int Options, typename StrideType> class Ref
    189   : public RefBase<Ref<PlainObjectType, Options, StrideType> >
    190 {
    191   private:
    192     typedef internal::traits<Ref> Traits;
    193     template<typename Derived>
    194     inline Ref(const PlainObjectBase<Derived>& expr,
    195                typename internal::enable_if<bool(Traits::template match<Derived>::MatchAtCompileTime),Derived>::type* = 0);
    196   public:
    197 
    198     typedef RefBase<Ref> Base;
    199     EIGEN_DENSE_PUBLIC_INTERFACE(Ref)
    200 
    201 
    202     #ifndef EIGEN_PARSED_BY_DOXYGEN
    203     template<typename Derived>
    204     inline Ref(PlainObjectBase<Derived>& expr,
    205                typename internal::enable_if<bool(Traits::template match<Derived>::MatchAtCompileTime),Derived>::type* = 0)
    206     {
    207       EIGEN_STATIC_ASSERT(static_cast<bool>(Traits::template match<Derived>::MatchAtCompileTime), STORAGE_LAYOUT_DOES_NOT_MATCH);
    208       Base::construct(expr.derived());
    209     }
    210     template<typename Derived>
    211     inline Ref(const DenseBase<Derived>& expr,
    212                typename internal::enable_if<bool(Traits::template match<Derived>::MatchAtCompileTime),Derived>::type* = 0)
    213     #else
    214     template<typename Derived>
    215     inline Ref(DenseBase<Derived>& expr)
    216     #endif
    217     {
    218       EIGEN_STATIC_ASSERT(static_cast<bool>(internal::is_lvalue<Derived>::value), THIS_EXPRESSION_IS_NOT_A_LVALUE__IT_IS_READ_ONLY);
    219       EIGEN_STATIC_ASSERT(static_cast<bool>(Traits::template match<Derived>::MatchAtCompileTime), STORAGE_LAYOUT_DOES_NOT_MATCH);
    220       enum { THIS_EXPRESSION_IS_NOT_A_LVALUE__IT_IS_READ_ONLY = Derived::ThisConstantIsPrivateInPlainObjectBase};
    221       Base::construct(expr.const_cast_derived());
    222     }
    223 
    224     EIGEN_INHERIT_ASSIGNMENT_OPERATORS(Ref)
    225 
    226 };
    227 
    228 // this is the const ref version
    229 template<typename TPlainObjectType, int Options, typename StrideType> class Ref<const TPlainObjectType, Options, StrideType>
    230   : public RefBase<Ref<const TPlainObjectType, Options, StrideType> >
    231 {
    232     typedef internal::traits<Ref> Traits;
    233   public:
    234 
    235     typedef RefBase<Ref> Base;
    236     EIGEN_DENSE_PUBLIC_INTERFACE(Ref)
    237 
    238     template<typename Derived>
    239     inline Ref(const DenseBase<Derived>& expr,
    240                typename internal::enable_if<bool(Traits::template match<Derived>::ScalarTypeMatch),Derived>::type* = 0)
    241     {
    242 //      std::cout << match_helper<Derived>::HasDirectAccess << "," << match_helper<Derived>::OuterStrideMatch << "," << match_helper<Derived>::InnerStrideMatch << "\n";
    243 //      std::cout << int(StrideType::OuterStrideAtCompileTime) << " - " << int(Derived::OuterStrideAtCompileTime) << "\n";
    244 //      std::cout << int(StrideType::InnerStrideAtCompileTime) << " - " << int(Derived::InnerStrideAtCompileTime) << "\n";
    245       construct(expr.derived(), typename Traits::template match<Derived>::type());
    246     }
    247 
    248   protected:
    249 
    250     template<typename Expression>
    251     void construct(const Expression& expr,internal::true_type)
    252     {
    253       Base::construct(expr);
    254     }
    255 
    256     template<typename Expression>
    257     void construct(const Expression& expr, internal::false_type)
    258     {
    259       m_object.lazyAssign(expr);
    260       Base::construct(m_object);
    261     }
    262 
    263   protected:
    264     TPlainObjectType m_object;
    265 };
    266 
    267 } // end namespace Eigen
    268 
    269 #endif // EIGEN_REF_H
    270