// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2011 Benoit Jacob <jacob.benoit.1@gmail.com>
// Copyright (C) 2011-2014 Gael Guennebaud <gael.guennebaud@inria.fr>
// Copyright (C) 2011-2012 Jitse Niesen <jitse@maths.leeds.ac.uk>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.


#ifndef EIGEN_COREEVALUATORS_H
#define EIGEN_COREEVALUATORS_H

namespace Eigen {
  
namespace internal {

// This class returns the evaluator kind from the expression storage kind.
// Default assumes index based accessors
template<typename StorageKind>
struct storage_kind_to_evaluator_kind {
  typedef IndexBased Kind;
};

// This class returns the evaluator shape from the expression storage kind.
// It can be Dense, Sparse, Triangular, Diagonal, SelfAdjoint, Band, etc.
template<typename StorageKind> struct storage_kind_to_shape;

template<> struct storage_kind_to_shape<Dense>                  { typedef DenseShape Shape;           };
template<> struct storage_kind_to_shape<PermutationStorage>     { typedef PermutationShape Shape;     };
template<> struct storage_kind_to_shape<TranspositionsStorage>  { typedef TranspositionsShape Shape;  };

// Evaluators have to be specialized with respect to various criteria such as:
//  - storage/structure/shape
//  - scalar type
//  - etc.
// Therefore, we need specialization of evaluator providing additional template arguments for each kind of evaluators.
// We currently distinguish the following kind of evaluators:
// - unary_evaluator    for expressions taking only one arguments (CwiseUnaryOp, CwiseUnaryView, Transpose, MatrixWrapper, ArrayWrapper, Reverse, Replicate)
// - binary_evaluator   for expression taking two arguments (CwiseBinaryOp)
// - product_evaluator  for linear algebra products (Product); special case of binary_evaluator because it requires additional tags for dispatching.
// - mapbase_evaluator  for Map, Block, Ref
// - block_evaluator    for Block (special dispatching to a mapbase_evaluator or unary_evaluator)

template< typename T,
          typename LhsKind   = typename evaluator_traits<typename T::Lhs>::Kind,
          typename RhsKind   = typename evaluator_traits<typename T::Rhs>::Kind,
          typename LhsScalar = typename traits<typename T::Lhs>::Scalar,
          typename RhsScalar = typename traits<typename T::Rhs>::Scalar> struct binary_evaluator;

template< typename T,
          typename Kind   = typename evaluator_traits<typename T::NestedExpression>::Kind,
          typename Scalar = typename T::Scalar> struct unary_evaluator;
          
// evaluator_traits<T> contains traits for evaluator<T> 

template<typename T>
struct evaluator_traits_base
{
  // TODO check whether these two indirections are really needed.
  // Basically, if nobody overwrite type and nestedType, then, they can be dropped
//   typedef evaluator<T> type;
//   typedef evaluator<T> nestedType;
  
  // by default, get evaluator kind and shape from storage
  typedef typename storage_kind_to_evaluator_kind<typename traits<T>::StorageKind>::Kind Kind;
  typedef typename storage_kind_to_shape<typename traits<T>::StorageKind>::Shape Shape;
  
  // 1 if assignment A = B assumes aliasing when B is of type T and thus B needs to be evaluated into a
  // temporary; 0 if not.
  static const int AssumeAliasing = 0;
};

// Default evaluator traits
template<typename T>
struct evaluator_traits : public evaluator_traits_base<T>
{
};


// By default, we assume a unary expression:
template<typename T>
struct evaluator : public unary_evaluator<T>
{
  typedef unary_evaluator<T> Base;
  EIGEN_DEVICE_FUNC explicit evaluator(const T& xpr) : Base(xpr) {}
};


// TODO: Think about const-correctness

template<typename T>
struct evaluator<const T>
  : evaluator<T>
{ };

// ---------- base class for all writable evaluators ----------

// TODO this class does not seem to be necessary anymore
template<typename ExpressionType>
struct evaluator_base
{
//   typedef typename evaluator_traits<ExpressionType>::type type;
//   typedef typename evaluator_traits<ExpressionType>::nestedType nestedType;
  typedef evaluator<ExpressionType> type;
  typedef evaluator<ExpressionType> nestedType;
  
  // FIXME is it really usefull?
  typedef typename traits<ExpressionType>::StorageIndex StorageIndex;
  // TODO that's not very nice to have to propagate all these traits. They are currently only needed to handle outer,inner indices.
  typedef traits<ExpressionType> ExpressionTraits;
};

// -------------------- Matrix and Array --------------------
//
// evaluator<PlainObjectBase> is a common base class for the
// Matrix and Array evaluators.
// Here we directly specialize evaluator. This is not really a unary expression, and it is, by definition, dense,
// so no need for more sophisticated dispatching.

template<typename Derived>
struct evaluator<PlainObjectBase<Derived> >
  : evaluator_base<Derived>
{
  typedef PlainObjectBase<Derived> PlainObjectType;
  typedef typename PlainObjectType::Scalar Scalar;
  typedef typename PlainObjectType::CoeffReturnType CoeffReturnType;
  typedef typename PlainObjectType::PacketScalar PacketScalar;
  typedef typename PlainObjectType::PacketReturnType PacketReturnType;

  enum {
    IsRowMajor = PlainObjectType::IsRowMajor,
    IsVectorAtCompileTime = PlainObjectType::IsVectorAtCompileTime,
    RowsAtCompileTime = PlainObjectType::RowsAtCompileTime,
    ColsAtCompileTime = PlainObjectType::ColsAtCompileTime,
    
    CoeffReadCost = NumTraits<Scalar>::ReadCost,
    Flags = compute_matrix_evaluator_flags< Scalar,Derived::RowsAtCompileTime,Derived::ColsAtCompileTime,
                                            Derived::Options,Derived::MaxRowsAtCompileTime,Derived::MaxColsAtCompileTime>::ret
  };
  
  EIGEN_DEVICE_FUNC evaluator()
    : m_data(0),
      m_outerStride(IsVectorAtCompileTime  ? 0 
                                           : int(IsRowMajor) ? ColsAtCompileTime 
                                           : RowsAtCompileTime)
  {}
  
  EIGEN_DEVICE_FUNC explicit evaluator(const PlainObjectType& m)
    : m_data(m.data()), m_outerStride(IsVectorAtCompileTime ? 0 : m.outerStride()) 
  { }

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index row, Index col) const
  {
    if (IsRowMajor)
      return m_data[row * m_outerStride.value() + col];
    else
      return m_data[row + col * m_outerStride.value()];
  }

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index index) const
  {
    return m_data[index];
  }

  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index row, Index col)
  {
    if (IsRowMajor)
      return const_cast<Scalar*>(m_data)[row * m_outerStride.value() + col];
    else
      return const_cast<Scalar*>(m_data)[row + col * m_outerStride.value()];
  }

  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index index)
  {
    return const_cast<Scalar*>(m_data)[index];
  }

  template<int LoadMode> 
  PacketReturnType packet(Index row, Index col) const
  {
    if (IsRowMajor)
      return ploadt<PacketScalar, LoadMode>(m_data + row * m_outerStride.value() + col);
    else
      return ploadt<PacketScalar, LoadMode>(m_data + row + col * m_outerStride.value());
  }

  template<int LoadMode> 
  PacketReturnType packet(Index index) const
  {
    return ploadt<PacketScalar, LoadMode>(m_data + index);
  }

  template<int StoreMode> 
  void writePacket(Index row, Index col, const PacketScalar& x)
  {
    if (IsRowMajor)
      return pstoret<Scalar, PacketScalar, StoreMode>
	            (const_cast<Scalar*>(m_data) + row * m_outerStride.value() + col, x);
    else
      return pstoret<Scalar, PacketScalar, StoreMode>
                    (const_cast<Scalar*>(m_data) + row + col * m_outerStride.value(), x);
  }

  template<int StoreMode> 
  void writePacket(Index index, const PacketScalar& x)
  {
    return pstoret<Scalar, PacketScalar, StoreMode>(const_cast<Scalar*>(m_data) + index, x);
  }

protected:
  const Scalar *m_data;

  // We do not need to know the outer stride for vectors
  variable_if_dynamic<Index, IsVectorAtCompileTime  ? 0 
                                                    : int(IsRowMajor) ? ColsAtCompileTime 
                                                    : RowsAtCompileTime> m_outerStride;
};

template<typename Scalar, int Rows, int Cols, int Options, int MaxRows, int MaxCols>
struct evaluator<Matrix<Scalar, Rows, Cols, Options, MaxRows, MaxCols> >
  : evaluator<PlainObjectBase<Matrix<Scalar, Rows, Cols, Options, MaxRows, MaxCols> > >
{
  typedef Matrix<Scalar, Rows, Cols, Options, MaxRows, MaxCols> XprType;
  
  evaluator() {}

  EIGEN_DEVICE_FUNC explicit evaluator(const XprType& m)
    : evaluator<PlainObjectBase<XprType> >(m) 
  { }
};

template<typename Scalar, int Rows, int Cols, int Options, int MaxRows, int MaxCols>
struct evaluator<Array<Scalar, Rows, Cols, Options, MaxRows, MaxCols> >
  : evaluator<PlainObjectBase<Array<Scalar, Rows, Cols, Options, MaxRows, MaxCols> > >
{
  typedef Array<Scalar, Rows, Cols, Options, MaxRows, MaxCols> XprType;

  evaluator() {}
  
  EIGEN_DEVICE_FUNC explicit evaluator(const XprType& m)
    : evaluator<PlainObjectBase<XprType> >(m) 
  { }
};

// -------------------- Transpose --------------------

template<typename ArgType>
struct unary_evaluator<Transpose<ArgType>, IndexBased>
  : evaluator_base<Transpose<ArgType> >
{
  typedef Transpose<ArgType> XprType;
  
  enum {
    CoeffReadCost = evaluator<ArgType>::CoeffReadCost,    
    Flags = evaluator<ArgType>::Flags ^ RowMajorBit
  };

  EIGEN_DEVICE_FUNC explicit unary_evaluator(const XprType& t) : m_argImpl(t.nestedExpression()) {}

  typedef typename XprType::Scalar Scalar;
  typedef typename XprType::CoeffReturnType CoeffReturnType;
  typedef typename XprType::PacketScalar PacketScalar;
  typedef typename XprType::PacketReturnType PacketReturnType;

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index row, Index col) const
  {
    return m_argImpl.coeff(col, row);
  }

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index index) const
  {
    return m_argImpl.coeff(index);
  }

  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index row, Index col)
  {
    return m_argImpl.coeffRef(col, row);
  }

  EIGEN_DEVICE_FUNC typename XprType::Scalar& coeffRef(Index index)
  {
    return m_argImpl.coeffRef(index);
  }

  template<int LoadMode>
  PacketReturnType packet(Index row, Index col) const
  {
    return m_argImpl.template packet<LoadMode>(col, row);
  }

  template<int LoadMode>
  PacketReturnType packet(Index index) const
  {
    return m_argImpl.template packet<LoadMode>(index);
  }

  template<int StoreMode> 
  void writePacket(Index row, Index col, const PacketScalar& x)
  {
    m_argImpl.template writePacket<StoreMode>(col, row, x);
  }

  template<int StoreMode> 
  void writePacket(Index index, const PacketScalar& x)
  {
    m_argImpl.template writePacket<StoreMode>(index, x);
  }

protected:
  typename evaluator<ArgType>::nestedType m_argImpl;
};

// -------------------- CwiseNullaryOp --------------------
// Like Matrix and Array, this is not really a unary expression, so we directly specialize evaluator.
// Likewise, there is not need to more sophisticated dispatching here.

template<typename NullaryOp, typename PlainObjectType>
struct evaluator<CwiseNullaryOp<NullaryOp,PlainObjectType> >
  : evaluator_base<CwiseNullaryOp<NullaryOp,PlainObjectType> >
{
  typedef CwiseNullaryOp<NullaryOp,PlainObjectType> XprType;
  typedef typename internal::remove_all<PlainObjectType>::type PlainObjectTypeCleaned;
  
  enum {
    CoeffReadCost = internal::functor_traits<NullaryOp>::Cost,
    
    Flags = (evaluator<PlainObjectTypeCleaned>::Flags
          &  (  HereditaryBits
              | (functor_has_linear_access<NullaryOp>::ret  ? LinearAccessBit : 0)
              | (functor_traits<NullaryOp>::PacketAccess    ? PacketAccessBit : 0)))
          | (functor_traits<NullaryOp>::IsRepeatable ? 0 : EvalBeforeNestingBit) // FIXME EvalBeforeNestingBit should be needed anymore
  };

  EIGEN_DEVICE_FUNC explicit evaluator(const XprType& n)
    : m_functor(n.functor()) 
  { }

  typedef typename XprType::CoeffReturnType CoeffReturnType;
  typedef typename XprType::PacketScalar PacketScalar;

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index row, Index col) const
  {
    return m_functor(row, col);
  }

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index index) const
  {
    return m_functor(index);
  }

  template<int LoadMode>
  PacketScalar packet(Index row, Index col) const
  {
    return m_functor.packetOp(row, col);
  }

  template<int LoadMode>
  PacketScalar packet(Index index) const
  {
    return m_functor.packetOp(index);
  }

protected:
  const NullaryOp m_functor;
};

// -------------------- CwiseUnaryOp --------------------

template<typename UnaryOp, typename ArgType>
struct unary_evaluator<CwiseUnaryOp<UnaryOp, ArgType>, IndexBased >
  : evaluator_base<CwiseUnaryOp<UnaryOp, ArgType> >
{
  typedef CwiseUnaryOp<UnaryOp, ArgType> XprType;
  
  enum {
    CoeffReadCost = evaluator<ArgType>::CoeffReadCost + functor_traits<UnaryOp>::Cost,
    
    Flags = evaluator<ArgType>::Flags & (
              HereditaryBits | LinearAccessBit | AlignedBit
            | (functor_traits<UnaryOp>::PacketAccess ? PacketAccessBit : 0))
  };

  EIGEN_DEVICE_FUNC explicit unary_evaluator(const XprType& op)
    : m_functor(op.functor()), 
      m_argImpl(op.nestedExpression()) 
  { }

  typedef typename XprType::CoeffReturnType CoeffReturnType;
  typedef typename XprType::PacketScalar PacketScalar;

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index row, Index col) const
  {
    return m_functor(m_argImpl.coeff(row, col));
  }

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index index) const
  {
    return m_functor(m_argImpl.coeff(index));
  }

  template<int LoadMode>
  PacketScalar packet(Index row, Index col) const
  {
    return m_functor.packetOp(m_argImpl.template packet<LoadMode>(row, col));
  }

  template<int LoadMode>
  PacketScalar packet(Index index) const
  {
    return m_functor.packetOp(m_argImpl.template packet<LoadMode>(index));
  }

protected:
  const UnaryOp m_functor;
  typename evaluator<ArgType>::nestedType m_argImpl;
};

// -------------------- CwiseBinaryOp --------------------

// this is a binary expression
template<typename BinaryOp, typename Lhs, typename Rhs>
struct evaluator<CwiseBinaryOp<BinaryOp, Lhs, Rhs> >
  : public binary_evaluator<CwiseBinaryOp<BinaryOp, Lhs, Rhs> >
{
  typedef CwiseBinaryOp<BinaryOp, Lhs, Rhs> XprType;
  typedef binary_evaluator<CwiseBinaryOp<BinaryOp, Lhs, Rhs> > Base;
  
  EIGEN_DEVICE_FUNC explicit evaluator(const XprType& xpr) : Base(xpr) {}
};

template<typename BinaryOp, typename Lhs, typename Rhs>
struct binary_evaluator<CwiseBinaryOp<BinaryOp, Lhs, Rhs>, IndexBased, IndexBased>
  : evaluator_base<CwiseBinaryOp<BinaryOp, Lhs, Rhs> >
{
  typedef CwiseBinaryOp<BinaryOp, Lhs, Rhs> XprType;
  
  enum {
    CoeffReadCost = evaluator<Lhs>::CoeffReadCost + evaluator<Rhs>::CoeffReadCost + functor_traits<BinaryOp>::Cost,
    
    LhsFlags = evaluator<Lhs>::Flags,
    RhsFlags = evaluator<Rhs>::Flags,
    SameType = is_same<typename Lhs::Scalar,typename Rhs::Scalar>::value,
    StorageOrdersAgree = (int(LhsFlags)&RowMajorBit)==(int(RhsFlags)&RowMajorBit),
    Flags0 = (int(LhsFlags) | int(RhsFlags)) & (
        HereditaryBits
      | (int(LhsFlags) & int(RhsFlags) &
           ( AlignedBit
           | (StorageOrdersAgree ? LinearAccessBit : 0)
           | (functor_traits<BinaryOp>::PacketAccess && StorageOrdersAgree && SameType ? PacketAccessBit : 0)
           )
        )
     ),
    Flags = (Flags0 & ~RowMajorBit) | (LhsFlags & RowMajorBit)
  };

  EIGEN_DEVICE_FUNC explicit binary_evaluator(const XprType& xpr)
    : m_functor(xpr.functor()),
      m_lhsImpl(xpr.lhs()), 
      m_rhsImpl(xpr.rhs())  
  { }

  typedef typename XprType::CoeffReturnType CoeffReturnType;
  typedef typename XprType::PacketScalar PacketScalar;

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index row, Index col) const
  {
    return m_functor(m_lhsImpl.coeff(row, col), m_rhsImpl.coeff(row, col));
  }

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index index) const
  {
    return m_functor(m_lhsImpl.coeff(index), m_rhsImpl.coeff(index));
  }

  template<int LoadMode>
  PacketScalar packet(Index row, Index col) const
  {
    return m_functor.packetOp(m_lhsImpl.template packet<LoadMode>(row, col),
                              m_rhsImpl.template packet<LoadMode>(row, col));
  }

  template<int LoadMode>
  PacketScalar packet(Index index) const
  {
    return m_functor.packetOp(m_lhsImpl.template packet<LoadMode>(index),
                              m_rhsImpl.template packet<LoadMode>(index));
  }

protected:
  const BinaryOp m_functor;
  typename evaluator<Lhs>::nestedType m_lhsImpl;
  typename evaluator<Rhs>::nestedType m_rhsImpl;
};

// -------------------- CwiseUnaryView --------------------

template<typename UnaryOp, typename ArgType>
struct unary_evaluator<CwiseUnaryView<UnaryOp, ArgType>, IndexBased>
  : evaluator_base<CwiseUnaryView<UnaryOp, ArgType> >
{
  typedef CwiseUnaryView<UnaryOp, ArgType> XprType;
  
  enum {
    CoeffReadCost = evaluator<ArgType>::CoeffReadCost + functor_traits<UnaryOp>::Cost,
    
    Flags = (evaluator<ArgType>::Flags & (HereditaryBits | LinearAccessBit | DirectAccessBit))
  };

  EIGEN_DEVICE_FUNC explicit unary_evaluator(const XprType& op)
    : m_unaryOp(op.functor()), 
      m_argImpl(op.nestedExpression()) 
  { }

  typedef typename XprType::Scalar Scalar;
  typedef typename XprType::CoeffReturnType CoeffReturnType;

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index row, Index col) const
  {
    return m_unaryOp(m_argImpl.coeff(row, col));
  }

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index index) const
  {
    return m_unaryOp(m_argImpl.coeff(index));
  }

  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index row, Index col)
  {
    return m_unaryOp(m_argImpl.coeffRef(row, col));
  }

  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index index)
  {
    return m_unaryOp(m_argImpl.coeffRef(index));
  }

protected:
  const UnaryOp m_unaryOp;
  typename evaluator<ArgType>::nestedType m_argImpl;
};

// -------------------- Map --------------------

// FIXME perhaps the PlainObjectType could be provided by Derived::PlainObject ?
// but that might complicate template specialization
template<typename Derived, typename PlainObjectType>
struct mapbase_evaluator;

template<typename Derived, typename PlainObjectType>
struct mapbase_evaluator : evaluator_base<Derived>
{
  typedef Derived  XprType;
  typedef typename XprType::PointerType PointerType;
  typedef typename XprType::Scalar Scalar;
  typedef typename XprType::CoeffReturnType CoeffReturnType;
  typedef typename XprType::PacketScalar PacketScalar;
  typedef typename XprType::PacketReturnType PacketReturnType;
  
  enum {
    IsRowMajor = XprType::RowsAtCompileTime,
    ColsAtCompileTime = XprType::ColsAtCompileTime,
    CoeffReadCost = NumTraits<Scalar>::ReadCost
  };
  
  EIGEN_DEVICE_FUNC explicit mapbase_evaluator(const XprType& map)
    : m_data(const_cast<PointerType>(map.data())),  
      m_xpr(map)
  {
    EIGEN_STATIC_ASSERT(EIGEN_IMPLIES(evaluator<Derived>::Flags&PacketAccessBit, internal::inner_stride_at_compile_time<Derived>::ret==1),
                        PACKET_ACCESS_REQUIRES_TO_HAVE_INNER_STRIDE_FIXED_TO_1);
  }
 
  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index row, Index col) const
  {
    return m_data[col * m_xpr.colStride() + row * m_xpr.rowStride()];
  }
  
  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index index) const
  {
    return m_data[index * m_xpr.innerStride()];
  }

  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index row, Index col)
  {
    return m_data[col * m_xpr.colStride() + row * m_xpr.rowStride()];
  }
  
  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index index)
  {
    return m_data[index * m_xpr.innerStride()];
  }
 
  template<int LoadMode> 
  PacketReturnType packet(Index row, Index col) const 
  {
    PointerType ptr = m_data + row * m_xpr.rowStride() + col * m_xpr.colStride();
    return internal::ploadt<PacketScalar, LoadMode>(ptr);
  }

  template<int LoadMode> 
  PacketReturnType packet(Index index) const 
  {
    return internal::ploadt<PacketScalar, LoadMode>(m_data + index * m_xpr.innerStride());
  }
  
  template<int StoreMode> 
  void writePacket(Index row, Index col, const PacketScalar& x) 
  {
    PointerType ptr = m_data + row * m_xpr.rowStride() + col * m_xpr.colStride();
    return internal::pstoret<Scalar, PacketScalar, StoreMode>(ptr, x);
  }
  
  template<int StoreMode> 
  void writePacket(Index index, const PacketScalar& x) 
  {
    internal::pstoret<Scalar, PacketScalar, StoreMode>(m_data + index * m_xpr.innerStride(), x);
  }
 
protected:
  PointerType m_data;
  const XprType& m_xpr;
};

template<typename PlainObjectType, int MapOptions, typename StrideType> 
struct evaluator<Map<PlainObjectType, MapOptions, StrideType> >
  : public mapbase_evaluator<Map<PlainObjectType, MapOptions, StrideType>, PlainObjectType>
{
  typedef Map<PlainObjectType, MapOptions, StrideType> XprType;
  typedef typename XprType::Scalar Scalar;
  
  enum {
    InnerStrideAtCompileTime = StrideType::InnerStrideAtCompileTime == 0
                             ? int(PlainObjectType::InnerStrideAtCompileTime)
                             : int(StrideType::InnerStrideAtCompileTime),
    OuterStrideAtCompileTime = StrideType::OuterStrideAtCompileTime == 0
                             ? int(PlainObjectType::OuterStrideAtCompileTime)
                             : int(StrideType::OuterStrideAtCompileTime),
    HasNoInnerStride = InnerStrideAtCompileTime == 1,
    HasNoOuterStride = StrideType::OuterStrideAtCompileTime == 0,
    HasNoStride = HasNoInnerStride && HasNoOuterStride,
    IsAligned = bool(EIGEN_ALIGN) && ((int(MapOptions)&Aligned)==Aligned),
    IsDynamicSize = PlainObjectType::SizeAtCompileTime==Dynamic,
    
    // TODO: should check for smaller packet types once we can handle multi-sized packet types
    AlignBytes = int(packet_traits<Scalar>::size) * sizeof(Scalar),
    
    KeepsPacketAccess = bool(HasNoInnerStride)
                        && ( bool(IsDynamicSize)
                           || HasNoOuterStride
                           || ( OuterStrideAtCompileTime!=Dynamic
                           && ((static_cast<int>(sizeof(Scalar))*OuterStrideAtCompileTime) % AlignBytes)==0 ) ),
    Flags0 = evaluator<PlainObjectType>::Flags,
    Flags1 = IsAligned ? (int(Flags0) | AlignedBit) : (int(Flags0) & ~AlignedBit),
    Flags2 = (bool(HasNoStride) || bool(PlainObjectType::IsVectorAtCompileTime))
           ? int(Flags1) : int(Flags1 & ~LinearAccessBit),
    Flags = KeepsPacketAccess ? int(Flags2) : (int(Flags2) & ~PacketAccessBit)
  };

  EIGEN_DEVICE_FUNC explicit evaluator(const XprType& map)
    : mapbase_evaluator<XprType, PlainObjectType>(map) 
  { }
};

// -------------------- Ref --------------------

template<typename PlainObjectType, int RefOptions, typename StrideType> 
struct evaluator<Ref<PlainObjectType, RefOptions, StrideType> >
  : public mapbase_evaluator<Ref<PlainObjectType, RefOptions, StrideType>, PlainObjectType>
{
  typedef Ref<PlainObjectType, RefOptions, StrideType> XprType;
  
  enum {
    Flags = evaluator<Map<PlainObjectType, RefOptions, StrideType> >::Flags
  };

  EIGEN_DEVICE_FUNC explicit evaluator(const XprType& ref)
    : mapbase_evaluator<XprType, PlainObjectType>(ref) 
  { }
};

// -------------------- Block --------------------

template<typename ArgType, int BlockRows, int BlockCols, bool InnerPanel,
         bool HasDirectAccess = internal::has_direct_access<ArgType>::ret> struct block_evaluator;
         
template<typename ArgType, int BlockRows, int BlockCols, bool InnerPanel> 
struct evaluator<Block<ArgType, BlockRows, BlockCols, InnerPanel> >
  : block_evaluator<ArgType, BlockRows, BlockCols, InnerPanel>
{
  typedef Block<ArgType, BlockRows, BlockCols, InnerPanel> XprType;
  typedef typename XprType::Scalar Scalar; 
  
  enum {
    CoeffReadCost = evaluator<ArgType>::CoeffReadCost,
    
    RowsAtCompileTime = traits<XprType>::RowsAtCompileTime,
    ColsAtCompileTime = traits<XprType>::ColsAtCompileTime,
    MaxRowsAtCompileTime = traits<XprType>::MaxRowsAtCompileTime,
    MaxColsAtCompileTime = traits<XprType>::MaxColsAtCompileTime,
    
    ArgTypeIsRowMajor = (int(evaluator<ArgType>::Flags)&RowMajorBit) != 0,
    IsRowMajor = (MaxRowsAtCompileTime==1 && MaxColsAtCompileTime!=1) ? 1
               : (MaxColsAtCompileTime==1 && MaxRowsAtCompileTime!=1) ? 0
               : ArgTypeIsRowMajor,
    HasSameStorageOrderAsArgType = (IsRowMajor == ArgTypeIsRowMajor),
    InnerSize = IsRowMajor ? int(ColsAtCompileTime) : int(RowsAtCompileTime),
    InnerStrideAtCompileTime = HasSameStorageOrderAsArgType
                             ? int(inner_stride_at_compile_time<ArgType>::ret)
                             : int(outer_stride_at_compile_time<ArgType>::ret),
    OuterStrideAtCompileTime = HasSameStorageOrderAsArgType
                             ? int(outer_stride_at_compile_time<ArgType>::ret)
                             : int(inner_stride_at_compile_time<ArgType>::ret),
    MaskPacketAccessBit = (InnerSize == Dynamic || (InnerSize % packet_traits<Scalar>::size) == 0)
                       && (InnerStrideAtCompileTime == 1)
                        ? PacketAccessBit : 0,
    
    // TODO: should check for smaller packet types once we can handle multi-sized packet types
    AlignBytes = int(packet_traits<Scalar>::size) * sizeof(Scalar),
    
    MaskAlignedBit = (InnerPanel && (OuterStrideAtCompileTime!=Dynamic) && (((OuterStrideAtCompileTime * int(sizeof(Scalar))) % AlignBytes) == 0)) ? AlignedBit : 0,
    FlagsLinearAccessBit = (RowsAtCompileTime == 1 || ColsAtCompileTime == 1 || (InnerPanel && (evaluator<ArgType>::Flags&LinearAccessBit))) ? LinearAccessBit : 0,    
    FlagsRowMajorBit = XprType::Flags&RowMajorBit,
    Flags0 = evaluator<ArgType>::Flags & ( (HereditaryBits & ~RowMajorBit) |
                                           DirectAccessBit |
                                           MaskPacketAccessBit |
                                           MaskAlignedBit),
    Flags = Flags0 | FlagsLinearAccessBit | FlagsRowMajorBit
  };
  typedef block_evaluator<ArgType, BlockRows, BlockCols, InnerPanel> block_evaluator_type;
  EIGEN_DEVICE_FUNC explicit evaluator(const XprType& block) : block_evaluator_type(block) {}
};

// no direct-access => dispatch to a unary evaluator
template<typename ArgType, int BlockRows, int BlockCols, bool InnerPanel>
struct block_evaluator<ArgType, BlockRows, BlockCols, InnerPanel, /*HasDirectAccess*/ false>
  : unary_evaluator<Block<ArgType, BlockRows, BlockCols, InnerPanel> >
{
  typedef Block<ArgType, BlockRows, BlockCols, InnerPanel> XprType;

  EIGEN_DEVICE_FUNC explicit block_evaluator(const XprType& block)
    : unary_evaluator<XprType>(block) 
  {}
};

template<typename ArgType, int BlockRows, int BlockCols, bool InnerPanel>
struct unary_evaluator<Block<ArgType, BlockRows, BlockCols, InnerPanel>, IndexBased>
  : evaluator_base<Block<ArgType, BlockRows, BlockCols, InnerPanel> >
{
  typedef Block<ArgType, BlockRows, BlockCols, InnerPanel> XprType;

  EIGEN_DEVICE_FUNC explicit unary_evaluator(const XprType& block)
    : m_argImpl(block.nestedExpression()), 
      m_startRow(block.startRow()), 
      m_startCol(block.startCol()) 
  { }
 
  typedef typename XprType::Scalar Scalar;
  typedef typename XprType::CoeffReturnType CoeffReturnType;
  typedef typename XprType::PacketScalar PacketScalar;
  typedef typename XprType::PacketReturnType PacketReturnType;

  enum {
    RowsAtCompileTime = XprType::RowsAtCompileTime
  };
 
  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index row, Index col) const
  { 
    return m_argImpl.coeff(m_startRow.value() + row, m_startCol.value() + col); 
  }
  
  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index index) const
  { 
    return coeff(RowsAtCompileTime == 1 ? 0 : index, RowsAtCompileTime == 1 ? index : 0);
  }

  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index row, Index col)
  { 
    return m_argImpl.coeffRef(m_startRow.value() + row, m_startCol.value() + col); 
  }
  
  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index index)
  { 
    return coeffRef(RowsAtCompileTime == 1 ? 0 : index, RowsAtCompileTime == 1 ? index : 0);
  }
 
  template<int LoadMode> 
  PacketReturnType packet(Index row, Index col) const 
  { 
    return m_argImpl.template packet<LoadMode>(m_startRow.value() + row, m_startCol.value() + col); 
  }

  template<int LoadMode> 
  PacketReturnType packet(Index index) const 
  { 
    return packet<LoadMode>(RowsAtCompileTime == 1 ? 0 : index,
                            RowsAtCompileTime == 1 ? index : 0);
  }
  
  template<int StoreMode> 
  void writePacket(Index row, Index col, const PacketScalar& x) 
  { 
    return m_argImpl.template writePacket<StoreMode>(m_startRow.value() + row, m_startCol.value() + col, x); 
  }
  
  template<int StoreMode> 
  void writePacket(Index index, const PacketScalar& x) 
  { 
    return writePacket<StoreMode>(RowsAtCompileTime == 1 ? 0 : index,
                                  RowsAtCompileTime == 1 ? index : 0,
                                  x);
  }
 
protected:
  typename evaluator<ArgType>::nestedType m_argImpl;
  const variable_if_dynamic<Index, ArgType::RowsAtCompileTime == 1 ? 0 : Dynamic> m_startRow;
  const variable_if_dynamic<Index, ArgType::ColsAtCompileTime == 1 ? 0 : Dynamic> m_startCol;
};

// TODO: This evaluator does not actually use the child evaluator; 
// all action is via the data() as returned by the Block expression.

template<typename ArgType, int BlockRows, int BlockCols, bool InnerPanel> 
struct block_evaluator<ArgType, BlockRows, BlockCols, InnerPanel, /* HasDirectAccess */ true>
  : mapbase_evaluator<Block<ArgType, BlockRows, BlockCols, InnerPanel>,
                      typename Block<ArgType, BlockRows, BlockCols, InnerPanel>::PlainObject>
{
  typedef Block<ArgType, BlockRows, BlockCols, InnerPanel> XprType;
  typedef typename XprType::Scalar Scalar;

  EIGEN_DEVICE_FUNC explicit block_evaluator(const XprType& block)
    : mapbase_evaluator<XprType, typename XprType::PlainObject>(block) 
  {
    // TODO: should check for smaller packet types once we can handle multi-sized packet types
    const int AlignBytes = int(packet_traits<Scalar>::size) * sizeof(Scalar);
    EIGEN_ONLY_USED_FOR_DEBUG(AlignBytes)
    // FIXME this should be an internal assertion
    eigen_assert(EIGEN_IMPLIES(evaluator<XprType>::Flags&AlignedBit, (size_t(block.data()) % AlignBytes) == 0) && "data is not aligned");
  }
};


// -------------------- Select --------------------
// TODO shall we introduce a ternary_evaluator?

// TODO enable vectorization for Select
template<typename ConditionMatrixType, typename ThenMatrixType, typename ElseMatrixType>
struct evaluator<Select<ConditionMatrixType, ThenMatrixType, ElseMatrixType> >
  : evaluator_base<Select<ConditionMatrixType, ThenMatrixType, ElseMatrixType> >
{
  typedef Select<ConditionMatrixType, ThenMatrixType, ElseMatrixType> XprType;
  enum {
    CoeffReadCost = evaluator<ConditionMatrixType>::CoeffReadCost
                  + EIGEN_SIZE_MAX(evaluator<ThenMatrixType>::CoeffReadCost,
                                   evaluator<ElseMatrixType>::CoeffReadCost),

    Flags = (unsigned int)evaluator<ThenMatrixType>::Flags & evaluator<ElseMatrixType>::Flags & HereditaryBits
  };

  inline EIGEN_DEVICE_FUNC  explicit evaluator(const XprType& select)
    : m_conditionImpl(select.conditionMatrix()),
      m_thenImpl(select.thenMatrix()),
      m_elseImpl(select.elseMatrix())
  { }
 
  typedef typename XprType::CoeffReturnType CoeffReturnType;

  inline EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index row, Index col) const
  {
    if (m_conditionImpl.coeff(row, col))
      return m_thenImpl.coeff(row, col);
    else
      return m_elseImpl.coeff(row, col);
  }

  inline EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index index) const
  {
    if (m_conditionImpl.coeff(index))
      return m_thenImpl.coeff(index);
    else
      return m_elseImpl.coeff(index);
  }
 
protected:
  typename evaluator<ConditionMatrixType>::nestedType m_conditionImpl;
  typename evaluator<ThenMatrixType>::nestedType m_thenImpl;
  typename evaluator<ElseMatrixType>::nestedType m_elseImpl;
};


// -------------------- Replicate --------------------

template<typename ArgType, int RowFactor, int ColFactor> 
struct unary_evaluator<Replicate<ArgType, RowFactor, ColFactor> >
  : evaluator_base<Replicate<ArgType, RowFactor, ColFactor> >
{
  typedef Replicate<ArgType, RowFactor, ColFactor> XprType;
  typedef typename XprType::CoeffReturnType CoeffReturnType;
  typedef typename XprType::PacketReturnType PacketReturnType;
  enum {
    Factor = (RowFactor==Dynamic || ColFactor==Dynamic) ? Dynamic : RowFactor*ColFactor
  };
  typedef typename internal::nested_eval<ArgType,Factor>::type ArgTypeNested;
  typedef typename internal::remove_all<ArgTypeNested>::type ArgTypeNestedCleaned;
  
  enum {
    CoeffReadCost = evaluator<ArgTypeNestedCleaned>::CoeffReadCost,
    
    Flags = (evaluator<ArgTypeNestedCleaned>::Flags & HereditaryBits & ~RowMajorBit) | (traits<XprType>::Flags & RowMajorBit)
  };

  EIGEN_DEVICE_FUNC explicit unary_evaluator(const XprType& replicate)
    : m_arg(replicate.nestedExpression()),
      m_argImpl(m_arg),
      m_rows(replicate.nestedExpression().rows()),
      m_cols(replicate.nestedExpression().cols())
  {}
 
  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index row, Index col) const
  {
    // try to avoid using modulo; this is a pure optimization strategy
    const Index actual_row = internal::traits<XprType>::RowsAtCompileTime==1 ? 0
                           : RowFactor==1 ? row
                           : row % m_rows.value();
    const Index actual_col = internal::traits<XprType>::ColsAtCompileTime==1 ? 0
                           : ColFactor==1 ? col
                           : col % m_cols.value();
    
    return m_argImpl.coeff(actual_row, actual_col);
  }
  
  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index index) const
  {
    // try to avoid using modulo; this is a pure optimization strategy
    const Index actual_index = internal::traits<XprType>::RowsAtCompileTime==1
                                  ? (ColFactor==1 ?  index : index%m_cols.value())
                                  : (RowFactor==1 ?  index : index%m_rows.value());
    
    return m_argImpl.coeff(actual_index);
  }

  template<int LoadMode>
  PacketReturnType packet(Index row, Index col) const
  {
    const Index actual_row = internal::traits<XprType>::RowsAtCompileTime==1 ? 0
                           : RowFactor==1 ? row
                           : row % m_rows.value();
    const Index actual_col = internal::traits<XprType>::ColsAtCompileTime==1 ? 0
                           : ColFactor==1 ? col
                           : col % m_cols.value();

    return m_argImpl.template packet<LoadMode>(actual_row, actual_col);
  }
  
  template<int LoadMode>
  PacketReturnType packet(Index index) const
  {
    const Index actual_index = internal::traits<XprType>::RowsAtCompileTime==1
                                  ? (ColFactor==1 ?  index : index%m_cols.value())
                                  : (RowFactor==1 ?  index : index%m_rows.value());

    return m_argImpl.template packet<LoadMode>(actual_index);
  }
 
protected:
  const ArgTypeNested m_arg; // FIXME is it OK to store both the argument and its evaluator?? (we have the same situation in evaluator_product)
  typename evaluator<ArgTypeNestedCleaned>::nestedType m_argImpl;
  const variable_if_dynamic<Index, ArgType::RowsAtCompileTime> m_rows;
  const variable_if_dynamic<Index, ArgType::ColsAtCompileTime> m_cols;
};


// -------------------- PartialReduxExpr --------------------
//
// This is a wrapper around the expression object. 
// TODO: Find out how to write a proper evaluator without duplicating
//       the row() and col() member functions.

template< typename ArgType, typename MemberOp, int Direction>
struct evaluator<PartialReduxExpr<ArgType, MemberOp, Direction> >
  : evaluator_base<PartialReduxExpr<ArgType, MemberOp, Direction> >
{
  typedef PartialReduxExpr<ArgType, MemberOp, Direction> XprType;
  typedef typename XprType::Scalar InputScalar;
  enum {
    TraversalSize = Direction==int(Vertical) ? int(ArgType::RowsAtCompileTime) :  int(XprType::ColsAtCompileTime)
  };
  typedef typename MemberOp::template Cost<InputScalar,int(TraversalSize)> CostOpType;
  enum {
    CoeffReadCost = TraversalSize==Dynamic ? Dynamic
                  : TraversalSize * evaluator<ArgType>::CoeffReadCost + int(CostOpType::value),
    
    Flags = (traits<XprType>::Flags&RowMajorBit) | (evaluator<ArgType>::Flags&HereditaryBits)
  };

  EIGEN_DEVICE_FUNC explicit evaluator(const XprType expr)
    : m_expr(expr)
  {}

  typedef typename XprType::CoeffReturnType CoeffReturnType;
 
  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index row, Index col) const
  { 
    return m_expr.coeff(row, col);
  }
  
  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index index) const
  { 
    return m_expr.coeff(index);
  }

protected:
  const XprType m_expr;
};


// -------------------- MatrixWrapper and ArrayWrapper --------------------
//
// evaluator_wrapper_base<T> is a common base class for the
// MatrixWrapper and ArrayWrapper evaluators.

template<typename XprType>
struct evaluator_wrapper_base
  : evaluator_base<XprType>
{
  typedef typename remove_all<typename XprType::NestedExpressionType>::type ArgType;
  enum {
    CoeffReadCost = evaluator<ArgType>::CoeffReadCost,
    Flags = evaluator<ArgType>::Flags
  };

  EIGEN_DEVICE_FUNC explicit evaluator_wrapper_base(const ArgType& arg) : m_argImpl(arg) {}

  typedef typename ArgType::Scalar Scalar;
  typedef typename ArgType::CoeffReturnType CoeffReturnType;
  typedef typename ArgType::PacketScalar PacketScalar;
  typedef typename ArgType::PacketReturnType PacketReturnType;

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index row, Index col) const
  {
    return m_argImpl.coeff(row, col);
  }

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index index) const
  {
    return m_argImpl.coeff(index);
  }

  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index row, Index col)
  {
    return m_argImpl.coeffRef(row, col);
  }

  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index index)
  {
    return m_argImpl.coeffRef(index);
  }

  template<int LoadMode> 
  PacketReturnType packet(Index row, Index col) const
  {
    return m_argImpl.template packet<LoadMode>(row, col);
  }

  template<int LoadMode> 
  PacketReturnType packet(Index index) const
  {
    return m_argImpl.template packet<LoadMode>(index);
  }

  template<int StoreMode> 
  void writePacket(Index row, Index col, const PacketScalar& x)
  {
    m_argImpl.template writePacket<StoreMode>(row, col, x);
  }

  template<int StoreMode> 
  void writePacket(Index index, const PacketScalar& x)
  {
    m_argImpl.template writePacket<StoreMode>(index, x);
  }

protected:
  typename evaluator<ArgType>::nestedType m_argImpl;
};

template<typename TArgType>
struct unary_evaluator<MatrixWrapper<TArgType> >
  : evaluator_wrapper_base<MatrixWrapper<TArgType> >
{
  typedef MatrixWrapper<TArgType> XprType;

  EIGEN_DEVICE_FUNC explicit unary_evaluator(const XprType& wrapper)
    : evaluator_wrapper_base<MatrixWrapper<TArgType> >(wrapper.nestedExpression())
  { }
};

template<typename TArgType>
struct unary_evaluator<ArrayWrapper<TArgType> >
  : evaluator_wrapper_base<ArrayWrapper<TArgType> >
{
  typedef ArrayWrapper<TArgType> XprType;

  EIGEN_DEVICE_FUNC explicit unary_evaluator(const XprType& wrapper)
    : evaluator_wrapper_base<ArrayWrapper<TArgType> >(wrapper.nestedExpression())
  { }
};


// -------------------- Reverse --------------------

// defined in Reverse.h:
template<typename PacketScalar, bool ReversePacket> struct reverse_packet_cond;

template<typename ArgType, int Direction>
struct unary_evaluator<Reverse<ArgType, Direction> >
  : evaluator_base<Reverse<ArgType, Direction> >
{
  typedef Reverse<ArgType, Direction> XprType;
  typedef typename XprType::Scalar Scalar;
  typedef typename XprType::CoeffReturnType CoeffReturnType;
  typedef typename XprType::PacketScalar PacketScalar;
  typedef typename XprType::PacketReturnType PacketReturnType;

  enum {
    PacketSize = internal::packet_traits<Scalar>::size,
    IsRowMajor = XprType::IsRowMajor,
    IsColMajor = !IsRowMajor,
    ReverseRow = (Direction == Vertical)   || (Direction == BothDirections),
    ReverseCol = (Direction == Horizontal) || (Direction == BothDirections),
    OffsetRow  = ReverseRow && IsColMajor ? PacketSize : 1,
    OffsetCol  = ReverseCol && IsRowMajor ? PacketSize : 1,
    ReversePacket = (Direction == BothDirections)
                    || ((Direction == Vertical)   && IsColMajor)
                    || ((Direction == Horizontal) && IsRowMajor),
                    
    CoeffReadCost = evaluator<ArgType>::CoeffReadCost,
    
    // let's enable LinearAccess only with vectorization because of the product overhead
    // FIXME enable DirectAccess with negative strides?
    Flags0 = evaluator<ArgType>::Flags,
    LinearAccess = ( (Direction==BothDirections) && (int(Flags0)&PacketAccessBit) )
                 ? LinearAccessBit : 0,

    Flags = int(Flags0) & (HereditaryBits | PacketAccessBit | LinearAccess)
  };
  typedef internal::reverse_packet_cond<PacketScalar,ReversePacket> reverse_packet;

  EIGEN_DEVICE_FUNC explicit unary_evaluator(const XprType& reverse)
    : m_argImpl(reverse.nestedExpression()),
      m_rows(ReverseRow ? reverse.nestedExpression().rows() : 0),
      m_cols(ReverseCol ? reverse.nestedExpression().cols() : 0)
  { }
 
  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index row, Index col) const
  {
    return m_argImpl.coeff(ReverseRow ? m_rows.value() - row - 1 : row,
                           ReverseCol ? m_cols.value() - col - 1 : col);
  }

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index index) const
  {
    return m_argImpl.coeff(m_rows.value() * m_cols.value() - index - 1);
  }

  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index row, Index col)
  {
    return m_argImpl.coeffRef(ReverseRow ? m_rows.value() - row - 1 : row,
                              ReverseCol ? m_cols.value() - col - 1 : col);
  }

  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index index)
  {
    return m_argImpl.coeffRef(m_rows.value() * m_cols.value() - index - 1);
  }

  template<int LoadMode>
  PacketScalar packet(Index row, Index col) const
  {
    return reverse_packet::run(m_argImpl.template packet<LoadMode>(
                                  ReverseRow ? m_rows.value() - row - OffsetRow : row,
                                  ReverseCol ? m_cols.value() - col - OffsetCol : col));
  }

  template<int LoadMode>
  PacketScalar packet(Index index) const
  {
    return preverse(m_argImpl.template packet<LoadMode>(m_rows.value() * m_cols.value() - index - PacketSize));
  }

  template<int LoadMode>
  void writePacket(Index row, Index col, const PacketScalar& x)
  {
    m_argImpl.template writePacket<LoadMode>(
                                  ReverseRow ? m_rows.value() - row - OffsetRow : row,
                                  ReverseCol ? m_cols.value() - col - OffsetCol : col,
                                  reverse_packet::run(x));
  }

  template<int LoadMode>
  void writePacket(Index index, const PacketScalar& x)
  {
    m_argImpl.template writePacket<LoadMode>
      (m_rows.value() * m_cols.value() - index - PacketSize, preverse(x));
  }
 
protected:
  typename evaluator<ArgType>::nestedType m_argImpl;

  // If we do not reverse rows, then we do not need to know the number of rows; same for columns
  const variable_if_dynamic<Index, ReverseRow ? ArgType::RowsAtCompileTime : 0> m_rows;
  const variable_if_dynamic<Index, ReverseCol ? ArgType::ColsAtCompileTime : 0> m_cols;
};


// -------------------- Diagonal --------------------

template<typename ArgType, int DiagIndex>
struct evaluator<Diagonal<ArgType, DiagIndex> >
  : evaluator_base<Diagonal<ArgType, DiagIndex> >
{
  typedef Diagonal<ArgType, DiagIndex> XprType;
  
  enum {
    CoeffReadCost = evaluator<ArgType>::CoeffReadCost,
    
    Flags = (unsigned int)evaluator<ArgType>::Flags & (HereditaryBits | LinearAccessBit | DirectAccessBit) & ~RowMajorBit
  };

  EIGEN_DEVICE_FUNC explicit evaluator(const XprType& diagonal)
    : m_argImpl(diagonal.nestedExpression()),
      m_index(diagonal.index())
  { }
 
  typedef typename XprType::Scalar Scalar;
  // FIXME having to check whether ArgType is sparse here i not very nice.
  typedef typename internal::conditional<!internal::is_same<typename ArgType::StorageKind,Sparse>::value,
                                         typename XprType::CoeffReturnType,Scalar>::type CoeffReturnType;

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index row, Index) const
  {
    return m_argImpl.coeff(row + rowOffset(), row + colOffset());
  }

  EIGEN_DEVICE_FUNC CoeffReturnType coeff(Index index) const
  {
    return m_argImpl.coeff(index + rowOffset(), index + colOffset());
  }

  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index row, Index)
  {
    return m_argImpl.coeffRef(row + rowOffset(), row + colOffset());
  }

  EIGEN_DEVICE_FUNC Scalar& coeffRef(Index index)
  {
    return m_argImpl.coeffRef(index + rowOffset(), index + colOffset());
  }

protected:
  typename evaluator<ArgType>::nestedType m_argImpl;
  const internal::variable_if_dynamicindex<Index, XprType::DiagIndex> m_index;

private:
  EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Index rowOffset() const { return m_index.value() > 0 ? 0 : -m_index.value(); }
  EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Index colOffset() const { return m_index.value() > 0 ? m_index.value() : 0; }
};


//----------------------------------------------------------------------
// deprecated code
//----------------------------------------------------------------------

// -------------------- EvalToTemp --------------------

// expression class for evaluating nested expression to a temporary

template<typename ArgType> class EvalToTemp;

template<typename ArgType>
struct traits<EvalToTemp<ArgType> >
  : public traits<ArgType>
{ };

template<typename ArgType>
class EvalToTemp
  : public dense_xpr_base<EvalToTemp<ArgType> >::type
{
 public:
 
  typedef typename dense_xpr_base<EvalToTemp>::type Base;
  EIGEN_GENERIC_PUBLIC_INTERFACE(EvalToTemp)
 
  explicit EvalToTemp(const ArgType& arg)
    : m_arg(arg)
  { }
 
  const ArgType& arg() const
  {
    return m_arg;
  }

  Index rows() const 
  {
    return m_arg.rows();
  }

  Index cols() const 
  {
    return m_arg.cols();
  }

 private:
  const ArgType& m_arg;
};
 
template<typename ArgType>
struct evaluator<EvalToTemp<ArgType> >
  : public evaluator<typename ArgType::PlainObject>::type
{
  typedef EvalToTemp<ArgType>                   XprType;
  typedef typename ArgType::PlainObject         PlainObject;
  typedef typename evaluator<PlainObject>::type Base;
  
  typedef evaluator type;
  typedef evaluator nestedType;

  EIGEN_DEVICE_FUNC explicit evaluator(const XprType& xpr)
    : m_result(xpr.rows(), xpr.cols())
  {
    ::new (static_cast<Base*>(this)) Base(m_result);
    // TODO we should simply do m_result(xpr.arg());
    call_dense_assignment_loop(m_result, xpr.arg());
  }

  // This constructor is used when nesting an EvalTo evaluator in another evaluator
  EIGEN_DEVICE_FUNC evaluator(const ArgType& arg)
    : m_result(arg.rows(), arg.cols())
  {
    ::new (static_cast<Base*>(this)) Base(m_result);
    // TODO we should simply do m_result(xpr.arg());
    call_dense_assignment_loop(m_result, arg);
  }

protected:
  PlainObject m_result;
};

} // namespace internal

} // end namespace Eigen

#endif // EIGEN_COREEVALUATORS_H