From 88bb2087c100d21f40546829759ebd58d14947ff Mon Sep 17 00:00:00 2001
From: Benoit Jacob <jacob.benoit.1@gmail.com>
Date: Tue, 5 Aug 2008 21:55:57 +0000
Subject: [PATCH] New implementation of Swap as discussed, reusing Assign.
 Makes LU run 10% faster overall.

---
 Eigen/src/Core/Swap.h                     | 136 ++++++++++++++--------
 Eigen/src/Core/util/ForwardDeclarations.h |   1 +
 2 files changed, 90 insertions(+), 47 deletions(-)

diff --git a/Eigen/src/Core/Swap.h b/Eigen/src/Core/Swap.h
index 3b864789e..0ee57017e 100644
--- a/Eigen/src/Core/Swap.h
+++ b/Eigen/src/Core/Swap.h
@@ -25,8 +25,94 @@
 #ifndef EIGEN_SWAP_H
 #define EIGEN_SWAP_H
 
-template <typename Derived, typename OtherDerived, bool IsVector = Derived::IsVectorAtCompileTime>
-struct ei_swap_selector;
+/** \class SwapWrapper
+  *
+  * \brief Expression which must be nested by value
+  *
+  * \param ExpressionType the type of the object of which we are requiring nesting-by-value
+  *
+  * This class is the return type of MatrixBase::nestByValue()
+  * and most of the time this is the only way it is used.
+  *
+  * \sa MatrixBase::nestByValue()
+  */
+template<typename ExpressionType>
+struct ei_traits<SwapWrapper<ExpressionType> >
+{
+  typedef typename ExpressionType::Scalar Scalar;
+  enum {
+    RowsAtCompileTime = ExpressionType::RowsAtCompileTime,
+    ColsAtCompileTime = ExpressionType::ColsAtCompileTime,
+    MaxRowsAtCompileTime = ExpressionType::MaxRowsAtCompileTime,
+    MaxColsAtCompileTime = ExpressionType::MaxColsAtCompileTime,
+    Flags = ExpressionType::Flags,
+    CoeffReadCost = ExpressionType::CoeffReadCost
+  };
+};
+
+template<typename ExpressionType> class SwapWrapper
+  : public MatrixBase<SwapWrapper<ExpressionType> >
+{
+  public:
+
+    EIGEN_GENERIC_PUBLIC_INTERFACE(SwapWrapper)
+    typedef typename ei_packet_traits<Scalar>::type Packet;
+
+    inline SwapWrapper(ExpressionType& matrix) : m_expression(matrix) {}
+
+    inline int rows() const { return m_expression.rows(); }
+    inline int cols() const { return m_expression.cols(); }
+    inline int stride() const { return m_expression.stride(); }
+
+    template<typename OtherDerived>
+    void copyCoeff(int row, int col, const MatrixBase<OtherDerived>& other)
+    {
+      OtherDerived& _other = other.const_cast_derived();
+      ei_internal_assert(row >= 0 && row < rows()
+                         && col >= 0 && col < cols());
+      Scalar tmp = m_expression.coeff(row, col);
+      m_expression.coeffRef(row, col) = _other.coeff(row, col);
+      _other.coeffRef(row, col) = tmp;
+    }
+
+    template<typename OtherDerived>
+    void copyCoeff(int index, const MatrixBase<OtherDerived>& other)
+    {
+      OtherDerived& _other = other.const_cast_derived();
+      ei_internal_assert(index >= 0 && index < m_expression.size());
+      Scalar tmp = m_expression.coeff(index);
+      m_expression.coeffRef(index) = _other.coeff(index);
+      _other.coeffRef(index) = tmp;
+    }
+
+    template<typename OtherDerived, int LoadStoreMode>
+    void copyPacket(int row, int col, const MatrixBase<OtherDerived>& other)
+    {
+      OtherDerived& _other = other.const_cast_derived();
+      ei_internal_assert(row >= 0 && row < rows()
+                        && col >= 0 && col < cols());
+      Packet tmp = m_expression.template packet<LoadStoreMode>(row, col);
+      m_expression.template writePacket<LoadStoreMode>(row, col,
+        _other.template packet<LoadStoreMode>(row, col)
+      );
+      _other.template writePacket<LoadStoreMode>(row, col, tmp);
+    }
+
+    template<typename OtherDerived, int LoadStoreMode>
+    void copyPacket(int index, const MatrixBase<OtherDerived>& other)
+    {
+      OtherDerived& _other = other.const_cast_derived();
+      ei_internal_assert(index >= 0 && index < m_expression.size());
+      Packet tmp = m_expression.template packet<LoadStoreMode>(index);
+      m_expression.template writePacket<LoadStoreMode>(index,
+        _other.template packet<LoadStoreMode>(index)
+      );
+      _other.template writePacket<LoadStoreMode>(index, tmp);
+    }
+
+  protected:
+    ExpressionType m_expression;
+};
 
 /** swaps *this with the expression \a other.
   *
@@ -41,51 +127,7 @@ template<typename Derived>
 template<typename OtherDerived>
 void MatrixBase<Derived>::swap(const MatrixBase<OtherDerived>& other)
 {
-  MatrixBase<OtherDerived> *_other = const_cast<MatrixBase<OtherDerived>*>(&other);
-
-  // disable that path: it makes LU decomposition fail ! I can't see the bug though.
-  if(false /*SizeAtCompileTime == Dynamic*/)
-  {
-    ei_swap_selector<Derived,OtherDerived>::run(derived(),other.const_cast_derived());
-  }
-  else // SizeAtCompileTime != Dynamic
-  {
-    typename Derived::Eval buf(*this);
-    *this = other;
-    *_other = buf;
-  }
+  SwapWrapper<Derived>(derived()).lazyAssign(other);
 }
 
-template<typename Derived, typename OtherDerived>
-struct ei_swap_selector<Derived,OtherDerived,true>
-{
-  inline static void run(Derived& src, OtherDerived& other)
-  {
-    typename Derived::Scalar tmp;
-    ei_assert(OtherDerived::IsVectorAtCompileTime && src.size() == other.size());
-    for(int i = 0; i < src.size(); i++)
-    {
-      tmp = src.coeff(i);
-      src.coeffRef(i) = other.coeff(i);
-      other.coeffRef(i) = tmp;
-    }
-  }
-};
-
-template<typename Derived, typename OtherDerived>
-struct ei_swap_selector<Derived,OtherDerived,false>
-{
-  inline static void run(Derived& src, OtherDerived& other)
-  {
-    typename Derived::Scalar tmp;
-    for(int j = 0; j < src.cols(); j++)
-      for(int i = 0; i < src.rows(); i++)
-      {
-        tmp = src.coeff(i, j);
-        src.coeffRef(i, j) = other.coeff(i, j);
-        other.coeffRef(i, j) = tmp;
-      }
-  }
-};
-
 #endif // EIGEN_SWAP_H
diff --git a/Eigen/src/Core/util/ForwardDeclarations.h b/Eigen/src/Core/util/ForwardDeclarations.h
index 067ccd0b0..a886a90d0 100644
--- a/Eigen/src/Core/util/ForwardDeclarations.h
+++ b/Eigen/src/Core/util/ForwardDeclarations.h
@@ -41,6 +41,7 @@ class Matrix;
 
 template<typename ExpressionType, unsigned int Added, unsigned int Removed> class Flagged;
 template<typename ExpressionType> class NestByValue;
+template<typename ExpressionType> class SwapWrapper;
 template<typename MatrixType> class Minor;
 template<typename MatrixType, int BlockRows=Dynamic, int BlockCols=Dynamic,
          int DirectAccessStatus = ei_traits<MatrixType>::Flags&DirectAccessBit> class Block;