1 // This file is part of Eigen, a lightweight C++ template library 2 // for linear algebra. 3 // 4 // Copyright (C) 2009 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_NOALIAS_H 11 #define EIGEN_NOALIAS_H 12 13 namespace Eigen { 14 15 /** \class NoAlias 16 * \ingroup Core_Module 17 * 18 * \brief Pseudo expression providing an operator = assuming no aliasing 19 * 20 * \param ExpressionType the type of the object on which to do the lazy assignment 21 * 22 * This class represents an expression with special assignment operators 23 * assuming no aliasing between the target expression and the source expression. 24 * More precisely it alloas to bypass the EvalBeforeAssignBit flag of the source expression. 25 * It is the return type of MatrixBase::noalias() 26 * and most of the time this is the only way it is used. 27 * 28 * \sa MatrixBase::noalias() 29 */ 30 template<typename ExpressionType, template <typename> class StorageBase> 31 class NoAlias 32 { 33 typedef typename ExpressionType::Scalar Scalar; 34 public: 35 NoAlias(ExpressionType& expression) : m_expression(expression) {} 36 37 /** Behaves like MatrixBase::lazyAssign(other) 38 * \sa MatrixBase::lazyAssign() */ 39 template<typename OtherDerived> 40 EIGEN_STRONG_INLINE ExpressionType& operator=(const StorageBase<OtherDerived>& other) 41 { return internal::assign_selector<ExpressionType,OtherDerived,false>::run(m_expression,other.derived()); } 42 43 /** \sa MatrixBase::operator+= */ 44 template<typename OtherDerived> 45 EIGEN_STRONG_INLINE ExpressionType& operator+=(const StorageBase<OtherDerived>& other) 46 { 47 typedef SelfCwiseBinaryOp<internal::scalar_sum_op<Scalar>, ExpressionType, OtherDerived> SelfAdder; 48 SelfAdder tmp(m_expression); 49 typedef typename internal::nested<OtherDerived>::type OtherDerivedNested; 50 typedef typename internal::remove_all<OtherDerivedNested>::type _OtherDerivedNested; 51 internal::assign_selector<SelfAdder,_OtherDerivedNested,false>::run(tmp,OtherDerivedNested(other.derived())); 52 return m_expression; 53 } 54 55 /** \sa MatrixBase::operator-= */ 56 template<typename OtherDerived> 57 EIGEN_STRONG_INLINE ExpressionType& operator-=(const StorageBase<OtherDerived>& other) 58 { 59 typedef SelfCwiseBinaryOp<internal::scalar_difference_op<Scalar>, ExpressionType, OtherDerived> SelfAdder; 60 SelfAdder tmp(m_expression); 61 typedef typename internal::nested<OtherDerived>::type OtherDerivedNested; 62 typedef typename internal::remove_all<OtherDerivedNested>::type _OtherDerivedNested; 63 internal::assign_selector<SelfAdder,_OtherDerivedNested,false>::run(tmp,OtherDerivedNested(other.derived())); 64 return m_expression; 65 } 66 67 #ifndef EIGEN_PARSED_BY_DOXYGEN 68 template<typename ProductDerived, typename Lhs, typename Rhs> 69 EIGEN_STRONG_INLINE ExpressionType& operator+=(const ProductBase<ProductDerived, Lhs,Rhs>& other) 70 { other.derived().addTo(m_expression); return m_expression; } 71 72 template<typename ProductDerived, typename Lhs, typename Rhs> 73 EIGEN_STRONG_INLINE ExpressionType& operator-=(const ProductBase<ProductDerived, Lhs,Rhs>& other) 74 { other.derived().subTo(m_expression); return m_expression; } 75 76 template<typename Lhs, typename Rhs, int NestingFlags> 77 EIGEN_STRONG_INLINE ExpressionType& operator+=(const CoeffBasedProduct<Lhs,Rhs,NestingFlags>& other) 78 { return m_expression.derived() += CoeffBasedProduct<Lhs,Rhs,NestByRefBit>(other.lhs(), other.rhs()); } 79 80 template<typename Lhs, typename Rhs, int NestingFlags> 81 EIGEN_STRONG_INLINE ExpressionType& operator-=(const CoeffBasedProduct<Lhs,Rhs,NestingFlags>& other) 82 { return m_expression.derived() -= CoeffBasedProduct<Lhs,Rhs,NestByRefBit>(other.lhs(), other.rhs()); } 83 #endif 84 85 protected: 86 ExpressionType& m_expression; 87 }; 88 89 /** \returns a pseudo expression of \c *this with an operator= assuming 90 * no aliasing between \c *this and the source expression. 91 * 92 * More precisely, noalias() allows to bypass the EvalBeforeAssignBit flag. 93 * Currently, even though several expressions may alias, only product 94 * expressions have this flag. Therefore, noalias() is only usefull when 95 * the source expression contains a matrix product. 96 * 97 * Here are some examples where noalias is usefull: 98 * \code 99 * D.noalias() = A * B; 100 * D.noalias() += A.transpose() * B; 101 * D.noalias() -= 2 * A * B.adjoint(); 102 * \endcode 103 * 104 * On the other hand the following example will lead to a \b wrong result: 105 * \code 106 * A.noalias() = A * B; 107 * \endcode 108 * because the result matrix A is also an operand of the matrix product. Therefore, 109 * there is no alternative than evaluating A * B in a temporary, that is the default 110 * behavior when you write: 111 * \code 112 * A = A * B; 113 * \endcode 114 * 115 * \sa class NoAlias 116 */ 117 template<typename Derived> 118 NoAlias<Derived,MatrixBase> MatrixBase<Derived>::noalias() 119 { 120 return derived(); 121 } 122 123 } // end namespace Eigen 124 125 #endif // EIGEN_NOALIAS_H 126
