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- // This file is part of Eigen, a lightweight C++ template library
- // for linear algebra.
- //
- // Copyright (C) 2009 Gael Guennebaud <gael.guennebaud@inria.fr>
- //
- // 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_NOALIAS_H
- #define EIGEN_NOALIAS_H
- namespace Eigen {
- /** \class NoAlias
- * \ingroup Core_Module
- *
- * \brief Pseudo expression providing an operator = assuming no aliasing
- *
- * \tparam ExpressionType the type of the object on which to do the lazy assignment
- *
- * This class represents an expression with special assignment operators
- * assuming no aliasing between the target expression and the source expression.
- * More precisely it alloas to bypass the EvalBeforeAssignBit flag of the source expression.
- * It is the return type of MatrixBase::noalias()
- * and most of the time this is the only way it is used.
- *
- * \sa MatrixBase::noalias()
- */
- template<typename ExpressionType, template <typename> class StorageBase>
- class NoAlias
- {
- public:
- typedef typename ExpressionType::Scalar Scalar;
-
- explicit NoAlias(ExpressionType& expression) : m_expression(expression) {}
-
- template<typename OtherDerived>
- EIGEN_DEVICE_FUNC
- EIGEN_STRONG_INLINE ExpressionType& operator=(const StorageBase<OtherDerived>& other)
- {
- call_assignment_no_alias(m_expression, other.derived(), internal::assign_op<Scalar,typename OtherDerived::Scalar>());
- return m_expression;
- }
-
- template<typename OtherDerived>
- EIGEN_DEVICE_FUNC
- EIGEN_STRONG_INLINE ExpressionType& operator+=(const StorageBase<OtherDerived>& other)
- {
- call_assignment_no_alias(m_expression, other.derived(), internal::add_assign_op<Scalar,typename OtherDerived::Scalar>());
- return m_expression;
- }
-
- template<typename OtherDerived>
- EIGEN_DEVICE_FUNC
- EIGEN_STRONG_INLINE ExpressionType& operator-=(const StorageBase<OtherDerived>& other)
- {
- call_assignment_no_alias(m_expression, other.derived(), internal::sub_assign_op<Scalar,typename OtherDerived::Scalar>());
- return m_expression;
- }
- EIGEN_DEVICE_FUNC
- ExpressionType& expression() const
- {
- return m_expression;
- }
- protected:
- ExpressionType& m_expression;
- };
- /** \returns a pseudo expression of \c *this with an operator= assuming
- * no aliasing between \c *this and the source expression.
- *
- * More precisely, noalias() allows to bypass the EvalBeforeAssignBit flag.
- * Currently, even though several expressions may alias, only product
- * expressions have this flag. Therefore, noalias() is only usefull when
- * the source expression contains a matrix product.
- *
- * Here are some examples where noalias is usefull:
- * \code
- * D.noalias() = A * B;
- * D.noalias() += A.transpose() * B;
- * D.noalias() -= 2 * A * B.adjoint();
- * \endcode
- *
- * On the other hand the following example will lead to a \b wrong result:
- * \code
- * A.noalias() = A * B;
- * \endcode
- * because the result matrix A is also an operand of the matrix product. Therefore,
- * there is no alternative than evaluating A * B in a temporary, that is the default
- * behavior when you write:
- * \code
- * A = A * B;
- * \endcode
- *
- * \sa class NoAlias
- */
- template<typename Derived>
- NoAlias<Derived,MatrixBase> MatrixBase<Derived>::noalias()
- {
- return NoAlias<Derived, Eigen::MatrixBase >(derived());
- }
- } // end namespace Eigen
- #endif // EIGEN_NOALIAS_H
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