/src/Geometry_Eigen/Eigen/src/Core/NoAlias.h

  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@inria.fr>
  5//
  6// Eigen is free software; you can redistribute it and/or
  7// modify it under the terms of the GNU Lesser General Public
  8// License as published by the Free Software Foundation; either
  9// version 3 of the License, or (at your option) any later version.
 10//
 11// Alternatively, you can redistribute it and/or
 12// modify it under the terms of the GNU General Public License as
 13// published by the Free Software Foundation; either version 2 of
 14// the License, or (at your option) any later version.
 15//
 16// Eigen is distributed in the hope that it will be useful, but WITHOUT ANY
 17// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 18// FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License or the
 19// GNU General Public License for more details.
 20//
 21// You should have received a copy of the GNU Lesser General Public
 22// License and a copy of the GNU General Public License along with
 23// Eigen. If not, see <http://www.gnu.org/licenses/>.
 24
 25#ifndef EIGEN_NOALIAS_H
 26#define EIGEN_NOALIAS_H
 27
 28/** \class NoAlias
 29  * \ingroup Core_Module
 30  *
 31  * \brief Pseudo expression providing an operator = assuming no aliasing
 32  *
 33  * \param ExpressionType the type of the object on which to do the lazy assignment
 34  *
 35  * This class represents an expression with special assignment operators
 36  * assuming no aliasing between the target expression and the source expression.
 37  * More precisely it alloas to bypass the EvalBeforeAssignBit flag of the source expression.
 38  * It is the return type of MatrixBase::noalias()
 39  * and most of the time this is the only way it is used.
 40  *
 41  * \sa MatrixBase::noalias()
 42  */
 43template<typename ExpressionType, template <typename> class StorageBase>
 44class NoAlias
 45{
 46    typedef typename ExpressionType::Scalar Scalar;
 47  public:
 48    NoAlias(ExpressionType& expression) : m_expression(expression) {}
 49
 50    /** Behaves like MatrixBase::lazyAssign(other)
 51      * \sa MatrixBase::lazyAssign() */
 52    template<typename OtherDerived>
 53    EIGEN_STRONG_INLINE ExpressionType& operator=(const StorageBase<OtherDerived>& other)
 54    { return internal::assign_selector<ExpressionType,OtherDerived,false>::run(m_expression,other.derived()); }
 55
 56    /** \sa MatrixBase::operator+= */
 57    template<typename OtherDerived>
 58    EIGEN_STRONG_INLINE ExpressionType& operator+=(const StorageBase<OtherDerived>& other)
 59    {
 60      typedef SelfCwiseBinaryOp<internal::scalar_sum_op<Scalar>, ExpressionType, OtherDerived> SelfAdder;
 61      SelfAdder tmp(m_expression);
 62      typedef typename internal::nested<OtherDerived>::type OtherDerivedNested;
 63      typedef typename internal::remove_all<OtherDerivedNested>::type _OtherDerivedNested;
 64      internal::assign_selector<SelfAdder,_OtherDerivedNested,false>::run(tmp,OtherDerivedNested(other.derived()));
 65      return m_expression;
 66    }
 67
 68    /** \sa MatrixBase::operator-= */
 69    template<typename OtherDerived>
 70    EIGEN_STRONG_INLINE ExpressionType& operator-=(const StorageBase<OtherDerived>& other)
 71    {
 72      typedef SelfCwiseBinaryOp<internal::scalar_difference_op<Scalar>, ExpressionType, OtherDerived> SelfAdder;
 73      SelfAdder tmp(m_expression);
 74      typedef typename internal::nested<OtherDerived>::type OtherDerivedNested;
 75      typedef typename internal::remove_all<OtherDerivedNested>::type _OtherDerivedNested;
 76      internal::assign_selector<SelfAdder,_OtherDerivedNested,false>::run(tmp,OtherDerivedNested(other.derived()));
 77      return m_expression;
 78    }
 79
 80#ifndef EIGEN_PARSED_BY_DOXYGEN
 81    template<typename ProductDerived, typename Lhs, typename Rhs>
 82    EIGEN_STRONG_INLINE ExpressionType& operator+=(const ProductBase<ProductDerived, Lhs,Rhs>& other)
 83    { other.derived().addTo(m_expression); return m_expression; }
 84
 85    template<typename ProductDerived, typename Lhs, typename Rhs>
 86    EIGEN_STRONG_INLINE ExpressionType& operator-=(const ProductBase<ProductDerived, Lhs,Rhs>& other)
 87    { other.derived().subTo(m_expression); return m_expression; }
 88
 89    template<typename Lhs, typename Rhs, int NestingFlags>
 90    EIGEN_STRONG_INLINE ExpressionType& operator+=(const CoeffBasedProduct<Lhs,Rhs,NestingFlags>& other)
 91    { return m_expression.derived() += CoeffBasedProduct<Lhs,Rhs,NestByRefBit>(other.lhs(), other.rhs()); }
 92
 93    template<typename Lhs, typename Rhs, int NestingFlags>
 94    EIGEN_STRONG_INLINE ExpressionType& operator-=(const CoeffBasedProduct<Lhs,Rhs,NestingFlags>& other)
 95    { return m_expression.derived() -= CoeffBasedProduct<Lhs,Rhs,NestByRefBit>(other.lhs(), other.rhs()); }
 96#endif
 97
 98  protected:
 99    ExpressionType& m_expression;
100};
101
102/** \returns a pseudo expression of \c *this with an operator= assuming
103  * no aliasing between \c *this and the source expression.
104  *
105  * More precisely, noalias() allows to bypass the EvalBeforeAssignBit flag.
106  * Currently, even though several expressions may alias, only product
107  * expressions have this flag. Therefore, noalias() is only usefull when
108  * the source expression contains a matrix product.
109  *
110  * Here are some examples where noalias is usefull:
111  * \code
112  * D.noalias()  = A * B;
113  * D.noalias() += A.transpose() * B;
114  * D.noalias() -= 2 * A * B.adjoint();
115  * \endcode
116  *
117  * On the other hand the following example will lead to a \b wrong result:
118  * \code
119  * A.noalias() = A * B;
120  * \endcode
121  * because the result matrix A is also an operand of the matrix product. Therefore,
122  * there is no alternative than evaluating A * B in a temporary, that is the default
123  * behavior when you write:
124  * \code
125  * A = A * B;
126  * \endcode
127  *
128  * \sa class NoAlias
129  */
130template<typename Derived>
131NoAlias<Derived,MatrixBase> MatrixBase<Derived>::noalias()
132{
133  return derived();
134}
135
136#endif // EIGEN_NOALIAS_H