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Initial commit for a modified ei_nested logic.

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This commit is contained in:
Hauke Heibel 2009-11-30 18:56:56 +01:00
parent 66534b782c
commit 1c2e476fa7
1 changed files with 54 additions and 7 deletions
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61
Eigen/src/Core/util/XprHelper.h
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@ -171,6 +171,46 @@ template<typename T> struct ei_plain_matrix_type_row_major
template<typename T> struct ei_must_nest_by_value { enum { ret = false }; };
template<typename T> struct ei_must_nest_by_value<NestByValue<T> > { enum { ret = true }; };
/**
* Just a sanity check in order to verify that NestByValue is never
* used in combination with Matrix. Currently, I don't see a use case
* for nesting matrices by value. When an expression requires a temporary
* this should be handled through PlainMatrixType (i.e. arithmetic cost
* check + eval before nesting check).
* Note: If this were happening there were no harm but - if we are sure
* this does not happen, we can actually get rid of NestByValue!
**/
template <typename T> struct ei_is_nested_matrix { typedef int ok; };
template<typename _Scalar, int _Rows, int _Cols, int _Options, int _MaxRows, int _MaxCols>
struct ei_is_nested_matrix< NestByValue< Matrix<_Scalar, _Rows, _Cols, _Options, _MaxRows, _MaxCols> > > {};
/**
* The reference selector for template expressions. The idea is that we don't
* need to use references for expressions since they are light weight proxy
* objects which should generate no copying overhead.
**/
template <typename T>
struct ei_ref_selector
{
typedef T type;
};
/**
* Matrices on the other hand side should only be copied, when it is sure
* we gain by copying (see arithmetic cost check and eval before nesting flag).
* Note: This is an optimization measure that comprises potential (though little)
* to create erroneous code. Any user, utilizing ei_nested outside of
* Eigen needs to take care that no references to temporaries are
* stored or that this potential danger is at least communicated
* to the user.
**/
template<typename _Scalar, int _Rows, int _Cols, int _Options, int _MaxRows, int _MaxCols>
struct ei_ref_selector< Matrix<_Scalar, _Rows, _Cols, _Options, _MaxRows, _MaxCols> >
{
typedef typename Matrix<_Scalar, _Rows, _Cols, _Options, _MaxRows, _MaxCols> MatrixType;
typedef MatrixType const& type;
};
/** \internal Determines how a given expression should be nested into another one.
* For example, when you do a * (b+c), Eigen will determine how the expression b+c should be
* nested into the bigger product expression. The choice is between nesting the expression b+c as-is, or
@ -195,15 +235,22 @@ template<typename T, int n=1, typename PlainMatrixType = typename ei_eval<T>::ty
CostEval = (n+1) * int(NumTraits<typename ei_traits<T>::Scalar>::ReadCost),
CostNoEval = (n-1) * int(ei_traits<T>::CoeffReadCost)
};
typedef typename ei_is_nested_matrix<T>::ok is_ok;
typedef typename ei_meta_if<
ei_must_nest_by_value<T>::ret,
T,
typename ei_meta_if<
(int(ei_traits<T>::Flags) & EvalBeforeNestingBit)
|| ( int(CostEval) <= int(CostNoEval) ),
PlainMatrixType,
const T&
>::ret
T,
typename ei_meta_if<
( int(ei_traits<T>::Flags) & EvalBeforeNestingBit ) ||
( int(CostEval) <= int(CostNoEval) ),
PlainMatrixType,
#ifdef EIGEN_OLD_NESTED
const T&
#else
typename ei_ref_selector<T>::type
#endif
>::ret
>::ret type;
};