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Clarify note in nested_eval for evaluator creating temporaries.

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Gael Guennebaud 2015-10-09 14:57:51 +02:00
parent ae38910693
commit a4cc4c1e5e
1 changed files with 5 additions and 3 deletions
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8
Eigen/src/Core/util/XprHelper.h
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@ -396,9 +396,11 @@ template<typename T, int n, typename PlainObject = typename eval<T>::type> struc
DynamicAsInteger = 10000,
ScalarReadCost = NumTraits<typename traits<T>::Scalar>::ReadCost,
ScalarReadCostAsInteger = ScalarReadCost == Dynamic ? int(DynamicAsInteger) : int(ScalarReadCost),
CoeffReadCost = evaluator<T>::CoeffReadCost, // TODO What if an evaluator evaluate itself into a tempory?
// Then CoeffReadCost will be small but we still have to evaluate if n>1...
// The solution might be to ask the evaluator if it creates a temp. Perhaps we could even ask the number of temps?
CoeffReadCost = evaluator<T>::CoeffReadCost, // NOTE What if an evaluator evaluate itself into a tempory?
// Then CoeffReadCost will be small (e.g., 1) but we still have to evaluate, especially if n>1.
// This situation is already taken care by the EvalBeforeNestingBit flag, which is turned ON
// for all evaluator creating a temporary. This flag is then propagated by the parent evaluators.
// Another solution could be to count the number of temps?
CoeffReadCostAsInteger = CoeffReadCost == Dynamic ? int(DynamicAsInteger) : int(CoeffReadCost),
NAsInteger = n == Dynamic ? int(DynamicAsInteger) : n,
CostEvalAsInteger = (NAsInteger+1) * ScalarReadCostAsInteger + CoeffReadCostAsInteger,