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Merged
lmoneta merged 3 commits into from
Apr 13, 2017
Merged

Improvements and new interfaces in KahanSum #485

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6986e9c
Extend use cases to iterables
xvallspl Apr 6, 2017
7c92d54
Change interface to accept raw pointers as iterators
xvallspl Apr 6, 2017
020dcdb
Add option to provide an initial value in KahanSum
xvallspl Apr 6, 2017
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Change interface to accept raw pointers as iterators
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@xvallspl
xvallspl committed Apr 6, 2017
commit 7c92d5483618c84f09cf5acef202790492f23fdc
22 changes: 11 additions & 11 deletions math/mathcore/inc/Math/Util.h
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Original file line number Diff line number Diff line change
Expand Up @@ -92,21 +92,21 @@ namespace ROOT {
fSum = t;
}

/// Iterate over an iterable container of values and accumulate on the exising result
template<class Container>
void Add(const Container &elements)
{
static_assert(!std::is_same<decltype(++(elements.begin()), elements.end(), elements.front()), T>::value, "argument is not a container of the same type as the KahanSum class");
for (auto e : elements) this->Add(e);
/// Iterate over a datastructure referenced by a pointer and accumulate on the exising result
template<class Iterator>
void Add(const Iterator begin, const Iterator end)
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@dpiparo dpiparo Apr 6, 2017

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@xvallspl, @lmoneta : is it really better to have begin and end here? Can't we pass something to iterate on? With range based looping this would not imply any code change in the body of the methods.

{
static_assert(!std::is_same<decltype(*begin), T>::value, "Iterator points to an element of the different type than the KahanSum class");
for( auto it = begin; it!=end; it++ ) this->Add(*it);
}

/// Iterate over an iterable and return the result of its accumulation
template<class Container>
static T Accumulate(const Container &elements)
/// Iterate over a datastructure referenced by a pointer and return the result of its accumulation
template<class Iterator>
static T Accumulate(const Iterator begin, const Iterator end)
{
static_assert(!std::is_same<decltype(++(elements.begin()), elements.end(), elements.front()), T>::value, "argument is not a container of the same type as the KahanSum class");
static_assert(!std::is_same<decltype(*begin), T>::value, "Iterator points to an element of the different type than the KahanSum class");
KahanSum init;
init.Add(elements);
init.Add(begin, end);
return init.fSum;
}

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4 changes: 2 additions & 2 deletions math/mathcore/test/testKahan.cxx
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Expand Up @@ -5,8 +5,8 @@ int KahanTest()
{
std::vector<double> numbers = {0.01, 0.001, 0.0001, 0.000001, 0.00000000001};
ROOT::Math::KahanSum<double> k;
k.Add(numbers);
auto result = ROOT::Math::KahanSum<double>::Accumulate(numbers);
k.Add(numbers.begin(), numbers.end());
auto result = ROOT::Math::KahanSum<double>::Accumulate(numbers.begin(), numbers.end());
if (k.Result() != result) return 1;
return 0;
}
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