Iterators - JBludau/kokkos GitHub Wiki

Kokkos::Experimental::{begin, cbegin, end, cend}

Header File: Kokkos_Core.hpp

template <class DataType, class... Properties>
KOKKOS_INLINE_FUNCTION auto begin(const Kokkos::View<DataType, Properties...>& view);  (1)

template <class DataType, class... Properties>
KOKKOS_INLINE_FUNCTION auto cbegin(const Kokkos::View<DataType, Properties...>& view); (2)

template <class DataType, class... Properties>
KOKKOS_INLINE_FUNCTION auto end(const Kokkos::View<DataType, Properties...>& view);    (3)

template <class DataType, class... Properties>
KOKKOS_INLINE_FUNCTION auto cend(const Kokkos::View<DataType, Properties...>& view);   (4)

Description

  • (1,2) return a Kokkos random access iterator to the beginning of view
  • (3,4) return a Kokkos random access iterator to the element past the end of view

Notes

  • the returned iterator is a random access for performance reasons

  • view is taken as const because, within each function, we are not changing the view itself: the returned iterator operates on the view without changing its structure.

  • dereferencing an iterator must be done within an execution space where view is accessible

  • cbegin, cend ensure that the dereferenced iterator is const-qualified

Parameters and Requirements

  • view: must be a rank-1 view with LayoutLeft, LayoutRight, or LayoutStride

Example

namespace KE = Kokkos::Experimental;
using view_type = Kokkos::View<int*>;
view_type a("a", 15);

auto it = KE::begin(a);
// if dereferenced (within a proper execution space), can modify the content of `a`

auto itc = KE::cbegin(a);
// if dereferenced (within a proper execution space), can only read the content of `a`

Kokkos::Experimental::distance

template <class IteratorType>
KOKKOS_INLINE_FUNCTION
constexpr typename IteratorType::difference_type distance(IteratorType first, IteratorType last);

Description

Returns the number of steps needed to go from first to last.

Parameters and Requirements

  • first, last: range to calculate distance of

Return

The number of steps needed to go from first to last. The value may be negative if random-access iterators are used.

Example

namespace KE = Kokkos::Experimental;
Kokkos::View<double*> a("a", 13);

auto it1 = KE::begin(a);
auto it2 = it1 + 4;
const auto stepsA = KE::distance(it1, it2);
// stepsA should be equal to 4

const auto stepsB = KE::distance(it2, it1);
// stepsB should be equal to -4

Kokkos::Experimental::iter_swap

template <class IteratorType>
void iter_swap(IteratorType first, IteratorType last);

Description

Swaps the values of the elements the given iterators are pointing to.

Parameters and Requirements

  • first, last: iterators to swap

Notes

Currently, the API does not have an execution space parameter because the operation is performed in the default execution space. The operation fences the default execution space.

Return

None

Example

namespace KE = Kokkos::Experimental;
Kokkos::View<double*> a("a", 13);

auto it1 = KE::begin(a);
auto it2 = it1 + 4;
KE::swap(it1, it2);
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