StdNonModSeq

NonModifyingSequenceOperation

Header File: Kokkos_Core.hpp

All algorithms are currently in the Kokkos::Experimental namespace.

Kokkos::Experimental::find

template <class ExecutionSpace, class InputIterator, class T>
InputIterator find(const ExecutionSpace& exespace,                              (1)
                   InputIterator first, InputIterator last,
                   const T& value);

template <class ExecutionSpace, class InputIterator, class T>
InputIterator find(const std::string& label, const ExecutionSpace& exespace,    (2)
                   InputIterator first, InputIterator last,
                   const T& value);

template <class ExecutionSpace, class DataType, class... Properties, class T>
auto find(const ExecutionSpace& exespace,                                       (3)
          const ::Kokkos::View<DataType, Properties...>& view,
          const T& value);

template <class ExecutionSpace, class DataType, class... Properties, class T>
auto find(const std::string& label, const ExecutionSpace& exespace,             (4)
          const ::Kokkos::View<DataType, Properties...>& view,
          const T& value);

Description

Returns an iterator to the first element in [first, last) that equals value. Equality is checked using operator==.

• (1,2): overload set accepting iterators
• (3,4): overload set accepting views

Parameters and Requirements

• exespace:
  • execution space instance
• label:
  • string forwarded to all implementation kernels for debugging purposes
  • for 1, the default string is: "Kokkos::find_iterator_api_default"
  • for 3, the default string is: "Kokkos::find_view_api_default"
• first, last:
  • range of elements to search in
  • must be random access iterators, e.g., returned from Kokkos::Experimental::(c)begin/(c)end
  • must represent a valid range, i.e., last >= first (this condition is checked in debug mode)
  • must be accessible from exespace
• view:
  • must be rank-1, and have LayoutLeft, LayoutRight, or LayoutStride
  • must be accessible from exespace

Return

• (1,2): InputIterator instance pointing to the first element that equals value, or last if no elements is found
• (2,3): iterator to the first element that equals value, or Kokkos::Experimental::end(view) if none is found

Example

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

auto exespace = Kokkos::DefaultExecutionSpace;
auto it1 = KE::find(exespace, KE::cbegin(a), KE::cend(a), 5);

// assuming OpenMP is enabled and "a" is host-accessible, you can also do
auto it2 = KE::find(Kokkos::OpenMP(), KE::begin(a), KE::end(a), 5);

Kokkos::Experimental::find_if

template <class ExecutionSpace, class InputIterator, class PredicateType>
InputIterator find_if(const ExecutionSpace& exespace,                              (1)
                      InputIterator first, InputIterator last,
                      PredicateType pred);

template <class ExecutionSpace, class InputIterator, class PredicateType>
InputIterator find_if(const std::string& label, const ExecutionSpace& exespace,    (2)
                      InputIterator first, InputIterator last,
                      PredicateType pred);

template <class ExecutionSpace, class DataType, class... Properties, class PredicateType>
auto find_if(const ExecutionSpace& exespace,
             const ::Kokkos::View<DataType, Properties...>& view,                  (3)
             PredicateType pred);

template <class ExecutionSpace, class DataType, class... Properties, class PredicateType>
auto find_if(const std::string& label, const ExecutionSpace& exespace,
             const ::Kokkos::View<DataType, Properties...>& view,                  (4)
             PredicateType pred);

Description

Returns an iterator to the first element in [first, last) for which the predicate returns true.

• (1,2): overload set accepting iterators
• (3,4): overload set accepting views

Parameters and Requirements

• exespace, first, last, view: same as in find (TODO: link)
• label:
  • for 1, the default string is: "Kokkos::find_if_iterator_api_default"
  • for 3, the default string is: "Kokkos::find_if_view_api_default"
• pred:
  • unary predicate which returns true for the required element; pred(v) must be valid to be called from the execution space passed, and convertible to bool for every argument v of type (possible const) value_type, where value_type is the value type of InputIterator, and must not modify v.
  • must conform to:

  struct Predicate
  {
     KOKKOS_INLINE_FUNCTION
     bool operator()(const /*type needed */ & operand) const { return /* ... */; }
  
     // or, also valid
  
     KOKKOS_INLINE_FUNCTION
     bool operator()(/*type needed */ operand) const { return /* ... */; }
  };

Return

• (1,2): InputIterator instance pointing to the first element satisfying condition, or last if no elements is found
• (2,3): iterator to the first element that equals value, or Kokkos::Experimental::end(view) if none is found

Example

namespace KE = Kokkos::Experimental;

template<class ValueType>
struct EqualsValue
{
  const ValueType m_value;
  EqualsValFunctor(ValueType value) : m_value(value){}

  KOKKOS_INLINE_FUNCTION
  bool operator()(const ValueType & operand) const {
    return operand == m_value;
  }
};

using view_type = Kokkos::View<int*>;
view_type a("a", 15);
// fill a somehow

// create predicate
EqualsValue<int> p(5);

auto exespace = Kokkos::DefaultExecutionSpace;
auto it1 = KE::find_if(exespace, KE::begin(a), KE::end(a), p);

// assuming OpenMP is enabled, then you can also explicitly call
auto it2 = KE::find_if(Kokkos::OpenMP(), KE::begin(a), KE::end(a), p);