hpx/parallel/algorithms/transform_exclusive_scan.hpp#

See Public API for a list of names and headers that are part of the public HPX API.

namespace hpx

Functions

template<typename InIter, typename OutIter, typename BinOp, typename UnOp, typename T = typename std::iterator_traits<InIter>::value_type>
OutIter transform_exclusive_scan(InIter first, InIter last, OutIter dest, T init, BinOp &&binary_op, UnOp &&unary_op)#

Transforms each element in the range [first, last) with unary_op, then computes an exclusive prefix sum operation using binary_op over the resulting range, with init as the initial value, and writes the results to the range beginning at dest. “exclusive” means that the i-th input element is not included in the i-th sum. Formally, assigns through each iterator i in [dest, d_first + (last - first)) the value of the generalized noncommutative sum of init, unary_op(*j)… for every j in [first, first + (i - d_first)) over binary_op, where generalized noncommutative sum GNSUM(op, a1, …, a N) is defined as follows:

  • if N=1, a1

  • if N > 1, op(GNSUM(op, a1, …, aK), GNSUM(op, aM, …, aN)) for any K where 1 < K+1 = M <= N In other words, the summation operations may be performed in arbitrary order, and the behavior is nondeterministic if binary_op is not associative.

The reduce operations in the parallel transform_exclusive_scan algorithm invoked without an execution policy object execute in sequential order in the calling thread.

Neither unary_op nor binary_op shall invalidate iterators or subranges, or modify elements in the ranges [first,last) or [result,result + (last - first)).

The behavior of transform_exclusive_scan may be non-deterministic for a non-associative predicate.

Note

Complexity: O(last - first) applications of each of binary_op and unary_op.

Note

GENERALIZED_NONCOMMUTATIVE_SUM(op, a1, …, aN) is defined as:

  • a1 when N is 1

  • op(GENERALIZED_NONCOMMUTATIVE_SUM(op, a1, …, aK), GENERALIZED_NONCOMMUTATIVE_SUM(op, aM, …, aN) where 1 < K+1 = M <= N.

Template Parameters
  • InIter – The type of the source iterators used (deduced). This iterator type must meet the requirements of an input iterator.

  • OutIter – The type of the iterator representing the destination range (deduced). This iterator type must meet the requirements of an output iterator.

  • BinOp – The type of binary_op.

  • UnOp – The type of unary_op.

  • T – The type of the value to be used as initial (and intermediate) values (deduced).

Parameters
  • first – Refers to the beginning of the sequence of elements the algorithm will be applied to.

  • last – Refers to the end of the sequence of elements the algorithm will be applied to.

  • dest – Refers to the beginning of the destination range.

  • init – The initial value for the generalized sum.

  • binary_op – Binary FunctionObject that will be applied to the result of unary_op, the results of other binary_op, and init.

  • unary_op – Unary FunctionObject that will be applied to each element of the input range. The return type must be acceptable as input to binary_op.

Returns

The transform_exclusive_scan algorithm returns a returns OutIter. The transform_exclusive_scan algorithm returns the output iterator to the element in the destination range, one past the last element copied.

template<typename ExPolicy, typename FwdIter1, typename FwdIter2, typename BinOp, typename UnOp, typename T = typename std::iterator_traits<FwdIter1>::value_type>
parallel::util::detail::algorithm_result<ExPolicy, FwdIter2>::type transform_exclusive_scan(ExPolicy &&policy, FwdIter1 first, FwdIter1 last, FwdIter2 dest, T init, BinOp &&binary_op, UnOp &&unary_op)#

Assigns through each iterator i in [result, result + (last - first)) the value of GENERALIZED_NONCOMMUTATIVE_SUM(binary_op, init, conv(*first), …, conv(*(first + (i - result) - 1))). Executed according to the policy.

The reduce operations in the parallel transform_exclusive_scan algorithm invoked with an execution policy object of type sequenced_policy execute in sequential order in the calling thread.

The reduce operations in the parallel transform_exclusive_scan algorithm invoked with an execution policy object of type parallel_policy or parallel_task_policy are permitted to execute in an unordered fashion in unspecified threads, and indeterminately sequenced within each thread.

Neither unary_op nor binary_op shall invalidate iterators or subranges, or modify elements in the ranges [first,last) or [result,result + (last - first)).

The behavior of transform_exclusive_scan may be non-deterministic for a non-associative predicate.

Note

Complexity: O(last - first) applications of each of binary_op and unary_op.

Note

GENERALIZED_NONCOMMUTATIVE_SUM(op, a1, …, aN) is defined as:

  • a1 when N is 1

  • op(GENERALIZED_NONCOMMUTATIVE_SUM(op, a1, …, aK), GENERALIZED_NONCOMMUTATIVE_SUM(op, aM, …, aN) where 1 < K+1 = M <= N.

Template Parameters
  • ExPolicy – The type of the execution policy to use (deduced). It describes the manner in which the execution of the algorithm may be parallelized and the manner in which it executes the assignments.

  • FwdIter1 – The type of the source iterators used (deduced). This iterator type must meet the requirements of an forward iterator.

  • FwdIter2 – The type of the iterator representing the destination range (deduced). This iterator type must meet the requirements of an forward iterator.

  • BinOp – The type of binary_op.

  • UnOp – The type of unary_op.

  • T – The type of the value to be used as initial (and intermediate) values (deduced).

Parameters
  • policy – The execution policy to use for the scheduling of the iterations.

  • first – Refers to the beginning of the sequence of elements the algorithm will be applied to.

  • last – Refers to the end of the sequence of elements the algorithm will be applied to.

  • dest – Refers to the beginning of the destination range.

  • init – The initial value for the generalized sum.

  • binary_op – Binary FunctionObject that will be applied in to the result of unary_op, the results of other binary_op, and init.

  • unary_op – Unary FunctionObject that will be applied to each element of the input range. The return type must be acceptable as input to binary_op.

Returns

The transform_exclusive_scan algorithm returns a hpx::future<FwdIter2> if the execution policy is of type sequenced_task_policy or parallel_task_policy and returns FwdIter2 otherwise. The transform_exclusive_scan algorithm returns the output iterator to the element in the destination range, one past the last element copied.