cpp/algorithm/transform inclusive scan: Difference between revisions

template< class InputIt, class OutputIt,
          class UnaryOperation, class BinaryOperation >
OutputIt transform_inclusive_scan( InputIt first, InputIt last,
                                   OutputIt d_first, UnaryOperation unary_op,
                                   BinaryOperation binary_op );

template< class ExecutionPolicy, class InputIt, class OutputIt,
          class UnaryOperation, class BinaryOperation >
OutputIt transform_inclusive_scan( ExecutionPolicy&& policy,
                                   InputIt first, InputIt last,
                                   OutputIt d_first, UnaryOperation unary_op,
                                   BinaryOperation binary_op );

template< class InputIt, class OutputIt,
          class UnaryOperation, class BinaryOperation, class T >
OutputIt transform_inclusive_scan( InputIt first, InputIt last,
                                   OutputIt d_first, UnaryOperation unary_op,
                                   BinaryOperation binary_op, T init );

template< class ExecutionPolicy, class InputIt, class OutputIt,
          class UnaryOperation, class BinaryOperation, class T >
OutputIt transform_inclusive_scan( ExecutionPolicy&& policy,
                                   InputIt first, InputIt last,
                                   OutputIt d_first, UnaryOperation unary_op,
                                   BinaryOperation binary_op, T init );

Transforms each element in the range [first, last) with unary_op, then computes an inclusive prefix sum operation using binary_op over the resulting range, optionally with init as the initial value, and writes the results to the range beginning at d_first. "inclusive" means that the i-th input element is included in the i-th sum.

Formally, assigns through each iterator i in [d_first, d_first + (last - first)) the value of

• for overloads (1-2), the generalized noncommutative sum of unary_op(*j)... for every j in [first, first + (i - d_first + 1)) over binary_op,
• for overloads (3-4), the generalized noncommutative sum of init, unary_op(*j)... for every j in [first, first + (i - d_first + 1)) over binary_op,

where generalized noncommutative sum GNSUM(op, a1, ..., aN) 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.

Overloads (2, 4) are executed according to policy, and do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.

unary_op and binary_op shall not invalidate iterators or subranges, nor modify elements in the ranges [first, last) or [d_first, d_first + (last - first)). Otherwise, the behavior is undefined.

Parameters

Return value

Iterator to the element past the last element written.

Complexity

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

Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

• If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
• If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Notes

unary_op is not applied to init.

Example

See also