25 Algorithms library [algorithms]

25.10 Generalized numeric operations [numeric.ops]

25.10.8 Exclusive scan [exclusive.scan]

template<class InputIterator, class OutputIterator, class T>
  constexpr OutputIterator
    exclusive_scan(InputIterator first, InputIterator last,
                   OutputIterator result, T init);

Effects: Equivalent to: return exclusive_scan(first, last, result, init, plus<>());

🔗

template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2, class T>
  ForwardIterator2
    exclusive_scan(ExecutionPolicy&& exec,
                   ForwardIterator1 first, ForwardIterator1 last,
                   ForwardIterator2 result, T init);

Effects: Equivalent to: return exclusive_scan(std::forward<ExecutionPolicy>(exec), first, last, result, init, plus<>());

🔗

template<class InputIterator, class OutputIterator, class T, class BinaryOperation>
  constexpr OutputIterator
    exclusive_scan(InputIterator first, InputIterator last,
                   OutputIterator result, T init, BinaryOperation binary_op);
template<class ExecutionPolicy,
         class ForwardIterator1, class ForwardIterator2, class T, class BinaryOperation>
  ForwardIterator2
    exclusive_scan(ExecutionPolicy&& exec,
                   ForwardIterator1 first, ForwardIterator1 last,
                   ForwardIterator2 result, T init, BinaryOperation binary_op);

Mandates: All of

(3.1)
binary_op(init, init),
(3.2)
binary_op(init, *first), and
(3.3)
binary_op(*first, *first)

are convertible to T.

Preconditions:

(4.1)
T meets the Cpp17MoveConstructible (Table 28) requirements.
(4.2)
binary_op neither invalidates iterators or subranges, nor modifies elements in the ranges [first, last] or [result, result + (last - first)].

Effects: For each integer K in [0, last - first) assigns through result + K the value of: GENERALIZED_NONCOMMUTATIVE_SUM( binary_op, init, *(first + 0), *(first + 1), ..., *(first + K - 1))

Returns: The end of the resulting range beginning at result.

Complexity:

O (last - first)

applications of binary_op.

Remarks: result may be equal to first.

[Note 1:

The difference between exclusive_scan and inclusive_scan is that exclusive_scan excludes the

i^{th}

input element from the

i^{th}

sum.

If binary_op is not mathematically associative, the behavior of exclusive_scan might be nondeterministic.

— end note]