[adjacent.difference]

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template<class InputIterator, class OutputIterator>
  constexpr OutputIterator
    adjacent_difference(InputIterator first, InputIterator last,
                        OutputIterator result);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2>
  ForwardIterator2
    adjacent_difference(ExecutionPolicy&& exec,
                        ForwardIterator1 first, ForwardIterator1 last, ForwardIterator2 result);

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

Mandates:

(2.1)
For the overloads with no ExecutionPolicy, T is constructible from *first. acc (defined below) is writable ([iterator.requirements.general]) to the result output iterator. The result of the expression binary_op(val, std::move(acc)) is writable to result.
(2.2)
For the overloads with an ExecutionPolicy, the result of the expressions binary_op(*first, *first) and *first are writable to result.

Preconditions:

(3.1)
For the overloads with no ExecutionPolicy, T meets the Cpp17MoveAssignable (Table 30) requirements.
(3.2)
For all overloads, in the ranges [first, last] and [result, result + (last - first)], binary_op neither modifies elements nor invalidate iterators or subranges.239

Effects: For the overloads with no ExecutionPolicy and a non-empty range, the function creates an accumulator acc of type T, initializes it with *first, and assigns the result to *result.

For every iterator i in [first + 1, last) in order, creates an object val whose type is T, initializes it with *i, computes binary_op(val, std::move(acc)), assigns the result to *(result + (i - first)), and move assigns from val to acc.

For the overloads with an ExecutionPolicy and a non-empty range, performs *result = *first.

Then, for every d in [1, last - first - 1], performs *(result + d) = binary_op(*(first + d), *(first + (d - 1))).

Remarks: For the overloads with no ExecutionPolicy, result may be equal to first.

For the overloads with an ExecutionPolicy, the ranges [first, last) and [result, result + (last - first)) shall not overlap.

239)

The use of fully closed ranges is intentional.

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25 Algorithms library [algorithms]

25.10 Generalized numeric operations [numeric.ops]

25.10.11 Adjacent difference [adjacent.difference]