std::transform_exclusive_scan

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

template< class ExecutionPolicy, class InputIt,
          class OutputIt, class UnaryOperation,
          class T, class BinaryOperation >
OutputIt transform_exclusive_scan( ExecutionPolicy&& policy,
                                   InputIt first, InputIt last,
                                   OutputIt d_first, UnaryOperation unary_op,
                                   T init, BinaryOperation binary_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 d_first. "exclusive" means that the i-th input element is not included in the i-th sum.

Formally, assigns through each iterator i in [d_first, 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, a
1, ..., a
N) is defined as follows:

• if N=1, a
  1
• if N > 1, op(GNSUM(op, a
  1, ..., a
  K), GNSUM(op, a
  M, ..., a
  N)) 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.

Overload (2) is executed according to policy, and does 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 overload with a template parameter named ExecutionPolicy reports errors as follows:

• If execution of a function invoked as part of the algorithm throws an exception, std::terminate is called.
• If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Notes

unary_op is not applied to init.

Example

See also