Difference between revisions of "cpp/algorithm/exclusive scan"
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}} | }} | ||
{{dcl | since=c++17 | num= 2 |1= | {{dcl | since=c++17 | num= 2 |1= | ||
| − | template< class ExecutionPolicy, class | + | template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T > |
| − | + | ForwardIt2 exclusive_scan( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, | |
| − | + | ForwardIt2 d_first, T init);}} | |
{{dcl | since=c++17 | num= 3 |1= | {{dcl | since=c++17 | num= 3 |1= | ||
template< class InputIt, class OutputIt, | template< class InputIt, class OutputIt, | ||
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}} | }} | ||
{{dcl | since=c++17 | num= 4 |1= | {{dcl | since=c++17 | num= 4 |1= | ||
| − | template< class ExecutionPolicy, class | + | template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, |
class T, class BinaryOperation > | class T, class BinaryOperation > | ||
| − | + | ForwardIt2 exclusive_scan( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, | |
| − | + | ForwardIt2 d_first, T init, BinaryOperation binary_op );}} | |
{{dcl end}} | {{dcl end}} | ||
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In other words, the summation operations may be performed in arbitrary order, and the behavior is nondeterministic if {{tt|binary_op}} is not associative. | In other words, the summation operations may be performed in arbitrary order, and the behavior is nondeterministic if {{tt|binary_op}} is not associative. | ||
| − | Overloads {{v|2,4}} are executed according to {{tt|policy}}. | + | Overloads {{v|2,4}} are executed according to {{tt|policy}}. {{cpp/enable_if| {{c|std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>}} is true.}} |
{{tt|binary_op}} shall not invalidate iterators or subranges, nor modify elements in the ranges | {{tt|binary_op}} shall not invalidate iterators or subranges, nor modify elements in the ranges | ||
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{{par req concept | InputIt | InputIterator}} | {{par req concept | InputIt | InputIterator}} | ||
{{par req concept | OutputIt | OutputIterator}} | {{par req concept | OutputIt | OutputIterator}} | ||
| + | {{par req concept | ForwardIt1, ForwardIt2 | ForwardIterator}} | ||
{{par end}} | {{par end}} | ||
Revision as of 11:47, 6 March 2017
| Defined in header <numeric>
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| template< class InputIt, class OutputIt, class T > OutputIt exclusive_scan( InputIt first, InputIt last, |
(1) | (since C++17) |
| template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T > ForwardIt2 exclusive_scan( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 last, |
(2) | (since C++17) |
| template< class InputIt, class OutputIt, class T, class BinaryOperation > |
(3) | (since C++17) |
| template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2, class T, class BinaryOperation > |
(4) | (since C++17) |
Computes an exclusive prefix sum operation using binary_op (or std::plus<>() for overloads (1-2)) for the range [first, last), using 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, *j... for every j in [first, first + (i - d_first)) 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. This overload participates in overload resolution only if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.
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.
Contents |
Parameters
| first, last | - | the range of elements to sum |
| d_first | - | the beginning of the destination range; may be equal to first
|
| policy | - | the execution policy to use. See execution policy for details. |
| init | - | the initial value |
| binary_op | - | binary Template:concept that will be applied in to the result of dereferencing the input iterators, the results of other binary_op, and init.
|
| Type requirements
Template:par req concept Template:par req concept Template:par req concept | ||
Return value
Iterator to the element past the last element written.
Complexity
O(last - first) applications of the binary operation
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
ExecutionPolicyis one of the standard policies, std::terminate is called. For any otherExecutionPolicy, the behavior is implementation-defined. - If the algorithm fails to allocate memory, std::bad_alloc is thrown.
Example
| This section is incomplete Reason: no example |
See also
| computes the differences between adjacent elements in a range (function template) | |
| sums up or folds a range of elements (function template) | |
| computes the partial sum of a range of elements (function template) | |
| (C++17) |
applies an invocable, then calculates exclusive scan (function template) |
| (C++17) |
similar to std::partial_sum, includes the ith input element in the ith sum (function template) |
