From Jason Turner

[exclusive.scan]

C++17 → C++20 3.7 KB 50 lines
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Archived: C++17 | C++20
Markdown: C++17 | C++20
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tmp/tmpgz710j6q/{from.md → to.md} RENAMED
@@ -1,26 +1,26 @@
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  ### Exclusive scan <a id="exclusive.scan">[[exclusive.scan]]</a>
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  ``` cpp
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  template<class InputIterator, class OutputIterator, class T>
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- OutputIterator exclusive_scan(InputIterator first, InputIterator last,
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- OutputIterator result,
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- T init);
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  ```
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  *Effects:* Equivalent to:
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  ``` cpp
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  return exclusive_scan(first, last, result, init, plus<>());
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  ```
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  ``` cpp
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  template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2, class T>
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- ForwardIterator2 exclusive_scan(ExecutionPolicy&& exec,
 
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  ForwardIterator1 first, ForwardIterator1 last,
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- ForwardIterator2 result,
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- T init);
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  ```
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  *Effects:* Equivalent to:
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  ``` cpp
@@ -28,28 +28,35 @@ return exclusive_scan(std::forward<ExecutionPolicy>(exec),
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  first, last, result, init, plus<>());
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  ```
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  ``` cpp
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  template<class InputIterator, class OutputIterator, class T, class BinaryOperation>
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- OutputIterator exclusive_scan(InputIterator first, InputIterator last,
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- OutputIterator result,
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- T init, BinaryOperation binary_op);
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  template<class ExecutionPolicy,
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  class ForwardIterator1, class ForwardIterator2, class T, class BinaryOperation>
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- ForwardIterator2 exclusive_scan(ExecutionPolicy&& exec,
 
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  ForwardIterator1 first, ForwardIterator1 last,
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- ForwardIterator2 result,
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- T init, BinaryOperation binary_op);
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  ```
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- *Requires:*
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- - `T` shall be `MoveConstructible` (Table  [[tab:moveconstructible]]).
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- - All of `binary_op(init, init)`, `binary_op(init, *first)`, and
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- `binary_op(*first, *first)` shall be convertible to `T`.
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- - `binary_op` shall neither invalidate iterators or subranges, nor
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- modify elements in the ranges \[`first`, `last`\] or \[`result`,
 
 
 
 
 
 
 
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  `result + (last - first)`\].
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  *Effects:* For each integer `K` in \[`0`, `last - first`) assigns
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  through `result + K` the value of:
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@@ -63,9 +70,9 @@ GENERALIZED_NONCOMMUTATIVE_SUM(
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  *Complexity:* 𝑂(`last - first`) applications of `binary_op`.
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  *Remarks:* `result` may be equal to `first`.
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  [*Note 1*: The difference between `exclusive_scan` and `inclusive_scan`
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- is that `exclusive_scan` excludes the `i`th input element from the `i`th
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  sum. If `binary_op` is not mathematically associative, the behavior of
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  `exclusive_scan` may be nondeterministic. — *end note*]
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  ### Exclusive scan <a id="exclusive.scan">[[exclusive.scan]]</a>
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  ``` cpp
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  template<class InputIterator, class OutputIterator, class T>
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+ constexpr OutputIterator
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+ exclusive_scan(InputIterator first, InputIterator last,
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+ OutputIterator result, T init);
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  ```
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  *Effects:* Equivalent to:
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  ``` cpp
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  return exclusive_scan(first, last, result, init, plus<>());
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  ```
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  ``` cpp
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  template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2, class T>
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+ ForwardIterator2
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+ exclusive_scan(ExecutionPolicy&& exec,
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  ForwardIterator1 first, ForwardIterator1 last,
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+ ForwardIterator2 result, T init);
 
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  ```
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  *Effects:* Equivalent to:
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  ``` cpp
 
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  first, last, result, init, plus<>());
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  ```
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  ``` cpp
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  template<class InputIterator, class OutputIterator, class T, class BinaryOperation>
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+ constexpr OutputIterator
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+ exclusive_scan(InputIterator first, InputIterator last,
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+ OutputIterator result, T init, BinaryOperation binary_op);
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  template<class ExecutionPolicy,
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  class ForwardIterator1, class ForwardIterator2, class T, class BinaryOperation>
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+ ForwardIterator2
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+ exclusive_scan(ExecutionPolicy&& exec,
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  ForwardIterator1 first, ForwardIterator1 last,
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+ ForwardIterator2 result, T init, BinaryOperation binary_op);
 
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  ```
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+ *Mandates:* All of
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+ - `binary_op(init, init)`,
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+ - `binary_op(init, *first)`, and
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+ - `binary_op(*first, *first)`
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+
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+ are convertible to `T`.
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+
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+ *Preconditions:*
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+
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+ - `T` meets the *Cpp17MoveConstructible* ([[cpp17.moveconstructible]])
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+ requirements.
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+ - `binary_op` neither invalidates iterators or subranges, nor modifies
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+ elements in the ranges \[`first`, `last`\] or \[`result`,
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  `result + (last - first)`\].
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  *Effects:* For each integer `K` in \[`0`, `last - first`) assigns
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  through `result + K` the value of:
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  *Complexity:* 𝑂(`last - first`) applications of `binary_op`.
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  *Remarks:* `result` may be equal to `first`.
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  [*Note 1*: The difference between `exclusive_scan` and `inclusive_scan`
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+ is that `exclusive_scan` excludes the iᵗʰ input element from the iᵗʰ
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  sum. If `binary_op` is not mathematically associative, the behavior of
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  `exclusive_scan` may be nondeterministic. — *end note*]
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