[algorithms.parallel.overloads]

# 26 Algorithms library [[algorithms]](./#algorithms)

## 26.3 Parallel algorithms [[algorithms.parallel]](algorithms.parallel#overloads)

### 26.3.5 Parallel algorithm overloads [algorithms.parallel.overloads]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L598)

Parallel algorithms are algorithm overloads[.](#1.sentence-1)

Each parallel algorithm overload
has an additional function parameter P of type T&& as the first function parameter,
where T is the execution policy template parameter[.](#1.sentence-2)

[*Note [1](#note-1)*:

Not all algorithms have parallel algorithm overloads[.](#1.sentence-3)

— *end note*]

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L608)

Unless otherwise specified,
the semantics of calling a parallel algorithm overload are identical to
calling the corresponding algorithm overload without the parameter P,
using all but the first argument[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L614)

Unless otherwise specified,
the complexity requirements of a parallel algorithm overload
are relaxed from the complexity requirements of the corresponding overload
without the parameter P as follows:
when the guarantee says “at most *expr*” or
“exactly *expr*”
and does not specify the number of assignments or swaps, and*expr* is not already expressed with O() notation,
the complexity of the algorithm shall be O(expr)[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L626)

A parallel algorithm
with a template parameter named ExecutionPolicy shall not participate in overload resolution unless
that template parameter satisfies [*execution-policy*](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]")[.](#4.sentence-1)