STL algorithms are algorithmically optimized. Improve performance with algorithms that are both algorithmically and programmatically optimized by using Parallel STL. Parallel STL is an implementation of C++ standard library algorithms for the next version of the C++ standard, commonly called C++17, that supports execution policies and is specifically optimized for Intel® processors. Pass one of the following values as the first parameter in an algorithm call to specify the desired execution policy.
| Execution policy | Meaning |
|---|
| seq | Execute sequentially. |
| unseq | Use SIMD. (Requires SIMD-safe functions.) |
| par | Use multithreading. (Requires thread-safe functions.) |
| par_unseq | Use SIMD and multithreading. (Requires SIMD-safe and thread-safe functions.) |
Parallel STL supports SIMD and multithreading execution policies for a subset of algorithms if random access iterators are provided. Execution remains sequential for all other algorithms.