forked from OSchip/llvm-project
41 lines
2.3 KiB
Markdown
41 lines
2.3 KiB
Markdown
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# Parallel STL
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Parallel STL is an implementation of the C++ standard library algorithms with support for execution policies,
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as specified in ISO/IEC 14882:2017 standard, commonly called C++17. The implementation also supports the unsequenced
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execution policy specified in Parallelism TS version 2 and proposed for the next version of the C++ standard in the
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C++ working group paper P1001R1.
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Parallel STL offers efficient support for both parallel and vectorized execution of algorithms. For sequential
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execution, it relies on an available implementation of the C++ standard library.
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## Prerequisites
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To use Parallel STL, you must have the following software installed:
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* C++ compiler with:
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* Support for C++11
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* Support for OpenMP* 4.0 SIMD constructs
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* Threading Building Blocks (TBB) which is available to download in the GitHub [repository](https://github.com/01org/tbb/)
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## Known Issues or limitations
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unseq and par_unseq policies only have effect with compilers that
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support '#pragma omp simd' or '#pragma simd'.
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Parallel and vector execution is only supported for the algorithms
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if random access iterators are provided, while for other iterator
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types the execution will remain serial.
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The following algorithms do not allow efficient SIMD execution:
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includes, inplace_merge, merge, nth_element, partial_sort,
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partial_sort_copy, set_difference, set_intersection,
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set_symmetric_difference, set_union, sort, stable_partition,
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stable_sort, unique.
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The initial value type for exclusive_scan, inclusive_scan,
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transform_exclusive_scan, transform_inclusive_scan shall satisfy
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the DefaultConstructible requirements. A default constructed-instance
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of the initial value type shall be the identity element for binary_op.
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For max_element, min_element, minmax_element, partial_sort,
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partial_sort_copy, sort, stable_sort the dereferenced value type of
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the provided iterators shall be DefaultConstructible.
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For remove, remove_if, unique the dereferenced value type of the provided
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iterators shall be MoveConstructible.
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The following algorithms require additional O(n) memory space for parallel
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execution: copy_if, inplace_merge, partial_sort, partial_sort_copy,
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partition_copy, remove, remove_if, rotate, sort, stable_sort, unique,
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unique_copy.
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