Difference between revisions of "cpp/experimental/simd/where expression"
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< cpp | experimental | simd
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| − | The class template where_expression abstracts the notion of selected elements | + | The class template {{tt|where_expression}} abstracts the notion of selected elements |
| − | of a given | + | of a given lvalue of arithmetic or data-parallel type. Selected elements are the elements of the lvalue (of type {{tt|V}}) for which the corresponding element of the mask (of type {{tt|M}}) is true. Operators applied to objects of type {{tt|where_expression<M, V>}} are applied only to selected elements. All other elements are left unchanged. |
| + | |||
| + | Use the {{rlpt|where}} function to construct {{tt|where_expression}} objects. | ||
===Template parameters=== | ===Template parameters=== | ||
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===Example=== | ===Example=== | ||
| + | {{example | ||
| + | |code= | ||
| + | #include <experimental/simd> | ||
| + | #include <iostream> | ||
| + | namespace stdx = std::experimental; | ||
| + | |||
| + | void print(auto const& a) | ||
| + | { | ||
| + | for (std::size_t i{}; i != std::size(a); ++i) | ||
| + | std::cout << a[i] << ' '; | ||
| + | std::cout << '\n'; | ||
| + | } | ||
| + | |||
| + | template <class A> | ||
| + | stdx::simd<int, A> my_abs(stdx::simd<int, A> x) | ||
| + | { | ||
| + | where(x < 0, x) = -x; | ||
| + | return x; | ||
| + | } | ||
| + | int main() | ||
| + | { | ||
| + | const stdx::native_simd<int> a([](int i) { return i - 2; }); | ||
| + | print(a); | ||
| + | const auto b = my_abs(a); | ||
| + | print(b); | ||
| + | } | ||
| + | }} | ||
{{langlinks|zh}} | {{langlinks|zh}} | ||
Revision as of 11:29, 20 April 2023
| Defined in header <experimental/simd>
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| template< class M, class V > class where_expression; |
(parallelism TS v2) | |
The class template where_expression abstracts the notion of selected elements
of a given lvalue of arithmetic or data-parallel type. Selected elements are the elements of the lvalue (of type V) for which the corresponding element of the mask (of type M) is true. Operators applied to objects of type where_expression<M, V> are applied only to selected elements. All other elements are left unchanged.
Use the where function to construct where_expression objects.
Template parameters
| M | - | The mask type |
| V | - | The value type M applies on |
Valid combinations of (M, V) are: (simd_mask<T, Abi>, simd<T, Abi>), (simd_mask<T, Abi>, simd_mask<T, Abi>), (bool, T).
Member functions
| assigns to selected positions (public member function) | |
| compound operators (public member function) | |
| increment and decrement operators (public member function) | |
| loads from address to selected positions (public member function) |
Example
Run this code
#include <experimental/simd> #include <iostream> namespace stdx = std::experimental; void print(auto const& a) { for (std::size_t i{}; i != std::size(a); ++i) std::cout << a[i] << ' '; std::cout << '\n'; } template <class A> stdx::simd<int, A> my_abs(stdx::simd<int, A> x) { where(x < 0, x) = -x; return x; } int main() { const stdx::native_simd<int> a([](int i) { return i - 2; }); print(a); const auto b = my_abs(a); print(b); }
