< cpp‎ | experimental‎ | simd
Defined in header <experimental/simd>
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.

[edit] Template parameters

M - The mask type
V - The value type M applies on

Valid combinations of (MV) are:

  • (simd_mask<T, Abi>simd<T, Abi>),
  • (simd_mask<T, Abi>simd_mask<T, Abi>),
  • (boolT).

[edit] 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)

[edit] Example

#include <cstddef>
#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; });
    const auto b = my_abs(a);

Possible output:

-2 -1 0 1 
2 1 0 1