std::experimental::find_first_set, std::experimental::find_last_set

 

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Extensions for parallelism v2

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exception_list
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execution::vector_policy	execution::unsequenced_policy
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induction reductionreduction_plusreduction_minusreduction_multiplies	reduction_bit_andreduction_bit_orreduction_bit_xorreduction_minreduction_max	for_loopfor_loop_stridedfor_loop_nfor_loop_n_strided
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SIMD library

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simd	simd_mask
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simd_abi::scalar simd_abi::fixed_size	simd_abi::native simd_abi::compatible	simd_abi::max_fixed_size simd_abi::deduce
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element_aligned_tagelement_aligned	vector_aligned_tagvector_aligned	overaligned_tagoveraligned
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where	where_expression	const_where_expression
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simd_caststatic_simd_cast	to_fixed_sizeto_compatibleto_native	splitsplit_by concat
Algorithms
min max	minmax clamp
Reduction
reducehminhmax
Mask reduction
all_ofany_ofnone_ofsome_of	popcount find_first_setfind_last_set
Traits
is_simdis_simd_mask is_abi_tag is_simd_flag_type	simd_size memory_alignment rebind_simdresize_simd
Math functions

 

Defined in header <experimental/simd>
template< class T, class Abi > int find_first_set( const simd_mask<T, Abi>& k );	(1)	(parallelism TS v2)
template< class T, class Abi > int find_last_set( const simd_mask<T, Abi>& k );	(2)	(parallelism TS v2)

1) Returns the lowest index i where k[i] is true.

2) Returns the greatest index i where k[i] is true.

The behavior is undefined if any_of(k) is false.

Parameters

k

-

the simd_mask to apply the reduction to

Return value

An int in the range [​0​, simd_size_v<T, Abi>).

Example

Run this code

#include <cstddef>
#include <experimental/simd>
#include <iostream>
 
namespace stdx = std::experimental;
 
template<typename Abi>
int find(stdx::simd_mask<Abi> const& v)
{
    if (stdx::any_of(v))
        return find_first_set(v);
    return -1;
}
 
int main()
{
    stdx::simd_mask<short> a{0};
    a[2] = a[a.size() - 2] = 1;
 
    for (std::size_t i = 0; i < a.size(); ++i)
        std::cout << a[i] << ' ';
    std::cout << '\n';
 
    std::cout << "find_first_set: " << stdx::find_first_set(a) << '\n';
    std::cout << "find_last_set: " << stdx::find_last_set(a) << '\n';
    std::cout << "find: " << find(a) << '\n';
    a[2] = 0;
    std::cout << "find: " << find(a) << '\n';
    a[a.size() - 2] = 0;
    std::cout << "find: " << find(a) << '\n';
}

Possible output:

0 0 1 0 0 0 1 0 
find_first_set: 2
find_last_set: 6
find: 2
find: 6
find: -1