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

 

C++

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Feature test macros (C++20)

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Technical specifications

Symbols index

External libraries

 

Technical specifications

Filesystem library (filesystem TS)

Library fundamentals (library fundamentals TS)

Library fundamentals 2 (library fundamentals TS v2)

Library fundamentals 3 (library fundamentals TS v3)

Extensions for parallelism (parallelism TS)

Extensions for parallelism 2 (parallelism TS v2)

Extensions for concurrency (concurrency TS)

Extensions for concurrency 2 (concurrency TS v2)

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Extensions for parallelism v2

Parallel exceptions
exception_list
Additional execution policies
execution::vector_policy	execution::unsequenced_policy
Algorithms
induction reductionreduction_plusreduction_minusreduction_multiplies	reduction_bit_andreduction_bit_orreduction_bit_xorreduction_minreduction_max	for_loopfor_loop_stridedfor_loop_nfor_loop_n_strided
execution::no_vec
execution::ordered_update_t
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define_task_blockdefine_task_block_restore_thread
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SIMD library

Main classes
simd	simd_mask
ABI tags
simd_abi::scalar simd_abi::fixed_size	simd_abi::native simd_abi::compatible	simd_abi::max_fixed_size simd_abi::deduce
Alignment tags
element_aligned_tagelement_aligned	vector_aligned_tagvector_aligned	overaligned_tagoveraligned
Where expression
where	where_expression	const_where_expression
Casts
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 <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