std::experimental::reduce, std::experimental::hmin, std::experimental::hmax

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

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)

Concepts (concepts TS)

Ranges (ranges TS)

Reflection (reflection TS)

Mathematical special functions (special functions TR)

 

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
Task blocks
task_block
task_cancelled_exception
define_task_blockdefine_task_block_restore_thread
Data-parallel vectors

 

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, class BinaryOperation = std::plus<> > T reduce( const simd<T, Abi>& v, BinaryOperation binary_op = {} );	(1)	(parallelism TS v2)
template< class M, class V, class BinaryOperation > typename V::value_type reduce( const const_where_expression<M, V>& x,         typename V::value_type identity_element, BinaryOperation binary_op = {} );	(2)	(parallelism TS v2)
template< class M, class V > typename V::value_type reduce( const const_where_expression<M, V>& x, std::plus<> binary_op ) noexcept;	(3)	(parallelism TS v2)
template< class M, class V > typename V::value_type reduce( const const_where_expression<M, V>& x, std::multiplies<> binary_op ) noexcept;	(4)	(parallelism TS v2)
template< class M, class V > typename V::value_type reduce( const const_where_expression<M, V>& x, std::bit_and<> binary_op ) noexcept;	(5)	(parallelism TS v2)
template< class M, class V > typename V::value_type reduce( const const_where_expression<M, V>& x, std::bit_or<> binary_op ) noexcept;	(6)	(parallelism TS v2)
template< class M, class V > typename V::value_type reduce( const const_where_expression<M, V>& x, std::bit_xor<> binary_op ) noexcept;	(7)	(parallelism TS v2)
template< class T, class Abi > T hmin( const simd<T, Abi>& v ) noexcept;	(8)	(parallelism TS v2)
template< class M, class V > typename V::value_type hmin( const const_where_expression<M, V>& x ) noexcept;	(9)	(parallelism TS v2)
template< class T, class Abi > T hmax( const simd<T, Abi>& v ) noexcept;	(10)	(parallelism TS v2)
template< class M, class V > typename V::value_type hmax( const const_where_expression<M, V>& x ) noexcept;	(11)	(parallelism TS v2)

1) Reduces all values in v over binary_op.

2) Reduces the values in x where the associated mask element is true over binary_op.

3) Returns the sum of all values in x where the associated mask element is true.

4) Returns the product of all values in x where the associated mask element is true.

5) Returns the aggregation using bitwise-and of all values in x where the associated mask element is true.

6) Returns the aggregation using bitwise-or of all values in x where the associated mask element is true.

7) Returns the aggregation using bitwise-xor of all values in x where the associated mask element is true.

8) Reduces all values in v over std::min.

9) Reduces all values in x where the associated mask element is true over std::min.

10) Reduces all values in v over std::max.

11) Reduces all values in x where the associated mask element is true over std::max.

The behavior is non-deterministic if binary_op is not associative or not commutative.

Parameters

v	-	the simd vector to apply the reduction to
x	-	the return value of a where expression to apply the reduction to
identity_element	-	a value that acts as identity element for binary_op; binary_op(identity_element, a) == a must hold for all finite a of type V::value_type
binary_op	-	binary FunctionObject that will be applied in unspecified order to arguments of type V::value_type or simd<V::value_type, A>, with unspecified ABI tag A. binary_op(v, v) must be convertible to V.

Example

Run this code

#include <array>
#include <cstddef>
#include <iostream>
#include <numeric>
 
#include <experimental/simd>
namespace stdx = std::experimental;
 
int main()
{
    using V = stdx::native_simd<float>;
    V acc = 0;
 
    alignas(stdx::memory_alignment_v<V>) std::array<float, 1024> data;
    std::iota(data.begin(), data.end(), 0);
 
    for (std::size_t i = 0; i < data.size(); i += acc.size())
        acc += V(&data[i], stdx::vector_aligned);
    std::cout << "reduce(" << acc[0];
 
    for (std::size_t i = 1; i < V::size(); ++i)
        std::cout << ", " << acc[i];
    std::cout << ") = (1024 - 1) * 1024 / 2 = " << reduce(acc) << '\n';
}

Possible output:

reduce(130560, 130816, 131072, 131328) = (1024 - 1) * 1024 / 2 = 523776

See also

reduce (C++17)

similar to std::accumulate, except out of order (function template)