std::experimental::reduce

 

C++

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Feature test macros (C++20)

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Concepts library (C++20)

Metaprogramming library (C++11)

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Ranges library (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)

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

 

Data-parallel vector 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	split concat
Algorithms
min max	minmax clamp
Reduction
hmin hmax	reduce
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 = 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, 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, 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, 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, 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, bit_xor<> binary_op ) noexcept;	(7)	(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.

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

Output:

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

See also

Template:cpp/experimental/simd hminTemplate:cpp/experimental/simd hmax

reduce (C++17)

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