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project_6/cccl_upstream/thrust/testing/scatter.cu
EngineX CI 56fd68e7dd [INFRA] Import NVIDIA/CCCL upstream as optimization reference library
CCCL (CUDA C++ Core Libraries) provides:
- CUB: device/block/warp-level GPU primitives (reduce, scan, sort, topk)
- Thrust: high-level parallel algorithms (transform_reduce, sort, scan)
- libcudacxx: CUDA C++ standard library (atomics, barriers, memory)
- cudax: experimental features (memory resources, allocators)
- Tuning policies: per-SM hardware-specific algorithm parameters

Competition optimization vectors mapped to CCCL:
- Output TPS (83% weight): warp_reduce, block_reduce, device_topk
- Input TPS (14% weight): device_scan, block_load, prefetch
- Cache TPS (3% weight): prefix caching strategy patterns
- Memory (0.9 util): pooled/cached/buddy allocators

Source: https://github.com/NVIDIA/cccl (shallow clone, HEAD only)
License: Apache-2.0
2026-07-30 09:35:51 +00:00

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#include <thrust/fill.h>
#include <thrust/iterator/counting_iterator.h>
#include <thrust/iterator/discard_iterator.h>
#include <thrust/iterator/retag.h>
#include <thrust/scatter.h>
#include <thrust/sequence.h>
#include <algorithm>
#include <unittest/unittest.h>
template <class Vector>
void TestScatterSimple()
{
Vector map{6, 3, 1, 7, 2};
Vector src{0, 1, 2, 3, 4};
Vector dst(8, 0);
thrust::scatter(src.begin(), src.end(), map.begin(), dst.begin());
Vector ref{0, 2, 4, 1, 0, 0, 0, 3};
ASSERT_EQUAL(dst, ref);
}
DECLARE_INTEGRAL_VECTOR_UNITTEST(TestScatterSimple);
template <typename InputIterator1, typename InputIterator2, typename RandomAccessIterator>
void scatter(my_system& system, InputIterator1, InputIterator1, InputIterator2, RandomAccessIterator)
{
system.validate_dispatch();
}
void TestScatterDispatchExplicit()
{
thrust::device_vector<int> vec(1);
my_system sys(0);
thrust::scatter(sys, vec.begin(), vec.begin(), vec.begin(), vec.begin());
ASSERT_EQUAL(true, sys.is_valid());
}
DECLARE_UNITTEST(TestScatterDispatchExplicit);
template <typename InputIterator1, typename InputIterator2, typename RandomAccessIterator>
void scatter(my_tag, InputIterator1, InputIterator1, InputIterator2, RandomAccessIterator output)
{
*output = 13;
}
void TestScatterDispatchImplicit()
{
thrust::device_vector<int> vec(1);
thrust::scatter(thrust::retag<my_tag>(vec.begin()),
thrust::retag<my_tag>(vec.begin()),
thrust::retag<my_tag>(vec.begin()),
thrust::retag<my_tag>(vec.begin()));
ASSERT_EQUAL(13, vec.front());
}
DECLARE_UNITTEST(TestScatterDispatchImplicit);
template <typename T>
void TestScatter(const size_t n)
{
const size_t output_size = std::min((size_t) 10, 2 * n);
thrust::host_vector<T> h_input(n, (T) 1);
thrust::device_vector<T> d_input(n, (T) 1);
thrust::host_vector<unsigned int> h_map = unittest::random_integers<unsigned int>(n);
for (size_t i = 0; i < n; i++)
{
h_map[i] = h_map[i] % output_size;
}
thrust::device_vector<unsigned int> d_map = h_map;
thrust::host_vector<T> h_output(output_size, (T) 0);
thrust::device_vector<T> d_output(output_size, (T) 0);
thrust::scatter(h_input.begin(), h_input.end(), h_map.begin(), h_output.begin());
thrust::scatter(d_input.begin(), d_input.end(), d_map.begin(), d_output.begin());
ASSERT_EQUAL(h_output, d_output);
}
DECLARE_VARIABLE_UNITTEST(TestScatter);
template <typename T>
void TestScatterToDiscardIterator(const size_t n)
{
const size_t output_size = std::min((size_t) 10, 2 * n);
thrust::host_vector<T> h_input(n, (T) 1);
thrust::device_vector<T> d_input(n, (T) 1);
thrust::host_vector<unsigned int> h_map = unittest::random_integers<unsigned int>(n);
for (size_t i = 0; i < n; i++)
{
h_map[i] = h_map[i] % output_size;
}
thrust::device_vector<unsigned int> d_map = h_map;
thrust::scatter(h_input.begin(), h_input.end(), h_map.begin(), thrust::make_discard_iterator());
thrust::scatter(d_input.begin(), d_input.end(), d_map.begin(), thrust::make_discard_iterator());
// there's nothing to check -- just make sure it compiles
}
DECLARE_VARIABLE_UNITTEST(TestScatterToDiscardIterator);
template <class Vector>
void TestScatterIfSimple()
{
Vector flg{0, 1, 0, 1, 0};
Vector map{6, 3, 1, 7, 2};
Vector src{0, 1, 2, 3, 4};
Vector dst(8, 0);
thrust::scatter_if(src.begin(), src.end(), map.begin(), flg.begin(), dst.begin());
Vector ref{0, 0, 0, 1, 0, 0, 0, 3};
ASSERT_EQUAL(dst, ref);
}
DECLARE_INTEGRAL_VECTOR_UNITTEST(TestScatterIfSimple);
template <typename InputIterator1, typename InputIterator2, typename InputIterator3, typename RandomAccessIterator>
void scatter_if(my_system& system, InputIterator1, InputIterator1, InputIterator2, InputIterator3, RandomAccessIterator)
{
system.validate_dispatch();
}
void TestScatterIfDispatchExplicit()
{
thrust::device_vector<int> vec(1);
my_system sys(0);
thrust::scatter_if(sys, vec.begin(), vec.begin(), vec.begin(), vec.begin(), vec.begin());
ASSERT_EQUAL(true, sys.is_valid());
}
DECLARE_UNITTEST(TestScatterIfDispatchExplicit);
template <typename InputIterator1, typename InputIterator2, typename InputIterator3, typename RandomAccessIterator>
void scatter_if(my_tag, InputIterator1, InputIterator1, InputIterator2, InputIterator3, RandomAccessIterator output)
{
*output = 13;
}
void TestScatterIfDispatchImplicit()
{
thrust::device_vector<int> vec(1);
thrust::scatter_if(
thrust::retag<my_tag>(vec.begin()),
thrust::retag<my_tag>(vec.begin()),
thrust::retag<my_tag>(vec.begin()),
thrust::retag<my_tag>(vec.begin()),
thrust::retag<my_tag>(vec.begin()));
ASSERT_EQUAL(13, vec.front());
}
DECLARE_UNITTEST(TestScatterIfDispatchImplicit);
template <typename T>
class is_even_scatter_if
{
public:
_CCCL_HOST_DEVICE bool operator()(const T i) const
{
return (i % 2) == 0;
}
};
template <typename T>
void TestScatterIf(const size_t n)
{
const size_t output_size = std::min((size_t) 10, 2 * n);
thrust::host_vector<T> h_input(n, (T) 1);
thrust::device_vector<T> d_input(n, (T) 1);
thrust::host_vector<unsigned int> h_map = unittest::random_integers<unsigned int>(n);
for (size_t i = 0; i < n; i++)
{
h_map[i] = h_map[i] % output_size;
}
thrust::device_vector<unsigned int> d_map = h_map;
thrust::host_vector<T> h_output(output_size, (T) 0);
thrust::device_vector<T> d_output(output_size, (T) 0);
thrust::scatter_if(
h_input.begin(), h_input.end(), h_map.begin(), h_map.begin(), h_output.begin(), is_even_scatter_if<unsigned int>());
thrust::scatter_if(
d_input.begin(), d_input.end(), d_map.begin(), d_map.begin(), d_output.begin(), is_even_scatter_if<unsigned int>());
ASSERT_EQUAL(h_output, d_output);
}
DECLARE_VARIABLE_UNITTEST(TestScatterIf);
template <typename T>
void TestScatterIfToDiscardIterator(const size_t n)
{
const size_t output_size = std::min((size_t) 10, 2 * n);
thrust::host_vector<T> h_input(n, (T) 1);
thrust::device_vector<T> d_input(n, (T) 1);
thrust::host_vector<unsigned int> h_map = unittest::random_integers<unsigned int>(n);
for (size_t i = 0; i < n; i++)
{
h_map[i] = h_map[i] % output_size;
}
thrust::device_vector<unsigned int> d_map = h_map;
thrust::scatter_if(
h_input.begin(),
h_input.end(),
h_map.begin(),
h_map.begin(),
thrust::make_discard_iterator(),
is_even_scatter_if<unsigned int>());
thrust::scatter_if(
d_input.begin(),
d_input.end(),
d_map.begin(),
d_map.begin(),
thrust::make_discard_iterator(),
is_even_scatter_if<unsigned int>());
}
DECLARE_VARIABLE_UNITTEST(TestScatterIfToDiscardIterator);
template <typename Vector>
void TestScatterCountingIterator()
{
Vector source(10);
thrust::sequence(source.begin(), source.end(), 0);
Vector map(10);
thrust::sequence(map.begin(), map.end(), 0);
Vector output(10);
// source has any_system_tag
thrust::fill(output.begin(), output.end(), 0);
thrust::scatter(thrust::make_counting_iterator(0), thrust::make_counting_iterator(10), map.begin(), output.begin());
ASSERT_EQUAL(output, map);
// map has any_system_tag
thrust::fill(output.begin(), output.end(), 0);
thrust::scatter(source.begin(), source.end(), thrust::make_counting_iterator(0), output.begin());
ASSERT_EQUAL(output, map);
// source and map have any_system_tag
thrust::fill(output.begin(), output.end(), 0);
thrust::scatter(thrust::make_counting_iterator(0),
thrust::make_counting_iterator(10),
thrust::make_counting_iterator(0),
output.begin());
ASSERT_EQUAL(output, map);
}
DECLARE_INTEGRAL_VECTOR_UNITTEST(TestScatterCountingIterator);
template <typename Vector>
void TestScatterIfCountingIterator()
{
Vector source(10);
thrust::sequence(source.begin(), source.end(), 0);
Vector map(10);
thrust::sequence(map.begin(), map.end(), 0);
Vector stencil(10, 1);
Vector output(10);
// source has any_system_tag
thrust::fill(output.begin(), output.end(), 0);
thrust::scatter_if(
thrust::make_counting_iterator(0), thrust::make_counting_iterator(10), map.begin(), stencil.begin(), output.begin());
ASSERT_EQUAL(output, map);
// map has any_system_tag
thrust::fill(output.begin(), output.end(), 0);
thrust::scatter_if(source.begin(), source.end(), thrust::make_counting_iterator(0), stencil.begin(), output.begin());
ASSERT_EQUAL(output, map);
// source and map have any_system_tag
thrust::fill(output.begin(), output.end(), 0);
thrust::scatter_if(
thrust::make_counting_iterator(0),
thrust::make_counting_iterator(10),
thrust::make_counting_iterator(0),
stencil.begin(),
output.begin());
ASSERT_EQUAL(output, map);
}
DECLARE_INTEGRAL_VECTOR_UNITTEST(TestScatterIfCountingIterator);