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#include <thrust/iterator/counting_iterator.h>
#include <thrust/iterator/transform_iterator.h>
#include <thrust/iterator/permutation_iterator.h>
#include <thrust/functional.h>
#include <thrust/fill.h>
#include <thrust/device_vector.h>
#include <thrust/copy.h>
#include <iostream>
// this example illustrates how to make strided access to a range of values
// examples:
// strided_range([0, 1, 2, 3, 4, 5, 6], 1) -> [0, 1, 2, 3, 4, 5, 6]
// strided_range([0, 1, 2, 3, 4, 5, 6], 2) -> [0, 2, 4, 6]
// strided_range([0, 1, 2, 3, 4, 5, 6], 3) -> [0, 3, 6]
// ...
template <typename Iterator>
class strided_range
{
public:
typedef typename thrust::iterator_difference<Iterator>::type difference_type;
struct stride_functor : public thrust::unary_function<difference_type,difference_type>
{
difference_type stride;
stride_functor(difference_type stride)
: stride(stride) {}
__host__ __device__
difference_type operator()(const difference_type& i) const
{
return stride * i;
}
};
typedef typename thrust::counting_iterator<difference_type> CountingIterator;
typedef typename thrust::transform_iterator<stride_functor, CountingIterator> TransformIterator;
typedef typename thrust::permutation_iterator<Iterator,TransformIterator> PermutationIterator;
// type of the strided_range iterator
typedef PermutationIterator iterator;
// construct strided_range for the range [first,last)
strided_range(Iterator first, Iterator last, difference_type stride)
: first(first), last(last), stride(stride) {}
iterator begin(void) const
{
return PermutationIterator(first, TransformIterator(CountingIterator(0), stride_functor(stride)));
}
iterator end(void) const
{
return begin() + ((last - first) + (stride - 1)) / stride;
}
protected:
Iterator first;
Iterator last;
difference_type stride;
};
int main(void)
{
thrust::device_vector<int> data(8);
data[0] = 10;
data[1] = 20;
data[2] = 30;
data[3] = 40;
data[4] = 50;
data[5] = 60;
data[6] = 70;
data[7] = 80;
// print the initial data
std::cout << "data: ";
thrust::copy(data.begin(), data.end(), std::ostream_iterator<int>(std::cout, " ")); std::cout << std::endl;
typedef thrust::device_vector<int>::iterator Iterator;
// create strided_range with indices [0,2,4,6]
strided_range<Iterator> evens(data.begin(), data.end(), 2);
std::cout << "sum of even indices: " << thrust::reduce(evens.begin(), evens.end()) << std::endl;
// create strided_range with indices [1,3,5,7]
strided_range<Iterator> odds(data.begin() + 1, data.end(), 2);
std::cout << "sum of odd indices: " << thrust::reduce(odds.begin(), odds.end()) << std::endl;
// set odd elements to 0 with fill()
std::cout << "setting odd indices to zero: ";
thrust::fill(odds.begin(), odds.end(), 0);
thrust::copy(data.begin(), data.end(), std::ostream_iterator<int>(std::cout, " ")); std::cout << std::endl;
return 0;
}
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