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#include <thrust/host_vector.h>
#include <thrust/random.h>
#include <thrust/remove.h>
#include "include/host_device.h"
// This example generates random points in the
// unit square [0,1)x[0,1) and then removes all
// points where x^2 + y^2 > 1
//
// The x and y coordinates are stored in separate arrays
// and a zip_iterator is used to combine them together
template <typename T>
struct is_outside_circle
{
template <typename Tuple>
inline __host__ __device__ bool operator()(const Tuple& tuple) const
{
// unpack the tuple into x and y coordinates
const T x = thrust::get<0>(tuple);
const T y = thrust::get<1>(tuple);
if (x * x + y * y > 1)
{
return true;
}
else
{
return false;
}
}
};
int main()
{
const size_t N = 20;
// generate random points in the unit square on the host
thrust::default_random_engine rng;
thrust::uniform_real_distribution<float> u01(0.0f, 1.0f);
thrust::host_vector<float> x(N);
thrust::host_vector<float> y(N);
for (size_t i = 0; i < N; i++)
{
x[i] = u01(rng);
y[i] = u01(rng);
}
// print the initial points
std::cout << std::fixed;
std::cout << "Generated " << N << " points" << std::endl;
for (size_t i = 0; i < N; i++)
{
std::cout << "(" << x[i] << "," << y[i] << ")" << std::endl;
}
std::cout << std::endl;
// remove points where x^2 + y^2 > 1 and determine new array sizes
size_t new_size =
thrust::remove_if(thrust::make_zip_iterator(thrust::make_tuple(x.begin(), y.begin())),
thrust::make_zip_iterator(thrust::make_tuple(x.end(), y.end())),
is_outside_circle<float>())
- thrust::make_zip_iterator(thrust::make_tuple(x.begin(), y.begin()));
// resize the vectors (note: this does not free any memory)
x.resize(new_size);
y.resize(new_size);
// print the filtered points
std::cout << "After stream compaction, " << new_size << " points remain" << std::endl;
for (size_t i = 0; i < new_size; i++)
{
std::cout << "(" << x[i] << "," << y[i] << ")" << std::endl;
}
return 0;
}
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