Question

如何将包含交错浮点数的设备数组转换为推力矢量运算的CUDA推力元组。

目的：我使用CUDA上的Marching Cubes生成一个粗略的顶点列表。输出是顶点列表，具有冗余且无连接。我希望得到一个唯一顶点的列表，然后是这些独特顶点的索引缓冲区，所以我可以执行一些操作，如网格简化等...

float *devPtr; //this is device pointer that holds an array of floats
//6 floats represent a vertex, array size is vertsCount*6*sizeof(float).
//format is [v0x, v0y, v0z, n0x, n0y, n0z, v1x, v1y, v1z, n1x, ...]

typedef thrust::tuple<float, float, float, float, float, float> MCVertex;

thrust::device_vector<MCVertex> inputVertices(vertsCount);

//copy from *devPtr to inputVertices.

//use something like unique to get rid of redundancies.
thrust::unique(inputVertices.begin(), inputVertices.end());

如何实现副本，或者还有其他更好的方法吗？

Answer 1

无需复制，您可以使用thrust::zip_iterator和strided_range iterator的组合。

以下示例适用于3个连续值彼此属于的浮点数列表。它当然可以扩展到支持更多，这只是打字的问题。

第一步是将一些演示数据加载到GPU上，这会使用thrust::device_vector，但这会产生一个float*指针，就像你一样。

基于strided_range迭代器和thrust::zip_iterator，数据首先进行排序，然后进行压缩。此代码使用C ++ 11功能，因此使用以下命令编译它：

nvcc -std=c++11 unique.cu -o unique

运行./unique时的输出是：

1 2 3 4 5 6

<强> unique.cu

#include <thrust/device_vector.h>
#include <iostream>
#include <thrust/unique.h>
#include <thrust/iterator/zip_iterator.h>
#include <thrust/sort.h>
#include <thrust/execution_policy.h>

template<typename... Iterators>
__host__ __device__
thrust::zip_iterator<thrust::tuple<Iterators...>> zip(Iterators... its)
{
    return thrust::make_zip_iterator(thrust::make_tuple(its...));
}

template <typename Iterator>
struct strided_range
{
    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()
{
    const int stride = 3;
    const int num = 3;

    const int size = stride * num;

    float values[size] = {1,2,3,
                          4,5,6,
                          1,2,3};


    // in this example I use thrust vectors to simplify copying from host to device
    thrust::host_vector<float> h_vec (values, values+size);
    thrust::device_vector<float> d_vec = h_vec;

    // in your case, dev_ptr is your input pointer
    float* dev_ptr = thrust::raw_pointer_cast(d_vec.data());

    auto first =  strided_range<float*>(dev_ptr,   dev_ptr + size+1-stride,   stride);
    auto second = strided_range<float*>(dev_ptr+1, dev_ptr + size+1-stride+1, stride);
    auto third =  strided_range<float*>(dev_ptr+2, dev_ptr + size+1-stride+2, stride);

    auto zip_begin = zip(first.begin(),second.begin(), third.begin());
    auto zip_end = zip(first.end(), second.end(), third.end());

    thrust::sort(thrust::device, zip_begin, zip_end);
    auto new_end = thrust::unique(thrust::device, zip_begin,zip_end);
    std::size_t new_size = stride * (new_end - zip_begin);

    // use the underlying thrust::device_vector again to simplify printing
    thrust::copy(d_vec.begin(), d_vec.begin()+new_size, std::ostream_iterator<float>(std::cout, " "));
    std::cout << std::endl;

    return 0;
}

顺便说一句：在尝试获取唯一值时，请注意浮点不准确。

我还创建了上面示例的通用版本，该版本自动构建zip_iterator并适用于任意数量的连续元素。由于官方推文版本尚不支持可变元组，我们使用std::tuple构建所需的元组类型，然后将其转换为thrust::tuple。如果Andrew Corrigan's branch of thrust（它增加了对可变元组的支持）被合并到推力大师中，我们可以完全避免使用std :: tuple。

使用以下代码编译此示例：

nvcc generic_unique.cu -std=c++11 -o generic_unique

运行./generic_unique时的输出是：

input data: 1 2 3 4 5 6 0 0 0 0 0 0 1 2 3 4 5 6 0 0 0 0 0 0 1 2 3 4 5 6 0 0 0 0 0 0 0 0 0 0 0 0 
after sort: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 
after unique: 0 0 0 0 0 0 1 2 3 4 5 6

<强> generic_unique.cu

#include <tuple>
#include <thrust/tuple.h>
#include <thrust/device_vector.h>
#include <iostream>
#include <thrust/unique.h>
#include <thrust/iterator/zip_iterator.h>
#include <thrust/sort.h>
#include <thrust/execution_policy.h>

// adapted from https://github.com/thrust/thrust/blob/master/examples/strided_range.cu
template <typename Iterator, typename thrust::iterator_difference<Iterator>::type stride>
class strided_range
{
public:
    typedef typename thrust::iterator_difference<Iterator>::type difference_type;

    //template <difference_type stride>
    struct stride_functor : public thrust::unary_function<difference_type,difference_type>
    {
        __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)
        : first(first), last(last) {}

    iterator begin(void) const
    {
        return PermutationIterator(first, TransformIterator(CountingIterator(0), stride_functor()));
    }

    iterator end(void) const
    {
        return begin() + ((last - first) + (stride - 1)) / stride;
    }

protected:
    Iterator first;
    Iterator last;
};

// copied from http://stackoverflow.com/a/16853775/678093
template<typename, typename>
struct append_to_type_seq { };

template<typename T, typename... Ts, template<typename...> class TT>
struct append_to_type_seq<T, TT<Ts...>>
{
    using type = TT<Ts..., T>;
};

template<typename T, unsigned int N, template<typename...> class TT>
struct repeat
{
    using type = typename
        append_to_type_seq<
            T,
            typename repeat<T, N-1, TT>::type
            >::type;
};

template<typename T, template<typename...> class TT>
struct repeat<T, 0, TT>
{
    using type = TT<>;
};

template<typename Tuple> struct std_to_thrust_tuple;
template<typename...T> struct std_to_thrust_tuple<std::tuple<T...>> {
  using type = thrust::tuple<T...>;
};

template<typename IteratorType, std::size_t stride>
class zipped_strided_range
{
public:

    typedef typename strided_range<IteratorType, stride>::iterator SingleIterator;
    typedef typename repeat<SingleIterator, stride, std::tuple>::type StdIteratorTuple;
    typedef typename std_to_thrust_tuple<StdIteratorTuple>::type IteratorTuple;
    typedef decltype(thrust::make_zip_iterator(IteratorTuple())) ZipIterator;

    zipped_strided_range(IteratorType first, IteratorType last) : first(first), last(last)
    {
        assign<0>();
    }

    ZipIterator begin() const
    {
        return thrust::make_zip_iterator(begin_tuple);
    }

    ZipIterator end() const
    {
        return thrust::make_zip_iterator(end_tuple);
    }

protected:

    template <std::size_t index>
    void assign(typename std::enable_if< (index < stride) >::type* = 0)
    {
        strided_range<IteratorType,stride> strided_range_iterator(first+index, last-(stride-1)+index);

        thrust::get<index>(begin_tuple) = strided_range_iterator.begin();
        thrust::get<index>(end_tuple) = strided_range_iterator.end();
        assign<index+1>();
    }

    template <std::size_t index>
    void assign(typename std::enable_if< (index == stride) >::type* = 0)
    {
        // end recursion
    }

    IteratorType first;
    IteratorType last;

    IteratorTuple begin_tuple;
    IteratorTuple end_tuple;
};


int main()
{

    const int stride = 6;
    const int num = 6;

    const int size = stride * num;

    float values[size] = {1,2,3,4,5,6,
                          0,0,0,0,0,0,
                          1,2,3,4,5,6,
                          0,0,0,0,0,0,
                          1,2,3,4,5,6,
                          0,0,0,0,0,0
    };


    // in this example I use thrust vectors to simplify copying from host to device
    // it also simplifies printing
    thrust::host_vector<float> h_vec (values, values+size);
    thrust::device_vector<float> d_vec = h_vec;

    std::cout << "input data: ";
    thrust::copy(d_vec.begin(), d_vec.end(), std::ostream_iterator<float>(std::cout, " "));
    std::cout << std::endl;

    // in your case, dev_ptr is your input pointer
    float* dev_ptr = thrust::raw_pointer_cast(d_vec.data());

    zipped_strided_range<float*, stride> zipped(dev_ptr, dev_ptr+size);


    thrust::sort(thrust::device, zipped.begin(), zipped.end());

    std::cout << "after sort: ";
    thrust::copy(d_vec.begin(), d_vec.end(), std::ostream_iterator<float>(std::cout, " "));
    std::cout << std::endl;

    auto new_end = thrust::unique(thrust::device, zipped.begin(), zipped.end());
    std::size_t new_size = stride * (new_end - zipped.begin());

    std::cout << "after unique: ";
    d_vec.resize(new_size);
    thrust::copy(d_vec.begin(), d_vec.end(), std::ostream_iterator<float>(std::cout, " "));
    std::cout << std::endl;

    return 0;
}

Answer 2

首先，感谢m.s.的回答，因为它指出了我正确的方向。

请注意，如果您使用的是Microsoft Visual Studio，则只有VS2013支持可变元组。

对于主机编译器的c ++ 11功能支持列表（如VS2013中的cl.exe），请使用以下链接。 https://msdn.microsoft.com/en-us/library/hh567368.aspx

PS：确保您正在构建v120平台工具集以利用可变参数模板功能。

感谢@ Robert Crovella，默认情况下使用VS2013设置[-std = c ++ 11]，因此无需设置标记。

回到手头的问题，这是我如何使用m.s.中的代码解决它，但使用thrust :: device_ptr而不是原始指针。

#include <iostream>
#include "thrust\host_vector.h"
#include "thrust\device_vector.h"
#include "thrust\sort.h"
#include "thrust\unique.h"
#include "thrust\binary_search.h"
#include "thrust\iterator\zip_iterator.h"
#include "thrust\execution_policy.h"

template <typename Iterator>
struct strided_range
{
    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;
};

//forcing it to be a 3-tuple one instead of using variadic templates
template<typename Iterator>
__host__ __device__
thrust::zip_iterator<thrust::tuple<Iterator, Iterator, Iterator>> zip(const         Iterator& sr1, const Iterator& sr2, const Iterator& sr3)
{
    return thrust::make_zip_iterator(thrust::make_tuple(sr1, sr2, sr3));
}

int main()
{

    const int stride = 3;
    const int num = 6;

    const int size = stride * num;

    //values on host
    float values[size] = { 1, 2, 3,
        4, 5, 6,
        1, 2, 3,
        4, 5, 6,
        1, 2, 3,
        7, 8, 9 };
    //ptr for device
    float *d_data;
    //allocate memory on the device
    cudaMalloc((void**)&d_data, size*sizeof(float));
    //copy from host to device
    cudaMemcpy(d_data, values, size*sizeof(float), cudaMemcpyHostToDevice);

    //a typedef for device_ptr<float>
    typedef thrust::device_ptr<float> floatdevptr;

    //cast our raw pointer to device pointer
    floatdevptr dev_dataptr = thrust::device_pointer_cast(d_data);

    //create a device_vector from the dev_dataptr
    thrust::device_vector<float> d_vec(dev_dataptr, dev_dataptr + size);
    //make a copy
    thrust::device_vector<float> d_veccopy = d_vec;

    //create a device_vector to hold indices (6 indices for 6 vertices)
    thrust::device_vector<unsigned int> indices( num );

    //print input values
    std::cout << "Input Values : ";
    thrust::copy(d_vec.begin(), d_vec.begin() + size, std::ostream_iterator<float>(std::cout, " "));
    std::cout << std::endl;

    //a typedef for our strided_range<device_ptr<float>>
    typedef strided_range<floatdevptr>::iterator floatdevptr_stridedrangeiterator;

    //create the strided_range for x, y and z;
    strided_range<floatdevptr> dvx = strided_range<floatdevptr>(dev_dataptr + 0, dev_dataptr + size - stride + 1, stride);
    strided_range<floatdevptr> dvy = strided_range<floatdevptr>(dev_dataptr + 1, dev_dataptr + size - stride + 2, stride);
    strided_range<floatdevptr> dvz = strided_range<floatdevptr>(dev_dataptr + 2, dev_dataptr + size - stride + 3, stride);

    //create zip_iterator for the vertex
    auto zip_dv_first = zip<floatdevptr_stridedrangeiterator>(dvx.begin(), dvy.begin(), dvz.begin());
    auto zip_dv_last = zip<floatdevptr_stridedrangeiterator>(dvx.end(), dvy.end(), dvz.end());

    //sort
    thrust::sort(zip_dv_first, zip_dv_last);
    //remove duplicates
    auto new_dv_last = thrust::unique(zip_dv_first, zip_dv_last);
    //compute new size
    std::size_t new_dv_size = stride * (new_dv_last - zip_dv_first);

    //create the same for the copy.
    strided_range<floatdevptr> dvcpyx = strided_range<floatdevptr>(d_veccopy.data() + 0, d_veccopy.data() + size - stride + 1, stride);
    strided_range<floatdevptr> dvcpyy = strided_range<floatdevptr>(d_veccopy.data() + 1, d_veccopy.data() + size - stride + 2, stride);
    strided_range<floatdevptr> dvcpyz = strided_range<floatdevptr>(d_veccopy.data() + 2, d_veccopy.data() + size - stride + 3, stride);

    auto zip_dvcpy_first = zip<floatdevptr_stridedrangeiterator>(dvcpyx.begin(), dvcpyy.begin(), dvcpyz.begin());
    auto zip_dvcpy_last = zip<floatdevptr_stridedrangeiterator>(dvcpyx.end(), dvcpyy.end(), dvcpyz.end());

    //find index of each input vertex in the list of unique vertices
    thrust::lower_bound(zip_dv_first, new_dv_last,
        zip_dvcpy_first, zip_dvcpy_last,
        indices.begin());

    // print unique vertex data
    std::cout << "Output Values : ";
    thrust::copy(d_vec.begin(), d_vec.begin() + new_dv_size, std::ostream_iterator<float>(std::cout, " "));
    std::cout << std::endl;
    // print the indices
    std::cout << "Index Values : ";
    thrust::copy(indices.begin(), indices.end(), std::ostream_iterator<float>(std::cout, " "));
    std::cout << std::endl;
}

输出是：

Input Values : 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 7 8 9 
Output Values : 1 2 3 4 5 6 7 8 9 
Index Values : 0 1 0 1 0 2

将CUDA设备交错数组转换为元组以进行向量运算

2 个答案: