写一个简单的推力函子对某些压缩数组进行操作 [英] Writing a simple thrust functor operating on some zipped arrays

问题描述

我试图使用zip和排列迭代器执行 thrust :: reduce_by_key 。
，即在几个虚拟置换数组的压缩数组上执行此操作。
我在编写函数 density_update 的语法时遇到问题。

I am trying to perform a thrust::reduce_by_key using zip and permutation iterators. i.e. doing this on a zipped array of several 'virtual' permuted arrays. I am having trouble in writing the syntax for the functor density_update.

但是首先要设置问题。

这是我的函数调用：

thrust::reduce_by_key(  dflagt,
                        dflagtend,
                        thrust::make_zip_iterator( 
                            thrust::make_tuple(
                                thrust::make_permutation_iterator(dmasst, dmapt), 
                                thrust::make_permutation_iterator(dvelt, dmapt),
                                thrust::make_permutation_iterator(dmasst, dflagt),
                                thrust::make_permutation_iterator(dvelt, dflagt)
                            )
                        ),
                        thrust::make_discard_iterator(),
                        danswert,
                        thrust::equal_to<int>(),
                        density_update()
                  ) 

dmapt ， dflagt 的类型为 thrust :: device_ptr< int> 和 dvelt ， dmasst 和 danst 的类型为
thrust :: device_ptr< double> 。

dmapt, dflagt are of type thrust::device_ptr<int> and dvelt , dmasst and danst are of type thrust::device_ptr<double>.

（它们是对原始cuda数组的推式封装）

(They are thrust wrappers to my raw cuda arrays)

数组 mapt 和 flagt 都是索引向量，从中我需要从数组中执行收集操作 dmasst 和 dvelt 。

The arrays mapt and flagt are both index vectors from which I need to perform a gather operation from the arrays dmasst and dvelt.

还原步骤后，我打算将数据写入 danswert 数组。由于在缩减中使用了多个数组，显然我使用zip迭代器。

After the reduction step I intend to write my data to the danswert array. Since multiple arrays are being used in the reduction, obviously I am using zip iterators.

我的问题在于编写函数 density_update ，这是二进制操作。

My problem lies in writing the functor density_update which is binary operation.

struct density_update
{
  typedef thrust::device_ptr<double> ElementIterator;
  typedef thrust::device_ptr<int>   IndexIterator;
  typedef thrust::permutation_iterator<ElementIterator,IndexIterator> PIt;

  typedef thrust::tuple< PIt , PIt , PIt, PIt> Tuple;
  __host__ __device__
  double operator()(const Tuple& x , const Tuple& y)
  {   
      return    thrust::get<0>(*x) * (thrust::get<1>(*x) - thrust::get<3>(*x)) + \
                thrust::get<0>(*y) * (thrust::get<1>(*y) - thrust::get<3>(*y));
  }
};

返回的值是 double 。为什么二进制操作看起来像上面的函子是
不重要。我只是想知道我将如何纠正以上的语法。
如上所示，代码引发了大量的编译错误。我不知道我在哪里错了。

The value being returned is a double . Why the binary operation looks like the above functor is not important. I just want to know how I would go about correcting the above syntactically. As shown above the code is throwing a number of compilation errors. I am not sure where I have gone wrong.

我在Ubuntu 10.10的GTX 570上使用CUDA 4.0

I am using CUDA 4.0 on GTX 570 on Ubuntu 10.10

推荐答案

density_update 不应该接收迭代器的元组作为参数 - 它需要迭代器的引用的元组。

density_update should not receive tuples of iterators as parameters -- it needs tuples of the iterators' references.

原则，你可以根据各种迭代器的特定引用类型写入 density_update :: operator（）更简单的让编译器推断参数的类型：

In principle you could write density_update::operator() in terms of the particular reference type of the various iterators, but it's simpler to have the compiler infer the type of the parameters:

struct density_update
{
  template<typename Tuple>
  __host__ __device__
  double operator()(const Tuple& x, const Tuple& y)
  {   
    return thrust::get<0>(x) * (thrust::get<1>(x) - thrust::get<3>(x)) + \
           thrust::get<0>(y) * (thrust::get<1>(y) - thrust::get<3>(y));
  }
};

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