Using functors in CUDA - cuda

Question

I have the following class functor in CUDA
class forSecondMax{
private:
int toExclude;
public:
__device__ void setToExclude(int val){
toExclude = val;
}
__device__ bool operator ()
(const DereferencedIteratorTuple& lhs, const DereferencedIteratorTuple& rhs)
{
using thrust::get;
//if you do <=, returns last occurence of largest element. < returns first
if (get<0>(lhs)== get<2>(lhs) /*&& get<0>(rhs) == get<2>(rhs)*/ && get<0>(lhs) != toExclude/* && get<0>(rhs)!= toExclude */) return get<1>(lhs) < get<1>(rhs); else
return true ;
}
};
is there a way to set the value of toExclude from the host?

Answer 1

All you need to do to solve achieve this is to define a constructor for the functor which sets the data member from an argument. So your class would look something like this:
class forSecondMax{
private:
int toExclude;
public:
__device__ __host__ forSecondMax(int x) : toExclude(x) {};
__device__ __host__ bool operator ()
(const DereferencedIteratorTuple& lhs,
const DereferencedIteratorTuple& rhs)
{
using thrust::get;
if (get<0>(lhs)== get<2>(lhs) && get<0>(lhs) != toExclude)
return get<1>(lhs) < get<1>(rhs);
else
return true ;
}
};
[disclaimer: written in browser, never tested or compiled, use at own risk]
To set the value prior to passing the functor to a thrust algorithm, create and instance of the functor and pass it to the thrust call, for example:
forSecondMax op(10);
thrust::remove_if(A.begin(), A.end(), op);
which would set the data member toExclude to a value of 10 in a new instance of the class, and use the instance in the stream compaction call.