OpenCl kernel code

2
votes

I am very new to OpenCL (started today). I am having a hard time in realizing the kernel code for adding numbers of an array in the following fashion: If A[]=[1,2,3,4,5,6,7,8,9,10], then the sum should be sum[]=[4,10,16];

i.e, sum[i]=A[i]+A[i+2]; 
     i=i+3;

I have tried the following code but it does not seem to work.

std::string kernel_code =
        "   void kernel simple_add(global const int* A, global const int* B, global int* C){ "
        "   int x =0;"
        "   int i =get_global_id(0);"
        "   SUM[x]=A[i]+A[i+2];"
        "   i=i+3;
        "   x++;"
        "   }  ";

I am certain this is not the way to do it. Suggestions in this regard would be appreciated.

1
c++opencl

1 Answers

1
votes

You should calculate i as if the work item were the only one in the set. gid is the global id of the work item, and i needs to be three times that. You also don't need to modify gid or i after they are used. This is not optimal, but it will get you the correct answer.

void kernel simple_add(global const int* A, global const int* SUM){
    int gid = get_global_id(0);
    int i = gid * 3;
    SUM[gid]=A[i]+A[i+2];
}