Please Explain this code!

cudaPitchedPtr pitchPtr = make_cudaPitchedPtr( (void*)deviceData, dimx*sizeof(float), dimx, dimy );
printf(“cudaPitchedPtr: %s\n”, cudaGetErrorString(cudaGetLastError()));
cudaExtent ca_extent;
ca_extent.width = 3;
ca_extent.height = 3;
ca_extent.depth = 3;
cudaMalloc3D( &pitchPtr, ca_extent);
cudaMemset3D( pitchPtr, 0, ca_extent);

cudaMemcpy3DParms cpy_params = {0};
cpy_params.srcPtr   = make_cudaPitchedPtr( (void*)hostInput, dimx * sizeof(float), dimx, dimy );
cpy_params.dstPtr   = pitchPtr;
cpy_params.extent   = ca_extent;
cpy_params.kind     = cudaMemcpyHostToDevice;
cudaMemcpy3D( &cpy_params );

please give a line by line explanation of what is happening here. I would really appreciate


If this code directly follows the next block code, it does absolutely nothing useful (except perhaps leak the previously allocated memory pointed to deviceData). Otherwise it is just filling in a pitchedPtr structure. It doesn’t interact with the API in any way.

This allocates the 3x3 byte extent (which will be padded for alignment purposes) using cudaMalloc3D(), then zeros it using cudaMemset3D().

This is going to do a cudaMemcpy3D using a source pointer manufactured by the make_cudaPitchedPtr(). This will, in all likelyhood, fail, because the srcPtr value should be returned from a previous cudaMalloc3D call (unless the supplied dimensions dimx and dimy somehow have been calculated include the required padding and alignment requirements).