Is nppiFilter() convolution implemented using FFT?

NPP provides a 2D image convolution function called nppiFilter_8u_C1R().

Does anyone know whether nppiFilter is implemented using direct convolution or FFT?

I’m currently using nppiFilter in my image processing code, and I’m wondering whether I should explore doing my convolutions with cuFFT for better performance. My convolution filter is fairly big, so using cuFFT might offer a speedup unless nppiFilter is already built on top of cuFFT.