What's the meaning of the params x,y,z,w in function cudaCreateChannelDesc

cudaCreateChannelDesc(int x, int y, int z, int w, enum cudaChannelFormatKind f);

Now i have an example code: cudaCreateChannelDesc(32, 0, 0, 0, cudaChannelFormatKindFloat);

I have no idea about why x=32,y=z=w=0.Could anybody help me?