is the Cg noise() function supported?

Over in the Cg Tutorial, they say there’s a standard noise() function that will return a consistent random result: The Cg Tutorial - Appendix E. Cg Standard Library Functions

So I tried it out in one of my shaders, and it doesn’t throw a syntax error, but it also seems to always return 0 - the way I can tell is that this:

half4 t = half4( noise(whatever), 0, 0, 1 );  
o.Albedo = t.rgb;
o.Alpha = t.a;

looks the same as this:

half4 t = half4( 0, 0, 0, 1 );
o.Albedo = t.rgb;
o.Alpha = t.a;

Am I doing it wrong or is that expected?

I’ve just been told that it’s typically not supported in most implementations of Cg. So. Ok.