I was not really sure whether it would change the behavior, a more detailed explanation would be greatly appreciated.
Even if it changes the behavior it comes with a great speed up, especially if...

Done. :)
With the proposed changes I get at least ~4900 fps on my GTS 450 compared to ~4500 fps without the changes.

EDIT:
Just for the discussion: A noise provided by the hardware and the GLSL...

Really a nice noise.
I would like to discuss some major speed improvements with the original author but I can't find any contact information.

--las/Mercury

EDIT:...