I have seen a VCDS long coding simulator somewhere on the 'net before, but I don't seem to have the link any more

What this simulator allowed you to do was to input the long coding from various controllers, change the coding and it then showed you what Bit's each change had enabled.

Has anyone else come across anything similar?

FWIW I am looking into changing a couple of codes on our cars (TT and Superb) and it would be easier if I can find this simulator again so I can experiment without the car being connected.
(I have already tried it the 'long way' with no results, but I am very reluctant to change a Bit when there is either no description of it or is even not present - so it would require changing the Binary code itself)