That movie was so good but was entirely overshadowed by the release of The Matrix, which released just 2 months earlier - I think people assumed that The 13th Floor was just a Matrix knock-off, which it wasn't. Both were great, of course, but 13th Floor just got a bum deal with it's release date I think.
In the Black Mirror episode U.S.S Callister, the game development firm is located on the 13th floor :)
There are limits to floating point precision; should have used FP64
once it starts skipping the integers you can really see the glitch in the matrix