[avoid3d]

I don't understand what you mean?

10 things to store, 1000 buckets to store in, less than 0.1 probability of a collision? That seams both not very impressive or even correct?

[thomasahle]

It's just a rough (but certain for all n) upper bound. The precise probability for your case seems to be slightly greater than 0.01. The point is that you can replace a precise, expensive equality test with a second hash with greater range.