But the chance of the initial random positions being near each other is very very low.
If you pick a billion random numbers in an 80 bit space, the chance you have a collision is one in a million. (2^80 / (2^30)^2)
If you pick a thousand random starting points and generate a million sequential numbers each, the chance your starting points are sufficiently close to each other to cause an overlap is one in a trillion. ((2^80 / 2^20) / (2^10)^2)
In that one in a trillion case, you'll likely end up with half a million collisions, which might matter to you. But if you care about 0 collisions versus 1+ collisions, pick the monotonic version.
