Generating unique random numbers

Robert van Herk rherk at
Tue Jun 14 10:36:52 EDT 2005

Hello all,

Is it possible to generate random numbers that are "unique"  in O(1) in 

I mean something like the GUID-thingy Windows uses.

Of course, I could create unique numbers by incrementing a global value, 
but for security reasons I need random numbers. Also, I could use a list 
of numbers already in use, but this would mean that I'd not be able to 
generate a new number in O(1).

Any ideas?


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