Re: [Boost-users] Newbie question: Random numbers.

From: Greg Link (link_at_[hidden])
Date: 2006-05-19 11:16:19

One particularly effective technique is to seed it once, and only  
once. Iterate (through the random stream) a bit, then save that value  
to a file. Anytime your program closes, just grab one last number  
from the stream, save it to the file, and re-load that as your next  
seed. That way you're using one (and only one) random sequence for  
all runs of your program, and since any good random number generator  
(e.g. Mersenne Twister, etc) is pretty close to random along an  
entire stream, you're doing pretty well. Re-seeding naively can be  
dangerous, as it's not just entropy you want in a seed - it's things  
like relative primality, etc. As noted, seeding with a clock isn't  
nearly as effective as most think. Process ID's tend to be 'low' (not  
11+ bits long, at least), as do ThreadID's, and other such things.  
Not nearly as much entropy as many think.

- Greg

On May 19, 2006, at 11:08 AM, Peter Dimov wrote:

> Andrew Holden wrote:
>
>> Does anybody else know of other good sources of entropy to seed the
>> generator?
>
> On Windows I use QueryPerformanceCounter, GetCurrentProcessId,
> GetCurrentThreadId and GlobalMemoryStatus as entropy sources.  
> OpenSSL uses
> the contents of the screen.
>
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