[Help-smalltalk] Re : Limits of Random changed due the mersenne twister

[Mathieu Suen]

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Re : [Help-smalltalk] Limits of Random changed due the mersenne twister
De : Mathieu Suen <address@hidden> Ajouter dans les contacts 
À : Holger Hans Peter Freyther <address@hidden>  
________________________________

----- Message d'origine ----
> De : Holger Hans Peter Freyther <address@hidden>
> À : Paolo Bonzini <address@hidden>
> Cc : GNU Smalltalk <address@hidden>
> Envoyé le : Mar 19 juillet 2011, 18h 05min 24s
> Objet : Re: [Help-smalltalk] Limits of Random changed due the mersenne twister
> 
> On 07/19/2011 03:48 PM, Paolo Bonzini wrote:
> 
> > Yes, it should be  enough to add a handler for the failure of
> > #nextLimit:, and combine a  few random integers together before scaling
> > the result down to the limit  value.
> > 
> > Probably the numbers you were getting were not random at  all, so it's
> > good that it now fails. :)
> 
> One more Mersenne Twister  question. So if someone knows a row of 624 random
> numbers, he knows the  internal state of the twister... does it make sense to
> reseed more  often?


For me you don't know the state of the twister. This is because the operation:
  y = mt[mt_index];
  y ^= (y >> 11);
  y ^= (y << 7) & 0x9d2c5680;
  y ^= (y << 15) & 0xefc60000;
  y ^= (y >> 18);

is not reversible.


> 
> not a crypto expert
>      holger
> 
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