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List:       gmp-discuss
Subject:    mpz_probab_prime_p reproducibility
From:       pierre () chachatelier ! fr (Pierre Chatelier)
Date:       2016-11-16 21:29:55
Message-ID: 9C66F327-990A-4EC8-9C0A-897239A7B352 () chachatelier ! fr
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Hello,

> > I think that indeed, the *results* are the same (the contrary would be
> > a real problem), but not the execution.
> > 
> I'd love to grasp the logic behind that reasoning. :-)
It makes perfect sense for me but under the light of what follows, I just fooled \
myself.

> > The set of miller rabin tests seems not to be the same for two
> > consecutive calls, since there is the
> > mpz_urandomm (x, rstate, nm3) part (and that no deterministic seed
> > seems to be used for the randstate)
> 
> I suggest that you add some printing to the code before you insist on
> your interpretation.  (I suppose we could clarify the manual about
> initial state of gmp_randstate_t.)

Aaaaaannnd obviously you are right.
I checked that gmp_randinit_default() performs a non-documented, but definitely not \
undefined state initialization. I really believed that a seed was needed after that.

I don't know yet if gmp_randinit_default() is architecture- or platform-dependent, \
but I will investigate.

Pierre


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