Problem with gmp_randinit_set

[Pedro Gimeno]

Torbjörn Granlund wrote, On 2017-02-15 00:45:
> Pedro Gimeno <gmpdiscuss at formauri.es> writes:
> 
>   Torbjörn Granlund wrote, On 2017-02-14 01:41:
>   
>   > One can change Mersenne_Twister_Generator_Noseed to
>   > Mersenne_Twister_Generator to fix this (and move __gmp_randiset_mt to
>   > randmts.c as mandated by Mersenne_Twister_Generator's scope), and then
>   > your code supposedly runs without a crash.  But I don't see why one ever
>   > wants Mersenne_Twister_Generator_Noseed, which suggests my understanding
>   > of this code is very poor indeed.
>   
>   It's been about 15 years ago, but my recollection is that the rationale behind the _Noseed version was to avoid a dependency on randmts.c, and it seems I neglected to consider this use case.
>   
>   I agree with your fix.
>   
> I realised a serious flaw with that fix; it introduces a dependency from
> mpn_random* to mpz.  That's not OK, I'm afraid.

Ah, yes, that was a problem that needed to be avoided. Thanks for looking into this.

One possible fix would be to resurrect my patch for a different seeding routine, which was based on the xxtea encryption algorithm. That one is faster and uses far less mpz code, and I think it wouldn't be difficult to get rid of mpz usage totally. It was written in or before 2006, I believe, and I rebased it in 2009, so merging it with current code might be troublesome. Fortunately, that part of the code doesn't seem to have changed a lot.

The problem is that it wouldn't be a good idea to apply that patch to stable versions, because it causes the sequences to be different.

I've attached the patch as it was in 2009 (against revision af3f365253c5).
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