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Re: Random numbers broken on 64-bit platforms
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From: |
Andreas Rottmann |
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Subject: |
Re: Random numbers broken on 64-bit platforms |
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Date: |
Sun, 18 Jul 2010 01:18:07 +0200 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux) |
Andreas Rottmann <address@hidden> writes:
> Hi!
>
> While implementing SRFI-27, I noticed that Guile's RNG is quite broken
> on 64-bit platforms (where unsigned long is 64 bit). This has two
> consequences:
>
> - Crashes for some numbers between 2^32 and 2^63; for example try this:
>
> (random (expt 2 46))
>
> - Bignum random numbers will be seriously distorted in their
> distribution, since scm_c_random() only returns 32 random bits, and
> that function is used by scm_c_random_bignum(), which expects it to
> return a `unsigned long' worth of random bits, AFAICT.
>
> I believe the attached patch fixes this issue.
>
I should add that this affects both 1.8.7 and current git.
Regards, Rotty
--
Andreas Rottmann -- <http://rotty.yi.org/>