GNU bug report logs - #32605
[w64] (random) never returns negative

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Message #65 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Andy Moreton <andrewjmoreton <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: Re: bug#32605: [w64] (random) never returns negative
Date: Sat, 14 Aug 2021 19:47:22 +0100

On Sat 14 Aug 2021, Eli Zaretskii wrote:

>> From: Andy Moreton <andrewjmoreton <at> gmail.com>
>> Date: Sat, 14 Aug 2021 14:40:35 +0100
>> 
>> >> On 32bit builds both options are roughly equivalent.
>> >> On 64bit builds option (b) is better as option (a) does unnecessary work.
>> >
>> > The above assumes we will never call 'random' except via 'get_random'.
>> > Is that something we want to bet on?
>> 
>> Option (b) fixes bugs in the current code. Currently 'get_random' is the
>> only caller of 'random'.  If inefficiency is a problem after later code
>> changes, then then this issue can be revisited.
>> 
>> Another option is to replace the imlementation of 'random' in w32.c with
>> a different PRNG that can generate 31 bits more efficiently than using 3
>> calls to 'rand_as183'.
>> 
>> Yet another possibility is to use 'getrandom' from gnulib instead of all
>> of this Windows specific code, but that may bring a fresh set of
>> concerns to be considered.
>
> Thanks, I've decided to go with a hybrid approach that doesn't change
> how 32-bit builds behaved up to now.

That looks fine, and the bug reported by the OP now appears fixed in
testing on 32bit and 64bit builds.

    AndyM

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