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bug#32605: [w64] (random) never returns negative
From: |
Eli Zaretskii |
Subject: |
bug#32605: [w64] (random) never returns negative |
Date: |
Thu, 12 Aug 2021 16:42:35 +0300 |
> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: 32605@debbugs.gnu.org, Eli Zaretskii <eliz@gnu.org>
> Date: Thu, 12 Aug 2021 15:17:46 +0200
>
> Andy Moreton <andrewjmoreton@gmail.com> writes:
>
> >> This bug seems specific to 64 bit Windows builds.
> >
> > ON 64bit Windows, sysdep.c sets RAND_BITS to 31, but random (in w32.c)
> > only provides 30 bits. It looks like the mixing in get_random does not
> > result in the top fixnum bit being set.
>
> So it's this:
>
> int
> random (void)
> {
> /* rand_as183 () gives us 15 random bits...hack together 30 bits. */
> return ((rand_as183 () << 15) | rand_as183 ());
> }
>
> So running rand_as183 and taking another bit from that might do the
> trick? Eli, do you have any comments here?
The 'random' emulation in w32.c was never adapted to w64.
Instead of calling rand_as183 one more time, perhaps it's better to
trivially transform the value we have? Something like
int val = ((rand_as183 () << 15) | rand_as183 ());
#ifdef __x86_64__
return 2 * val - 0x3FFFFFFF;
#else
return val;
#endif
Andy, can you test this, please?
- bug#32605: [w64] (random) never returns negative, Lars Ingebrigtsen, 2021/08/12
- bug#32605: [w64] (random) never returns negative,
Eli Zaretskii <=
- bug#32605: [w64] (random) never returns negative, Andy Moreton, 2021/08/12
- bug#32605: [w64] (random) never returns negative, Eli Zaretskii, 2021/08/13
- bug#32605: [w64] (random) never returns negative, Andy Moreton, 2021/08/13
- bug#32605: [w64] (random) never returns negative, Eli Zaretskii, 2021/08/14
- bug#32605: [w64] (random) never returns negative, Andy Moreton, 2021/08/14
- bug#32605: [w64] (random) never returns negative, Eli Zaretskii, 2021/08/14
- bug#32605: [w64] (random) never returns negative, Andy Moreton, 2021/08/14
- bug#32605: [w64] (random) never returns negative, Eli Zaretskii, 2021/08/14
- bug#32605: [w64] (random) never returns negative, Andy Moreton, 2021/08/14
- bug#32605: [w64] (random) never returns negative, Eli Zaretskii, 2021/08/14