On Wed, 11 Oct 2017 04:25:32 -0700, sisyphus wrote:
> Hi,
> Some anomalous rounding behaviour on Ubuntu-16.04 was noted at
> http://www.perlmonks.org/?node_id=1200326
>
> Here are the specifics:
>
> $ perl6 --version
> This is Rakudo version 2017.07 built on MoarVM version 2017.07
> implementing Perl 6.c.
>
> =======
> Issue 1
> =======
>
> $ perl6 -e 'say Int(2e25);'
> 20000000000000001811939328
> $ perl6 -e 'say Int(20e24);'
> 19999999999999997516972032
>
> That seems odd because 2e25 and 20e24 are exactly equivalent.
>
> =======
> Issue 2
> =======
>
> $ perl6 -e 'say "WTF" if 1.000000000000001e0 == 1e0;'
> WTF
>
> That seems odd because 1.000000000000001e0 and 1e0 are quite different
> double precision values. According to perl5:
>
> $ perl -le 'print scalar reverse unpack "h*", pack "d<",
> 1.000000000000001e0;'
> 3ff0000000000005
> $ perl -le 'print scalar reverse unpack "h*", pack "d<", 1e0;'
> 3ff0000000000000
>
> Is it the intention of the perl6 developers that such discrepancies will be
> addressed ?
>
> Cheers,
> Rob
Thank you for the report. All the issues mentioned in the ticket are now fixed.
- The mentioned printf issues look to have been resolved as well,
even though no work to printf itself was done.
- Somehow fixing Num stringification alone fixed the
`1.000000000000001e0 == 1e0` bug. That was surprising and I filed
https://github.com/rakudo/rakudo/issues/1647 to investigate that further
- Support for '%a' in sprintf was mentioned in the ticket, but I suggest
if there's real interest for that format, a separate ticket to be opened
- There a Num-involved precision issue with drift in Str->Num->Str chains,
filed as https://github.com/rakudo/rakudo/issues/1651
Fix: https://github.com/MoarVM/MoarVM/commit/067c0594103a025
https://github.com/MoarVM/MoarVM/commit/8841c4241b4faa8
https://github.com/MoarVM/MoarVM/commit/af2eb8a7f7d4344
https://github.com/MoarVM/MoarVM/commit/4d3fc2818d0032b
https://github.com/rakudo/rakudo/commit/8422d7b4e23678b
https://github.com/rakudo/rakudo/commit/a2a2a745c4242d1
Test: https://github.com/perl6/roast/commit/01d02dafb6
https://github.com/perl6/roast/commit/b6d5364fe0
https://github.com/perl6/roast/commit/855af84f82
https://github.com/perl6/roast/commit/f4a6c635f4
https://github.com/perl6/roast/commit/d1faf1d049
