[erlang-questions] Big band playing

[Richard Carlsson]

These days (since version 6, 2014), the GNU Multiple Precision Library (
https://gmplib.org/) is available under LGPL v3, which is compatible with
the Apache 2.0 license that Erlang is using (since OTP 18, 2015). Perhaps
it would be a good idea to start using the heavily optimized GMP code now
instead of Erlang's own bignum implementation. At least, to make it a build
time option.

        /Richard


Den sön 16 dec. 2018 kl 19:08 skrev Mikael Pettersson <mikpelinux@REDACTED
>:

> On Sat, Dec 15, 2018 at 8:19 PM Kostis Sagonas <kostis@REDACTED> wrote:
> >
> > On 12/15/18 7:30 PM, Mikael Pettersson wrote:
> > > On Fri, Dec 14, 2018 at 4:32 PM Kostis Sagonas<kostis@REDACTED>
> wrote:
> > >> We have been playing with CutEr (https://github.com/aggelgian/cuter),
> a
> > >> Concolic unit testing tool for Erlang, and discovered the following
> bug
> > >> in the implementation of bitwise and (band/2) operator:
> > >>
> > >> Erlang/OTP 21 [erts-10.2] [source-2bf2b70] [64-bit] [smp:8:8]
> > >> [ds:8:8:10] [async-threads:1] [hipe] [sharing-preserving]
> > >>
> > >> Eshell V10.2  (abort with ^G)
> > >> 1> (-1299341865233935136534120785510400) band (-1).
> > >> -1299341865233953583278194495062016
> > >>
> > >>
> > >> which is the wrong result, of course.
> > >>
> > >> Most likely, it has existed forever.
> > > Looks like an old bug, I was able to reproduce it with every release
> > > back to R16B03 (R15B03 wouldn't build due to perl errors).
> >
> > I was able to reproduce this on an old R12 version that I still have
> around:
> >
> > Erlang (BEAM) emulator version 5.6.5 [source] [64-bit] [smp:64]
> > [async-threads:0] [hipe] [kernel-poll:false]
> >
> > Eshell V5.6.5  (abort with ^G)
> > 1> (-1299341865233935136534120785510400) band (-1).
> > -1299341865233953583278194495062016
> >
> >
> > I would not be surprised if this bug existed even before Erlang/OTP
> > became open source.
>
> I did some more debugging, but wasn't able to pin-point the error (I
> have two suspects, but the big.c code is non-obvious so it's difficult
> to tell).
> Anyway, I opened https://bugs.erlang.org/browse/ERL-804 for this
> issue, linking back to your original post here.
>
> /Mikael
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