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Id: 130713
Status: open
Priority: 0/
Queue: perl6

Owner: Nobody
Requestors: elizabeth <liz [at] dijkmat.nl>
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To: rakudobug [...] perl.org
From: Elizabeth Mattijsen <liz [...] dijkmat.nl>
Subject: 42.expmod(-1,1) hangs
Date: Fri, 3 Feb 2017 22:32:40 +0100
CC: Dana Jacobsen <dana.jacobsen [...] gmail.com>
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The combination of parameters -1,1 like this, causes nqp::expmod_I to hang. Assume this is a MoarVM issue, as this does not appear to be an issue on MoarVM. Spotted by Dana Jacobsen++
Subject: Re: [perl #130713] 42.expmod(-1,1) hangs
From: Brandon Allbery <allbery.b [...] gmail.com>
To: perl6-compiler <perl6-compiler [...] perl.org>
CC: bugs-bitbucket [...] rt.perl.org
Date: Fri, 3 Feb 2017 16:34:33 -0500
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On Fri, Feb 3, 2017 at 4:33 PM, Elizabeth Mattijsen <perl6-bugs-followup@perl.org> wrote:
Show quoted text
Assume this is a MoarVM issue, as this does not appear to be an issue on MoarVM.

...which of those was supposed to be something else?


--
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From: Elizabeth Mattijsen <liz [...] dijkmat.nl>
Subject: Re: [perl #130713] 42.expmod(-1,1) hangs
To: perl6-compiler <perl6-compiler [...] perl.org>
Date: Fri, 3 Feb 2017 22:40:52 +0100
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> On 3 Feb 2017, at 22:34, Brandon Allbery <allbery.b@gmail.com> wrote: > > > On Fri, Feb 3, 2017 at 4:33 PM, Elizabeth Mattijsen <perl6-bugs-followup@perl.org> wrote: > Assume this is a MoarVM issue, as this does not appear to be an issue on MoarVM. > > ...which of those was supposed to be something else?
The second: there’s no problem on the JVM. Good catch! Note to self: do not do bugreports after having been to Delirium in Brussels. :-) Liz
Date: Fri, 3 Feb 2017 22:41:21 +0100
To: Brandon Allbery via RT <perl6-bugs-followup [...] perl.org>
From: Elizabeth Mattijsen <liz [...] dijkmat.nl>
Subject: Re: [perl #130713] 42.expmod(-1,1) hangs
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Show quoted text
> On 3 Feb 2017, at 22:34, Brandon Allbery <allbery.b@gmail.com> wrote: > > > On Fri, Feb 3, 2017 at 4:33 PM, Elizabeth Mattijsen <perl6-bugs-followup@perl.org> wrote: > Assume this is a MoarVM issue, as this does not appear to be an issue on MoarVM. > > ...which of those was supposed to be something else?
The second: there’s no problem on the JVM. Good catch! Note to self: do not do bugreports after having been to Delirium in Brussels. :-) Liz
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It seems like we literally just pass the values into libtommath's mp_exptmod. It then just infinitely loops around inside of fast_mp_invmod. Perhaps we can see if a newer version of libtommath changed something about that and perhaps fixed our problem?
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There's a github issue that relates to this. Applying this change to our tommath makes expmod(42, -1, 1) terminate successfully. https://github.com/libtom/libtommath/issues/67


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