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Message-ID:  <524F0DA5.4040106@morningstar2.co.uk>
Date:         Fri, 4 Oct 2013 19:49:09 +0100
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From: Joseph Wright <joseph.wright@MORNINGSTAR2.CO.UK>
Subject: Re: Bug in l3fp for sines near 2pi
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Status: R

On 04/10/2013 08:50, Andrew Parsloe wrote:
> I recently stumbled on the following bug in the l3fp package:
> 
> \fp_eval:n { sin( 2pi - .0001 ) } ==> 9999.999000000002
> 
> which seems a little excessive for a function bounded by +1, -1.
> 
> \fp_eval:n { sin( 2pi - .001 ) } seems to evaluate correctly. The value
> between .001 and .0001 where the bug arises is between .001853071795,
> which is too small and brings on the error, and .001853071796, which
> doesn't.

Thanks for the bug report: I've logged it as
https://github.com/latex3/svn-mirror/issues/155, and assigned it to
Bruno :-) (He wrote the FPU!). As I've said in the issue database, this
looks like a range-reduction failure to me. Range reduction is known to
be 'hard', so that's not that surprising.

> P.S. Is this a *very* quiet list, or have I not configured things
> correctly so that I'm missing postings to it?

List traffic varies: there are lots of ideas to discuss but getting
feedback is not always easy even when there is time for us to ask the
questions!
-- 
Joseph Wright