Re: [Boost-bugs] [Boost C++ Libraries] #6171: nonconforming behavior of inverse functions on branch cuts

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #6171: nonconforming behavior of inverse functions on branch cuts
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-12-13 22:23:08

#6171: nonconforming behavior of inverse functions on branch cuts
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  Reporter:  Richard B. Kreckel <kreckel@…>         |       Owner:  johnmaddock
      Type:  Bugs                                   |      Status:  closed     
 Milestone:  To Be Determined                       |   Component:  math       
   Version:  Boost 1.48.0                           |    Severity:  Problem    
Resolution:  fixed                                  |    Keywords:             
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Comment (by anonymous):

 Thanks for applying this patch. I've tried it and it passes my tests.

 I see only one potential problem in the way acosh has been fixed: it tests
 the sign of the imaginary part of the result of the acos function. It is
 generally much safer to test the location in the complex plain of input
 variables like z.imag() instead of the location of intermediate results
 like result.imag(). This is because intermediate results may suffer from
 roundoff.

 My original patch avoided this problem I'm seeing problems related to this
 in various projects (e.g. GLibC
 http://cygwin.com/bugzilla/show_bug.cgi?id=13305). Please consider
 applying the patch I'm going to attach next.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/6171#comment:4>
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