Re: [Boost-users] [Math] Accuracy test failures on QNX 6.4.0

Subject: Re: [Boost-users] [Math] Accuracy test failures on QNX 6.4.0
From: John Maddock (john_at_[hidden])
Date: 2008-11-27 05:05:58

Niklas Angare wrote:
>>> Any feedback from QNX on the cause of the issue?  It would be nice
>>> understand what's going on just in case it's something we can fix.
>>
>> Nothing yet. I've reported the issue here:
>> http://community.qnx.com/sf/go/projects.core_os/discussion.newcode.topc5091
>>
>>> Ah no, there really was a bug in the Boost.Math code that was
>>> exposed by a less than fully accurate fmod implementation on that
>>> platform.
>>
>> Is this and the other accuracy problems something to worry about
>> when doing simple calculations with doubles?

Maybe, maybe not :-(

The default behaviour is that to ensure accuracy, each special function is 
actually evaluated internally at the next available precision up - so for 
example:

tgamma<float>   evaluated at double precision internally.
tgamma<double>   evaluated at long double precision internally.

There are configuration macros to change this behaviour if needed (or just 
disable long double support full stop): but for now the double-precision 
tests all appear to be passing.  It's a worry though :-(

John.