Re: [Boost-users] [Boost.UTF] Strange (failed) result on comparing floats

Subject: Re: [Boost-users] [Boost.UTF] Strange (failed) result on comparing floats
From: Paul A. Bristow (pbristow_at_[hidden])
Date: 2010-03-31 13:38:47

> -----Original Message-----
> From: boost-users-bounces_at_[hidden] [mailto:boost-users-bounces_at_[hidden]] On Behalf Of Steven Watanabe
> Sent: Wednesday, March 31, 2010 3:35 PM
> To: boost-users_at_[hidden]
> Subject: Re: [Boost-users] [Boost.UTF] Strange (failed) result on comparing floats
> 
> AMDG
> 
> Olaf Peter wrote:
> > I'm checking some data of consistence using boost's unit test framework
> > (1.42):
> >
> > BOOST_CHECK_CLOSE( *v[1].y.max, -43.0e-3,
> >     std::numeric_limits<double>::epsilon() );
> >
> > which fails with:
> >
> > difference{1.6137e-14%} between *v[1].y.max{-0.043000000000000003} and
> > -43.0e-3{-0.042999999999999997} exceeds 2.2204460492503131e-16%
> >
> > where v is a std::vector,y a struct and max a boost::optional<double>.
> > The data where parsed by boost.spirit. This is the only failed test case
> > from 16 parsed doubles. What's gone wrong here? Do I miss something?
> >
> 
> epsilon is too small.  BOOST_CHECK_CLOSE treats the
> argument as a percent, so there's an extra factor of 0.01, which
> means that this comparison is effectively for equality.

Well spotted Steven.

BOOST_CHECK_CLOSE_FRACTION( *v[1].y.max, -43.0e-3, std::numeric_limits<double>::epsilon() );

is what you meant?

Our esteemed and illustrious author of the invaluable Test library was begged not to use percents but ...

Paul

---
Paul A. Bristow
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Kendal, UK   LA8 8AB
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