From kde-core-devel  Tue Jun 23 20:59:12 2009
From: Michael Pyne <mpyne () kde ! org>
Date: Tue, 23 Jun 2009 20:59:12 +0000
To: kde-core-devel
Subject: Re: Review Request: KColorSpace::KHCY::KHCY(const & QColor)
Message-Id: <200906231659.19429.mpyne () kde ! org>
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On Tuesday 23 June 2009 01:52:18 Oswald Buddenhagen wrote:
> On Mon, Jun 22, 2009 at 07:15:39PM -0400, Michael Pyne wrote:
> > I think the best answer in this case is to ensure as much as possible,
> > comparisons are done against 0.0 (i.e. don't do if (a =3D=3D b), but do=
 c =3D a
> > - b; if(c =3D=3D 0.0) )
>
> i really have to wonder what the technical foundation of that idea is,
> because to me it doesn't make any sense.

Well if all you're really worried about is dividing against zero then you c=
an=20
compare against 0.0 (which is really the only equality comparison you can d=
o=20
on floating point since it is exact and so are its conversions to different=
=20
forms).

You do need to make sure that the value you're dividing by is the value you=
're=20
comparing against though, which is why I recommended using the named tempor=
ary=20
variable.  I suppose this doesn't work if the division will be performed at=
 a=20
lower precision (which from my understanding of x86, could happen when usin=
g=20
the FPU), since what is not quite zero as an 80-bit double could be convert=
ed=20
to a 64-bit zero.

If we're really that worried about it I think Olivier's solution would be j=
ust=20
fine (i.e. qFuzzyCompare).

Regards,
 - Michael Pyne

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