I'm confused, Tim.  As best I can remember, floating point numbers can
reasonably be compared to one another using inequalities.  My understanding
is that it's *equality* comparisons that are often misleading and should be
avoided.  If I've misunderstood your point please help me understand.
Thanks.

Bob Jarvis
Compuware @ Timken

> -----Original Message-----
> From: Tim Rowledge [mailto:tim at sumeru.stanford.edu]
> Sent: Tuesday, September 14, 2004 2:33 PM
> To: squeak-dev at lists.squeakfoundation.org
> Subject: RE: Float equality? (was: [BUG] Float NaN's)
> 
> 
> "Jarvis, Robert P. (Bob) (Contingent)" <bob.jarvis at timken.com> wrote:
> 
> > The best practice I'm aware of for handling equality 
> calculations with
> > Floats is avoid them completely.  You should establish what 
> you consider to
> > be an acceptable epsilon value based on your understanding 
> of your data and
> > use it as follows:
> > 
> > 	maxEpsilon = 0.000001.
> > 		.
> > 		.
> > 		.
> > 	(f1 - f2) abs < maxEpsilon
> > 		ifTrue: ["f1 and f2 are approximately equal"]
> > 		ifFalse: ["f1 and f2 are not approximately equal"]
> Argh! Bob, you just broke your own advice. Is that a dagger, er float
> comparison, I see before me?
> 
> Worse yet, to be meaningful the epsilon probably ought to be a
> percentage/fraction and not an absolute value since the precision of
> Floats is different to the range. (Apologies if I'm not using the
> currently fashonable terms). So, if we postulate an extremely limited
> form of Float with only 4sf we would perhaps do
> (f1 / f2 < 1.0001 and:[f2 / f1 <1.0001])
> 	ifTrue:[approx equal]
> 	ifFalse[not really equal]
> And of course it still uses a comparison. :-(
> 
> Like you said, don't use'em if precision is important. In fact, don't
> ese them at all. Then we could use all that silicon on the cpu for
> something more useful.
> 
> 
> tim
> --
> Tim Rowledge, tim at sumeru.stanford.edu, http://sumeru.stanford.edu/tim
> Strange OpCodes: HSJ: Hop, Skip and Jump
> 

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