[Pharo-dev] float & fraction equality bug

Nicolas Cellier nicolas.cellier.aka.nice at gmail.com
Thu Nov 9 09:36:09 EST 2017


Nope, not a bug.

If you use Float, then you have to know that (x -y) isZero and (x = y) are
two different things.
Example; Float infinity

In your case you want to protect against (x-y) isZero, so just do that.

2017-11-09 15:15 GMT+01:00 Tudor Girba <tudor at tudorgirba.com>:

> Hi,
>
> I just stumbled across this bug related to the equality between fraction
> and float:
> https://pharo.fogbugz.com/f/cases/20488/x-y-iff-x-y-0-is-
> not-preserved-in-Pharo
>
> In essence, the problem can be seen that by doing this, you get a
> ZeroDivide:
> x := 0.1.
> y := (1/10).
> x = y ifFalse: [ 1 / (x - y) ]
>
> The issue seems to come from the Float being turned to a Fraction, rather
> than the Fraction being turned into a Float:
>
> Fraction(Number)>>adaptToFloat: rcvr andCompare: selector
> "If I am involved in comparison with a Float, convert rcvr to a
> Fraction. This way, no bit is lost and comparison is exact."
>
> rcvr isFinite
> ifFalse: [
> selector == #= ifTrue: [^false].
> selector == #~= ifTrue: [^true].
> rcvr isNaN ifTrue: [^ false].
> (selector = #< or: [selector = #'<='])
> ifTrue: [^ rcvr positive not].
> (selector = #> or: [selector = #'>='])
> ifTrue: [^ rcvr positive].
> ^self error: 'unknow comparison selector'].
>
> ^ *rcvr asTrueFraction perform: selector with: self*
>
> Even if the comment says that the comparison is exact, to me this is a bug
> because it seems to fail doing that. What do you think?
>
> Cheers,
> Doru
>
>
> --
> www.tudorgirba.com
> www.feenk.com
>
> "Problem solving should be focused on describing
> the problem in a way that makes the solution obvious."
>
>
>
>
>
>
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