According to IEEE 754, the base of Pharo Float, *finite* values shall
behave like old plain arithmetic.
On 2017-11-09 15:36, Nicolas Cellier wrote:
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 <[email protected]
<mailto:[email protected]>>:
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
<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 <http://www.tudorgirba.com>
www.feenk.com <http://www.feenk.com>
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