2009/7/7 Ignacio Vivona <[email protected]>: > Why not the opposite? The default behavior is 13/10 = 1.3 yields true and > the new behavior (13/10) asFloat = 1.3 equals false. > This kind of behavior is a real pain in languages like java, i are you > bringing this to the smalltalk world? >
Hi Ignacio. If you'd provide a rationale for the behaviour you're proposing we could argue. Otherwise my answer would just be speculation. If 1.3 is 13/10 explain why 1.3*1.3 is not 169/100. As I told before, you should better use ScaledDecimals if you rely on such assertions. Cheers Nicolas > 2009/7/7 Hernan Wilkinson <[email protected]> >> >> Hi Nicolas, >> thank you for your answer. I'm aware of the float representation >> problems. But this new behavior sounds more confusing, at least to me... I >> mean, 1.3 is not a number with representation problems so why do we have to >> make this difference? I understand you are trying to avoid the problems >> sometimes floats generate, but I think that doing so we are loosing some >> abstraction from the number representation type. >> Correct me if I wrong, but doesn't this new behavior means that always, >> in any number comparison, we need to coerse the number to float? Because 1.3 >> asFraction = (13/10) returns false but 1.3 = (13/10) asFloat returns true... >> I mean, if we have a = b and the values of those variables are calculated by >> some process such that a is 1.3 and b is 13/10, the comparison will not >> work, so we need to explicitly write "a asFloat = b asFloat" just in case >> any of those variables reference a float, even though none of them will ever >> do... but then "(1/2) = 0.5" returns true... I don't know, I don't like it >> that much... >> >> On Tue, Jul 7, 2009 at 3:56 PM, Nicolas Cellier >> <[email protected]> wrote: >>> >>> Hi Hernan, >>> This is the new Behavior of Float comparison and it is desired. >>> >>> 1) 1.3 is represented in machine as >>> (1.3 significandAsInteger printStringRadix: 2) , '.0e' , (1.3 exponent >>> - Float precision + 1) printString. >>> -> '2r10100110011001100110011001100110011001100110011001101.0e-52' >>> >>> Or if you prefer: >>> (1.3 asTrueFraction numerator printStringBase: 2) , '/' , (1.3 >>> asTrueFraction denominator printStringBase: 2). >>> -> >>> '10100110011001100110011001100110011001100110011001101/10000000000000000000000000000000000000000000000000000' >>> >>> As you can see, this is quite different from 13/10. >>> >>> However, you can test (13/10) asFloat = 1.3 and that happens to be >>> true, but that won't always be true. >>> >>> 2) comparing Float with strict equality is a dangerous game. Floating >>> point operation are inherently inexact and thus asserting an exact >>> equality is considered a bad practice. >>> >>> 3) basing comparisons and equality tests on inexact arithmetic rather >>> than on exact arithmetic leads to weird behaviours. See >>> http://bugs.squeak.org/view.php?id=3374 >>> >>> >>> So i do not consider this fragment of code alone as a bug but as a >>> feature. >>> There might be some code depending on the old behaviour that can >>> eventually break. >>> If you have such an example in true application, I'm interested. >>> I think we'd better fix such code to not rely on exact equality... >>> >>> Cheers. >>> >>> Nicolas >>> >>> >>> >>> 2009/7/7 Hernan Wilkinson <[email protected]>: >>> > I added this new issue that happens on the latest image. >>> > I'm posting it here because I think it is an important bug because it >>> > affects the number model. >>> > The problem is related with all fractions who's denominator is not >>> > power of >>> > two. (130/100 = 1.3 or 1/5 = 0.2, etc) >>> > (See >>> > >>> > Float>>adaptToFraction: rcvr andCompare: selector where it does >>> > .... >>> > "Try to avoid asTrueFraction because it can cost" >>> > selector == #= ifTrue: [ >>> > rcvr denominator isPowerOfTwo ifFalse: [^false]]. >>> > >>> > ...) >>> > >>> > >>> > Hernan. >>> > >>> > >>> > >>> > _______________________________________________ >>> > Pharo-project mailing list >>> > [email protected] >>> > http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project >>> > >>> >>> _______________________________________________ >>> Pharo-project mailing list >>> [email protected] >>> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project >> >> >> _______________________________________________ >> Pharo-project mailing list >> [email protected] >> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project > > > > -- > Hope is for sissies (Gregory House, M.D.) > > _______________________________________________ > Pharo-project mailing list > [email protected] > http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project > _______________________________________________ Pharo-project mailing list [email protected] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
