Oh, just something I forgot to mention: ScaledDecimal should behave the way you expect.
1.3s1 = (13/10). -> true. 1.3s2*1.3s2 = 1.69s2. -> true 1.3 * 1.3 = 1.69. -> false Nicolas 2009/7/7 Nicolas Cellier <[email protected]>: > 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
