2016-10-26 13:11 GMT+02:00 test <wkass...@libello.com>: > Hi Nicolas, > regarding rounding Fractions: > i use fractions if i want to get an exact result (eg for comparing the > result with Float calculations). if #round: returns a Float all further > calcs (with Fractions) will get contaminated, since the rest will become > Floats too. Hence the "asScaledDecimal: numberOfWishedDecimal" seems better > to me, but i wonder why these transformations at the end are necessary at > all? just for the looks? i'd suppose every person, who knows how to use > Fractions, also knows how to append a #asScaledDecimal: to a result by > himself, should he want that. > > taking as an example financial calcs that first use 2 decimals. > occasionaly the final result will be basepoints, often small ones like > 0.003. with scaledDecimals the result would be (ok, look like) 0 since > scaledDecimals also contaminate the calc. of course one could correct this > simply with an #asScaledDecimal:3 at the end. nevertheless a first look at > the zero result would surprise me for a tenth of a second. > werner > > > Hi Werner, I don't know the purpose of round: at all. Most often this kind of message was used before printing probably because lack of versatile formatted print messages. In Squeak I replaced most usages of roundTo: by printShowing(Max)DecimalPlaces:. Now if it has been added in Pharo and other languages, there must be some use cases I presume. Maybe the analysis could be carried on these use cases?
Beware, converting a Fraction asScaledDecimal will NOT round. Only the printString is rounded, but the number keeps its whole precision. Example (1/3 asScaledDecimal: 1)*3 = 1.0s, not 0.9s. ScaledDecimals as they are now are just Fraction with a different printString... Not very much added value. Nicolas > On 10/26/2016 09:58 AM, Nicolas Cellier wrote: > > > > 2016-10-26 9:14 GMT+02:00 stepharo <steph...@free.fr>: > >> Hi nicolas >> >> So what is the solution? We can integrate fast a solution. >> I would really like to see them fix in Pharo 60. >> I'm writing a book for newbie and this is the third time I change one >> chapter >> so may be I should stop and throw away this chapter. >> >> > 1) for Fraction: > > round: numberOfWishedDecimal > v := 10 raisedTo: numberOfWishedDecimal. > ^ ((self * v) rounded / v) asFloat > > or just replace asFloat if you wish to remain exact: > > round: numberOfWishedDecimal > v := 10 raisedTo: numberOfWishedDecimal. > ^ ((self * v) rounded / v) asScaledDecimal: numberOfWishedDecimal > > 2) for Float, it is in 15471: > > round: numberOfWishedDecimal > | v maxNumberOfDecimals | > maxNumberOfDecimals := self class precision - 1 - (self exponent max: > self class emin). > maxNumberOfDecimals < numberOfWishedDecimal ifTrue: [^self]. > v := 10 raisedTo: numberOfWishedDecimal. > ^ ((self asFraction * v) rounded / v) asFloat > > or if Fraction already answers a Float: > > round: numberOfWishedDecimal > | maxNumberOfDecimals | > maxNumberOfDecimals := self class precision - 1 - (self exponent max: > self class emin). > maxNumberOfDecimals < numberOfWishedDecimal ifTrue: [^self]. > ^ self asFraction round: numberOfWishedDecimal > > It's slower than current implementation, but will round exactly to the > nearest Float. > It's possible to have faster implementation up to 22 decimals if you > provide a fused-multiply-accumulate primitive... > > >
