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 On 10/26/2016 09:58 AM, Nicolas Cellier wrote:
2016-10-26 9:14 GMT+02:00 stepharo <stepharo@free.fr <mailto:stepharo@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...