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 <[email protected]
<mailto:[email protected]>>:
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...
