2016-10-26 9:14 GMT+02:00 stepharo <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...


You see I'm not good in math so even if I try hard I will not have a good solution.
This is the same for marcus and most people in our team.
I reopened these issues.

Stef



2016-10-25 23:22 GMT+02:00 stepharo <stepharo@free.fr>:

Ok for the advice

Now round: aNumberOfDigits seems to work fine.

Stef



I hate to say that, but try in python, they got it right...

��
Le 25/10/16 �� 11:05, Henrik Johansen a ��crit��:
+1.

Unless you're dealing with fixed precision* entities, it's usually better to specify digits to display in printing methods themselves (#printShowingDecimalPlaces: & friends in base image).
As per previous discussions around this that arise every second year or so, rounding the number itself (as long as we're dealing with floats) will never work as you want reliably.

Cheers,
Henry

* And in that case, you'd use ScaledDecimals��

On 23 Oct 2016, at 7:08 , phil@highoctane.be wrote:

I use the Printf package for that.

v := 65.456.
'With 2 decimal digits: %5.2f, or 3 like this: %6.3f'��
printf: {v. v}.

With 2 decimal digits: 65.45, or 3 like this: 65.456


Printf

I am just used to C printf and well, I like the way it works.

Phil