2015-05-02 23:10 GMT+02:00 Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com>:

>
>
> 2015-05-02 23:04 GMT+02:00 Nicolas Cellier <
> nicolas.cellier.aka.nice at gmail.com>:
>
>>
>>
>> 2015-05-02 22:32 GMT+02:00 Levente Uzonyi <leves at elte.hu>:
>>
>>> On Sat, 2 May 2015, Nicolas Cellier wrote:
>>>
>>>
>>>>
>>>> 2015-05-02 18:27 GMT+02:00 <commits at source.squeak.org>:
>>>>       A new version of Kernel was added to project The Inbox:
>>>>       http://source.squeak.org/inbox/Kernel-mtf.924.mcz
>>>>
>>>>       ==================== Summary ====================
>>>>
>>>>       Name: Kernel-mtf.924
>>>>       Author: mtf
>>>>       Time: 2 May 2015, 12:26:05.675 pm
>>>>       UUID: 7f688860-5202-4c0d-8ece-8723fe7317d6
>>>>       Ancestors: Kernel-nice.923
>>>>
>>>>       Copied Number >> #round: from Pharo. One of 3 methods needed to
>>>> make the Artefact pdf library work on squeak:
>>>>       https://sites.google.com/site/artefactpdf/
>>>>
>>>>       =============== Diff against Kernel-nice.923 ===============
>>>>
>>>>       Item was added:
>>>>       + ----- Method: Float>>round: (in category 'truncation and round
>>>> off') -----
>>>>       + round: numberOfWishedDecimal
>>>>       +         "only leave a fixed amount of decimal"
>>>>       +         "10.12345 round: 2 => 10.12"
>>>>       +
>>>>       +         | v |
>>>>       +         v := 10 raisedTo: numberOfWishedDecimal.
>>>>       +         ^ ((self * v) rounded / v) asFloat
>>>>       + !
>>>>
>>>>
>>>> self assert: (Float fmax round: 2) = Float fmax.
>>>>
>>>> It's probably not very important for artefact, but if this method has a
>>>> wider usage than artefact, then it should better be robust to overflow...
>>>>
>>>>       Item was added:
>>>>       + ----- Method: Fraction>>round: (in category 'truncation and
>>>> round off') -----
>>>>       + round: numberOfWishedDecimal
>>>>       +       ^self asFloat round: numberOfWishedDecimal!
>>>>
>>>>
>>>> Transforming exact arithmetic into inexact Float sounds like heresy to
>>>> me ;)
>>>> That's a questionable choice.
>>>> Why this cult to Float would be necessary here?
>>>>
>>>>       Item was added:
>>>>       + ----- Method: Integer>>round: (in category 'truncation and
>>>> round off') -----
>>>>       + round: numberOfWishedDecimal
>>>>       +       ^self!
>>>>
>>>>       Item was added:
>>>>       + ----- Method: Number>>round: (in category 'truncation and round
>>>> off') -----
>>>>       + round: numberOfWishedDecimal
>>>>       +       self subclassResponsibility!
>>>>
>>>>
>>>> If it's subclass responsibility, then it must be implemented in
>>>> ScaledDecimal.
>>>> This is not necessary in Pharo, because ScaledDecimal has been moved
>>>> under Fraction, but it is in Squeak.
>>>> I'd rather see Float implementation moved up (without the asFloat) and
>>>> Float invoking super asFloat...
>>>>
>>>> I didn't check artefact, but I suspect that the usage is just to
>>>> printShowingMaxDecimals: numberOfWishedDecimal, which would make the whole
>>>> method
>>>> moot.
>>>>
>>>
>>> The method was probably written by someone who's not aware of #roundTo:.`
>>>
>>
>> No, this is because 'x roundTo: (10 raisedTo: n) reciprocal' is a bit
>> worse than '(x * (10 raisedTo: n) asFloat) rounded / (10 raisedTo: n)
>> asFloat'
>> Indeed, in the first one you perform one more inexact operation (1/100 ~=
>> 0.01).
>>
>> But anyway, these are vain efforts, because #round: in Pharo still
>> cumulates several inexact operations and thus will sometimes fail to
>> deliver the correct answer.
>>
>> For example:
>>     self assert: 1.0005 < (5/10000+1) ==> ((1.0005 round: 3) = 1).
>> alas, it answers 1.001 and differs from printShowingMaxDecimalPlaces: 3...
>> Definitely not top quality.
>>
>> I think Pharo did not integrate printShowingMaxDecimalPlaces: so that
>> probably explains the mistake.
>> Or maybe they were influenced by Python round, but should have checked
>> how it is implemented:
>> For example, see
>> https://github.com/python/cpython/blob/c7688b44387d116522ff53c0927169db45969f0e/Python/pymath.c
>>
>> double round(double x) { double absx, y; absx = fabs(x); y = floor(absx);
>> if (absx - y >= 0.5) y += 1.0; return copysign(y, x); }
>>
>
> Oups, that's round without argument...
>
>

It is rather in
https://github.com/python/cpython/blob/12f02a041ecca16d61352548dc4573095f0dae10/Objects/floatobject.c
And it is using dtoa, that is equivalent to ^(Float readFrom: (self
printShowingDecimalPlaces: n) readStream)


>
>> That should translate easily in Smalltalk if REALLY necessary...
>>
>>
>> You're right about the printing thing in Artefact. I replaced #round:
>>> with #printOn:maxDecimalPlaces: in my image.
>>>
>>>
>> Easy to guess, the only other possible use I can think of, is naive
>> monetary apps; that makes two reasons to ban the message ;)
>>
>>
>>
>> Levente
>>>
>>>
>>>> Nicolas
>>>>
>>>>
>>>
>>>
>>>
>>
>
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