[Cuis-dev] More on The Cuis Book

[Ignacio Sniechowski]

Thanks!
I will try that method.

*Ignacio Sniechowski*



















On Mon, Mar 6, 2023 at 4:55 PM Martin McClure <martin at hand2mouse.com> wrote:

> Hi Nacho,
>
> If what you want is to produce a rounded *print string*, rather than a
> rounded* number*, one can use a formatted printing message, such as
> #printShowingDecimalPlaces:.
>
> Regards,
> -Martin
>
> On 3/6/23 04:03, Ignacio Sniechowski wrote:
>
> Thanks for your response, Martin!
> I thought that #roundTo: only affected representation, but it seems that
> there are some caveats when applied to floatings.
> I've experimented with 0.1, 0.01, and 0.001, and this misrepresentation
> affects other numbers in the interval. So the lesson would be: be careful
> with #roundUp: & similar methods when using floating as the imagined or
> expected representation could fail.
>
> Thanks again
> Nacho
>
>
> *Ignacio Sniechowski*
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> On Sun, Mar 5, 2023 at 10:34 PM Martin McClure <martin at hand2mouse.com>
> wrote:
>
>> On 3/5/23 16:51, Ignacio Sniechowski via Cuis-dev wrote:
>>
>> Float pi to: 5 by: 1/3 do: [:i | Transcript show: (i roundTo: 0.01) ;
>> space] ⇒ 3.14 3.47 3.81 4.14 4.47 4.81
>> *"*3.14 3.47 3.81 4.14 4.47 4.8100000000000005" the last number is not
>> rounded...
>> What is especially intriguing is the last case...that 4.8100000000000005
>> is not rounded.
>>
>>
>> Hi Nacho,
>>
>> Ah, welcome the lovely and confusing world of decimal expressions of
>> binary floating-point numbers.
>>
>> What is not obvious here is that the last case *is* rounded.
>>
>> "roundTo: 0.01" requests that the result be an exact multiple of 0.01.
>> But 0.01 is not exactly representable as a floating-point number, so the
>> closest Float is used, and that float is a bit greater than 1/100.
>>
>> 0.01 asFraction > (1/100) ==> true
>>
>> So we end up with a float that is 481 * 0.01, which is a little more than
>> 481 / 100, *and* there exists a different float which is closer to 481 /
>> 100. Every float has a unique default print string. The string '4.81' is
>> used for that other float, so we have to use the string
>> '4.8100000000000005' for the float that is the correct result of the
>> expression.
>>
>> Regards,
>> -Martin
>>
>
>
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