Re: [Gambas-user] rounding a half

[Jussi Lahtinen <jussi.lahtinen@xxxxxxxxx>]

Hmmm... no this seems like a fundamental problem in floating points.
You could do something like this:

RETURN->_float.value = floor((PARAM->_float.value / power + 0.5) * t) / t *
power;

Where t is double with a large value. This would hide the problem into
smaller decimal places.
Not sure it's worth it. Probably implementing arbitrary precision datatype
would be the right way. Benoit?


Jussi



On Mon, Dec 9, 2024 at 5:24 PM Jussi Lahtinen <jussi.lahtinen@xxxxxxxxx>
wrote:

> Interesting... this is a floating point presentation problem. Should be
> fixable.
> It is due to the internally used floor. And the problem occurs in Gambas
> as well:
>
> Print (1.055 / 0.01 + 0.5);; Floor((1.055 / 0.01 + 0.5))
> 106 105
>
>
> Jussi
>
>
> On Mon, Dec 9, 2024 at 2:19 PM wig <wig@xxxxxxxxx> wrote:
>
>>
>>
>> I would think that rounding a half would always react the same, either
>> up or down;
>>
>> f = 1.015
>>
>> Print "Round(" & f & ", -2) = " & Round(f, -2)
>>
>> Result:
>>
>> Round(1.015, -2) = 1.02
>>
>> f = 1.055
>>
>> Print "Round(" & f & ", -2) = " & Round(f, -2)
>>
>> Round(1.055, -2) = 1.05
>>
>> What should I expect?
>>
>> I used Gambas 3.18.4
>>
>> System info see attach
>>
>> Kind greetings,
>>
>> Wig
>>
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>