OT: Re: is dwt alive?
aarti_pl
aarti at interia.pl
Sun Jul 11 23:53:46 PDT 2010
W dniu 2010-07-11 23:39, aarti_pl pisze:
> W dniu 2010-07-11 22:45, "Jérôme M. Berger" pisze:
>> aarti_pl wrote:
>>> I just would like to say that it is a great news! After discovering that
>>> for Java:
>>> ----
>>> double sum = 0.0;
>>> for (int i = 0; i< 10; i++) sum += 0.1;
>>> ----
>>>
>>> sum is equal: 0.9999999999999999
>>>
>>> I am looking at D with greater and greater sentiment :-) SWT and good
>>> precision of calculations is necessary for my program...
>>>
>> Are you sure D is better? In C, you get 0.99999999999999988898 (not
>> surprising since 0.1 cannot be represented exactly in base 2) and I
>> would expect D to give the same result...
>>
>> Jerome
>
> On my computer it is exactly 1.0 (one).
>
> I know that there is explanation of why it is like that, as I found
> article about it. I did not get deeper into it (good few pages of text)
> as I believe there must better solution for programmers.
>
> My calculator shows proper results, spreadsheet shows proper results and
> I think that calculations in my program for such a big fractions should
> also give correct result.
>
> Just thought: maybe calculations in D are done internally in more than
> 64bits and then casted into 64bits? It's a bit surprising for me that C
> is also wrong about this sum...
>
> BR
> Marcin Kuszczak
> (aarti_pl)
Ok. You are right. D is not better in this case. It seems that it's just
writeln cut number of decimal digits and printed 1.
Using:
writefln("%.25f", sum);
we get:
0.99999999999999988897
Does it mean that the only way to get better precision is to use some
custom classes like BigDecimal in Java?
BR
Marcin Kuszczak
(aarti_pl)
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