Re: 1.0 divided by 10 = 0.10000000000000001?
Re: 1.0 divided by 10 = 0.10000000000000001?
- Subject: Re: 1.0 divided by 10 = 0.10000000000000001?
- From: Greg Herlihy <email@hidden>
- Date: Tue, 28 Mar 2006 18:48:00 -0800
- Thread-topic: 1.0 divided by 10 = 0.10000000000000001?
There are two number classes that have come up in this discussion, hence the
confusion: NSDecimal and its likely replacement: "long double".
The former is base-10 while the latter is not. But since long doubles have
such great precision and are much faster than NSDecimals when performing
calculations, it is likely that NSDecimalNumbers will be deprecated in favor
of long doubles - probably whenever Leopard is released. Another necessary
change before that could happen though will be to add long double support to
NSNumber.
Greg
On 3/28/06 5:42 PM, "Derrick Bass" <email@hidden> wrote:
>> Folks
>>
>> If there is a documentation bug here, or even if it isn't clear,
>> then please file a bug.
>>
> The documentation quite clearly says NSDecimalNumber is base-10.
> We're trying to determine is whether or not that is correct. Marcel,
> based on (what I think is a pretty inconclusive) comment from Chris
> Kane, thinks yes (NSDecimalNumber is base-2), while I see no reason
> to doubt the docs based on what he's presented.
>
> Since both Marcel and I are both using the fallacy of appealing to
> authority (Chris Kane is his case, the Apple documentation in mine),
> I'd thought I'd throw in a little evidence.
>
> I ported the first portion of Kahan's famous (another appeal to
> authority) "paranoia" program (see, e.g. <http://
> orion.math.iastate.edu/burkardt/c_src/paranoia/paranoia.html>) to
> test NSDecimalNumber. It confirms that it is base-10, although the
> precision is less than the documentation says (34 digits; the docs
> say 38).
>
> I'm enclosing my port so anyone who's interested can check to be sure
> I did it right.
>
> Derrick
>
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