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From Paul Davis <paul.joseph.da...@gmail.com>
Subject Re: Fixed precision of floating point number not respected in views
Date Tue, 19 Feb 2013 12:57:07 GMT
It used mochijson2 which uses mochinum.erl which uses arbitrary
precision arithmetic which makes this a lot easier (IIRC, its the
ability to raise numbers to arbitrarily large powers).

I do agree the behavior would be nice if it could be provided but the
runtime cost is prohibitive if implemented in Erlang (arbitrary
precision arithmetic is also generally slower than FPU operations).

Also, so we're being more specific, it returned numbers with the
fewest number of digits required that could then be fed into a
standard libc parsing algorithm to return the same floating point
representation based on what's in RAM. There are other assumptions and
caveats related to the various thingers as well.

On Tue, Feb 19, 2013 at 6:47 AM, Volker Mische <volker.mische@gmail.com> wrote:
> On 02/19/2013 10:13 AM, Paul Davis wrote:
>> On Tue, Feb 19, 2013 at 3:09 AM, Robert Newson <rnewson@apache.org> wrote:
>>> "I have stored fixed precision numbers in a database". You haven't,
>>> unfortunately, because you can't. Javascript only has one kind of
>>> number, 64-bit floating point.
>>>
>>
>> Its a tidge more complicated than that. Its actually a combination of
>> the Erlang JSON decoder/encoder roundtrip plus the JavaScript decoder.
>
> I remember that older version of Apache CouchDB (IIRC 1.1) did return
> the numbers as they were put it. Don't know which decoder was used back
> then.
>
> I'd love to see this behaviour coming back.
>
> Cheers,
>   Volker
>
>>
>>>
>>> If you want fixed precision, you'll need to store your numbers in
>>> strings and manipulate them that way too. A quick google in the past
>>> has shown a few "bignum" libraries for Javascript.
>>>
>>
>> Though the end result is the same. If you need fixed precision
>> numbers, then using JSON's syntax for "numbers with decimal points and
>> non-zero digits after the decimal point" will lead to surprising
>> results and lack of fidelity.
>>
>> I've had a few discussions on this for Jiffy in terms of round
>> tripping something as trivial as 1.1 through a JSON decoder/encoder
>> pair. Turns out this is really really hard.
>>
>> Here's the Python ticket where they added it to the language for a
>> good discussion on the details required to make this actually work:
>>
>> http://bugs.python.org/issue1580
>>
>>> B.
>>>
>>> On 19 February 2013 08:20, Luca Morandini <lmorandini@ieee.org> wrote:
>>>> On 02/19/2013 07:05 PM, Luca Morandini wrote:
>>>>>
>>>>> Folks,
>>>>>
>>>>> I have stored fixed precision numbers in a database, but when they are
>>>>> spit out by
>>>>> a view, the precision is full, and -which is worse- the trailing decimal
>>>>> digits
>>>>> are not all zeroes.
>>>>
>>>>
>>>> In the CouchDB: The Definitive Guide", I have found out that "most clients"
>>>> would interpret, say, 15.7 as 15.69999999999 (or so), which I suppose is
>>>> exactly what I observed... but what is meant as "client" in this context,
a
>>>> view engine ?
>>>>
>>>> Anyway, any view to tune this feature of the JavaScript view engine ?
>>>>
>>>>
>>>> Regards,
>>>>
>>>> Luca Morandini
>>>> Data Architect - AURIN project
>>>> Department of Computing and Information Systems
>>>> University of Melbourne
>>>> Tel. +61 03 903 58 380
>>>> Skype: lmorandini
>>>>
>

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