gnc_numeric: fractional displays and rounding

[Charles Day]

On Thu, Aug 7, 2008 at 9:51 AM, Charles Day <cedayiv at gmail.com> wrote:

> On Thu, Aug 7, 2008 at 1:48 AM, Christian Stimming <stimming at tuhh.de>wrote:
>
>> Am Mittwoch, 6. August 2008 18:43 schrieb Charles Day:
>> > On Thu, Jul 31, 2008 at 5:13 PM, Charles Day <cedayiv at gmail.com> wrote:
>> > >> Sorry, yes, you're right. Here's a corrected second table:
>> > >>
>> > >>  round force_fit decimal  non-decimal
>> > >>  ===== ========= ======= =============
>> > >>      0         0   0.999       0 + 1/3
>> > >>      1         0   1.000       0 + 1/3
>> > >>      0         1   0.999         0.333 *a better example might be 2/3
>> > >> (prints as 0.666)
>> > >>      1         1   1.000         0.333 *a better example might be 2/3
>> > >> (prints as 0.667)
>> > >
>> > > While I'm at it, shall I make 1/3 print simply as "1/3" instead of "0
>> +
>> > > 1/3" in the first two cases?
>> >
>> > Can anyone confirm the intended meaning of the force_fit option? Shall I
>> go
>> > ahead with these changes?
>>
>> I can't confirm the *intended* meaning, but your explained meaning makes
>> perfect sense to me. IMHO you can go ahead with these changes.
>>
>
> When reading through the code again, I realized that "force_fit" works
> slightly different than I thought. Without "force_fit" turned on, any number
> of digits will be printed. So I think what I will do is just make fractions
> always print as fractions and rounding will not work on them.
>
> If we need to display non-decimal numbers in decimal form, using either
> truncation or rounding, then I think we need to add a new option of
> "force_decimal". If you want me to add that option, let me know. Below is
> the corrected (again) before and after.
>
> Let's say there is a decimal value of 9999/10000, a non-decimal value of
> 2/3, and max_decimal_places is 3. Depending on how you set round and
> force_fit, you CURRENTLY get the following output by calling
> xaccPrintAmount():
>
>  round force_fit decimal  non-decimal
>  ===== ========= ======= =============
>      0         0  0.9999       0 + 2/3
>      1         0  0.9999       0 + 2/3
>      0         1  0.999        0 + 2/3
>      1         1  1.000  0 + 4003/6000
>
> After patching, this is how it would work. Only the non-decimal column is
> different:
>
>  round force_fit decimal  non-decimal
>  ===== ========= ======= =============
>      0         0  0.9999           2/3
>      1         0  0.9999           2/3
>      0         1  0.999            2/3
>      1         1  1.000            2/3
>
> If we add a "force_decimal" option (and I don't know that this is needed),
> this is how it would work. Note that "force_decimal" implies using
> max_decimal_places on non-decimals:
>
>  round force_fit force_decimal decimal  non-decimal
>  ===== ========= ============= ======= =============
>      0         0             0  0.9999           2/3
>      1         0             0  0.9999           2/3
>      0         1             0  0.999            2/3
>      1         1             0  1.000            2/3
>      0         0             1  0.9999         0.666
>      1         0             1  0.9999         0.667
>      0         1             1  0.999          0.666
>      1         1             1  1.000          0.667
>
> So for now I will just write a patch to go from the first table to the
> second.
>

Patch committed as r17457 with backport requested.


>
>
>> Regards
>>
>> Christian
>>
>
> Cheers,
> Charles
>