AUDIT: r17421 - gnucash/trunk/lib/libqof/qof - Add a new function to the gnc_numeric library that converts denominators to exact powers of ten.

[Charles Day]

On Tue, Sep 16, 2008 at 2:40 PM, Charles Day <cedayiv at gmail.com> wrote:

> On Tue, Sep 16, 2008 at 10:54 AM, Charles Day <cedayiv at gmail.com> wrote:
>
>> On Tue, Sep 16, 2008 at 9:38 AM, Andreas Köhler <andi5.py at gmx.net> wrote:
>>
>>> Hi,
>>>
>>> On Mon, 2008-09-01 at 22:09 +0200, Andreas Köhler wrote:
>>> > Hi Charles,
>>> >
>>> > On Sun, 2008-07-27 at 11:33 -0400, Charles Day wrote:
>>> > > Trac: http://svn.gnucash.org/trac/changeset/17421
>>> > > Log:
>>> > > Add a new function to the gnc_numeric library that converts
>>> denominators to exact powers of ten.
>>> >
>>> > > Modified: gnucash/trunk/lib/libqof/qof/gnc-numeric.c
>>> > > ===================================================================
>>> > > --- gnucash/trunk/lib/libqof/qof/gnc-numeric.c      2008-07-27
>>> 15:11:19 UTC (rev 17420)
>>> > > +++ gnucash/trunk/lib/libqof/qof/gnc-numeric.c      2008-07-27
>>> 15:33:23 UTC (rev 17421)
>>> > > +  fraction = converted_val.denom;
>>> > > +  if (fraction <= 0)
>>> > > +    return FALSE;
>>> >
>>> > out of curiosity, what is the reason for disallowing negative
>>> > denominators?  I am not sure whether there is a gnc_numeric API
>>> function
>>> > to switch signs of nom and denom safely, but I am sure that doing it is
>>> > possible :-) But maybe the current behavior is actually desired.
>>>
>>> I just noticed that ignoring negative denominators means that 1/(-10) is
>>> now printed as "1 * 10", where it was printed as "10.00" before.  Is
>>> that a regression we have to fix or not?
>>>
>>
>> I can see how that would happen, because in previous versions, non-decimal
>> fractions were forced to print in decimal form in some places. So even
>> though the old routines considered 1/(-10) non-decimal, it would print it as
>> decimal anyway. I think this takes us back to the original discussion.
>> Should go ahead and add support for negative denominators to
>> gnc_numeric_to_decimal()? I must only take less than 5 lines of code.
>>
>
> Here's the first attempt at that change. How are you testing these numbers?
>

I went ahead and committed this change in r17554. Calling
gnc_numeric_to_decimal on 4/-3 now gets you 12. However, there is an
overflow danger because gnc_numeric_convert()  doesn't check for that
(apparently this has been a problem for some time). Someone else should
probably look at that, as I am no expert on 64-bit/128-bit math.

-Charles


> $ svn diff
> Index: gnc-numeric.c
> ===================================================================
> --- gnc-numeric.c       (revision 17505)
> +++ gnc-numeric.c       (working copy)
> @@ -1043,7 +1043,14 @@
>
>    converted_val = *a;
>    if (converted_val.denom <= 0)
> -    return FALSE;
> +  {
> +    converted_val = gnc_numeric_convert(converted_val, 1,
> GNC_DENOM_EXACT);
> +    if (gnc_numeric_check(converted_val) != GNC_ERROR_OK)
> +      return FALSE;
> +    *a = converted_val;
> +    *max_decimal_places = decimal_places;
> +    return TRUE;
> +  }
>
>    /* Zero is easily converted. */
>    if (converted_val.num == 0)
>
>
>>
>>
>>> Ciao,
>>> -- andi5
>>>
>>
>> Cheers,
>> Charles
>>
>
>