Re: BUG #15925: Loss of precision converting money to numeric

> Hmm, yeah, anything approaching INT64_MAX has a problem.
> The issue is that cash_numeric() does the equivalent of
>
> SELECT 9223372036854775807::numeric / 100::numeric;
>
> and if you try that by hand you indeed get
>
> 92233720368547758
>
> because select_div_scale() has decided that it need not produce
> any fractional digits.  We can force its hand by making the input
> have the required number of fractional digits *before* dividing,
> which is a bit weird on its face but gets the job done, per the
> comment therein:
>
>     * The result scale of a division isn't specified in any SQL standard. For
>     * PostgreSQL we select a result scale that will give at least
>     * NUMERIC_MIN_SIG_DIGITS significant digits, so that numeric gives a
>     * result no less accurate than float8; but use a scale not less than
>     * either input's display scale.
>
> (NUMERIC_MIN_SIG_DIGITS is 16, whence the problem for a 17-digit result.
> Maybe we should consider raising that, but I'm hesitant to consider such
> a far-reaching change just to make cash_numeric happy.)
>
> I intend to apply the attached patch.

Thanks Tom,

the response is illuminating. And a same-day patch is legendary.

Thank you for your work.
Slawo