Re: Rounding strategy

On Thu, 2021-04-22 at 13:50 -0400, Tom Lane wrote:
> Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at> writes:
> > On Mon, 2021-04-19 at 08:00 +0000, PG Doc comments form wrote:
> > > The 'round' mathematical function documentation doesn't specify its rounding
> > > strategy. If this would be documented then users can rely on its rounding
> > > behavior. For double precision the rounding probably depends on your
> > > platform. For numeric the function seems to round to nearest with ties going
> > > away from zero (sometimes referred to as "round half up). 6.5 -> 7.0 and
> > > -6.5 -> -7.0.
> >
> > Here is a proposed patch.
>
> LGTM, although I think we can be a bit more specific about the float
> case. I suggest
>
> ... by rounding away from 0. For <type>double precision</type>,
> the tie-breaking behavior is platform dependent, but
> <quote>round to nearest even</quote> is the most common rule.

Makes sense. Here is an updated patch.

Yours,
Laurenz Albe