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  1. Doc: document the tie-breaking behavior of the round() function.

  1. Rounding strategy

    The Post Office <noreply@postgresql.org> — 2021-04-19T08:00:07Z

    The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/13/functions-math.html
Description:

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.

  2. Re: Rounding strategy

    Laurenz Albe <laurenz.albe@cybertec.at> — 2021-04-19T15:37:14Z

    On Mon, 2021-04-19 at 08:00 +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/13/functions-math.html
> Description:
> 
> 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.

+1

Yours,
Laurenz Albe

  3. Re: Rounding strategy

    Laurenz Albe <laurenz.albe@cybertec.at> — 2021-04-22T16:54:54Z

    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.

Yours,
Laurenz Albe

  4. Re: Rounding strategy

    Tom Lane <tgl@sss.pgh.pa.us> — 2021-04-22T17:50:20Z

    Laurenz Albe <laurenz.albe@cybertec.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.

			regards, tom lane

  5. Re: Rounding strategy

    Laurenz Albe <laurenz.albe@cybertec.at> — 2021-04-23T07:40:04Z

    On Thu, 2021-04-22 at 13:50 -0400, Tom Lane wrote:
> Laurenz Albe <laurenz.albe@cybertec.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

  6. Re: Rounding strategy

    Laurenz Albe <laurenz.albe@cybertec.at> — 2021-04-23T08:51:41Z

    On Fri, 2021-04-23 at 09:40 +0200, Laurenz Albe wrote:
> Makes sense.  Here is an updated patch.

I see that you have already committed your proposed version.
Thanks!

Yours,
Laurenz Albe

  7. Re: Rounding strategy

    rudolphfroger@dreamsolution.nl — 2021-04-23T16:15:22Z

    Thanks a lot!

Cheers, Rudolph

On 23-04-2021 10:51, Laurenz Albe wrote:
> On Fri, 2021-04-23 at 09:40 +0200, Laurenz Albe wrote:
>> Makes sense.  Here is an updated patch.
> 
> I see that you have already committed your proposed version.
> Thanks!
> 
> Yours,
> Laurenz Albe
>