Message-ID: <dbd3c64d0113b4eeeb1330bfa3ca99000c582df4.camel@cybertec.at>
Subject: Re: Rounding strategy
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: rudolphfroger@dreamsolution.nl, pgsql-docs@lists.postgresql.org
Date: Fri, 23 Apr 2021 09:40:04 +0200
In-Reply-To: <1100756.1619113820@sss.pgh.pa.us>
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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

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