Re: Rounding to even for numeric data type

On 29/03/15 13:07, David G. Johnston wrote:
> On Sat, Mar 28, 2015 at 3:59 PM, Michael Paquier
> <michael(dot)paquier(at)gmail(dot)com <mailto:michael(dot)paquier(at)gmail(dot)com>>wrote:
>
> On Sun, Mar 29, 2015 at 5:34 AM, Gavin Flower
> <GavinFlower(at)archidevsys(dot)co(dot)nz
> <mailto:GavinFlower(at)archidevsys(dot)co(dot)nz>> wrote:
> > On 28/03/15 21:58, Dean Rasheed wrote:
> > [...]
> >>
> >>
> >> Andrew mentioned that there have been complaints from people doing
> >> calculations with monetary data that we don't implement
> >> round-to-nearest-even (Banker's) rounding. It's actually the
> case that
> >> various different financial calculations demand different specific
> >> rounding modes, so it wouldn't be enough to simply change the
> default
> >> - we would have to provide a choice of modes.
> >
> > [...]
> >
> > Could the 2 current round functions have cousins that included
> an extra char
> > parameter (or string), that indicated the type of rounding?
>
> >
> > So we don't end up with an explosion of rounding functions, yet
> could cope
> > with a limited set of additional rounding modes initially, and
> possibly
> > others in the future.
>
> Instead of extending round, isn't what we are looking at here a new
> data type? I have doubts that we only want to have a way to switch
> round() between different modes. Hence, what we could do is:
> 1) Mention in the docs that numeric does round-half-away-from-zero
> 2) Add regression tests for numeric(n,m) and round(numeric)
> 3) Add a TODO item for something like numeric2, doing rounding-at-even
> (this could be an extension as well), but with the number of
> duplication that it may have with numeric, an in-core type would make
> sense, to facilitate things exposing some of structures key structures
> would help.
>
>
> So, create a numeric type for each possible rounding mode​? That
> implies at least two types, round-half-even and
> round-half-away-from-zero, with suitable abbreviations: numeric_rhe,
> numeric_raz.
>
> If the goal is to make plain numeric IEEE standard conforming then
> giving the user a way to switch all existing numeric types to
> numeric_raz would be nice.
>
> Implicit casts between each of the various numeric types would be
> needed and understandable.
>
> I'm pondering calling them numeric_eng and numeric_bus (for
> engineering and business respectively)...
>
> David J.
>
In Java, there are 8 rounding modes specified:

https://docs.oracle.com/javase/8/docs/api/java/math/RoundingMode.html

Some of these may be relevant to pg.

Cheers,
Gavin