Re: Rounding to even for numeric data type

On Sat, Mar 28, 2015 at 3:59 PM, Michael Paquier <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> 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.