Re: Rounding rule for P1788/M0037.01
> Date: Mon, 29 Oct 2012 12:30:59 -0400
> To: stds-1788 <stds-1788@xxxxxxxxxxxxxxxxx>
> From: Michel Hack <mhack@xxxxxxx>
> Subject: Rounding rule for P1788/M0037.01
>
> Vincent Lefèvre wrote:
> > "if there are two closest numbers, we use rounding to even,
> > i.e., select the one whose binary expansion ends in 0"
> >
> > This only makes sense for some number formats, even not all
> > floating-point formats (as phrased above, for floating-point
> > formats, the radix needs to be even and the precision >= 2).
>
> Perhaps we should offer a friendly amendment to replace that
> paragraph:
>
> "if there are two closest numbers, we use the default
> rounding mode defined for the format."
>
> This would also allow COBOL to use ties-away-from-zero, which
> is permitted by IEEE 754-2008 for decimal formats.
>
> The problem with odd radices (or single-bit binary) is that
> there is no deterministic unbiased rounding method. So if we
> wanted a generally-acceptable method applicable to all formats,
> about the only ones that make sense are ties-away-from zero (a
> method sanctioned by IEEE 754-2008) or ties-towards-zero (which
> might have slightly less cumulative roundoff effects for formats
> where ties-to-even does not work).
>
> Michel.
> ---Sent: 2012-10-29 16:41:36 UTC
I think we can safely reject systems with odd radices
as hosts for 1788. Or. for that matter, systems with
radices other than 2 or 10. IMHO, of course. - Dan