[Cfp-interest] Three round nearest modes and FLT_ROUNDS

[Ian McIntosh]

If you wanted to implement augmented operations in software, would 
you want access to the roundTiesToZero rounding mode?

  - Ian

At 23/10/2018 02:36 PM -0700, Fred J. Tydeman wrote:
>On Tue, 23 Oct 2018 12:06:37 -0700 Jim Thomas wrote:
> >
> >My understanding is that 754-2019 does not intend for 
> roundTiesToZero to be a new user selectable rounding direction.
>
>Agreed.
>
> >C 7.31.4 already reserves the names with an FE_ prefix, so the 
> names would be available if a future revision of 754 added a user 
> selectable rounding direction. It wouldn't be appropriate for C to 
> get in front of 754 on this.
>
>I was not clear.  There is no requirement that anyone support TiesToZero for
>anything other than the augmented operations.  Therefore, there is no
>requirement that any implementations define FE_TONEARESTTOZERO.
>However, if an implementation were to define such a user selectable
>rounding mode, I am asking that we specify the spelling of it now.
>
>The other issue is:
>
>Given that there could be multiple different meanings for Round to Nearest,
>what should FLT_ROUNDS be?  Should FLT_ROUNDS have a value
>for each of the possible FE_* rounding macros?  Should there be a
>one-to-one mapping between FLT_ROUNDS and the FE_* rounding modes?
>
>
>
>---
>Fred J. Tydeman        Tydeman Consulting
>tydeman at tybor.com      Testing, numerics, programming
>+1 (702) 608-6093      Vice-chair of PL22.11 (ANSI "C")
>Sample C99+FPCE tests: http://www.tybor.com
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>
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