Re: Motion 4
On 2009-04-09 05:34:29 -0700, Dan Zuras Intervals wrote:
> We have said nothing about NaN support yet. And, indeed,
> there are good reasons for excluding NaNs from valid
> intervals. I don't think we will attach any significance
> to signed zeros for practical reasons (we cannot control
> them) but I may be wrong. So the compiler options you
> speak of my be useful.
Motion 4 should be clear about what it requires.
> But if your real concern is for user defined precisions,
> I will point out that they exist now in 754-2008.
Yes, but for instance, I don't think that supporting one of
the basic formats should be required for P1788. And what about
subnormal support[*]? (FYI, MPFR does not support subnormals
directly, and it seems that users don't need them, except for
emulating the IEEE 754 standard.)
[*] The property x != y ==> o(x - y) != 0 may be useful in FP
arithmetic, but I doubt that one needs something similar in IA,
in particular because the returned interval will often contain 0
in case of a cancellation.
Also, we may want to specify IA on elementary functions. In such
a case, would Motion 4 imply that they need to be supported at
the IEEE 754 level? IA may be less demanding, e.g. for trig
functions (sin, cos, tan) on very large values.
--
Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.org/>
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Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)