Re: Motion 4: P1788 on non-754?
On 2009-04-12 16:10:18 -0500, Corliss, George wrote:
> At one level, how something may be implemented is not the concern of the
> standard. At that level, the underlying hardware is irrelevant. At another
> level, if something is impossible to implement (efficiently, depending on
> one's point of view), there is no point putting it into a standard. Hence,
> discussions leading to a standard SHOULD sometimes include discussions about
> implementations. That is messy enough if the discussions are about possible
> implementations in 754. The discussion complexity is probably unbounded if
> we admit discussions of possible implementations on ANY architecture, known
> or imagined.
Not necessarily. IMHO, an arithmetic (not necessarily floating-point)
with exceptions and directed rounding (possibly not correct rounding,
but an implementation should provide error bounds, so that the user
can know how tight his intervals will be) should be sufficient to
define an interval arithmetic.
Let's take an example: the double-double arithmetic, which can be
implemented thanks to IEEE 754 BTW (so, on most architectures), and
which is often used to extend the precision. I wonder if directed
rounding is also used in practice with it, but anyway, this is
possible. Should P1788 ignore such arithmetics? Is there any reason
why such arithmetics would make IA definition significantly more
complicated?
--
Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.org/>
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Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)