Re: Motion 31: V04.2 Revision of proposed Level 1 text
On 2012-02-23 12:09:58 +0100, Ulrich Kulisch wrote:
> Am 21.02.2012 14:48, schrieb Vincent Lefevre:
> >On 2012-02-21 09:14:29 +0100, Ulrich Kulisch wrote:
> >>The dot product is a fundamental operation in Numerical Analysis.
> >Not for everyone. If it were so important, it would have been
> >required in IEEE 754-2008. And most languages don't even have
> >a dot product function.
> >
> Vincent:
>
> all vector units provide a dot product and IEEE 754-2008 recommends it.
> These dot products are inexact and not of much use for interval arithmetic.
> By pipelining the exact dot product comes with the same speed up than the
> dot products on conventional vector units. I have no doubts that languages
> would support the dot product as soon as the exact dot product or complete
> arithmetic is available. IEEE 1788 is supposed to form the future.
I don't disagree if a correctly-rounded *interval* dot product is
recommended by IEEE 1788. But IEEE 1788 mustn't contradict IEEE 754.
If a language provides an IEEE-754 conforming dot product (thus not
necessarily correctly rounded), it shouldn't prevent one from having
an IEEE 1788 conforming interval arithmetic.
If IEEE 1788 specified a correctly-rounded dot product, this would
mean that we could end up with two dot product functions in the
language, one standard, and one a bit less standard (e.g. if IEEE
1788 is made optional by the language). This would be a nightmare
for developers to decide what they should do for portability.
Really, the right solution is to revise IEEE 754.
--
Vincent Lefèvre <vincent@xxxxxxxxxx> - Web: <http://www.vinc17.net/>
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Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)