Re: [9fans] circular fonctions: precision?

[tlaronde@polynum.com]

On Sun, Oct 02, 2011 at 02:44:35PM -0400, erik quanstrom wrote:
> > IEEE754-1985 didn't specify circular, hyperbolic or other
> > advanced functions. You can have 754 compliant hardware and
> > not implement these functions. In any case the standard can
> > not dictate the accuracy of functions not specified in it. An
> > iterative algorithm may lose more than 1 bit of accuracy since
> > iterations won't be done in infinite precision. One can not
> > assume accuracy to a bit even where these functions are
> > imeplemented in h/w.  For x86, accuracy may be specified in
> > some Intel or AMD manual.
>
> that wasn't my reading of the spec.  so you're saying that if
> the iterative algorithm loops 53 times, it's free to return any
> answer whatever and still be compliant?

There is a document titled "What Every Computer Scientist Should know
About Floating Point Arithmetic", by David Goldberg that states
precisely this: IEEE754 standardized what could be standardized, and
only that. There are many lengths of rope left...

Hence my question to know if "someone" has specified that, for the plan9
implementation, even if the implementation of the circular functions
has no uniq accuracy, at least for the domain of definition and whatever
hardware, the answer is not inaccurate of more than some defined
epsilon. (That could be enough for the range of geographic coordinates,
in my case.)

--
        Thierry Laronde <tlaronde +AT+ polynum +dot+ com>
                      http://www.kergis.com/
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