[Mesa-dev] Precision of float and trigonometric functions on i965

[Jason Ekstrand]

On Dec 11, 2014 11:13 AM, "Ilia Mirkin" <imirkin at alum.mit.edu> wrote:
>
> On Thu, Dec 11, 2014 at 2:10 PM, Chris Forbes <chrisf at ijw.co.nz> wrote:
> > Iago,
> >
> > This doesn't matter for GL conformance -- but the impression I get is
> > that dEQP is aiming at something more.
> >
> > In any case, the usual problem with this is inaccurate range
> > reduction, which is fixable in software at some performance cost. The
> > C library does this, for example.
>
> Probably related to this:
>
>
https://randomascii.wordpress.com/2014/10/09/intel-underestimates-error-bounds-by-1-3-quintillion/

That's a fun article, but beside the point for what we probably care
about.  No one cares about precisely computing sin(pi) to hundreds of
decimal places on a GPU.

If we really want to fix the issue, we can do range reduction at the cost
of probably a couple extra instructions.  That said, I doubt this will be
an issue in real life as x % pi begins to get fairly imprecise at those
magnitudes.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/mesa-dev/attachments/20141211/493dde10/attachment.html>