Re: Changing the default i387 precision

[Joerg Sonnenberger <joerg%britannica.bec.de@localhost>]

On Mon, May 06, 2013 at 07:59:14AM -0400, Greg Troxel wrote:
> 
> Joerg Sonnenberger <joerg%britannica.bec.de@localhost> writes:
> 
> > On Sat, May 04, 2013 at 12:33:08PM -0400, Greg Troxel wrote:
> >> I still cannot follow exactly what you are proposing to change.
> >
> > The default rounding mode to give full internal precision.
> 
> I think that by default, programs should get behavior compliant with
> IEEE754.

Almost noone wants to have IEEE754 behavior with i387. It is hideously
expensive. We don't provide it at the moment either, since e.g.
underflows don't happen at the correct time. Setting the default
rounding precision fixes the behavior of some operations and leaves
others intact. There is no work around for that. As I said before, the
only real way to get IEEE754 float and double behavior with decent
performance (and frankly, decent performance in general) is to use SSE.

Joerg