Re: Directed rounding

[Eric Walter]

Dear John,

Thanks for you quick replies and suggestions. As far as I am able to 
judge, you are absolutely right, and what would be needed is a simple 
access to fegetround and fesetround. Unfortunately, I will not be able 
to make it possible. I was just suggesting that it could be a useful 
feature for those who care about the accuracy of their floatting point 
computations, and a plus compared to MATLAB ands Scilab, which do not 
offer it.

Best regards,

Eric

Le 17/09/2015 17:58, John W. Eaton a écrit :
> On 09/17/2015 11:57 AM, John W. Eaton wrote:
> > On 09/17/2015 11:43 AM, Juan Pablo Carbajal wrote:
> > > On Thu, Sep 17, 2015 at 4:47 PM, Eric Walter
> > > <address@hidden> wrote:
> > > > Dear colleagues,
> > > >
> > > > If this is not already the case, would you please consider making
> > > > directed
> > > > rounding, as made available on all IEEE 747 compliant processors, 
> > > > simply
> > > > accessible to gnu-octave users? This would help assessing the 
> > > > number of
> > > > significant digits in the results of floatting-point computation.
> > > >
> > > > Best regards,
> > > >
> > > > Eric Walter
> > >
> > > Dear Eric,
> > >
> > > I might not get the point correctly, but are the functions round, fix,
> > > floor, ceil, sign, chop not doing what you need?
> >
> > Please file a feature request "bug" on the bug tracker.
> >
> > If I understand correctly, you are asking to make the functions
> > fegetround and fesetround available in Octave if they are supported by
> > the system, correct?
> >
> > It should not be too hard for you to write your own wrappers for those
> > functions.  I'd probably define them to accept/return strings like
> > "nearest", "up", "down", "toward-zero" or similar.
> >
> > If you do write your own, please consider contributing them.
> >
> > Thanks,
> >
> > jwe
>
> Also, FWIW, the GNU C Library manual has this to say about changing 
> rounding modes:
>
>    You should avoid changing the rounding mode if possible.  It can be
> an expensive operation; also, some hardware requires you to compile your
> program differently for it to work.  The resulting code may run slower.
> See your compiler documentation for details.
>
> jwe