Hello,
Thanks for your answers !
Effectively, the code compiles with option -double but not with default option
-single.
I'll use -double precision waiting for the fix !
Thank you
Pierre
> Hi,
>
> Right, the compiler try to factorize a multiplication by 0 ! Another way to
> see the problem it to compare :
>
> process= (_*cos(1/2*ma.PI)^3,_,_*cos(-1/2*ma.PI)^3);
>
>
> and
>
> process= (_*cos(1/2*ma.PI)^3,_,_*cos(-1/2*ma.PI)^3) :> _;
>
>
> in simple and double precision.
>
> Clearly, the factorization rule needs to be fixed
>
> Thanks for discovering the problem !
>
> Yann
>
> Yann Orlarey
>
> Directeur scientifique
> www.grame.fr
>
> 2016-09-24 18:33 GMT+02:00 Julius Smith <j...@ccrma.stanford.edu>:
> > This looks like numerical failure in the optimization by the Faust
> > compiler. You can see it approaching this situation in the following
> > simplified case:
> >
> > process=(_*cos(ma.PI/2),_,_*cos(0-ma.PI/2)):>_;
> >
> > which compiles to
> >
> > output0[i] = (FAUSTFLOAT)(6.123234e-17f * (((1.633124e+16f *
> > (float)input1[i]) + (float)input0[i]) + (float)input2[i]));
> >
> > Since cos(PI/2) = 0, the input coefficients are approximately 0,1,0,
> > which become (numerically) eps,1,eps, where eps = 6.123234e-17f in
> > this particular case. Factoring out eps gives 1/eps for the
> > coefficient of input1, which became infinity in the previous example
> > (numerical bug... 1/eps should possibly go to MAX_FLOAT, but not inf).
> > If there were a third signal multiplied by eps, then this factoring
> > would save a multiply, but in this case there are two multiplies
> > either way.
> >
> > I would personally like to be able to set a magnitude threshold below
> > which numbers are flushed to zero. Then the compiler would see
> > coefficients (0,1,0) in this case and not try to factor out the 0.
> >
> > - Julius
> >
> > On Fri, Sep 23, 2016 at 7:26 AM, Stéphane Letz <l...@grame.fr> wrote:
> > > The generated C++ code is incorrect (see this "(inf.0f *
> >
> > (float)input1[i]))) » subexpression), so probably a bug in the compiler.
> >
> > > Stéphane
> > >
> > >> Le 23 sept. 2016 à 13:28, Pierre Lecomte <pierre.leco...@gadz.org> a
> >
> > écrit :
> > >> import("stdfaust.lib");
> > >> process=(_*cos(1/2*ma.PI)^3,_,_*cos(-1/2*ma.PI)^3):>_;
> > >
> > > ------------------------------------------------------------
> >
> > ------------------
> >
> > > _______________________________________________
> > > Faudiostream-users mailing list
> > > Faudiostream-users@lists.sourceforge.net
> > > https://lists.sourceforge.net/lists/listinfo/faudiostream-users
> >
> > --
> > Julius O. Smith III <j...@ccrma.stanford.edu>
> > Professor of Music and, by courtesy, Electrical Engineering
> > CCRMA, Stanford University
> > http://ccrma.stanford.edu/~jos/
> >
> > ------------------------------------------------------------
> > ------------------
> > _______________________________________________
> > Faudiostream-users mailing list
> > Faudiostream-users@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/faudiostream-users
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