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):>_;
>
>
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>
--
Julius O. Smith III <j...@ccrma.stanford.edu>
Professor of Music and, by courtesy, Electrical Engineering
CCRMA, Stanford University
http://ccrma.stanford.edu/~jos/
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