Hello,
This is not a bug-report or something like this, just I am curios.
Yesterday I was playing with fi.fb_fcomb() and I'm a bit puzzled.
Let's talk about fb_comb() first, they both have the same pattern.
Two questions:
---------------------------------------------------------------------
Why does it have ": mem" at the end? This makes sense sometimes but
- its purpose is not documented.
- the comment refers to ~jos/paspFeedback_Comb_Filters.html
but with this "mem" the difference equation doesn't match
that of mentioned in the link above.
- user can easily add ": mem" himself if needed.
---------------------------------------------------------------------
But the main question is that the part before ": mem"
(+ <: de.delay(maxdel,N-1),_) ~ *(-aN) : !,*(b0)
looks suboptimal and overcomplicated to me. I mean,
+ ~ -aN * de.delay(maxdel,N-1) : *(b0);
or
*(-aN) + *(b0) ~ de.delay(maxdel,N-1);
should do the same but
- look more simple/understandable
- do not create the extra delay line
---------------------------------------------------------------------
Let's compare the generated code just in case.
f1(maxdel,N,b0,aN) = (+ <: de.delay(maxdel,N-1),_) ~ *(-aN) : !,*(b0);
f2(maxdel,N,b0,aN) = + ~ -aN * de.delay(maxdel,N-1) : *(b0);
Current implementation:
process = f1(10,10, .3, .7);
compiles to
float fVec0[10];
float fRec0[2];
int fSampleRate;
void compute(int count, FAUSTFLOAT** inputs, FAUSTFLOAT** outputs)
{
FAUSTFLOAT* input0 = inputs[0];
FAUSTFLOAT* output0 = outputs[0];
for (int i0 = 0; i0 < count; i0 = i0 + 1) {
float fTemp0 = float(input0[i0]) - 0.7f * fRec0[1];
fVec0[0] = fTemp0;
fRec0[0] = fVec0[9];
float fRec1 = fTemp0;
output0[i0] = FAUSTFLOAT(0.3f * fRec1);
for (int j0 = 9; j0 > 0; j0 = j0 - 1) {
fVec0[j0] = fVec0[j0 - 1];
}
fRec0[1] = fRec0[0];
}
}
while
process = f2(10,10, .3, .7);
compiles to
float fRec0[11];
int fSampleRate;
void compute(int count, FAUSTFLOAT** inputs, FAUSTFLOAT** outputs)
{
FAUSTFLOAT* input0 = inputs[0];
FAUSTFLOAT* output0 = outputs[0];
for (int i0 = 0; i0 < count; i0 = i0 + 1) {
fRec0[0] = float(input0[i0]) - 0.7f * fRec0[10];
output0[i0] = FAUSTFLOAT(0.3f * fRec0[0]);
for (int j0 = 10; j0 > 0; j0 = j0 - 1) {
fRec0[j0] = fRec0[j0 - 1];
}
}
}
and to me f2() certainly looks more readable than f1().
Thanks,
Oleg.
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