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A Look at the Generated C++ code
Running Faust with no architecture file, e.g.,
> faust cpgrir.dspcauses the C++ signal-processing code to be printed on the standard output, as shown for this example in Fig.K.6. Notice how the constant subexpressions are computed only once per instance in the instanceInit member function. Also, even in instanceInit, which is only called once, repeated computation of
is avoided by use of the temporary variable fConst1,
and division by 2 is converted to multiplication by 
.
class mydsp : public dsp {
private:
float fConst0; float fConst1;
int iVec0[2]; float fConst2;
int iVec1[3]; float fConst3; float fRec0[3];
public:
virtual int getNumInputs() { return 0; }
virtual int getNumOutputs() { return 1; }
static void classInit(int samplingFreq) { }
virtual void instanceInit(int samplingFreq) {
fSamplingFreq = samplingFreq;
fConst0 = expf((0 - (314.159271f / fSamplingFreq)));
fConst1 = (fConst0 * fConst0);
for (int i=0; i<2; i++) iVec0[i] = 0;
fConst2 = ((2 * fConst0) * cosf((2764.601562f
/ fSamplingFreq)));
for (int i=0; i<3; i++) iVec1[i] = 0;
fConst3 = (0.500000f * (1 - fConst1));
for (int i=0; i<3; i++) fRec0[i] = 0; }
virtual void init(int samplingFreq) {
classInit(samplingFreq);
instanceInit(samplingFreq); }
virtual void buildUserInterface(UI* interface) {
interface->openVerticalBox("faust");
interface->closeBox(); }
virtual void compute (int count, float** input,
float** output) {
float* output0 = output[0];
for (int i=0; i<count; i++) {
iVec0[0] = 1;
int iTemp0 = iVec0[1];
iVec1[0] = (1 - iTemp0);
fRec0[0] = (((fConst3 * (1 - (iTemp0 + iVec1[2])))
+ (fConst2 * fRec0[1]))
- (fConst1 * fRec0[2]));
output0[i] = fRec0[0];
// post processing
fRec0[2] = fRec0[1]; fRec0[1] = fRec0[0];
iVec1[2] = iVec1[1]; iVec1[1] = iVec1[0];
iVec0[1] = iVec0[0];
}
}
};
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Previous: Testing a Faust Filter Section
Next: Generating a Pure Data (PD) Plugin
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Julius Smith's background is in electrical engineering (BS Rice 1975, PhD Stanford 1983). He is presently Professor of Music and Associate Professor (by courtesy) of Electrical Engineering at Stanford's Center for Computer Research in Music and Acoustics (CCRMA), teaching courses and pursuing research related to signal processing applied to music and audio systems. See http://ccrma.stanford.edu/~jos/ for details.
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