size_t FirFilterDesigner::wdfirCx (
T& filtCoeff,
FIRFilter::filter_type type,
Real ripple,
Real twNorm,
Real flNorm,
Real fhNorm,
size_t minTaps,
size_t maxTaps)
{
if ((type==FIRFilter::lowpass)||(type==FIRFilter::highpass))
{
//design a real filter and mux the imaginary zeros in there to make it complex
RealArray r;
size_t ret = wdfir(r, type, ripple, twNorm, flNorm, 0, minTaps,maxTaps);
muxImaginaryZeros(r, filtCoeff);
return ret;
}
else
{
//create a lowpass or highpass filter and tune the filter with a complex tune to make the bandpass filter
FIRFilter::filter_type inputType=FIRFilter::lowpass;
if (type==FIRFilter::bandstop)
inputType=FIRFilter::highpass;
RealArray r;
size_t ret = wdfir(r, inputType, ripple, twNorm, fabs(fhNorm-flNorm)/2.0, 0, minTaps,maxTaps);
filtCoeff.resize(ret);
//tune the filter outputs to the specified center frequency
//the tune phase is 2*pi*fc_norm = 2*pi*((fhNorm+flNorm)/2) = pi*(fhNorm+flNorm)
Real tunePhaseUpdate=M_PI*(fhNorm+flNorm);
Complex phasor(cos(tunePhaseUpdate),sin(tunePhaseUpdate));
Complex tuner(phasor);
for (size_t i=0; i!=ret; i++)
{
filtCoeff[i]=r[i]*tuner;
tuner*=phasor;
}
return ret;
}
}
std::vector<std::complex<T> > getTwiddleFactors(size_t N, bool fwd,
size_t Lm1Qm1 = std::numeric_limits<size_t>::max)
{
std::vector<std::complex<T> > factors(std::min(N, Lm1Qm1));
if(factors.size() > 0)
{
factors[0] = 1;
if(factors.size() > 1)
{
// Use high-precision multiplication of phasors.
typedef std::complex<long double> HighPrecComplex;
long double phase = 2*3.14159265358979323846/N;
HighPrecComplex phasor(cos(phase), fwd ? -sin(phase) : sin(phase));
HighPrecComplex tmp(phasor);
factors[1] = tmp;
for(size_t i = 2; i < factors.size(); ++i)
factors[i] = tmp = tmp * phasor;
}
}
return factors;
}
