sdrangel/sdrbase/dsp/fftfilt.h

/*
 * Filters from Fldigi.
*/

#ifndef	_FFTFILT_H
#define	_FFTFILT_H

#include <complex>
#include <cmath>

#include "gfft.h"
#include "export.h"

//----------------------------------------------------------------------

class SDRBASE_API fftfilt {
enum {NONE, BLACKMAN, HAMMING, HANNING};

public:
	typedef std::complex<float> cmplx;

	fftfilt(int len);
	fftfilt(float f1, float f2, int len);
	fftfilt(float f2, int len);
	~fftfilt();
// f1 < f2 ==> bandpass
// f1 > f2 ==> band reject
	void create_filter(float f1, float f2);
	void create_dsb_filter(float f2);
    void create_asym_filter(float fopp, float fin); //!< two different filters for in band and opposite band
    void create_rrc_filter(float fb, float a); //!< root raised cosine. fb is half the band pass

	int noFilt(const cmplx& in, cmplx **out);
	int runFilt(const cmplx& in, cmplx **out);
	int runSSB(const cmplx& in, cmplx **out, bool usb, bool getDC = true);
	int runDSB(const cmplx& in, cmplx **out, bool getDC = true);
	int runAsym(const cmplx & in, cmplx **out, bool usb); //!< Asymmetrical fitering can be used for vestigial sideband

protected:
	int flen;
	int flen2;
	g_fft<float> *fft;
	cmplx *filter;
    cmplx *filterOpp;
	cmplx *data;
	cmplx *ovlbuf;
	cmplx *output;
	int inptr;
	int pass;
	int window;

	inline float fsinc(float fc, int i, int len)
	{
	    int len2 = len/2;
		return (i == len2) ? 2.0 * fc:
				sin(2 * M_PI * fc * (i - len2)) / (M_PI * (i - len2));
	}

	inline float _blackman(int i, int len)
	{
		return (0.42 -
				 0.50 * cos(2.0 * M_PI * i / len) +
				 0.08 * cos(4.0 * M_PI * i / len));
	}

	/** RRC function in the frequency domain. Zero frequency is on the sides with first half in positive frequencies
	 * and second half in negative frequencies */
	inline cmplx frrc(float fb, float a, int i, int len)
	{
        float x = i/(float)len; // normalize to [0..1]
        x = 0.5-fabs(x-0.5); // apply symmetry: now both halves overlap near 0
        float tr = fb*a; // half the transition zone

        if (x < fb-tr)
        {
            return 1.0; // in band
        }
        else if (x < fb+tr) // transition
        {
            float y = ((x-(fb-tr)) / (2.0*tr))*M_PI;
            return (cos(y) + 1.0f)/2.0f;
        }
        else
        {
            return 0.0; // out of band
        }
	}

	void init_filter();
	void init_dsb_filter();
};



/* Sliding FFT filter from Fldigi */
class SDRBASE_API sfft {
#define K1 0.99999
public:
	typedef std::complex<float> cmplx;
	sfft(int len);
	~sfft();
	void run(const cmplx& input);
	void fetch(float *result);
private:
	int fftlen;
	int first;
	int last;
	int ptr;
	struct vrot_bins_pair;
	vrot_bins_pair *vrot_bins;
	cmplx *delay;
	float k2;
};

#endif