path: root/gr-filter/lib/firdes.cc

/* -*- c++ -*- */
/*
 * Copyright 2002,2007,2008,2012 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * GNU Radio is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3, or (at your option)
 * any later version.
 *
 * GNU Radio is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with GNU Radio; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <filter/firdes.h>
#include <stdexcept>

using std::vector;

namespace gr {
  namespace filter {
    
#define IzeroEPSILON 1E-21               /* Max error acceptable in Izero */

    static double Izero(double x)
    {
      double sum, u, halfx, temp;
      int n;
      
      sum = u = n = 1;
      halfx = x/2.0;
      do {
	temp = halfx/(double)n;
	n += 1;
	temp *= temp;
	u *= temp;
	sum += u;
      } while (u >= IzeroEPSILON*sum);
      return(sum);
    }
    
    
    //
    //	=== Low Pass ===
    //
    
    vector<float>
    firdes::low_pass_2(double gain,
		       double sampling_freq,    // Hz
		       double cutoff_freq,      // Hz BEGINNING of transition band
		       double transition_width, // Hz width of transition band
		       double attenuation_dB,   // attenuation dB
		       win_type window_type,
		       double beta)             // used only with Kaiser
    {
      sanity_check_1f(sampling_freq, cutoff_freq, transition_width);
      
      int ntaps = compute_ntaps_windes(sampling_freq,
				       transition_width,
				       attenuation_dB);
 
      // construct the truncated ideal impulse response
      // [sin(x)/x for the low pass case]

      vector<float> taps(ntaps);
      vector<float> w = window(window_type, ntaps, beta);

      int M = (ntaps - 1) / 2;
      double fwT0 = 2 * M_PI * cutoff_freq / sampling_freq;
      for(int n = -M; n <= M; n++) {
	if (n == 0)
	  taps[n + M] = fwT0 / M_PI * w[n + M];
	else {
	  // a little algebra gets this into the more familiar sin(x)/x form
	  taps[n + M] =  sin(n * fwT0) / (n * M_PI) * w[n + M];
	}
      }

      // find the factor to normalize the gain, fmax.
      // For low-pass, gain @ zero freq = 1.0

      double fmax = taps[0 + M];
      for(int n = 1; n <= M; n++)
	fmax += 2 * taps[n + M];

      gain /= fmax;	// normalize

      for(int i = 0; i < ntaps; i++)
	taps[i] *= gain;

      return taps;
    }

    vector<float>
    firdes::low_pass(double gain,
		     double sampling_freq,
		     double cutoff_freq,	// Hz center of transition band
		     double transition_width,	// Hz width of transition band
		     win_type window_type,
		     double beta)		// used only with Kaiser
    {
      sanity_check_1f(sampling_freq, cutoff_freq, transition_width);

      int ntaps = compute_ntaps(sampling_freq,
				transition_width,
				window_type, beta);

      // construct the truncated ideal impulse response
      // [sin(x)/x for the low pass case]
      
      vector<float> taps(ntaps);
      vector<float> w = window(window_type, ntaps, beta);

      int M = (ntaps - 1) / 2;
      double fwT0 = 2 * M_PI * cutoff_freq / sampling_freq;

      for(int n = -M; n <= M; n++) {
	if(n == 0)
	  taps[n + M] = fwT0 / M_PI * w[n + M];
	else {
	  // a little algebra gets this into the more familiar sin(x)/x form
	  taps[n + M] =  sin(n * fwT0) / (n * M_PI) * w[n + M];
	}
      }

      // find the factor to normalize the gain, fmax.
      // For low-pass, gain @ zero freq = 1.0
      
      double fmax = taps[0 + M];
      for(int n = 1; n <= M; n++)
	fmax += 2 * taps[n + M];

      gain /= fmax;	// normalize

      for(int i = 0; i < ntaps; i++)
	taps[i] *= gain;

      return taps;
    }


    //
    //	=== High Pass ===
    //
    
    vector<float>
    firdes::high_pass_2(double gain,
			double sampling_freq,
			double cutoff_freq,       // Hz center of transition band
			double transition_width,  // Hz width of transition band
			double attenuation_dB,    // attenuation dB
			win_type window_type,
			double beta)              // used only with Kaiser
    {
      sanity_check_1f(sampling_freq, cutoff_freq, transition_width);
      
      int ntaps = compute_ntaps_windes(sampling_freq,
				       transition_width,
				       attenuation_dB);

      // construct the truncated ideal impulse response times the window function
      
      vector<float> taps(ntaps);
      vector<float> w = window(window_type, ntaps, beta);

      int M = (ntaps - 1) / 2;
      double fwT0 = 2 * M_PI * cutoff_freq / sampling_freq;

      for(int n = -M; n <= M; n++) {
	if(n == 0)
	  taps[n + M] = (1 - (fwT0 / M_PI)) * w[n + M];
	else {
	  // a little algebra gets this into the more familiar sin(x)/x form
	  taps[n + M] =  -sin(n * fwT0) / (n * M_PI) * w[n + M];
	}
      }

      // find the factor to normalize the gain, fmax.
      // For high-pass, gain @ fs/2 freq = 1.0
      
      double fmax = taps[0 + M];
      for(int n = 1; n <= M; n++)
	fmax += 2 * taps[n + M] * cos(n * M_PI);
      
      gain /= fmax; // normalize
      
      for(int i = 0; i < ntaps; i++)
	taps[i] *= gain;

      return taps;
    }


    vector<float>
    firdes::high_pass(double gain,
                      double sampling_freq,
                      double cutoff_freq,       // Hz center of transition band
                      double transition_width,  // Hz width of transition band
                      win_type window_type,
                      double beta)              // used only with Kaiser
    {
      sanity_check_1f(sampling_freq, cutoff_freq, transition_width);

      int ntaps = compute_ntaps(sampling_freq,
				transition_width,
				window_type, beta);
      
      // construct the truncated ideal impulse response times the window function

      vector<float> taps(ntaps);
      vector<float> w = window(window_type, ntaps, beta);

      int M = (ntaps - 1) / 2;
      double fwT0 = 2 * M_PI * cutoff_freq / sampling_freq;

      for(int n = -M; n <= M; n++) {
	if(n == 0)
	  taps[n + M] = (1 - (fwT0 / M_PI)) * w[n + M];
	else {
	  // a little algebra gets this into the more familiar sin(x)/x form
	  taps[n + M] =  -sin(n * fwT0) / (n * M_PI) * w[n + M];
	}
      }

      // find the factor to normalize the gain, fmax.
      // For high-pass, gain @ fs/2 freq = 1.0
      
      double fmax = taps[0 + M];
      for(int n = 1; n <= M; n++)
	fmax += 2 * taps[n + M] * cos(n * M_PI);

      gain /= fmax; // normalize

      for(int i = 0; i < ntaps; i++)
	taps[i] *= gain;

      return taps;
    }

    //
    //      === Band Pass ===
    //

    vector<float>
    firdes::band_pass_2(double gain,
			double sampling_freq,
			double low_cutoff_freq,	 // Hz center of transition band
			double high_cutoff_freq, // Hz center of transition band
			double transition_width, // Hz width of transition band
			double attenuation_dB,   // attenuation dB
			win_type window_type,
			double beta)		 // used only with Kaiser
    {
      sanity_check_2f(sampling_freq,
		      low_cutoff_freq,
		      high_cutoff_freq, transition_width);

      int ntaps = compute_ntaps_windes(sampling_freq,
				       transition_width,
				       attenuation_dB);

      vector<float> taps(ntaps);
      vector<float> w = window(window_type, ntaps, beta);

      int M = (ntaps - 1) / 2;
      double fwT0 = 2 * M_PI * low_cutoff_freq / sampling_freq;
      double fwT1 = 2 * M_PI * high_cutoff_freq / sampling_freq;

      for(int n = -M; n <= M; n++) {
	if (n == 0)
	  taps[n + M] = (fwT1 - fwT0) / M_PI * w[n + M];
	else {
	  taps[n + M] =  (sin(n * fwT1) - sin(n * fwT0)) / (n * M_PI) * w[n + M];
	}
      }

      // find the factor to normalize the gain, fmax.
      // For band-pass, gain @ center freq = 1.0
      
      double fmax = taps[0 + M];
      for(int n = 1; n <= M; n++)
	fmax += 2 * taps[n + M] * cos(n * (fwT0 + fwT1) * 0.5);

      gain /= fmax;	// normalize

      for(int i = 0; i < ntaps; i++)
	taps[i] *= gain;

      return taps;
    }


    vector<float>
    firdes::band_pass(double gain,
		      double sampling_freq,
		      double low_cutoff_freq,	// Hz center of transition band
		      double high_cutoff_freq,	// Hz center of transition band
		      double transition_width,	// Hz width of transition band
		      win_type window_type,
		      double beta)		// used only with Kaiser
    {
      sanity_check_2f(sampling_freq,
		      low_cutoff_freq,
		      high_cutoff_freq,
		      transition_width);

      int ntaps = compute_ntaps(sampling_freq,
				transition_width,
				window_type, beta);

      // construct the truncated ideal impulse response times the window function

      vector<float> taps(ntaps);
      vector<float> w = window(window_type, ntaps, beta);

      int M = (ntaps - 1) / 2;
      double fwT0 = 2 * M_PI * low_cutoff_freq / sampling_freq;
      double fwT1 = 2 * M_PI * high_cutoff_freq / sampling_freq;
      
      for(int n = -M; n <= M; n++) {
	if (n == 0)
	  taps[n + M] = (fwT1 - fwT0) / M_PI * w[n + M];
	else {
	  taps[n + M] =  (sin(n * fwT1) - sin(n * fwT0)) / (n * M_PI) * w[n + M];
	}
      }

      // find the factor to normalize the gain, fmax.
      // For band-pass, gain @ center freq = 1.0

      double fmax = taps[0 + M];
      for(int n = 1; n <= M; n++)
	fmax += 2 * taps[n + M] * cos(n * (fwT0 + fwT1) * 0.5);

      gain /= fmax;	// normalize

      for(int i = 0; i < ntaps; i++)
	taps[i] *= gain;

      return taps;
    }

    //
    //	=== Complex Band Pass ===
    //

    vector<gr_complex>
    firdes::complex_band_pass_2(double gain,
				double sampling_freq,
				double low_cutoff_freq,	 // Hz center of transition band
				double high_cutoff_freq, // Hz center of transition band
				double transition_width, // Hz width of transition band
				double attenuation_dB,   // attenuation dB
				win_type window_type,
				double beta)		 // used only with Kaiser
    {
      sanity_check_2f_c(sampling_freq,
			low_cutoff_freq,
			high_cutoff_freq,
			transition_width);

      int ntaps = compute_ntaps_windes(sampling_freq,
				       transition_width,
				       attenuation_dB);

      vector<gr_complex> taps(ntaps);
      vector<float> lptaps(ntaps);
      vector<float> w = window(window_type, ntaps, beta);

      lptaps = low_pass_2(gain, sampling_freq,
			  (high_cutoff_freq - low_cutoff_freq)/2,
			  transition_width, attenuation_dB,
			  window_type, beta);

      gr_complex *optr = &taps[0];
      float *iptr = &lptaps[0];
      float freq = M_PI * (high_cutoff_freq + low_cutoff_freq)/sampling_freq;
      float phase = 0;
      if (lptaps.size() & 01) {
	phase = - freq * ( lptaps.size() >> 1 );
      } 
      else 
	phase = - freq/2.0 * ((1 + 2*lptaps.size()) >> 1);

      for(unsigned int i = 0; i < lptaps.size(); i++) {
	*optr++ = gr_complex(*iptr * cos(phase), *iptr * sin(phase));
	iptr++, phase += freq;
      }

      return taps;
    }


    vector<gr_complex>
    firdes::complex_band_pass(double gain,
			      double sampling_freq,
			      double low_cutoff_freq,	// Hz center of transition band
			      double high_cutoff_freq,	// Hz center of transition band
			      double transition_width,	// Hz width of transition band
			      win_type window_type,
			      double beta)		// used only with Kaiser
    {
      sanity_check_2f_c (sampling_freq,
			 low_cutoff_freq,
			 high_cutoff_freq,
			 transition_width);

      int ntaps = compute_ntaps(sampling_freq,
				transition_width,
				window_type, beta);

      // construct the truncated ideal impulse response times the window function

      vector<gr_complex> taps(ntaps);
      vector<float> lptaps(ntaps);
      vector<float> w = window(window_type, ntaps, beta);

      lptaps = low_pass(gain, sampling_freq,
			(high_cutoff_freq - low_cutoff_freq)/2,
			transition_width, window_type, beta);

      gr_complex *optr = &taps[0];
      float *iptr = &lptaps[0];
      float freq = M_PI * (high_cutoff_freq + low_cutoff_freq)/sampling_freq;
      float phase = 0;
      if(lptaps.size() & 01) {
	phase = - freq * ( lptaps.size() >> 1 );
      } 
      else
	phase = - freq/2.0 * ((1 + 2*lptaps.size()) >> 1);

      for(unsigned int i=0;i<lptaps.size();i++) {
	*optr++ = gr_complex(*iptr * cos(phase), *iptr * sin(phase));
	iptr++, phase += freq;
      }

      return taps;
    }

    //
    //	=== Band Reject ===
    //

    vector<float>
    firdes::band_reject_2(double gain,
			  double sampling_freq,
			  double low_cutoff_freq,  // Hz center of transition band
			  double high_cutoff_freq, // Hz center of transition band
			  double transition_width, // Hz width of transition band
			  double attenuation_dB,   // attenuation dB
			  win_type window_type,
			  double beta)		  // used only with Kaiser
    {
      sanity_check_2f(sampling_freq,
		      low_cutoff_freq,
		      high_cutoff_freq,
		      transition_width);

      int ntaps = compute_ntaps_windes(sampling_freq,
				       transition_width,
				       attenuation_dB);

      // construct the truncated ideal impulse response times the window function

      vector<float> taps(ntaps);
      vector<float> w = window(window_type, ntaps, beta);

      int M = (ntaps - 1) / 2;
      double fwT0 = 2 * M_PI * low_cutoff_freq / sampling_freq;
      double fwT1 = 2 * M_PI * high_cutoff_freq / sampling_freq;

      for(int n = -M; n <= M; n++) {
	if (n == 0)
	  taps[n + M] = 1.0 + ((fwT0 - fwT1) / M_PI * w[n + M]);
	else {
	  taps[n + M] =  (sin(n * fwT0) - sin(n * fwT1)) / (n * M_PI) * w[n + M];
	}
      }

      // find the factor to normalize the gain, fmax.
      // For band-reject, gain @ zero freq = 1.0

      double fmax = taps[0 + M];
      for(int n = 1; n <= M; n++)
	fmax += 2 * taps[n + M];

      gain /= fmax;	// normalize

      for(int i = 0; i < ntaps; i++)
	taps[i] *= gain;

      return taps;
    }

    vector<float>
    firdes::band_reject(double gain,
  		        double sampling_freq,
		        double low_cutoff_freq,	 // Hz center of transition band
		        double high_cutoff_freq, // Hz center of transition band
		        double transition_width, // Hz width of transition band
		        win_type window_type,
		        double beta)		 // used only with Kaiser
    {
      sanity_check_2f(sampling_freq,
		      low_cutoff_freq,
		      high_cutoff_freq,
		      transition_width);

      int ntaps = compute_ntaps(sampling_freq,
				transition_width,
				window_type, beta);

      // construct the truncated ideal impulse response times the window function

      vector<float> taps(ntaps);
      vector<float> w = window(window_type, ntaps, beta);

      int M = (ntaps - 1) / 2;
      double fwT0 = 2 * M_PI * low_cutoff_freq / sampling_freq;
      double fwT1 = 2 * M_PI * high_cutoff_freq / sampling_freq;

      for(int n = -M; n <= M; n++) {
	if (n == 0)
	  taps[n + M] = 1.0 + ((fwT0 - fwT1) / M_PI * w[n + M]);
	else {
	  taps[n + M] =  (sin(n * fwT0) - sin(n * fwT1)) / (n * M_PI) * w[n + M];
	}
      }

      // find the factor to normalize the gain, fmax.
      // For band-reject, gain @ zero freq = 1.0

      double fmax = taps[0 + M];
      for(int n = 1; n <= M; n++)
	fmax += 2 * taps[n + M];

      gain /= fmax;	// normalize

      for(int i = 0; i < ntaps; i++)
	taps[i] *= gain;

      return taps;
    }

    //
    // Hilbert Transform
    //

    vector<float>
    firdes::hilbert(unsigned int ntaps,
		    win_type windowtype,
		    double beta)
    {
      if(!(ntaps & 1))
	throw std::out_of_range("Hilbert:  Must have odd number of taps");

      vector<float> taps(ntaps);
      vector<float> w = window (windowtype, ntaps, beta);
      unsigned int h = (ntaps-1)/2;
      float gain=0;
      for(unsigned int i = 1; i <= h; i++) {
	if(i & 1) {
	  float x = 1/(float)i;
	  taps[h+i] = x * w[h+i];
	  taps[h-i] = -x * w[h-i];
	  gain = taps[h+i] - gain;
	}
	else
	  taps[h+i] = taps[h-i] = 0;
      }

      gain = 2 * fabs(gain);
      for(unsigned int i = 0; i < ntaps; i++)
	taps[i] /= gain;
      return taps;
    }
    
    //
    // Gaussian
    //

    vector<float>
    firdes::gaussian(double gain,
		     double spb,
		     double bt,
		     int ntaps)
    {
      vector<float> taps(ntaps);
      double scale = 0;
      double dt = 1.0/spb;
      double s = 1.0/(sqrt(log(2.0)) / (2*M_PI*bt));
      double t0 = -0.5 * ntaps;
      double ts;
      for(int i=0;i<ntaps;i++) {
	t0++;
	ts = s*dt*t0;
	taps[i] = exp(-0.5*ts*ts);
	scale += taps[i];
      }
      for(int i=0;i<ntaps;i++)
	taps[i] = taps[i] / scale * gain;

      return taps;
    }


    //
    // Root Raised Cosine
    //

    vector<float>
    firdes::root_raised_cosine(double gain,
			       double sampling_freq,
			       double symbol_rate,
			       double alpha,
			       int ntaps)
    {
      ntaps |= 1;	// ensure that ntaps is odd

      double spb = sampling_freq/symbol_rate; // samples per bit/symbol
      vector<float> taps(ntaps);
      double scale = 0;
      for(int i = 0; i < ntaps; i++) {
	double x1,x2,x3,num,den;
	double xindx = i - ntaps/2;
	x1 = M_PI * xindx/spb;
	x2 = 4 * alpha * xindx / spb;
	x3 = x2*x2 - 1;

	if(fabs(x3) >= 0.000001) {  // Avoid Rounding errors...
	  if(i != ntaps/2)
	    num = cos((1+alpha)*x1) + sin((1-alpha)*x1)/(4*alpha*xindx/spb);
	  else
	    num = cos((1+alpha)*x1) + (1-alpha) * M_PI / (4*alpha);
	  den = x3 * M_PI;
	}
	else {
	  if(alpha==1) {
	    taps[i] = -1;
	    continue;
	  }
	  x3 = (1-alpha)*x1;
	  x2 = (1+alpha)*x1;
	  num = (sin(x2)*(1+alpha)*M_PI
		 - cos(x3)*((1-alpha)*M_PI*spb)/(4*alpha*xindx)
		 + sin(x3)*spb*spb/(4*alpha*xindx*xindx));
	  den = -32 * M_PI * alpha * alpha * xindx/spb;
	}
	taps[i] = 4 * alpha * num / den;
	scale += taps[i];
      }
      
      for(int i = 0; i < ntaps; i++)
	taps[i] = taps[i] * gain / scale;

      return taps;
    }

    //
    //	=== Utilities ===
    //

    // delta_f / width_factor gives number of taps required.
    static const float width_factor[5] = {   // indexed by win_type
      3.3,		// WIN_HAMMING
      3.1,		// WIN_HANN
      5.5,              // WIN_BLACKMAN
      2.0,              // WIN_RECTANGULAR
      //5.0             // WIN_KAISER  (guesstimate compromise)
      //2.0             // WIN_KAISER  (guesstimate compromise)
      10.0		// WIN_KAISER
    };

    int
    firdes::compute_ntaps_windes(double sampling_freq,
			         double transition_width, // this is frequency, not relative frequency
			   	 double attenuation_dB)
    {
      // Based on formula from Multirate Signal Processing for
      // Communications Systems, fredric j harris
      int ntaps = (int)(attenuation_dB*sampling_freq/(22.0*transition_width));
      if ((ntaps & 1) == 0)	// if even...
	ntaps++;		// ...make odd
      return ntaps;
    }

    int
    firdes::compute_ntaps(double sampling_freq,
			  double transition_width,
			  win_type window_type,
			  double beta)
    {
      // normalized transition width
      double delta_f = transition_width / sampling_freq;

      // compute number of taps required for given transition width
      int ntaps = (int)(width_factor[window_type] / delta_f + 0.5);
      if((ntaps & 1) == 0)	// if even...
	ntaps++;		// ...make odd

      return ntaps;
    }

    double
    firdes::bessi0(double x)
    {
      double ax,ans;
      double y;

      ax=fabs(x);
      if (ax < 3.75) {
	y=x/3.75;
	y*=y;
	ans=1.0+y*(3.5156229+y*(3.0899424+y*(1.2067492
			     +y*(0.2659732+y*(0.360768e-1+y*0.45813e-2)))));
      }
      else {
	y=3.75/ax;
	ans=(exp(ax)/sqrt(ax))*(0.39894228+y*(0.1328592e-1
			+y*(0.225319e-2+y*(-0.157565e-2+y*(0.916281e-2
			+y*(-0.2057706e-1+y*(0.2635537e-1+y*(-0.1647633e-1
			+y*0.392377e-2))))))));
	}
	return ans;
    }

    vector<float>
    firdes::window (win_type type, int ntaps, double beta)
    {
      vector<float> taps(ntaps);
      int M = ntaps - 1;          // filter order

      switch (type) {
      case WIN_RECTANGULAR:
	for(int n = 0; n < ntaps; n++)
	  taps[n] = 1;

      case WIN_HAMMING:
	for(int n = 0; n < ntaps; n++)
	  taps[n] = 0.54 - 0.46 * cos((2 * M_PI * n) / M);
	break;
	
      case WIN_HANN:
	for(int n = 0; n < ntaps; n++)
	  taps[n] = 0.5 - 0.5 * cos((2 * M_PI * n) / M);
	break;
	
      case WIN_BLACKMAN:
	for(int n = 0; n < ntaps; n++)
	  taps[n] = 0.42 - 0.50 * cos((2*M_PI * n) / (M-1))
	    - 0.08 * cos((4*M_PI * n) / (M-1));
	break;

      case WIN_BLACKMAN_hARRIS:
	for(int n = -ntaps/2; n < ntaps/2; n++)
	  taps[n+ntaps/2] = 0.35875 + 0.48829*cos((2*M_PI * n) / (float)M) +
	    0.14128*cos((4*M_PI * n) / (float)M) + 0.01168*cos((6*M_PI * n) / (float)M);
	break;

      case WIN_KAISER:
	{
	  double IBeta = 1.0/Izero(beta);
	  double inm1 = 1.0/((double)(ntaps));
	  double temp;
	  //fprintf(stderr, "IBeta = %g; inm1 = %g\n", IBeta, inm1);
	  
	  for(int i=0; i<ntaps; i++) {
	    temp = i * inm1;
	    //fprintf(stderr, "temp = %g\n", temp);
	    taps[i] = Izero(beta*sqrt(1.0-temp*temp)) * IBeta;
	    //fprintf(stderr, "taps[%d] = %g\n", i, taps[i]);
	  }
	}
      break;

      default:
	throw std::out_of_range("firdes:window: type out of range");
      }
      
      return taps;
    }

    void
    firdes::sanity_check_1f(double sampling_freq,
			    double fa,			// cutoff freq
			    double transition_width)
    {
      if(sampling_freq <= 0.0)
	throw std::out_of_range("firdes check failed: sampling_freq > 0");

      if(fa <= 0.0 || fa > sampling_freq / 2)
	throw std::out_of_range("firdes check failed: 0 < fa <= sampling_freq / 2");

      if(transition_width <= 0)
	throw std::out_of_range("gr_dirdes check failed: transition_width > 0");
    }

    void
    firdes::sanity_check_2f(double sampling_freq,
			    double fa,			// first cutoff freq
			    double fb,			// second cutoff freq
			    double transition_width)
    {
      if (sampling_freq <= 0.0)
	throw std::out_of_range("firdes check failed: sampling_freq > 0");

      if (fa <= 0.0 || fa > sampling_freq / 2)
	throw std::out_of_range("firdes check failed: 0 < fa <= sampling_freq / 2");
      
      if (fb <= 0.0 || fb > sampling_freq / 2)
	throw std::out_of_range("firdes check failed: 0 < fb <= sampling_freq / 2");
      
      if (fa > fb)
	throw std::out_of_range("firdes check failed: fa <= fb");
      
      if (transition_width <= 0)
	throw std::out_of_range("firdes check failed: transition_width > 0");
    }

    void
    firdes::sanity_check_2f_c(double sampling_freq,
			      double fa,		// first cutoff freq
			      double fb,		// second cutoff freq
			      double transition_width)
    {
      if(sampling_freq <= 0.0)
	throw std::out_of_range("firdes check failed: sampling_freq > 0");

      if(fa < -sampling_freq / 2 || fa > sampling_freq / 2)
	throw std::out_of_range("firdes check failed: 0 < fa <= sampling_freq / 2");

      if(fb < -sampling_freq / 2  || fb > sampling_freq / 2)
	throw std::out_of_range("firdes check failed: 0 < fb <= sampling_freq / 2");

      if(fa > fb)
	throw std::out_of_range("firdes check failed: fa <= fb");

      if(transition_width <= 0)
	throw std::out_of_range("firdes check failed: transition_width > 0");
    }

  } /* namespace filter */
} /* namespace gr */