text: //
  // iirdecim_crcf_example.c
  //
  // This example demonstrates the interface to the iirdecim (infinite
  // impulse response decimator) family of objects.
  //
  
  #include <stdio.h>
  #include <stdlib.h>
  #include <math.h>
  #include <getopt.h>
  
  #include "liquid.h"
  
  #define OUTPUT_FILENAME "iirdecim_crcf_example.m"
  
  // print usage/help message
  void usage()
  {
      printf("iirdecim_crcf_example:\n");
      printf("  u/h   : print usage/help\n");
      printf("  M     : decimation factor, M > 1, default: 4\n");
      printf("  n     : number of input samples, default: 400\n");
  }
  
  
  int main(int argc, char*argv[]) {
      // options
      unsigned int M=4;               // decimation rate
      unsigned int num_samples=400;   // number of input samples
  
      int dopt;
      while ((dopt = getopt(argc,argv,"uhM:n:")) != EOF) {
          switch (dopt) {
          case 'u':
          case 'h': usage();                      return 0;
          case 'M': M = atoi(optarg);             break;
          case 'n': num_samples = atoi(optarg);   break;
          default:
              exit(1);
          }
      }
  
      // validate options
      if (M < 2) {
          fprintf(stderr,"error: %s, decim factor must be greater than 1\n", argv[0]);
          exit(1);
      } else if (num_samples < 1) {
          fprintf(stderr,"error: %s, must have at least one sample\n", argv[0]);
          usage();
          return 1;
      }
  
      // ensure number of samples is divisible by M
      num_samples += (num_samples % M);
  
      // create decimator from prototype
      unsigned int order = 8;
      iirdecim_crcf q = iirdecim_crcf_create_default(M,order);
  
      // compute group delay
      float delay = iirdecim_crcf_groupdelay(q,0.0f);
  
      // generate input signal and decimate
      float complex x[num_samples];   // input samples
      float complex y[num_samples/M]; // output samples
      unsigned int i;
      unsigned int w_len = num_samples > 4*delay ? num_samples - 4*delay : num_samples;
      for (i=0; i<num_samples; i++) {
          x[i] =  cexpf(_Complex_I*(2*M_PI*0.03*i - 0.3*i*i/(float)num_samples));
          x[i] *= i < w_len ? hamming(i,w_len) : 0.0f;
      }
  
      // decimate input
      for (i=0; i<num_samples/M; i++)
          iirdecim_crcf_execute(q, &x[M*i], &y[i]);
  
      // destroy decimator object
      iirdecim_crcf_destroy(q);
  
  #if 0
      // print results to screen
      printf("x(t) :\n");
      for (i=0; i<num_samples; i++)
          printf("  x(%4u) = %8.4f + j*%8.4f;\n", i, crealf(x[i]), cimagf(x[i]));
  
      printf("y(t) :\n");
      for (i=0; i<num_samples; i++) {
          printf("  y(%4u) = %8.4f + j*%8.4f;", i, crealf(y[i]), cimagf(y[i]));
          if ( (i >= M*m) && ((i%M)==0))
              printf(" **\n");
          else
              printf("\n");
      }
  #endif
  
      // 
      // export output file
      //
      FILE * fid = fopen(OUTPUT_FILENAME,"w");
      fprintf(fid,"%% %s: auto-generated file\n\n", OUTPUT_FILENAME);
      fprintf(fid,"clear all;\n");
      fprintf(fid,"close all;\n");
      fprintf(fid,"M = %u;\n", M);
      fprintf(fid,"delay = %f;\n", delay);
      fprintf(fid,"num_samples = %u;\n", num_samples);
      fprintf(fid,"x = zeros(1,num_samples);\n");
      fprintf(fid,"y = zeros(1,num_samples/M);\n");
  
      for (i=0; i<num_samples; i++)
          fprintf(fid,"x(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(x[i]), cimagf(x[i]));
  
      for (i=0; i<num_samples/M; i++)
          fprintf(fid,"y(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(y[i]), cimagf(y[i]));
  
      fprintf(fid,"\n\n");
      fprintf(fid,"tx = [0:(num_samples  -1)];\n");
      fprintf(fid,"ty = [0:(num_samples/M-1)]*M - delay;\n");
      fprintf(fid,"figure;\n");
      fprintf(fid,"subplot(2,1,1);\n");
      fprintf(fid,"    plot(tx,real(x),'-s','MarkerSize',1,ty,real(y),'-s','MarkerSize',3);\n");
      fprintf(fid,"    legend('input','decim','location','northeast');\n");
      fprintf(fid,"    axis([0 num_samples -1.2 1.2]);\n");
      fprintf(fid,"    xlabel('time');\n");
      fprintf(fid,"    ylabel('real');\n");
      fprintf(fid,"    grid on;\n");
      fprintf(fid,"subplot(2,1,2);\n");
      fprintf(fid,"    plot(tx,imag(x),'-s','MarkerSize',1,ty,imag(y),'-s','MarkerSize',3);\n");
      fprintf(fid,"    legend('input','decim','location','northeast');\n");
      fprintf(fid,"    axis([0 num_samples -1.2 1.2]);\n");
      fprintf(fid,"    xlabel('time');\n");
      fprintf(fid,"    ylabel('imag');\n");
      fprintf(fid,"    grid on;\n");
      
      // plot spectral response
      fprintf(fid,"nfft = 2048;\n");
      fprintf(fid,"X  = 20*log10(abs(fftshift(fft(x/length(x),nfft))));\n");
      fprintf(fid,"Y  = 20*log10(abs(fftshift(fft(y/length(y),nfft))));\n");
      fprintf(fid,"fx = [0:(nfft-1)]/nfft - 0.5;\n");
      fprintf(fid,"fy = fx / M;\n");
      fprintf(fid,"figure;\n");
      fprintf(fid,"plot(fx,X,'-','Color',[0.5 0.5 0.5],...\n");
      fprintf(fid,"     fy,Y,'-','Color',[0.0 0.5 0.3],'LineWidth',2);\n");
      fprintf(fid,"legend('input','interp','location','northeast');\n");
      fprintf(fid,"grid on;\n");
      fprintf(fid,"xlabel('Normalized Frequency [f/Fs]');\n");
      fprintf(fid,"ylabel('PSD [dB]');\n");
      fprintf(fid,"axis([-0.5 0.5 -100 0]);\n");
  
      fclose(fid);
      printf("results written to %s.\n",OUTPUT_FILENAME);
  
      printf("done.\n");
      return 0;
  }
  