bpmprocess/freq_to_sample.c

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#include <bpm/bpm_messages.h>
#include <bpm/bpm_process.h>


/*
  This routine returns the sample number corresponding to the frequency, note
  that this routine is not aware of the nyquist bands, and just keeps on 
  counting from 0 -> fs. 
  
  @param  fs       sampling frequency
  @param  ns       number of samples
  @param  tsample  the queried frequency of the sample
  @param  isample  the returned sample number
  
  @return BPM_SUCCESS upon success, BPM_FAILURE upon failure
*/
int freq_to_sample( double fs, int ns, double f, int *iS ) {

  double fi;
  int i;

  if ( f < 0. ) {
    *iS = 0;
    return BPM_SUCCESS;
  }
  
  for ( i=0; i<ns; i++ ) {
    // get the frequency corrsponding to sample i
    fi = ( (double) i + 0.5 ) / ( (double) ns ) * fs;
    if ( ABS( f - fi ) <  ( fs / (double) ns ) ) break;
  }

  *iS = i;

  
  return BPM_SUCCESS;
}

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