rf-tools/src/broadcast_fm/fir_filters/FIR_Audio_Filter_Filter.c

#include "FIR_Audio_Filter_Filter.h"

static double filter_taps[FIR_AUDIO_FILTER_FILTER_TAP_NUM] = {
  0.005517301037304242,
  0.010958468006496662,
  0.010240455922518009,
  0.01626919575760614,
  0.017121566138134488,
  0.019559785776548867,
  0.018573985808748823,
  0.016981674306998703,
  0.013027824505458897,
  0.008348299295171996,
  0.002827934347197235,
  -0.0022439756999176066,
  -0.006402028253938463,
  -0.008814800382330594,
  -0.009267566652943171,
  -0.007703207526723216,
  -0.004562291988505165,
  -0.0005232995432083925,
  0.003518575437801644,
  0.006694025550492667,
  0.008294079489543669,
  0.007965160640712026,
  0.005755920521670115,
  0.0021526778614508585,
  -0.0020452123559512488,
  -0.005875787341622662,
  -0.008425796705843449,
  -0.009052315787298352,
  -0.00752225339131066,
  -0.0040990782652213,
  0.00049750332784811,
  0.005234144776188673,
  0.008990696285244222,
  0.010798308794869566,
  0.010105847532439045,
  0.006897132667607324,
  0.0017653188321013905,
  -0.00420373081909947,
  -0.00964286796105942,
  -0.013192556860158036,
  -0.013826393925481531,
  -0.011121337171052629,
  -0.005396493245103629,
  0.0022726920185823602,
  0.010240805979570002,
  0.016615084025158867,
  0.019654280140049052,
  0.018177759921499358,
  0.011915646666813001,
  0.0016581423845507999,
  -0.010757223751418863,
  -0.02270805003461664,
  -0.03121367797048097,
  -0.033501256492323245,
  -0.027529898309997605,
  -0.012463160702206726,
  0.011056274270822274,
  0.04090736333522399,
  0.07374003152391906,
  0.10546517736325783,
  0.131881590198464,
  0.1493758864385702,
  0.1554926121172843,
  0.1493758864385702,
  0.131881590198464,
  0.10546517736325783,
  0.07374003152391906,
  0.04090736333522399,
  0.011056274270822274,
  -0.012463160702206726,
  -0.027529898309997605,
  -0.033501256492323245,
  -0.03121367797048097,
  -0.02270805003461664,
  -0.010757223751418863,
  0.0016581423845507999,
  0.011915646666813001,
  0.018177759921499358,
  0.019654280140049052,
  0.016615084025158867,
  0.010240805979570002,
  0.0022726920185823602,
  -0.005396493245103629,
  -0.011121337171052629,
  -0.013826393925481531,
  -0.013192556860158036,
  -0.00964286796105942,
  -0.00420373081909947,
  0.0017653188321013905,
  0.006897132667607324,
  0.010105847532439045,
  0.010798308794869566,
  0.008990696285244222,
  0.005234144776188673,
  0.00049750332784811,
  -0.0040990782652213,
  -0.00752225339131066,
  -0.009052315787298352,
  -0.008425796705843449,
  -0.005875787341622662,
  -0.0020452123559512488,
  0.0021526778614508585,
  0.005755920521670115,
  0.007965160640712026,
  0.008294079489543669,
  0.006694025550492667,
  0.003518575437801644,
  -0.0005232995432083925,
  -0.004562291988505165,
  -0.007703207526723216,
  -0.009267566652943171,
  -0.008814800382330594,
  -0.006402028253938463,
  -0.0022439756999176066,
  0.002827934347197235,
  0.008348299295171996,
  0.013027824505458897,
  0.016981674306998703,
  0.018573985808748823,
  0.019559785776548867,
  0.017121566138134488,
  0.01626919575760614,
  0.010240455922518009,
  0.010958468006496662,
  0.005517301037304242
};

void FIR_Audio_Filter_Filter_init(FIR_Audio_Filter_Filter* f) {
  int i;
  for(i = 0; i < FIR_AUDIO_FILTER_FILTER_TAP_NUM; ++i)
    f->history[i] = 0;
  f->last_index = 0;
}

void FIR_Audio_Filter_Filter_put(FIR_Audio_Filter_Filter* f, double input) {
  f->history[f->last_index++] = input;
  if(f->last_index == FIR_AUDIO_FILTER_FILTER_TAP_NUM)
    f->last_index = 0;
}

double FIR_Audio_Filter_Filter_get(FIR_Audio_Filter_Filter* f) {
  double acc = 0;
  int index = f->last_index, i;
  for(i = 0; i < FIR_AUDIO_FILTER_FILTER_TAP_NUM; ++i) {
    index = index != 0 ? index-1 : FIR_AUDIO_FILTER_FILTER_TAP_NUM-1;
    acc += f->history[index] * filter_taps[i];
  };
  return acc;
}