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static double desired_7kHz_lowpass[] = {1.0, 0.0};
static double weights_7kHz_lowpass[] = {0.1, 0.1};
double *calc_coefficients_7kHz_lowpass(int rate)
{
double *result = (double *)malloc(32*sizeof(double));
double bands[4];
bands[0] = 0.0; bands[1] = 6800.0/rate;
bands[2] = 8500.0/rate; bands[3] = 0.5;
remez(result, 32, 2, bands,
desired_7kHz_lowpass, weights_7kHz_lowpass, BANDPASS);
return result;
}
#if 0
int16_t firfilter(int16_t *buf, int pos, int len, int count, double *coefficients)
{
double result = 0.0;
// Back 32 samples, maybe wrapping in buffer.
pos = (pos+len-count)%len;
// And do the multiply-accumulate
while (count--) {
result += buf[pos++] * *coefficients++; pos %= len;
}
return result;
}
#endif
int16_t firfilter(int16_t *buf, int pos, int len, int count, double *coefficients)
{
double result = 0.0;
int count1, count2;
int16_t *ptr;
if (pos >= count) {
pos -= count;
count1 = count; count2 = 0;
}
else {
count2 = pos;
count1 = count - pos;
pos = len - count1;
}
//fprintf(stderr, "pos=%d, count1=%d, count2=%d\n", pos, count1, count2);
// high part of window
ptr = &buf[pos];
while (count1--) result += *ptr++ * *coefficients++;
// wrapped part of window
while (count2--) result += *buf++ * *coefficients++;
return result;
}
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