for (i=0;i<len;i++)
for (i=len-1;i>=0;i--)
void predictor_three_tap(float *x, int len, int period, float *gain){   int i;   for (i=0;i<len;i++)   {      x[i] -= gain[0]*x[i-period] + gain[1]*x[i-period-1] + gain[2]*x[i-period-2];   }}