iir1.c

用dsp解压mp3程序的算法

/********************************************************************
*  iir1.c - Function for IIR filtering using direct-form I structure
********************************************************************/
float iir1(x,y,b,nb,a,na)

float *x, *y;		// x is input vector, y is output vector
float *b, *a;		// numerator and denominator coefficients
int nb, na;		// length of coefficient vectors
{
  float yn = 0.0;	// output of IIR filter, y(n)
  float yn1 = 0.0;	// temporary storage for feedforward section
  float yn2 = 0.0;	// temporary storage for feedback section
  int i,j;		// loop index

  for (i=0; i<nb; ++i)	// feedforward section
  {
    yn1 += b[i]*x[i];
  }

  for (j=1; j<ab; ++j)	// feedback section
  {
    yn2 += a[j]*y[j];
  }

  yn = yn1-yn2;		// combine two sections
  return(yn);		// return y(n) to calling function
}