Texas Instruments TI DSPLIB – Understanding the DSP_iirlat All-Pole IIR Lattice Filter

DSP_iirlat

DSP_iirlat	All-Pole IIR Lattice Filter
Function
		void DSP_iirlat(const short * restrict x, int nx, const short * restrict k, int nk, int
		* restrict b, short * restrict r)
Arguments		x[nx]	Input vector (16-bit).
		nx	Length of input vector.
		k[nk]	Reflection coefficients in Q.15 format.
		nk	Number of reflection coefficients/lattice stages. Must be >=4.
			Make multiple of 2 to avoid bank conflicts.
		b[nk+1]	Delay line elements from previous call. Should be initialized to
			all zeros prior to the first call.
		r[nx]	Output vector (16-bit).
Description		This routine implements a real all-pole IIR filter in lattice structure (AR lattice).
		The filter consists of nk lattice stages. Each stage requires one reflection
		coefficient k and one delay element b. The routine takes an input vector x[] and
		returns the filter output in r[]. Prior to the first call of the routine, the delay
		elements in b[] should be set to zero. The input data may have to be pre-scaled
		to avoid overflow or achieve better SNR. The reflections coefficients lie in the
		range −1.0 < k < 1.0. The order of the coefficients is such that k[nk−1]
		corresponds to the first lattice stage after the input and k[0] corresponds to the
		last stage.
Algorithm		This is the C equivalent of the assembly code without restrictions. Note that
		the assembly code is hand optimized and restrictions may apply.
		void iirlat(short *x, int nx, short *k, int nk, int *b,
		short *r)
	{
		int rt;		/* output	*/
		int i, j;

for (j=0; j<nx; j++)

{

rt = x[j] << 15;

for (i = nk − 1; i >= 0; i−−)

{

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