Texas Instruments TMS320C64X manual DSPfirsym, Symmetric FIR Filter

DSP_fir_sym

DSP_fir_sym	Symmetric FIR Filter
Function
		void DSP_fir_sym (const short * restrict x, const short * restrict h, short * re-
		strict r, int nh, int nr, int s)
Arguments		x[nr+2*nh]	Pointer to input array of size nr + 2*nh. Must be double-word
			aligned.
		h[nh+1]	Pointer to coefficient array of size nh + 1. Coefficients are in
			normal order and only half (nh+1 out of 2*nh+1) are required.
			Must be double-word aligned.
		r[nr]	Pointer to output array of size nr. Must be word aligned.
		nh	Number of coefficients. Must be multiple of 8. The number of
			original symmetric coefficients is 2*nh+1.
		nr	Number of samples to calculate. Must be multiple of 4.
		s	Number of insignificant digits to truncate; e.g., 15 for Q.15
			input data and coefficients.
Description		This function applies a symmetric filter to the input samples. The filter tap array
		h[] provides ‘nh+1’ total filter taps. The filter tap at h[nh] forms the center point
		of the filter. The taps at h[nh − 1] through h[0] form a symmetric filter about this
		central tap. The effective filter length is thus 2*nh+1 taps.
		The filter is performed on 16-bit data with 16-bit coefficients, accumulating
		intermediate results to 40-bit precision. The accumulator is rounded and
		truncated according to the value provided in ‘s’. This allows a variety of
		Q-points to be used.
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 DSP_fir_sym(short *x, short *h, short *r, int nh, int nr,
		int s)
	{

int	i, j;
long	y0;
long	round = (long) 1 << (s − 1);

for (j = 0; j < nr; j++) { y0 = round;

for (i = 0; i < nh; i++)

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