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DSP_fir_r4
4-46
FIR Filter (when the number of coefficients is a multiple of 4)
DSP_fir_r4
Function void DSP_fir_r4 (const short * restrict x, const short * restrict h, short * restrict
r, int nh, int nr)
Arguments x[nr+nh−1] Pointer to input array of size nr + nh – 1.
h[nh] Pointer to coefficient array of size nh (coefficients must be in
reverse order).
r[nr] Pointer to output array of size nr.
nh Number of coefficients. Must be multiple of 4 and ≥8.
nr Number of samples to calculate. Must be multiple of 4.
Description Computes a real FIR filter (direct-form) using coefficients stored in vector h[ ].
The real data input is stored in vector x[ ]. The filter output result is stored in
vector r[ ]. This FIR operates on 16-bit data with a 32-bit accumulate. The filter
calculates nr output samples using nh coefficients.
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_r4(short *x, short *h, short *r, int nh, int nr)
{
int i, j, sum;
for (j = 0; j < nr; j++) {
sum = 0;
for (i = 0; i < nh; i++)
sum += x[i + j] * h[i];
r[j] = sum >> 15;
}
}