Analog Devices VISUALDSP++ 3.5 Manual page 476

DSP Run-Time Library Reference
#define fir_init(state, coeffs, delay, ncoeffs, index) \
(state).h = (coeffs);
(state).d = (delay);
(state).p = (delay);
(state).k = (ncoeffs); \
(state).l = (index)
The characteristics of the filter are dependent upon the number of filter
coefficients and their values, and on the decimation index supplied by the
calling program. A pointer to the coefficients should be stored in
and should be set to the number of coefficients. The decimation
s->k
index is supplied to the function in
Each filter should have its own delay line which is a vector of type
and whose length is equal to the number of coefficients. The vector should
be initially cleared to zero and should not otherwise be modified by the
user program. The structure member
delay line, and the function uses
within the vector.
Algorithm
−
k 1
∑
=
i y ) ( i x (
=
j 0
where i = 0,1,...,(n/l) - 1
Domain
-1.0 to + 1.0
4-60
\
\
\
s->p
* l - j * ) h ( k 1 - + j )
VisualDSP++ 3.5 C/C++ Compiler and Library Manual
.
s->l
should be set to the start of the
s->d
to keep track of its current position
for ADSP-219x DSPs
,
s->h
fract16