Add interface to query coefficients from chain

src/libiir/200_filter.c

@@ -217,6 +217,25 @@ iir_filter(struct iir_filter_t* fi, double samp)
 
 
 
+int
+iir_filter_coeff_sets(const struct iir_filter_t* fi)
+{
+    int count;
+    for(count = 0; fi; ++count) fi = fi->next;
+    return count;
+}
+
+
+
+struct iir_coeff_t*
+iir_filter_coeff_set(const struct iir_filter_t* fi, int idx)
+{
+    while(idx--) fi = fi->next;
+    return iir_coeff_new(fi->nc, fi->c, fi->nd, fi->d);
+}
+
+
+
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src/libiir/200_filter.h

@@ -121,6 +121,35 @@ double iir_filter(struct iir_filter_t* fi, double samp);
 
 
 
+/*! \brief Count number of coefficient sets in IIR filter chain
+
+\param fi Filter object.
+\returns Number of coefficient sets in chain (≥1).
+
+Returns the number of discrete IIR filter coefficient sets used in the filter
+object \a fi. There will always be at least one set.
+
+*/
+int iir_filter_coeff_sets(const struct iir_filter_t* fi);
+
+
+
+/*! \brief Get IIR coefficient set from filter chain
+
+\param fi Filter object.
+\param idx Index of coefficient set (0 ≤ \a idx < \ref iir_filter_coeff_sets()).
+\returns Newly-allocated coefficient set object.
+
+Extracts the IIR filter coefficient set for the given step (\a idx) in the chain
+of filters in \a fi. Returns a newly-allocated filter coefficient set object
+which can be freed with \ref iir_coeff_free().
+
+*/
+struct iir_coeff_t* iir_filter_coeff_set(const struct iir_filter_t* fi,
+    int idx);
+
+
+
 /*!@}*/
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