Add coefficient query functions

Add some functions that allow the opaque struct iir_coeff_t to be queried
in order to retrieve the number and value of the filter coefficients.

src/libiir/200_iir.c

@@ -58,6 +58,35 @@ iir_coeff_free(struct iir_coeff_t* coeff)
 
 
 
+/* iir_coeff_get_*()
+ *  Functions for querying the coefficients that make up an IIR filter.
+ */
+int
+iir_coeff_get_nc(const struct iir_coeff_t* coeff)
+{
+    return coeff->nc;
+}
+
+int
+iir_coeff_get_nd(const struct iir_coeff_t* coeff)
+{
+    return coeff->nd;
+}
+
+double
+iir_coeff_get_c(const struct iir_coeff_t* coeff, int idx)
+{
+    return coeff->c[idx];
+}
+
+double
+iir_coeff_get_d(const struct iir_coeff_t* coeff, int idx)
+{
+    return coeff->d[idx];
+}
+
+
+
 /* struct iir_filter_t
  *  An instantiated IIR filter. This is actually a linked list node, so that we
  *  can create chains of filters. It also has a copy of the coefficients so that

src/libiir/200_iir.h

@@ -69,6 +69,48 @@ void iir_coeff_free(struct iir_coeff_t* coeff);
 
 
 
+/*! \brief Query number of C coefficients.
+
+\param coeff Pointer to IIR filter object.
+\returns Number of C coefficients (≥1).
+
+*/
+int iir_coeff_get_nc(const struct iir_coeff_t* coeff);
+
+
+
+/*! \brief Query number of D coefficients.
+
+\param coeff Pointer to IIR filter object.
+\returns Number of D coefficients (≥1).
+
+*/
+int iir_coeff_get_nd(const struct iir_coeff_t* coeff);
+
+
+
+/*! \brief Get value of C coefficient.
+
+\param coeff Pointer to IIR filter object.
+\param idx Index of coefficient (≥0, < \ref iir_coeff_get_nc()).
+\returns C coefficient value.
+
+*/
+double iir_coeff_get_c(const struct iir_coeff_t* coeff, int idx);
+
+
+
+/*! \brief Get value of D coefficient.
+
+\param coeff Pointer to IIR filter object.
+\param idx Index of coefficient (≥0, < \ref iir_coeff_get_nd()).
+\returns D coefficient value.
+
+*/
+double iir_coeff_get_d(const struct iir_coeff_t* coeff, int idx);
+
+
+
 /* opaque structure */
 struct iir_filter_t;