From b12a49542a1985d6b1638eb56609fa033eda0a30 Mon Sep 17 00:00:00 2001
From: Laurence Withers <lwithers@guralp.com>
Date: Mon, 7 Jul 2014 11:57:16 +0000
Subject: [PATCH] Add interface to query coefficients from chain

---
 src/libiir/200_filter.c | 19 +++++++++++++++++++
 src/libiir/200_filter.h | 29 +++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/src/libiir/200_filter.c b/src/libiir/200_filter.c
index d69b62b..3fb7f2d 100644
--- a/src/libiir/200_filter.c
+++ b/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);
+}
+
+
+
 /* options for text editors
 vim: expandtab:ts=4:sw=4
 */
diff --git a/src/libiir/200_filter.h b/src/libiir/200_filter.h
index 247a8ba..0ea2ea5 100644
--- a/src/libiir/200_filter.h
+++ b/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 &lt; \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);
+
+
+
 /*!@}*/
 /* options for text editors
 vim: expandtab:ts=4:sw=4:syntax=c.doxygen