From caef87fe90d566637ef2fe2e10c10b7086de5e4c Mon Sep 17 00:00:00 2001
From: Jared Boone <jboone@earfeast.com>
Date: Tue, 4 Aug 2015 15:00:38 -0700
Subject: [PATCH] Refactor IIRBiquadFilter to separate configuration structure.

---
 firmware/baseband/dsp_iir.hpp | 18 ++++++++++--------
 firmware/baseband/main.cpp    | 30 ++++++++++++++----------------
 2 files changed, 24 insertions(+), 24 deletions(-)

diff --git a/firmware/baseband/dsp_iir.hpp b/firmware/baseband/dsp_iir.hpp
index 9a7602e9b..8fb12f055 100644
--- a/firmware/baseband/dsp_iir.hpp
+++ b/firmware/baseband/dsp_iir.hpp
@@ -26,16 +26,19 @@
 
 #include "dsp_types.hpp"
 
+struct iir_biquad_config_t {
+	const std::array<float, 3> b;
+	const std::array<float, 3> a;
+};
+
 class IIRBiquadFilter {
 public:
 	// http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt
 
 	// Assume all coefficients are normalized so that a0=1.0
 	constexpr IIRBiquadFilter(
-		std::array<float, 3> b,
-		std::array<float, 3> a
-	) : b(b),
-		a(a)
+		const iir_biquad_config_t& config
+	) : config(config)
 	{
 	}
 
@@ -51,8 +54,7 @@ public:
 	}
 
 private:
-	const std::array<float, 3> b;
-	const std::array<float, 3> a;
+	const iir_biquad_config_t config;
 	std::array<float, 3> x { { 0.0f, 0.0f, 0.0f } };
 	std::array<float, 3> y { { 0.0f, 0.0f, 0.0f } };
 
@@ -63,8 +65,8 @@ private:
 
 		y[0] = y[1];
 		y[1] = y[2];
-		y[2] = b[0] * x[2] + b[1] * x[1] + b[2] * x[0]
-		                   - a[1] * y[1] - a[2] * y[0];
+		y[2] = config.b[0] * x[2] + config.b[1] * x[1] + config.b[2] * x[0]
+		                          - config.a[1] * y[1] - config.a[2] * y[0];
 
 		return y[2];
 	}
diff --git a/firmware/baseband/main.cpp b/firmware/baseband/main.cpp
index e731c261f..15ff75d0a 100755
--- a/firmware/baseband/main.cpp
+++ b/firmware/baseband/main.cpp
@@ -175,6 +175,16 @@ private:
 	}
 };
 
+static constexpr iir_biquad_config_t audio_hpf_config {
+	{  0.93346032f, -1.86687724f,  0.93346032f },
+	{  1.0f       , -1.97730264f,  0.97773668f }
+};
+
+static constexpr iir_biquad_config_t non_audio_hpf_config {
+	{  0.51891061f, -0.95714180f,  0.51891061f },
+	{  1.0f       , -0.79878302f,  0.43960231f }
+};
+
 class FMSquelch {
 public:
 	bool execute(buffer_s16_t audio) {
@@ -203,10 +213,7 @@ private:
 
 	// nyquist = 48000 / 2.0
 	// scipy.signal.iirdesign(wp=8000 / nyquist, ws= 4000 / nyquist, gpass=1, gstop=18, ftype='ellip')
-	IIRBiquadFilter non_audio_hpf {
-		{  0.51891061f, -0.95714180f,  0.51891061f },
-		{  1.0f       , -0.79878302f,  0.43960231f }
-	};
+	IIRBiquadFilter non_audio_hpf { non_audio_hpf_config };
 };
 
 static volatile bool channel_spectrum_request_update { false };
@@ -332,10 +339,7 @@ private:
 	const fir_taps_real<64>& channel_filter_taps = taps_64_lp_031_070_tfilter;
 	dsp::decimate::FIRAndDecimateBy2Complex<64> channel_filter { channel_filter_taps.taps };
 	dsp::demodulate::AM demod;
-	IIRBiquadFilter audio_hpf {
-		{  0.93346032f, -1.86687724f,  0.93346032f },
-		{  1.0f       , -1.97730264f,  0.97773668f }
-	};
+	IIRBiquadFilter audio_hpf { audio_hpf_config };
 };
 
 class NarrowbandFMAudio : public BasebandProcessor {
@@ -393,10 +397,7 @@ private:
 	dsp::decimate::FIRAndDecimateBy2Complex<64> channel_filter { channel_filter_taps.taps };
 	dsp::demodulate::FM demod { 48000, 7500 };
 
-	IIRBiquadFilter audio_hpf {
-		{  0.93346032f, -1.86687724f,  0.93346032f },
-		{  1.0f       , -1.97730264f,  0.97773668f }
-	};
+	IIRBiquadFilter audio_hpf { audio_hpf_config };
 	FMSquelch squelch;
 };
 
@@ -461,10 +462,7 @@ private:
 	const fir_taps_real<64>& audio_filter_taps = taps_64_lp_156_198;
 	dsp::decimate::FIR64AndDecimateBy2Real audio_filter { audio_filter_taps.taps };
 
-	IIRBiquadFilter audio_hpf {
-		{  0.93346032f, -1.86687724f,  0.93346032f },
-		{  1.0f       , -1.97730264f,  0.97773668f }
-	};
+	IIRBiquadFilter audio_hpf { audio_hpf_config };
 };
 
 class FSKProcessor : public BasebandProcessor {