From e69c476a417e680b97dd567d465793cf1cb8de5a Mon Sep 17 00:00:00 2001
From: Ahmet Inan <xdsopl@googlemail.com>
Date: Sun, 30 Nov 2014 17:02:51 +0100
Subject: [PATCH] moved ddc to ddc.rsh, made filter order less flexible

---
 app/src/main/rs/ddc.rsh    | 42 ++++++++++++++++++++++++++++++++++++++
 app/src/main/rs/decoder.rs | 30 ++++++---------------------
 app/src/main/rs/ema.rsh    | 15 +++++++-------
 3 files changed, 56 insertions(+), 31 deletions(-)
 create mode 100644 app/src/main/rs/ddc.rsh

diff --git a/app/src/main/rs/ddc.rsh b/app/src/main/rs/ddc.rsh
new file mode 100644
index 0000000..61f2d5e
--- /dev/null
+++ b/app/src/main/rs/ddc.rsh
@@ -0,0 +1,42 @@
+/*
+Copyright 2014 Ahmet Inan <xdsopl@googlemail.com>
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+ */
+
+#ifndef DDC_RSH
+#define DDC_RSH
+
+#include "complex.rsh"
+#include "ema.rsh"
+#include "phasor.rsh"
+
+typedef struct {
+    phasor_t phasor;
+    cema_cascade_t lowpass;
+} ddc_t;
+
+static ddc_t ddc(float carrier, float bandwidth, float rate)
+{
+    return (ddc_t){
+        phasor(-carrier, rate),
+        cema_cutoff_cascade(bandwidth, rate)
+    };
+}
+
+static complex_t convert(ddc_t *ddc, float amp)
+{
+    return cfilter(&ddc->lowpass, amp * rotate(&ddc->phasor));
+}
+
+#endif
\ No newline at end of file
diff --git a/app/src/main/rs/decoder.rs b/app/src/main/rs/decoder.rs
index 398d43b..49349e8 100644
--- a/app/src/main/rs/decoder.rs
+++ b/app/src/main/rs/decoder.rs
@@ -19,7 +19,7 @@ limitations under the License.
 
 #include "complex.rsh"
 #include "ema.rsh"
-#include "phasor.rsh"
+#include "ddc.rsh"
 
 short *audio_buffer;
 uchar *value_buffer;
@@ -78,20 +78,6 @@ static float scottieDX_estimator(int length)
     return filter(&variance, deviation * deviation);
 }
 
-static phasor_t cnt_phasor;
-static cema_cascade_t cnt_lowpass;
-static complex_t cnt_ddc(float amp)
-{
-    return cfilter(&cnt_lowpass, amp * rotate(&cnt_phasor));
-}
-
-static phasor_t dat_phasor;
-static cema_cascade_t dat_lowpass;
-static complex_t dat_ddc(float amp)
-{
-    return cfilter(&dat_lowpass, amp * rotate(&dat_phasor));
-}
-
 static float cnt_fmd_scale;
 static float cnt_fmd(complex_t baseband)
 {
@@ -111,6 +97,7 @@ static float dat_fmd(complex_t baseband)
 }
 
 static ema_t avg_power, leader_lowpass;
+static ddc_t cnt_ddc, dat_ddc;
 static int sample_rate, mode, even_hpos;
 static int maximum_variance, minimum_sync_length;
 static int scanline_length, minimum_length, maximum_length;
@@ -401,13 +388,8 @@ void initialize(float rate, int length, int width, int height)
     avg_power = ema_cutoff(10.0f, sample_rate);
     leader_lowpass = ema_cutoff(100.0f, sample_rate);
 
-    static const int filter_order = 11;
-    static cema_t cnt_ema_cascade[filter_order], dat_ema_cascade[filter_order];
-    cnt_lowpass = cema_cutoff_cascade(cnt_ema_cascade, cnt_bandwidth, sample_rate, filter_order);
-    dat_lowpass = cema_cutoff_cascade(dat_ema_cascade, dat_bandwidth, sample_rate, filter_order);
-
-    cnt_phasor = phasor(-cnt_carrier, sample_rate);
-    dat_phasor = phasor(-dat_carrier, sample_rate);
+    cnt_ddc = ddc(cnt_carrier, cnt_bandwidth, sample_rate);
+    dat_ddc = ddc(dat_carrier, dat_bandwidth, sample_rate);
 
     cnt_fmd_scale = sample_rate / (M_PI * cnt_bandwidth);
     dat_fmd_scale = sample_rate / (M_PI * dat_bandwidth);
@@ -683,8 +665,8 @@ void decode(int samples) {
         if (filter(&avg_power, power) < 0.0000001f)
             continue;
 
-        complex_t cnt_baseband = cnt_ddc(amp);
-        complex_t dat_baseband = dat_ddc(amp);
+        complex_t cnt_baseband = convert(&cnt_ddc, amp);
+        complex_t dat_baseband = convert(&dat_ddc, amp);
 
         float cnt_value = cnt_fmd(cnt_baseband);
         float dat_value = dat_fmd(dat_baseband);
diff --git a/app/src/main/rs/ema.rsh b/app/src/main/rs/ema.rsh
index b5972f9..8ec797f 100644
--- a/app/src/main/rs/ema.rsh
+++ b/app/src/main/rs/ema.rsh
@@ -28,9 +28,9 @@ typedef struct {
     float a;
 } cema_t;
 
+static const int cema_cascade_order = 11;
 typedef struct {
-    cema_t *ema;
-    int order;
+    cema_t ema[cema_cascade_order];
 } cema_cascade_t;
 
 static float ema_cutoff_a(float cutoff, float rate)
@@ -60,11 +60,12 @@ static cema_t cema_cutoff(float cutoff, float rate)
     return cema(ema_cutoff_a(cutoff, rate));
 }
 
-static cema_cascade_t cema_cutoff_cascade(cema_t *ema, float cutoff, float rate, int order)
+static cema_cascade_t cema_cutoff_cascade(float cutoff, float rate)
 {
-    for (int i = 0; i < order; ++i)
-        ema[i] = cema_cutoff(cutoff / sqrt(rootn(2.0f, order) - 1.0f), rate);
-    return (cema_cascade_t){ ema, order };
+    cema_cascade_t cascade;
+    for (int i = 0; i < cema_cascade_order; ++i)
+        cascade.ema[i] = cema_cutoff(cutoff / sqrt(rootn(2.0f, cema_cascade_order) - 1.0f), rate);
+    return cascade;
 }
 
 static inline float filter(ema_t *ema, float input)
@@ -79,7 +80,7 @@ static inline complex_t __attribute__((overloadable)) cfilter(cema_t *ema, compl
 
 static complex_t __attribute__((overloadable)) cfilter(cema_cascade_t *cascade, complex_t input)
 {
-    for (int i = 0; i < cascade->order; ++i)
+    for (int i = 0; i < cema_cascade_order; ++i)
         input = cfilter(cascade->ema + i, input);
     return input;
 }