From 9dcbdbdc69b8e7e01c4ca8876346e9d54ccc6135 Mon Sep 17 00:00:00 2001
From: Ahmet Inan <xdsopl@googlemail.com>
Date: Thu, 8 Jan 2015 22:18:50 +0100
Subject: [PATCH] use cic filter for decimation in analyzer

---
 app/src/main/rs/cic.rsh  | 55 ++++++++++++++++++++++++++++++++++++++++
 app/src/main/rs/stft.rsh | 12 +++++++--
 2 files changed, 65 insertions(+), 2 deletions(-)
 create mode 100644 app/src/main/rs/cic.rsh

diff --git a/app/src/main/rs/cic.rsh b/app/src/main/rs/cic.rsh
new file mode 100644
index 0000000..5c8ab79
--- /dev/null
+++ b/app/src/main/rs/cic.rsh
@@ -0,0 +1,55 @@
+/*
+Copyright 2015 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 CIC_RSH
+#define CIC_RSH
+
+typedef struct {
+    int prev_comb, prev_int;
+} cic_t;
+
+static const int cic_cascade_order = 5;
+typedef struct {
+    cic_t cic[cic_cascade_order];
+} cic_cascade_t;
+
+static int cic_comb(cic_t *cic, int input)
+{
+    int output = input - cic->prev_comb;
+    cic->prev_comb = input;
+    return output;
+}
+
+static int cic_int(cic_t *cic, int input)
+{
+    return cic->prev_int = input + cic->prev_int;
+}
+
+static int cic_comb_cascade(cic_cascade_t *cascade, int input)
+{
+    for (int i = 0; i < cic_cascade_order; ++i)
+        input = cic_comb(cascade->cic + i, input);
+    return input;
+}
+
+static int cic_int_cascade(cic_cascade_t *cascade, int input)
+{
+    for (int i = 0; i < cic_cascade_order; ++i)
+        input = cic_int(cascade->cic + i, input);
+    return input;
+}
+
+#endif
\ No newline at end of file
diff --git a/app/src/main/rs/stft.rsh b/app/src/main/rs/stft.rsh
index 831f12d..f8ed371 100644
--- a/app/src/main/rs/stft.rsh
+++ b/app/src/main/rs/stft.rsh
@@ -22,6 +22,7 @@ limitations under the License.
 #include "utils.rsh"
 #include "complex.rsh"
 #include "radix2.rsh"
+#include "cic.rsh"
 #include "stft_generated.rsh"
 
 static inline uchar4 rainbow(float v)
@@ -43,11 +44,18 @@ static void freq_marker(int freq)
 static void spectrum_analyzer(int amplitude)
 {
     const int M = 7;
-    static int n;
+    static int n, m;
     static complex_t input[radix2_N];
     static complex_t output[radix2_N];
+    static cic_cascade_t cascade;
 
-    input[(n/M)&(radix2_N-1)] += complex(stft_w[n] * amplitude, 0.0f);
+    int tmp = cic_int_cascade(&cascade, amplitude);
+    if (++m < M)
+        return;
+    m = 0;
+    amplitude = cic_comb_cascade(&cascade, tmp);
+
+    input[n&(radix2_N-1)] += complex(stft_w[n] * amplitude, 0.0f);
     if (++n >= stft_N) {
         n = 0;
         // yep, were wasting 3x performance