1 files changed, 89 insertions, 0 deletions
diff --git a/services/sensorservice/legacy/SecondOrderLowPassFilter.cpp b/services/sensorservice/legacy/SecondOrderLowPassFilter.cpp
new file mode 100644
index 0000000..eeb6d1e
--- /dev/null
+++ b/services/sensorservice/legacy/SecondOrderLowPassFilter.cpp
@@ -0,0 +1,89 @@
+/*
+ * Copyright (C) 2010 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#include <stdint.h>
+#include <sys/types.h>
+#include <math.h>
+
+#include <cutils/log.h>
+
+#include "SecondOrderLowPassFilter.h"
+
+// ---------------------------------------------------------------------------
+
+namespace android {
+// ---------------------------------------------------------------------------
+
+SecondOrderLowPassFilter::SecondOrderLowPassFilter(float Q, float fc)
+    : iQ(1.0f / Q), fc(fc)
+{
+}
+
+void SecondOrderLowPassFilter::setSamplingPeriod(float dT)
+{
+    K = tanf(float(M_PI) * fc * dT);
+    iD = 1.0f / (K*K + K*iQ + 1);
+    a0 = K*K*iD;
+    a1 = 2.0f * a0;
+    b1 = 2.0f*(K*K - 1)*iD;
+    b2 = (K*K - K*iQ + 1)*iD;
+}
+
+// ---------------------------------------------------------------------------
+
+BiquadFilter::BiquadFilter(const SecondOrderLowPassFilter& s)
+    : s(s)
+{
+}
+
+float BiquadFilter::init(float x)
+{
+    x1 = x2 = x;
+    y1 = y2 = x;
+    return x;
+}
+
+float BiquadFilter::operator()(float x)
+{
+    float y = (x + x2)*s.a0 + x1*s.a1 - y1*s.b1 - y2*s.b2;
+    x2 = x1;
+    y2 = y1;
+    x1 = x;
+    y1 = y;
+    return y;
+}
+
+// ---------------------------------------------------------------------------
+
+CascadedBiquadFilter::CascadedBiquadFilter(const SecondOrderLowPassFilter& s)
+    : mA(s), mB(s)
+{
+}
+
+float CascadedBiquadFilter::init(float x)
+{
+    mA.init(x);
+    mB.init(x);
+    return x;
+}
+
+float CascadedBiquadFilter::operator()(float x)
+{
+    return mB(mA(x));
+}
+
+// ---------------------------------------------------------------------------
+}; // namespace android