From aa8b569eb652c22821b93a6e543449a52ad21158 Mon Sep 17 00:00:00 2001
From: Lajos Molnar <lajos@google.com>
Date: Tue, 22 Apr 2014 16:31:54 -0700
Subject: stagefright: add ClockEstimator API and WindowedLinearFitEstimator

Change-Id: I74474c385848a8eab2ac0da7c069510378e2b217
---
 include/media/stagefright/ClockEstimator.h | 110 +++++++++++++++++++++++++++++
 1 file changed, 110 insertions(+)
 create mode 100644 include/media/stagefright/ClockEstimator.h

(limited to 'include')

diff --git a/include/media/stagefright/ClockEstimator.h b/include/media/stagefright/ClockEstimator.h
new file mode 100644
index 0000000..2fd6e75
--- /dev/null
+++ b/include/media/stagefright/ClockEstimator.h
@@ -0,0 +1,110 @@
+/*
+**
+** Copyright 2014, 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.
+*/
+
+#ifndef CLOCK_ESTIMATOR_H_
+
+#define CLOCK_ESTIMATOR_H_
+
+
+#include <utils/RefBase.h>
+#include <utils/Vector.h>
+
+namespace android {
+// ---------------------------------------------------------------------------
+
+struct ClockEstimator : RefBase {
+    virtual double estimate(double x, double y) = 0;
+    virtual void reset() = 0;
+};
+
+struct WindowedLinearFitEstimator : ClockEstimator {
+    struct LinearFit {
+        /**
+         * Fit y = a * x + b, where each input has a weight
+         */
+        double mX;  // sum(w_i * x_i)
+        double mXX; // sum(w_i * x_i^2)
+        double mY;  // sum(w_i * y_i)
+        double mYY; // sum(w_i * y_i^2)
+        double mXY; // sum(w_i * x_i * y_i)
+        double mW;  // sum(w_i)
+
+        LinearFit();
+        void reset();
+        void combine(const LinearFit &lf);
+        void add(double x, double y, double w);
+        void scale(double w);
+        double interpolate(double x);
+        double size() const;
+
+        DISALLOW_EVIL_CONSTRUCTORS(LinearFit);
+    };
+
+    /**
+     * Estimator for f(x) = y' where input y' is noisy, but
+     * theoretically linear:
+     *
+     *      y' =~ y = a * x + b
+     *
+     * It uses linear fit regression over a tapering rolling window
+     * to get an estimate for y (from the current and past inputs
+     * (x, y')).
+     *
+     *     ____________
+     *    /|          |\
+     *   / |          | \
+     *  /  |          |  \   <--- new data (x, y')
+     * /   |   main   |   \
+     * <--><----------><-->
+     * tail            head
+     *
+     * weight is 1 under the main window, tapers exponentially by
+     * the factors given in the head and the tail.
+     *
+     * Assuming that x and y' are monotonic, that x is somewhat
+     * evenly sampled, and that a =~ 1, the estimated y is also
+     * going to be monotonic.
+     */
+    WindowedLinearFitEstimator(
+            size_t headLength = 5, double headFactor = 0.5,
+            size_t mainLength = 0, double tailFactor = 0.99);
+
+    virtual void reset();
+
+    // add a new sample (x -> y') and return an estimated value for the true y
+    virtual double estimate(double x, double y);
+
+private:
+    Vector<double> mXHistory; // circular buffer
+    Vector<double> mYHistory; // circular buffer
+    LinearFit mHead;
+    LinearFit mMain;
+    LinearFit mTail;
+    double mHeadFactorInv;
+    double mTailFactor;
+    double mFirstWeight;
+    size_t mHistoryLength;
+    size_t mHeadLength;
+    size_t mNumSamples;
+    size_t mSampleIx;
+
+    DISALLOW_EVIL_CONSTRUCTORS(WindowedLinearFitEstimator);
+};
+
+}; // namespace android
+
+#endif
-- 
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