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-rw-r--r--dom/media/webrtc/libwebrtcglue/RunningStat.h48
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diff --git a/dom/media/webrtc/libwebrtcglue/RunningStat.h b/dom/media/webrtc/libwebrtcglue/RunningStat.h
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+/* Any copyright is dedicated to the Public Domain.
+ http://creativecommons.org/publicdomain/zero/1.0/ */
+/* Adapted from "Accurately computing running variance - John D. Cook"
+ http://www.johndcook.com/standard_deviation.html */
+
+#ifndef RUNNING_STAT_H_
+#define RUNNING_STAT_H_
+#include <math.h>
+
+namespace mozilla {
+
+class RunningStat {
+ public:
+ RunningStat() : mN(0), mOldM(0.0), mNewM(0.0), mOldS(0.0), mNewS(0.0) {}
+
+ void Clear() { mN = 0; }
+
+ void Push(double x) {
+ mN++;
+
+ // See Knuth TAOCP vol 2, 3rd edition, page 232
+ if (mN == 1) {
+ mOldM = mNewM = x;
+ mOldS = 0.0;
+ } else {
+ mNewM = mOldM + (x - mOldM) / mN;
+ mNewS = mOldS + (x - mOldM) * (x - mNewM);
+
+ // set up for next iteration
+ mOldM = mNewM;
+ mOldS = mNewS;
+ }
+ }
+
+ int NumDataValues() const { return mN; }
+
+ double Mean() const { return (mN > 0) ? mNewM : 0.0; }
+
+ double Variance() const { return (mN > 1) ? mNewS / (mN - 1) : 0.0; }
+
+ double StandardDeviation() const { return sqrt(Variance()); }
+
+ private:
+ int mN;
+ double mOldM, mNewM, mOldS, mNewS;
+};
+} // namespace mozilla
+#endif // RUNNING_STAT_H_