1 files changed, 48 insertions, 0 deletions
diff --git a/dom/media/webrtc/libwebrtcglue/RunningStat.h b/dom/media/webrtc/libwebrtcglue/RunningStat.h
new file mode 100644
index 0000000000..7a0e88f193
--- /dev/null
+++ b/dom/media/webrtc/libwebrtcglue/RunningStat.h
@@ -0,0 +1,48 @@
+/* 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_