From f8d9ac5d13dd37b8b57af0478e77ba1e75c813aa Mon Sep 17 00:00:00 2001
From: Stefan Boberg <stefan@boberg.org>
Date: Tue, 11 May 2021 13:05:39 +0200
Subject: Adding zenservice code

---
 zencore/stats.cpp | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 zencore/stats.cpp

(limited to 'zencore/stats.cpp')

diff --git a/zencore/stats.cpp b/zencore/stats.cpp
new file mode 100644
index 000000000..f8cdc8fbb
--- /dev/null
+++ b/zencore/stats.cpp
@@ -0,0 +1,73 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+
+#include "zencore/stats.h"
+#include <doctest/doctest.h>
+#include <cmath>
+#include "zencore/timer.h"
+
+//
+// Derived from https://github.com/dln/medida/blob/master/src/medida/stats/ewma.cc
+//
+
+namespace zen {
+
+static constexpr int	kTickInterval	  = 5;	// In seconds
+static constexpr double kSecondsPerMinute = 60.0;
+static constexpr int	kOneMinute		  = 1;
+static constexpr int	kFiveMinutes	  = 5;
+static constexpr int	kFifteenMinutes	  = 15;
+
+static double kM1_ALPHA	 = 1.0 - std::exp(-kTickInterval / kSecondsPerMinute / kOneMinute);
+static double kM5_ALPHA	 = 1.0 - std::exp(-kTickInterval / kSecondsPerMinute / kFiveMinutes);
+static double kM15_ALPHA = 1.0 - std::exp(-kTickInterval / kSecondsPerMinute / kFifteenMinutes);
+
+static uint64_t CountPerTick   = GetHifreqTimerFrequencySafe() * kTickInterval;
+static uint64_t CountPerSecond = GetHifreqTimerFrequencySafe();
+
+void
+EWMA::Tick(double Alpha, uint64_t Interval, uint64_t Count, bool IsInitialUpdate)
+{
+	double InstantRate = double(Count) / Interval;
+
+	if (IsInitialUpdate)
+	{
+		m_rate = InstantRate;
+	}
+	else
+	{
+		m_rate += Alpha * (InstantRate - m_rate);
+	}
+}
+
+double
+EWMA::Rate() const
+{
+	return m_rate * CountPerSecond;
+}
+
+//////////////////////////////////////////////////////////////////////////
+
+TEST_CASE("Stats")
+{
+	SUBCASE("Simple")
+	{
+		EWMA ewma1;
+		ewma1.Tick(kM1_ALPHA, CountPerSecond, 5, true);
+
+		CHECK(ewma1.Rate() - 5 < 0.001);
+
+		for (int i = 0; i < 60; ++i)
+			ewma1.Tick(kM1_ALPHA, CountPerSecond, 10, false);
+
+		CHECK(ewma1.Rate() - 10 < 0.001);
+
+		ewma1.Tick(kM1_ALPHA, CountPerSecond, 10, false);
+	}
+}
+
+void
+stats_forcelink()
+{
+}
+
+}  // namespace zen
-- 
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