1 files changed, 126 insertions, 0 deletions
diff --git a/dependencies/pkg/mod/github.com/!vivid!cortex/ewma@v1.2.0/ewma.go b/dependencies/pkg/mod/github.com/!vivid!cortex/ewma@v1.2.0/ewma.go
new file mode 100644
index 0000000..44d5d53
--- /dev/null
+++ b/dependencies/pkg/mod/github.com/!vivid!cortex/ewma@v1.2.0/ewma.go
@@ -0,0 +1,126 @@
+// Package ewma implements exponentially weighted moving averages.
+package ewma
+
+// Copyright (c) 2013 VividCortex, Inc. All rights reserved.
+// Please see the LICENSE file for applicable license terms.
+
+const (
+	// By default, we average over a one-minute period, which means the average
+	// age of the metrics in the period is 30 seconds.
+	AVG_METRIC_AGE float64 = 30.0
+
+	// The formula for computing the decay factor from the average age comes
+	// from "Production and Operations Analysis" by Steven Nahmias.
+	DECAY float64 = 2 / (float64(AVG_METRIC_AGE) + 1)
+
+	// For best results, the moving average should not be initialized to the
+	// samples it sees immediately. The book "Production and Operations
+	// Analysis" by Steven Nahmias suggests initializing the moving average to
+	// the mean of the first 10 samples. Until the VariableEwma has seen this
+	// many samples, it is not "ready" to be queried for the value of the
+	// moving average. This adds some memory cost.
+	WARMUP_SAMPLES uint8 = 10
+)
+
+// MovingAverage is the interface that computes a moving average over a time-
+// series stream of numbers. The average may be over a window or exponentially
+// decaying.
+type MovingAverage interface {
+	Add(float64)
+	Value() float64
+	Set(float64)
+}
+
+// NewMovingAverage constructs a MovingAverage that computes an average with the
+// desired characteristics in the moving window or exponential decay. If no
+// age is given, it constructs a default exponentially weighted implementation
+// that consumes minimal memory. The age is related to the decay factor alpha
+// by the formula given for the DECAY constant. It signifies the average age
+// of the samples as time goes to infinity.
+func NewMovingAverage(age ...float64) MovingAverage {
+	if len(age) == 0 || age[0] == AVG_METRIC_AGE {
+		return new(SimpleEWMA)
+	}
+	return &VariableEWMA{
+		decay: 2 / (age[0] + 1),
+	}
+}
+
+// A SimpleEWMA represents the exponentially weighted moving average of a
+// series of numbers. It WILL have different behavior than the VariableEWMA
+// for multiple reasons. It has no warm-up period and it uses a constant
+// decay.  These properties let it use less memory.  It will also behave
+// differently when it's equal to zero, which is assumed to mean
+// uninitialized, so if a value is likely to actually become zero over time,
+// then any non-zero value will cause a sharp jump instead of a small change.
+// However, note that this takes a long time, and the value may just
+// decays to a stable value that's close to zero, but which won't be mistaken
+// for uninitialized. See http://play.golang.org/p/litxBDr_RC for example.
+type SimpleEWMA struct {
+	// The current value of the average. After adding with Add(), this is
+	// updated to reflect the average of all values seen thus far.
+	value float64
+}
+
+// Add adds a value to the series and updates the moving average.
+func (e *SimpleEWMA) Add(value float64) {
+	if e.value == 0 { // this is a proxy for "uninitialized"
+		e.value = value
+	} else {
+		e.value = (value * DECAY) + (e.value * (1 - DECAY))
+	}
+}
+
+// Value returns the current value of the moving average.
+func (e *SimpleEWMA) Value() float64 {
+	return e.value
+}
+
+// Set sets the EWMA's value.
+func (e *SimpleEWMA) Set(value float64) {
+	e.value = value
+}
+
+// VariableEWMA represents the exponentially weighted moving average of a series of
+// numbers. Unlike SimpleEWMA, it supports a custom age, and thus uses more memory.
+type VariableEWMA struct {
+	// The multiplier factor by which the previous samples decay.
+	decay float64
+	// The current value of the average.
+	value float64
+	// The number of samples added to this instance.
+	count uint8
+}
+
+// Add adds a value to the series and updates the moving average.
+func (e *VariableEWMA) Add(value float64) {
+	switch {
+	case e.count < WARMUP_SAMPLES:
+		e.count++
+		e.value += value
+	case e.count == WARMUP_SAMPLES:
+		e.count++
+		e.value = e.value / float64(WARMUP_SAMPLES)
+		e.value = (value * e.decay) + (e.value * (1 - e.decay))
+	default:
+		e.value = (value * e.decay) + (e.value * (1 - e.decay))
+	}
+}
+
+// Value returns the current value of the average, or 0.0 if the series hasn't
+// warmed up yet.
+func (e *VariableEWMA) Value() float64 {
+	if e.count <= WARMUP_SAMPLES {
+		return 0.0
+	}
+
+	return e.value
+}
+
+// Set sets the EWMA's value.
+func (e *VariableEWMA) Set(value float64) {
+	e.value = value
+	if e.count <= WARMUP_SAMPLES {
+		e.count = WARMUP_SAMPLES + 1
+	}
+}