maths: remove unused package (#19516)

Added in 2025 and appears to be unused.

Updates #cleanup

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

2 files changed, 0 insertions, 250 deletions

diff --git a/maths/ewma.go b/maths/ewma.go
deleted file mode 100644
index 1946081cf..000000000
--- a/maths/ewma.go
+++ /dev/null
@@ -1,72 +0,0 @@
-// Copyright (c) Tailscale Inc & contributors
-// SPDX-License-Identifier: BSD-3-Clause
-
-// Package maths contains additional mathematical functions or structures not
-// found in the standard library.
-package maths
-
-import (
-	"math"
-	"time"
-)
-
-// EWMA is an exponentially weighted moving average supporting updates at
-// irregular intervals with at most nanosecond resolution.
-// The zero value will compute a half-life of 1 second.
-// It is not safe for concurrent use.
-// TODO(raggi): de-duplicate with tstime/rate.Value, which has a more complex
-// and synchronized interface and does not provide direct access to the stable
-// value.
-type EWMA struct {
-	value    float64 // current value of the average
-	lastTime int64   // time of last update in unix nanos
-	halfLife float64 // half-life in seconds
-}
-
-// NewEWMA creates a new EWMA with the specified half-life. If halfLifeSeconds
-// is 0, it defaults to 1.
-func NewEWMA(halfLifeSeconds float64) *EWMA {
-	return &EWMA{
-		halfLife: halfLifeSeconds,
-	}
-}
-
-// Update adds a new sample to the average. If t is zero or precedes the last
-// update, the update is ignored.
-func (e *EWMA) Update(value float64, t time.Time) {
-	if t.IsZero() {
-		return
-	}
-	hl := e.halfLife
-	if hl == 0 {
-		hl = 1
-	}
-	tn := t.UnixNano()
-	if e.lastTime == 0 {
-		e.value = value
-		e.lastTime = tn
-		return
-	}
-
-	dt := (time.Duration(tn-e.lastTime) * time.Nanosecond).Seconds()
-	if dt < 0 {
-		// drop out of order updates
-		return
-	}
-
-	// decay = 2^(-dt/halfLife)
-	decay := math.Exp2(-dt / hl)
-	e.value = e.value*decay + value*(1-decay)
-	e.lastTime = tn
-}
-
-// Get returns the current value of the average
-func (e *EWMA) Get() float64 {
-	return e.value
-}
-
-// Reset clears the EWMA to its initial state
-func (e *EWMA) Reset() {
-	e.value = 0
-	e.lastTime = 0
-}
diff --git a/maths/ewma_test.go b/maths/ewma_test.go
deleted file mode 100644
index 9fddf34e1..000000000
--- a/maths/ewma_test.go
+++ /dev/null
@@ -1,178 +0,0 @@
-// Copyright (c) Tailscale Inc & contributors
-// SPDX-License-Identifier: BSD-3-Clause
-
-package maths
-
-import (
-	"slices"
-	"testing"
-	"time"
-)
-
-// some real world latency samples.
-var (
-	latencyHistory1 = []int{
-		14, 12, 15, 6, 19, 12, 13, 13, 13, 16, 17, 11, 17, 11, 14, 15, 14, 15,
-		16, 16, 17, 14, 12, 16, 18, 14, 14, 11, 15, 15, 25, 11, 15, 14, 12, 15,
-		13, 12, 13, 15, 11, 13, 15, 14, 14, 15, 12, 15, 18, 12, 15, 22, 12, 13,
-		10, 14, 16, 15, 16, 11, 14, 17, 18, 20, 16, 11, 16, 14, 5, 15, 17, 12,
-		15, 11, 15, 20, 12, 17, 12, 17, 15, 12, 12, 11, 14, 15, 11, 20, 14, 13,
-		11, 12, 13, 13, 11, 13, 11, 15, 13, 13, 14, 12, 11, 12, 12, 14, 11, 13,
-		12, 12, 12, 19, 14, 13, 13, 14, 11, 12, 10, 11, 15, 12, 14, 11, 11, 14,
-		14, 12, 12, 11, 14, 12, 11, 12, 14, 11, 12, 15, 12, 14, 12, 12, 21, 16,
-		21, 12, 16, 9, 11, 16, 14, 13, 14, 12, 13, 16,
-	}
-	latencyHistory2 = []int{
-		18, 20, 21, 21, 20, 23, 18, 18, 20, 21, 20, 19, 22, 18, 20, 20, 19, 21,
-		21, 22, 22, 19, 18, 22, 22, 19, 20, 17, 16, 11, 25, 16, 18, 21, 17, 22,
-		19, 18, 22, 21, 20, 18, 22, 17, 17, 20, 19, 10, 19, 16, 19, 25, 17, 18,
-		15, 20, 21, 20, 23, 22, 22, 22, 19, 22, 22, 17, 22, 20, 20, 19, 21, 22,
-		20, 19, 17, 22, 16, 16, 20, 22, 17, 19, 21, 16, 20, 22, 19, 21, 20, 19,
-		13, 14, 23, 19, 16, 10, 19, 15, 15, 17, 16, 18, 14, 16, 18, 22, 20, 18,
-		18, 21, 15, 19, 18, 19, 18, 20, 17, 19, 21, 19, 20, 19, 20, 20, 17, 14,
-		17, 17, 18, 21, 20, 18, 18, 17, 16, 17, 17, 20, 22, 19, 20, 21, 21, 20,
-		21, 24, 20, 18, 12, 17, 18, 17, 19, 19, 19,
-	}
-)
-
-func TestEWMALatencyHistory(t *testing.T) {
-	type result struct {
-		t time.Time
-		v float64
-		s int
-	}
-
-	for _, latencyHistory := range [][]int{latencyHistory1, latencyHistory2} {
-		startTime := time.Date(2025, 1, 1, 12, 0, 0, 0, time.UTC)
-		halfLife := 30.0
-
-		ewma := NewEWMA(halfLife)
-
-		var results []result
-		sum := 0.0
-		for i, latency := range latencyHistory {
-			t := startTime.Add(time.Duration(i) * time.Second)
-			ewma.Update(float64(latency), t)
-			sum += float64(latency)
-
-			results = append(results, result{t, ewma.Get(), latency})
-		}
-		mean := sum / float64(len(latencyHistory))
-		min := float64(slices.Min(latencyHistory))
-		max := float64(slices.Max(latencyHistory))
-
-		t.Logf("EWMA Latency History (half-life: %.1f seconds):", halfLife)
-		t.Logf("Mean latency: %.2f ms", mean)
-		t.Logf("Range: [%.1f, %.1f]", min, max)
-
-		t.Log("Samples: ")
-		sparkline := []rune("▁▂▃▄▅▆▇█")
-		var sampleLine []rune
-		for _, r := range results {
-			idx := int(((float64(r.s) - min) / (max - min)) * float64(len(sparkline)-1))
-			if idx >= len(sparkline) {
-				idx = len(sparkline) - 1
-			}
-			sampleLine = append(sampleLine, sparkline[idx])
-		}
-		t.Log(string(sampleLine))
-
-		t.Log("EWMA:    ")
-		var ewmaLine []rune
-		for _, r := range results {
-			idx := int(((r.v - min) / (max - min)) * float64(len(sparkline)-1))
-			if idx >= len(sparkline) {
-				idx = len(sparkline) - 1
-			}
-			ewmaLine = append(ewmaLine, sparkline[idx])
-		}
-		t.Log(string(ewmaLine))
-		t.Log("")
-
-		t.Logf("Time       | Sample | Value  | Value - Sample")
-		t.Logf("")
-
-		for _, result := range results {
-			t.Logf("%10s | % 6d | % 5.2f | % 5.2f", result.t.Format("15:04:05"), result.s, result.v, result.v-float64(result.s))
-		}
-
-		// check that all results are greater than the min, and less than the max of the input,
-		// and they're all close to the mean.
-		for _, result := range results {
-			if result.v < float64(min) || result.v > float64(max) {
-				t.Errorf("result %f out of range [%f, %f]", result.v, min, max)
-			}
-
-			if result.v < mean*0.9 || result.v > mean*1.1 {
-				t.Errorf("result %f not close to mean %f", result.v, mean)
-			}
-		}
-	}
-}
-
-func TestHalfLife(t *testing.T) {
-	start := time.Date(2025, 1, 1, 12, 0, 0, 0, time.UTC)
-
-	ewma := NewEWMA(30.0)
-	ewma.Update(10, start)
-	ewma.Update(0, start.Add(30*time.Second))
-
-	if ewma.Get() != 5 {
-		t.Errorf("expected 5, got %f", ewma.Get())
-	}
-
-	ewma.Update(10, start.Add(60*time.Second))
-	if ewma.Get() != 7.5 {
-		t.Errorf("expected 7.5, got %f", ewma.Get())
-	}
-
-	ewma.Update(10, start.Add(90*time.Second))
-	if ewma.Get() != 8.75 {
-		t.Errorf("expected 8.75, got %f", ewma.Get())
-	}
-}
-
-func TestZeroValue(t *testing.T) {
-	start := time.Date(2025, 1, 1, 12, 0, 0, 0, time.UTC)
-
-	var ewma EWMA
-	ewma.Update(10, start)
-	ewma.Update(0, start.Add(time.Second))
-
-	if ewma.Get() != 5 {
-		t.Errorf("expected 5, got %f", ewma.Get())
-	}
-
-	ewma.Update(10, start.Add(2*time.Second))
-	if ewma.Get() != 7.5 {
-		t.Errorf("expected 7.5, got %f", ewma.Get())
-	}
-
-	ewma.Update(10, start.Add(3*time.Second))
-	if ewma.Get() != 8.75 {
-		t.Errorf("expected 8.75, got %f", ewma.Get())
-	}
-}
-
-func TestReset(t *testing.T) {
-	start := time.Date(2025, 1, 1, 12, 0, 0, 0, time.UTC)
-
-	ewma := NewEWMA(30.0)
-	ewma.Update(10, start)
-	ewma.Update(0, start.Add(30*time.Second))
-
-	if ewma.Get() != 5 {
-		t.Errorf("expected 5, got %f", ewma.Get())
-	}
-
-	ewma.Reset()
-
-	if ewma.Get() != 0 {
-		t.Errorf("expected 0, got %f", ewma.Get())
-	}
-
-	ewma.Update(10, start.Add(90*time.Second))
-	if ewma.Get() != 10 {
-		t.Errorf("expected 10, got %f", ewma.Get())
-	}
-}