time-smoother

go.mod

@@ -3,6 +3,7 @@ module github.com/polygon-io/go-app-ticker-wall
 go 1.16
 
 require (
+	github.com/dterei/gotsc v0.0.0-20160722215413-e78f872945c6
 	github.com/goxjs/gl v0.0.0-20210104184919-e3fafc6f8f2a
 	github.com/goxjs/glfw v0.0.0-20191126052801-d2efb5f20838
 	github.com/polygon-io/nanovgo v0.0.0-20210406222537-1c1e04bebee3

go.sum

@@ -1,6 +1,8 @@
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/dterei/gotsc v0.0.0-20160722215413-e78f872945c6 h1:iD62k/20LzNdTc2bmrOTQ4xgRbI0uJvOxTkEAmd20eQ=
+github.com/dterei/gotsc v0.0.0-20160722215413-e78f872945c6/go.mod h1:P4N3xGqi52atrdlMBXpsAGTqRnLgZ8uDhlkQ7HEYGgo=
 github.com/go-gl/gl v0.0.0-20210315015930-ae072cafe09d h1:o81yRlBATU4PRn97lydmsq8hTRNXI4wlR/VvUQhFRVY=
 github.com/go-gl/gl v0.0.0-20210315015930-ae072cafe09d/go.mod h1:482civXOzJJCPzJ4ZOX/pwvXBWSnzD4OKMdH4ClKGbk=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20210311203641-62640a716d48 h1:QrUfZrT8n72FUuiABt4tbu8PwDnOPAbnj3Mql1UhdRI=

time_smoother/time.go

@@ -0,0 +1,111 @@
+package time_smoother
+
+import (
+	"math"
+	"time"
+
+	"github.com/dterei/gotsc"
+)
+
+type TimeSmoother struct {
+	lastRdtsc      uint64 // last cycle count
+	lastRdtscNanos uint64 // last cycle-synced time
+	lastSystemTime uint64 // last system time
+	rdtscTime      uint64 // time to call rdtsc
+
+	clockSpeed          float64
+	clockSpeedDecayRate float64
+
+	adjustedTimeRate float64 // nanos per clock
+
+	syncInterval uint64
+
+	stop chan bool
+}
+
+func (t *TimeSmoother) Stop() {
+	t.stop <- true
+}
+
+func (t *TimeSmoother) GetTime() time.Time {
+	tnow := gotsc.BenchStart()
+
+	// delta in cycles
+	tDelta := float64(tnow - t.lastRdtsc)
+
+	nanosNow := int64(tDelta*t.adjustedTimeRate) + int64(t.lastRdtscNanos)
+
+	return time.Unix(0, nanosNow)
+}
+
+//
+func (t *TimeSmoother) sync(systemTime, rdtsc uint64) {
+	elapsedCycles := rdtsc - t.lastRdtsc
+	elapsedNanos := int64(systemTime) - int64(t.lastSystemTime)
+
+	nanosNow := int64(float64(elapsedCycles)*t.adjustedTimeRate) + int64(t.lastRdtscNanos) // current extrapolated time
+
+	newClock := float64(elapsedNanos) / float64(elapsedCycles)
+	t.clockSpeed = t.clockSpeedDecayRate*t.clockSpeed + (1-t.clockSpeedDecayRate)*newClock
+
+	targetSystemTime := int64(systemTime + t.syncInterval)
+	timeRate := float64(targetSystemTime-nanosNow) / t.clockSpeed
+	if timeRate < 0 {
+		timeRate = 0.0
+	}
+
+	t.adjustedTimeRate = timeRate
+	t.lastSystemTime = systemTime
+	t.lastRdtsc = rdtsc
+	t.lastRdtscNanos = uint64(nanosNow)
+}
+
+func (t *TimeSmoother) daemon() {
+	ticker := time.NewTicker(time.Duration(t.syncInterval))
+	for {
+		select {
+		case <-ticker.C:
+			systemTime := time.Now().UnixNano()
+			rdtsc := gotsc.BenchStart() - t.rdtscTime
+			t.sync(uint64(systemTime), rdtsc)
+		case <-t.stop:
+			return
+		}
+	}
+}
+
+// gets an initial estimate of the system clock speed
+func (t *TimeSmoother) initClock() {
+	sys1 := time.Now()
+	rdtsc1 := gotsc.BenchStart()
+	time.Sleep(time.Second)
+	rdtsc2 := gotsc.BenchEnd()
+	sysDelta := time.Since(sys1)
+
+	cycles := rdtsc2 - rdtsc1 - 2*t.rdtscTime
+	elapsedTime := sysDelta.Nanoseconds()
+
+	clockSpeed := float64(elapsedTime) / float64(cycles)
+	t.clockSpeed = clockSpeed
+}
+
+func NewTimeSmoother() *TimeSmoother {
+	smoother := TimeSmoother{}
+	smoother.rdtscTime = gotsc.TSCOverhead() / 2 // this function measures calling twice
+	smoother.lastSystemTime = uint64(time.Now().UnixNano())
+	smoother.lastRdtsc = gotsc.BenchStart() - smoother.rdtscTime
+	smoother.lastRdtscNanos = smoother.lastSystemTime
+
+	smoother.initClock()
+	smoother.adjustedTimeRate = smoother.clockSpeed
+
+	half_life := 10.0 // 10 second half life
+	smoother.clockSpeedDecayRate = math.Pow(2, -1.0/half_life)
+	smoother.syncInterval = 100_000_000 // 100 ms
+
+	smoother.stop = make(chan bool)
+
+	go smoother.daemon()
+
+	return &smoother
+}