From 8fb8f7b7d5e006e9bfea2468cd9cd1f545dc6915 Mon Sep 17 00:00:00 2001
From: Juliusz Chroboczek <jch@irif.fr>
Date: Sat, 2 May 2020 18:41:18 +0200
Subject: [PATCH] Implement NTP time.

---
 mono/mono.go      | 22 ++++++++++++++++++++++
 mono/mono_test.go | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/mono/mono.go b/mono/mono.go
index e17eafb..82ba5c7 100644
--- a/mono/mono.go
+++ b/mono/mono.go
@@ -10,6 +10,10 @@ func fromDuration(d time.Duration, hz uint32) uint64 {
 	return uint64(d) * uint64(hz) / uint64(time.Second)
 }
 
+func toDuration(tm uint64, hz uint32) time.Duration {
+	return time.Duration(tm * uint64(time.Second) / uint64(hz))
+}
+
 func Now(hz uint32) uint64 {
 	return fromDuration(time.Since(epoch), hz)
 }
@@ -17,3 +21,21 @@ func Now(hz uint32) uint64 {
 func Microseconds() uint64 {
 	return Now(1000000)
 }
+
+var ntpEpoch = time.Date(1900, 1, 1, 0, 0, 0, 0, time.UTC)
+
+func NTPToTime(ntp uint64) time.Time {
+	sec := uint32(ntp >> 32)
+	frac := uint32(ntp & 0xFFFFFFFF)
+	return ntpEpoch.Add(
+		time.Duration(sec) * time.Second +
+			((time.Duration(frac) * time.Second) >> 32),
+	)
+}
+
+func TimeToNTP(tm time.Time) uint64 {
+	d := tm.Sub(ntpEpoch)
+	sec := uint32(d / time.Second)
+	frac := uint32(d % time.Second)
+	return (uint64(sec) << 32) + (uint64(frac) << 32) / uint64(time.Second)
+}
diff --git a/mono/mono_test.go b/mono/mono_test.go
index f592c83..26c2e13 100644
--- a/mono/mono_test.go
+++ b/mono/mono_test.go
@@ -5,6 +5,18 @@ import (
 	"time"
 )
 
+func TestDuration(t *testing.T) {
+	a := fromDuration(time.Second, 48000)
+	if a != 48000 {
+		t.Errorf("Expected 48000, got %v", a)
+	}
+
+	b := toDuration(48000, 48000)
+	if b != time.Second {
+		t.Errorf("Expected %v, got %v", time.Second, b)
+	}
+}
+
 func differs(a, b, delta uint64) bool {
 	if a < b {
 		a, b = b, a
@@ -27,3 +39,29 @@ func TestMono(t *testing.T) {
 		t.Errorf("Expected %v, got %v", 4000, d)
 	}
 }
+
+func TestNTP(t *testing.T) {
+	now := time.Now()
+	ntp := TimeToNTP(now)
+	now2 := NTPToTime(ntp)
+	ntp2 := TimeToNTP(now2)
+
+	diff1 := now2.Sub(now)
+	if diff1 < 0 {
+		diff1 = -diff1
+	}
+	if diff1 > time.Nanosecond {
+		t.Errorf("Expected %v, got %v (diff=%v)",
+			now, now2, diff1)
+	}
+
+	diff2 := int64(ntp2 - ntp)
+	if diff2 < 0 {
+		diff2 = -diff2
+	}
+	if diff2 > (1 << 8) {
+		t.Errorf("Expected %v, got %v (diff=%v)",
+			ntp, ntp2, float64(diff2) / float64(1<<32))
+	}
+
+}