fix timestamp encode error after some hours (#206)

previous formula was: uint32(a + uint32(b))
this formula overflows two times, while it should overflow once.
new formula is: uint32(uint64(a) + uint64(b))

pkg/rtptime/decoder_test.go

@@ -0,0 +1,96 @@
+package rtptime
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestDecoderNegativeDiff(t *testing.T) {
+	d := NewDecoder(90000)
+
+	i := uint32(0)
+	pts := d.Decode(i)
+	require.Equal(t, time.Duration(0), pts)
+
+	i += 90000 * 2
+	pts = d.Decode(i)
+	require.Equal(t, 2*time.Second, pts)
+
+	i -= 90000 * 1
+	pts = d.Decode(i)
+	require.Equal(t, 1*time.Second, pts)
+
+	i += 90000 * 2
+	pts = d.Decode(i)
+	require.Equal(t, 3*time.Second, pts)
+}
+
+func TestDecoderOverflow(t *testing.T) {
+	d := NewDecoder(90000)
+
+	i := uint32(0xFFFFFFFF - 90000 + 1)
+	secs := time.Duration(0)
+	pts := d.Decode(i)
+	require.Equal(t, time.Duration(0), pts)
+
+	const stride = 1500
+	lim := uint32(uint64(0xFFFFFFFF + 1 - (stride * 90000)))
+
+	for n := 0; n < 100; n++ {
+		// overflow
+		i += 90000 * stride
+		secs += stride
+		pts = d.Decode(i)
+		require.Equal(t, secs*time.Second, pts)
+
+		// reach 2^32 slowly
+		secs += stride
+		i += 90000 * stride
+		for ; i < lim; i += 90000 * stride {
+			pts = d.Decode(i)
+			require.Equal(t, secs*time.Second, pts)
+			secs += stride
+		}
+	}
+}
+
+func TestDecoderOverflowAndBack(t *testing.T) {
+	d := NewDecoder(90000)
+
+	pts := d.Decode(0xFFFFFFFF - 90000 + 1)
+	require.Equal(t, time.Duration(0), pts)
+
+	pts = d.Decode(90000)
+	require.Equal(t, 2*time.Second, pts)
+
+	pts = d.Decode(0xFFFFFFFF - 90000 + 1)
+	require.Equal(t, time.Duration(0), pts)
+
+	pts = d.Decode(0xFFFFFFFF - 90000 + 1 - 90000)
+	require.Equal(t, -1*time.Second, pts)
+
+	pts = d.Decode(0xFFFFFFFF - 90000 + 1)
+	require.Equal(t, time.Duration(0), pts)
+
+	pts = d.Decode(90000)
+	require.Equal(t, 2*time.Second, pts)
+}
+
+func BenchmarkDecoder(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		func() {
+			d := NewDecoder(90000)
+			n := uint32(0)
+			for j := 0; j < 200; j++ {
+				if (j % 2) == 0 {
+					n += 90000
+				} else {
+					n -= 45000
+				}
+				d.Decode(n)
+			}
+		}()
+	}
+}