Change to calculate the real NTP in TimeTicks.

media/cast/cast_defines.h

Index: media/cast/cast_defines.h
diff --git a/media/cast/cast_defines.h b/media/cast/cast_defines.h
index 0778638551eec7f9559bb5e6190549c396a90baf..2e0b3acf62e59cc54cc33bdc3d388fd37d7fec22 100644
--- a/media/cast/cast_defines.h
+++ b/media/cast/cast_defines.h
@@ -54,16 +54,15 @@ typedef std::map<uint8, PacketIdSet> MissingFramesAndPacketsMap;
 // TODO(pwestin): Re-factor the functions bellow into a class with static
 // methods.
 
+// January 1970, in NTP seconds.
+// Network Time Protocol (NTP), which is in seconds relative to 0h UTC on
+// 1 January 1900.
+static const int64 kUnixEpochInNtpSeconds = GG_INT64_C(2208988800);
+
 // Magic fractional unit. Used to convert time (in microseconds) to/from
 // fractional NTP seconds.
 static const double kMagicFractionalUnit = 4.294967296E3;
 
-// Network Time Protocol (NTP), which is in seconds relative to 0h UTC on
-// 1 January 1900.
-static const int64 kNtpEpochDeltaSeconds = GG_INT64_C(9435484800);
-static const int64 kNtpEpochDeltaMicroseconds =
-    kNtpEpochDeltaSeconds * base::Time::kMicrosecondsPerSecond;
-
 inline bool IsNewerFrameId(uint8 frame_id, uint8 prev_frame_id) {
   return (frame_id != prev_frame_id) &&
       static_cast<uint8>(frame_id - prev_frame_id) < 0x80;
@@ -107,20 +106,24 @@ inline void ConvertTimeToFractions(int64 time_us,
       (time_us % base::Time::kMicrosecondsPerSecond) * kMagicFractionalUnit);
 }
 
-inline void ConvertTimeToNtp(const base::TimeTicks& time,
-                             uint32* ntp_seconds,
-                             uint32* ntp_fractions) {
-  int64 time_us = time.ToInternalValue() - kNtpEpochDeltaMicroseconds;
-  ConvertTimeToFractions(time_us, ntp_seconds, ntp_fractions);
+inline void ConvertTimeTicksToNtp(const base::TimeTicks& time,
+                                  uint32* ntp_seconds,
+                                  uint32* ntp_fractions) {
+  base::TimeDelta elapsed_since_unix_epoch =
+      time - base::TimeTicks::UnixEpoch();
+
+  int64 ntp_time_us = elapsed_since_unix_epoch.InMicroseconds() +
+      (kUnixEpochInNtpSeconds * base::Time::kMicrosecondsPerSecond);
+
+  ConvertTimeToFractions(ntp_time_us, ntp_seconds, ntp_fractions);
 }
 
-inline base::TimeTicks ConvertNtpToTime(uint32 ntp_seconds,
-                                        uint32 ntp_fractions) {
+inline base::TimeTicks ConvertNtpToTimeTicks(uint32 ntp_seconds,
+                                             uint32 ntp_fractions) {
   int64 ntp_time_us = static_cast<int64>(ntp_seconds) *
-       base::Time::kMicrosecondsPerSecond;
+      base::Time::kMicrosecondsPerSecond;
   ntp_time_us += static_cast<int64>(ntp_fractions) / kMagicFractionalUnit;
-  return base::TimeTicks::FromInternalValue(ntp_time_us +
-      kNtpEpochDeltaMicroseconds);
+  return base::TimeTicks() + base::TimeDelta::FromMicroseconds(ntp_time_us);

[miu, 2013/10/30 19:33:35]

This reverse conversion needs to map NTP time back to UNIX time, and then
convert to TimeTicks using TimeTicks::UnixEpoch().  Something like:

  base::TimeDelta elapsed_since_unix_epoch = base::TimeDelta::FromMicroseconds(
      ntp_time_us - (kUnixEpochInNtpSeconds *
base::Time::kMicrosecondsPerSecond));
  return base::TimeTicks::UnixEpoch() + elapsed_since_unix_epoch;

It would be helpful if there was a unit test somewhere that demonstrated these
functions are inverses of each other.  RtcpTest.NtpAndTime only tests that the
deltas are computed correctly.

[pwestin, 2013/10/30 23:14:30]

Done.

 }
 
 }  // namespace cast