[rtp_rtcp] time helper functions

webrtc/modules/rtp_rtcp/source/time_util.h

+/*
+ *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_MODULES_RTP_RTCP_SOURCE_TIME_UTIL_H_
+#define WEBRTC_MODULES_RTP_RTCP_SOURCE_TIME_UTIL_H_
+
+#include "webrtc/base/basictypes.h"
+#include "webrtc/system_wrappers/include/ntp_time.h"
+
+namespace webrtc {
+
+// Converts NTP timestamp to RTP timestamp.
+inline uint32_t NtpToRtp(NtpTime ntp, uint32_t freq) {
+  uint32_t tmp = (static_cast<uint64_t>(ntp.fractions()) * freq) >> 32;
+  return ntp.seconds() * freq + tmp;
+}
+// Return the current RTP timestamp from the NTP timestamp
+// returned by the specified clock.
+inline uint32_t CurrentRtp(const Clock& clock, uint32_t freq) {
+  return NtpToRtp(NtpTime(clock), freq);
+}
+
+// Helper function for compact ntp representation:
+// RFC 3550, Section 4. Time Format.
+// Wallclock time is represented using the timestamp format of
+// the Network Time Protocol (NTP).
+// ...
+// In some fields where a more compact representation is
+// appropriate, only the middle 32 bits are used; that is, the low 16
+// bits of the integer part and the high 16 bits of the fractional part.
+inline uint32_t CompactNtp(NtpTime ntp) {
+  return (ntp.seconds() << 16) | (ntp.fractions() >> 16);
+}

[åsapersson, 2015/12/21 15:16:20]

Maybe add a comment that a Ntp difference up to ~18 hours should convert
correctly.

[danilchap, 2015/12/21 16:14:34]

Done.

+inline uint32_t CompactNtpIntervalToMs(uint32_t ntp) {

[åsapersson, 2015/12/21 15:16:20]

call this ntp_diff?

[danilchap, 2015/12/21 16:14:34]

good idea. Called it compact_ntp_interval:
compact_ to stress it is not a difference between full-scale ntp timestamps.
_interval instead of _diff because diff feels like only two values could be
involved, but there is code where it is calculated from 3 values (rtt = received
- delay - send; received and send are timestamps and delay is an interval).

+  return static_cast<uint64_t>(ntp) * 1000 / (1 << 16);
+}
+
+}  // namespace webrtc
+#endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_TIME_UTIL_H_