Introduce helper class NtpTime

webrtc/modules/rtp_rtcp/source/ntp_time.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_NTP_TIME_H_
+#define WEBRTC_MODULES_RTP_RTCP_SOURCE_NTP_TIME_H_
+
+#include "webrtc/base/basictypes.h"
+#include "webrtc/system_wrappers/include/clock.h"
+
+namespace webrtc {
+namespace rtcp {
+
+class NtpTime {
+ public:
+  NtpTime() : seconds_(0), fractions_(0) {}
+  explicit NtpTime(const Clock& clock) {
+    clock.CurrentNtp(seconds_, fractions_);
+  }
+  NtpTime(uint32_t seconds, uint32_t fractions)
+      : seconds_(seconds), fractions_(fractions) {}
+
+  NtpTime(const NtpTime&) = default;
+  NtpTime& operator=(const NtpTime&) = default;
+
+  void SetCurrent(const Clock& clock) {
+    clock.CurrentNtp(seconds_, fractions_);
+  }
+  void Set(uint32_t seconds, uint32_t fractions) {
+    seconds_ = seconds;
+    fractions_ = fractions;
+  }
+  void clear() { seconds_ = fractions_ = 0; }

[sprang_webrtc, 2015/11/12 15:34:48]

Assign separately

[danilchap, 2015/11/12 19:05:31]

Done.

+
+  int64_t ToMs() const { return Clock::NtpToMs(seconds_, fractions_); }
+  uint32_t MidNtp() const { return (seconds_ << 16) | (fractions_ >> 16); }

[sprang_webrtc, 2015/11/12 15:34:48]

I think this one deserves a comment :)

[danilchap, 2015/11/12 19:05:31]

(bad excuse)RTCPUtility::MidNtp I took this from don't have one :)

this one seems RTP specific (mentioned in rfc3611, section 4.5 dlrr report
block, LRR and DLRR). Used to calculate delays (so do not use full scale and
full precision of the ntp time)

[sprang_webrtc, 2015/11/16 09:55:25]

Ah, so great that we get one now!

+
+  // Conversion to bool to test if we have a valid value.
+  explicit operator bool() const { return seconds_ != 0 || fractions_ != 0; }

[sprang_webrtc, 2015/11/12 15:34:48]

When would this be used? Are we implicitly saying time 0 is not a valid number?
I think testing for equality with NtpTime(0, 0) would be more clear in that
case, or the use of rtc::Otional for instance.

[danilchap, 2015/11/12 19:05:31]

To make it more explicit conversion to bool replaced with function 'valid'.

This kind of test used in RtcpReciver to check if NtpTime was ever received. 
According to NTP standard value 0/0 considered invalid.
RFC1305, Data format section:  "There will exist an 200-picosecond interval,
henceforth ignored, every 136 years when the 64-bit field will be zero and thus
considered invalid."

[sprang_webrtc, 2015/11/16 09:55:25]

Gotcha. A comment to that affect would be great. :)

[danilchap, 2015/11/16 11:01:33]

Done.

+
+  uint32_t seconds() const { return seconds_; }
+  uint32_t fractions() const { return fractions_; }
+
+ private:
+  uint32_t seconds_;
+  uint32_t fractions_;
+};
+
+}  // namespace rtcp
+}  // namespace webrtc
+#endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_NTP_TIME_H_