cast/streaming/ntp_time.cc

// Copyright 2019 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "cast/streaming/ntp_time.h"

#include "util/osp_logging.h"

namespace openscreen {
namespace cast {

namespace {

// The number of seconds between 1 January 1900 and 1 January 1970.
constexpr NtpSeconds kTimeBetweenNtpEpochAndUnixEpoch{INT64_C(2208988800)};

}  // namespace

NtpTimeConverter::NtpTimeConverter(Clock::time_point now,
                                   std::chrono::seconds since_unix_epoch)
    : start_time_(now),
      since_ntp_epoch_(
          std::chrono::duration_cast<NtpSeconds>(since_unix_epoch) +
          kTimeBetweenNtpEpochAndUnixEpoch) {}

NtpTimeConverter::~NtpTimeConverter() = default;

NtpTimestamp NtpTimeConverter::ToNtpTimestamp(
    Clock::time_point time_point) const {
  const Clock::duration time_since_start = time_point - start_time_;
  const auto whole_seconds =
      std::chrono::duration_cast<NtpSeconds>(time_since_start);
  const auto remainder =
      std::chrono::duration_cast<NtpFraction>(time_since_start - whole_seconds);
  return AssembleNtpTimestamp(since_ntp_epoch_ + whole_seconds, remainder);
}

Clock::time_point NtpTimeConverter::ToLocalTime(NtpTimestamp timestamp) const {
  auto ntp_seconds = NtpSecondsPart(timestamp);
  // Year 2036 wrap-around check: If the NTP timestamp appears to be a
  // point-in-time before 1970, assume the 2036 wrap-around has occurred, and
  // adjust to compensate.
  if (ntp_seconds <= kTimeBetweenNtpEpochAndUnixEpoch) {
    constexpr NtpSeconds kNtpSecondsPerEra{INT64_C(1) << 32};
    ntp_seconds += kNtpSecondsPerEra;
  }

  const auto whole_seconds = ntp_seconds - since_ntp_epoch_;
  const auto seconds_since_start =
      Clock::to_duration(whole_seconds) + start_time_;
  const auto remainder = Clock::to_duration(NtpFractionPart(timestamp));
  return seconds_since_start + remainder;
}

}  // namespace cast
}  // namespace openscreen