text: /******************************************************************************
  * Copyright Authors DustinKsi@ Youibot 2019. All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  * http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  *****************************************************************************/
  
  #pragma once
  
  #include <chrono>
  #include <ostream>
  #include <ratio>
  
  #include "dsfmapping/common/port.h"
  
  namespace DsFMapping {
  namespace common {
  
  constexpr int64 kUtsEpochOffsetFromUnixEpochInSeconds = (719162ll * 24ll * 60ll * 60ll);
  
  struct UniversalTimeScaleClock {
    using rep = int64;
    using period = std::ratio<1, 10000000>;
    using duration = std::chrono::duration<rep, period>;
    using time_point = std::chrono::time_point<UniversalTimeScaleClock>;
    static constexpr bool is_steady = true;
  };
  
  // Represents Universal Time Scale durations and timestamps which are 64-bit
  // integers representing the 100 nanosecond ticks since the Epoch which is
  // January 1, 1 at the start of day in UTC.
  using Duration = UniversalTimeScaleClock::duration;
  using Time = UniversalTimeScaleClock::time_point;
  
  // Convenience functions to create common::Durations.
  Duration FromSeconds(double seconds);
  Duration FromMilliseconds(int64 milliseconds);
  
  // Returns the given duration in seconds.
  double ToSeconds(Duration duration);
  double ToSeconds(std::chrono::steady_clock::duration duration);
  
  // Creates a time from a Universal Time Scale.
  Time FromUniversal(int64 ticks);
  
  // Outputs the Universal Time Scale timestamp for a given Time.
  int64 ToUniversal(Time time);
  
  // For logging and unit tests, outputs the timestamp integer.
  std::ostream& operator<<(std::ostream& os, Time time);
  
  // CPU time consumed by the thread so far, in seconds.
  double GetThreadCpuTimeSeconds();
  
  }  // namespace common
  }  // namespace DsFMapping
  
  // 	    * ^          ^ *
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