text: /*
   * Copyright 2016 The Cartographer Authors
   *
   * 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.
   */
  
  #include "cartographer/common/time.h"
  
  #include <time.h>
  
  #include <cerrno>
  #include <cstring>
  #include <string>
  
  #include "glog/logging.h"
  
  namespace cartographer {
  namespace common {
  
  Duration FromSeconds(const double seconds) {
    return std::chrono::duration_cast<Duration>(
        std::chrono::duration<double>(seconds));
  }
  
  double ToSeconds(const Duration duration) {
    return std::chrono::duration_cast<std::chrono::duration<double>>(duration)
        .count();
  }
  
  double ToSeconds(const std::chrono::steady_clock::duration duration) {
    return std::chrono::duration_cast<std::chrono::duration<double>>(duration)
        .count();
  }
  
  Time FromUniversal(const int64 ticks) { return Time(Duration(ticks)); }
  
  // 转换时间戳的单位
  int64 ToUniversal(const Time time) { return time.time_since_epoch().count(); }
  
  std::ostream& operator<<(std::ostream& os, const Time time) {
    os << std::to_string(ToUniversal(time));
    return os;
  }
  
  common::Duration FromMilliseconds(const int64 milliseconds) {
    return std::chrono::duration_cast<Duration>(
        std::chrono::milliseconds(milliseconds));
  }
  
  double GetThreadCpuTimeSeconds() {
  #ifndef WIN32
    struct timespec thread_cpu_time;
    CHECK(clock_gettime(CLOCK_THREAD_CPUTIME_ID, &thread_cpu_time) == 0)
        << std::strerror(errno);
    return thread_cpu_time.tv_sec + 1e-9 * thread_cpu_time.tv_nsec;
  #else
    return 0.;
  #endif
  }
  
  }  // namespace common
  }  // namespace cartographer
  