text: // Copyright (c) 2012 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.
  
  // Time represents an absolute point in coordinated universal time (UTC),
  // internally represented as microseconds (s/1,000,000) since the Windows epoch
  // (1601-01-01 00:00:00 UTC) (See http://crbug.com/14734).  System-dependent
  // clock interface routines are defined in time_PLATFORM.cc.
  //
  // TimeDelta represents a duration of time, internally represented in
  // microseconds.
  //
  // TimeTicks represents an abstract time that is most of the time incrementing
  // for use in measuring time durations. It is internally represented in
  // microseconds.  It can not be converted to a human-readable time, but is
  // guaranteed not to decrease (if the user changes the computer clock,
  // Time::Now() may actually decrease or jump).  But note that TimeTicks may
  // "stand still", for example if the computer suspended.
  //
  // These classes are represented as only a 64-bit value, so they can be
  // efficiently passed by value.
  
  #ifndef BUTIL_TIME_TIME_H_
  #define BUTIL_TIME_TIME_H_
  
  #include <time.h>
  
  #include "butil/base_export.h"
  #include "butil/basictypes.h"
  #include "butil/build_config.h"
  
  #if defined(OS_MACOSX)
  #include <CoreFoundation/CoreFoundation.h>
  // Avoid Mac system header macro leak.
  #undef TYPE_BOOL
  #endif
  
  #if defined(OS_POSIX)
  #include <unistd.h>
  #include <sys/time.h>
  #endif
  
  #if defined(OS_WIN)
  // For FILETIME in FromFileTime, until it moves to a new converter class.
  // See TODO(iyengar) below.
  #include <windows.h>
  #endif
  
  #include <limits>
  
  #ifdef BAIDU_INTERNAL
  // gejun: Force inclusion of ul_def.h and undef conflict macros
  #include <ul_def.h>
  #undef Uchar
  #undef Ushort
  #undef Uint
  #undef Max
  #undef Min
  #undef Exchange
  #endif // BAIDU_INTERNAL
  
  namespace butil {
  
  class Time;
  class TimeTicks;
  
  // TimeDelta ------------------------------------------------------------------
  
  class BUTIL_EXPORT TimeDelta {
   public:
    TimeDelta() : delta_(0) {
    }
  
    // Required by clang++ 11 on MacOS catalina
    TimeDelta(const TimeDelta& other) : delta_(other.delta_) {}
  
    // Converts units of time to TimeDeltas.
    static TimeDelta FromDays(int days);
    static TimeDelta FromHours(int hours);
    static TimeDelta FromMinutes(int minutes);
    static TimeDelta FromSeconds(int64_t secs);
    static TimeDelta FromMilliseconds(int64_t ms);
    static TimeDelta FromMicroseconds(int64_t us);
    static TimeDelta FromSecondsD(double secs);
    static TimeDelta FromMillisecondsD(double ms);
    static TimeDelta FromMicrosecondsD(double us);
  
  #if defined(OS_WIN)
    static TimeDelta FromQPCValue(LONGLONG qpc_value);
  #endif
  
    // Converts an integer value representing TimeDelta to a class. This is used
    // when deserializing a |TimeDelta| structure, using a value known to be
    // compatible. It is not provided as a constructor because the integer type
    // may be unclear from the perspective of a caller.
    static TimeDelta FromInternalValue(int64_t delta) {
      return TimeDelta(delta);
    }
  
    // Returns the maximum time delta, which should be greater than any reasonable
    // time delta we might compare it to. Adding or subtracting the maximum time
    // delta to a time or another time delta has an undefined result.
    static TimeDelta Max();
  
    // Returns the internal numeric value of the TimeDelta object. Please don't
    // use this and do arithmetic on it, as it is more error prone than using the
    // provided operators.
    // For serializing, use FromInternalValue to reconstitute.
    int64_t ToInternalValue() const {
      return delta_;
    }
  
    // Returns true if the time delta is the maximum time delta.
    bool is_max() const {
      return delta_ == std::numeric_limits<int64_t>::max();
    }
  
  #if defined(OS_POSIX)
    struct timespec ToTimeSpec() const;
  #endif
  
    // Returns the time delta in some unit. The F versions return a floating
    // point value, the "regular" versions return a rounded-down value.
    //
    // InMillisecondsRoundedUp() instead returns an integer that is rounded up
    // to the next full millisecond.
    int InDays() const;
    int InHours() const;
    int InMinutes() const;
    double InSecondsF() const;
    int64_t InSeconds() const;
    double InMillisecondsF() const;
    int64_t InMilliseconds() const;
    int64_t InMillisecondsRoundedUp() const;
    int64_t InMicroseconds() const;
  
    TimeDelta& operator=(TimeDelta other) {
      delta_ = other.delta_;
      return *this;
    }
  
    // Computations with other deltas.
    TimeDelta operator+(TimeDelta other) const {
      return TimeDelta(delta_ + other.delta_);
    }
    TimeDelta operator-(TimeDelta other) const {
      return TimeDelta(delta_ - other.delta_);
    }
  
    TimeDelta& operator+=(TimeDelta other) {
      delta_ += other.delta_;
      return *this;
    }
    TimeDelta& operator-=(TimeDelta other) {
      delta_ -= other.delta_;
      return *this;
    }
    TimeDelta operator-() const {
      return TimeDelta(-delta_);
    }
  
    // Computations with ints, note that we only allow multiplicative operations
    // with ints, and additive operations with other deltas.
    TimeDelta operator*(int64_t a) const {
      return TimeDelta(delta_ * a);
    }
    TimeDelta operator/(int64_t a) const {
      return TimeDelta(delta_ / a);
    }
    TimeDelta& operator*=(int64_t a) {
      delta_ *= a;
      return *this;
    }
    TimeDelta& operator/=(int64_t a) {
      delta_ /= a;
      return *this;
    }
    int64_t operator/(TimeDelta a) const {
      return delta_ / a.delta_;
    }
  
    // Defined below because it depends on the definition of the other classes.
    Time operator+(Time t) const;
    TimeTicks operator+(TimeTicks t) const;
  
    // Comparison operators.
    bool operator==(TimeDelta other) const {
      return delta_ == other.delta_;
    }
    bool operator!=(TimeDelta other) const {
      return delta_ != other.delta_;
    }
    bool operator<(TimeDelta other) const {
      return delta_ < other.delta_;
    }
    bool operator<=(TimeDelta other) const {
      return delta_ <= other.delta_;
    }
    bool operator>(TimeDelta other) const {
      return delta_ > other.delta_;
    }
    bool operator>=(TimeDelta other) const {
      return delta_ >= other.delta_;
    }
  
   private:
    friend class Time;
    friend class TimeTicks;
    friend TimeDelta operator*(int64_t a, TimeDelta td);
  
    // Constructs a delta given the duration in microseconds. This is private
    // to avoid confusion by callers with an integer constructor. Use
    // FromSeconds, FromMilliseconds, etc. instead.
    explicit TimeDelta(int64_t delta_us) : delta_(delta_us) {
    }
  
    // Delta in microseconds.
    int64_t delta_;
  };
  
  inline TimeDelta operator*(int64_t a, TimeDelta td) {
    return TimeDelta(a * td.delta_);
  }
  
  // Time -----------------------------------------------------------------------
  
  // Represents a wall clock time in UTC.
  class BUTIL_EXPORT Time {
   public:
    static const int64_t kMillisecondsPerSecond = 1000;
    static const int64_t kMicrosecondsPerMillisecond = 1000;
    static const int64_t kMicrosecondsPerSecond = kMicrosecondsPerMillisecond *
                                                kMillisecondsPerSecond;
    static const int64_t kMicrosecondsPerMinute = kMicrosecondsPerSecond * 60;
    static const int64_t kMicrosecondsPerHour = kMicrosecondsPerMinute * 60;
    static const int64_t kMicrosecondsPerDay = kMicrosecondsPerHour * 24;
    static const int64_t kMicrosecondsPerWeek = kMicrosecondsPerDay * 7;
    static const int64_t kNanosecondsPerMicrosecond = 1000;
    static const int64_t kNanosecondsPerSecond = kNanosecondsPerMicrosecond *
                                               kMicrosecondsPerSecond;
  
  #if !defined(OS_WIN)
    // On Mac & Linux, this value is the delta from the Windows epoch of 1601 to
    // the Posix delta of 1970. This is used for migrating between the old
    // 1970-based epochs to the new 1601-based ones. It should be removed from
    // this global header and put in the platform-specific ones when we remove the
    // migration code.
    static const int64_t kWindowsEpochDeltaMicroseconds;
  #endif
  
    // Represents an exploded time that can be formatted nicely. This is kind of
    // like the Win32 SYSTEMTIME structure or the Unix "struct tm" with a few
    // additions and changes to prevent errors.
    struct BUTIL_EXPORT Exploded {
      int year;          // Four digit year "2007"
      int month;         // 1-based month (values 1 = January, etc.)
      int day_of_week;   // 0-based day of week (0 = Sunday, etc.)
      int day_of_month;  // 1-based day of month (1-31)
      int hour;          // Hour within the current day (0-23)
      int minute;        // Minute within the current hour (0-59)
      int second;        // Second within the current minute (0-59 plus leap
                         //   seconds which may take it up to 60).
      int millisecond;   // Milliseconds within the current second (0-999)
  
      // A cursory test for whether the data members are within their
      // respective ranges. A 'true' return value does not guarantee the
      // Exploded value can be successfully converted to a Time value.
      bool HasValidValues() const;
    };
  
    // Contains the NULL time. Use Time::Now() to get the current time.
    Time() : us_(0) {
    }
  
    // Required by clang++ 11 on MacOS catalina
    Time(const Time& other) : us_(other.us_) {}
  
    // Returns true if the time object has not been initialized.
    bool is_null() const {
      return us_ == 0;
    }
  
    // Returns true if the time object is the maximum time.
    bool is_max() const {
      return us_ == std::numeric_limits<int64_t>::max();
    }
  
    // Returns the time for epoch in Unix-like system (Jan 1, 1970).
    static Time UnixEpoch();
  
    // Returns the current time. Watch out, the system might adjust its clock
    // in which case time will actually go backwards. We don't guarantee that
    // times are increasing, or that two calls to Now() won't be the same.
    static Time Now();
  
    // Returns the maximum time, which should be greater than any reasonable time
    // with which we might compare it.
    static Time Max();
  
    // Returns the current time. Same as Now() except that this function always
    // uses system time so that there are no discrepancies between the returned
    // time and system time even on virtual environments including our test bot.
    // For timing sensitive unittests, this function should be used.
    static Time NowFromSystemTime();
  
    // Converts to/from time_t in UTC and a Time class.
    // TODO(brettw) this should be removed once everybody starts using the |Time|
    // class.
    static Time FromTimeT(time_t tt);
    time_t ToTimeT() const;
  
    // Converts time to/from a double which is the number of seconds since epoch
    // (Jan 1, 1970).  Webkit uses this format to represent time.
    // Because WebKit initializes double time value to 0 to indicate "not
    // initialized", we map it to empty Time object that also means "not
    // initialized".
    static Time FromDoubleT(double dt);
    double ToDoubleT() const;
  
  #if defined(OS_POSIX)
    // Converts the timespec structure to time. MacOS X 10.8.3 (and tentatively,
    // earlier versions) will have the |ts|'s tv_nsec component zeroed out,
    // having a 1 second resolution, which agrees with
    // https://developer.apple.com/legacy/library/#technotes/tn/tn1150.html#HFSPlusDates.
    static Time FromTimeSpec(const timespec& ts);
  #endif
  
    // Converts to/from the Javascript convention for times, a number of
    // milliseconds since the epoch:
    // https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date/getTime.
    static Time FromJsTime(double ms_since_epoch);
    double ToJsTime() const;
  
    // Converts to Java convention for times, a number of
    // milliseconds since the epoch.
    int64_t ToJavaTime() const;
  
  #if defined(OS_POSIX)
    static Time FromTimeVal(struct timeval t);
    struct timeval ToTimeVal() const;
  #endif
  
  #if defined(OS_MACOSX)
    static Time FromCFAbsoluteTime(CFAbsoluteTime t);
    CFAbsoluteTime ToCFAbsoluteTime() const;
  #endif
  
  #if defined(OS_WIN)
    static Time FromFileTime(FILETIME ft);
    FILETIME ToFileTime() const;
  
    // The minimum time of a low resolution timer.  This is basically a windows
    // constant of ~15.6ms.  While it does vary on some older OS versions, we'll
    // treat it as static across all windows versions.
    static const int kMinLowResolutionThresholdMs = 16;
  
    // Enable or disable Windows high resolution timer. If the high resolution
    // timer is not enabled, calls to ActivateHighResolutionTimer will fail.
    // When disabling the high resolution timer, this function will not cause
    // the high resolution timer to be deactivated, but will prevent future
    // activations.
    // Must be called from the main thread.
    // For more details see comments in time_win.cc.
    static void EnableHighResolutionTimer(bool enable);
  
    // Activates or deactivates the high resolution timer based on the |activate|
    // flag.  If the HighResolutionTimer is not Enabled (see
    // EnableHighResolutionTimer), this function will return false.  Otherwise
    // returns true.  Each successful activate call must be paired with a
    // subsequent deactivate call.
    // All callers to activate the high resolution timer must eventually call
    // this function to deactivate the high resolution timer.
    static bool ActivateHighResolutionTimer(bool activate);
  
    // Returns true if the high resolution timer is both enabled and activated.
    // This is provided for testing only, and is not tracked in a thread-safe
    // way.
    static bool IsHighResolutionTimerInUse();
  #endif
  
    // Converts an exploded structure representing either the local time or UTC
    // into a Time class.
    static Time FromUTCExploded(const Exploded& exploded) {
      return FromExploded(false, exploded);
    }
    static Time FromLocalExploded(const Exploded& exploded) {
      return FromExploded(true, exploded);
    }
  
    // Converts an integer value representing Time to a class. This is used
    // when deserializing a |Time| structure, using a value known to be
    // compatible. It is not provided as a constructor because the integer type
    // may be unclear from the perspective of a caller.
    static Time FromInternalValue(int64_t us) {
      return Time(us);
    }
  
    // Converts a string representation of time to a Time object.
    // An example of a time string which is converted is as below:-
    // "Tue, 15 Nov 1994 12:45:26 GMT". If the timezone is not specified
    // in the input string, FromString assumes local time and FromUTCString
    // assumes UTC. A timezone that cannot be parsed (e.g. "UTC" which is not
    // specified in RFC822) is treated as if the timezone is not specified.
    // TODO(iyengar) Move the FromString/FromTimeT/ToTimeT/FromFileTime to
    // a new time converter class.
    static bool FromString(const char* time_string, Time* parsed_time) {
      return FromStringInternal(time_string, true, parsed_time);
    }
    static bool FromUTCString(const char* time_string, Time* parsed_time) {
      return FromStringInternal(time_string, false, parsed_time);
    }
  
    // For serializing, use FromInternalValue to reconstitute. Please don't use
    // this and do arithmetic on it, as it is more error prone than using the
    // provided operators.
    int64_t ToInternalValue() const {
      return us_;
    }
  
    // Fills the given exploded structure with either the local time or UTC from
    // this time structure (containing UTC).
    void UTCExplode(Exploded* exploded) const {
      return Explode(false, exploded);
    }
    void LocalExplode(Exploded* exploded) const {
      return Explode(true, exploded);
    }
  
    // Rounds this time down to the nearest day in local time. It will represent
    // midnight on that day.
    Time LocalMidnight() const;
  
    Time& operator=(Time other) {
      us_ = other.us_;
      return *this;
    }
  
    // Compute the difference between two times.
    TimeDelta operator-(Time other) const {
      return TimeDelta(us_ - other.us_);
    }
  
    // Modify by some time delta.
    Time& operator+=(TimeDelta delta) {
      us_ += delta.delta_;
      return *this;
    }
    Time& operator-=(TimeDelta delta) {
      us_ -= delta.delta_;
      return *this;
    }
  
    // Return a new time modified by some delta.
    Time operator+(TimeDelta delta) const {
      return Time(us_ + delta.delta_);
    }
    Time operator-(TimeDelta delta) const {
      return Time(us_ - delta.delta_);
    }
  
    // Comparison operators
    bool operator==(Time other) const {
      return us_ == other.us_;
    }
    bool operator!=(Time other) const {
      return us_ != other.us_;
    }
    bool operator<(Time other) const {
      return us_ < other.us_;
    }
    bool operator<=(Time other) const {
      return us_ <= other.us_;
    }
    bool operator>(Time other) const {
      return us_ > other.us_;
    }
    bool operator>=(Time other) const {
      return us_ >= other.us_;
    }
  
   private:
    friend class TimeDelta;
  
    explicit Time(int64_t us) : us_(us) {
    }
  
    // Explodes the given time to either local time |is_local = true| or UTC
    // |is_local = false|.
    void Explode(bool is_local, Exploded* exploded) const;
  
    // Unexplodes a given time assuming the source is either local time
    // |is_local = true| or UTC |is_local = false|.
    static Time FromExploded(bool is_local, const Exploded& exploded);
  
    // Converts a string representation of time to a Time object.
    // An example of a time string which is converted is as below:-
    // "Tue, 15 Nov 1994 12:45:26 GMT". If the timezone is not specified
    // in the input string, local time |is_local = true| or
    // UTC |is_local = false| is assumed. A timezone that cannot be parsed
    // (e.g. "UTC" which is not specified in RFC822) is treated as if the
    // timezone is not specified.
    static bool FromStringInternal(const char* time_string,
                                   bool is_local,
                                   Time* parsed_time);
  
    // The representation of Jan 1, 1970 UTC in microseconds since the
    // platform-dependent epoch.
    static const int64_t kTimeTToMicrosecondsOffset;
  
  #if defined(OS_WIN)
    // Indicates whether fast timers are usable right now.  For instance,
    // when using battery power, we might elect to prevent high speed timers
    // which would draw more power.
    static bool high_resolution_timer_enabled_;
    // Count of activations on the high resolution timer.  Only use in tests
    // which are single threaded.
    static int high_resolution_timer_activated_;
  #endif
  
    // Time in microseconds in UTC.
    int64_t us_;
  };
  
  // Inline the TimeDelta factory methods, for fast TimeDelta construction.
  
  // static
  inline TimeDelta TimeDelta::FromDays(int days) {
    // Preserve max to prevent overflow.
    if (days == std::numeric_limits<int>::max())
      return Max();
    return TimeDelta(days * Time::kMicrosecondsPerDay);
  }
  
  // static
  inline TimeDelta TimeDelta::FromHours(int hours) {
    // Preserve max to prevent overflow.
    if (hours == std::numeric_limits<int>::max())
      return Max();
    return TimeDelta(hours * Time::kMicrosecondsPerHour);
  }
  
  // static
  inline TimeDelta TimeDelta::FromMinutes(int minutes) {
    // Preserve max to prevent overflow.
    if (minutes == std::numeric_limits<int>::max())
      return Max();
    return TimeDelta(minutes * Time::kMicrosecondsPerMinute);
  }
  
  // static
  inline TimeDelta TimeDelta::FromSeconds(int64_t secs) {
    // Preserve max to prevent overflow.
    if (secs == std::numeric_limits<int64_t>::max())
      return Max();
    return TimeDelta(secs * Time::kMicrosecondsPerSecond);
  }
  
  // static
  inline TimeDelta TimeDelta::FromMilliseconds(int64_t ms) {
    // Preserve max to prevent overflow.
    if (ms == std::numeric_limits<int64_t>::max())
      return Max();
    return TimeDelta(ms * Time::kMicrosecondsPerMillisecond);
  }
  
  // static
  inline TimeDelta TimeDelta::FromSecondsD(double secs) {
    // Preserve max to prevent overflow.
    if (secs == std::numeric_limits<double>::infinity())
      return Max();
    return TimeDelta((int64_t)(secs * Time::kMicrosecondsPerSecond));
  }
  
  // static
  inline TimeDelta TimeDelta::FromMillisecondsD(double ms) {
    // Preserve max to prevent overflow.
    if (ms == std::numeric_limits<double>::infinity())
      return Max();
    return TimeDelta((int64_t)(ms * Time::kMicrosecondsPerMillisecond));
  }
  
  // static
  inline TimeDelta TimeDelta::FromMicroseconds(int64_t us) {
    // Preserve max to prevent overflow.
    if (us == std::numeric_limits<int64_t>::max())
      return Max();
    return TimeDelta(us);
  }
  
  // static
  inline TimeDelta TimeDelta::FromMicrosecondsD(double us) {
    // Preserve max to prevent overflow.
    if (us == std::numeric_limits<double>::infinity())
      return Max();
    return TimeDelta((int64_t)us);
  }
  
  inline Time TimeDelta::operator+(Time t) const {
    return Time(t.us_ + delta_);
  }
  
  // TimeTicks ------------------------------------------------------------------
  
  class BUTIL_EXPORT TimeTicks {
   public:
    // We define this even without OS_CHROMEOS for seccomp sandbox testing.
  #if defined(OS_LINUX)
    // Force definition of the system trace clock; it is a chromeos-only api
    // at the moment and surfacing it in the right place requires mucking
    // with glibc et al.
    static const clockid_t kClockSystemTrace = 11;
  #endif
  
    TimeTicks() : ticks_(0) {
    }
  
    // Required by clang++ 11 on MacOS catalina
    TimeTicks(const TimeTicks& other) : ticks_(other.ticks_) {}
  
    // Platform-dependent tick count representing "right now."
    // The resolution of this clock is ~1-15ms.  Resolution varies depending
    // on hardware/operating system configuration.
    static TimeTicks Now();
  
    // Returns a platform-dependent high-resolution tick count. Implementation
    // is hardware dependent and may or may not return sub-millisecond
    // resolution.  THIS CALL IS GENERALLY MUCH MORE EXPENSIVE THAN Now() AND
    // SHOULD ONLY BE USED WHEN IT IS REALLY NEEDED.
    static TimeTicks HighResNow();
  
    static bool IsHighResNowFastAndReliable();
  
    // FIXME(gejun): CLOCK_THREAD_CPUTIME_ID behaves differently in different
    // glibc. To avoid potential bug, disable ThreadNow() always.
    // Returns true if ThreadNow() is supported on this system.
    static bool IsThreadNowSupported() {
        return false;
    }
  
    // Returns thread-specific CPU-time on systems that support this feature.
    // Needs to be guarded with a call to IsThreadNowSupported(). Use this timer
    // to (approximately) measure how much time the calling thread spent doing
    // actual work vs. being de-scheduled. May return bogus results if the thread
    // migrates to another CPU between two calls.
    static TimeTicks ThreadNow();
  
    // Returns the current system trace time or, if none is defined, the current
    // high-res time (i.e. HighResNow()). On systems where a global trace clock
    // is defined, timestamping TraceEvents's with this value guarantees
    // synchronization between events collected inside chrome and events
    // collected outside (e.g. kernel, X server).
    static TimeTicks NowFromSystemTraceTime();
  
  #if defined(OS_WIN)
    // Get the absolute value of QPC time drift. For testing.
    static int64_t GetQPCDriftMicroseconds();
  
    static TimeTicks FromQPCValue(LONGLONG qpc_value);
  
    // Returns true if the high resolution clock is working on this system.
    // This is only for testing.
    static bool IsHighResClockWorking();
  
    // Enable high resolution time for TimeTicks::Now(). This function will
    // test for the availability of a working implementation of
    // QueryPerformanceCounter(). If one is not available, this function does
    // nothing and the resolution of Now() remains 1ms. Otherwise, all future
    // calls to TimeTicks::Now() will have the higher resolution provided by QPC.
    // Returns true if high resolution time was successfully enabled.
    static bool SetNowIsHighResNowIfSupported();
  
    // Returns a time value that is NOT rollover protected.
    static TimeTicks UnprotectedNow();
  #endif
  
    // Returns true if this object has not been initialized.
    bool is_null() const {
      return ticks_ == 0;
    }
  
    // Converts an integer value representing TimeTicks to a class. This is used
    // when deserializing a |TimeTicks| structure, using a value known to be
    // compatible. It is not provided as a constructor because the integer type
    // may be unclear from the perspective of a caller.
    static TimeTicks FromInternalValue(int64_t ticks) {
      return TimeTicks(ticks);
    }
  
    // Get the TimeTick value at the time of the UnixEpoch. This is useful when
    // you need to relate the value of TimeTicks to a real time and date.
    // Note: Upon first invocation, this function takes a snapshot of the realtime
    // clock to establish a reference point.  This function will return the same
    // value for the duration of the application, but will be different in future
    // application runs.
    static TimeTicks UnixEpoch();
  
    // Returns the internal numeric value of the TimeTicks object.
    // For serializing, use FromInternalValue to reconstitute.
    int64_t ToInternalValue() const {
      return ticks_;
    }
  
    TimeTicks& operator=(TimeTicks other) {
      ticks_ = other.ticks_;
      return *this;
    }
  
    // Compute the difference between two times.
    TimeDelta operator-(TimeTicks other) const {
      return TimeDelta(ticks_ - other.ticks_);
    }
  
    // Modify by some time delta.
    TimeTicks& operator+=(TimeDelta delta) {
      ticks_ += delta.delta_;
      return *this;
    }
    TimeTicks& operator-=(TimeDelta delta) {
      ticks_ -= delta.delta_;
      return *this;
    }
  
    // Return a new TimeTicks modified by some delta.
    TimeTicks operator+(TimeDelta delta) const {
      return TimeTicks(ticks_ + delta.delta_);
    }
    TimeTicks operator-(TimeDelta delta) const {
      return TimeTicks(ticks_ - delta.delta_);
    }
  
    // Comparison operators
    bool operator==(TimeTicks other) const {
      return ticks_ == other.ticks_;
    }
    bool operator!=(TimeTicks other) const {
      return ticks_ != other.ticks_;
    }
    bool operator<(TimeTicks other) const {
      return ticks_ < other.ticks_;
    }
    bool operator<=(TimeTicks other) const {
      return ticks_ <= other.ticks_;
    }
    bool operator>(TimeTicks other) const {
      return ticks_ > other.ticks_;
    }
    bool operator>=(TimeTicks other) const {
      return ticks_ >= other.ticks_;
    }
  
   protected:
    friend class TimeDelta;
  
    // Please use Now() to create a new object. This is for internal use
    // and testing. Ticks is in microseconds.
    explicit TimeTicks(int64_t ticks) : ticks_(ticks) {
    }
  
    // Tick count in microseconds.
    int64_t ticks_;
  
  #if defined(OS_WIN)
    typedef DWORD (*TickFunctionType)(void);
    static TickFunctionType SetMockTickFunction(TickFunctionType ticker);
  #endif
  };
  
  inline TimeTicks TimeDelta::operator+(TimeTicks t) const {
    return TimeTicks(t.ticks_ + delta_);
  }
  
  }  // namespace butil
  
  #endif  // BUTIL_TIME_TIME_H_
  