マイクロ秒を計る - sugawara @ ウィキ

Mac OS X Tips

• CoreServices mach_absolute_timeを使う。

  #include <CoreServices/CoreServices.h>
  #include <mach/mach.h>
  #include <mach/mach_time.h>
  #include <unistd.h>
  
  uint64_t start;
  uint64_t end;
  uint64_t elapsed;
  Nanoseconds elapsedNano;
  
  start = mach_absolute_time();
  ...
  end = mach_abdolute_time();
  elapsed = end - start;
  elapsedNano = AbsoluteToNanoseconds( *(AbsoluteTime *)&elapsed );
  
  

• Carbon Driver Servisec Libraryを使う。 UpTime()はPowerPCのTime Base Register(TBR)を見るらしい。 CoreServices.frameworkが必要（？）。

  #include <Carbon/Carbon.h>
  
  AbsoluteTime before, after, diff;
  Nanoseconds  nanosec;
  double microsec;
  
  before = UpTime();
  ...
  after = UpTime();
  diff = SubAbsoluteFromAbsolute( after, before );
  nanosec = AbsoluteToNanoseconds( diff );
  microsec = (float)UnsignedWideToUInt64( nanosec ) / 1000.0;
  

またはTime ManagerのMicroseconds()を使う。

• BSD

  int gettimeofday( struct timeval* tp, struct timezone *tzp );
  

  を使う。 ※long型なのでオーバーフローに注意！ 使い方の例

  #include <sys/time.h>
  struct timeval before, after;
  gettimeofday( &before, NULL );
  ....
  gettimeofday( &after, NULL );
  long microsec = after.tv_usec - before.tv_usec;
  

  timevalとtimezoneは以下の通り。

  struct timeval {
      long tv_sec; /* seconds since Jan. 1,1970 */
      long tv_usec; /* and microseconds */
  };
  struct timezone {
      int tz_minuteswest; /* of Greenwich */
      int tz_dsttime; /* type of dst correction to apply */
  };
  

• Cocoa NSDateを使う。