iOS获取代码执行时间精确到纳秒

#import <mach/mach.h>
#import <mach/mach_time.h>
- (void)test {
      uint64_t start = mach_absolute_time();
       
       // 这里放入你想要测量的代码
       
       uint64_t end = mach_absolute_time();
       
       uint64_t elapsed = end - start;
       
       mach_timebase_info_data_t timebase;
       mach_timebase_info(&timebase);
       
       double elapsedNano = (double)elapsed * (double)timebase.numer / (double)timebase.denom;
       
       NSLog(@"Elapsed Time: %f nanoseconds", elapsedNano);
}