IOS测试程序运行耗时

iOS设备相对于电脑，内存和处理能力有限，所以一段代码或者程序运行的时间需要时刻注意，这里提供两种获取精确时间的方法。

方法一：使用系统时间

 NSDate* tmpStartData = [[NSDate date] retain];
 //You code here...
 double deltaTime = [[NSDate date] timeIntervalSinceDate:tmpStartData];
 NSLog(@">>>>>>>>>>cost time = %f ms", deltaTime*);

方法二：

 #import <mach/mach_time.h>

 uint64_t start = mach_absolute_time();
 //You code here...
 uint64_t end = mach_absolute_time();
 uint64_t elapsed = end - start;mach_timebase_info_data_t info;
 if (mach_timebase_info (&info) != KERN_SUCCESS)
 {
     printf ("mach_timebase_info failed\n");
 }
 uint64_t nanosecs = elapsed * info.numer / info.denom;
 uint64_t millisecs = nanosecs / ;
 NSLog(@">>>>>>>>>>cost time = %ld ms", millisecs);