How to Implement latency in microseconds in MFC

Transferred from Baidu Library:

Delayus

 1 void DelayUs(int uDelay) 2 { 3  4     LARGE_INTEGER litmp; 5     LONGLONG QPart1,QPart2; 6  7     double dfMinus,dfFreq,dfTim; 8      9     /*10         Pointer to a variable that the function sets, in counts per second, to the current performance-counter frequency. 11         If the installed hardware does not support a high-resolution performance counter, 12         the value passed back through this pointer can be zero. 13 14     */15     QueryPerformanceFrequency(&litmp);16 17     dfFreq = (double)litmp.QuadPart;18 19     /*20         Pointer to a variable that the function sets, in counts, to the current performance-counter value. 21     */22     QueryPerformanceCounter(&litmp);23 24     QPart1 = litmp.QuadPart;25     do26     {27            QueryPerformanceCounter(&litmp);28         QPart2 = litmp.QuadPart;29         dfMinus = (double)(QPart2-QPart1);30         dfTim = dfMinus/dfFreq;31      }while(dfTim<0.000001 * uDelay);32 }

If you understand the above functions, you can also use some of the Code in it to test the execution time of many functions.

Of course, this function is still a bit risky. If the timer overflows during a delay period, this value may be inaccurate and needs to be handled with caution.

For example, if (dfminus <0)

Break;

This assumes that the hardware timer is counted in an increase.