QueryPerformanceFrequency/QueryPerformanceCounter 获取代码精确运行时间

	QueryPerformanceFrequency(&nFreq);QueryPerformanceCounter(&nBeginTime);Sleep(1000);QueryPerformanceCounter(&nEndTime);time = (double)(nEndTime.QuadPart - nBeginTime.QuadPart) / (double)nFreq.QuadPart;