C / C++ / MFC

RunThread->SetThreadPriority(THREAD_PRIORITY_TIME_CRITICAL) ;


	FILETIME time1;
	FILETIME time2;


	::GetSystemTimeAsFileTime(&time1) ;		// get the current time
	
	while (...)
		{
		::GetSystemTimeAsFileTime(&time2) ;		// get the current time
		delay = (m_spectra_frequency * spectra_collected) - CalculateElapsedTime(&time1, &time2) ;
		if (delay >= 0.001)
			Sleep((unsigned long)(delay * 1000.0)) ;
		}




double CalculateElapsedTime(FILETIME *start, FILETIME *current)
{
	double	elapsed_time ;
	__int64	st ;
	__int64	ct ;
	__int32	*p ;

	p = (__int32*)&st ;
	*p++ = start->dwLowDateTime ;
	*p = start->dwHighDateTime ;
	//st = (start->dwHighDateTime << 32) + start->dwLowDateTime ;
	p = (__int32*)&ct ;
	*p++ = current->dwLowDateTime ;
	*p = current->dwHighDateTime ;
	//ct = (current->dwHighDateTime << 32) + current->dwLowDateTime ;
	elapsed_time = (double)(ct - st) ;
	elapsed_time /= 10000000.0 ;	// convert from 100ns intervals to seconds
	return elapsed_time ;
}