一个精度很高的计时器

//---------------------------------------------------------------------------
// get the millseconds from the demo start - time line
//---------------------------------------------------------------------------
float GetTime()
{
  static bool init = false;
  static bool hires = false;
  static __int64 freq = 1;
  if(!init)
  {
    hires = !QueryPerformanceFrequency((LARGE_INTEGER *)&freq);
    if(!hires)
      freq = 1000;
    init = true;
  }

  __int64 now;

  if(hires)
    QueryPerformanceCounter((LARGE_INTEGER *)&now);
  else
    now = GetTickCount();

  return (float)((double)now / (double)freq);
}