[AD] windows time functions

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in function:

unsigned long al_current_time(void)
  /* XXX: Maybe use QueryPerformanceCounter? */
  return timeGetTime() - _al_win_initial_time;

more comments:

QueryPerformanceCounter, obtains its value from the CPU upon which the current thread is running. If the thread switches to another CPU, it is possibly for the value to completely change.
There are currently no intelligent solutions to this problem.
Some solutions i have heard of: - Mask the calling thread to a specific CPU, (which kind of defeats the point in having multi-processor machines). - Run it in a thread that is locked to a specific CPU, and use CriticalSections to access it.. ( which defeats the Query[Performace]Counter() )

QueryPerformanceCounter is also documented as jumping in value which can create non-linear values being returned.

Problems with timeGetTime() :

unless you run the timeBeginTime() and timeEndTime() timeGetTime()'s resolution can be as much as 8-10ms sloppy. which for anything like trying to sync a screen draw/flip can cause significant error in calculations.

al_current_time()'s   wrap length.   49days :(
I know many (99.9%) of you are going to say "whose stupid enough to be using an allegro app for 49 days"... well.. I do!

I do like the recently proposed solution on a.cc using a struct { int32_t hi; uint32_t lo; } when lo wraps hi++ then accessor functions _al_get_current_time32() { return t.lo; } and _al_get_current_time64() { return (__int64)t; }


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