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From: rmh@apple.com (Rick Holzgrafe)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Animation
Message-ID: <12151@goofy.Apple.COM>
Date: 18 Feb 91 22:50:08 GMT
Sender: usenet@Apple.COM
Organization: Apple Computer, Inc.
Lines: 38
References:<1961.27B4BFB4@stjhmc.fidonet.org> <145515@tiger.oxy.edu>

In article <145515@tiger.oxy.edu> schorsch@oxy.edu (Brent William 
Schorsch) writes:
> Baudoin Raoult writes in a message to All
> >  tmp := TickCount;  while tmp=Tickcount do { nothing } ;  
CopyBits(.....)
> 
> Lawson English says:
> >To make sure that you get the most accurate reading (and the longest 
time i
> which to do your drawing) use GetTrapAddress to bypass the Trap 
Dispatcher a
> jump directly to TickCount. Otherwise, you have 100+ CPU cycles of 
overhead
> 
> if you're going to go against guideline, why not use the global variable
> Ticks. (unless you're running under A/UX)...
> This seems safer to me.. (not to metion faster)
> -Brent

It's not safer - and you yourself just gave one reason why: it won't run 
under A/UX. This is a portent of the future: not that A/UX will take over, 
but that low-memory globals will not be supported forever.

GetTrapAddress may not work forever either (we are recommending against 
its use, as Brent implies) but directly accessing some low-memory globals 
is already broken in some environments, while GetTrapAddress at least 
still works. If you *must* bypass the trap mechanism, GetTrapAddress is 
safer than accessing Ticks directly.

(BTW - in most environments, it's also nearly as fast. TickCount is a very 
short, fast routine, if you avoid the trap overhead.)

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Rick Holzgrafe              |    {sun,voder,nsc,mtxinu,dual}!apple!rmh
Software Engineer           | AppleLink HOLZGRAFE1          rmh@apple.com
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