rcopm@koel.UUCP (08/14/87)
g'dae,
This may appear as trivia to some, but I would dearly love to hear from
anyone who *knows* the answers to any of the below. I have made my
(un)educated guesses, and would like them confirmed.
(1) What is the behaviour of the function "TickCount"
(alias the Global "Ticks") when at the limit of its range?
(2) Am I correct in assuming that this limit is 2^31 - 1?
(3) Does it rollover to 0?
(4) Does the System behave correctly when the rollover occurs?
According to my assumptions above, this should occur once every 13 odd
months for a constantly running Mac.
C'mon folks, stop chuckling, I'm serious. I intend to use this info.
Thankyou,
Paul Menon.
Dept of Communication & Electronic Engineering,
Royal Melbourne Institute of Technology,
124 Latrobe St, Melbourne, 3000, Australia
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PHONE: +61 3 660 2619.tecot@apple.UUCP (08/18/87)
In article <284@koel.rmit.oz> rcopm@koel.rmit.oz (Paul Menon) writes: >g'dae, > > This may appear as trivia to some, but I would dearly love to hear from >anyone who *knows* the answers to any of the below. I have made my >(un)educated guesses, and would like them confirmed. > >(1) What is the behaviour of the function "TickCount" > (alias the Global "Ticks") when at the limit of its range? See below. >(2) Am I correct in assuming that this limit is 2^31 - 1? It depends. If you assume that Ticks is signed (which it really isn't), then yes, the limit is in fact 2^31-1. If you treat it correctly as unsigned, then the limit is 2^32-1. The important thing to remember is that it really doesn't matter which way you handle it (I don't know how you would use the unsigned model in pascal), as long as you are consistent. The system always treats Ticks as unsigned, applications may do otherwise. >(3) Does it rollover to 0? It depends. Unsigned - yes. 2^32-1 + 1 becomes 0. If you are looking at it as signed, then 2^31-1 becomes -(2^31). It still doesn't matter if you are consistent. >(4) Does the System behave correctly when the rollover occurs? Almost. I tested it out myself on a Mac SE. First of all realize that there are two rollover points. One for signed values (7FFFFFFF->80000000) and one for unsigned values (FFFFFFFF->00000000). The first rollover point is not noticed by the ROM (it uses the unsigned interpretation). The second point has only one side-effect I noticed: The caret (TEIdle) "skips" at the rollover point and then continues normally. But once every thirteen months sin't too bad, huh? _emt