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From: dillon@CORY.BERKELEY.EDU (Matt Dillon)
Newsgroups: comp.sys.amiga
Subject: Re: Printer drivers and Aztec 3.04a
Message-ID: <8705100229.AA00570@cory.Berkeley.EDU>
Date: Sat, 9-May-87 22:29:49 EDT
Article-I.D.: cory.8705100229.AA00570
Posted: Sat May  9 22:29:49 1987
Date-Received: Sun, 10-May-87 08:58:48 EDT
Sender: daemon@ucbvax.BERKELEY.EDU
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	Aztec uses A4 as its base register for global data ONLY in the small
data model.  BUT (and I think Aztec made the correct decision here), it will
NOT use A4 at all in it's large data model unless you give it a specific
compile-time flag saying it's ok.  This is so small and large data segments
can be mixed freely.

	Aztec uses D0,D1,D2,D3,A0, and A1 as scratch (doesn't bother to save).
You can specify a 'super compatibility mode' flag, +p I believe, which causes
Aztec to save D2/D3 (thus conforming with amiga specs).  However, this is a 
problem only if some external routine calls aztec.  Definately not a problem
when Aztec calls some external routine.

	(P.S. A good guess as to why 4 data registers are 'scratch' is because
most, if not all expressions can be calculated utilizing 4 temporary registers)

	And we all know that Aztec doesn't bother to save A6 when it makes
library calls.  This is a deficiency in the library code to make those calls
rather than in the Aztec compiler.  Frankly, the increase in speed isn't
noticeable and it would have been well worth the effort to save that register.
Of course, those people with the commercial version could simply fixup those
library modules since they have the source, but this is not desireable because
the source would then be incompatible with everybody else's compiler.

				-Matt