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From: imp@crayview.msi.umn.edu (Chuck Lukaszewski)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Register saving conventions
Summary: No need for everything
Message-ID: <6600@umn-cs.cs.umn.edu>
Date: 9 Aug 88 16:23:20 GMT
References: <664@iraun1.ira.uka.de> <1133@lzsc.ATT.COM> <15055@santra.UUCP>
Sender: news@umn-cs.cs.umn.edu
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In article <15055@santra.UUCP>, jmunkki@santra.HUT.FI (Juri Munkki) writes:
> In article <1133@lzsc.ATT.COM> mkg@lzsc.ATT.COM (Marsh Gosnell) writes:
> >When I patch traps I make it a point to save/restore everything (D0-D7/A0-A4)

There really is no need for this.  Juri is right about the cycle consumption
of register saving.  At a minimum, you can ignore D0-D2 and A0-A1 because Apple
says you can trash them.  Indeed, the ROM code makes no assumptions about these
five registers.

In point of fact, given the above about D0-D2/A0-A1, you need no register store
code at all because the trap dispatcher handles the other registers for you, so
you're just wasting stack space and CPU cycles.

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