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From: toddpw@nntp-server.caltech.edu (Todd P. Whitesel)
Newsgroups: comp.sys.apple2
Subject: Re: ML subroutines (Oops, I think I owe Randy a slight apology!)
Message-ID: <1991Apr26.225542.5640@nntp-server.caltech.edu>
Date: 26 Apr 91 22:55:42 GMT
References: <3397@kluge.fiu.edu> <13845@ucrmath.ucr.edu> <112122@tut.cis.ohio-state.edu> <13954@ucrmath.ucr.edu> <1991Apr26.221735.4063@nntp-server.caltech.edu>
Organization: California Institute of Technology, Pasadena
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Sorry to follow my own article, but I just realized we are misinterpreting
Randy's comments.

[I wrote this]
>Randy, now I'm convinced you're thinking like a 6502 assembly programmer.

This is incorrect, but I realized it as I was skimming the article when it
showed up in nn. I didn't try to cancel the post because I don't want to
retype the gunk about Orca and the DBR trick.

What Randy is thinking like is a RISC machine programmer, more specifically
to emulate a zillion-register RISC machine on the 65816 using an aligned
direct page. What I and I suspect many other on the group thought he was
talking about was using the direct page for globals and scratch, and the
stack relative for automatic variables -- I should have realized it because
I said it myself earlier today in another thread, it's such a ludicrous
idea that it couldn't have been the intended meaning, but when people don't
see the reasonable interpretation right away they too readily assume the
worst...

The idea of using the DP as a RISC machine emulator has LOTS of merit.
For one thing, it would be the only reasonable way to teach GCC the
65816, although I don't think any of us is up to messing with a behemoth
like GCC.

The main reservations I have about the idea are that function enter and
exit could get really nasty, and that there is a hideous problem with
using a fixed direct page for autos -- you can't safely pass pointers
to them because they might be saved/restored by the called function.
I suppose you could have all autos 'officially' on the stack, but that would
be really gross and the floating dp would still be faster except for floating
point calculations -- but are usually handed to SANE, and get done on an
aligned dp.

Todd Whitesel
toddpw @ tybalt.caltech.edu