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From: harald@ccicpg.UUCP ( Harald Milne)
Newsgroups: comp.sys.mac,comp.sys.amiga
Subject: Re: Code Optimization
Message-ID: <10164@ccicpg.UUCP>
Date: 28 Jan 88 10:58:29 GMT
References: <4776@watdragon.waterloo.edu>
Distribution: comp
Organization: CCI CPD, Irvine CA
Lines: 62

In article <4776@watdragon.waterloo.edu>, palarson@watdragon.waterloo.edu (Paul Larson) writes:
> The Mac and Amiga worlds are currently in the process of changing from the
> 68000 processor to the similar, but more powerful 68020.  The 68030 has also
> been rumoured to be lurking somewhere on the horizon.  However, regardless of
> whether a '000 or a '020 is installed, the same code is used. 

	Yes and no. There should be no difference in code generation on the
Amiga.

> Thus, if a 
> system is using the more advanced '020, it is using code which was written for
> a more primitive, though similar, processor and thus the code does not take
> proper advantage of the more advanced features of the more modern processors.

	Well here is the no answer. The Amiga makes use of shared libraries,
not unlike the shared memory concept in System V UNIX. Just what advanced
features are you talking about? Cache management, floating point coproccessor
interface, or what?

	Cache management is one thing, and the Amiga OS uses it (yes the
cache is turned on), if a 68020 is detected. The OS does this on boot.

	In terms of floating point, things are very different here. Floating
point operations on the Amiga are not compiled "inline", they are called.
If you have a 68000, you can use the standard software emulation (IEEE). If
you have the 68020, and have the 68881 or 68882 present (also detected on boot) you can simply replace the math library, and use 68881/68882 instructions
directly. No recompiles, no changes, existing software is upward compatabible.

> The same agrument applies for the math co-processors, the 68881 and its new
> sibling the 68882, which are rapidly becoming more popular on home computers.

	Uh, they are? What do you have? A MacII? At a $4000.00 base price, this
revolution is not comming soon. We are talking about some expensive hardware!
But after what I read in the latest Unix/World, the 68000 family could fall
out of favor, meaning lower prices for us all. That could make it popular.

> The code optimizer, if properly written, could remove the inefficiency of
> using primitive code on an advanced processor, simply by modifying the
> code to take advantage of the features of the more advanced processor.

	Well you lost me completely here. What advantages are not being used?

> Since not everyone has a 68020, it would be left up to the user to decide
> whether or not (s)he wants the code of a program modified in such a way.
> The optimizer could also be written to rewrite the program code so as
> to take advantage of a coprocessor, it one is present.

	No rewriting needed for the Amiga.

	The Amiga handles all this.

> Is there some fundamental problem with what is described above?  Is anyone
> working on such an optimizer?
> I welcome your comments and criticisms.

	Just what I mentioned so far.

> 	Johan Larson
-- 
Work: Computer Consoles Inc. (CCI), Advanced Development Group (ADG)
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