Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cbmvax!jesup
From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.arch
Subject: Re: Low End NeXTs (was Re: Desktop publishing)
Message-ID: <20631@cbmvax.commodore.com>
Date: 15 Apr 91 06:58:04 GMT
References: <27fa3350.6bc2@petunia.CalPoly.EDU> <1991Apr03.232400.1560@kithrup.COM> <1991Apr4.125122.1@capd.jhuapl.edu> <1991Apr5.172533.6717@agate.berkeley.edu> <1991Apr7.065105.25586@zoo.toronto.edu> <23724@as0c.sei.cmu.edu>
Reply-To: jesup@cbmvax.commodore.com (Randell Jesup)
Organization: Commodore, West Chester, PA
Lines: 27

In article <23724@as0c.sei.cmu.edu> firth@sei.cmu.edu (Robert Firth) writes:
>My rough calculations (again, based on the documentation) agree with
>Henry's.  As with the 68020, the indexed address modes are on balance
>slower than the equivalent naive code using only the 68000 address
>modes.  Once in a while, you'll be able to avoid an extra register
>save and restore, for a marginal gain; but in general, forget them.

	I mostly agree, though note that the '020 had more overhead on the
new modes than the '030 did - on an '030, some of the modes are actually
a win (I think d8(An,Xn*scale) becomes a win, for example, in certain cases).
I use a compiler that has different specific '020/'030 optimizations, and
on an '030 it is more willing to use some of the new addressing modes.  I
don't know if the '040 has maintained the split-point of utility, but I
wouldn't be suprised if it were in about the same spot.
 
	The 32-bit multiply and divide on the '020 and above are a large
win.  For certain types of code (not the general case - cpu blitter code,
for example) the bitfield instructions are a win, and of course the barrel-
shifter.

-- 
Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.commodore.com  BIX: rjesup  
Disclaimer: Nothing I say is anything other than my personal opinion.
Thus spake the Master Ninjei: "To program a million-line operating system
is easy, to change a man's temperament is more difficult."
(From "The Zen of Programming")  ;-)