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Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!genrad!decvax!tektronix!orca!mako!jans
From: jans@mako.UUCP (Jan Steinman)
Newsgroups: net.micro.68k,net.micro.16k
Subject: Re: PDP11s vs the micros
Message-ID: <847@mako.UUCP>
Date: Tue, 9-Jul-85 13:07:07 EDT
Article-I.D.: mako.847
Posted: Tue Jul  9 13:07:07 1985
Date-Received: Thu, 11-Jul-85 20:24:39 EDT
References: <1617@hao.UUCP>
Reply-To: jans@mako.UUCP (Jan Steinman)
Distribution: net
Organization: Tektronix, Wilsonville OR
Lines: 29
Xref: watmath net.micro.68k:997 net.micro.16k:348
Summary: 

In article <1617@hao.UUCP> hull@hao.UUCP (Howard Hull) writes:
>The double indirect, a concept always difficult to teach to the neophites, is
>now declared dead.  For all practical purposes, it has been buried in the
>nested-line formats of structured programming topology.

Not so!  Our NS32000 C compiler regularly produces memory indirect references
whenever a pointer is declared as an automatic variable:

	movd	0(4(fp)),rX	;Get the data pointed to by the data pointed
				;  to by the frame pointer plus four.

Although I'm not familiar with PDP11 assembly, it appears that National lacks
the general-purpose autoincrement, but adds the (more useful, in my opinion)
ability to offset from the first base before indirection, and then you can
even throw a scaled index on top of the final address if you want, which means
you no longer have to forget your base when double-indirecting through a
table.

While I agree that most applications are content with the output of a
compiler, writing tight assembly code, using all the features a machine has to
offer, is not dead.  I make heavy use of the NS32000 memory indirect
addressing mode, which is excellent for such things as traversing linked-lists
in dynamically typed languages.  (Get a pointer to an object, look through the
object for a terminator, etc.)  My only wish is that Nati had given all the
general purpose registers this facility, so I wouldn't have to shuffle the
SP or FP around so much!
-- 
:::::: Jan Steinman		Box 1000, MS 61-161	(w)503/685-2843 ::::::
:::::: tektronix!tekecs!jans	Wilsonville, OR 97070	(h)503/657-7703 ::::::