Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!helios!tamuts!n233dk
From: n233dk@tamuts.tamu.edu (Rick Grevelle)
Newsgroups: comp.sys.handhelds
Subject: Re: RPL constructs
Message-ID: <9206@helios.TAMU.EDU>
Date: 17 Oct 90 06:52:22 GMT
References: <11408@life.ai.mit.edu>
Sender: usenet@helios.TAMU.EDU
Organization: Texas A&M University
Lines: 60


In article <11408@life.ai.mit.edu> you write:
>
>   Could someone who knows, please describe how conditionals, loops,
>and CASEs are stored internally? I need it to get SAD 1.02 to
>disassemble RPL code. Actually, it already does, but I intend to
>supply macros for common RPL constructs to get the indentation
>correct.
>

I not quite sure what it is that you're asking; are you wanting someone
to explain how machine code handles these items, or are you asking about
the prefixed machine routines that RPL calls to handle decision making?
By common RPL constructs I assume you mean the later; but please explain 
further.

>   Oh, and could someone explain what reals (i.e. 64-bit floating
>point words) look like? Things like how the exponent is stored, the
>exponent sign, the mantissa sign, etc. I haven't done any thorough
>investigation here, and only know vaguely what is what.

Alonzo Gariepy explains this in his Processor Notes in terms of the various
fields used within the internal registers.  Here is a simplification of it.

                         Internal Real
                 
                    s mmmmmmmmmmmm s ee ppppp
    
i)   The lower case s's indicate the sign of the mantissa and exponent.  For 
     positive values a zero is used, and a nine is used for negative values.

ii)  The twelve lower case m's represent the mantissa.

iii) The two lower case e's are the exponent.

iv)  And the lower case p's are the prolog #02933h.

>   Also, please voice your opinion on the following (PROGRAM and END
>are SAD macros, which currently is the only way to define proper
>indentation among other things) format:

Whoa!  I don't know about this; it could be a potential copy right violation.
Don't get me wrong, you're doing an extraordinaryly good job; obviously you're
quite knowledgeable.  But HP is a rather large and powerful corporation, with
high dollar attorneys on retainer.  Posting, without permission, portions of
code from the 48's ROM on which HP holds the copyright is a very grey area.

Personally, I'm little paranoid about much of the material alluded to in my
postings.  I am almost certain that by now HP must hate me.  However, I once
discussed the matter with Alonzo, from whose opinion I formed my currenlty
used guidelines for posting to the net, so there is probably no reason for
me to worry.
 
As for as my opinion on your format is concerned; it is EXCELLENT!  It looks
almost identical to RPL disassemblies I've been doing by hand since the 28.
I'm looking forward to this latest version of SAD, with it I could cover ten
times the amount of territory than in the past.  No one has yet to produce,
outside of HP, an RPL disassembler this accurate; at least of which I know.

Rick Grevelle