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From: ForthNet@willett.pgh.pa.us (ForthNet articles from GEnie)
Newsgroups: comp.lang.forth
Subject: for us beginners?  Help
Message-ID: <2090.UUL1.3#5129@willett.pgh.pa.us>
Date: 11 Dec 90 02:57:39 GMT
Organization: String, Scotch tape, and Paperclips.  (in Pgh, PA)
Lines: 50

Category 2,  Topic 5
Message 170       Sun Dec 09, 1990
D.RUFFER [Dennis]            at 23:10 EST
 
Re: DALE SMITH

 > What's the best way to code things like xfer protocols that have
 > goto's jumping from a case inside a while loop to some things
 > back before the loop started?  Or go to one of several error
 > exits? There is lots of stuff like that in the sz/rz programs.

Ah, glad to see someone else is going to try to tackle the zmodem protocol. 
I've tried, and gave up half way in the middle.  Well, I didn't actually give
up, I still have the code, but I haven't had time to ever finish it.  In the
process of trying to code Chuck Forsberg's C code (not the most structured
stuff that I ever saw), I wrote up the following:

    ( Simple GOTO in Forth )
 CODE @R ( - a   P: Fetch return stack pointer )   R PUSH   NEXT
 CODE !R ( a -   P: Store return stack pointer )   R POP    NEXT

 : LABEL ( name \ -   P: Define a label to goto )   2VARIABLE
           ;CODE   R 1 CELLS W) MOV   I 2 CELLS W) MOV   NEXT

 : goto ( -   P: Return to the label that is compiled next )
          R> @ ( cfa of label )  CELL+ 2@ !R  >R ;
 : exit ( -   P: Exit from where label is used )
          R> @ ( cfa of label )  CELL+ @ !R ;

 EXIT    LABEL loop ( -   P: Looping label for test )
 : test ( n -   P: A test for these features )   loop
          DUP .  1- ?DUP IF  goto loop  THEN  exit loop
          1 ABORT" Didn't work" ;

It is written for polyFORTH, but might be able to be translated to something
else.  In pF assembler code, R is the return stack pointer register and W
points to the CFA of the word being executed.

This allowed me to get close.  I was building it on top of my PFMODEM stuff
that is in the library.  Let me know if you want some incomplete source code,
and I will upload it.  However, it sure isn't anywhere close to being
something that works yet.  I don't even think I ever got the transfer side of
it coded, but you are welcome to whatever I've got.

Hope to see what you can come up with.

DaR
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