From: akcs.joehorn@hpcvbbs.cv.hp.com (Joseph K. Horn)
Newsgroups: comp.sys.hp48
Subject: Re: Needed ASC De/Compressor
Date: 12 Nov 92 06:40:02 GMT
Article-I.D.: hpcvbbs.2b01faf3.2123.1comp.sys.hp48.1


                  ASCII Encoding HP 48SX Objects
                          by Bill Wickes

Sending an HP 48SX object via electronic mail can be difficult if the
object does not have an ASCII form, such as is the case for library
objects.  There are various encoding schemes available on different
computer systems, but these require that the sender and receiver have
similar computers, or at least compatible encode/decode schemes.  The
programs listed below perform the encoding and decoding on the HP 48SX
itself, which has the advantage of being completely independent of any
computer.

The programs are nominally called \->ASC and ASC\->.  The former takes
an object from the stack and converts it to a string, in which each
nibble of the object and its checksum is converted to a character 0-9 or
A-F.  (The object must be in RAM, otherwise a "ROM Object" error is
returned.) For sake of easy inclusion in email letters, the string is
broken up by linefeed characters after every 64 characters.

ASC\-> is the inverse of \->ASC: it takes a string created by \->ASC and
converts it back into an object.  When you transmit the encoded strings,
be sure not to change the string; ASC\-> uses the checksum encoded in
the string to verify that the decoding is correct.  An "Invalid String"
error is returned if the result object does not match the original
object encoded by \->ASC.  When you upload a string to your computer,
use HP 48 translate mode 3 so that the HP 48 will convert any CR/LF's
back to LF's when the string is later downloaded.

Two versions of ASC\-> are included here.  The first (P1) is in HP 48
user language, using SYSEVALs to execute system objects.  P2 is a string
that the setup program uses P1 to decode into an executable ASC\->
--then P1 is discarded.  The second version is more compact than the
first, and also uneditable and therefore safer (but it can't be
transmitted in ASCII form, which helps to make the point of this
exercise).

Here are the programs, contained in a directory:

(start)
%%HP: T(3)A(D)F(.);
DIR
P1              @ ASC\-> Version 1.
\<<
  IF DUP TYPE 2 \=/
  THEN "Not A String" DOERR
  END RCWS \-> ws
  \<< 16 STWS
    #0 NEWOB SWAP DUP SIZE
    IF DUP 4 <
    THEN DROP SWAP DROP "Invalid String" DOERR
    END 
    DUP 65 / IP - 4 - # 18CEAh SYSEVAL 
    "" OVER # 61C1Ch SYSEVAL
    SWAP # 6641F8000AF02DCCh
    # 130480679BF8CC0h # 518Ah SYSEVAL
    # 19610313418D7EA4h # 518Ah SYSEVAL
    # 7134147114103123h # 518Ah SYSEVAL
    # 5F6A971131607414h # 518Ah SYSEVAL
    # 12EA1717EA3F130Ch # 518Ah SYSEVAL
    # 280826B3012808F4h # 518Ah SYSEVAL
    # 6B7028080BEE9091h # 518Ah SYSEVAL
    # BE5DC1710610C512h # 518Ah SYSEVAL
    # 705D00003431A078h # 518Ah SYSEVAL
    # 3D8FA26058961431h # 518Ah SYSEVAL
    # 312B0514h # 518Ah SYSEVAL 
    # 18F23h SYSEVAL 
    DUP BYTES DROP 4 ROLL
    IF ==
    THEN SWAP DROP
    ELSE DROP "Invalid String" DOERR
    END ws STWS
  \>>
\>>

P2       @ ASC\->  Version 2.  To be converted by ASC\-> version 1.

"D9D20D29512BF81D0040D9D20E4A209000000007566074726636508813011920
140007FE30B9F060ED3071040CA1304EC3039916D9D2085230B9F06C2A201200
094E66716C696460235472796E676933A1B21300ED30FD5502C230C1C1632230
CCD20FA0008F14660CC8FB97608403104AE7D814313016913213014117414317
414706131179A6F5C031F3AE7171AE214F8082103B6280821909EEB0808207B6
215C0160171CD5EB870A13430000D50713416985062AF8D341508813044950B9
F06BBF06EFC36B9F0644230C2A201200094E66716C696460235472796E676933
A1B2130B21300373"

P3       @\->ASC.     To be converted by ASC\->.
"D9D20D2951881304495032230FD5502C230A752688130ADB467FE30322306AC3
0CB916E0E30CBD30F6E30C1C1632230CCD20DC0008F14660CC8FB97608403104
AE7D8143130169174147061741431311534AC6B4415141534946908D9B026155
4A6F53131F3AE731A014C161AE215F08082103A6280821939EEC08082170A621
4C161170CD56B870A18503430000D5071351796A9F8D2D02639916D9D2085230
C2A209100025F4D402F426A6563647933A1B2130A2116B213033C0"

SETUP             @Automatic setup program
\<< P2 P1 'ASC\->' STO
    P3 ASC\-> '\->ASC' STO
    { P1 P2 P3 SETUP } PURGE
\>>

END
(end)

Installation instructions:

1.  Edit the above text between (start) and (end) into a text file named
CONV (for example).  Be sure that you leave the strings exactly as
entered above, with no extra spaces or other invisible characters at the
beginnings or ends of the lines.
2.  Set the HP 48SX into ASCII transfer mode.
3.  Using Kermit, download CONV text file to the 48, verify its checksum
(6C8Ah).
4.  Execute CONV to make it the current directory.
5.  Execute SETUP.
6.  The directory CONV now contains ASC\-> and \->ASC, ready to use.

To archive the decoded versions of ASC\-> and \->ASC back on your
computer, be sure to set the HP 48SX in binary transfer mode before
uploading.

Disclaimers:

* Use the programs at your own risk.  Any time you delve into the
SYSEVAL world, there are increased dangers.  Archive your 48 memory
before experimenting with these programs!  Also, verify the checksums of
objects defined above to make sure they have been downloaded correctly,
before executing ASC\->.

* I will not answer questions about how the programs work.  This is not
because of any great secrecy, but rather because it's hard to give any
answer that doesn't lead to more questions, and more, and more...

* 48 hackers are welcome to mine any nuggets they can from the programs,
and from the fact that \->ASC is a convenient way to decompile an
object.

Bill Wickes