From <@IBM1.CC.Lehigh.Edu:LJM3@LEHIGH.BITNET> Mon Oct 30 16:25:13 1989
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Date:     MON OCT 30, 1989 17.15.31 EST
From: "Al McLennan" <LJM3%LEHIGH.BITNET@IBM1.CC.Lehigh.Edu>
Subject:  New en/decoder
To: "David J. Camp" <DAVID@WUBIOS>
Status: OR

This past summer I got involved with XFER-L, which was put together to
tackle the transfer problems PHYS-L was having.  (Both lists at
UCF1VM.)  The result was an encode/decoder combination (lcoder.exe)
which can do either XXE or HEX alphabets.  It is set up so on decoding
any characters extraneous to the encoding alphabet are stripped out;
this makes it immune to a chronic problem with our MUSIC system, which
can't handle wrong-format transmission.
I'm sending a file below which can be used to construct it, and would
very much appreciate any comments from you.  It was written in
assembler, and I'll send source if you're interested.
Regards, Al
********File follows********


STARTUP.KIT, by Al McLennan, LJM3@LEHIGH.bitnet

The purpose of this file is to construct the program LCODER.EXE, which
is a PC-based encoder/decoder for file transfers.

This file contains three parts which are separated by cut lines
(=========).  The first part is these instructions. With your word
processor, you should separate out the second and third parts into two
files. (Note the warning below regarding some word processors.)

The second part is assembly code for a very short decoder. This part
should be put into a file called SHORT.SRC

Finally there is the desired program in hex-coded form, which MUST be
filed as LCODER.HEX.

After you have both files SHORT.SRC and LCODER.HEX you can assemble
your short decoder using DEBUG (which comes with DOS). To do this, at
the DOS prompt enter

        debug < short.src

You then sit back and watch debug assemble the code, which takes (on
my old XT) about 20 seconds.  The program short.com should emerge.
You only use this once, to decode LCODER.HEX into LCODER.EXE, by
typing SHORT at the DOS prompt.  SHORT.COM has no other use, and so
can be deleted once you have obtained LCODER.EXE.  Be sure to make the
file LCODER.HEX before you run SHORT, as SHORT.COM will have nothing
to do if it can't find LCODER.HEX in the current directory.

This procedure may seem convoluted, but is one solution to the problem
that you can't get a decoder because of the reason you want it.

You have no doubt obtained this file by transfer over bitnet, and so
it may be mangled. However this is a straight text file, and any
mangling may be evident on inspection.  If it doesn't work and doesn't
look right, perhaps you can fix it up.  One of the main points is that
between the first line of code for short.com ("a 100") and the 150-
something'th line ("ret") there should be no blank lines, then there
should be one blank line, and finally 11 consecutive lines with no
blanks.  The last two of these lines should be "w" and "q".   (Extra
spaces anywhere don't hurt.  The blank line, for example, can contain
spaces.)

It is possible that your word processor may introduce extraneous
control and extended-ASCII characters.  This will cause DEBUG to
display an error message and the resulting SHORT.COM will probably
hang-up your PC.  If your word processor is of this kind, it should
have both a "document" and a "non-document" mode.  The file SHORT.SRC
should be written as a non-document file to avoid the problem.
LCODER.HEX can be written in either mode, as the extraneous characters
should not affect the decoding process.

After you have obtained LCODER.EXE, it can be used to encode files, or
to decode files which were encoded by itself.  Encoding can be done
with the XXE alphabet, which was developed by Phil Howard, adapted to
MS-DOS by David Camp, and revised for Turbo-C by Karl-l. Noell. There
is also the option of using the HEX alphabet, consisting of the
characters 0-9, A-F. HEX files are somewhat longer, but may be more
immune to transfer problems. On encoding, LCODER gives the output file
an extension of XFR or HEX depending on which alphabet is used.  The
output file contains a two-line HEX-encoded header (following the
"begin") which has directory information on the encoded file, a
checksum for the header, and a two-byte CRC for the encoded data.  On
decoding, any characters extraneous to the encoding alphabet are
stripped out, and information in the header is used to help insure
faithful reproduction of the original file. Unfortunately, the
decoding method and header also make LCODER incompatible with other
encode/decoders.

================ cut here for short.src ========================
a 100
push cs
pop es
cld
mov bx,00c8
mov ah,4a
int 21
mov sp,0c80
mov ah,48
mov bx,0300
int 21
mov [024a],ax
mov ah,48
mov bx,0150
int 21
mov bp,ax
call 0153
call 01d4
call 0176
call 01f5
call 0134
mov ax,4c00
int 21
mov dx,023f
mov ah,3c
xor cx,cx
int 21
jb 012f
mov bx,ax
mov cx,[024e]
mov ds,bp
xor dx,dx
mov ax,4000
int 21
mov ah,3e
int 21
ret
mov dx,0234
mov ax,3d00
int 21
jb 012f
mov bx,ax
push ds
mov cx,2ee0
xor dx,dx
mov ax,[024a]
mov ds,ax
mov ax,3f00
int 21
pop ds
jb 012f
mov [024c],ax
ret
xor bx,bx
mov cx,[024c]
mov ax,[024a]
mov es,ax
mov di,bx
mov si,0252
mov al,[si]
repnz
scasb
jcxz 012f
mov bx,di
es:
mov al,[di]
inc di
dec cx
jcxz 012f
call 01c0
jb 018c
inc si
cmp al,[si]
jnz 0181
cmp si,025b
jb 018c
mov ax,di
add ax,[0250]
mov si,ax
xor di,di
mov cx,[024c]
sub cx,si
mov [024c],cx
push ds
push es
pop ds
repz
movsb
pop ds
ret
cmp al,30
jb 01d2
cmp al,39
jbe 01d0
cmp al,41
jb 01d2
cmp al,46
ja 01d2
clc
ret
stc
ret
push ds
mov ax,[024a]
mov es,ax
xor si,si
mov di,si
mov cx,[024c]
jcxz 01ef
push es
pop ds
lodsb
call 01c0
jb 01ed
stosb
loop 01e6
pop ds
mov [024c],di
ret
push dx
push ds
xor dx,dx
mov cx,[024c]
shr cx,1
mov es,bp
mov ax,[024a]
mov ds,ax
xor si,si
xor di,di
call 0216
loop 020a
pop ds
pop dx
mov [024e],di
ret
push cx
lodsw
cmp al,39
jbe 021e
sub al,07
sub al,30
mov cl,04
shl al,cl
cmp ah,39
jbe 022c
sub ah,07
sub ah,30
add al,ah
stosb
pop cx
ret

e 234
6C 63 6F 64 65 72 2E 68 65 78 00 6C
e 240
63 6F 64 65 72 2E 65 78 65 00 00 00 00 00 00 00
e 250
6E 00 36 32 36 35 36 37 36 39 36 45 00 00 00 00
n short.com
rcx
15c
w
q

===================== end of short.src ====================

Now pick out the remaining material and file it as lcoder.hex.

===================== start of lcoder.hex =================
Lehigh coder. Version 0.6.
Comments to Al McLennan, LJM3@LEHIGH.bitnet.

Directory entry for encoded file:
LCODER.EXE      5264        20 OCT 89    08:56

begin
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end of coded data
===================== end of lcoder.hex ====================