🚀 go-pugleaf

I have just attempted to convert gnu-compress4.01 to produce compressed 
output suitable for feeding into LZWDecode filter in Level II postscript.  It
works up to the first token length change.  Before beating my haed against the 
wall, I would like to know if anyone already has c code for LZWEncode.

It is like unix compress, BUT

a/ does not start with the magic number and the bit length
b/ DOES start with an explicit table clear  256(10)
c/ appears to change bit length smoothly without a buffer flush
d/ ends with an EOD token (what a good idea!) 257(10)
e/ pushes bits the other way - i.e. the MSBit 
     first (CLEAR is 0x80 0x0.. not 0x00 0x8..)

This is based on the Postscript Language Reference Manual *SECOND* edition 
pp.130 132 - (yes it is worth buying!)

If anyone can correct my interpretation or provide more info, I will post a
corrected article.

Hint:  If you want to test any of these filters, you can let your Laserwriter
IIf or IIg or your Tek Phaser II PXe/i do it for you - they can encode and
decode.  
Here is some smaple  code


%!
%designed as a quick test bdb 6/92
(filter test: ) print
/=print where not {/=print {(               ) cvs print} def 1} if pop % 1 or dict
statusdict begin revision (                           ) 
	printername product
  	print ([) print print (] rev. ) print =print (  ) print
	pagecount =print ( pages ) print
end

(\nLZWEncode ASCII info following this file:\n) print
realtime
(%stdout) (w) file
  /ASCIIHexEncode filter dup
    /LZWEncode filter dup /FILTER exch def
     { FILTER (%stdin) (r) file 256 string readstring 
	{writestring} {writestring closefile closefile 
	 (\nEND: ) print
	 realtime exch sub 1000 div =print ( sec ) print exit} ifelse} loop
-----A---B

% replace the above line (-----A)with your test data line(s) - up to about 20k chars
% the example -----A---B comes from the  Ps Lang. Ref Man (45 45 45 45 45 65...)

Sample run:
===========
% setenv PRINTER scu_colour
% /usr/local/cap/lwpr ~/ps/foo.ps
abInit: [ddp:   4.23, 51], [GW:   4.23, 33] starting
Status: status: idle
status: idle
Sending /users/prl1/bdb112/ps/foo.ps
filter test: Phaser II PXe[Phaser II PXe] rev. 2  103 pages
LZWEncode ASCII info following this file:
800B6050220C0C840A8080>
END: 0.0 sec bdb112@rsphy1>

Note the line 800B.... is the same as p 132. Ps Lang. Ref Man

--
	-Boyd Blackwell
Plasma Research Lab, RSPhysSE, ANU/ GPO Box 4 /Canberra ACT 2601/AUSTRALIA
internet: bdb112@prl1.anu.edu.au
PHONE: +61 62 49 2482 +61 62 51 2605(h) FAX: Boyd Blackwell, PRL +61 62 49 1884