CRunch and UNCRunch LZH Release Documentation
                               September, 1989

What this is:

   This library contains versions of programs to perform compression of, 
   decompression of, and typing of files via the LZH algorithm.  The algorithm 
   and its history are covered below.

   In the purest sense, this is really a release of the CRLZH.REL and 
   UNLZH.REL (CRunch LZH and UNcrunch LZH) code.  However, without a 
   convenient (and familiar) user interface, the encoding method is of little 
   use to the typical user.

   As a quick means to an end, the algorithm has been grafted (with 
   permission) to Steve Greenberg's CRUNCH, and UNCRUNCH programs.  (There is 
   a separate TYPELZ graft.)  The resulting program files (CRLZH and UNCRLZH) 
   are, at this time, offered as an official release (the beta test period 
   being completed), on a restricted distribution basis: Permission is granted 
   to use or copy these files provided that such use is non-profit in nature.

What LZH compression does and how it compares:

   FIRST - It's SLOW.  Much slower than CRUNCH.  About even with the old 
   SQueeze.  It's the nature of the algorithm, but few complaints have been 
   recieved about that fact.  This release is marginally faster than the beta 
   test version.

   The most impressive aspect of the algorithm is that it compresses further 
   than CRUNCH.  The nature of material being compressed is important - prose 
   and high level language code will compress the best.  Since the algorithm 
   depends, in part, on patterns within the file being compressed, it is 
   surprising to discover that it does a better job (in general) on .COM files 
   than CRUNCH.

   Examples:
    CRUNCH of SLR180.COM   106% ratio   (actually made a larger file)
    CRLZH  of SLR180.COM    84% ratio
    CRUNCH of TYPELZ22.Z80  45% ratio
    CRLZH  of TYPELZ22.Z80  40% ratio
    CRUNCH of 'C' source    45% ratio   (typical 'C' src selected at random)
    CRLZH  of 'C' source    33% ratio   (same file as above)

A small history:

   I am NOT the originator of the LZH encoding.  The program that started my 
   whole involvement in the introduction of this method of compression to the 
   8-bit world bears the following opening comments:
      /*
      * LZHUF.C English version 1.0
      * Based on Japanese version 29-NOV-1988
      * LZSS coded by Haruhiko OKUMURA
      * Adaptive Huffman Coding coded by Haruyasu YOSHIZAKI
      * Edited and translated to English by Kenji RIKITAKE
      */

   This 'C' program implemented the compression algorithm of the LHARC program 
   which arrived on the US scene in the spring of '89.

   Being of a curious nature, I figured I'd play with the algorithm just to 
   understand it (the internal comments were, indeed, sparse - leaving MUCH to 
   the reader's contemplation/reverse engineering) while 'better minds' than I 
   tackled it in earnest.

   Months passed.  I found that I was 'mastering' the algorithm (read that as 
   demonstrating to myself that I understood it) by converting it piece-wise 
   to assembly language.  After a while, I was left with a 'C' language main 
   program, run time library, and I/O with the business end of the compression 
   and decompression implemented entirely in assembly language.  Since the 
   expected event of one of the 'heavies' in the PD and/or compression world 
   releasing a CP/M version of the compression algorithm hadn't come to pass, 
   I set about making a version myself.

   The natural choice was to substitute CRUNCH (UNCR and TYPELZ) for my 
   vestigial 'C' main program.  After some 'customizations' of the algorithm 
   (adding reserved codes and tailoring the table sizes to produce a good 
   trade-off between the available CP/M memory space and execution speed), the  
   programs in this LBR were generated.

   At this time, let me take the opportunity to thank Mr. Greenberg for making 
   the CRUNCH and UNCR programs and releasing the code.  Without the 
   availability of those programs (and his permission), I probably would not 
   have set out upon the final phase of this project.  His coding allowed me 
   to easily 'graft' my encoding and decoding subroutines to the main programs 
   to rapidly create these release versions.

BETA TEST RESULTS:

   Approximately 1 month of beta test was used, during which time no algorithm 
   bugs were reported.  Some complaints about the fact that the UNCRLZH 
   program assumed <filname>.?Z? when invoked with <filename>.* were received, 
   and, accordingly, the character used in the case of a .* extension has been 
   made a configuration item.

Parting shots:

       The author will not be responsible for any damage, loss, etc.  caused 
       by the use of these programs.

R. Warren
Sysop, The Elephant's Graveyard (Z-Node#9)
619-270-3148 (PCP area CASDI)