Re: [MI400] compression algorithms

[Dave McKenzie <davemck@xxxxxxxxxxxxx>]

On Thursday 02 October 2003 11:12, Steve Richter wrote:
> The CPRDATA opcode uses either the TERSE or IBM LZ1 algorithm.  Both of
> these are IBM algoritms.  Any idea where the source code or description of
> these algoritms can be found?

I don't know.  But LZ1 is the Lempel-Ziv algorithm, so it's probably similar to 
what's used in PKZIP, Gzip, etc.  see:

http://www.info-zip.org

>
> Also, are these the algorithms used when a save file is compressed and
> compacted?

No, strangely enough, save files are compressed with the Convert Character to 
SNA (CVTCS) MI instruction, which does simple run-length encoding (RLE) in 
which strings of repeated characters are coded as a length byte and the 
repeated byte.  See:

http://publib.boulder.ibm.com/iseries/v5r1/ic2924/tstudio/tech_ref/mi/CVTCS.htm

>
> I want to be able to list the contents of a compressed save file from a pc
> program.  Maybe, hopefully, the content list of a save file is not
> compressed?

It is, but the CVTCS algorithm would be fairly simple to implement in a PC pgm.

--Dave

>
>
> thanks a lot,
>
> -Steve
>
> http://domino.watson.ibm.com/tchjr/journalindex.nsf/0/d0fd77dbf2b0b0e385256
>b fa0067fbe1?OpenDocument