Path: utzoo!utgpu!attcan!uunet!steinmetz!davidsen From: davidsen@steinmetz.ge.com (William E. Davidsen Jr) Newsgroups: comp.binaries.ibm.pc.d Subject: Re: SIMTEL20 to ban ARC files Keywords: lzw, atob/btoa, 7 bit pure Message-ID: <12266@steinmetz.ge.com> Date: 29 Sep 88 18:14:48 GMT References:<12229@steinmetz.ge.com> <1221@ndmath.UUCP> Reply-To: davidsen@crdos1.UUCP (bill davidsen) Organization: General Electric CRD, Schenectady, NY Lines: 39 In article <1221@ndmath.UUCP> cww@ndmath.UUCP (Clarence W. Wilkerson) writes: | | I think the comparisons offered by Bill Davidsen are most | indicative of the effect of 16 bit compress compresses on | Unix system. With a 12 bit compress, I don't think you would | see such a large difference. A good point, but... I tried creating a zoo archive using the "no compression" flag, then compressing it. Same order of magnitude of results, compressed with arc, zoo, 12 or 16 bit compress. The results were all the same, but if the archive being compressed had a relatively small number of discrete tokens the 12 bit compress was actually smaller by 8 bytes. As a further test I created a file holding an "ls -lR" listing of a small subdirectory, then catted three copies into a 2nd file, and eight copies of the 2nd file into a 3rd. I then compressed the files with zoo, and here are the results. Archive foo.zoo: Length CF Size Now Date Time -------- --- -------- --------- -------- 3619 57% 1543 29 Sep 88 14:10:16 x 10857 68% 3457 29 Sep 88 14:10:16 y 86856 79% 18601 29 Sep 88 14:10:18 z -------- --- -------- --------- -------- 101332 77% 23601 3 files The reason the compression gets better on the same data is that the LVW algorithm "learns" about the data, and therefore does a better job as long as the data are similar. Using more bits only makes a big difference when a LOT of data is being processed, and the number of tokens to be remembered becomes larger than will fit in 12 bits. -- bill davidsen (wedu@ge-crd.arpa) {uunet | philabs}!steinmetz!crdos1!davidsen "Stupidity, like virtue, is its own reward" -me