Author: Eran
Date: 05:52:46 06/16/00
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On June 16, 2000 at 04:04:12, guy haworth wrote: > >I don't know what compression technique Eugene Nalimov uses ... but I think he >finishes up with a file of self-contained 8Kb physical blocks of compressed >data. > >For some compression functions 'COMPRESS', I guess you could prove, because of >the way the function works that: > > COMPRESS [ COMPRESS (file) ] = COMPRESS (file) .... > >i.e. the COMPRESS function is 'idempotent' in matho terms. > > >As other replies indicate, if COMPRESS-1 is any good, you should not (by >definition) expect to get any benefit out of applying it, or another compression >function, on the resultant compressed file. > >As I was just about to confirm this myself, I've just done it: > > kppkp.nbw = 33,320KB = 34,119,680 bytes > winzip(kppkp.nbw) = 34,118,774 bytes > winzip(winzip(Kppkp.nbw)) = 34,050,433 bytes > >What does this prove? > >First, it shows that EN's compression technique is pretty good as winzip doesn't >make much of an impression. > >Secondly, it shows that winzip isn't formally idempotent - but again, it can't >make much of an impression on the files it creates. > >G
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