Messages in this thread | | | From | Guillaume Lacôte <> | Subject | Re: Using compression before encryption in device-mapper | Date | Wed, 14 Apr 2004 12:02:07 +0200 |
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> > Oops ! I thought it was possible to guarantee with the Huffman encoding > > (which is more basic than Lempev-Zif) that the compressed data use no > > more than 1 bit for every byte (i.e. 12,5% more space). > > Makes sense, although I'd like to see the proof first. Shouldn't be > too hard to do. > I was referring to the paper by Jeffrey Scott Vitter "Design and Analysis of Dynamic Huffman Codes" (accessible through http://acm.org). It defines a refinement of the well-known dynamic Huffman algorithm by Faller, Gallager and Knuth such that the encoded length will use at most _one_ more bit per encoded letter than the optimal two-pass Huffman algorithm (it is also shown that the FGK algorithm an use twice the optimal length + on more bit per letter).
My conclusion comes from the fact that for every text, the optimal two-pass huffman encoding can _not_ be longer than the native encoding (apart from the dictionnary encoding).
Actually I plan to implement the easier FGK algorithm first - if the whole matter makes sense.
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