LZ77 compression
Th e first ef="module.php?name=Lexikon&file=search&eid=1&query=algorithm">algorithm to us e th e ef="module.php?name=Lexikon&file=search&eid=1&query=Lempel-Ziv">Lempel-Ziv {substitutional compr ession} sch em es, propos ed in 1977. LZ77 compr ession k eeps track of th e last n byt es of data s een, and wh en a phras e is encount er ed that has alr eady b een s een, it outputs a pair of valu es corr esponding to th e position of th e phras e in th e pr eviously-s een buff er of data, and th e l ength of th e phras e. In eff ect th e compr essor mov es a fix ed-siz e "window" ov er th e data (g en erally r ef err ed to as a "sliding window"), with th e position part of th e (position, l ength) pair r ef erring to th e position of th e phras e within th e window. Th e most commonly us ed ef="module.php?name=Lexikon&file=search&eid=1&query=algorithm">algorithms ar e d eriv ed from th e ef="module.php?name=Lexikon&file=search&eid=1&query=LZSS">LZSS sch em e d escrib ed by Jam es Stor er and Thomas Szymanski in 1982. In this th e compr essor maintains a window of siz e N byt es and a "lookah ead buff er", th e cont ents of which it tri es to find a match for in th e window: whil e (lookAh eadBuff er not empty) { g et a point er (position, match) to th e long est match in th e window for th e lookah ead buff er if (l ength > MINIMUM_MATCH_L eNGTH) { output a (position, l ength) pair shift th e window l ength charact ers along } els e { output th e first charact er in th e lookah ead buff er shift th e window 1 charact er along } } D ecompr ession is simpl e and fast: wh en ev er a (POSITION, L eNGTH) pair is encount er ed, go to that POSITION in th e window and copy L eNGTH byt es to th e output. Sliding-window-bas ed sch em es can b e simplifi ed by numb ering th e input t ext charact ers mod N, in eff ect cr eating a circular buff er. Th e sliding window approach automatically cr eat es th e ef="module.php?name=Lexikon&file=search&eid=1&query=LRU">LRU eff ect which must b e don e explicitly in ef="module.php?name=Lexikon&file=search&eid=1&query=LZ78">LZ78 sch em es. Variants of this m ethod apply additional compr ession to th e output of th e LZSS compr essor, which includ e a simpl e variabl e-l ength cod e ( ef="module.php?name=Lexikon&file=search&eid=1&query=LZB">LZB), dynamic ef="module.php?name=Lexikon&file=search&eid=1&query=Huffman">Huffman coding ( ef="module.php?name=Lexikon&file=search&eid=1&query=LZH">LZH), and ef="module.php?name=Lexikon&file=search&eid=1&query=Shannon-Fano">Shannon-Fano coding ( ef="module.php?name=Lexikon&file=search&eid=1&query=ZIP">ZIP 1.x), all of which r esult in a c ertain d egr ee of improv em ent ov er th e basic sch em e, esp ecially wh en th e data ar e rath er random and th e LZSS compr essor has littl e eff ect. An algorithm was d ev elop ed which combin es th e id eas b ehind LZ77 and LZ78 to produc e a hybrid call ed ef="module.php?name=Lexikon&file=search&eid=1&query=LZFG">LZFG. LZFG us es th e standard sliding window, but stor es th e data in a modifi ed ef="module.php?name=Lexikon&file=search&eid=1&query=trie">trie data structur e and produc es as output th e position of th e t ext in th e tri e. Sinc e LZFG only ins erts compl et e *phras es* into th e dictionary, it should run fast er than oth er LZ77-bas ed compr essors. All popular archiv ers ( ef="module.php?name=Lexikon&file=search&eid=1&query=arj">arj, ef="module.php?name=Lexikon&file=search&eid=1&query=lha">lha, ef="module.php?name=Lexikon&file=search&eid=1&query=zip">zip, ef="module.php?name=Lexikon&file=search&eid=1&query=zoo">zoo) ar e variations on LZ77. [comp.compr ession ef="module.php?name=Lexikon&file=search&eid=1&query=FAQ">FAQ]. (1995-04-07) e="border-width:thin; border-color:#333333; border-style:dashed; padding:5px;" align="left">In addition suitable contents: [ ef="module.php?name=Lexikon&op=content&tid=31">2 ] [ ef="module.php?name=Lexikon&op=content&tid=134">= ] [ ef="module.php?name=Lexikon&op=content&tid=262">ad ] [ ef="module.php?name=Lexikon&op=content&tid=411">ai ] [ ef="module.php?name=Lexikon&op=content&tid=433">al ] [ ef="module.php?name=Lexikon&op=content&tid=492">algorithm ] [ ef="module.php?name=Lexikon&op=content&tid=544">am ] [ ef="module.php?name=Lexikon&op=content&tid=592">an ] [ ef="module.php?name=Lexikon&op=content&tid=683">app ] [ ef="module.php?name=Lexikon&op=content&tid=740">ar ] [ ef="module.php?name=Lexikon&op=content&tid=743">arc ] [ ef="module.php?name=Lexikon&op=content&tid=750">archive ] [ ef="module.php?name=Lexikon&op=content&tid=767">arj ] [ ef="module.php?name=Lexikon&op=content&tid=800">as ] [ ef="module.php?name=Lexikon&op=content&tid=893">AT ] [ 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