49 lines
1.3 KiB
Text
49 lines
1.3 KiB
Text
-- demo\rosetta\LZW_compression.exw
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with javascript_semantics
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function compress(string uncompressed)
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integer dict = new_dict(), dictSize = 255, c
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sequence result = {}
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string word = ""
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for i=0 to 255 do setd(""&i,i,dict) end for
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for c in uncompressed do
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if getd_index(word&c,dict) then
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word &= c
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else
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result &= getd(word,dict)
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dictSize += 1
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setd(word&c,dictSize,dict)
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word = ""&c
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end if
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end for
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if word!="" then
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result &= getd(word,dict)
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end if
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destroy_dict(dict)
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return result
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end function
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function decompress(sequence compressed)
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integer dict = new_dict(), dictSize = 255, k, ki
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string dent = "", result = "", word = ""
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for i=0 to 255 do setd(i,""&i,dict) end for
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for k in compressed do
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if getd_index(k,dict) then
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dent = getd(k,dict)
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elsif k=dictSize then
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dent = word&word[1]
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else
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crash("error")
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end if
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result &= dent
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setd(dictSize,word&dent[1],dict)
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dictSize += 1
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word = dent
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end for
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destroy_dict(dict)
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return result
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end function
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constant example = "TOBEORNOTTOBEORTOBEORNOT"
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sequence com = compress(example)
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pp(com,{pp_IntCh,true,pp_Maxlen,90})
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?decompress(com)
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