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07.27.2008 at 10:45PM PDT, ID: 23599816
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7.3

LZW Compression/Decompression in Visual Basic 6.0

Asked by The_Cyclone in Visual Basic Programming, Microsoft Visual Basic.Net, Algorithms

Tags: ,

I have to write a compression algorithm in Visual Basic 6.0 that does not depend or use any other third-party DLL files.
So I chose LZW algorithm to implement.
I've written this code, I think Compress part works well, but de-compress does not work well...
Here is my compress and decompress functions:Start Free Trial 
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Public Function LZW_Compress(ByVal UncompressedData As String) As String
 
    Dim w As String
    Dim c As String
    Dim wc As String
    Dim dic As New Dictionary
    Dim Output As String
    Dim Code As Long
    
    Dim i As Long
    dic.InitializeDictionary
     
    w = ""
    For i = 1 To Len(UncompressedData)
        
        c = Mid(UncompressedData, i, 1)
        wc = w + c
        If dic.IsExists(wc) Then
            w = wc
        Else
            Code = dic.GetIndexOf(w)
            Output = Output & IIf(Output = "", "", ",") & Code
            Code = dic.Add(wc)
            w = c
        End If
        
        '?
    
    Next i
    
    Output = Output & IIf(Output = "", "", ",") & dic.GetIndexOf(w)
    
    LZW_Compress = Output
 
End Function
 
Public Function LZW_Decompress(ByVal CompressedData As String) As String
    
    If CompressedData = "" Then Exit Function
    
    Dim dic As New Dictionary
    
    dic.InitializeDictionary
 
    Dim Output As String
    Dim Entry As String
 
    Dim k As String
    Dim w As String
    Dim i As Long
    
    Dim arrCompressedData() As String
    arrCompressedData = Split(CompressedData, ",")
    
    w = arrCompressedData(0)
    Output = Output & dic.GetValue(w)
    
    For i = 1 To UBound(arrCompressedData)
    
        k = arrCompressedData(i)
        
        If dic.IsIndexExists(k) Then
        
            Entry = dic.GetValue(k)
            
        ElseIf k = dic.Length Then
            
            Entry = dic.GetValue(w) + dic.mrtLeft(dic.GetValue(w), 1)
            
        Else
        
            MsgBox "Bad compressed"
            
        End If
        
        Output = Output + Entry
        
        dic.Add (dic.GetValue(w) + dic.mrtLeft(Entry, 1))
        
        w = dic.GetIndexOf(Entry)
        
    Next
    
    LZW_Decompress = Output
    
End Function
[+][-]07.27.2008 at 10:47PM PDT, ID: 22100860

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[+][-]07.28.2008 at 12:07AM PDT, ID: 22101135

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About this solution

Zones: Visual Basic Programming, Microsoft Visual Basic.Net, Algorithms
Tags: Visual Basic 6.0, LZW Compression
Sign Up Now!
Solution Provided By: Mortaza_doulaty
Participating Experts: 1
Solution Grade: A
 
 
[+][-]07.28.2008 at 04:54AM PDT, ID: 22102214

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