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Topic: yEnc basic implementation

Torsten Rienow
Member

posted May 02, 2003 12:45 PM

Please visit www.yenc.org to unterstand what yEnc is.
In short, yEnc is an encoding sheme similar to UUE or BASE64
with much (much much much) less overhead and encoded data.
I use it to encode text/binary data for storage in XML files.


#Compile ExeSub yEncodeBuffer(ByVal inBuf As Dword, ByVal cbInBuf As Dword, ByVal outBuf As Dword, ByRef cbOutUsed As Dword)
    #Register None
    Dim bTemp   As Byte
    Dim bIn     As Byte Ptr
    Dim bOut    As Byte Ptr
    bIn     = inBuf
    bOut    = outBuf
    For bIn = inBuf To (inBuf + cbInbuf - 1)
        bTemp = @bIn
        bTemp = bTemp + 42
        Select Case bTemp
            Case 0, 9, 10, 13, 46, 61
                @bOut = 61
                Incr bOut
                Incr cbOutUsed
                @bOut = bTemp + 64
                Incr bOut
                Incr cbOutUsed
            Case Else
                @bOut = bTemp
                Incr bOut
                Incr cbOutUsed
        End Select
    Next
End Sub
Sub yDecodeBuffer(ByVal inBuf As Dword, ByVal cbInBuf As Dword, ByVal outBuf As Dword, ByRef cbOutUsed As Dword)
    #Register None
    Dim bTemp   As Byte
    Dim bIn     As Byte Ptr
    Dim bOut    As Byte Ptr
    bIn     = inBuf
    bOut    = outBuf
    For bIn = inBuf To (inBuf + cbInbuf - 1)
        bTemp = @bIn
        If bTemp = 61 Then
            Incr bIn
            bTemp = @bIn - 64
        End If
        bTemp = bTemp - 42
        @bOut = bTemp
        Incr bOut
    Next
        
End Sub
Function PBMain
 
    Dim s1 As String
    Dim s2 As String
    Dim cb As Dword
    
    s1 = "Hallo" + Chr$(253)
    MsgBox "Text : " +  s1 + $CrLf + "Length : " + Str$(Len(s1)) , , "Before yCoding"
    s2 = Space$(Len(s1) * 2)
    yEncodeBuffer StrPtr(s1), Len(s1), StrPtr(s2), cb
    MsgBox "Text : " + s2 + $CrLf + "Length : " + Str$(cb) , , "yCoded"    s1 = s2
    s2 = Space$(Len(s1))
    yDecodeBuffer StrPtr(s1), Len(s1), StrPtr(s2), cb
    MsgBox "Text : " + Mid$(s2,1,cb) + $CrLf + "Length : " + Str$(cb) , , "Restored from yCode"
    
          
End Function

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Steve Smith
Member

posted August 01, 2004 10:28 PM

Torsten, I started writing my own yEnc tool and it didn't seem to be decoding correctly. When I do a file compare of the original picture and the decoded version, the binary gets screwed up somewhere in the file. So I trashed mine and used yours, thinking I was doing something wrong. But using your program, I have the same problem. I have tried multiple files. It always seems to start having problems at byte 124 and then the comparison gets out of sync. have you noticed anything, or is it just me?

Steve

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