Working with LZ (Lempel-Ziv) compression APIs [ All Languages » VB »  ZIP-Unzip] Total Hit ( 6469) Rate this article:     Poor     Excellent   Submit Your Question/Comment about this article Rating Click here to download the attached file

Lempel-Ziv compression is a lossless compression algorithm, which means that no data is lost when compressing and decompressing the file, as opposed to lossy compression algorithms such as JPEG, where some data is lost each time data compression and decompression occur. NTFS volumes support file compression on an individual file basis. The file compression algorithm used by NTFS is Lempel-Ziv compression. Each type of data-compression algorithm minimizes redundant data in a unique manner. For example, the Huffman encoding algorithm assigns a code to characters in a file based on how frequently those characters occur. Another compression algorithm, called run-length encoding, generates a two-part value for repeated characters: the first part specifies the number of times the character is repeated, and the second part identifies the character. Another compression algorithm, known as the Lempel-Ziv algorithm, converts variable-length strings into fixed-length codes that consume less space than the original strings. In this article I will show you how to create a very simple to use class which you can use to compress and decompress files using LZ Compression method. Step-By-Step Example - Create a standard exe project - Add one class module and rename it to CLZCompression - Add 3 commandbutton controls on the form1 - Add 3 textbox controls on the form1 (for text3 set MultiLine=True and scroolbar=verticle) - Add two label controls - Add the following code in form1 Form1.frm Click here to copy the following block '//This sample will work 8 times faster if you run compiled version Dim lzComp As New CLZCompression Private Sub Command1_Click()   Dim t   t = Timer   Me.Caption = "Compressing the file..."   If lzComp.Compress(Text1, Text2) = True Then     Me.Caption = "It took " & Timer - t & " seconds to compress the file"     MsgBox "Compressed file path : " & Text2, vbInformation     Label1.Caption = Round(FileLen(Text1) / 1000, 2) & " KB"     Label2.Caption = Round(FileLen(Text2) / 1000, 2) & " KB"     '//Textbox only look up to first null character so whe have to remove all nulls to display full content     Text3 = Replace(FileText(Text2), vbNullChar, "")  '//Compressed file content (Which wont be readable)   Else     MsgBox "Error in compress file", vbCritical     Me.Caption = "Failed to compress"   End If End Sub Private Sub Command2_Click()   Dim t   t = Timer   Me.Caption = "Decompressing the file..."   If lzComp.Expand(Text2, Text1) = True Then     Me.Caption = "It took " & Timer - t & " seconds to Decompress the file"     MsgBox "Decompressed file path : " & Text1, vbInformation     Label1.Caption = Round(FileLen(Text1) / 1000, 2) & " KB"     Label2.Caption = Round(FileLen(Text2) / 1000, 2) & " KB"     '//Textbox only look up to first null character so whe have to remove all nulls to display full content     Text3 = Replace(FileText(Text1), vbNullChar, "")  '//Compressed file content (Which wont be readable)   Else     MsgBox "Error in compress file", vbCritical     Me.Caption = "Failed to Decompress"   End If End Sub Function FileText(ByVal FileName As String) As String   Dim handle As Integer   ' ensure that the file exists   If Len(Dir$(FileName)) = 0 Then     Err.Raise 53     ' File not found   End If   Dim f As Integer   Dim s As String   handle = FreeFile   Open FileName For Binary Access Read As handle   s = Space(LOF(handle))   Get #handle, , s   Close handle   FileText = s End Function '//This will read from compressed file without creating any decompressed file on the disk Private Sub Command3_Click()   '//Textbox only look up to first null character so whe have to remove all nulls to display full content   Text3 = Replace(lzComp.ReadFromCompressedFile(Text2, 0, 0), vbNullChar, "") End Sub Private Sub Form_Load()   Label1.Caption = ""   Label2.Caption = ""   Command1.Caption = "Compress"   Command2.Caption = "Decompress"   Command3.Caption = "Read From Compressed File in one step"   Text1.Text = App.Path & "\test.txt"  '//File to compress   Text2.Text = App.Path & "\test.tx_"  '//Compressed file save path End Sub - Add the following code in the CLZCompression class module CLZCompression.cls Click here to copy the following block Option Explicit Private Const OF_READ As Long = &H0 Private Const OF_CREATE As Long = &H1000 Private Const OFS_MAXPATHNAME  As Integer = 128 Private Const NORMAL_PRIORITY_CLASS As Long = &H20 Private Const INFINITE As Long = -1 Private Const BUFFERSIZE As Integer = 4096 Private Const N As Integer = 4096 Private Const f As Integer = 18 Private Const NIL As Long = N Private Const THRESHOLD As Integer = 2 Private hSource As Long Private hDestination As Long Private ret As Long Private bytesOfDest As Long Private b As Single Private m_SaveFilename As String Private m_LoadFilename As String Private Infinity As Long Private InBuffer() As Byte Private OutBuffer() As Byte Private DataLen As Long Private BufferPointer As Long Private textsize As Long Private codesize As Long Private textbuf(N + f - 1) As Byte Private matchposition As Integer Private matchlength As Byte Private lson(N + 1) As Integer Private rson(N + 257) As Integer Private dad(N + 1) As Integer Private Infile As Integer Private Outfile As Integer Private InLen As Long Private InPointer As Long Private OutPointer As Long Private InFilePointer As Long Private OutFilePointer As Long Private Const Blocklen As Integer = 1 Private Type Header   Magic As Long   Magic2 As Long   Magic3 As Integer   Filesize As Long End Type Private Type OFSTRUCT   cBytes As Byte   fFixedDisk As Byte   nErrCode As Integer   Reserved1 As Integer   Reserved2 As Integer   szPathName(OFS_MAXPATHNAME) As Byte End Type Private Compressheader As Header Private Declare Function GetExpandedName Lib "lz32.dll" Alias "GetExpandedNameA" ( _     ByVal lpszSource As String, _     ByVal lpszBuffer As String) As Long Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" ( _     Destination As Any, _     Source As Any, _     ByVal Length As Long) '//CopyLZFile and LZCopy both are same (No difference at all) 'Private Declare Function CopyLZFile Lib "lz32.dll" ( _ '    ByVal hfSource As Long, _ '    ByVal hfDest As Long) As Long Private Declare Function LZCopy Lib "lz32.dll" ( _     ByVal hfSource As Long, _     ByVal hfDest As Long) As Long Private Declare Function LZOpenFile Lib "lz32.dll" Alias "LZOpenFileA" ( _     ByVal lpszFile As String, _     lpOf As OFSTRUCT, _     ByVal style As Long) As Long Private Declare Sub LZClose Lib "lz32.dll" (ByVal hfFile As Long) Private Declare Function LZInit Lib "lz32.dll" ( _     ByVal hfSrc As Long) As Long Private Declare Function LZRead Lib "lz32.dll" ( _     ByVal hfFile As Long, _     ByVal lpvBuf As String, _     ByVal cbread As Long) As Long Private Declare Function LZSeek Lib "lz32.dll" ( _     ByVal hfFile As Long, _     ByVal lOffset As Long, _     ByVal nOrigin As Long) As Long '//The LZDone function is obsolete. It is provided only for compatibility '//with 16-bit versions of Windows. Win32-based applications should use the LZOpenFile function. Private Declare Sub LZDone Lib "lz32.dll" () '//The LZStart function is obsolete. It is provided only for compatibility '//with 16-bit versions of Windows. Win32-based applications should use the LZCopy function. Private Declare Function LZStart Lib "lz32" () As Long Private Function GetByte() As Byte   On Error GoTo errHandler   InFilePointer& = InFilePointer& + 1   If InPointer& = BUFFERSIZE Then     Get Infile, , InBuffer     GetByte = InBuffer(0)     InPointer& = 1   Else           'NOT INPOINTER&...     GetByte = InBuffer(InPointer&)     InPointer& = InPointer& + 1   End If   Exit Function errHandler:   Err.Raise Err.Number, Err.Description End Function Private Sub PutByte(ByVal TheByte As Byte)   On Error GoTo errHandler   OutFilePointer& = OutFilePointer& + 1   If OutPointer& = BUFFERSIZE - 1 Then     OutBuffer(BUFFERSIZE - 1) = TheByte     BufferPointer& = 0     Put Outfile, , OutBuffer     OutPointer& = 0   Else           'NOT OUTPOINTER&...     OutBuffer(OutPointer&) = TheByte     OutPointer& = OutPointer& + 1   End If   Exit Sub errHandler:   Err.Raise Err.Number, Err.Description End Sub Private Sub FDeleteNode(ByVal p As Integer)   On Error GoTo errHandler   Dim q As Integer   If dad(p) = NIL Then     Exit Sub   End If   If rson(p) = NIL Then     q = lson(p)   ElseIf lson(p) = NIL Then 'NOT RSON(P)...     q = rson(p)   Else           'NOT LSON(P)...     q = lson(p)     If rson(q) <> NIL Then       Do         q = rson(q)       Loop While rson(q) <> NIL       rson(dad(q)) = lson(q)       dad(lson(q)) = dad(q)       lson(q) = lson(p)       dad(lson(p)) = q     End If     rson(q) = rson(p)     dad(rson(p)) = q   End If   dad(q) = dad(p)   If rson(dad(p)) = p Then     rson(dad(p)) = q   Else           'NOT RSON(DAD(P))...     lson(dad(p)) = q   End If   dad(p) = NIL   Exit Sub errHandler:   Err.Raise Err.Number, Err.Description End Sub Private Sub FInitTree()   On Error GoTo errHandler   Dim i As Integer   For i = N + 1 To (N + 256)     rson(i) = NIL   Next i   For i = 0 To N - 1     dad(i) = NIL   Next i   Exit Sub errHandler:   Err.Raise Err.Number, Err.Description End Sub Private Sub FInsertNode(ByVal r As Integer)   On Error GoTo errHandler   Dim i  As Integer   Dim p  As Integer   Dim cmp As Integer   Dim key As Integer   Dim x  As Long   Dim x1 As Integer   Dim x2 As Integer   cmp = 1   key = r   p = N + 1 + textbuf(r)   rson(r) = NIL   lson(r) = NIL   matchlength = 0   Infinity& = 2147483647   For x& = 0 To Infinity&     If cmp >= 0 Then       If rson(p) <> NIL Then         p = rson(p)       Else       'NOT RSON(P)...         rson(p) = r         dad(r) = p         Exit Sub       End If     Else         'NOT CMP...       If lson(p) <> NIL Then         p = lson(p)       Else       'NOT LSON(P)...         lson(p) = r         dad(r) = p         Exit Sub       End If     End If     For i = 1 To f - 1       x1 = textbuf(r + i)       x2 = textbuf(p + i)       cmp = x1 - x2       If cmp <> 0 Then         Exit For       End If     Next i     If i > matchlength Then       matchposition = p       matchlength = i       If matchlength >= f Then         Exit For       End If     End If   Next x   dad(r) = dad(p)   lson(r) = lson(p)   rson(r) = rson(p)   dad(lson(p)) = r   dad(rson(p)) = r   If rson(dad(p)) = p Then     rson(dad(p)) = r   Else           'NOT RSON(DAD(P))...     lson(dad(p)) = r   End If   dad(p) = NIL   Exit Sub errHandler:   Err.Raise Err.Number, Err.Description End Sub Private Sub FlushBuffer()   On Error GoTo errHandler   Dim WriteBuffer() As Byte   If OutPointer& > 0 Then     ReDim WriteBuffer(OutPointer - 1)     CopyMemory WriteBuffer(0), OutBuffer(0), OutPointer     Put Outfile, , WriteBuffer   Else           'NOT OUTPOINTER&...   End If   Exit Sub errHandler:   Err.Raise Err.Number, Err.Description End Sub '///////////////////////////////////////////////////// '//There is no inbuilt function to compress a file '//so we have to built our own algorith to compress '//a file using LZ Compression Algorithm '///////////////////////////////////////////////////// Private Sub LZCompFile(ByVal file1 As Integer, _             ByVal file2 As Integer)   On Error GoTo errHandler   Dim codebuf(17)   As Byte   Dim codebufptr   As Integer   Dim i        As Integer   Dim cc       As Byte   Dim r        As Integer   Dim s        As Integer   Dim lenn      As Integer   Dim lastmatchlength As Integer   Dim mask      As Byte   Infile = file1   Outfile = file2   DataLen = LOF(Infile)   With Compressheader     .Filesize = DataLen     .Magic = &H44445A53     .Magic2 = &H3327F088     .Magic3 = &H41   End With         'Compressheader   Put Outfile, , Compressheader   FInitTree   codebuf(0) = 0   codebufptr = 1   mask = 1   s = 0   r = N - f   For i = s To r - 1     textbuf(i) = 32   Next i   OpenBuffer   For lenn = 0 To f - 1     If InFilePointer& = InLen& Then       Exit For     End If     cc = GetByte     textbuf(r + lenn) = cc   Next lenn   textsize = lenn   If textsize = 0 Then     Exit Sub   End If   For i = 1 To f     FInsertNode (r - i)   Next i   FInsertNode (r)   Do     If matchlength > lenn Then       matchlength = lenn     End If     If matchlength <= THRESHOLD Then       matchlength = 1       codebuf(0) = (codebuf(0) Or mask)       codebuf(codebufptr) = textbuf(r)       codebufptr = codebufptr + 1     Else         'NOT MATCHLENGTH...       matchposition = matchposition + 2       codebuf(codebufptr) = ((matchposition) And 255)  'Achtung normal ohne + 2       codebufptr = codebufptr + 1       codebuf(codebufptr) = (((matchposition \ 16) And 240) Or (matchlength - (THRESHOLD + 1))) And 255       codebufptr = codebufptr + 1     End If     mask = (mask * 2) And 255     If mask = 0 Then       For i = 0 To codebufptr - 1         PutByte codebuf(i)       Next i       codesize = codesize + codebufptr       codebuf(0) = 0       mask = 1       codebufptr = mask     End If     lastmatchlength = matchlength     For i = 0 To lastmatchlength - 1       If InFilePointer& = InLen& Then         Exit For       End If       cc = GetByte       FDeleteNode (s)       textbuf(s) = cc       If s < (f - 1) Then         textbuf(s + N) = cc       End If       s = (s + 1) And (N - 1)       r = (r + 1) And (N - 1)       FInsertNode (r)     Next i     textsize = textsize + i     Do While i < lastmatchlength       i = i + 1       FDeleteNode (s)       s = (s + 1) And (N - 1)       r = (r + 1) And (N - 1)       lenn = lenn - 1       If lenn <> 0 Then         FInsertNode (r)       End If     Loop   Loop While lenn > 0   If codebufptr > 1 Then     For i = 0 To codebufptr - 1       PutByte codebuf(i)     Next i     codesize = codesize + codebufptr   End If   FlushBuffer   Exit Sub errHandler:   Err.Raise Err.Number, Err.Description End Sub Private Sub OpenBuffer()   On Error GoTo errHandler   ReDim InBuffer(BUFFERSIZE - 1) As Byte   ReDim OutBuffer(BUFFERSIZE - 1) As Byte   InLen& = DataLen&   Get Infile, , InBuffer   InPointer& = 0   InFilePointer& = 0   OutPointer& = 0   OutFilePointer& = 0   Exit Sub errHandler:   Err.Raise Err.Number, Err.Description End Sub Public Property Get SaveFilename() As String   SaveFilename = m_SaveFilename End Property Public Property Let SaveFilename(ByVal vNewValue As String)   m_SaveFilename = vNewValue End Property Public Property Get LoadFilename() As String   LoadFilename = m_LoadFilename End Property Public Property Let LoadFilename(ByVal vNewValue As String)   m_LoadFilename = vNewValue End Property '/////////////////////////////////////////////////////////////////////////////// '//This function will compress a specified file using LZ Compression Algorithm '/////////////////////////////////////////////////////////////////////////////// Public Function Compress(Optional LoadName As String = vbNullString, _              Optional SaveName As String = vbNullString) As Boolean   On Error GoTo errHandler   Dim FileNumber As Integer   Dim FileNumber2 As Integer   If LenB(LoadName) = 0 Then     LoadName = m_LoadFilename   End If   If LenB(SaveName) = 0 Then     SaveName = m_SaveFilename   End If   FileNumber = FreeFile   Open LoadName For Binary As FileNumber   FileNumber2 = FreeFile   Open SaveName For Binary As FileNumber2   LZCompFile FileNumber, FileNumber2   Close FileNumber   Close FileNumber2   Compress = True   Exit Function errHandler:   Debug.Print Err.Description End Function '/////////////////////////////////////////////////////////////////////////////// '//This function will Decompress a file which is compressed using LZ Compression Algorithm '//LZCopy API automatically decompress and create a new file '/////////////////////////////////////////////////////////////////////////////// Public Function Expand(Optional LoadName As String = vbNullString, _                Optional SaveName As String = vbNullString) As Boolean   On Error GoTo errHandler   Dim openStruct As OFSTRUCT   If LenB(LoadName) = 0 Then     LoadName = m_LoadFilename   End If   If LenB(SaveName) = 0 Then     If m_SaveFilename = "" Then       SaveName = String(255, 0)              '//Convert "test.tx_" to "test.txt"       SaveName = ExpandedName(LoadName)            Else       SaveName = m_SaveFilename     End If   End If   hSource& = LZOpenFile(LoadName, openStruct, OF_READ)   hDestination& = LZOpenFile(SaveName, openStruct, OF_CREATE)   ret& = bytesOfDest = LZCopy(hSource&, hDestination&)   LZClose hDestination&   LZClose hSource&   Expand = True   Exit Function errHandler:   Debug.Print Err.Description End Function Public Function ReadFromCompressedFile(Optional FileName As String = vbNullString, _       Optional StartPosition As Long = 0, Optional NBytesToRead As Long = 0) As String   On Error GoTo errHandler   Dim FileData As String   Dim hFile As Long, ret As Long, DataLen As Long   Dim openStruct As OFSTRUCT   If LenB(FileName) = 0 Then     FileName = m_LoadFilename   End If   hFile = LZOpenFile(FileName, openStruct, OF_READ)   If hFile > 0 Then     If NBytesToRead = 0 Then  '//Full       FileData = Space$(FileLen(FileName))     Else         '//Only N Bytes       FileData = Space$(NBytesToRead)     End If     DataLen = Len(FileData)     If StartPosition > 0 Then       ' 0 = Moves the file pointer lOffset bytes from the beginning of the file.       ' 1 = Moves the file pointer lOffset bytes from the current position.       ' 2 = Moves the file pointer lOffset bytes from the end of the file.       If LZSeek(hFile, StartPosition, 0) Then         ret = LZRead(hFile, FileData, DataLen)         LZClose hFile '//Always Always Always ..close the open file       Else         LZClose hFile '//Always Always Always ..close the open file         Err.Raise Err.Number, "API Error #" & Err.LastDllError       End If     Else       ret = LZRead(hFile, FileData, DataLen)       LZClose hFile  '//Always Always Always ..close the open file       If ret = 0 Then FileData = ""     End If   Else     Err.Raise Err.Number, Err.Description   End If   ReadFromCompressedFile = FileData   Exit Function errHandler:   LZClose hFile      '//Always Always Always ..close the open file   Err.Raise Err.Number, Err.Description End Function Public Function ExpandedName(FileName As String) As String   Dim Buffer As String   Buffer = String(255, 0)   GetExpandedName FileName, Buffer   ExpandedName = Left$(Buffer, InStr(1, Buffer, Chr$(0)) - 1) End Function

Related Article(s)

GetFileOwner - Get the owner of an NTFS file

Handling NTFS Permissions Part -1 (handling kernel object permissions)

Handling NTFS Permissions Part-2 (handling user object permissions)

Handling NTFS Permissions Part-3 (handling shared resource permissions)

Handling NTFS Permissions Part-4 (handling registry key permissions)

Handling NTFS Permissions Part-5 (handling printer permissions)

Working with file time APIs

Taking advantage of EFS (Encrypted File System) APIs in Win2K/XP

Taking advantage of NTFS inbuilt compression using APIs (Only for NTFS file system)

Submitted By : Nayan Patel  (Member Since : 5/26/2004 12:23:06 PM)
	Job Description : He is the moderator of this site and currently working as an independent consultant. He works with VB.net/ASP.net, SQL Server and other MS technologies. He is MCSD.net, MCDBA and MCSE. In his free time he likes to watch funny movies and doing oil painting.
View all (893) submissions by this author  (Birth Date : 7/14/1981 )