comp_lzsslazy.bas

包含几十个加密解密类和压缩解压缩类,DES,LZW,Huffman

            Next
        End If
        Call AddToHistory(AddText)
    Loop
    ReDim ByteArray(Stream(0).Position - 1)
    For X = 0 To Stream(0).Position - 1
        ByteArray(X) = Stream(0).Data(X)
    Next
End Sub

Private Sub AddToHistory(AddText As String)
    If Len(History) + Len(AddText) < MaxHistory Then
        History = History & AddText
        AddText = ""
        Exit Sub
    ElseIf Len(History) < MaxHistory Then
        HistPos = Len(History)
        History = History & Left(AddText, MaxHistory - Len(History))
        AddText = Mid(AddText, MaxHistory - HistPos + 1)
        HistPos = 1
    End If
    Do
        If HistPos + Len(AddText) < MaxHistory Then
            Mid(History, HistPos, Len(AddText)) = AddText
            HistPos = HistPos + Len(AddText)
            AddText = ""
        Else
            If HistPos <= MaxHistory Then
                Mid(History, HistPos, MaxHistory - HistPos + 1) = Left(AddText, MaxHistory - HistPos + 1)
                AddText = Mid(AddText, MaxHistory - HistPos + 2)
            End If
            HistPos = 1
        End If
    Loop While AddText <> ""
End Sub

Private Function Check_For_Better_Match(DataArray() As Byte, Data As String, Position As Long) As Boolean
    Dim SearchStr As String
    Dim TempHistory As String
    Dim TempHistPos As Long
    Dim TempMaxHistory As Long
    Dim StartFrom As Long
    Dim StartPos As Long
    Dim MaxPos As Long
    Dim NuPos As Long
    Dim StartBitGain As Integer
    Dim NewBitGain As Integer
    Dim X As Long
    If Len(Data) > 255 Then Exit Function
'make backup of variables
    TempHistory = History
    TempHistPos = HistPos
    TempMaxHistory = MaxHistory
    StartFrom = Position - Len(Data)
    MaxPos = Position
'store the first byte into history
    Call AddToHistory(Chr(DataArray(StartFrom)))
    StartPos = StartFrom + 1
    NuPos = StartPos
    StartBitGain = Len(Data) * 8 - 24
    SearchStr = ""
    Do While NuPos <= UBound(DataArray) And StartPos < MaxPos
        If SearchStr = "" Then
            For X = 1 To Len(Data) + 1
                If NuPos <= UBound(DataArray) Then
                    SearchStr = SearchStr & Chr(DataArray(NuPos))
                    NuPos = NuPos + 1
                End If
            Next
        End If
        If NuPos <= UBound(DataArray) And StartPos < MaxPos Then
            If InStr(History, SearchStr & Chr(DataArray(NuPos))) <> 0 Then
'is maximum compression length reached?
                If Len(SearchStr) = 258 Then
                    History = TempHistory
                    HistPos = TempHistPos
                    MaxHistory = TempMaxHistory
                    If StartPos - StartFrom < 3 Then
                        For X = 1 To StartPos - StartFrom
                            Call AddBitsToStream(Stream(0), 0, 1)
                            Call AddBitsToStream(Stream(3), ASC(Left(Data, 1)), 8)
                            Call AddToHistory(Left(Data, 1))
                            Data = Mid(Data, 2)
                        Next
                        Check_For_Better_Match = True
                    Else
                        Data = Left(Data, StartPos - StartFrom)
                        Position = StartPos
                        Check_For_Better_Match = False
                    End If
                    Exit Function
                End If
                SearchStr = SearchStr & Chr(DataArray(NuPos))
                NuPos = NuPos + 1
            Else
                If Len(SearchStr) < 3 Then
                    StartPos = StartPos + 1
                    NuPos = StartPos
                    SearchStr = ""
                Else
                    NewBitGain = Len(SearchStr) * 8 - 24 - ((StartPos - StartFrom) * 9)
                    If NewBitGain > StartBitGain Then
                        History = TempHistory
                        HistPos = TempHistPos
                        MaxHistory = TempMaxHistory
                        If StartPos - StartFrom < 3 Then
                            For X = 1 To StartPos - StartFrom
                                Call AddBitsToStream(Stream(0), 0, 1)
                                Call AddBitsToStream(Stream(3), ASC(Left(Data, 1)), 8)
                                Call AddToHistory(Left(Data, 1))
                                Data = Mid(Data, 2)
                            Next
                            Check_For_Better_Match = True
                        Else
                            Data = Left(Data, StartPos - StartFrom)
                            Position = StartPos
                            Check_For_Better_Match = False
                        End If
                        Exit Function
                    Else
                        StartPos = StartPos + 1
                        NuPos = StartPos
                        SearchStr = ""
                    End If
                End If
            End If
        End If
    Loop
    History = TempHistory
    HistPos = TempHistPos
    MaxHistory = TempMaxHistory
    Check_For_Better_Match = False
End Function

Private Sub init_LZSS()
    Dim X As Integer
    For X = 0 To 3
        ReDim Stream(X).Data(10)
        Stream(X).BitPos = 0
        Stream(X).Buffer = 0
        Stream(X).Position = 0
    Next
    History = ""
    HistPos = 1
End Sub

'this sub will add an amount of bits to a certain stream
Private Sub AddBitsToStream(Toarray As LZSSStream, Number As Integer, Numbits As Integer)
    Dim X As Long
    If Numbits = 8 And Toarray.BitPos = 0 Then
        If Toarray.Position > UBound(Toarray.Data) Then ReDim Preserve Toarray.Data(Toarray.Position + 500)
        Toarray.Data(Toarray.Position) = Number And &HFF
        Toarray.Position = Toarray.Position + 1
        Exit Sub
    End If
    For X = Numbits - 1 To 0 Step -1
        Toarray.Buffer = Toarray.Buffer * 2 + (-1 * ((Number And 2 ^ X) > 0))
        Toarray.BitPos = Toarray.BitPos + 1
        If Toarray.BitPos = 8 Then
            If Toarray.Position > UBound(Toarray.Data) Then ReDim Preserve Toarray.Data(Toarray.Position + 500)
            Toarray.Data(Toarray.Position) = Toarray.Buffer
            Toarray.BitPos = 0
            Toarray.Buffer = 0
            Toarray.Position = Toarray.Position + 1
        End If
    Next
End Sub

'this sub will read an amount of bits from the inputstream
Private Function ReadBitsFromArray(FromArray() As Byte, FromPos As Long, FromBit As Byte, Numbits As Integer) As Long
    Dim X As Integer
    Dim Temp As Long
    If FromBit = 0 And Numbits = 8 Then
        ReadBitsFromArray = FromArray(FromPos)
        FromPos = FromPos + 1
        Exit Function
    End If
    For X = 1 To Numbits
        Temp = Temp * 2 + (-1 * ((FromArray(FromPos) And 2 ^ (7 - FromBit)) > 0))
        FromBit = FromBit + 1
        If FromBit = 8 Then
            If FromPos + 1 > UBound(FromArray) Then
                Do While X < Numbits
                    Temp = Temp * 2
                    X = X + 1
                Loop
                FromPos = FromPos + 1
                Exit For
            End If
            FromPos = FromPos + 1
            FromBit = 0
        End If
    Next
    ReadBitsFromArray = Temp
End Function

Private Function ReadASCFromArray(WhichArray() As Byte, FromPos As Long) As Integer
    ReadASCFromArray = WhichArray(FromPos)
    FromPos = FromPos + 1
End Function