Attribute VB_Name = "Comp_ReducerDynamic"


Option Explicit

'This is a 1 run method but we have to keep the whole contents
'in memory until some variables are saved wich are needed bij the decompressor

'This compressor makes use of a dictionary and code the ascii character
'to the position it is located in
'for every character it has to store a header and location
'there are 7 headers which will tell yo the amount of bits to read
'for the location
'example:
'header :   positions
'   0   :   0/1
'   1   :   2/3/4/5
'   2   :   6/7/8/9/10/11/12/13
'   3   :   14/15/16/17/18/19/20/21/22/23/24/25/26/27/28/29
'   etc'etc
'The header will have 1,2 or 3 bits depending on the numbers of chars to compress
'The dictionary is build up from the most common char to the least common char
'if as char must be stored which is the 6'ed most common char in the dictionary
'then the posiotion in the dictionary will be 6 but since we start the
'the value 0 the position will be 6-1=5
'5 will fall within the range of header 1
'so the headerbits will be 001 with will tell us to store 2 bits more
'for the position of the char
'since header 1 start with position 2 we can substract this from the
'actual position 5-2=3 which can be stored in 2 bits 11
'so the code to store the 6'ed character wil be 001 11
'this reducer don't have to store the dictionary into te output stream
'cause it will be created on the flow

Private Type BytePos
    Data() As Byte
    Position As Long
    Buffer As Integer
    BitPos As Integer
End Type
Private Stream(1) As BytePos    '0=control 1=BitStreams

Private CharCount(256) As Long

Private Dictionary As String
Private BitsForHeader As Integer   '1=max 6 chars  2=max 30 chars  3=more then 30 chars

Private Sub Init_ReducerDynamic()
    Dim X As Integer
'   controller bits 000-111 for 1 to 8 which tel the numbers of bits to read
'   bits to store
'   2 * 1 bit
'   4 * 2 bits
'   2^? bits * ? bits
'
'   256 characters can be stored in
'   2*1+4*2+8*3+16*4+32*5+64*6+128*7+2*8 bits + 256 * 3 controlerbits
    Dictionary = ""
    For X = 0 To 255
        Dictionary = Dictionary & Chr(X)
        CharCount(X) = 0
    Next
    CharCount(256) = 0
    BitsForHeader = 3
    For X = 0 To 1
        ReDim Stream(X).Data(500)
        Stream(X).BitPos = 0
        Stream(X).Buffer = 0
        Stream(X).Position = 0
    Next
End Sub

Public Sub Compress_ReducerDynamic(ByteArray() As Byte)
    Dim X As Long
    Dim Y As Long
    Dim NoMore As Boolean
    Dim Most As Long
    Dim NewFileLen As Long
    Dim Nuchar As Byte
    Dim CharCount(255) As Long
    Call Init_ReducerDynamic
'whe only read the stream and convert them to bitstreams
    For X = 0 To UBound(ByteArray)
        Call AddValueToStream(CInt(ByteArray(X)))
    Next
'send the EOF-marker
    Call AddValueToStream(256)
'lets fill the leftovers
    For X = 0 To 1
        Do While Stream(X).BitPos > 0
            Call AddBitsToStream(Stream(X), 0, 1)
        Loop
    Next
'Lets restore the bounderies
    For X = 0 To 1
        ReDim Preserve Stream(X).Data(Stream(X).Position - 1)
    Next
'whe calculate the new length of the new data
    NewFileLen = 0
    For X = 0 To 1
        NewFileLen = NewFileLen + UBound(Stream(X).Data) + 1
    Next
    ReDim ByteArray(NewFileLen + 3)
'here we store the compressed data
    NewFileLen = 0
    For X = 0 To 0
        ByteArray(NewFileLen) = Int(UBound(Stream(X).Data) / &H10000) And &HFF
        NewFileLen = NewFileLen + 1
        ByteArray(NewFileLen) = Int(UBound(Stream(X).Data) / &H100) And &HFF
        NewFileLen = NewFileLen + 1
        ByteArray(NewFileLen) = UBound(Stream(X).Data) And &HFF
        NewFileLen = NewFileLen + 1
    Next
    For X = 0 To 1
        For Y = 0 To UBound(Stream(X).Data)
            ByteArray(NewFileLen) = Stream(X).Data(Y)
            NewFileLen = NewFileLen + 1
        Next
    Next
End Sub

Public Sub DeCompress_ReducerDynamic(ByteArray() As Byte)
    Dim OutStream() As Byte
    Dim OutPos As Long
    Dim InposCont As Long
    Dim InContBit As Integer
    Dim InposData As Long
    Dim InDataBit As Integer
    Dim Char As Integer
    Dim Numbits As Integer
    Dim X As Long
    ReDim OutStream(500)
    Call Init_ReducerDynamic
    InposCont = 0
    InposData = 0
    For X = 0 To 2
        InposData = CLng(InposData) * 256 + ByteArray(InposCont)
        InposCont = InposCont + 1
    Next
    InposData = InposData + InposCont + 1
    InContBit = 0
    InDataBit = 0
    OutPos = 0
    Do
        Numbits = ReadBitsFromArray(ByteArray, InposCont, InContBit, BitsForHeader) + 1
        Char = ReadBitsFromArray(ByteArray, InposData, InDataBit, Numbits)
        Char = ExpanderBits(Numbits, Char)
        If Char = 256 Then Exit Do
        Call AddCharToArray(OutStream, OutPos, CByte(Char))
    Loop
    ReDim ByteArray(OutPos - 1)
    For X = 0 To OutPos - 1
        ByteArray(X) = OutStream(X)
    Next
End Sub

Private Function ReducerBits(Char As Integer) As Integer
    Dim DiPos As Integer
    Dim TotPos As Integer
    Dim Y As Integer
    If Char = 256 Then ReducerBits = 8: Char = 255: Exit Function
    DiPos = InStr(Dictionary, Chr(Char)) - 1
    Call update_Model(Char)
    For Y = 1 To 8
        If DiPos >= TotPos And DiPos < TotPos + 2 ^ Y Then
            ReducerBits = Y
            Char = DiPos - TotPos
            Exit Function
        End If
        TotPos = TotPos + 2 ^ Y
    Next
End Function

Private Function ExpanderBits(BitsNum As Integer, BytePos As Integer) As Integer
    If BitsNum = 8 And BytePos = 255 Then ExpanderBits = 256: Exit Function
    Dim TotPos As Integer
    Dim Y As Integer
    For Y = 1 To BitsNum - 1
        TotPos = TotPos + 2 ^ Y
    Next
    TotPos = TotPos + BytePos + 1
    ExpanderBits = ASC(Mid(Dictionary, TotPos, 1))
    Call update_Model(ExpanderBits)
End Function

Private Sub update_Model(Char As Integer)
    Dim DictPos As Integer
    Dim OldPos As Integer
    Dim Temp As Long
    DictPos = InStr(Dictionary, Chr(Char))
    OldPos = DictPos
    CharCount(DictPos) = CharCount(DictPos) + 1
    Do While DictPos > 1 And CharCount(DictPos) >= CharCount(DictPos - 1)
        Temp = CharCount(DictPos - 1)
        CharCount(DictPos - 1) = CharCount(DictPos)
        CharCount(DictPos) = Temp
        DictPos = DictPos - 1
    Loop
    If OldPos = DictPos Then Exit Sub
    Dictionary = Left(Dictionary, DictPos - 1) & Chr(Char) & Mid(Dictionary, DictPos, OldPos - DictPos) & Mid(Dictionary, OldPos + 1)
End Sub

Private Sub AddValueToStream(Number As Integer)
    Dim BitsDeep As Integer
    BitsDeep = ReducerBits(Number)
    Call AddBitsToStream(Stream(0), BitsDeep - 1, BitsForHeader)
    Call AddBitsToStream(Stream(1), Number, BitsDeep)
End Sub

'this sub will add an amount of bits to a sertain stream
Private Sub AddBitsToStream(Toarray As BytePos, 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 function will return a value out of the amaunt of bits you asked for
Private Function ReadBitsFromArray(FromArray() As Byte, FromPos As Long, FromBit As Integer, Numbits As Integer) As Long
    Dim X As Integer
    Dim Temp As Long
    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

'this sub will add a char into the outputstream
Private Sub AddCharToArray(Toarray() As Byte, ToPos As Long, Char As Byte)
    If ToPos > UBound(Toarray) Then ReDim Preserve Toarray(ToPos + 500)
    Toarray(ToPos) = Char
    ToPos = ToPos + 1
End Sub