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cCRC32.cls
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cCRC32.cls
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VERSION 1.0 CLASS
BEGIN
MultiUse = -1 'True
Persistable = 0 'NotPersistable
DataBindingBehavior = 0 'vbNone
DataSourceBehavior = 0 'vbNone
MTSTransactionMode = 0 'NotAnMTSObject
END
Attribute VB_Name = "cCRC32"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = True
Attribute VB_PredeclaredId = False
Attribute VB_Exposed = False
'--------------------------------------------------------------------------------
' Component : cCRC32
' Project : ViOrb5
'
' Description: This code is taken from the VB.NET CRC32 algorithm
' provided by Paul (wpsjr1@succeed.net) - Excellent work!
'
' Modified :
'--------------------------------------------------------------------------------
Option Explicit
Private crc32Table() As Long
Private Const BUFFER_SIZE As Long = 8192
Public Function GetByteArrayCrc32(ByRef buffer() As Byte) As Long
Dim crc32Result As Long
crc32Result = &HFFFFFFFF
Dim i As Integer
Dim iLookup As Integer
For i = LBound(buffer) To UBound(buffer)
iLookup = (crc32Result And &HFF) Xor buffer(i)
crc32Result = ((crc32Result And &HFFFFFF00) \ &H100) And 16777215 ' nasty shr 8 with vb :/
crc32Result = crc32Result Xor crc32Table(iLookup)
Next i
GetByteArrayCrc32 = Not (crc32Result)
End Function
Public Function GetFileCrc32(ByRef stream As cBinaryFileStream) As Long
Dim crc32Result As Long
crc32Result = &HFFFFFFFF
Dim buffer(0 To BUFFER_SIZE - 1) As Byte
Dim readSize As Long
readSize = BUFFER_SIZE
Dim count As Integer
count = stream.Read(buffer, readSize)
Dim i As Integer
Dim iLookup As Integer
Dim tot As Integer
Do While (count > 0)
For i = 0 To count - 1
iLookup = (crc32Result And &HFF) Xor buffer(i)
crc32Result = ((crc32Result And &HFFFFFF00) \ &H100) And 16777215 ' nasty shr 8 with vb :/
crc32Result = crc32Result Xor crc32Table(iLookup)
Next i
count = stream.Read(buffer, readSize)
Loop
GetFileCrc32 = Not (crc32Result)
End Function
Private Sub Class_Initialize()
' This is the official polynomial used by CRC32 in PKZip.
' Often the polynomial is shown reversed (04C11DB7).
Dim dwPolynomial As Long
dwPolynomial = &HEDB88320
Dim i As Integer, j As Integer
ReDim crc32Table(256)
Dim dwCrc As Long
For i = 0 To 255
dwCrc = i
For j = 8 To 1 Step -1
If (dwCrc And 1) Then
dwCrc = ((dwCrc And &HFFFFFFFE) \ 2&) And &H7FFFFFFF
dwCrc = dwCrc Xor dwPolynomial
Else
dwCrc = ((dwCrc And &HFFFFFFFE) \ 2&) And &H7FFFFFFF
End If
Next j
crc32Table(i) = dwCrc
Next i
End Sub