Attribute VB_Name = "Module1"

Private aCRC8Table(255) As Integer


Public Function calculateiButtonCRC(ByVal buffer As String) As String
    Dim temp As String
     
     CRC8Setup
     
    If Len(buffer) = 20 Then
        temp = Mid(buffer, 3, 16)
        calculateiButtonCRC = Hex$(CRC8(temp))
    Else
        calculateiButtonCRC = "Too short"
    End If
        
End Function


Public Function CRC8(sMessage As String) As Integer
' Given table is already setup.
' Set iCRC = 0
' For each byte in message
'''   calculate iCRC = (iCRC >> 8) ^ Table[(iCRC & 0xFF) ^ byte]
'     calculate iCRC = table( iCRC xor byte )
' Return iCRC
    
    Dim iCRC As Integer
    Dim i As Integer
    Dim bytNum As Byte
    Dim bytString As String
    Dim ia As Integer

    iCRC = 0
'    For i = 1 To Len(sMessage)
'        bytC = Asc(Mid(sMessage, i, 1))
'        bytT = (iCRC And &HFF) Xor bytC
'        ia = uiShiftRightBy8(iCRC)
'        iCRC = ia Xor aCRC8Table(bytT)
'    Next

     For i = 1 To Len(sMessage) Step 2
        bytString = "&H" + (Mid(sMessage, i, 2))
        bytNum = CLng(bytString)
        iCRC = aCRC8Table(iCRC Xor bytNum)
    Next
    
    
    CRC8 = iCRC

End Function

Public Function uiShiftRightBy8(x As Integer) As Integer
    ' Shift 16-bit integer value to right by 8 bits
    ' Avoiding problem with sign bit
    Dim iNew As Integer
    iNew = (x And &H7FFF) \ 256
    If (x And &H8000) <> 0 Then
        iNew = iNew Or &H80
    End If
    uiShiftRightBy8 = iNew
End Function

Public Function CRC8Setup()

    Dim vntA As Variant
    Dim i As Integer

'    0, 94, 188, 226, 97, 63, 221, 131, 194, 156, 126, 32, 163, 253, 31, 65,
'    157, 195, 33, 127, 252, 162, 64, 30, 95, 1, 227, 189, 62, 96, 130, 220,
'    35, 125, 159, 193, 66, 28, 254, 160, 225, 191, 93, 3, 128, 222, 60, 98,
'    190, 224, 2, 92, 223, 129, 99, 61, 124, 34, 192, 158, 29, 67, 161, 255,

'    70, 24, 250, 164, 39, 121, 155, 197, 132, 218, 56, 102, 229, 187, 89, 7,
'    219, 133, 103, 57, 186, 228, 6, 88, 25, 71, 165, 251, 120, 38, 196, 154,
'    101, 59, 217, 135, 4, 90, 184, 230, 167, 249, 27, 69, 198, 152, 122, 36,
'    248, 166, 68, 26, 153, 199, 37, 123, 58, 100, 134, 216, 91, 5, 231, 185,

'    140, 210, 48, 110, 237, 179, 81, 15, 78, 16, 242, 172, 47, 113, 147, 205,
'    17, 79, 173, 243, 112, 46, 204, 146, 211, 141, 111, 49, 178, 236, 14, 80,
'    175, 241, 19, 77, 206, 144, 114, 44, 109, 51, 209, 143, 12, 82, 176, 238,
'    50, 108, 142, 208, 83, 13, 239, 177, 240, 174, 76, 18, 145, 207, 45, 115,

'    202, 148, 118, 40, 171, 245, 23, 73, 8, 86, 180, 234, 105, 55, 213, 139,
'    87, 9, 235, 181, 54, 104, 138, 212, 149, 203, 41, 119, 244, 170, 72, 22,
'    233, 183, 85, 11, 136, 214, 52, 106, 43, 117, 151, 201, 74, 20, 246, 168,
'    116, 42, 200, 150, 21, 75, 169, 247, 182, 232, 10, 84, 215, 137, 107, 53);

    ' Use variant array kludge to set up table
    vntA = Array( _
        0, 94, 188, 226, 97, 63, 221, 131, 194, 156, 126, 32, 163, 253, 31, 65, _
        157, 195, 33, 127, 252, 162, 64, 30, 95, 1, 227, 189, 62, 96, 130, 220, _
        35, 125, 159, 193, 66, 28, 254, 160, 225, 191, 93, 3, 128, 222, 60, 98, _
        190, 224, 2, 92, 223, 129, 99, 61, 124, 34, 192, 158, 29, 67, 161, 255)

        
    For i = 0 To 63
        aCRC8Table(i) = vntA(i - 0)
    Next
    
    vntA = Array( _
        70, 24, 250, 164, 39, 121, 155, 197, 132, 218, 56, 102, 229, 187, 89, 7, _
        219, 133, 103, 57, 186, 228, 6, 88, 25, 71, 165, 251, 120, 38, 196, 154, _
        101, 59, 217, 135, 4, 90, 184, 230, 167, 249, 27, 69, 198, 152, 122, 36, _
        248, 166, 68, 26, 153, 199, 37, 123, 58, 100, 134, 216, 91, 5, 231, 185)
    
    For i = 64 To 127
        aCRC8Table(i) = vntA(i - 64)
    Next
    
    vntA = Array( _
        140, 210, 48, 110, 237, 179, 81, 15, 78, 16, 242, 172, 47, 113, 147, 205, _
        17, 79, 173, 243, 112, 46, 204, 146, 211, 141, 111, 49, 178, 236, 14, 80, _
        175, 241, 19, 77, 206, 144, 114, 44, 109, 51, 209, 143, 12, 82, 176, 238, _
        50, 108, 142, 208, 83, 13, 239, 177, 240, 174, 76, 18, 145, 207, 45, 115)

    For i = 128 To 191
        aCRC8Table(i) = vntA(i - 128)
    Next
    
    vntA = Array( _
        202, 148, 118, 40, 171, 245, 23, 73, 8, 86, 180, 234, 105, 55, 213, 139, _
        87, 9, 235, 181, 54, 104, 138, 212, 149, 203, 41, 119, 244, 170, 72, 22, _
        233, 183, 85, 11, 136, 214, 52, 106, 43, 117, 151, 201, 74, 20, 246, 168, _
        116, 42, 200, 150, 21, 75, 169, 247, 182, 232, 10, 84, 215, 137, 107, 53)
    
    For i = 192 To 255
        aCRC8Table(i) = vntA(i - 192)
    Next
    
End Function