Public Class Form1
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
 
 
 
        Dim checksumcalculator = New CRC16CCITT( _
          CRC16CCITT.InitialCRCValue.NonZero2)
        Dim knut
        Dim value() As Byte = System.Text.Encoding.ASCII.GetBytes( _
          "6C20536574696F20322C31")
        MsgBox(Format(checksumcalculator.ComputeCheckSum(value), "X2")) ' 29B1
 
    End Sub
End Class
 
Public Class CRC16CCITT
    Public Enum InitialCRCValue
        Zeroes = 0
        NonZero1 = &HFFFF
        NonZero2 = &H1D0F
    End Enum
 
    Private Const poly As UShort = &H8408
    Dim table() As UShort = {&H0, &H1189, &H2312, &H329B, &H4624, &H57AD, _
      &H6536, &H74BF, &H8C48, &H9DC1, &HAF5A, &HBED3, &HCA6C, &HDBE5, &HE97E, _
      &HF8F7, &H1081, &H108, &H3393, &H221A, &H56A5, &H472C, &H75B7, &H643E, _
      &H9CC9, &H8D40, &HBFDB, &HAE52, &HDAED, &HCB64, &HF9FF, &HE876, &H2102, _
      &H308B, &H210, &H1399, &H6726, &H76AF, &H4434, &H55BD, &HAD4A, &HBCC3, _
      &H8E58, &H9FD1, &HEB6E, &HFAE7, &HC87C, &HD9F5, &H3183, &H200A, &H1291, _
      &H318, &H77A7, &H662E, &H54B5, &H453C, &HBDCB, &HAC42, &H9ED9, &H8F50, _
      &HFBEF, &HEA66, &HD8FD, &HC974, &H4204, &H538D, &H6116, &H709F, &H420, _
      &H15A9, &H2732, &H36BB, &HCE4C, &HDFC5, &HED5E, &HFCD7, &H8868, &H99E1, _
      &HAB7A, &HBAF3, &H5285, &H430C, &H7197, &H601E, &H14A1, &H528, &H37B3, _
      &H263A, &HDECD, &HCF44, &HFDDF, &HEC56, &H98E9, &H8960, &HBBFB, &HAA72, _
      &H6306, &H728F, &H4014, &H519D, &H2522, &H34AB, &H630, &H17B9, &HEF4E, _
      &HFEC7, &HCC5C, &HDDD5, &HA96A, &HB8E3, &H8A78, &H9BF1, &H7387, &H620E, _
      &H5095, &H411C, &H35A3, &H242A, &H16B1, &H738, &HFFCF, &HEE46, &HDCDD, _
      &HCD54, &HB9EB, &HA862, &H9AF9, &H8B70, &H8408, &H9581, &HA71A, &HB693, _
      &HC22C, &HD3A5, &HE13E, &HF0B7, &H840, &H19C9, &H2B52, &H3ADB, &H4E64, _
      &H5FED, &H6D76, &H7CFF, &H9489, &H8500, &HB79B, &HA612, &HD2AD, &HC324, _
      &HF1BF, &HE036, &H18C1, &H948, &H3BD3, &H2A5A, &H5EE5, &H4F6C, &H7DF7, _
      &H6C7E, &HA50A, &HB483, &H8618, &H9791, &HE32E, &HF2A7, &HC03C, &HD1B5, _
      &H2942, &H38CB, &HA50, &H1BD9, &H6F66, &H7EEF, &H4C74, &H5DFD, &HB58B, _
      &HA402, &H9699, &H8710, &HF3AF, &HE226, &HD0BD, &HC134, &H39C3, &H284A, _
      &H1AD1, &HB58, &H7FE7, &H6E6E, &H5CF5, &H4D7C, &HC60C, &HD785, &HE51E, _
      &HF497, &H8028, &H91A1, &HA33A, &HB2B3, &H4A44, &H5BCD, &H6956, &H78DF, _
      &HC60, &H1DE9, &H2F72, &H3EFB, &HD68D, &HC704, &HF59F, &HE416, &H90A9, _
      &H8120, &HB3BB, &HA232, &H5AC5, &H4B4C, &H79D7, &H685E, &H1CE1, &HD68, _
      &H3FF3, &H2E7A, &HE70E, &HF687, &HC41C, &HD595, &HA12A, &HB0A3, &H8238, _
      &H93B1, &H6B46, &H7ACF, &H4854, &H59DD, &H2D62, &H3CEB, &HE70, &H1FF9, _
      &HF78F, &HE606, &HD49D, &HC514, &HB1AB, &HA022, &H92B9, &H8330, &H7BC7, _
      &H6A4E, &H58D5, &H495C, &H3DE3, &H2C6A, &H1EF1, &HF78}
    Dim intValue As UShort = 0
 
    Public Function ComputeCheckSum(ByVal bytes As Byte()) As UShort
        Dim crc As UShort = Me.intValue
        For i As Integer = 0 To bytes.Length - 1
            crc = CUShort(((crc << 8) Xor table(((crc >> 8) Xor (&HFF And _
              bytes(i))))))
        Next
        Return crc
    End Function
 
    Public Function ComputeCheckSumBytes(ByVal bytes As Byte()) As Byte()
        Dim crc As UShort = ComputeCheckSum(bytes)
        Return BitConverter.GetBytes(crc)
    End Function
 
    Public Sub New(ByVal initialvalue As InitialCRCValue)
        Me.intValue = CUShort(initialvalue)
        Dim temp, a As UShort
        For i As Integer = 0 To table.Length - 1
            temp = 0
            a = CUShort(i << 8)
            For j As Integer = 0 To 7
                If ((temp Xor a) And &H8000) <> 0 Then
                    temp = CUShort((temp << 1) Xor poly)
                Else
                    temp <<= 1
                End If
                a <<= 1
            Next
            table(i) = temp
        Next
    End Sub
End Class