Excel VBA 的 CRC8 计算

Question

我正在用 Excel VBA 的 CRC8 计算打破我的头脑。我在 VBA 中编写了一个函数，其中 returns CRC8 值稍后可以存储到单元格中。但是，在打印相同内容时，我收到一条错误消息 "OverFlow"。

我在 "ShiftLeft = Num * (2 ^ Places)"

处的函数中溢出

Function CRCPrateek(CRCrng As Range) As Integer

    Dim CRC As Integer
    Dim length As Integer
    Dim Hexbyte As Integer
    Dim i As Integer

    'Initial CRC seed is Zero CRC = H00
    'The real part of the CRC. Where I commented "Polynomial", it used to be a # define
    'Polynomial 7. 'I replaced the word Polynomial with 7, however that means the 7 may
    'be subject to change depending on the version of the crc you are running.
    'To loop it for each cell in the range

    For Each cel In CRCrng
        'Verify if there is atleast one cell to work on
        If Len(cel) > 0 Then
            Hexbyte = cel.Value
            CRC = CRC Xor Hexbyte
            For i = 0 To 7
                If Not CRC And H80 Then
                    CRC = ShiftLeft(CRC, 1)
                    CRC = CRC Xor 7
                Else
                    CRC = ShiftLeft(CRC, 1)
                End If
             Next
        End If
    Next
    CRCPrateek = CRC
End Function

Function ShiftLeft(Num As Integer, Places As Integer) As Integer

    ShiftLeft = Num * (2 ^ Places)

End Function

Answer 1

您处理的是 2 字节整数，而不是字节。此外，我怀疑 cell.value 确实是一个十六进制值 - 而不是像 '3F' 这样的十六进制字符串，您必须先将其转换为数值（在 0..255 范围内）。
要创建真正的字节数组和字节 CRC，请参考此解决方案：Calculating CRC8 in VBA

溢出的解决办法就是在移位前屏蔽最高位。

Answer 2

其他人的努力和建议帮助我找到了正确的答案；我发布了我编写的用于计算 CRC8 的通用函数。它给了我想要的结果，我还对照其他 CRC 计算器对其进行了检查。

'GENERATE THE CRC 

Function CRCPrateek(ByVal crcrng As Range) As Long
Dim crc As Byte
Dim length As Byte
Dim Hexbyte As String
Dim DecByte As Byte
Dim i As Byte

' Initial CRC seed is Zero
crc = &H0

'The real part of the CRC. Where I commented "Polynomial", it used to be a # define
'Polynomial 7. I replaced the word Polynomial with 7, however that means the 7 may
'be subject to change depending on the version of the crc you are running.

'To loop it for each cell in the range
For Each cel In crcrng
    'Verify if there is atleast one cell to work on
 '  If Len(cel) > 0 Then
       DecByte = cel.Value
       crc = crc Xor DecByte
       For i = 0 To 7
            If ((crc And &H80) <> 0) Then
                crc = ShiftLeft(crc, 1)
                crc = crc Xor 7
            Else
                crc = ShiftLeft(crc, 1)
            End If
       Next
  ' End If
Next

CRCPrateek = crc
End Function    

Function ShiftLeft(ByVal Num As Byte, ByVal Places As Byte) As Byte
ShiftLeft = ((Num * (2 ^ Places)) And &HFF)
End Function

'END OF CRC

在调用上述函数时，您唯一需要作为参数传递到这里的是单元格的范围（具有小数（在单元格中使用 HEX2DEC）值。

'EXAMPLE CALL TO CRC FUNCTION FROM A SUB

'select the crc Range
Set crcrng = Range("I88", "U88")
crc = CRCPrateek(crcrng)
Sheet1.Cells(88, 22).Value = crc
MsgBox ("CRC value is " & Sheet1.Cells(86, 22).Value & "(in HEX) ")

注意：此函数将输入值作为小数，以十进制计算 CRC 值，稍后在返回 CRC 值后，您可以将其存储在任何其他单元格中，并通过在单元格中使用公式 DEC2HEX 将其转换回十六进制

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