例如VB.NET计算字符串或字节数组的CRC16

Question

参考此链接计算字符串或字节数组的CRC32我修改了代码，以便计算CRC16而不是CRC32，然而我得到了错误的结果，有人能告诉我错误在哪里吗？

Private Sub Main()
Crc16.ComputeChecksum(Encoding.UTF8.GetBytes("Some string"))
End Sub
    Public Class CRC16
Shared table As UShort()
Shared Sub New()
    Dim poly As UShort = &HA001US 'calculates CRC-16 using A001 polynomial (modbus)
    table = New UShort(255) {}
    Dim temp As UShort = 0
    For i As UShort = 0 To table.Length - 1
        temp = i
        For j As Integer = 8 To 1 Step -1
            If (temp And 1) = 1 Then
                temp = CUShort((temp >> 1) Xor poly)
            Else
                temp >>= 1
            End If
        Next
        table(i) = temp
    Next
End Sub
Public Shared Function ComputeChecksum(ByVal bytes As Byte()) As UShort
    Dim crc As UShort = &H0US ' The calculation start with 0x00
    For i As Integer = 0 To bytes.Length - 1
        Dim index As Byte = CByte(((crc) And &HFF) Xor bytes(i))
        crc = CUShort((crc >> 8) Xor table(index))
    Next
    Return Not crc
End Function
End Class

Answer 1

试试这个，它正在为仪器控制工作VB6代码。（sCommand是一个包含所有字节的临时字符串，Result被添加到sCommand中，Modbus首先使用LSB，TextToString和StringToAscii是将可读字符串"FF EE"转换为ASCII并返回的函数，因此它们在这里不感兴趣。）：

Private Sub cmdCRC16_Click()
Dim sCommand As String
Dim x As Long
Dim y As Long
Dim lCRC As Long
sCommand = TextToString(txtASCII)
'Initial value
lCRC = 65535 '(&HFFFF results in Integer -1)
For x = 1 To Len(sCommand)
    lCRC = lCRC Xor Asc(Mid(sCommand, x, 1))
    For y = 1 To 8
        If (lCRC Mod 2) > 0 Then
            lCRC = (lCRC And 65534) / 2
            lCRC = lCRC Xor 40961 '(&HA001 results in whatever negative integer)
        Else
            lCRC = (lCRC And 65534) / 2
        End If
    Next y
Next x
'Add CRC with LSB first
sCommand = sCommand + Chr(lCRC And 255)
sCommand = sCommand + Chr((lCRC And 65280) / 256)
txtASCII = StringToASCII(sCommand)

结束子

Answer 2

我刚刚遇到了同样的问题。简单的解决方案是在结尾省略否定，所以只需更改你的"Return Not crc"；至"；返回crc"；你会好起来的。

CRC-16有各种变体；CRC-16"；通常指的是IBM变体；ARC"；。它使用的XorOut值为零。参见16位参数化CRC算法目录。