疑問 - CRC16檢查碼

[JOVI]

各位前輩~小弟不材，特來請教。
小弟有一設備傳輸時須算出檢查碼，但是其Protocol是C語言，小弟所學的是vb，所以一值轉不過去，訪間的crc16檢查碼vb範例小弟有試過，但解出來(0xC1,0x61)都與手冊的結果有出入(0xD8,0x93)，所以還請各位前輩幫忙解惑(把c範例轉換成vb)。

小弟網路找到的vb範例

Private Sub Command1_Click()
Dim databyte(2) As Byte
databyte(0) = &H5
databyte(1) = &H0
databyte(2) = &H0
MsgBox CRC16(databyte)
End Sub

Private Function CRC16(data() As Byte) As String
      Dim CRC16Hi As Byte
      Dim CRC16Lo As Byte
      CRC16Hi = &HFF
      CRC16Lo = &HFF
      Dim i As Integer
      Dim iIndex As Long
      For i = 0 To UBound(data)
        iIndex = CRC16Lo Xor data(i)
        CRC16Lo = CRC16Hi Xor GetCRCLo(iIndex)       '低位?理
        CRC16Hi = GetCRCHi(iIndex)                     '高位?理
      Next i
'      CRC16Hi = CRC16Hi Xor &HFF
'''
'     CRC16Lo = CRC16Lo Xor &HFF
      Dim ReturnData(1) As Byte
      ReturnData(0) = CRC16Hi        'CRC高位
      ReturnData(1) = CRC16Lo        'CRC低位
      CRC16 = Hex(CRC16Hi) & Hex(CRC16Lo)

    End Function

    'CRC低位字?值表
    Function GetCRCLo(Ind As Long) As Byte
      GetCRCLo = Choose(Ind + 1, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, _
&H80, &H41, &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40)
    End Function

    'CRC高位字?值表
    Function GetCRCHi(Ind As Long) As Byte
      GetCRCHi = Choose(Ind + 1, &H0, &HC0, &HC1, &H1, &HC3, &H3, &H2, &HC2, &HC6, &H6, &H7, &HC7, &H5, &HC5, &HC4, &H4, &HCC, &HC, &HD, &HCD, &HF, &HCF, &HCE, &HE, &HA, &HCA, &HCB, &HB, &HC9, &H9, &H8, &HC8, &HD8, &H18, &H19, &HD9, &H1B, &HDB, &HDA, &H1A, &H1E, &HDE, &HDF, &H1F, &HDD, &H1D, &H1C, &HDC, &H14, &HD4, &HD5, &H15, &HD7, &H17, &H16, &HD6, &HD2, &H12, &H13, &HD3, &H11, &HD1, &HD0, &H10, &HF0, &H30, &H31, &HF1, &H33, &HF3, &HF2, &H32, &H36, &HF6, &HF7, &H37, &HF5, &H35, &H34, &HF4, &H3C, &HFC, &HFD, &H3D, &HFF, &H3F, &H3E, &HFE, &HFA, &H3A, &H3B, &HFB, &H39, &HF9, &HF8, &H38, &H28, &HE8, &HE9, &H29, &HEB, &H2B, &H2A, &HEA, &HEE, &H2E, &H2F, &HEF, &H2D, &HED, &HEC, &H2C, &HE4, &H24, &H25, &HE5, &H27, &HE7, &HE6, &H26, &H22, &HE2, &HE3, &H23, &HE1, &H21, &H20, &HE0, &HA0, &H60, _
&H61, &HA1, &H63, &HA3, &HA2, &H62, &H66, &HA6, &HA7, &H67, &HA5, &H65, &H64, &HA4, &H6C, &HAC, &HAD, &H6D, &HAF, &H6F, &H6E, &HAE, &HAA, &H6A, &H6B, &HAB, &H69, &HA9, &HA8, &H68, &H78, &HB8, &HB9, &H79, &HBB, &H7B, &H7A, &HBA, &HBE, &H7E, &H7F, &HBF, &H7D, &HBD, &HBC, &H7C, &HB4, &H74, &H75, &HB5, &H77, &HB7, &HB6, &H76, &H72, &HB2, &HB3, &H73, &HB1, &H71, &H70, &HB0, &H50, &H90, &H91, &H51, &H93, &H53, &H52, &H92, &H96, &H56, &H57, &H97, &H55, &H95, &H94, &H54, &H9C, &H5C, &H5D, &H9D, &H5F, &H9F, &H9E, &H5E, &H5A, &H9A, &H9B, &H5B, &H99, &H59, &H58, &H98, &H88, &H48, &H49, &H89, &H4B, &H8B, &H8A, &H4A, &H4E, &H8E, &H8F, &H4F, &H8D, &H4D, &H4C, &H8C, &H44, &H84, &H85, &H45, &H87, &H47, &H46, &H86, &H82, &H42, &H43, &H83, &H41, &H81, &H80, &H40)
    End Function

手冊範例:
輸入值為 0x05,0x00,0x00
解出值為 0xD8,0x93

unsigned int CRC_Check(unsigned char *ary,unsigned char len)
{
 unsigned int crc;
 unsigned char i,j;

  crc=0xFFFF;
  for(i=0;i<len;i++,ary++)
      {
      crc=((unsigned int))*ary <<8)^crc;
      for(j=0;j<8;j==)
          {
          if(crc & 0x8000)
              crc=(crc<<1)^0x1021;
          else
              crc<<=1;
          }
      }
      return(crc ^ 0xFFFF);
}

[mini]

VB 那個個人不懂
至於C 轉成 VB
主要把運算子搞清楚
轉換起來就沒問題了

<<8 是指二位元運算，向左移8個位元
<<1 表示乘2
<<2 表示乘4
所以 <<8 表示乘 256
那為何不直接用 * 256呢？
因為 << 有捨棄多出的位元 及 運算快的作用
(unsigned int 佔4個byte 可表示0~0xFFFFFFFF)
如果體質不好的編譯器用 *的話可能會溢位也不一定

^crc 表示 位元XOR運算子

因為 VB沒有 位移運算子 的用法
所以只能用 * 256
又
VB的 Long
使用 4 個位元組 -2,147,483,648 到 2,147,483,647
所以可能必須用 Single 來兌換 C的 unsigned int
而且必須多一道判斷當大於 &HFFFFFFFF 之處理 (Temp=Temp Mod &HFFFFFFFF)

至於C的 ^ 就使用 Xor 是沒問題的

[JOVI]

感謝大大的解說，小弟大致明瞭一些，等小弟測試成功，再將程式碼貼上來