XL 2019 VBA : Calcul checksum xor d'une chaine de longueur variable

Function CheckSum(ByVal X As String) As String
   Dim S As Byte, P As Integer
   For P = 1 To Len(X)
      S = S Xor Asc(Mid$(X, P, 1))
      Next P
   CheckSum = Right$("0" & Hex$(S), 2)
   End Function

   CheckSum = X & Right$("0" & Hex$(S), 2)

Function Chkxor(ByVal X As String) As String
   Dim S As Byte, P As Integer
   For P = 1 To Len(X)
      S = S Xor Asc(Mid$(X, P, 1))
      Next P
   Chkxor = Right$("0" & Hex$(S), 2)
   End Function

Sub TestXor()
  Dim cell As Range, chk As Long, i As Long, str1 As String
    For Each cell In Range("A2:A1000")
    If Not IsEmpty(cell) Then
      str1 = cell.Value
    chk = Asc(Left$(str1, 1))
      For i = 2 To Len(str1)
          chk = chk Xor Asc(Mid$(str1, i, 1))
      Next i
      cell.Offset(, 2).Value = cell.Value & Right$("00" & Hex$(chk), 2)
      End If
  Next cell
End Sub

Sub CHAINXOR()
  Dim Arr As Variant,  i As Long,  lastRow As Long
  lastRow = Range("A" & Rows.Count).End(xlUp).Row
  Arr = Range("A2:A" & lastRow).Value
    For i = 1 To UBound(Arr)
        If Arr(i, 1) <> "" Then Arr(i, 1) = Arr(i, 1) & Chkxor(Arr(i, 1))
    Next i
  Range("C2").Resize(UBound(Arr), 1) = Arr
End Sub

Option Explicit

Sub Essai()
  Dim n&: n = Cells(Rows.Count, 1).End(3).Row: If n = 1 Then Exit Sub
  Dim Tbl, chn$, lng As Byte, c As Byte, p As Byte, i&
  Tbl = [A1].Resize(n, 2): Tbl(1, 2) = "string 2"
  For i = 2 To n
    chn = Tbl(i, 1): lng = Len(chn): c = 0
    If lng = 10 Then
      For p = 1 To 10
        c = c Xor Asc(Mid$(chn, p, 1))
      Next p
      Tbl(i, 2) = chn & Right$("0" & Hex$(c), 2)
    End If
  Next i
  Application.ScreenUpdating = 0: [A1].Resize(n, 2) = Tbl
End Sub

 If lng = 10 Then
      For p = 1 To 10