Validate International Securities Identification Number

Calculate an International Securities Identification Number (ISIN)

An International Securities Identification Number (ISIN) is a unique international identifier for a financial security such as a stock or bond.

It consists of an exchange identifier, usually a two character ISO country code, followed by nine characters to identify the security. If the security code is less then nine characters, it is left-padded with zeroes (ASCII character 48). The final character is a checksum between '0' and '9' (ASCII 48 to 57).

VB6

<lang VB6> Option Explicit

Function MakeIsinCode(Exchange As String, security As String)

   Dim numLeadingZeroes As Integer
   
   numLeadingZeroes = 9 - Len(security)
   
   Dim leader As String
   
   leader = Exchange & String(numLeadingZeroes, "0") & security
   
   MakeIsinCode = leader & CStr(IsinCheckDigit(leader))

End Function

Function IsinCheckDigit(ByVal security As String) As Integer

   Dim digits As String
   
   Dim i As Integer
   
   For i = 1 To Len(security)
       Dim ch As String
       
       ch = UCase(Mid(security, i, 1))
       
       If ch >= "A" And ch <= "Z" Then
           ' A to Z translated to "10", "11", .. "35"
           digits = digits & CStr(Asc(ch) - 55)
       ElseIf ch >= "0" And ch <= "9" Then
           digits = digits & ch
       Else
           Err.Raise 50001, , "Security must contain only letters and digits"
       End If
   Next
   
   Dim total As Integer
   Dim tmp As Integer
   
   total = 0
   
   'If rightmost even, "other" digits for doubling are 2,4,6. If rightmost odd, they're 1,3,5.
   'rightmost digit is always doubled, so start with it and work backwards
   Dim other As Boolean
   other = True
   
   For i = Len(digits) To 1 Step -1
       tmp = CInt(Mid(digits, i, 1))
       
       If other Then
           If tmp < 5 Then
               ' 0 to 4 map to 0,2,4,6,8
               total = total + (tmp * 2)
           Else
               ' 5 to 9 map to 1,3,5,7,9
               total = total + ((tmp * 2) - 9)
           End If
       Else
           total = total + tmp
       End If
       
       'Toggle doubling flag
       other = Not other
   Next
   
   'Last Mod 10 is to wrap 10 to zero
   IsinCheckDigit = (10 - (total Mod 10)) Mod 10

End Function

</lang>