ISIN code

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

From <http://rosettacode.org/wiki/Calculate_International_Securities_Identification_Number>