< Public Function MessageDigest (Text As String, Code As String) As String (?)

Comments

    
    
    '
    ' Returns a 4-letter code calculated from the message
    'This is generally used to "digitally sign" a message, i.e. it's easier
    'to produce a digest from the message than it is to producea message with
    'a given digest.
    '
    'This is a relatively insecure implementation, designed for low-risk
    'usage.  For more security, use the MD5 hash calculation (see link from
    'the PHP home page for more details)

Public Function MessageDigest (Text As String, Code As String) As String

    Dim i As Integer
    Dim Modulo As Long
    Dim MaxNum As Long
    Dim Multiplier As Integer
    Dim Count As Long
    Dim Adder As Integer
    
    Modulo = 36 ^ 4 + Asc(Left(Code, 1))
    MaxNum = 36 ^ 4
    Adder = Asc(Right(Code, 1))
    
    Const Alphabet As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"
    
    
    
    For i = 1 To Len(Text)
        Count = Count + (Asc(Mid(Text, i, 1)) ^ 3) + Adder
        Count = Count - Int(Count / Modulo) * Modulo
    Next i
    
    Count = Count - Int(Count / MaxNum) * MaxNum
        
    Dim CharNum As Integer
    Dim Char As String

    For i = 3 To 0 Step -1
        CharNum = Int(Count / (36 ^ i))
        Char = Mid(Alphabet, CharNum + 1, 1)
        Count = Count - (CharNum * (36 ^ i))
        
        MessageDigest = MessageDigest & Char
    Next i
End Function

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