Const logE = 0.434294481903252
 
Function Entropy(ByVal text As Variant) As Double
Dim count(0 To 255) As Long
Dim freq(0 To 255) As Double
Dim i
For i = 1 To Len(text)
DoEvents
count(Asc(Mid(text, i, 1))) = count(Asc(Mid(text, i, 1))) + 1
Next i
For i = 0 To 255
DoEvents
freq(i) = count(i) / Len(text)
If freq(i) > 0 Then
Entropy = Entropy - freq(i) * (Log10(freq(i)) / Log10(2))
End If
Next i
End Function
 
Function Log10(ByVal number As Double) As Double
Log10 = Log(number) * logE
End Function