Strings schnell zählen

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''' <summary>
''' Diese Funktion zählt die Anzahl eines Strings innerhalb eines anderen Strings
''' </summary>
''' <param name="Expression">Der String in dem gesucht werden soll</param>
''' <param name="FindWhat">Der String nach dem gesucht werden soll</param>
''' <param name="CompareMethod">Gibt die Vergleichsmethode an, Binary ist CaseSensitive</param>
Public Function CountString(ByVal Expression As String, ByVal FindWhat As String, Optional ByVal CompareMethod As Microsoft.VisualBasic.CompareMethod = CompareMethod.Text) As Long
    Dim Count As Long = 0
    Dim CurrPos As Long = 0
    Dim OldPos As Long = 0
    Dim FindWhatLen As Integer = FindWhat.Length
    Dim StepLen As Integer = 1
    Do
        CurrPos = InStr(CurrPos + StepLen, Expression, FindWhat, CompareMethod)
        If CurrPos <> OldPos And CurrPos <> 0 Then
            Count += 1
            OldPos = CurrPos
            StepLen = FindWhatLen
        Else
            Exit Do
        End If
    Loop
    Return Count
End Function