Optimizing byte array to string encoder

[dbasnett]

Assuming the algorithm I posted is correct...

        Dim buf(255) As Byte 'test buffer

        'generate all possible byte values for testing
        For bv As Integer = 0 To 255
            buf(bv) = CByte(bv)
        Next


        Dim eqAsByte As Byte = Asc("=")
        Dim critCH() As Byte = New Byte() {0, _
                                           Asc(ControlChars.Tab), _
                                           Asc(ControlChars.Lf), _
                                           Asc(ControlChars.Cr), _
                                           eqAsByte}

        Dim encodedBuf As New List(Of Byte)
        'encode
        For Each byt As Byte In buf 'fetch the character
            Dim addByte As Integer
            If Not critCH.Contains(byt) Then 'is it critical
                'no
                addByte = byt + 42
            Else
                'yes, is a critical? character
                encodedBuf.Add(eqAsByte) 'add equal sign to output
                addByte = byt + 64
            End If
            addByte = addByte And 255
            encodedBuf.Add(CByte(addByte))
        Next

        Dim outBuf() As Byte = encodedBuf.ToArray
        'Debug.WriteLine(System.Text.ASCIIEncoding.ASCII.GetChars(encodedBuf.ToArray))

edit - Wow!