Adding 32-bit binary in Visual Basic

Question

I have to calculate the IPv4 subnet address which can be achieved by adding the IP address binary to the subnet mask binary. I can convert them both to binary with this code

    Public Function Dec2Bin(ByVal DeciValue As Long, Optional ByVal NoOfBits As Integer = 8) _
 As String
    Dim i As Integer
    Do While DeciValue > (2 ^ NoOfBits) - 1
        NoOfBits = NoOfBits + 8
    Loop
    Dec2Bin = vbNullString
    For i = 0 To (NoOfBits - 1)
        Dec2Bin = CStr((DeciValue And 2 ^ i) / 2 ^ i) & Dec2Bin
    Next i
End Function

But now how do I add the two 32-bit strings together in order to get the subnet adress? I also have the dec-to-bin function, so I don't need any help with that.

Answer 1

So, I suspect DeciValue is your IP address in 32-bit numeric representation and NoOfBits is the number of bits in the subnet mask (as 8 for 255.0.0.0, 16 for 255.255.0.0 and 24 for 255.255.255.0 etc).

What you can do is this:

Public Function Network_Address(IP as UInteger, Optional Mask as UInteger = 0)
    If Mask = 0 Then
        Mask = 8 * ((IP >> 30) + 1)
    End If
    Network_Address = IP And (4294967295 Xor ((2 ^ (32 - Mask)) - 1))
End Function

Now you have the network address as its numeric representation. I suspect thats what you want.

This function will also detect the IP subnet mask size automatically if none is specified.