A better Excel Bin2Dec function (signed)?

I was wondering if 开发者_StackOverflow社区anyone had written a better Bin2Dec VBA macro for Excel in than the one included. I'm looking for a function that can take arbitrarily large binary numbers (within ~16 bits), and uses the signed bit. Excel's BIN2DEC function overflows after 12 bits, and it generally very ugly (Excel isn't too great since numbers overflow quickly as well). Any help?

Wrote one:

Function Bin2SignedDec(sMyBin As String) As Long
    Dim x As Integer
    Dim iLen As Integer
    Dim sign As Boolean
    Dim tmp As String

    sign = Mid(sMyBin, 1, 1) = "1"


    iLen = Len(sMyBin) - 1
    For x = 0 To iLen
        tmp = Mid(sMyBin, iLen - x + 1, 1)
        If sign Then
            If tmp = "1" Then
                tmp = "0"
            Else
                tmp = "1"
            End If
        End If
        Bin2SignedDec = Bin2SignedDec + _
          tmp * 2 ^ x
    Next
    If sign Then
        Bin2SignedDec = (Bin2SignedDec * -1) - 1
    End If

End Function

This link got me started