Handling Large Hex in VBScript

VBScript doesn't inherently support hex constants over 8 bits in length so I made a little function that attempts to handle large Hex strings and convert them to Decimals. It should be noted that Doubles lose precision in the E15 range of magnitude so beware using anything too large:

Function HexToDec(strHex)
    Dim i
    Dim size
    Dim ret
    size = Len(strHex) - 1
    ret = CDbl(0)
    For i = 0 To size
        ret = ret + CDbl("&H" & Mid(strHex, size - i + 1, 1)) * (CDbl(16) ^ CDbl(i))
    Next
    HexToDec = ret
End Function
Function DecToHex(dblNumber)
    Dim Q
    Dim ret

    ret = ""
    Q = CDbl(Fix(dblNumber))
    While Q > 0
        ret = Hex(Q - Fix(Q / 16) * 16) & ret
        Q = Fix(Q / CDbl(16))
    Wend
    DecToHex = ret
End Function

Called like this:

ret = HexToDec("0C0BA715B2223D47A8CAC87BE5D9679")
ret = DecToHex(CDBL(16843216856846468461654862))