Bitwise And with Large Numbers in VBA - vba

Question

I keep getting an Overflow on the bitwise and in this first function. I fixed the other overflows by converting from Long to Currency (still seems weird), but I can't get this And to work.
Any ideas? I'm just trying to convert some IP addresses to CIDRs and calculate some host numbers.
Option Explicit
Public Function ConvertMaskToCIDR(someIP As String, someMask As String)
Dim ipL As Variant
ipL = iPToNum(someIP)
Dim maskL As Variant
maskL = iPToNum(someMask)
maskL = CDec(maskL)
'Convert Mask to CIDR(1-30)
Dim oneBit As Variant
oneBit = 2147483648#
oneBit = CDec(oneBit)
Dim CIDR As Integer
CIDR = 0
Dim x As Integer
For x = 31 To 0 Step -1
If (maskL And oneBit) = oneBit Then
CIDR = CIDR + 1
Else
Exit For
End If
oneBit = oneBit / 2# 'Shift one bit to the right (>> 1)
Next
Dim answer As String
answer = numToIp(ipL And maskL) & " /" & CStr(CIDR)
End Function
Public Function NumHostsInCidr(CIDR As Integer) As Currency
Dim mask As Currency
mask = maskFromCidr(CIDR)
NumHostsInCidr = iPnumOfHosts(mask)
End Function
Private Function maskFromCidr(ByVal CIDR As Integer) As Currency
'x = 32 - CIDR
'z = (2^x)-1
'return z xor 255.255.255.255
maskFromCidr = CLng(2 ^ ((32 - CIDR)) - 1) Xor 4294967295# '255.255.255.255
End Function
Private Function iPnumOfHosts(ByVal IPmsk As Currency) As Currency 'a mask for the host portion
'255.255.255.0 XOR 255.255.255.255 = 255 so 0 to 255 is 256 hosts
iPnumOfHosts = IPmsk Xor 4294967295# '255.255.255.255 , calculate the number of hosts
End Function
Private Function numToIp(ByVal theIP As Currency) As String 'convert number back to IP
Dim IPb(3) As Byte '4 octets
Dim theBit As Integer
theBit = 31 'work MSb to LSb
Dim addr As String 'accumulator for address
Dim x As Integer
For x = 0 To 3 'four octets
Dim y As Integer
For y = 7 To 0 Step -1 '8 bits
If (theIP And CLng(2 ^ theBit)) = CLng(2 ^ theBit) Then 'if the bit is on
IPb(x) = IPb(x) + CByte(2 ^ y) 'accumulate
End If
theBit = theBit - 1
Next
addr = addr & CStr(IPb(x)) & "." 'add current octet to string
Next
numToIp = trimLast(addr, ".")
End Function
Private Function iPToNum(ByVal ip As String) As Currency
Dim IPpart As Variant
Dim IPbyte(3) As Byte
IPpart = Split(ip, ".")
Dim x As Integer
For x = 0 To 3
IPbyte(x) = CByte(IPpart(x))
Next x
iPToNum = (IPbyte(0) * (256 ^ 3)) + (IPbyte(1) * (256 ^ 2)) + (IPbyte(2) * 256#) + IPbyte(3)
End Function
Private Function trimLast(str As String, chr As String)
'****
'* Remove "chr" (if it exists) from end of "str".
'****
trimLast = str
If Right(str, 1) = chr Then trimLast = Left(str, Len(str) - 1)
End Function

Answer 1

Whoah,
it is definitelly interesting functionality. But I would do this in very different way. I would treat IP adress and Mask as array of four bytes. Moreover as far as I remeber (well it was some time ago) CIDR and mask can be converted to each other in very simply way (did you looked at the table?). Why don't you apply bitwise operations to each byte separatelly?
BR.
edit: ok I looked closer at the code. The reason why it is overflowing is that you can't use currency and and. I think and is internally defined as Long and can't return any bigger values. It is very common in other languages too. I remember that once I had this problem in other language (Pascal?). You can try to replace and by division. It will be slow but it can't be matter here I suppose. Other solution is, like I wrote, to treat those valueas all the time as byte arrays and perform bitwise operations on each byte.

Answer 2

This is an entirely mathematical approach to working with IPv4 addresses in VBA (Excel specifically).
The first three functions are serving a strictly supporting role.
Support #1:
Public Function RoundDouble(ByVal Number As Double, ByVal Places As Long) As Double
On Error GoTo Err_RoundDouble
Dim i As Long
Dim j As Long
i = 0
j = 0
While Number < -(2 ^ 14)
Number = Number + (2 ^ 14)
i = i - 1
Wend
While Number > (2 ^ 14)
Number = Number - (2 ^ 14)
i = i + 1
Wend
While Number < -(2 ^ 5)
Number = Number + (2 ^ 5)
j = j - 1
Wend
While Number > (2 ^ 5)
Number = Number - (2 ^ 5)
j = j + 1
Wend
RoundDouble = Round(Number, Places) + (i * (2 ^ 14)) + (j * (2 ^ 5))
Exit_RoundDouble:
Exit Function
Err_RoundDouble:
MsgBox Err.Description
Resume Exit_RoundDouble
End Function
Support #2:
Public Function RoundDownDouble(ByVal Number As Double, ByVal Places As Long) As Double
On Error GoTo Err_RoundDownDouble
Dim i As Double
i = RoundDouble(Number, Places)
If Number < 0 Then
If i < Number Then
RoundDownDouble = i + (10 ^ -Places)
Else
RoundDownDouble = i
End If
Else
If i > Number Then
RoundDownDouble = i - (10 ^ -Places)
Else
RoundDownDouble = i
End If
End If
Exit_RoundDownDouble:
Exit Function
Err_RoundDownDouble:
MsgBox Err.Description
Resume Exit_RoundDownDouble
End Function
Support #3
Public Function ModDouble(ByVal Number As Double, ByVal Divisor As Double) As Double
On Error GoTo Err_ModDouble
Dim rndNumber As Double
Dim rndDivisor As Double
Dim intermediate As Double
rndNumber = RoundDownDouble(Number, 0)
rndDivisor = RoundDownDouble(Divisor, 0)
intermediate = rndNumber / rndDivisor
ModDouble = (intermediate - RoundDownDouble(intermediate, 0)) * rndDivisor
Exit_ModDouble:
Exit Function
Err_ModDouble:
MsgBox Err.Description
Resume Exit_ModDouble
End Function
This first function will convert a Double back into an IP address.
Public Function NUMtoIP(ByVal Number As Double) As String
On Error GoTo Err_NUMtoIP
Dim intIPa As Double
Dim intIPb As Double
Dim intIPc As Double
Dim intIPd As Double
If Number < 0 Then Number = Number * -1
intIPa = RoundDownDouble(ModDouble(Number, (2 ^ 32)) / (2 ^ 24), 0)
intIPb = RoundDownDouble(ModDouble(Number, (2 ^ 24)) / (2 ^ 16), 0)
intIPc = RoundDownDouble(ModDouble(Number, (2 ^ 16)) / (2 ^ 8), 0)
intIPd = ModDouble(Number, (2 ^ 8))
NUMtoIP = intIPa & "." & intIPb & "." & intIPc & "." & intIPd
Exit_NUMtoIP:
Exit Function
Err_NUMtoIP:
MsgBox Err.Description
Resume Exit_NUMtoIP
End Function
This second function is strictly to convert from IPv4 dotted octet format to a Double.
Public Function IPtoNUM(ByVal IP_String As String) As Double
On Error GoTo Err_IPtoNUM
Dim intIPa As Integer
Dim intIPb As Integer
Dim intIPc As Integer
Dim intIPd As Integer
Dim DotLoc1 As Integer
Dim DotLoc2 As Integer
Dim DotLoc3 As Integer
Dim DotLoc4 As Integer
DotLoc1 = InStr(1, IP_String, ".", vbTextCompare)
DotLoc2 = InStr(DotLoc1 + 1, IP_String, ".", vbTextCompare)
DotLoc3 = InStr(DotLoc2 + 1, IP_String, ".", vbTextCompare)
DotLoc4 = InStr(DotLoc3 + 1, IP_String, ".", vbTextCompare)
If DotLoc1 > 1 And DotLoc2 > DotLoc1 + 1 And _
DotLoc3 > DotLoc2 + 1 And DotLoc4 = 0 Then
intIPa = CInt(Mid(IP_String, 1, DotLoc1))
intIPb = CInt(Mid(IP_String, DotLoc1 + 1, DotLoc2 - DotLoc1))
intIPc = CInt(Mid(IP_String, DotLoc2 + 1, DotLoc3 - DotLoc2))
intIPd = CInt(Mid(IP_String, DotLoc3 + 1, 3))
If intIPa <= 255 And intIPa >= 0 And intIPb <= 255 And intIPb >= 0 And _
intIPc <= 255 And intIPc >= 0 And intIPd <= 255 And intIPd >= 0 Then
IPtoNUM = (intIPa * (2 ^ 24)) + (intIPb * (2 ^ 16)) + _
(intIPc * (2 ^ 8)) + intIPd
Else
IPtoNUM = 0
End If
Else
IPtoNUM = 0
End If
Exit_IPtoNUM:
Exit Function
Err_IPtoNUM:
MsgBox Err.Description
Resume Exit_IPtoNUM
End Function
Next we have the conversion from an IPv4 address to it's bitmask representation (assuming that the source entry is a string containing only the dotted octet format of the subnet mask).
Public Function IPtoBitMask(ByVal strIP_Address As String) As Integer
On Error GoTo Err_IPtoBitMask
IPtoBitMask = (32 - Application.WorksheetFunction.Log((2 ^ 32 - IPtoNUM(strIP_Address)), 2))
Exit_IPtoBitMask:
Exit Function
Err_IPtoBitMask:
MsgBox Err.Description
Resume Exit_IPtoBitMask
End Function
This last one is to convert a bitmask back into dotted octet format.
Public Function BitMasktoIP(ByVal intBit_Mask As Integer) As String
On Error GoTo Err_BitMasktoIP
BitMasktoIP = NUMtoIP((2 ^ 32) - (2 ^ (32 - intBit_Mask)))
Exit_BitMasktoIP:
Exit Function
Err_BitMasktoIP:
MsgBox Err.Description
Resume Exit_BitMasktoIP
End Function
Edited to remove leftover debugging code (it's been working for me so long, that I had entirely forgotten about it).
As an aside, it is faster to perform mathematical operations on a computer than it is to work with a string.

Answer 3

This was my "cheating" way:
Option Explicit
Public Function ConvertMaskToCIDR(varMask As Variant) As String
Dim strCIDR As String
Dim mask As String
mask = CStr(varMask)
Select Case mask
Case "255.255.255.255":
strCIDR = "/32"
Case "255.255.255.254":
strCIDR = "/31"
Case "255.255.255.252":
strCIDR = "/30"
Case "255.255.255.248":
strCIDR = "/29"
Case "255.255.255.240":
strCIDR = "/28"
Case "255.255.255.224":
strCIDR = "/27"
Case "255.255.255.192":
strCIDR = "/26"
Case "255.255.255.128":
strCIDR = "/25"
Case "255.255.255.0":
strCIDR = "/24"
Case "255.255.254.0":
strCIDR = "/23"
Case "255.255.252.0":
strCIDR = "/22"
Case "255.255.248.0":
strCIDR = "/21"
Case "255.255.240.0":
strCIDR = "/20"
Case "255.255.224.0":
strCIDR = "/19"
Case "255.255.192.0":
strCIDR = "/18"
Case "255.255.128.0":
strCIDR = "/17"
Case "255.255.0.0":
strCIDR = "/16"
Case "255.254.0.0":
strCIDR = "/15"
Case "255.252.0.0":
strCIDR = "/14"
Case "255.248.0.0":
strCIDR = "/13"
Case "255.240.0.0":
strCIDR = "/12"
Case "255.224.0.0":
strCIDR = "/11"
Case "255.192.0.0":
strCIDR = "/10"
Case "255.128.0.0":
strCIDR = "/9"
Case "255.0.0.0":
strCIDR = "/8"
Case "254.0.0.0":
strCIDR = "/7"
Case "252.0.0.0":
strCIDR = "/6"
Case "248.0.0.0":
strCIDR = "/5"
Case "240.0.0.0":
strCIDR = "/4"
Case "224.0.0.0":
strCIDR = "/3"
Case "192.0.0.0":
strCIDR = "/2"
Case "128.0.0.0":
strCIDR = "/1"
Case "0.0.0.0":
strCIDR = "/0"
End Select
ConvertMaskToCIDR = strCIDR
End Function
Public Function NumUsableIPs(cidr As String) As Long
Dim strHosts As String
If Len(cidr) > 3 Then
'They probably passed a whole address.
Dim slashIndex As String
slashIndex = InStr(cidr, "/")
If slashIndex = 0 Then
NumUsableIPs = 1
Exit Function
End If
cidr = Right(cidr, Len(cidr) - slashIndex + 1)
End If
Select Case cidr
Case "/32":
strHosts = 1
Case "/31":
strHosts = 0
Case "/30":
strHosts = 2
Case "/29":
strHosts = 6
Case "/28":
strHosts = 14
Case "/27":
strHosts = 30
Case "/26":
strHosts = 62
Case "/25":
strHosts = 126
Case "/24":
strHosts = 254
Case "/23":
strHosts = 508
Case "/22":
strHosts = 1016
Case "/21":
strHosts = 2032
Case "/20":
strHosts = 4064
Case "/19":
strHosts = 8128
Case "/18":
strHosts = 16256
Case "/17":
strHosts = 32512
Case "/16":
strHosts = 65024
Case "/15":
strHosts = 130048
Case "/14":
strHosts = 195072
Case "/13":
strHosts = 260096
Case "/12":
strHosts = 325120
Case "/11":
strHosts = 390144
Case "/10":
strHosts = 455168
Case "/9":
strHosts = 520192
Case "/8":
strHosts = 585216
Case "/7":
strHosts = 650240
Case "/6":
strHosts = 715264
Case "/5":
strHosts = 780288
Case "/4":
strHosts = 845312
Case "/3":
strHosts = 910336
Case "/2":
strHosts = 975360
Case "/1":
strHosts = 1040384
End Select
NumUsableIPs = strHosts
End Function