Long Datatype Overflow - excel

Question

I am trying to do some prime factorisation with my VBA excel and I am hitting the limit of the long data type -
Runtime Error 6 Overflow
Is there any way to get around this and still stay within VBA? I am aware that the obvious one would be to use another more appropriate programming language.
Lance's solution works in so far that I am able to get the big numbers into the variables now. However, when I try to apply the MOD function - bignumber MOD 2, for example - it still fails with error message
Runtime Error 6 Overflow

Answer 1

You can use Decimal data type. Quick hint from google: http://www.ozgrid.com/VBA/convert-to-decimal.htm

Answer 2

This is my Decimals.cls (VB6):
VERSION 1.0 CLASS
BEGIN
MultiUse = -1 'True
Persistable = 0 'NotPersistable
DataBindingBehavior = 0 'vbNone
DataSourceBehavior = 0 'vbNone
MTSTransactionMode = 0 'NotAnMTSObject
END
Attribute VB_Name = "Decimals"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = True
Attribute VB_PredeclaredId = False
Attribute VB_Exposed = True
Attribute VB_Ext_KEY = "SavedWithClassBuilder6" ,"Yes"
Attribute VB_Ext_KEY = "Top_Level" ,"Yes"
Option Explicit
'local variable(s) to hold property value(s)
Private mvarDec As Variant 'local copy
Public Property Let Dec(ByVal vData As Variant)
'used when assigning a value to the property, on the left side of an assignment.
'Syntax: X.Dec = 5
mvarDec = CDec(vData)
End Property
Public Property Get Dec() As Variant
Attribute Dec.VB_UserMemId = 0
'used when retrieving value of a property, on the right side of an assignment.
'Syntax: Debug.Print X.Dec
Dec = CDec(mvarDec)
End Property
and this is a testing program. The class has been setup so that you don't have to qualify with .Dec() on get and let.
Dim dec1 As New Std.Decimals
Dim dec2 As New Std.Decimals
Dim dec3 As New Std.Decimals
Dim modulus As New Std.Decimals
Sub main()
dec1 = "1000.000000001"
dec2 = "1000.00000000000001"
dec3 = dec1 + dec2
Debug.Print dec1
Debug.Print dec2
Debug.Print dec3
Debug.Print dec3 * dec3
Debug.Print dec3 / 10
Debug.Print dec3 / 100
Debug.Print Sqr(dec3)
modulus = dec1 - Int(dec1 / dec2) * dec2
Debug.Print modulus
End Sub
and sample run
1000.000000001
1000.00000000000001
2000.00000000100001
4000000.000004000040000001
200.000000000100001
20.0000000000100001
44.721359550007
0.00000000099999
1000.000000001
1000.00000000000001
2000.00000000100001
4000000.000004000040000001
200.000000000100001
20.0000000000100001
44.721359550007
0.00000000099999

Answer 3

Here is my "big multiply" routine for multiplying arbitrarily large numbers (eg 100 characters long). It works by splitting the input numbers, which are strings, into chunks of 7 digits (because then it can cross multiply them and store the results in Doubles).
eg bigmultiply("1934567803945969696433","4483838382211678") = 8674289372323895422678848864807544574
Function BigMultiply(ByVal s1 As String, ByVal s2 As String) As String
Dim x As Long
x = 7
Dim n1 As Long, n2 As Long, n As Long
n1 = Int(Len(s1) / x + 0.999999)
n2 = Int(Len(s2) / x + 0.999999)
n = n1 + n2
Dim i As Long, j As Long
ReDim za1(n1) As Double
i = Len(s1) Mod x
If i = 0 Then i = x
za1(1) = Left(s1, i)
i = i + 1
For j = 2 To n1
za1(j) = Mid(s1, i, x)
i = i + x
Next j
ReDim za2(n2) As Double
i = Len(s2) Mod x
If i = 0 Then i = x
za2(1) = Left(s2, i)
i = i + 1
For j = 2 To n2
za2(j) = Mid(s2, i, x)
i = i + x
Next j
ReDim z(n) As Double
Dim u1 As Long, u2 As Long
Dim e As String
e = String(x, "0")
For u1 = 1 To n1
i = u1
For u2 = 1 To n2
i = i + 1
z(i) = z(i) + za1(u1) * za2(u2)
Next u2
Next u1
Dim s As String, y As Double, w As Double, m As Long
m = n * x
s = String(m, "0")
y = 10 ^ x
For i = n To 1 Step -1
w = Int(z(i) / y)
Mid(s, i * x - x + 1, x) = Format(z(i) - w * y, e)
z(i - 1) = z(i - 1) + w
Next i
'truncate leading zeros
For i = 1 To m
If Mid$(s, i, 1) <> "0" Then Exit For
Next i
If i > m Then
BigMultiply = ""
Else
BigMultiply = Mid$(s, i)
End If
End Function

Answer 4

MOD is trying to convert your DECIMAL type to LONG before operating on it. You may need to write your own MOD function for the DECIMAL type. You might try this:
r = A - Int(A / B) * B
where A & B are DECIMAL subtype of VARIANT variables, and r might have to be that large also (depending on your needs), though I only tested on a long.