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POPerform a modulus in a huge number?
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copied!<p>I need to do a modulus operation on very large integers. The biggest integer supported by my platform (edit: .NET 2.0) is a 64 bit integer, which aren't big enough for the numbers I'm working with.</p> <p>How can I do a modulus on really big integers, like 12654875632126424875387321657498462167853687516876876?</p> <p>I have a solution that treats the number as a string and works it in pieces one by one, but I wanted to know if there's a better way.</p> <p>Here's my function treating the number as a string. It basically does long division the way you'd do it by hand.</p> <pre><code> Public Function MyMod(ByVal numberString As String, ByVal modby As Integer) As Integer Dim position As Integer = -1 Dim curSubtraction As Integer = 0 While position < numberString.Length - 1 position += 1 curSubtraction = curSubtraction * 10 + CInt(numberString.Substring(position, 1)) If (curSubtraction / modby) < 1 And position = numberString.Length - 1 Then Return curSubtraction ElseIf (curSubtraction / modby) < 1 Then Continue While Else curSubtraction = curSubtraction Mod modby End If End While Return curSubtraction End Function </code></pre> <p>Is there a cleaner, more efficient way?</p> <p>EDIT: To clarify, the integers are coming from IBAN bank account numbers. According to the specification, you have to convert the IBAN account number (containing letters) into one integer. Then, you do a modulus on the integer. So, I guess you could say that the real source of the integer to perform the modulus on is a string of digits.</p>

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