hagant hagant - 1 year ago 141
Vb.net Question

How to Random a biginteger in vb.net?

i have a problem when generate a random number,
for example i want generate a random number between 2 to 579018135005309

i try function random in vb.net, but it cant compute a BigInteger

Function RandomNumber(ByVal min As BigInteger, ByVal max As BigInteger) As BigInteger
Static Generate As System.Random = New System.Random()

Return Generate.Next(min, max)
End Function

any other way to get random number from a big value?

Answer Source

Not an expert on randomness, but thought this could be a fun little function to make.

A part of this answer is from the link in the comments above (C# A random BigInt generator), but extended to the requirement for them to be within a certain range.

This is what I came up with:

 Public Function GenerateRandom(min as biginteger, max as biginteger) As BigInteger

        ' find the range of number (so we can generate #s from 0 --> diff)
        Dim range as BigInteger = max - min

        ' create random bigint fitting for the range
        Dim rng = New RNGCryptoServiceProvider()
        Dim bytes As Byte() = range.ToByteArray()

        ' ensure positive number (remember we're using 0 --> diff)
        bytes(bytes.Length - 1) = bytes(bytes.Length - 1) And CByte(&H7f)

        ' add minimum to this positive number so that the number is now 
        ' a candiate for being between min&max
        Dim bigint = min + New BigInteger(bytes)

        ' since we now only have a random number within a certain number of
        ' bytes it could be out of range. If so, just try again.
        If (bigint > max)
            return GenerateRandom(min, max)
        End If

        ' we have a number in the given range!
        return bigint 

    End Function
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