Big Numbers

[Dmyze]

Is there a decent Big Numbers library for VB.NET?

I need to be able to multiply 3587551859 * 3587551859

[<ABX]

how's this???

Public Function StringMultiply(ByVal str1 As String, ByVal str2 As String) As String
 
        Dim strResult As String = "0"
 
        Dim intCarry As Integer
 
        For I As Integer = (str1.Length - 1) To 0 Step -1
 
            For X As Integer = (str2.Length - 1) To 0 Step -1
 
                Dim intPlaces As Integer = (str1.Length - 1 - I) + (str2.Length - 1 - X)
                'These places need to be appended before adding
                Dim strNewVal As String = CStr(Microsoft.VisualBasic.Val(str1.Chars(I)) * _
                    Microsoft.VisualBasic.Val(str2.Chars(X)))
 
                strNewVal = strNewVal.PadRight(strNewVal.Length + intPlaces)
 
                strResult = StringAdd(strResult, strNewVal)
            Next
 
        Next
 
        Return strResult
 
    End Function

Public Function StringAdd(ByVal str1 As String, ByVal str2 As String) As String
        'This can add until the Length Sum of str1 and str2 is greater then 65,000 or so
        Dim strResult As String
 
        If str1.Length > str2.Length Then
            str2 = str2.PadLeft(str1.Length, "0")
        Else
            str1 = str1.PadLeft(str2.Length, "0")
        End If
 
 
        'now both strings are the same length
 
        Dim sCarry As Short
 
        For I As Integer = (str1.Length - 1) To 0 Step -1 ' we add Right to left
            Dim intResult As Integer = Microsoft.VisualBasic.Val(str1.Chars(I)) + Microsoft.VisualBasic.Val(str2.Chars(I)) + sCarry
 
            If intResult > 9 Then
                sCarry = (intResult - (intResult Mod 10)) / 10
                intResult -= sCarry * 10
            Else
                sCarry = 0
            End If
 
            strResult &= intResult
 
        Next
 
        'Dont forget the sCarry
 
        strResult &= sCarry
 
        strResult = StrReverse(strResult).TrimStart("0")
        If strResult.Length = 0 Then
            Return "0"
        Else
            Return strResult
        End If
    End Function

[Dmyze]

Wow, thanks! It's fast too!

[Dmyze]

Do you have one for division as well?

[n1ghtowl]

I know this is an old thread but I figured this was better than starting a new one on the same subject.

I am glad to have found these functions here. does anyone have any for subtraction and division?.

Thanks

[Dmyze]

Sadly I can't remeber what project I needed this for and so I can't remeber if I figured the rest of it out.

Maybe someone out there has the answer.

[n1ghtowl]

thanks for the response Dmyze. I am trying to convert a VB6 App I have over to .Net. The VB to .Net conversion allowed the app to work but left it mainly using the old coding style.
I mainly need the ability to do basic math functions (add, subtract, divide, and multiply and squareroot)on very large numbers(up to 1000 digits). These cover 2 of them.
In case it helps any I am mainly after the execution speed as I have to run thousands of Calculations on these numbers.
Again thank you for any help in this matter.