I have a problem converting decimal to hex in vb.net-CodePudding

I'm trying to convert 64bit decimal to hex but I get a wrong result

Public Function DecToBinary(dec As Double) As String

        DecToBinary= Hex(dec)

End function

For dec=3689348814742970688 I get 0x3333333333436200 , I should get 0x3333333333436140

I will use the hex to get the binary data cause I couldn't find another way to get a string with the bits.

In the end 3689348814742970688 will become a string with bits "0011001100110011001100110011001100110011010000110110000101000000"

Thanks in advance

CodePudding user response：

Your assumption that dec contains 3689348814742970688 is wrong.

3689348814742970688 exceeds the precision range of a Double, so dec stores the "rounded" value of 3689348814742970880 instead.

To solve this issue, use a BigInteger from the System.Numerics namespace instead of a Double. It's .NET's data type for arbitrarily large integers.

' prints 3333333333436140    
Console.WriteLine(BigInteger.Parse("3689348814742970688").ToString("x"))

CodePudding user response：

This might work,

    Dim l As Long = 3689348814742970688L
    Dim s As String = Convert.ToString(l, 2)
    Debug.WriteLine(s.ToString.PadLeft(64, "0"c))

    l = Long.MaxValue
    s = Convert.ToString(l, 2)
    Debug.WriteLine(s.ToString.PadLeft(64, "0"c))