Arithmetic operation resulted in an overflow. blowfish algorythm

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when i execute this code:

VB

Dim bytearray() As Byte = System.IO.File.ReadAllBytes("C:\Users\Fery Ferdiansyah\Desktop\asd\asd.txt")
    Dim key() As Byte = System.Text.Encoding.UTF8.GetBytes("swagger")
    Dim bf As New blowfish2(key)

this syntax >> y = S(0, a) + S(1, b)<< in this function is arithmetic overflow:

VB

Private Function F(ByVal x As UInteger) As UInteger
        Dim a As UShort
        Dim b As UShort
        Dim c As UShort
        Dim d As UShort
        Dim y As UInteger

        d = CUShort((x And &HFF))
        x >>= 8
        c = CUShort((x And &HFF))
        x >>= 8
        b = CUShort((x And &HFF))
        x >>= 8
        a = CUShort((x And &HFF))
        y = S(0, a) + S(1, b)
        y = y Xor S(2, c)
        y = y + S(3, d)

        Return y
    End Function

could anyone help me to fix this function?

Posted 25-Jun-14 20:42pm

Member 10906746

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EvScott · Answer 1 · 2014-06-26T10:46:00

VB in general is unforgiving with it's data types. I suspect that there is a casting problem with the function S with a and b. a and b are results of ANDing with a hex value, and subsequently could return a negative result in S. You're adding the results of S to an unsigned integer, and the two aren't compatible.

You might (but don't hold me to it) resolve this by appending UI to your hex values like this:

x And &HFFUI