Simulating byte overflow in VB.NET

Question

I would like to simulate byte overflow in VB.NET. The code below achieves the correct result but I suspect this is not the most efficient method. Is there a simpler/better way to achieve this?

 Dim src As Byte = 232
 Dim key As Byte = 231
 Dim encoded As Byte = 0
 Dim decoded As Byte = 0

 ' Encode
 encoded = CByte((CInt(src) + CInt(key)) Mod 256I)

 ' Decode
 Dim tmp As Int32 = CInt(encoded) - CInt(key)
 decoded = CByte(IIf(tmp < 0, 256I + tmp, tmp))

 ' encoded = 207
 ' decoded = src = correct

if you want feedback on your working code, a better place to ask is codereview.stackexchange.com — sloth
– sloth, Commented Jun 17, 2014 at 13:15

Hans Passant · Accepted Answer · 2014-06-17 13:59:36Z

3

Yes, you can make that a lot faster. It however requires a project building option change. Add a new project to your solution. Right-click it, Properties, Build tab, scroll down, click the Advanced Compile Options button. Tick the "Remove integer overflow checks" option.

Now you can write it like this:

    Dim src As Byte = 232
    Dim key As Byte = 231
    Dim encoded As Byte = src + key
    Dim decoded As Byte = encoded - key

Which you'd do in Public methods you expose from your new project.

Do beware the very questionable utility of a Caesar cipher, it is far too easy to crack. The System.Cryptography namespace has much better alternatives, doesn't require you to tinker with global build options that have tricky side-effects either.

answered Jun 17, 2014 at 13:59

Hans Passant

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