Question

In VB.NET the following code causes an overflow.

    Dim t As UInt64
    t = UInt64.MaxValue
    t += 2UL

It is my understanding that in C it “wraps”. Assuming that is true, is there a way to mimic this in Visual Basic? I need this for an implementation of UInt128 I am trying to write.

Answer 1

I don’t know VB specifically (so you’ll have to convert it yourself) but the usual way of doing this is:

def add (value,addval):
    if value <= maxvalue - addval:
        return value + addval
    subval = maxvalue - addval + 1
    return value - subval

It basically figures out in advance whether there will be overflow and turns an add(N) operation into an sub(maxvalue-N+1) one.

Both the test and the add/sub are safe within the range 0..maxvalue.