Suppose you are porting a C code, for example, that sums 32 bit integers (Longs) to VB6. In C, when the result of a sum does not fit into an integer, it overflows silently. In VB, you will get a nasty runtime error instead.
So, this is a handy function to have under your belt: It adds two Longs and "silent overflows" if needed.
Public Function Add(ByVal LeftValue As Long, ByVal RightValue As Long) As Long
Const ADJUST As Double = 4294967296#
Dim Result As Variant
Result = CDec(LeftValue) + CDec(RightValue)
Select Case Result
Case Is Result = Result + CDec(ADJUST)
Case Is 2147483647
Result = Result - CDec(ADJUST)
Add = CLng(Result)