[wyldfire]

I don't know how codon does this. But I always supposed that existing optimized pythons like pypy map integer operations to native types and promote them to arbitrary precision when they encounter overflow. It's IMO a similar problem to "but what if someone decided to overwrite Int.__add__ with some other function?" - arguably these are weird/bad things to do but AFAIK permitted by the language semantics. So to fix problems like these you just make it work for the paranoid case and implement optimizations that rely on that not being common. When the weird behavior is detected you fall back to the slower path.