This is possible, but unless processor accelerated comes at a great cost. You'd need a branch after every math, unless the compiler could prove the math wouldn't overflow.

The ARM mode described elsewhere in the thread where there's an overflow flag that persists across operations would help; then you could do a check less frequently.

A mode were you get a processor exception would be great, if adding that doesn't add significant cost to operations that don't overflow. Assuming the response to such an exception is expected to be a core dump, the cost of generating such an exception can be high; of course if someone builds their bignumber library around the exception, that won't be great.