A circuit is provided which includes arithmetic computation logic configured to add or subtract operands of variable length to produce a result in a sign-magnitude data format. The circuit also includes an overflow detector to provide an overflow signal indicative of whether the result fits within a specified result length l. The overflow detector operates on the operands prior to the arithmetic computation logic producing the result to determine, independent of the result produced by the arithmetic computation logic, whether the result fits within the specified result length l.