1. An adder for adding a signal at a first input (A) and a second input (B) to produce an adder output (S), comprising: a bypass input (bypass); and a logic circuit, communicatively coupled to the bypass input (bypass), the first input (A), and the second input (B), the logic circuit configured to hold at least one of the first input (A) and the second input (B) according to the bypass input (bypass).