An integrated circuit includes an adder having a first adder circuit for receiving a portion of the operands to be summed, along with corresponding carry-in inputs. The first adder circuit provides a sum output and carry-out outputs. A second adder circuit receives another portion of the operands to be summed, along with corresponding carry-in inputs. Multiplexers between the first and second adder circuits determine whether the carry-in inputs to the second adder circuit are the same the carry-in inputs to the first adder circuit or whether the carry-in inputs to the second adder circuit are independent.