Inventors:
Ashutosh Goyal - Austin TX, US
Assignee:
International Business Machines Corporation - Armonk NY
International Classification:
G06F 7/507
Abstract:
A summing circuit for an adder decodes control signals to determine that the result should be manipulated, and generates a half-sum output which is used to produce a manipulated result based on the control signals. The half-sum output is combined with a previous carry bit to complete the sum operation. The control signals can invert the adder result, or force the result to be all 1's. These functions can be effectuated in a 3-way multiplexer that combines the operand inputs and control signals. For inversion, two separate logic circuits produce true and complement half-sums in parallel, and the appropriate half-sum is selected for the half-sum output. For a result of all 1's, a force control signal pulls the half-sum output node to electrical ground and the final output is manipulated by gating the carry signals with the force signal. The two functions are implemented without introducing additional delay.