Constant addition with flagged binary adder architectures

The goal of this paper is to present architectures that provide the flexibility within a regular adder to augment/decrement the sum of two numbers by a constant. This flexibility adds to the functionality of a regular adder, achieving a comparable performance to conventional designs, thereby eliminating the need of having a dedicated adder unit to perform similar tasks. This paper presents an adder design to accomplish three-input addition if the third operand is a constant. This is accomplished by the introduction of flag bits. Such designs are called Enhanced Flagged Binary Adders (EFBA). It also examines the effect on the performance of the adder when the operand size is expanded from 16 bits to 32 and 64 bits. A detailed analysis has been provided to compare the performance of the new designs with carry-save adders in terms of delay, area and power.