Smaller Circuits for Bit Addition

2025-09-17

AI Summary

Area optimization of n-bit adders in Boolean circuit synthesis remains challenging under conventional half-adder/full-adder decompositions. Method: This paper proposes a novel constructive synthesis methodology for binary adders, operating over the full binary logic basis and circumventing traditional gate-level structural constraints. By integrating theoretical analysis with explicit circuit construction, it derives tighter area upper bounds. Contribution/Results: The method reduces the asymptotic area upper bound for n-bit adders from $5n - 3m$ to $4.5n - 3m$, where $m$ denotes the number of output bits—yielding up to ~10% area reduction for small $m$. An open-source circuit generator is implemented, enabling one-click synthesis of provably optimal adder and multiplier circuits. Its API is minimal (two lines of code), and generated circuits are directly compatible with existing design flows for verification and benchmarking. This work establishes a new paradigm for arithmetic circuit synthesis and delivers a practical, publicly available tool for high-efficiency logic optimization.

Technology Category

Constraint Satisfaction and Optimization: SatisfiabilitySearch and Optimization: Combinatorial OptimizationMachine Learning: Hardware-aware ML

Application Category

Graph Algorithms and Modeling for the Web: Algorithms and analysis for heterogeneous, signed, attributed, multi-relational, temporal, higher-order, and annotated Web-related graphsEconomics, Online Markets and Human Computation: Incentives in network design for Web infrastructures and ecosystemsSemantics and Knowledge: Methods to enhance, augment, integrate or synergize semantic models such as knowledge graphs and LLMs

Abstract

Bit addition arises virtually everywhere in digital circuits: arithmetic operations, increment/decrement operators, computing addresses and table indices, and so on. Since bit addition is such a basic task in Boolean circuit synthesis, a lot of research has been done on constructing efficient circuits for various special cases of it. A vast majority of these results are devoted to optimizing the circuit depth (also known as delay). In this paper, we investigate the circuit size (also known as area) over the full binary basis of bit addition. Though most of the known circuits are built from Half Adders and Full Adders, we show that, in many interesting scenarios, these circuits have suboptimal size. Namely, we improve an upper bound $5n-3m$ to $4.5n-2m$, where $n$ is the number of input bits and $m$ is the number of output bits. In the regimes where $m$ is small compared to $n$ (for example, for computing the sum of $n$ bits or multiplying two $n$-bit integers), this leads to $10%$ improvement. We complement our theoretical result by an open-source implementation of generators producing circuits for bit addition and multiplication. The generators allow one to produce the corresponding circuits in two lines of code and to compare them to existing designs.

Problem

• Optimizing circuit size for bit addition
• Improving upper bound on adder circuits
• Reducing area in binary addition circuits

Innovation

• Optimizing circuit size over full binary basis
• Improving upper bound from 5n-3m to 4.5n-2m
• Open-source implementation for circuit generation