Approximator: A Software Tool for Automatic Generation of Approximate Arithmetic Circuits

Abstract

Approximate arithmetic circuits are an attractive alternative to accurate arithmetic circuits because they have significantly reduced delay, area, and power, albeit at the cost of some loss in accuracy. By keeping errors due to approximate computation within acceptable limits, approximate arithmetic circuits can be used for various practical applications such as digital signal processing, digital filtering, low power graphics processing, neuromorphic computing, hardware realization of neural networks for artificial intelligence and machine learning etc. The degree of approximation that can be incorporated into an approximate arithmetic circuit tends to vary depending on the error resiliency of the target application. Given this, the manual coding of approximate arithmetic circuits corresponding to different degrees of approximation in a hardware description language (HDL) may be a cumbersome and a time-consuming process—more so when the circuit is big. Therefore, a software tool that can automatically generate approximate arithmetic circuits of any size corresponding to a desired accuracy would not only aid the design flow but also help to improve a designer’s productivity by speeding up the circuit/system development. In this context, this paper presents ‘Approximator’, which is a software tool developed to automatically generate approximate arithmetic circuits based on a user’s specification. Approximator can automatically generate Verilog HDL codes of approximate adders and multipliers of any size based on the novel approximate arithmetic circuit architectures proposed by us. The Verilog HDL codes output by Approximator can be used for synthesis in an FPGA or ASIC (standard cell based) design environment. Additionally, the tool can perform error and accuracy analyses of approximate arithmetic circuits. The salient features of the tool are illustrated through some example screenshots captured during different stages of the tool use. Approximator has been made open-access on GitHub for the benefit of the research community, and the tool documentation is provided for the user’s reference.