Design and Analysis of High Performance Heterogeneous Block-based Approximate Adders

Ebrahim Farahmand, Ali Mahani, Muhammad Abdullah Hanif, Muhammad Shafique

Research output: Contribution to journalArticlepeer-review


Approximate computing is an emerging paradigm to improve the power and performance efficiency of error-resilient applications. As adders are one of the key components in almost all processing systems, a significant amount of research has been carried out toward designing approximate adders that can offer better efficiency than conventional designs; however, at the cost of some accuracy loss. In this article, we highlight a new class of energy-efficient approximate adders, namely, Heterogeneous Block-based Approximate Adders (HBAAs), and propose a generic configurable adder model that can be configured to represent a particular HBAA configuration. An HBAA, in general, is composed of heterogeneous sub-adder blocks of equal length, where each sub-adder can be an approximate sub-adder and have a different configuration. The sub-adders are mainly approximated through inexact logic and carry truncation. Compared to the existing design space, HBAAs provide additional design points that fall on the Pareto-front and offer a better quality-efficiency tradeoff in certain scenarios. Furthermore, to enable efficient design space exploration based on user-defined constraints, we propose an analytical model to efficiently evaluate the Probability Mass Function (PMF) of approximation error and other error metrics, such as Mean Error Distance (MED), Normalized Mean Error Distance (NMED), and Error Rate (ER) of HBAAs. The results show that HBAA configurations can provide around 15% reduction in area and up to 17% reduction in energy compared to state-of-the-art approximate adders.

Original languageEnglish (US)
Article number106
JournalACM Transactions on Embedded Computing Systems
Issue number6
StatePublished - Nov 9 2023


  • Approximate computing
  • accuracy
  • approximate adders
  • efficiency
  • error analysis
  • low latency
  • low power
  • performance estimation
  • quality
  • tradeoff

ASJC Scopus subject areas

  • Software
  • Hardware and Architecture


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