LeAp: Leading-one Detection-based Softcore Approximate Multipliers with Tunable Accuracy

Approximate multipliers are ubiquitously used in diverse applications by exploiting circuit simplification, mainly specialized for Application-Specific Integrated Circuit (ASIC) platforms. However, the intrinsic architectural specifications of Field-Programmable Gate Arrays (FPGAs) prohibited comparable resource gains when directly applying these techniques. LeAp is an area-, throughput-, and energy-efficient approximate multiplier for FPGAs which efficiently utilizes 6-input Look-up Tables (6-LUTs) and fast carry chains in its novel approximate log calculator to implement Mitchell's algorithm. Moreover, three novel error-refinement schemes with negligible area overhead and independent from multiplier-size, have boosted accuracy to>99%. Experimental results obtained from Vivado, Artificial Neural Network (ANN) and image processing applications indicate superiority of proposed multiplier over accurate and state-of-the-art approximate counterparts. In particular, LeAp outperforms the 32x32 accurate multiplier by achieving 69.7%, 14.7%, 42.1%, and 37.1% improvement in area, throughput, power, and energy, respectively. The library of RTL and behavioral implementations will be open-sourced at https://cfaed.tu-dresden.de/pd-downloads.