High-frequency Multispeculative Multiply-Accumulation Unit for Fused Posit Arithmetic

Abstract

Posit arithmetic offers a compelling alternative to the IEEE 754 floating-point standard, providing enhanced accuracy. Its fused multiply-accumulate operations avoid intermediate rounding, ensuring exact numerical reproducibility through the quire, a wide fixed-point accumulator spanning the format's full dynamic range to prevent precision loss and overflow during long accumulations. However, integrating such large accumulators incurs significant area and power overheads. This paper presents an optimized, high-frequency Multispeculative PositMAC architecture for 32- and 64-bits Posit. First, the pipeline is restructured to balance the different stages. Second, high-speed multiplication topologies are evaluated, showing that a Booth-4 scheme with Kogge-Stone adders meets a stringent 0.5ns target (2Ghz). Finally, the wide monolithic quire accumulator is replaced with a Multispeculative Adder, diminishing area up to 19.8\% while reducing energy consumption by more than 50\% when compared to the baseline. Compared to other state-of-the-art designs, our proposal achieves the highest operating frequency and reduces cycle time by up to 79.0\% with respect to 64-bit quire-enabled alternatives. This performance is attained without increasing resource overhead, as the design remains strictly smaller in area and achieves lower per-cycle energy consumption than all quire-capable counterparts.