Journal Article

Eight-Bit Vector SoftFloat Extension for the RISC-V Spike Simulator

Marcelli, Andrea, Mastrandrea, Antonio, Menichelli, Francesco, Barbirotta, Marcello, Cheikh, Abdallah, Olivieri, Mauro

2025

Overview

The recent demand for 8-bit floating-point (FP) formats is driven by their potential to accelerate domain-specific applications with intensive vector computations (e.g., machine learning, graphics, and data compression). This paper presents the design, implementation, and application of the software model of an 8-bit FP vector arithmetic operation set, compliant with the RISC-V vector instruction set architecture. The model has been developed as an extension of the SoftFloat library and integrated into the RISC-V reference instruction-level simulator Spike, providing the first open-source 8-bit SoftFloat extension for an instruction-set simulator. Based on the SoftFloat library templates for standard FP formats, the proposed extension implements the two widely used 8-bit formats E4M3 and E5M2 in both Open Compute Project (OCP) and IEEE 754 variants. In host-time micro-kernels, FP8 delivers +2–4% more elements per second versus FP32 (across vfadd/vfsub/vfmul) and ≈5% lower RSS; E4M3 and E5M2 perform similarly. Enabling FP8 in Spike increases the stripped binary by ~1.8% (mostly .text). The proposed extension was used to fully verify and correct errors in the vector FP unit design for the eProcessor European project, and continues to be used to verify other 8-bit FP unit implementations.

• Publisher: MDPI AG
• Subject: Accuracy / Array processors / Artificial intelligence / Computational linguistics / Computer vision / Data compression / Design / Efficiency / Floating point arithmetic / Instruction sets (computers) / Language processing / Libraries / Machine learning / Natural language interfaces / Natural language processing / Neural networks / RISC / Software / Workloads