arXiv:2602.00165cs.LG2026-02

用本福特定律优化大模型量化,提升小比特压缩下的精度

Benford's Law as a Distributional Prior for Post-Training Quantization of Large Language Models

  • 基于本福特定律设计非均匀量化码本,聚焦高频小数值权重
  • 4比特下Gemma-270M困惑度降低超10%,大模型也保持竞争力
  • 无需数据即可应用,可无缝融合现有量化方法提升性能

大型语言模型的快速发展加剧了压缩需求,权重量化是最常用技术。传统均匀量化假设参数均匀分布,与实际中高度偏斜的分布不符。本文提出Benford-Quant,一种受本福特定律启发的数据无关非均匀量化器,该定律预测首位数字呈对数分布。其将均匀网格替换为对数间距码本,为频繁出现的小幅值权重分配更多分辨率。理论与实证表明:(i) Transformer变换层权重接近本福特定律,而归一化层系统性偏离;(ii) 在小型语言模型上,Benford-Quant持续提升困惑度,4比特下Gemma-270M困惑度下降超过10%;(iii) 在更大模型上仍具竞争力,差异由过参数化效应解释。结果表明,在量化网格中引入本福特定律先验是低成本且有效的改进,尤其在极低比特场景下。虽未超越当前最优(如困惑度、LAMBADA任务),但该方法可与SmoothQuant、激活感知量化等无修改融合,有望进一步提升性能。

原文摘要 · Abstract (English)

The rapid growth of Large Language Models (LLMs) intensifies the need for effective compression, with weight quantization being the most widely adopted technique. Standard uniform quantizers assume that parameters are evenly distributed, an assumption at odds with the highly skewed distributions observed in practice. We propose Benford-Quant, a simple, data-free non-uniform quantizer inspired by Benford's Law, which predicts that leading digits follow a logarithmic distribution. Benford-Quant replaces the uniform grid with a log-spaced codebook, dedicating more resolution to the frequent small-magnitude weights. We provide both theoretical intuition and empirical evidence: (i) weights in transformer transformational layers adhere closely to Benford statistics, while normalization layers systematically deviate; (ii) on Small Language Models (SLMs), Benford-Quant consistently improves perplexity, reducing 4-bit perplexity on Gemma-270M by more than 10%; and (iii) on larger LLMs, it remains competitive, with differences explained by over-parameterization effects. Our results indicate that incorporating a Benford-inspired prior into quantization grids is a low-cost modification that yields accuracy gains in aggressive few-bit regimes. Although it is not able to surpass the state of the art in tasks such as perplexity and LAMBADA, the Benford-Quant approach can be hybridized with other quantization methods-such as SmoothQuant and Activation-Aware Quantization-without major pipeline modification, potentially improving their performance.

模型量化本福特定律小比特压缩LLM优化

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