SAM Decoding: Speculative Decoding via Suffix Automaton

Kavli Affiliate: Ke Wang

| First 5 Authors: Yuxuan Hu, Ke Wang, Xiaokang Zhang, Fanjin Zhang, Cuiping Li

| Summary:

Large Language Models (LLMs) have revolutionized natural language processing
by unifying tasks into text generation, yet their large parameter sizes and
autoregressive nature limit inference speed. SAM-Decoding addresses this by
introducing a novel retrieval-based speculative decoding method that uses a
suffix automaton for efficient and accurate draft generation. Unlike n-gram
matching used by the existing method, SAM-Decoding finds the longest suffix
match in generating text and text corpuss, achieving an average time complexity
of $O(1)$ per generation step. SAM-Decoding constructs static and dynamic
suffix automatons for the text corpus and input prompts, respectively, enabling
fast and precise draft generation. Meanwhile, it is designed as an approach
that can be combined with existing methods, allowing SAM-Decoding to adaptively
select a draft generation strategy based on the matching length, thus
increasing the inference speed of the LLM. When combined with Token Recycling,
evaluations show SAM-Decoding outperforms existing model-free methods,
achieving a speedup of $2.27times$ over autoregressive decoding on Spec-Bench.
When combined with EAGLE2, it reaches a speedup of $2.49times$, surpassing all
current approaches. Our code is available at
https://github.com/hyx1999/SAM-Decoding.

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