Signs Beat Floats: Low-Rank Double-Binary Adaptation for On-Device Fine-Tuning
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Abstract (arXiv)
On-device adaptation of large language models commonly keeps a quantized base model frozen while training and deploying a small, task-specific LoRA adapter. In the unmerged adapter-mode setting, however, the adapter is more than a compact storage module; it introduces an additional dense floating-point branch, maintains a trainable state for local updates, and acts as a unit of communication and hot-swapping.We introduce LoRDBA, a LoRA-compatible adapter that replaces both low-rank factors with binary sign carriers while representing magnitudes through lightweight, channel-wise scales, converting the dense adapter branch into two sign-accumulation matrix multiplications interleaved with channel-wise scaling. A finite-sample analysis shows that reconstruction quality is governed by the residual-to-magnitude ratio of the original LoRA factors. In adapter-mode experiments, LoRDBA outperforms low-bit baselines at matched model sizes while matching fp16 LoRA quality in selected regimes. The unmerged adapter incurs at most 8% prefill latency overhead at matched rank r=16 despite an over 10x reduction in adapter footprint, with moderate training memory overhead of approximately 1.6x that of fp16 LoRA.
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References · 28
- 2023QLoRA: Efficient Finetuning of Quantized LLMscited by 3,418
- 2022GPTQ: Accurate Post-Training Quantization for Generative Pre-trained Transformerscited by 1,919
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- 2024DoRA: Weight-Decomposed Low-Rank Adaptationcited by 758
- 2024LoRA+: Efficient Low Rank Adaptation of Large Modelscited by 377
- 2024PiSSA: Principal Singular Values and Singular Vectors Adaptation of Large Language Modelscited by 269
- 2023LoftQ: LoRA-Fine-Tuning-Aware Quantization for Large Language Modelscited by 196
- 2023BitNet: Scaling 1-bit Transformers for Large Language Modelscited by 189
- 2020ReActNet: Towards Precise Binary Neural Network with Generalized Activation Functionscited by 184
- 2023QA-LoRA: Quantization-Aware Low-Rank Adaptation of Large Language Modelscited by 155
- 2023S-LoRA: Serving Thousands of Concurrent LoRA Adapterscited by 152
16 more
- 2015Global Convergence of ADMM in Nonconvex Nonsmooth Optimizationcited by 98
- 2023Punica: Multi-Tenant LoRA Servingcited by 83
- 2024OneBit: Towards Extremely Low-bit Large Language Modelscited by 79
- 2017Extremely Low Bit Neural Network: Squeeze the Last Bit Out with ADMMcited by 61
- 2025Quantization Error Propagation: Revisiting Layer-Wise Post-Training Quantizationcited by 41
- 2024BitDelta: Your Fine-Tune May Only Be Worth One Bitcited by 39
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- 2025Addition is almost all you need: Compressing large language models with double binary factorizationcited by 3
- 2025More Than Bits: Multi-Envelope Double Binary Factorization for Extreme Quantizationcited by 3
- 2026OneComp: One-Line Revolution for Generative AI Model Compressioncited by 3
- 2025LoRAQuant: Mixed-Precision Quantization of LoRA to Ultra-Low Bitscited by 1
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- 2024LoRA Land: 310 Fine-tuned LLMs that Rival GPT-4, A Technical Report
- 2023INT2.1: Towards Fine-Tunable Quantized Large Language Models with Error Correction through Low-Rank Adaptation
- 2024Accurate and Efficient Fine-Tuning of Quantized Large Language Models Through Optimal Balance
- 2024LoRA-XS: Low-Rank Adaptation with Extremely Small Number of Parameters
- 2025Less is More: Resource-Efficient Low-Rank Adaptation
- 2025FALQON: Accelerating LoRA Fine-tuning with Low-Bit Floating-Point Arithmetic
- 2026Parameter Efficiency Is Not Memory Efficiency: Rethinking Fine-Tuning for On-Device LLM Adaptation
- 2025LowRA: Accurate and Efficient LoRA Fine-Tuning of LLMs under 2 Bits