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FIX Bug when dequantizing 4bit bnb weights #2847

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Oct 27, 2025
Merged

FIX Bug when dequantizing 4bit bnb weights #2847

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13 changes: 10 additions & 3 deletions src/peft/utils/integrations.py
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Original file line number Diff line number Diff line change
Expand Up @@ -88,16 +88,23 @@ def dequantize_bnb_weight(weight: torch.nn.Parameter, state=None):
"""Helper function to dequantize 4bit or 8bit bnb weights."""
import bitsandbytes as bnb

if state.SCB is None:
state.SCB = weight.SCB

device = weight.device

cls_name = weight.__class__.__name__
if cls_name == "Params4bit":
dequantized = bnb.functional.dequantize_4bit(weight.data, weight.quant_state)
return dequantized

# 8bit case
if state is None:
raise ValueError(
"No `state` was passed for bnb 8bit quantized weights. Please open an issue on the PEFT repository and "
"report the error: https://github.com/huggingface/peft/issues"
)

if state.SCB is None:
state.SCB = weight.SCB

if hasattr(bnb.functional, "int8_vectorwise_dequant"):
# Use bitsandbytes API if available (requires v0.45.0+)
dequantized = bnb.functional.int8_vectorwise_dequant(weight.data, state.SCB)
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