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convert-hf : simplify BitNet pre-quantization

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This still results in the exact same tensor weights and scales,
but it reveals some weirdness in the current algorithm.
This commit is contained in:
Francis Couture-Harpin 2024-06-26 16:24:40 -04:00
parent 89dc3b254c
commit 961e293833
1 changed files with 12 additions and 8 deletions
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20
convert-hf-to-gguf.py
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@ -265,7 +265,10 @@ class Model:
break
for new_name, data in ((n, d.squeeze().numpy()) for n, d in self.modify_tensors(data_torch, name, bid)):
data: np.ndarray = data # type hint
data: np.ndarray # type hint
if len(data.shape) == 0:
# otherwise single-value tensors get squeezed
data = data.reshape((1,))
n_dims = len(data.shape)
data_dtype = data.dtype
data_qtype: gguf.GGMLQuantizationType | None = None
@ -336,7 +339,7 @@ class Model:
shape = gguf.quant_shape_from_byte_shape(data.shape, data_qtype) if data.dtype == np.uint8 else data.shape
# reverse shape to make it similar to the internal ggml dimension order
shape_str = f"{{{', '.join(str(n) for n in reversed(shape)) or '1'}}}"
shape_str = f"{{{', '.join(str(n) for n in reversed(shape))}}}"
# n_dims is implicit in the shape
logger.info(f"{f'%-{max_name_len}s' % f'{new_name},'} {old_dtype} --> {data_qtype.name}, shape = {shape_str}")
@ -1446,12 +1449,13 @@ class BitnetModel(Model):
def weight_quant(self, weight):
dtype = weight.dtype
weight = weight.float()
s = 1 / weight.abs().mean().clamp(min=1e-5)
weight = (weight * s).round().clamp(-1, 1) / s
scale = weight.abs().max().unsqueeze(0)
weight = torch.where(weight.abs().less(1e-6), 0, weight).type(dtype)
weight = torch.sign(weight).type(dtype)
return weight.type(dtype), scale.type(torch.float32)
scale = weight.abs().mean().clamp(min=1e-5)
iscale = 1 / scale
weight = (weight * iscale).round().clamp(-1, 1)
# TODO: use the scale directly instead of inverting it twice
# (this is also unnecessarily doubly inverted upstream)
# ref: https://huggingface.co/1bitLLM/bitnet_b1_58-3B/blob/af89e318d78a70802061246bf037199d2fb97020/utils_quant.py#L10
return weight.type(dtype), (1 / iscale).type(torch.float32)
def modify_tensors(self, data_torch: Tensor, name: str, bid: int | None) -> Iterable[tuple[str, Tensor]]:
new_name = self.map_tensor_name(name)