Support inverse transform ue8m0 scale (#13285)

python/sglang/srt/layers/quantization/fp8_utils.py

@@ -504,6 +504,45 @@ def _transform_scale_ue8m0(sf, mn):
     return sf
 
 
+def inverse_transform_scale_ue8m0(sf_packed, mn):
+    sf_fp32 = _inverse_transform_scale_ue8m0_impl(sf_packed)
+    # Can call consistency check every time since this is only called on startup
+    sf_packed_recreated = _transform_scale_ue8m0(sf_fp32, mn=mn)
+    assert torch.all(
+        sf_packed == sf_packed_recreated
+    ), f"{sf_packed=} {sf_packed_recreated}"
+    return sf_fp32
+
+
+# Inverse impl can refer to DeepGEMM's torch impl in get_mn_major_tma_aligned_packed_ue8m0_tensor_torch_impl
+def _inverse_transform_scale_ue8m0_impl(sf_packed):
+    """
+    NOTE: We assume k is aligned
+    :param sf_packed: (scale_mn, scale_k/4) int32
+    :return: (scale_mn, scale_k), float32
+    """
+    block_size = 128
+    assert len(sf_packed.shape) == 2
+    assert sf_packed.dtype == torch.int32
+
+    mn_repeat_128, k_div_4 = sf_packed.shape
+    mn = mn_repeat_128 // block_size
+    k = k_div_4 * 4
+
+    # packed u8 -> fp32
+    sf_u8 = sf_packed.contiguous().flatten().view(torch.uint8).view(mn_repeat_128, k)
+    sf_fp32 = (sf_u8.to(torch.int32) << 23).view(torch.float32)
+
+    # remove repeat
+    sf_reshaped = sf_fp32.view(mn, block_size, k)
+    sf_unrepeated = sf_reshaped[:, 0:1, :]
+    assert torch.all(sf_unrepeated == sf_reshaped)
+    sf_unrepeated = sf_unrepeated.squeeze(1).contiguous()
+
+    assert sf_unrepeated.shape == (mn, k)
+    return sf_unrepeated
+
+
 # COPIED FROM DeepGEMM
 def per_block_cast_to_fp8(x: torch.Tensor) -> Tuple[torch.Tensor, torch.Tensor]:
     assert x.dim() == 2