From 8e6083bfcfe80bb8231fc22c3574cfb34af571ea Mon Sep 17 00:00:00 2001
From: fzyzcjy <5236035+fzyzcjy@users.noreply.github.com>
Date: Sat, 15 Nov 2025 16:34:32 +0800
Subject: [PATCH] Support inverse transform ue8m0 scale (#13285)

---
 .../srt/layers/quantization/fp8_utils.py      | 39 ++++++++++++++++
 test/srt/run_suite.py                         |  1 +
 test/srt/test_fp8_utils.py                    | 44 +++++++++++++++++++
 3 files changed, 84 insertions(+)
 create mode 100644 test/srt/test_fp8_utils.py

diff --git a/python/sglang/srt/layers/quantization/fp8_utils.py b/python/sglang/srt/layers/quantization/fp8_utils.py
index 747f123b3..ed62ebb01 100644
--- a/python/sglang/srt/layers/quantization/fp8_utils.py
+++ b/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
diff --git a/test/srt/run_suite.py b/test/srt/run_suite.py
index a649a569b..4b210d755 100644
--- a/test/srt/run_suite.py
+++ b/test/srt/run_suite.py
@@ -75,6 +75,7 @@ suites = {
         TestFile("test_eval_fp8_accuracy.py", 303),
         TestFile("test_fa3.py", 420),
         TestFile("test_flashmla.py", 230),
+        TestFile("test_fp8_utils.py", 5),
         TestFile("rotary_embedding/test_mrope.py", 10),
         TestFile("test_function_call_parser.py", 10),
         TestFile("test_fused_moe.py", 80),
diff --git a/test/srt/test_fp8_utils.py b/test/srt/test_fp8_utils.py
new file mode 100644
index 000000000..1e75d4855
--- /dev/null
+++ b/test/srt/test_fp8_utils.py
@@ -0,0 +1,44 @@
+import unittest
+
+import torch
+
+from sglang.srt.layers.quantization.fp8_utils import (
+    inverse_transform_scale_ue8m0,
+    quant_weight_ue8m0,
+    transform_scale_ue8m0,
+)
+from sglang.test.test_utils import CustomTestCase
+
+
+class TestInverseTransformScaleUe8m0(CustomTestCase):
+    def test_round_trip(self):
+        for _ in range(100):
+            weight_bf16 = torch.randn(
+                # DeepSeek V3 kv_b_proj
+                (32768, 512),
+                dtype=torch.bfloat16,
+                device="cuda",
+            )
+
+            weight_block_size = [128, 128]
+
+            qweight, sf_fp32_original = quant_weight_ue8m0(
+                weight_bf16, weight_block_size=weight_block_size
+            )
+            mn = qweight.shape[-2]
+
+            sf_packed_original = transform_scale_ue8m0(sf_fp32_original, mn=mn)
+            sf_fp32_recreated = inverse_transform_scale_ue8m0(sf_packed_original, mn=mn)
+
+            sf_packed_recreated = transform_scale_ue8m0(sf_fp32_recreated, mn=mn)
+
+            assert torch.all(
+                sf_packed_original == sf_packed_recreated
+            ), f"{sf_packed_original=} {sf_packed_recreated}"
+            assert torch.all(
+                sf_fp32_original == sf_fp32_recreated
+            ), f"{sf_fp32_original=} {sf_fp32_recreated}"
+
+
+if __name__ == "__main__":
+    unittest.main()