Fix verify acc failed of blockwise quantizer

Signed-off-by: wenjh <wenjh@sugon.com>

tests/pytorch/references/blockwise_quantizer_reference.py

@@ -130,6 +130,12 @@ class BlockwiseQuantizerReference:
         )
         qx = x_tiled * scale.reshape(M // tile_len, 1, K // tile_len, 1)
         qx = torch.clamp(qx, min=-dtype_max, max=dtype_max)
+        if quant_dtype == torch.int8:
+            positive_mask = qx >= 0
+            negative_mask = ~positive_mask
+            pos_part = torch.where(positive_mask, torch.floor(qx + 0.5), 0)
+            neg_part = torch.where(negative_mask, torch.ceil(qx - 0.5), 0)
+            qx = pos_part + neg_part
         qx = qx.to(dtype=quant_dtype)
         qx = qx.reshape(M, K)
         if unpadded_k != K or unpadded_m != M: