Add function to reverse 4bit weights for HPU (bitsandbytes-foundation#1757)

* Add function to reverse 4bit weights for HPU

* Fix lint error

Author: vivekgoe

bitsandbytes/backends/hpu/ops.py

@@ -3,12 +3,19 @@
 
 import torch
 
-from bitsandbytes.utils import _reverse_4bit_compress_format
-
 from ..._ops import register_kernel
 from ..utils import GAUDI_SW_VER
 
 
+# convert btw standard 4-bit compression format and ipex compression format
+# needed for backward compatibility with older versions of gaudi sw
+def _reverse_4bit_compress_format(weight: torch.Tensor):
+    out_1 = (weight & 0xF0) >> 4
+    out_2 = (weight & 0xF) << 4
+    out = out_1 | out_2
+    return out
+
+
 @register_kernel("bitsandbytes::dequantize_4bit", "hpu")
 def _(
     A: torch.Tensor,