Clean up bits generator TODO in PCAN interface

Remove the TODO to document how the bits generator works in the PCAN
interface by adding documentation and renaming the variables to make
things more clear.

Author: karlding

can/interfaces/pcan/pcan.py

@@ -216,11 +216,17 @@ def _get_formatted_error(self, error):
         """
 
         def bits(n):
-            """TODO: document"""
+            """
+            Iterate over all the set bits in `n`, returning the masked bits at
+            the set indices
+            """
             while n:
-                b = n & (~n+1)
-                yield b
-                n ^= b
+                # Create a mask to mask the lowest set bit in n
+                mask = (~n + 1)
+                masked_value = n & mask
+                yield masked_value
+                # Toggle the lowest set bit
+                n ^= masked_value
 
         stsReturn = self.m_objPCANBasic.GetErrorText(error, 0)
         if stsReturn[0] != PCAN_ERROR_OK: