mac/crc.py: make crc calculation more pythonic

liteeth/core/mac/crc.py

@@ -56,11 +56,12 @@ class LiteEthMACCRCEngine(Module):
             return r
 
         # compute and optimize the parallel implementation of the CRC's LFSR
+        taps = [x for x in range(width) if (1 << x) & polynom]
         curval = [[("state", i)] for i in range(width)]
         for i in range(data_width):
             feedback = curval.pop() + [("din", i)]
             for j in range(width-1):
-                if (polynom & (1<<(j+1))):
+                if j+1 in taps:
                     curval[j] += feedback
                 curval[j] = _optimize_eq(curval[j])
             curval.insert(0, feedback)