diff --git a/bit_difference.py b/bit_difference.py
index f6fe3f0..263660d 100644
--- a/bit_difference.py
+++ b/bit_difference.py
@@ -2,20 +2,16 @@
 
 import sys
 
-def xor_count(a, b):
-    xor = a ^ b
-    i = 0
-    while xor != 0:
-        i = i + (xor & 1)
-        xor = xor >> 1
-    return i
-
-
 def bitwise_difference(A):
+    l = len(A)
     s = 0
-    for i in range(len(A)):
-        for j in range(i+1,len(A)):
-            s = s + xor_count(A[i], A[j])
+    for i in range(32):
+        n1 = 0
+        for j in range(l):
+            n1 += A[j] & 1
+            A[j] = A[j] >> 1
+        n0 = l - n1
+        s += n1 * n0
     return s