Add bit_length emulator for python < 2.7

hyperloglog/hll.py

@@ -7,6 +7,19 @@
 from const import rawEstimateData, biasData, tresholdData
 
 
+def bit_length(w):
+    return w.bit_length()
+
+
+def bit_length_emu(w):
+    return len(bin(w)) - 2 if w > 0 else 0
+
+
+# Workaround for python < 2.7
+if not hasattr(int, 'bit_length'):
+    bit_length = bit_length_emu
+
+
 def get_treshold(p):
     return tresholdData[p - 4]
 
@@ -40,7 +53,7 @@ def get_alpha(p):
 
 
 def get_rho(w, max_width):
-    rho = max_width - w.bit_length() + 1
+    rho = max_width - bit_length(w) + 1
 
     if rho <= 0:
         raise ValueError('w overflow')

hyperloglog/test/test_hll.py

@@ -32,6 +32,24 @@ def test_rho(self):
         self.assertEqual(get_rho(1 << 31, 32), 1)
         self.assertRaises(ValueError, get_rho, 1 << 32, 32)
 
+    def test_rho_emu(self):
+        import hll
+        old = hll.bit_length
+        hll.bit_length = hll.bit_length_emu
+        try:
+            self.assertEqual(get_rho(0, 32), 33)
+            self.assertEqual(get_rho(1, 32), 32)
+            self.assertEqual(get_rho(2, 32), 31)
+            self.assertEqual(get_rho(3, 32), 31)
+            self.assertEqual(get_rho(4, 32), 30)
+            self.assertEqual(get_rho(5, 32), 30)
+            self.assertEqual(get_rho(6, 32), 30)
+            self.assertEqual(get_rho(7, 32), 30)
+            self.assertEqual(get_rho(1 << 31, 32), 1)
+            self.assertRaises(ValueError, get_rho, 1 << 32, 32)
+        finally:
+            hll.bit_length = old
+
     def test_init(self):
         s = HyperLogLog(0.05)
         self.assertEqual(s.p, 9)