Issue #3439: add bit_length method to int and long.
Thanks Fredrik Johansson and Victor Stinner for code,
Raymond Hettinger for review.
diff --git a/Lib/test/test_int.py b/Lib/test/test_int.py
index a2dc85f..ce18ad2 100644
--- a/Lib/test/test_int.py
+++ b/Lib/test/test_int.py
@@ -2,6 +2,7 @@
import unittest
from test.test_support import run_unittest, have_unicode
+import math
L = [
('0', 0),
@@ -240,6 +241,40 @@
self.assertEqual(int('2br45qc', 35), 4294967297L)
self.assertEqual(int('1z141z5', 36), 4294967297L)
+ def test_bit_length(self):
+ tiny = 1e-10
+ for x in xrange(-65000, 65000):
+ k = x.bit_length()
+ # Check equivalence with Python version
+ self.assertEqual(k, len(bin(x).lstrip('-0b')))
+ # Behaviour as specified in the docs
+ if x != 0:
+ self.assert_(2**(k-1) <= abs(x) < 2**k)
+ else:
+ self.assertEqual(k, 0)
+ # Alternative definition: x.bit_length() == 1 + floor(log_2(x))
+ if x != 0:
+ # When x is an exact power of 2, numeric errors can
+ # cause floor(log(x)/log(2)) to be one too small; for
+ # small x this can be fixed by adding a small quantity
+ # to the quotient before taking the floor.
+ self.assertEqual(k, 1 + math.floor(
+ math.log(abs(x))/math.log(2) + tiny))
+
+ self.assertEqual((0).bit_length(), 0)
+ self.assertEqual((1).bit_length(), 1)
+ self.assertEqual((-1).bit_length(), 1)
+ self.assertEqual((2).bit_length(), 2)
+ self.assertEqual((-2).bit_length(), 2)
+ for i in [2, 3, 15, 16, 17, 31, 32, 33, 63, 64]:
+ a = 2**i
+ self.assertEqual((a-1).bit_length(), i)
+ self.assertEqual((1-a).bit_length(), i)
+ self.assertEqual((a).bit_length(), i+1)
+ self.assertEqual((-a).bit_length(), i+1)
+ self.assertEqual((a+1).bit_length(), i+1)
+ self.assertEqual((-a-1).bit_length(), i+1)
+
def test_intconversion(self):
# Test __int__()
class ClassicMissingMethods: