diff options
Diffstat (limited to 'Lib/test/test_long.py')
| -rw-r--r-- | Lib/test/test_long.py | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/Lib/test/test_long.py b/Lib/test/test_long.py index 5addd2e..e648c0f 100644 --- a/Lib/test/test_long.py +++ b/Lib/test/test_long.py @@ -3,6 +3,7 @@ from test import test_support import sys import random +import math # Used for lazy formatting of failure messages class Frm(object): @@ -752,6 +753,42 @@ class LongTest(unittest.TestCase): self.assertRaises(OverflowError, long, float('-inf')) self.assertRaises(ValueError, long, float('nan')) + def test_bit_length(self): + tiny = 1e-10 + for x in xrange(-65000, 65000): + x = long(x) + 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((0L).bit_length(), 0) + self.assertEqual((1L).bit_length(), 1) + self.assertEqual((-1L).bit_length(), 1) + self.assertEqual((2L).bit_length(), 2) + self.assertEqual((-2L).bit_length(), 2) + for i in [2, 3, 15, 16, 17, 31, 32, 33, 63, 64, 234]: + a = 2L**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_main(): test_support.run_unittest(LongTest) |