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Issue #3439: add bit_length method to int and long.

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Thanks Fredrik Johansson and Victor Stinner for code,
Raymond Hettinger for review.
This commit is contained in:
Mark Dickinson 2008-12-17 16:14:37 +00:00
parent d0c3515bc5
commit 1a707981c8
8 changed files with 239 additions and 1 deletions
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35
Lib/test/test_int.py
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@ -2,6 +2,7 @@ import sys
import unittest
from test.test_support import run_unittest, have_unicode
import math
L = [
('0', 0),
@ -240,6 +241,40 @@ class IntTestCases(unittest.TestCase):
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: