No longer require string operations to find bit lengths.

Now that we no longer support Python 2.6, we can use int.bit_length()
instead. Co-authored by @adamantike.

2 files changed, 20 insertions, 44 deletions

diff --git a/rsa/common.py b/rsa/common.py
index 34142cc..4f8c0d9 100644
--- a/rsa/common.py
+++ b/rsa/common.py
@@ -31,9 +31,6 @@ def bit_size(num):
     Number of bits needed to represent a integer excluding any prefix
     0 bits.
 
-    As per definition from https://wiki.python.org/moin/BitManipulation and
-    to match the behavior of the Python 3 API.
-
     Usage::
 
         >>> bit_size(1023)
@@ -50,41 +47,11 @@ def bit_size(num):
     :returns:
         Returns the number of bits in the integer.
     """
-    if num == 0:
-        return 0
-    if num < 0:
-        num = -num
-
-    # Make sure this is an int and not a float.
-    num & 1
-
-    hex_num = "%x" % num
-    return ((len(hex_num) - 1) * 4) + {
-        '0': 0, '1': 1, '2': 2, '3': 2,
-        '4': 3, '5': 3, '6': 3, '7': 3,
-        '8': 4, '9': 4, 'a': 4, 'b': 4,
-        'c': 4, 'd': 4, 'e': 4, 'f': 4,
-    }[hex_num[0]]
-
-
-def _bit_size(number):
-    """
-    Returns the number of bits required to hold a specific long number.
-    """
-    if number < 0:
-        raise ValueError('Only nonnegative numbers possible: %s' % number)
-
-    if number == 0:
-        return 0
-
-    # This works, even with very large numbers. When using math.log(number, 2),
-    # you'll get rounding errors and it'll fail.
-    bits = 0
-    while number:
-        bits += 1
-        number >>= 1
 
-    return bits
+    try:
+        return num.bit_length()
+    except AttributeError:
+        raise TypeError('bit_size(num) only supports integers, not %r' % type(num))
 
 
 def byte_size(number):
diff --git a/tests/test_common.py b/tests/test_common.py
index ef32f61..e26e004 100644
--- a/tests/test_common.py
+++ b/tests/test_common.py
@@ -18,7 +18,7 @@
 import unittest
 import struct
 from rsa._compat import byte, b
-from rsa.common import byte_size, bit_size, _bit_size, inverse
+from rsa.common import byte_size, bit_size, inverse
 
 
 class TestByte(unittest.TestCase):
@@ -69,12 +69,21 @@ class TestBitSize(unittest.TestCase):
         self.assertEqual(bit_size((1 << 1024) + 1), 1025)
         self.assertEqual(bit_size((1 << 1024) - 1), 1024)
 
-        self.assertEqual(_bit_size(1023), 10)
-        self.assertEqual(_bit_size(1024), 11)
-        self.assertEqual(_bit_size(1025), 11)
-        self.assertEqual(_bit_size(1 << 1024), 1025)
-        self.assertEqual(_bit_size((1 << 1024) + 1), 1025)
-        self.assertEqual(_bit_size((1 << 1024) - 1), 1024)
+    def test_negative_values(self):
+        self.assertEqual(bit_size(-1023), 10)
+        self.assertEqual(bit_size(-1024), 11)
+        self.assertEqual(bit_size(-1025), 11)
+        self.assertEqual(bit_size(-1 << 1024), 1025)
+        self.assertEqual(bit_size(-((1 << 1024) + 1)), 1025)
+        self.assertEqual(bit_size(-((1 << 1024) - 1)), 1024)
+
+    def test_bad_type(self):
+        self.assertRaises(TypeError, bit_size, [])
+        self.assertRaises(TypeError, bit_size, ())
+        self.assertRaises(TypeError, bit_size, dict())
+        self.assertRaises(TypeError, bit_size, "")
+        self.assertRaises(TypeError, bit_size, None)
+        self.assertRaises(TypeError, bit_size, 0.0)
 
 
 class TestInverse(unittest.TestCase):