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.

1 files changed, 4 insertions, 37 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):