X-Git-Url: http://gitweb.pimeys.fr/?p=NK2015_Client_Python_Alpha.git;a=blobdiff_plain;f=rsa_source%2Frsa%2Fcommon.py;fp=rsa_source%2Frsa%2Fcommon.py;h=5ae92f05e4070ae10ec06b48b196edb923518ac4;hp=0000000000000000000000000000000000000000;hb=76e06d82c94bcb814b95419c7faaeacf4beb0155;hpb=d621c5224a44dc20bc2aaf661954fd1df65dd147

diff --git a/rsa_source/rsa/common.py b/rsa_source/rsa/common.py
new file mode 100644
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+++ b/rsa_source/rsa/common.py
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+# -*- coding: utf-8 -*-
+#
+#  Copyright 2011 Sybren A. Stüvel <sybren@stuvel.eu>
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+'''Common functionality shared by several modules.'''
+
+
+import math
+
+def bit_size(number):
+    '''Returns the number of bits required to hold a specific long number.
+
+    >>> bit_size(1023)
+    10
+    >>> bit_size(1024)
+    11
+    >>> bit_size(1025)
+    11
+
+    >>> bit_size(1 << 1024)
+    1025
+    >>> bit_size((1 << 1024) + 1)
+    1025
+    >>> bit_size((1 << 1024) - 1)
+    1024
+
+    '''
+
+    if number < 0:
+        raise ValueError('Only nonnegative numbers possible: %s' % number)
+
+    if number == 0:
+        return 1
+    
+    # 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
+
+
+def byte_size(number):
+    """Returns the number of bytes required to hold a specific long number.
+    
+    The number of bytes is rounded up.
+
+    >>> byte_size(1 << 1023)
+    128
+    >>> byte_size((1 << 1024) - 1)
+    128
+    >>> byte_size(1 << 1024)
+    129
+    """
+
+    return int(math.ceil(bit_size(number) / 8.0))
+
+if __name__ == '__main__':
+    import doctest
+    doctest.testmod()
+