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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()
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