82 lines
2.4 KiB
Python
82 lines
2.4 KiB
Python
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# -*- coding: utf-8 -*-
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#
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# (c) 2019, Felix Fontein <felix@fontein.de>
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#
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# Ansible is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# Ansible is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with Ansible. If not, see <http://www.gnu.org/licenses/>.
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from __future__ import absolute_import, division, print_function
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__metaclass__ = type
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import sys
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def binary_exp_mod(f, e, m):
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'''Computes f^e mod m in O(log e) multiplications modulo m.'''
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# Compute len_e = floor(log_2(e))
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len_e = -1
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x = e
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while x > 0:
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x >>= 1
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len_e += 1
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# Compute f**e mod m
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result = 1
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for k in range(len_e, -1, -1):
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result = (result * result) % m
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if ((e >> k) & 1) != 0:
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result = (result * f) % m
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return result
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def simple_gcd(a, b):
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'''Compute GCD of its two inputs.'''
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while b != 0:
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a, b = b, a % b
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return a
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def quick_is_not_prime(n):
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'''Does some quick checks to see if we can poke a hole into the primality of n.
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A result of `False` does **not** mean that the number is prime; it just means
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that we couldn't detect quickly whether it is not prime.
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'''
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if n <= 2:
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return True
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# The constant in the next line is the product of all primes < 200
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if simple_gcd(n, 7799922041683461553249199106329813876687996789903550945093032474868511536164700810) > 1:
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return True
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# TODO: maybe do some iterations of Miller-Rabin to increase confidence
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# (https://en.wikipedia.org/wiki/Miller%E2%80%93Rabin_primality_test)
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return False
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python_version = (sys.version_info[0], sys.version_info[1])
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if python_version >= (2, 7) or python_version >= (3, 1):
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# Ansible still supports Python 2.6 on remote nodes
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def count_bits(no):
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no = abs(no)
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if no == 0:
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return 0
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return no.bit_length()
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else:
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# Slow, but works
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def count_bits(no):
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no = abs(no)
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count = 0
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while no > 0:
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no >>= 1
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count += 1
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return count
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