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https://github.com/PurpleI2P/Boost-for-Android-Prebuilt
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84 lines
1.7 KiB
C++
84 lines
1.7 KiB
C++
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/*
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* (C) Copyright Nick Thompson 2018.
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* Use, modification and distribution are subject to the
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* Boost Software License, Version 1.0. (See accompanying file
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* LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_INTEGER_EXTENDED_EUCLIDEAN_HPP
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#define BOOST_INTEGER_EXTENDED_EUCLIDEAN_HPP
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#include <limits>
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#include <stdexcept>
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#include <boost/throw_exception.hpp>
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#include <boost/core/swap.hpp>
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#include <boost/core/enable_if.hpp>
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namespace boost { namespace integer {
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// From "The Joy of Factoring", Algorithm 2.7, with a small optimization to remove tmps from Wikipedia.
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// Solves mx + ny = gcd(m,n). Returns tuple with (gcd(m,n), x, y).
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template<class Z>
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struct euclidean_result_t
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{
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Z gcd;
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Z x;
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Z y;
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};
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template<class Z>
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typename boost::enable_if_c< std::numeric_limits< Z >::is_signed, euclidean_result_t< Z > >::type
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extended_euclidean(Z m, Z n)
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{
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if (m < 1 || n < 1)
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{
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BOOST_THROW_EXCEPTION(std::domain_error("extended_euclidean: arguments must be strictly positive"));
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}
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bool swapped = false;
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if (m < n)
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{
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swapped = true;
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boost::swap(m, n);
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}
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Z u0 = m;
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Z u1 = 1;
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Z u2 = 0;
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Z v0 = n;
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Z v1 = 0;
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Z v2 = 1;
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Z w0;
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Z w1;
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Z w2;
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while(v0 > 0)
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{
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Z q = u0/v0;
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w0 = u0 - q*v0;
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w1 = u1 - q*v1;
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w2 = u2 - q*v2;
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u0 = v0;
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u1 = v1;
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u2 = v2;
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v0 = w0;
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v1 = w1;
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v2 = w2;
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}
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euclidean_result_t< Z > result;
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result.gcd = u0;
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if (!swapped)
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{
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result.x = u1;
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result.y = u2;
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}
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else
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{
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result.x = u2;
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result.y = u1;
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}
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return result;
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}
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}}
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#endif
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