91 lines
1.7 KiB
C++
91 lines
1.7 KiB
C++
/*
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Copyright (c) 2013 Microsoft Corporation. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Author: Leonardo de Moura
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*/
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#include <utility>
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#include "util/debug.h"
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namespace lean {
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/**
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\brief Template for computing GCD using binary method
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*/
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template<typename T>
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static T gcd(T u, T v) {
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if (u == 0)
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return v;
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if (v == 0)
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return u;
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int k;
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for (k = 0; ((u | v) & 1) == 0; ++k) {
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u >>= 1;
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v >>= 1;
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}
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while ((u & 1) == 0)
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u >>= 1;
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do {
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while ((v & 1) == 0)
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v >>= 1;
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if (u < v) {
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v -= u;
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} else {
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T diff = u - v;
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u = v;
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v = diff;
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}
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v >>= 1;
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} while (v != 0);
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return u << k;
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}
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/**
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\brief Template for the extended GCD procedure
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*/
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template<typename T>
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void gcdext(T & r, T & a, T & b, T const & r1, T const & r2) {
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using std::swap;
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T aux, quot;
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T tmp1 = r1;
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T tmp2 = r2;
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a = 1;
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b = 0;
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T next_a, next_b;
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next_a = 0;
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next_b = 1;
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if (tmp1 < 0) tmp1 = -tmp1;
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if (tmp2 < 0) tmp2 = -tmp2;
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if (tmp1 < tmp2) {
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swap(tmp1, tmp2);
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swap(next_a, next_b);
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swap(a, b);
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}
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// tmp1 >= tmp2 >= 0
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// quot_rem in one function would be faster.
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while (tmp2 > 0) {
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lean_assert(tmp1 >= tmp2);
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aux = tmp2;
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quot = tmp1 / tmp2;
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tmp2 = tmp1 % tmp2;
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tmp1 = aux;
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aux = next_a;
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next_a = a - (quot * next_a);
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a = aux;
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aux = next_b;
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next_b = b - (quot * next_b);
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b = aux;
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}
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if (r1 < 0) a = -a;
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if (r2 < 0) b = -b;
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r = tmp1;
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}
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}
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