mirror of https://github.com/CGAL/cgal
66 lines
2.0 KiB
C++
66 lines
2.0 KiB
C++
// Copyright (c) 2007-2008 Inria Lorraine (France). All rights reserved.
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//
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// This file is part of CGAL (www.cgal.org); you can redistribute it and/or
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// modify it under the terms of the GNU Lesser General Public License as
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// published by the Free Software Foundation; version 2.1 of the License.
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// See the file LICENSE.LGPL distributed with CGAL.
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//
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// Licensees holding a valid commercial license may use this file in
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// accordance with the commercial license agreement provided with the software.
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//
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// This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
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// WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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//
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// $URL$
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// $Id$
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//
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// Author: Luis Peñaranda <luis.penaranda@loria.fr>
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#ifndef CGAL_RS__INVERSE_H
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#define CGAL_RS__INVERSE_H
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#include <stdint.h>
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#define n_(A) (A<0?-A:A)
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//#define u_(A) (A<0?-1:1)
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#define u_(A,C) (A<0?(C<0?1:-1):(C<0?-1:1))
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namespace CGAL{
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namespace RS_MGCD{
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class Inverse{
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protected:
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// given a and b, returns s such that gcd(a,b)=s*a+t*b (GCL, page 36)
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// s*a+t*q=1 => s is the inverse of a, mod q (pafe 173)
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static int64_t eea_s(uint32_t a,uint32_t b){
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int64_t c1,d1,r1;//,c2,d2,r2,t,s;
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uint32_t r,c,d;//,q;
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// a and b are positive, so a=n_(a) and b=n_(b)
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//c=n_(a); d=n_(b);
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c=a; d=b;
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c1=1; d1=0;
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//c2=0; d2=1;
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while(d){
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//q=c/d;
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r=c%d;
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r1=c1-d1*(c/d); //r2=c2-d2*q;
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c=d; c1=d1; //c2=d2;
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d=r; d1=r1; //d2=r2;
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}
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// gcd(a,b) is n_(c)
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//t=c2/(_u(b)*u_(c));
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// a and c are always positive, so s=c1/u_(a,c) equals c1
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//s=c1/u_(a,c);
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//return s;
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return c1;
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};
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}; // class Inverse
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} // namespace RS_MGCD
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} // namespace CGAL
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#endif // CGAL_RS__INVERSE_H
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// vim: tabstop=4: softtabstop=4: smarttab: shiftwidth=4: expandtab
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