// Copyright (c) 2000  Max-Planck-Institute Saarbruecken (Germany).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org)
//
// $URL: https://github.com/CGAL/cgal/blob/v5.1/Nef_2/include/CGAL/Nef_2/Polynomial_impl.h $
// $Id: Polynomial_impl.h 0779373 2020-03-26T13:31:46+01:00 Sébastien Loriot
// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
//
//
// Author(s)     : Michael Seel
//                 Andreas Fabri


namespace CGAL{

  namespace Nef {

inline
void Polynomial<int>::euclidean_div(
  const Polynomial<int>& f, const Polynomial<int>& g,
  Polynomial<int>& q, Polynomial<int>& r)
{
  r = f; r.copy_on_write();
  int rd=r.degree(), gd=g.degree(), qd;
  if ( rd < gd ) { q = Polynomial<int>(int(0)); }
  else { qd = rd-gd+1; q = Polynomial<int>(std::size_t(qd)); }
  while ( rd >= gd && !(r.is_zero())) {
    int S = r[rd] / g[gd];
    qd = rd-gd;
    q.coeff(qd) += S;
    r.minus_offsetmult(g,S,qd);
    rd = r.degree();
  }
  CGAL_postcondition( f==q*g+r );
}



inline
void Polynomial<int>::pseudo_div(
  const Polynomial<int>& f, const Polynomial<int>& g,
  Polynomial<int>& q, Polynomial<int>& r, int& D)
{
  CGAL_NEF_TRACEN("pseudo_div "<<f<<" , "<< g);
  int fd=f.degree(), gd=g.degree();
  if ( fd<gd )
  { q = Polynomial<int>(0); r = f; D = 1;
    CGAL_postcondition(Polynomial<int>(D)*f==q*g+r); return;
  }
  // now we know fd >= gd and f>=g
  int qd=fd-gd, delta=qd+1, rd=fd;
  { q = Polynomial<int>( std::size_t(delta) ); }; // workaround for SUNPRO
  int G = g[gd]; // highest order coeff of g
  D = G; while (--delta) D*=G; // D = G^delta
  Polynomial<int> res = Polynomial<int>(D)*f;
  CGAL_NEF_TRACEN("  pseudo_div start "<<res<<" "<<qd<<" "<<q.degree());
  while (qd >= 0) {
    int F = res[rd]; // highest order coeff of res
    int t = F/G;     // ensured to be integer by multiplication of D
    q.coeff(qd) = t;    // store q coeff
    res.minus_offsetmult(g,t,qd);
    if (res.is_zero()) break;
    rd = res.degree();
    qd = rd - gd;
  }
  r = res;
  CGAL_postcondition(Polynomial<int>(D)*f==q*g+r);
  CGAL_NEF_TRACEN("  returning "<<q<<", "<<r<<", "<< D);
}



inline
Polynomial<int> Polynomial<int>::gcd(
  const Polynomial<int>& p1, const Polynomial<int>& p2)
{ CGAL_NEF_TRACEN("gcd("<<p1<<" , "<<p2<<")");
  if ( p1.is_zero() ) {
    if ( p2.is_zero() ) return Polynomial<int>(int(1));
    else return p2.abs();
  }
  if ( p2.is_zero() )
    return p1.abs();

  Polynomial<int> f1 = p1.abs();
  Polynomial<int> f2 = p2.abs();
  int f1c = f1.content(), f2c = f2.content();
  f1 /= f1c; f2 /= f2c;
  int F = CGAL::gcd(f1c,f2c);
  Polynomial<int> q,r; int M=1,D;
  bool first = true;
  while ( ! f2.is_zero() ) {
    Polynomial<int>::pseudo_div(f1,f2,q,r,D);
    if (!first) M*=D;
    CGAL_NEF_TRACEV(f1);CGAL_NEF_TRACEV(f2);CGAL_NEF_TRACEV(q);CGAL_NEF_TRACEV(r);CGAL_NEF_TRACEV(M);
    r /= r.content();
    f1=f2; f2=r;
    first=false;
  }
  CGAL_NEF_TRACEV(f1.content());
  return Polynomial<int>(F)*f1.abs();
}




inline
void Polynomial<double>::euclidean_div(
  const Polynomial<double>& f, const Polynomial<double>& g,
  Polynomial<double>& q, Polynomial<double>& r)
{
  r = f; r.copy_on_write();
  int rd=r.degree(), gd=g.degree(), qd;
  if ( rd < gd ) { q = Polynomial<double>(double(0)); }
  else { qd = rd-gd+1; q = Polynomial<double>(std::size_t(qd)); }
  while ( rd >= gd && !(r.is_zero())) {
    double S = r[rd] / g[gd];
    qd = rd-gd;
    q.coeff(qd) += S;
    r.minus_offsetmult(g,S,qd);
    rd = r.degree();
  }
  CGAL_postcondition( f==q*g+r );
}



inline
void Polynomial<double>::pseudo_div(
  const Polynomial<double>& f, const Polynomial<double>& g,
  Polynomial<double>& q, Polynomial<double>& r, double& D)
{
  CGAL_NEF_TRACEN("pseudo_div "<<f<<" , "<< g);
  int fd=f.degree(), gd=g.degree();
  if ( fd<gd )
  { q = Polynomial<double>(0); r = f; D = 1;
    CGAL_postcondition(Polynomial<double>(D)*f==q*g+r); return;
  }
  // now we know fd >= gd and f>=g
  int qd=fd-gd, delta=qd+1, rd=fd;
  q = Polynomial<double>( std::size_t(delta) );
  double G = g[gd]; // highest order coeff of g
  D = G; while (--delta) D*=G; // D = G^delta
  Polynomial<double> res = Polynomial<double>(D)*f;
  CGAL_NEF_TRACEN("  pseudo_div start "<<res<<" "<<qd<<" "<<q.degree());
  while (qd >= 0) {
    double F = res[rd]; // highest order coeff of res
    double t = F/G;     // ensured to be integer by multiplication of D
    q.coeff(qd) = t;    // store q coeff
    res.minus_offsetmult(g,t,qd);
    if (res.is_zero()) break;
    rd = res.degree();
    qd = rd - gd;
  }
  r = res;
  CGAL_postcondition(Polynomial<double>(D)*f==q*g+r);
  CGAL_NEF_TRACEN("  returning "<<q<<", "<<r<<", "<< D);
}

inline
Polynomial<double> Polynomial<double>::gcd(
  const Polynomial<double>& p1, const Polynomial<double>& p2)
{ CGAL_NEF_TRACEN("gcd("<<p1<<" , "<<p2<<")");
  if ( p1.is_zero() ) {
    if ( p2.is_zero() ) return Polynomial<double>(double(1));
    else return p2.abs();
  }
  if ( p2.is_zero() )
    return p1.abs();

  Polynomial<double> f1 = p1.abs();
  Polynomial<double> f2 = p2.abs();
  double f1c = f1.content(), f2c = f2.content();
  f1 /= f1c; f2 /= f2c;
  Polynomial<double> q,r; double M=1,D;
  bool first = true;
  while ( ! f2.is_zero() ) {
    Polynomial<double>::pseudo_div(f1,f2,q,r,D);
    if (!first) M*=D;
    CGAL_NEF_TRACEV(f1);CGAL_NEF_TRACEV(f2);CGAL_NEF_TRACEV(q);CGAL_NEF_TRACEV(r);CGAL_NEF_TRACEV(M);
    r /= r.content();
    f1=f2; f2=r;
    first=false;
  }
  CGAL_NEF_TRACEV(f1.content());
  return Polynomial<double>(1)*f1.abs();
}


} // end namespace Nef
}//end namespace CGAL