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thue.c

/* $Id: thue.c,v 1.8 2000/11/03 21:00:29 karim Exp $

Copyright (C) 2000  The PARI group.

This file is part of the PARI/GP package.

PARI/GP is free software; you can redistribute it and/or modify it under the
terms of the GNU General Public License as published by the Free Software
Foundation. It is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY WHATSOEVER.

Check the License for details. You should have received a copy of it, along
with the package; see the file 'COPYING'. If not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */

/* Thue equation solver. In all the forthcoming remarks, "paper"
 * designs the paper "Thue Equations of High Degree", by Yu. Bilu and
 * G. Hanrot, J. Number Theory (1996). Note that numbering of the constants
 * is that of Hanrot's thesis rather than that of the paper.
 * The last part of the program (bnfisintnorm) was written by K. Belabas.
 */
#include "pari.h"

static int curne,r,s,t,deg,Prec,ConstPrec,numroot;
static GEN c1,c2,c3,c4,c5,c6,c7,c8,c10,c11,c12,c13,c14,c15,B0,x1,x2,x3,x0;
static GEN halpha,eps3,gdeg,A,MatNE,roo,MatFU,Delta,Lambda,delta,lambda;
static GEN Vect2,SOL,uftot;

GEN bnfisintnorm(GEN, GEN);

/* Check whether tnf is a valid structure */
static int
checktnf(GEN tnf)
{
  if (typ(tnf)!=t_VEC || (lg(tnf)!=8 && lg(tnf)!=3)) return 0;
  if (typ(tnf[1])!=t_POL) return 0;
  if (lg(tnf) != 8) return 1; /* s=0 */

  deg=lgef(tnf[1])-3;
  if (deg<=2) err(talker,"invalid polynomial in thue (need deg>2)");
  s=sturm((GEN)tnf[1]); t=(deg-s)>>1; r=s+t-1;
  (void)checkbnf((GEN)tnf[2]);
  if (typ(tnf[3]) != t_COL || lg(tnf[3]) != deg+1) return 0;
  if (typ(tnf[4]) != t_COL || lg(tnf[4]) != r+1) return 0;
  if (typ(tnf[5]) != t_MAT || lg(tnf[5]) != r+1
      || lg(gmael(tnf,5,1)) != deg+1) return 0;
  if (typ(tnf[6]) != t_MAT || lg(tnf[6])!=r+1
      || lg(gmael(tnf,6,1)) != r+1) return 0;
  if (typ(tnf[7]) != t_VEC || lg(tnf[7]) != 7) return 0;
  return 1;
}

static GEN distoZ(GEN z)
{
  GEN p1=gfrac(z);
  return gmin(p1, gsub(gun,p1));
}

/* Check whether a solution has already been found */
static int
_thue_new(GEN zz)
{
  int i;
  for (i=1; i<lg(SOL); i++)
    if (gegal(zz,(GEN)SOL[i])) return 0;
  return 1;
}

/* Compensates rounding errors for computation/display of the constants */
static GEN
myround(GEN Cst, GEN upd)
{
  return gmul(Cst, gadd(gun, gmul(upd,gpuigs(stoi(10),-10))));
}

/* Returns the index of the largest element in a vector */
static int
Vecmax(GEN Vec, int size)
{
  int k, tno = 1;
  GEN tmax = (GEN)Vec[1];
  for (k=2; k<=size; k++)
    if (gcmp((GEN)Vec[k],tmax)==1) { tmax=(GEN)Vec[k]; tno=k; }
  return tno;
}

/* Performs basic computations concerning the equation: buchinitfu, c1, c2 */
static void
inithue(GEN poly, long flag)
{
  GEN roo2, tmp, gpmin, de;
  int k,j;

  x0=gzero; x1=gzero; deg=lgef(poly)-3; gdeg=stoi(deg);

  if (!uftot)
  {
    uftot=bnfinit0(poly,1,NULL,Prec);
    if (uftot != checkbnf_discard(uftot))
      err(talker,"non-monic polynomial in thue");
    if (flag) certifybuchall(uftot);
    s=itos(gmael3(uftot,7,2,1));
    t=itos(gmael3(uftot,7,2,2));
  }
  /* Switch the roots to get the usual order */
  roo=roots(poly, Prec); roo2=cgetg(deg+1,t_COL);
  for (k=1; k<=s; k++) roo2[k]=roo[k];
  for (k=1; k<=t; k++)
  {
    roo2[k+s]=roo[2*k-1+s];
    roo2[k+s+t]=lconj((GEN)roo2[k+s]);
  }
  roo=roo2;

  r=s+t-1; halpha=gun;
  for (k=1; k<=deg; k++)
    halpha = gmul(halpha,gmax(gun,gabs((GEN)roo[k],Prec)));
  halpha=gdiv(glog(halpha,Prec),gdeg);

  de=derivpol(poly); c1=gabs(poleval(de,(GEN)roo[1]),Prec);
  for (k=2; k<=s; k++)
  {
    tmp=gabs(poleval(de,(GEN)roo[k]),Prec);
    if (gcmp(tmp,c1)==-1) c1=tmp;
  }

  c1=gdiv(gpui(gdeux,gsub(gdeg,gun),Prec),c1); c1=myround(c1,gun);
  c2=gabs(gsub((GEN)roo[1],(GEN)roo[2]),Prec);

  for (k=1; k<=deg; k++)
    for (j=k+1; j<=deg; j++)
    {
      tmp=gabs(gsub((GEN)roo[j],(GEN)roo[k]),Prec);
      if (gcmp(c2,tmp)==1) c2=tmp;
    }

  c2=myround(c2,stoi(-1));
  if (t==0) x0=gun;
  else
  {
    gpmin=gabs(poleval(de,(GEN)roo[s+1]),Prec);
    for (k=2; k<=t; k++)
    {
      tmp=gabs(poleval(de,(GEN)roo[s+k]),Prec);
      if (gcmp(tmp,gpmin)==-1) gpmin=tmp;
    }

    /* Compute x0. See paper, Prop. 2.2.1 */
    x0=gpui(gdiv(gpui(gdeux,gsub(gdeg,gun),Prec),
                 gmul(gpmin,
                  gabs((GEN)gimag(roo)[Vecmax(gabs(gimag(roo),Prec),deg)],Prec))),
          ginv(gdeg),Prec);
  }

  if (DEBUGLEVEL >=2) fprintferr("c1 = %Z\nc2 = %Z\n", c1, c2);

}

/* Computation of M, its inverse A and check of the precision (see paper) */
static void
T_A_Matrices(void)
{
  GEN mask, eps1, eps2, nia, m1, IntM;
  int i,j;

  m1=glog(gabs(MatFU,Prec),Prec); mask=gsub(gpui(gdeux,stoi(r),Prec),gun);
  m1=matextract(m1,mask,mask);

  A=invmat(m1); IntM=gsub(gmul(A,m1),idmat(r));

  eps2=gzero;
  for (i=1; i<=r; i++)
    for (j=1; j<=r; j++)
      if (gcmp(eps2,gabs(gcoeff(IntM,i,j),20)) == -1)
      eps2=gabs(gcoeff(IntM,i,j),20);

  eps1=gpui(gdeux,stoi((Prec-2)*32),Prec); eps2=gadd(eps2,ginv(eps1));

  nia=gzero;
  for (i=1; i<=r; i++)
    for (j=1; j<=r; j++)
      if (gcmp(nia,gabs(gcoeff(A,i,j),20)) == -1)
        nia = gabs(gcoeff(A,i,j),20);

  /* Check for the precision in matrix inversion. See paper, Lemma 2.4.2. */
  if (gcmp(gmul(gadd(gmul(stoi(r),gmul(nia,eps1)),eps2),
           gmul(gdeux,stoi(r))),gun) == -1)
    err(talker,"not enough precision in thue");

  eps3=gmul(gdeux,gmul(gmul(gsqr(stoi(r)),nia),
                   gadd(gmul(stoi(r),gdiv(nia,eps1)),eps2)));
  myround(eps3,gun);

  if (DEBUGLEVEL>=2) fprintferr("epsilon_3 -> %Z\n",eps3);
}

/* Computation of the constants c5, c7, c10, c12, c15 */
static void
ComputeConstants(void)
{
  int k;

  GEN Vect;

  Vect=cgetg(r+1,t_COL); for (k=1; k<=r; k++) Vect[k]=un;
  if (numroot <= r) Vect[numroot]=lsub(gun,gdeg);

  Delta=gmul(A,Vect);

  c5=(GEN)(gabs(Delta,Prec)[Vecmax(gabs(Delta,Prec),r)]);
  c5=myround(c5,gun); c7=mulsr(r,c5);
  c10=divsr(deg,c7); c13=divsr(deg,c5);


  if (DEBUGLEVEL>=2)
  {
    fprintferr("c5 = %Z\n",c5);
    fprintferr("c7 = %Z\n",c7);
    fprintferr("c10 = %Z\n",c10);
    fprintferr("c13 = %Z\n",c13);
  }
}

/* Computation of the constants c6, c8, c9 */
static void
ComputeConstants2(GEN poly, GEN rhs)
{
  GEN Vect1, tmp;
  int k;

  Vect1=cgetg(r+1,t_COL);
  for (k=1; k<=r; k++) Vect1[k]=un;
  Vect1=gmul(gabs(A,ConstPrec),Vect1);


  Vect2=cgetg(r+1,t_COL);
  for (k=1; k<=r; k++)
    { if (k!=numroot)
      { Vect2[k]=llog(gabs(gdiv(gsub((GEN)roo[numroot],(GEN)roo[k]),
                          gcoeff(MatNE,k,curne)),Prec),Prec); }
      else { Vect2[k]=llog(gabs(gdiv(rhs,gmul(poleval(derivpol(poly)
                                     ,(GEN)roo[numroot]),
                               gcoeff(MatNE,k,curne))),Prec),Prec);
      }                 
    }
  Lambda=gmul(A,Vect2);

  tmp=(GEN)Vect1[Vecmax(Vect1,r)];
  x2=gmax(x1,gpui(mulsr(10,mulrr(c4,tmp)),ginv(gdeg),ConstPrec));
  c14=mulrr(c4,tmp);

  c6=gabs((GEN)Lambda[Vecmax(gabs(Lambda,ConstPrec),r)],ConstPrec);
  c6=addrr(c6,dbltor(0.1)); c6=myround(c6,gun);

  c8=addrr(dbltor(1.23),mulsr(r,c6));
  c11=mulrr(mulsr(2,c3),gexp(divrr(mulsr(deg,c8),c7),ConstPrec));

  tmp=gexp(divrr(mulsr(deg,c6),c5),ConstPrec);
  c12=mulrr(mulsr(2,c3),tmp);
  c15=mulsr(2,mulrr(c14,tmp));

  if (DEBUGLEVEL>=2)
  {
    fprintferr("c6 = %Z\n",c6);
    fprintferr("c8 = %Z\n",c8);
    fprintferr("c11 = %Z\n",c11);
    fprintferr("c12 = %Z\n",c12);
    fprintferr("c14 = %Z\n",c14);
    fprintferr("c15 = %Z\n",c15);
  }
}

/* Computation of the logarithmic heights of the units */
static GEN
Logarithmic_Height(int s)
{
  int i;
  GEN LH=gun,mat;

  mat=gabs(MatFU,Prec);
  for (i=1; i<=deg; i++)
    LH = gmul(LH,gmax(gun,gabs(gcoeff(mat,i,s),Prec)));
  return gmul(gdeux,gdiv(glog(LH,Prec),gdeg));
}

/* Computation of the matrix ((\sigma_i(\eta_j)) used for M_1 and
   the computation of logarithmic heights */
static void
Compute_Fund_Units(GEN uf)
{
  int i,j;
  MatFU=cgetg(r+1,t_MAT);

  for (i=1; i<=r; i++)
    MatFU[i]=lgetg(deg+1,t_COL);
  for (i=1; i<=r; i++)
  {
    if (typ(uf[i])!=t_POL) err(talker,"incorrect system of units");
    for (j=1; j<=deg; j++)
      coeff(MatFU,j,i)=(long)poleval((GEN)uf[i],(GEN)roo[j]);
  }
}

/* Computation of the conjugates of the solutions to the norm equation */
static void
Conj_Norm_Eq(GEN ne, GEN *Hmu)
{
  int p,q,nesol,x;

  nesol=lg(ne); MatNE=(GEN)cgetg(nesol,t_MAT); (*Hmu)=cgetg(nesol,t_COL);

  for (p=1; p<nesol; p++) { MatNE[p]=lgetg(deg+1,t_COL); (*Hmu)[p]=un; }
  for (q=1; q<nesol; q++)
  {
    x=typ(ne[q]);
    if (x!=t_INT && x!=t_POL)
      err(talker,"incorrect solutions of norm equation");
    for (p=1; p<=deg; p++)
    {
      coeff(MatNE,p,q)=(long)poleval((GEN)ne[q],(GEN)roo[p]);
      /* Logarithmic height of the solutions of the norm equation */
      (*Hmu)[q]=lmul((GEN)(*Hmu)[q],gmax(gun,gabs(gcoeff(MatNE,p,q),Prec)));
    }
  }
  for (q=1; q<nesol; q++)
    (*Hmu)[q]=ldiv(glog((GEN)(*Hmu)[q],Prec),gdeg);
}

/* Compute Baker's bound c11, and B_0, the bound for the b_i's .*/
static void
Baker(GEN ALH, GEN Hmu)
{
  GEN c9=gun, gbak, hb0=gzero;
  int k,i1,i2;

  gbak = gmul(gmul(gdeg,gsub(gdeg,gun)),gsub(gdeg,gdeux));

  switch (numroot) {
  case 1: i1=2; i2=3; break;
  case 2: i1=1; i2=3; break;
  case 3: i1=1; i2=2; break;
  default: i1=1; i2=2; break;
  }

  /* For the symbols used for the computation of c11, see paper, Thm 2.3.1 */
  /* Compute h_1....h_r */
  for (k=1; k<=r; k++)
  {
    c9=gmul(c9,gmax((GEN)ALH[k],
                  gmax(ginv(gbak),
                     gdiv(gabs(glog(gdiv(gcoeff(MatFU,i1,k),
                                     gcoeff(MatFU,i2,k)),
                                Prec),Prec),gbak))));
  }

  /* Compute a bound for the h_0 */
  hb0=gadd(gmul(stoi(4),halpha),gadd(gmul(gdeux,(GEN)Hmu[curne]),
                                     gmul(gdeux,glog(gdeux,Prec))));
  hb0=gmax(hb0,gmax(ginv(gbak),
                    gdiv(gabs(glog(gdiv(gmul(gsub((GEN)roo[numroot],
                                                  (GEN)roo[i2]),
                                             gcoeff(MatNE,i1,curne)),
                                        gmul(gsub((GEN)roo[numroot],
                                      (GEN)roo[i1]),
                                             gcoeff(MatNE,i2,curne))),
                                   Prec),Prec),gbak)));
  c9=gmul(c9,hb0);
  /* Multiply c9 by the "constant" factor */
  c9=gmul(c9,gmul(gmul(gmul(stoi(18),mppi(Prec)),gpui(stoi(32),stoi(4+r),Prec)),
                  gmul(gmul(mpfact(r+3), gpowgs(gmul(gbak,stoi(r+2)), r+3)),
                         glog(gmul(gdeux,gmul(gbak,stoi(r+2))),Prec))));
  c9=myround(c9,gun);
  /* Compute B0 according to Lemma 2.3.3 */
  B0=gmax(gexp(gun,Prec),
        mulsr(2,divrr(addrr(mulrr(c9,glog(divrr(c9,c10),ConstPrec)),
                        glog(c11,ConstPrec)),c10)));

  if (DEBUGLEVEL>=2) fprintferr("Baker -> %Z\nB0 -> %Z\n",c9,B0);
}

/* Compute delta and lambda */
static void
Create_CF_Values(int i1, int i2, GEN *errdelta)
{
  GEN eps5;

  if (r>1)
    {
      delta=divrr((GEN)Delta[i2],(GEN)Delta[i1]);
      eps5=mulrs(eps3,r);
      *errdelta=mulrr(addsr(1,delta),
                  divrr(eps5,subrr(gabs((GEN)Delta[i1],ConstPrec),eps5)));

      lambda=gdiv(gsub(gmul((GEN)Delta[i2],(GEN)Lambda[i1]),
                   gmul((GEN)Delta[i1],(GEN)Lambda[i2])),
              (GEN)Delta[i1]);
    }
  else
    {
    GEN Pi2 = gmul2n(mppi(Prec),1);
      delta=gdiv(gcoeff(MatFU,2,1),gcoeff(MatFU,3,1));
    delta=gdiv(garg(delta,Prec),Pi2);
      *errdelta=gdiv(gpui(gdeux,stoi(-(Prec-2)*32+1),Prec),
                 gabs(gcoeff(MatFU,2,1),Prec));
      lambda=gmul(gdiv(gsub((GEN)roo[numroot],(GEN)roo[2]),
                   gsub((GEN)roo[numroot],(GEN)roo[3])),
              gdiv(gcoeff(MatNE,3,curne),gcoeff(MatNE,2,curne)));
    lambda=gdiv(garg(lambda,Prec),Pi2);
  }
  if (DEBUGLEVEL>=2) outerr(*errdelta);
}

/* Try to reduce the bound through continued fractions; see paper. */
static int
CF_First_Pass(GEN kappa, GEN errdelta)
{
  GEN q,ql,qd,l0;

  if (gcmp(gmul(dbltor(0.1),gsqr(mulri(B0,kappa))),ginv(errdelta))==1)
  {
    return -1;
  }

  q=denom(bestappr(delta, mulir(kappa, B0))); ql=mulir(q,lambda);
  qd=gmul(q,delta); ql=gabs(subri(ql, ground(ql)),Prec);
  qd=gabs(mulrr(subri(qd,ground(qd)),B0),Prec);
  l0=subrr(ql,addrr(qd,divri(dbltor(0.1),kappa)));
  if (signe(l0) <= 0)
  {
    if (DEBUGLEVEL>=2)
      fprintferr("CF_First_Pass failed. Trying again with larger kappa\n");
    return 0;
  }

    if (r>1)
      B0=divrr(glog(divrr(mulir(q,c15),l0),ConstPrec),c13);
    else
    B0=divrr(glog(divrr(mulir(q,c11),mulrr(l0,gmul2n(mppi(ConstPrec),1))),ConstPrec),c10);

    if (DEBUGLEVEL>=2)
    fprintferr("CF_First_Pass successful !!\nB0 -> %Z\n",B0);
    return 1;
  }

/* Check whether a "potential" solution is truly a solution. */
static void
Check_Solutions(GEN xmay1, GEN xmay2, GEN poly, GEN rhs)
{
  GEN xx1, xx2, yy1, yy2, zz, u;

  yy1=ground(greal(gdiv(gsub(xmay2,xmay1), gsub((GEN)roo[1],(GEN)roo[2]))));
  yy2=gneg(yy1);

  xx1=greal(gadd(xmay1,gmul((GEN)roo[1],yy1)));
  xx2=gneg(xx1);

  if (gcmp(distoZ(xx1),dbltor(0.0001))==-1)
  {
    xx1=ground(xx1);
    if (!gcmp0(yy1))
    {
      if (gegal(gmul(poleval(poly,gdiv(xx1,yy1)),
                 gpui(yy1,gdeg,Prec)),(GEN)rhs))
      {
      zz=cgetg(2,t_VEC); u=cgetg(3,t_VEC);
      u[1]=(long)xx1; u[2]=(long)yy1; zz[1]=(long)u;
      if (_thue_new(u)) SOL=concatsp(SOL,zz);
      }
    }
    else if (gegal(gpui(xx1,gdeg,Prec),(GEN)rhs))
    {
      zz=cgetg(2,t_VEC); u=cgetg(3,t_VEC);
      u[1]=(long)xx1; u[2]=(long)gzero; zz[1]=(long)u;
      if (_thue_new(u)) SOL=concatsp(SOL,zz);
    }

    xx2=ground(xx2);
    if (!gcmp0(yy2))
    {
      if (gegal(gmul(poleval(poly,gdiv(xx2,yy2)),
                 gpui(yy2,gdeg,Prec)),(GEN)rhs))
      {
      zz=cgetg(2,t_VEC); u=cgetg(3,t_VEC);
      u[1]=(long)xx2; u[2]=(long)yy2; zz[1]=(long)u;
      if (_thue_new(u)) SOL=concatsp(SOL,zz);
      }
    }
    else if (gegal(gpui(xx2,gdeg,Prec),(GEN)rhs))
    {
      zz=cgetg(2,t_VEC); u=cgetg(3,t_VEC);
      u[1]=(long)xx2; u[2]=(long)gzero; zz[1]=(long)u;
      if (_thue_new(u)) SOL=concatsp(SOL,zz);
    }
  }
}

static GEN
GuessQi(GEN *q1, GEN *q2, GEN *q3)
{
  GEN C, Lat, eps;

  C=gpui(stoi(10),stoi(10),Prec);
  Lat=idmat(3); mael(Lat,1,3)=(long)C; mael(Lat,2,3)=lround(gmul(C,delta));
  mael(Lat,3,3)=lround(gmul(C,lambda));

  Lat=lllint(Lat);
  *q1=gmael(Lat,1,1); *q2=gmael(Lat,1,2); *q3=gmael(Lat,1,3);

  eps=gabs(gadd(gadd(*q1,gmul(*q2,delta)),gmul(*q3,lambda)),Prec);
  return(eps);
}

static void
TotRat(void)
{
  err(bugparier,"thue (totally rational case)");
}

/* Check for solutions under a small bound (see paper) */
static void
Check_Small(int bound, GEN poly, GEN rhs)
{
  GEN interm, xx, zz, u, maxr, tmp, ypot, xxn, xxnm1, yy;
  long av = avma, lim = stack_lim(av,1);
  int x, j, bsupy, y;
  double bndyx;

  maxr=gabs((GEN)roo[1],Prec); for(j=1; j<=deg; j++)
    { if(gcmp(tmp=gabs((GEN)roo[j],Prec),maxr)==1) maxr=tmp; }

  bndyx=gtodouble(gadd(gpui(gabs(rhs,Prec),ginv(gdeg),Prec),maxr));

  for (x=-bound; x<=bound; x++)
  {
    if (low_stack(lim,stack_lim(av,1)))
    {
      if(DEBUGMEM>1) err(warnmem,"Check_small");
      SOL = gerepileupto(av, gcopy(SOL));
    }
    if (x==0)
      {
      ypot=gmul(stoi(gsigne(rhs)),ground(gpui(gabs(rhs,0),ginv(gdeg),Prec)));
      if (gegal(gpui(ypot,gdeg,0),rhs))
        {
          zz=cgetg(2,t_VEC); u=cgetg(3,t_VEC);
          u[1]=(long)ypot; u[2]=(long)gzero; zz[1]=(long)u;
          if (_thue_new(u)) SOL=concatsp(SOL,zz);
        }
      if (gegal(gpui(gneg(ypot),gdeg,0),rhs))
        {
          zz=cgetg(2,t_VEC); u=cgetg(3,t_VEC);
          u[1]=(long)gneg(ypot); u[2]=(long)gzero; zz[1]=(long)u;
          if (_thue_new(u)) SOL=concatsp(SOL,zz);
        }
      }
    else
      {
      bsupy=(int)(x>0?bndyx*x:-bndyx*x);
      
      xx=stoi(x); xxn=gpui(xx,gdeg,Prec);
      interm=gsub((GEN)rhs,gmul(xxn,(GEN)poly[2]));

      /* Verifier ... */
      xxnm1=xxn; j=2;
      while(gcmp0(interm))
        {
          xxnm1=gdiv(xxnm1,xx);
          interm=gmul((GEN)poly[++j],xxnm1);
        }

      for(y=-bsupy; y<=bsupy; y++)
        {
          yy=stoi(y);
          if(y==0) {
            if (gegal(gmul((GEN)poly[2],xxn),rhs))
            {
              zz=cgetg(2,t_VEC); u=cgetg(3,t_VEC);
              u[1]=(long)gzero; u[2]=(long)xx; zz[1]=(long)u;
              if (_thue_new(u)) SOL=concatsp(SOL,zz);
            }     
          }
           else if (gcmp0(gmod(interm,yy)))
             if(gegal(poleval(poly,gdiv(yy,xx)),gdiv(rhs,xxn)))
            /* Remplacer par un eval *homogene* */
             {
               zz=cgetg(2,t_VEC); u=cgetg(3,t_VEC);
               u[1]=(long)yy; u[2]=(long)xx; zz[1]=(long)u;
               if (_thue_new(u)) SOL=concatsp(SOL,zz);
            }
        }
      }
  }
}

/* Computes [x]! */
static double
fact(double x)
{
  double ft=1.0;
  x=(int)x; while (x>1) { ft*=x; x--; }
  return ft ;
}

/* From a polynomial and optionally a system of fundamental units for the
 * field defined by poly, computes all the relevant constants needed to solve
 * the equation P(x,y)=a whenever the solutions of N_{ K/Q }(x)=a.  Returns a
 * "tnf" structure containing
 *  1) the polynomial
 *  2) the bnf (used to solve the norm equation)
 *  3) roots, with presumably enough precision
 *  4) The logarithmic heights of units
 *  5) The matrix of conjugates of units
 *  6) its inverse
 *  7) a few technical constants
 */
GEN
thueinit(GEN poly, long flag, long prec)
{
  GEN thueres,ALH,csts,c0;
  long av,tetpil,k,st;
  double d,dr;

  av=avma;

  uftot=0;
  if (checktnf(poly)) { uftot=(GEN)poly[2]; poly=(GEN)poly[1]; }
  else
    if (typ(poly)!=t_POL) err(notpoler,"thueinit");
  if (degree(poly)<=2) err(talker,"invalid polynomial in thue (need deg>2)");

  if (!gisirreducible(poly)) err(redpoler,"thueinit");
  st=sturm(poly);
  if (st)
  {
    dr=(double)((st+lgef(poly)-5)>>1);
    d=(double)lgef(poly)-3; d=d*(d-1)*(d-2);
    /* Try to guess the precision by approximating Baker's bound.
     * Note that the guess is most of the time pretty generous,
     * ie 10 to 30 decimal digits above what is *really* necessary.
     * Note that the limiting step is the reduction. See paper.
     */
    Prec=3 + (long)((5.83 + (dr+4)*5 + log(fact(dr+3)) + (dr+3)*log(dr+2) +
                 (dr+3)*log(d) + log(log(2*d*(dr+2))) + (dr+1)) / 10.);
    ConstPrec=4;
    if (Prec<prec) Prec = prec;
    if (!checktnf(poly)) inithue(poly,flag);

    thueres=cgetg(8,t_VEC);
    thueres[1]=(long)poly;
    thueres[2]=(long)uftot;
    thueres[3]=(long)roo;
    Compute_Fund_Units(gmael(uftot,8,5));
    ALH=cgetg(r+1,t_COL);
    for (k=1; k<=r; k++) ALH[k]=(long)Logarithmic_Height(k);
    thueres[4]=(long)ALH;
    thueres[5]=(long)MatFU;
    T_A_Matrices();
    thueres[6]=(long)A;

    csts=cgetg(7,t_VEC);
    csts[1]=(long)c1; csts[2]=(long)c2; csts[3]=(long)halpha;
    csts[4]=(long)x0; csts[5]=(long)eps3;
    csts[6]=(long)stoi(Prec);

    thueres[7]=(long)csts; tetpil=avma;
    return gerepile(av,tetpil,gcopy(thueres));
  }

  thueres=cgetg(3,t_VEC); c0=gun; Prec=4;
  roo=roots(poly,Prec);
  for (k=1; k<lg(roo); k++)
    c0=gmul(c0, gimag((GEN)roo[k]));
  c0=ginv(gabs(c0,Prec));
  thueres[1]=(long)poly; thueres[2]=(long)c0;
  tetpil=avma; return gerepile(av,tetpil,gcopy(thueres));
}

/* Given a tnf structure as returned by thueinit, and a right-hand-side and
 * optionally the solutions to the norm equation, returns the solutions to
 * the Thue equation F(x,y)=a
 */
GEN
thue(GEN thueres, GEN rhs, GEN ne)
{
  GEN Kstart,Old_B0,ALH,errdelta,Hmu,c0,poly,csts,bd;
  GEN xmay1,xmay2,b,zp1,tmp,q1,q2,q3,ep;
  long Nb_It=0,upb,bi1,av,tetpil,i1,i2,i, flag,cf,fs;

  if (!checktnf(thueres)) err(talker,"not a tnf in thue");

  av=avma; SOL=cgetg(1,t_VEC);
  upb = 0; ep = NULL; /* gcc -Wall */

  if (lg(thueres)==8)
  {
    poly=(GEN)thueres[1]; deg=lgef(poly)-3; gdeg=stoi(deg);
    uftot=(GEN)thueres[2];
    roo=gcopy((GEN)thueres[3]);
    ALH=(GEN)thueres[4];
    MatFU=gcopy((GEN)thueres[5]);
    A=gcopy((GEN)thueres[6]);
    csts=(GEN)thueres[7];

    if (!ne) ne = bnfisintnorm(uftot, rhs);
    if (lg(ne)==1) { avma=av; return cgetg(1,t_VEC); }

    c1=gmul(gabs(rhs,Prec), (GEN)csts[1]); c2=(GEN)csts[2];
    halpha=(GEN)csts[3];
    if (t)
      x0 = gmul((GEN)csts[4],gpui(gabs(rhs,Prec), ginv(gdeg), Prec));
    eps3=(GEN)csts[5];
    Prec=gtolong((GEN)csts[6]);
    b=cgetg(r+1,t_COL);
    tmp=divrr(c1,c2);
    x1=gmax(x0,gpui(mulsr(2,tmp),ginv(gdeg),ConstPrec));
    if(DEBUGLEVEL >=2) fprintferr("x1 -> %Z\n",x1);

    c3=mulrr(dbltor(1.39),tmp);
    c4=mulsr(deg-1,c3);

    for (numroot=1; numroot<=s; numroot++)
    {
      ComputeConstants();
      Conj_Norm_Eq(ne,&Hmu);
      for (curne=1; curne<lg(ne); curne++)
      {
      ComputeConstants2(poly,rhs);
      Baker(ALH,Hmu);
      
      i1=Vecmax(gabs(Delta,Prec),r);
      if (i1!=1) i2=1; else i2=2;
      do
        {
          fs=0;   
          Create_CF_Values(i1,i2,&errdelta);
          if (DEBUGLEVEL>=2) fprintferr("Entering CF\n");
          Old_B0=gmul(B0,gdeux);

          /* Try to reduce B0 while
           * 1) there was less than 10 reductions
           * 2) the previous reduction improved the bound of more than 0.1.
           */
          while (Nb_It<10 && gcmp(Old_B0,gadd(B0,dbltor(0.1))) == 1 && fs<2)
            {
            cf=0; Old_B0=B0; Nb_It++; Kstart=stoi(10);
            while (!fs && CF_First_Pass(Kstart,errdelta) == 0 && cf < 8 )
              {
                cf++;
                Kstart=mulis(Kstart,10);
              }   
            if ( CF_First_Pass(Kstart,errdelta) == -1 )
              { ne = gerepileupto(av, gcopy(ne)); Prec+=10;
              if(DEBUGLEVEL>=2) fprintferr("Increasing precision\n");
              thueres=thueinit(thueres,0,Prec);
              return(thue(thueres,rhs,ne)); }

            if (cf==8 || fs) /* Semirational or totally rational case */
              {
                if (!fs)
                  { ep=GuessQi(&q1,&q2,&q3); }
                bd=gmul(denom(bestappr(delta,gadd(B0,gabs(q2,Prec))))
                      ,delta);
                bd=gabs(gsub(bd,ground(bd)),Prec);
                if(gcmp(bd,ep)==1 && !gcmp0(q3))
                  {
                  fs=1;
                      B0=gdiv(glog(gdiv(gmul(q3,c15),gsub(bd,ep)), Prec),c13);
                  if (DEBUGLEVEL>=2)
                        fprintferr("Semirat. reduction ok. B0 -> %Z\n",B0);
                  }
                else fs=2;
              }
            else fs=0;
            Nb_It=0; B0=gmin(Old_B0,B0); upb=gtolong(gceil(B0));
            }
          i2++; if (i2==i1) i2++;
        }
      while (fs == 2 && i2 <= r);
      
      if (fs == 2) TotRat();

      if (DEBUGLEVEL >=2) fprintferr("x2 -> %Z\n",x2);

      /* For each possible value of b_i1, compute the b_i's
       * and 2 conjugates of x-\alpha y. Then check.
       */
      zp1=dbltor(0.01);
      x3=gmax(x2,gpui(mulsr(2,divrr(c14,zp1)),ginv(gdeg),ConstPrec));

      for (bi1=-upb; bi1<=upb; bi1++)
      {
        flag=1;
        xmay1=gun; xmay2=gun;
        for (i=1; i<=r; i++)
        {
          b[i]=(long)gdiv(gsub(gmul((GEN)Delta[i],stoi(bi1)),
                                gsub(gmul((GEN)Delta[i],(GEN)Lambda[i1]),
                               gmul((GEN)Delta[i1],(GEN)Lambda[i]))),
                       (GEN)Delta[i1]);
          if (gcmp(distoZ((GEN)b[i]),zp1)==1) { flag=0; break; }
        }
      
        if(flag)
          {
            for(i=1; i<=r; i++)
            {
              b[i]=lround((GEN)b[i]);
              xmay1=gmul(xmay1,gpui(gcoeff(MatFU,1,i),(GEN)b[i],Prec));
              xmay2=gmul(xmay2,gpui(gcoeff(MatFU,2,i),(GEN)b[i],Prec));
            }
            xmay1=gmul(xmay1,gcoeff(MatNE,1,curne));
            xmay2=gmul(xmay2,gcoeff(MatNE,2,curne));
            Check_Solutions(xmay1,xmay2,poly,rhs);
          }
      }
      }
    }
    if (DEBUGLEVEL>=2) fprintferr("Checking for small solutions\n");
    Check_Small((int)(gtodouble(x3)),poly,rhs);
    tetpil=avma; return gerepile(av,tetpil,gcopy(SOL));
  }

  /* Case s=0. All the solutions are "small". */
  Prec=DEFAULTPREC; poly=(GEN)thueres[1]; deg=lgef(poly)-3;
  gdeg=stoi(deg); c0=(GEN)thueres[2];
  roo=roots(poly,Prec);
  Check_Small(gtolong(ground(gpui(gmul((GEN)poly[2],gdiv(gabs(rhs,Prec),c0)),
                                  ginv(gdeg),Prec) )), poly, rhs);
  tetpil=avma; return gerepile(av,tetpil,gcopy(SOL));
}

static GEN *Relations; /* primes above a, expressed on generators of Cl(K) */
static GEN *Partial;   /* list of vvectors, Partial[i] = Relations[1..i] * u[1..i] */
static GEN *gen_ord;   /* orders of generators of Cl(K) given in bnf */

static long *f;        /* f[i] = f(Primes[i]/p), inertial degree */
static long *n;        /* a = prod p^{ n_p }. n[i]=n_p if Primes[i] divides p */
static long *inext;    /* index of first P above next p, 0 if p is last */
static long *S;        /* S[i] = n[i] - sum_{ 1<=k<=i } f[k].u[k] */
static long *u;        /* We want principal ideals I = prod Primes[i]^u[i] */
static long **normsol; /* lists of copies of the u[] which are solutions */

static long Nprimes; /* length(Relations) = #{max ideal above divisors of a} */
static long sindex, smax; /* current index in normsol; max. index */

/* u[1..i] has been filled. Norm(u) is correct.
 * Check relations in class group then save it.
 */
static void
test_sol(long i)
{
  long k,*sol;

  if (Partial)
  {
    long av=avma;
    for (k=1; k<lg(Partial[1]); k++)
      if ( signe(modii( (GEN)Partial[i][k], gen_ord[k] )) )
        { avma=av; return; }
    avma=av;
  }
  if (sindex == smax)
  {
    long new_smax = smax << 1;
    long **new_normsol = (long **) new_chunk(new_smax+1);

    for (k=1; k<=smax; k++) new_normsol[k] = normsol[k];
    normsol = new_normsol; smax = new_smax;
  }
  sol = cgetg(Nprimes+1,t_VECSMALL);
  normsol[++sindex] = sol;

  for (k=1; k<=i; k++) sol[k]=u[k];
  for (   ; k<=Nprimes; k++) sol[k]=0;
  if (DEBUGLEVEL > 2)
  {
    fprintferr("sol = %Z\n",sol);
    if (Partial) fprintferr("Partial = %Z\n",Partial);
    flusherr();
  }
}
static void
fix_Partial(long i)
{
  long k, av = avma;
  for (k=1; k<lg(Partial[1]); k++)
    addiiz(
      (GEN) Partial[i-1][k],
            mulis((GEN) Relations[i][k], u[i]),
      (GEN) Partial[i][k]
    );
  avma=av;
}

/* Recursive loop. Suppose u[1..i] has been filled
 * Find possible solutions u such that, Norm(prod Prime[i]^u[i]) = a, taking
 * into account:
 *  1) the relations in the class group if need be.
 *  2) the factorization of a.
 */
static void
isintnorm_loop(long i)
{
  if (S[i] == 0) /* sum u[i].f[i] = n[i], do another prime */
  {
    int k;
    if (inext[i] == 0) { test_sol(i); return; }

    /* there are some primes left */
    if (Partial) gaffect(Partial[i], Partial[inext[i]-1]);
    for (k=i+1; k < inext[i]; k++) u[k]=0;
    i=inext[i]-1;
  }
  else if (i == inext[i]-2 || i == Nprimes-1)
  {
    /* only one Prime left above prime; change prime, fix u[i+1] */
    if (S[i] % f[i+1]) return;
    i++; u[i] = S[i-1] / f[i];
    if (Partial) fix_Partial(i);
    if (inext[i]==0) { test_sol(i); return; }
  }

  i++; u[i]=0;
  if (Partial) gaffect(Partial[i-1], Partial[i]);
  if (i == inext[i-1])
  { /* change prime */
    if (inext[i] == i+1 || i == Nprimes) /* only one Prime above p */
    {
      S[i]=0; u[i] = n[i] / f[i]; /* we already know this is exact */
      if (Partial) fix_Partial(i);
    }
    else S[i] = n[i];
  }
  else S[i] = S[i-1]; /* same prime, different Prime */
  for(;;)
  {
    isintnorm_loop(i); S[i]-=f[i]; if (S[i]<0) break;
    if (Partial)
      gaddz(Partial[i], Relations[i], Partial[i]);
    u[i]++;
  }
}

static void
get_sol_abs(GEN bnf, GEN a, GEN **ptPrimes)
{
  GEN dec, fact, primes, *Primes, *Fact;
  long *gcdlist, gcd,nprimes,Ngen,i,j;

  if (gcmp1(a))
  {
    long *sol = new_chunk(Nprimes+1);
    sindex = 1; normsol = (long**) new_chunk(2);
    normsol[1] = sol; for (i=1; i<=Nprimes; i++) sol[i]=0;
    return;
  }

  fact=factor(a); primes=(GEN)fact[1];
  nprimes=lg(primes)-1; sindex = 0;
  gen_ord = (GEN *) mael3(bnf,8,1,2); Ngen = lg(gen_ord)-1;

  Fact = (GEN*) new_chunk(1+nprimes);
  gcdlist = new_chunk(1+nprimes);

  Nprimes=0;
  for (i=1; i<=nprimes; i++)
  {
    long ldec;

    dec = primedec(bnf,(GEN)primes[i]); ldec = lg(dec)-1;
    gcd = itos(gmael(dec,1,4));

    /* check that gcd_{P|p} f_P | n_p */
    for (j=2; gcd>1 && j<=ldec; j++)
      gcd = cgcd(gcd,itos(gmael(dec,j,4)));

    gcdlist[i]=gcd;

    if (gcd != 1 && smodis(gmael(fact,2,i),gcd))
    {
      if (DEBUGLEVEL>2)
        { fprintferr("gcd f_P  does not divide n_p\n"); flusherr(); }
      return;
    }
    Fact[i] = dec; Nprimes += ldec;
  }

  f = new_chunk(1+Nprimes); u = new_chunk(1+Nprimes);
  n = new_chunk(1+Nprimes); S = new_chunk(1+Nprimes);
  inext = new_chunk(1+Nprimes);
  Primes = (GEN*) new_chunk(1+Nprimes);
  *ptPrimes = Primes;

  if (Ngen)
  {
    Partial = (GEN*) new_chunk(1+Nprimes);
    Relations = (GEN*) new_chunk(1+Nprimes);
  }
  else /* trivial class group, no relations to check */
    Relations = Partial = NULL;

  j=0;
  for (i=1; i<=nprimes; i++)
  {
    long k,lim,v, vn=itos(gmael(fact,2,i));

    gcd = gcdlist[i];
    dec = Fact[i]; lim = lg(dec);
    v = (i==nprimes)? 0: j + lim;
    for (k=1; k < lim; k++)
    {
      j++; Primes[j] = (GEN)dec[k];
      f[j] = itos(gmael(dec,k,4)) / gcd;
      n[j] = vn / gcd; inext[j] = v;
      if (Partial)
      Relations[j] = isprincipal(bnf,Primes[j]);
    }
  }
  if (Partial)
  {
    for (i=1; i <= Nprimes; i++)
      if (!gcmp0(Relations[i])) break;
    if (i > Nprimes) Partial = NULL; /* all ideals dividing a are principal */
  }
  if (Partial)
    for (i=0; i<=Nprimes; i++) /* Partial[0] needs to be initialized */
    {
      Partial[i]=cgetg(Ngen+1,t_COL);
      for (j=1; j<=Ngen; j++)
      {
      Partial[i][j]=lgeti(4);
      gaffect(gzero,(GEN) Partial[i][j]);
      }
    }
  smax=511; normsol = (long**) new_chunk(smax+1);
  S[0]=n[1]; inext[0]=1; isintnorm_loop(0);
}

static long
get_unit_1(GEN bnf, GEN pol, GEN *unit)
{
  GEN fu;
  long j;

  if (DEBUGLEVEL > 2)
    fprintferr("looking for a fundamental unit of norm -1\n");

  *unit = gmael3(bnf,8,4,2);  /* torsion unit */
  if (signe( gnorm(gmodulcp(*unit,pol)) ) < 0) return 1;

  fu = gmael(bnf,8,5); /* fundamental units */
  for (j=1; j<lg(fu); j++)
  {
    *unit = (GEN)fu[j];
    if (signe( gnorm(gmodulcp(*unit,pol)) ) < 0) return 1;
  }
  return 0;
}

GEN
bnfisintnorm(GEN bnf, GEN a)
{
  GEN nf,pol,res,unit,x,id, *Primes;
  long av = avma, tetpil,sa,i,j,norm_1;

  bnf = checkbnf(bnf); nf = (GEN)bnf[7]; pol = (GEN)nf[1];
  if (typ(a)!=t_INT)
    err(talker,"expected an integer in bnfisintnorm");
  sa = signe(a);
  if (sa == 0)  { res=cgetg(2,t_VEC); res[1]=zero; return res; }
  if (gcmp1(a)) { res=cgetg(2,t_VEC); res[1]=un;   return res; }

  get_sol_abs(bnf, absi(a), &Primes);

  res = cgetg(1,t_VEC); unit = NULL;
  norm_1 = 0; /* gcc -Wall */
  for (i=1; i<=sindex; i++)
  {
    id = gun; x = normsol[i];
    for (j=1; j<=Nprimes; j++) /* compute prod Primes[i]^u[i] */
      if (x[j])
      {
      GEN id2 = Primes[j];
      if (x[j] != 1) id2 = idealpow(nf,id2, stoi(x[j]));
      id = idealmul(nf,id,id2);
      }
    x = (GEN) isprincipalgenforce(bnf,id)[2];
    x = gmul((GEN)nf[7],x); /* x possible solution */
    if (signe(gnorm(gmodulcp(x,(GEN)nf[1]))) != sa)
    {
      if (! unit) norm_1 = get_unit_1(bnf,pol,&unit);
      if (norm_1) x = gmul(unit,x);
      else
      {
        if (DEBUGLEVEL > 2)
          fprintferr("%Z eliminated because of sign\n",x);
        x = NULL;
      }
    }
    if (x) res = concatsp(res, gmod(x,pol));
  }
  tetpil=avma; return gerepile(av,tetpil,gcopy(res));
}

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