int main()
{
  DUPFF f, g, cf, cg, h;
  f = DUPFFnew(1); f->coeffs[1] = 1; f->deg = 1;
  g = DUPFFnew(2); g->coeffs[2] = 1; g->deg = 2;

  h = DUPFFexgcd(&cf, &cg, f, g);
  h = h;
  return 0;
}
DUPFF DUPFFexgcd(DUPFF *fcofac, DUPFF *gcofac, const DUPFF f, const DUPFF g)
{
  DUPFF u, v, uf, ug, vf, vg;
  FFelem q, lcu, lcvrecip, p;
  int df, dg, du, dv;

  if (DUPFFdeg(f) < DUPFFdeg(g)) return DUPFFexgcd(gcofac, fcofac, g, f);
  if (DUPFFdeg(f) != 2 || DUPFFdeg(g) != 1) abort();
  if (f->coeffs[0] == 0) return f;
  p = 2;

  df = DUPFFdeg(f);  if (df < 0) df = 0; /* both inputs are zero */
  dg = DUPFFdeg(g);  if (dg < 0) dg = 0; /* one input is zero */
  u = DUPFFcopy(f);
  v = DUPFFcopy(g);

  uf = DUPFFnew(dg); uf->coeffs[0] = 1; uf->deg = 0;
  ug = DUPFFnew(df);
  vf = DUPFFnew(dg);
  vg = DUPFFnew(df); vg->coeffs[0] = 1; vg->deg = 0;

  while (DUPFFdeg(v) > 0)
  {
    dv = DUPFFdeg(v);
    lcvrecip = FFmul(1, v->coeffs[dv]);
    while (DUPFFdeg(u) >= dv)
    {
      du = DUPFFdeg(u);
      lcu = u->coeffs[du];
      q = FFmul(lcu, lcvrecip);
      DUPFFshift_add(u, v, du-dv, p-q);
      DUPFFshift_add(uf, vf, du-dv, p-q);
      DUPFFshift_add(ug, vg, du-dv, p-q);
    }
    DUPFFswap(u, v);
    DUPFFswap(uf, vf);
    DUPFFswap(ug, vg);
  }
  if (DUPFFdeg(v) == 0)
  {
    DUPFFswap(u, v);
    DUPFFswap(uf, vf);
    DUPFFswap(ug, vg);
  }
  DUPFFfree(vf);
  DUPFFfree(vg);
  DUPFFfree(v);
  *fcofac = uf;
  *gcofac = ug;
  return u;
}
Beispiel #3
0
DUPFF DMPZ_to_DUPFF(DMPZ f, int var, int *substitution)
{
  FFelem p = CurrentFF.prime;
  int df, d, c, i;
  DUPFF ans;
  DMPZ iter;
  
  df = DMPZdeg(f, var);
  ans = DUPFFnew(df);
  for(i=0; i<=df;i++) ans->coeffs[i] = 0;
  for(iter=f;iter;iter = iter->next)
  {
    d = iter->exps[var];
    c = mpz_fdiv_ui(iter->coeff, p);
    for(i=0; c!=0 && i<NVARS;i++)
      if (i != var)
        c = FFmul(c, FFpow(substitution[i], iter->exps[i]));
    ans->coeffs[d] += c;
    if (ans->coeffs[d] >= p) ans->coeffs[d] -= p;
  }
  for(i=df;i>=0;i--) if (ans->coeffs[i] != 0) break;
  ans->deg = i;
  return ans;
}