lowerP()

TowerPolynomial DPoly::lowerP	(	int	level,
		const TowerPolynomial	f )

Definition at line 1421 of file dpoly.cpp.

{
  int i, j;
  TowerPolynomial result;
  if (f == nullptr) return nullptr;
  int charac_as_int = static_cast<int>(charac);
  int newdeg = f->deg / charac_as_int;  // should be exact...
  if (level == 0)
    {
      result = alloc_poly_0(newdeg);
      // In this situation, we just need to grab every p*i coeff...
      for (i = 0, j = 0; i <= newdeg; i++, j += charac_as_int)
        result->arr.ints[i] = f->arr.ints[j];
    }
  else
    {
      result = alloc_poly_n(newdeg);
      mpz_t order;
      mpz_init(order);
      unsigned long extdeg = 1;
      for (i = 0; i < level; i++) extdeg *= degree_of_extension(i);
      mpz_ui_pow_ui(order, charac_as_int, extdeg - 1);
      for (i = 0, j = 0; i <= newdeg; i++, j += charac_as_int)
        {
          // need p-th roots of the coefficients.  So we take p^(n-1)
          // power (if coefficients are in field of size p^n)
          TowerPolynomial a = f->arr.polys[j];
          TowerPolynomial b = power_mod(level - 1, a, order, extensions[level - 1]);
          result->arr.polys[i] = b;
        }
      mpz_clear(order);
    }
  return result;
}

References alloc_poly_0(), alloc_poly_n(), charac, degree_of_extension(), extensions, power_mod(), and result().