Function sub

FHE/Ring_Element.cpp:125–157

}

void sub(Ring_Element& ans,const Ring_Element& a,const Ring_Element& b)
{
  assert(a.FFTD);
  if (a.rep!=b.rep)   { throw rep_mismatch(); }
  if (a.FFTD!=b.FFTD) { throw pr_mismatch();  }
  if (a.element.empty())
    {
      ans = b;
      ans.negate();
      return;
    }
  else if (b.element.empty())
    {
      ans = a;
      return;
    }

  if (&ans == &a)
    {
      ans -= b;
      return;
    }
  else if (&ans == &b)
    {
      ans.negate();
      ans += a;
      return;
    }

  ans.prepare(a);
  for (int i=0; i<(*ans.FFTD).phi_m(); i++)
    ans.element.push_back(a.element[i].sub(b.element[i], a.FFTD->get_prD()));
}