ecc_mod_pow_2k (const struct ecc_modulo *m,
		mp_limb_t *rp, const mp_limb_t *xp,
		unsigned k, mp_limb_t *tp)
{
  ecc_mod_sqr (m, rp, xp, tp);
  while (--k > 0)
    ecc_mod_sqr (m, rp, rp, tp);
}
ecc_mod_pow_2k (const struct ecc_modulo *m,
		mp_limb_t *rp, const mp_limb_t *xp,
		unsigned k, mp_limb_t *tp)
{
  ecc_mod_sqr (m, rp, xp, tp);
  while (--k > 0)
    ecc_mod_sqr (m, rp, rp, tp);
}