ecc_mod_sub (const struct ecc_modulo *m, mp_limb_t *rp,
	     const mp_limb_t *ap, const mp_limb_t *bp)
{
  mp_limb_t cy;
  cy = mpn_sub_n (rp, ap, bp, m->size);
  cy = mpn_cnd_sub_n (cy, rp, rp, m->B, m->size);
  cy = mpn_cnd_sub_n (cy, rp, rp, m->B, m->size);
  assert (cy == 0);  
}
ecc_mod_sub (const struct ecc_modulo *m, mp_limb_t *rp,
	     const mp_limb_t *ap, const mp_limb_t *bp)
{
  mp_limb_t cy;
  cy = mpn_sub_n (rp, ap, bp, m->size);
  cy = mpn_cnd_sub_n (cy, rp, rp, m->B, m->size);
  cy = mpn_cnd_sub_n (cy, rp, rp, m->B, m->size);
  assert (cy == 0);  
}