mpn-base256
void mpn_set_base256 (mp_limb_t *rp, mp_size_t rn, const uint8_t *xp, size_t xn);
mp_limb_t *rp
mp_size_t rn
const uint8_t *xp
size_t xn
void mpn_get_base256 (uint8_t *rp, size_t rn, const mp_limb_t *xp, mp_size_t xn);
uint8_t *rp
size_t rn
const mp_limb_t *xp
mp_size_t xn