ec_field_element_select
void ec_field_element_select(const EC_FIELD_MODULUS *fm, EC_FIELD_ELEMENT *r,
ec_field_element_select(&group->fm, &r->fe_x, &a->fe_x, &b->fe_x, conditional);
ec_field_element_select(&group->fm, &r->fe_y, &a->fe_y, &b->fe_y, conditional);
ec_field_element_select(&group->fm, &r->fe_z, &a->fe_z, &b->fe_z, conditional);