bn_mulw_addw
bn_mulw_addw(a, b, c, &r1, &r0);
bn_mulw_addw(a, b, c0, &x1, &r0);
bn_mulw_addw(a0, b, c, &c, &r0);
bn_mulw_addw(a1, b, c, &c, &r1);
bn_mulw_addw(a2, b, c, &c, &r2);
bn_mulw_addw(a3, b, c, &c, &r3);
bn_mulw_addw(a[0], w, carry, &carry, &r[0]);