MD5_SHIFT_12
FF(d, a, b, c, x_1, MD5_SHIFT_12, MD5_CONST_o(1)); /* 2 */
FF(d, a, b, c, x_5, MD5_SHIFT_12, MD5_CONST_o(5)); /* 6 */
FF(d, a, b, c, x_9, MD5_SHIFT_12, MD5_CONST_o(9)); /* 10 */
FF(d, a, b, c, x_13, MD5_SHIFT_12, MD5_CONST_o(13)); /* 14 */