/* Round 2 */
                a = GG (a, b, c, d, x[1], S21, 0xf61e2562L); /* 17 */
                d = GG (d, a, b, c, x[6], S22, 0xc040b340L); /* 18 */
                c = GG (c, d, a, b, x[11], S23, 0x265e5a51L); /* 19 */
                b = GG (b, c, d, a, x[0], S24, 0xe9b6c7aaL); /* 20 */
                a = GG (a, b, c, d, x[5], S21, 0xd62f105dL); /* 21 */
                d = GG (d, a, b, c, x[10], S22, 0x2441453L); /* 22 */
                c = GG (c, d, a, b, x[15], S23, 0xd8a1e681L); /* 23 */
                b = GG (b, c, d, a, x[4], S24, 0xe7d3fbc8L); /* 24 */
                a = GG (a, b, c, d, x[9], S21, 0x21e1cde6L); /* 25 */
                d = GG (d, a, b, c, x[14], S22, 0xc33707d6L); /* 26 */
                c = GG (c, d, a, b, x[3], S23, 0xf4d50d87L); /* 27 */
                b = GG (b, c, d, a, x[8], S24, 0x455a14edL); /* 28 */
                a = GG (a, b, c, d, x[13], S21, 0xa9e3e905L); /* 29 */
                d = GG (d, a, b, c, x[2], S22, 0xfcefa3f8L); /* 30 */
                c = GG (c, d, a, b, x[7], S23, 0x676f02d9L); /* 31 */
                b = GG (b, c, d, a, x[12], S24, 0x8d2a4c8aL); /* 32 */