@Test
  public void testQuarterRound() {
    int[] x = TestUtil.twoCompInt(new long[] {0x11111111, 0x01020304, 0x9b8d6f43, 0x01234567});
    ChaCha20Util.quarterRound(x, 0, 1, 2, 3);
    assertThat(x)
        .isEqualTo(
            TestUtil.twoCompInt(new long[] {0xea2a92f4, 0xcb1cf8ce, 0x4581472e, 0x5881c4bb}));
  }
https://tools.ietf.org/html/rfc7539#section-2.1.1
java_src/src/test/java/com/google/crypto/tink/aead/internal/ChaCha20UtilTest.java