private static long load4(byte[] in, int idx) {
    long result = load3(in, idx);
    result |= (long) (in[idx + 3] & 0xff) << 24;
    return result;
  }
Returns 4 bytes of {@code in} starting from {@code idx} in Little-Endian format.
java_src/src/main/java/com/google/crypto/tink/internal/Ed25519.java