*
 * @author Kevin Bourrillion
 * @since 11.0
 */
@Immutable
public interface HashFunction {
  /**
   * Begins a new hash code computation by returning an initialized, stateful {@code Hasher}
   * instance that is ready to receive data. Example:
   *
   * {@snippet :
   * HashFunction hf = Hashing.md5();
   * HashCode hc = hf.newHasher()
   *     .putLong(id)
   *     .putBoolean(isActive)

 *
 * @author Kevin Bourrillion
 * @since 11.0
 */
@Immutable
public interface HashFunction {
  /**
   * Begins a new hash code computation by returning an initialized, stateful {@code Hasher}
   * instance that is ready to receive data. Example:
   *
   * {@snippet :
   * HashFunction hf = Hashing.md5();
   * HashCode hc = hf.newHasher()
   *     .putLong(id)
   *     .putBoolean(isActive)

  }

  @Benchmark
  int hasher(int reps) {
    HashFunction hashFunction = hashFunctionEnum.getHashFunction();
    int result = 37;
    for (int i = 0; i < reps; i++) {
      result ^= hashFunction.newHasher().putBytes(testBytes).hash().asBytes()[0];
    }
    return result;
  }

  @Benchmark
  int hashFunction(int reps) {
    HashFunction hashFunction = hashFunctionEnum.getHashFunction();
    int result = 37;

    assertHashByteBufferMatchesBytes(hashFunction);
    assertHashByteBufferExhaustsBuffer(hashFunction);
    assertHashByteBufferPreservesByteOrder(hashFunction);
    assertHasherByteBufferPreservesByteOrder(hashFunction);
  }

  static void assertHashByteBufferMatchesBytes(HashFunction hashFunction) {
    Random rng = new Random(0L);

   *
   * @since 19.0
   */
  public static HashFunction concatenating(Iterable<HashFunction> hashFunctions) {
    checkNotNull(hashFunctions);
    // We can't use Iterables.toArray() here because there's no hash->collect dependency
    List<HashFunction> list = new ArrayList<>();
    for (HashFunction hashFunction : hashFunctions) {
      list.add(hashFunction);
    }

    SHA_256("SHA-256", Hashing.sha256()),
    SHA_384("SHA-384", Hashing.sha384()),
    SHA_512("SHA-512", Hashing.sha512());

    private final String algorithmName;
    private final HashFunction hashFn;

    Algorithm(String algorithmName, HashFunction hashFn) {
      this.algorithmName = algorithmName;
      this.hashFn = hashFn;
    }

    MessageDigest getMessageDigest() {
      try {

    SHA_256("SHA-256", Hashing.sha256()),
    SHA_384("SHA-384", Hashing.sha384()),
    SHA_512("SHA-512", Hashing.sha512());

    private final String algorithmName;
    private final HashFunction hashFn;

    Algorithm(String algorithmName, HashFunction hashFn) {
      this.algorithmName = algorithmName;
      this.hashFn = hashFn;
    }

    MessageDigest getMessageDigest() {
      try {

  // From http://docs.oracle.com/javase/7/docs/technotes/guides/security/StandardNames.html#Mac
  private static final ImmutableTable<String, SecretKey, HashFunction> ALGORITHMS =
      new ImmutableTable.Builder<String, SecretKey, HashFunction>()
          .put("HmacMD5", MD5_KEY, Hashing.hmacMd5(MD5_KEY))
          .put("HmacSHA1", SHA1_KEY, Hashing.hmacSha1(SHA1_KEY))

    assertHashByteBufferMatchesBytes(hashFunction);
    assertHashByteBufferExhaustsBuffer(hashFunction);
    assertHashByteBufferPreservesByteOrder(hashFunction);
    assertHasherByteBufferPreservesByteOrder(hashFunction);
  }

  static void assertHashByteBufferMatchesBytes(HashFunction hashFunction) {
    Random rng = new Random(0L);

      imports = "com.google.common.io.Files")
  public
  static HashCode hash(File file, HashFunction hashFunction) throws IOException {
    return asByteSource(file).hash(hashFunction);
  }

  /**
   * Fully maps a file read-only in to memory as per {@link
   * FileChannel#map(java.nio.channels.FileChannel.MapMode, long, long)}.
   *
   * <p>Files are mapped from offset 0 to its length.