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

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

   *
   * @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);
    }

      if (shouldHaveKnownHashes(method)) {
        HashFunction hashFunction = (HashFunction) method.invoke(Hashing.class);
        assertTrue(
            "There should be at least 3 entries in KNOWN_HASHES for " + hashFunction,
            KNOWN_HASHES.row(hashFunction).size() >= 3);
      }
    }
  }

  public void testKnownUtf8Hashing() {
    for (Cell<HashFunction, String, String> cell : KNOWN_HASHES.cellSet()) {

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

  static void assertHashByteBufferMatchesBytes(HashFunction hashFunction) {
    Random rng = new Random(0L);
    byte[] bytes = new byte[rng.nextInt(256) + 1];

      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.

 */
@Immutable
@ElementTypesAreNonnullByDefault
final class Murmur3_32HashFunction extends AbstractHashFunction implements Serializable {
  static final HashFunction MURMUR3_32 =
      new Murmur3_32HashFunction(0, /* supplementaryPlaneFix= */ false);
  static final HashFunction MURMUR3_32_FIXED =
      new Murmur3_32HashFunction(0, /* supplementaryPlaneFix= */ true);

  // 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))

   *
   * @throws IOException if an I/O error occurs while reading from this source
   */
  public HashCode hash(HashFunction hashFunction) throws IOException {
    Hasher hasher = hashFunction.newHasher();
    copyTo(Funnels.asOutputStream(hasher));
    return hasher.hash();
  }

  /**

      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.