new RegularImmutableSet<>(EMPTY_ARRAY, 0, EMPTY_ARRAY, 0);

  private final transient Object[] elements;
  private final transient int hashCode;
  // the same values as `elements` in hashed positions (plus nulls)
  @VisibleForTesting final transient @Nullable Object[] table;
  // 'and' with an int to get a valid table index.
  private final transient int mask;

  @Override
  @CanIgnoreReturnValue
  public final Hasher putByte(byte b) {
    buffer.put(b);
    munchIfFull();
    return this;
  }

  @Override
  @CanIgnoreReturnValue
  public final Hasher putShort(short s) {
    buffer.putShort(s);
    munchIfFull();
    return this;
  }

  @Override
  @CanIgnoreReturnValue
  public final Hasher putChar(char c) {
    buffer.putChar(c);

/**
 * This is an implementation of the HMACT64 keyed hashing algorithm.
 * HMACT64 is defined by Luke Leighton as a modified HMAC-MD5 (RFC 2104)
 * in which the key is truncated at 64 bytes (rather than being hashed
 * via MD5).
 */
public class HMACT64 extends MessageDigest implements Cloneable {

    private static final int BLOCK_LENGTH = 64;

    private static final byte IPAD = (byte) 0x36;

/**
 * This is an implementation of the HMACT64 keyed hashing algorithm.
 * HMACT64 is defined by Luke Leighton as a modified HMAC-MD5 (RFC 2104)
 * in which the key is truncated at 64 bytes (rather than being hashed
 * via MD5).
 */
class HMACT64 extends MessageDigest implements Cloneable {

    private static final int BLOCK_LENGTH = 64;

    private static final byte IPAD = (byte) 0x36;

	}

	if sipHashElement := hashKey("SIPMOD", "This will fail", 0, testUUID); sipHashElement != -1 {
		t.Errorf("Test: Expected \"-1\" but got \"%v\"", sipHashElement)
	}

	if sipHashElement := hashKey("UNKNOWN", "This will fail", 0, testUUID); sipHashElement != -1 {
		t.Errorf("Test: Expected \"-1\" but got \"%v\"", sipHashElement)
	}
}

// TestCrcHashMod - test crc hash.
func TestCrcHashMod(t *testing.T) {

///

## Hash and verify the passwords { #hash-and-verify-the-passwords }

Import the tools we need from `pwdlib`.

Create a PasswordHash instance with recommended settings - it will be used for hashing and verifying passwords.

/// tip

pwdlib also supports the bcrypt hashing algorithm but does not include legacy algorithms - for working with outdated hashes, it is recommended to use the passlib library.

* The **output model** should not have a password.
* The **database model** would probably need to have a hashed password.

/// danger

Never store user's plaintext passwords. Always store a "secure hash" that you can then verify.

If you don't know, you will learn what a "password hash" is in the [security chapters](security/simple-oauth2.md#password-hashing){.internal-link target=_blank}.

///

 * </ul>
 *
 * <h3>Providing input to a hash function</h3>
 *
 * <p>The primary way to provide the data that your hash function should act on is via a {@link
 * Hasher}. Obtain a new hasher from the hash function using {@link #newHasher}, "push" the relevant
 * data into it using methods like {@link Hasher#putBytes(byte[])}, and finally ask for the {@code
 * HashCode} when finished using {@link Hasher#hash}. (See an {@linkplain #newHasher example} of

 * </ul>
 *
 * <h3>Providing input to a hash function</h3>
 *
 * <p>The primary way to provide the data that your hash function should act on is via a {@link
 * Hasher}. Obtain a new hasher from the hash function using {@link #newHasher}, "push" the relevant
 * data into it using methods like {@link Hasher#putBytes(byte[])}, and finally ask for the {@code
 * HashCode} when finished using {@link Hasher#hash}. (See an {@linkplain #newHasher example} of

        // This test uses a real MD5 instance to verify the HMAC calculation logic
        // HMACT64 is a modified HMAC-MD5 where the key is truncated at 64 bytes
        // instead of being hashed when it exceeds the block size.

        byte[] key = { (byte) 0x0b, (byte) 0x0b, (byte) 0x0b, (byte) 0x0b, (byte) 0x0b, (byte) 0x0b, (byte) 0x0b, (byte) 0x0b, (byte) 0x0b,