} while ((byte1 = bytes[index++]) >= 0);

      if (byte1 < (byte) 0xE0) {
        // Two-byte form.
        if (index == end) {
          return false;
        }
        // Simultaneously check for illegal trailing-byte in leading position
        // and overlong 2-byte form.
        if (byte1 < (byte) 0xC2 || bytes[index++] > (byte) 0xBF) {
          return false;
        }
      } else if (byte1 < (byte) 0xF0) {

  private static int decode(char ch) {
    if (ch >= '0' && ch <= '9') {
      return ch - '0';
    }
    if (ch >= 'a' && ch <= 'f') {
      return ch - 'a' + 10;
    }
    throw new IllegalArgumentException("Illegal hexadecimal character: " + ch);
  }

  /**
   * Returns {@code true} if {@code object} is a {@link HashCode} instance with the identical byte
   * representation to this hash code.
   *

 *
 * <pre>{@code
 * void exampleBadCaller() {
 *   double d = sqrt(-1.0);
 * }
 * }</pre>
 *
 * <p>would be flagged as having called {@code sqrt()} with an illegal argument.
 *
 * <h3>Performance</h3>
 *
 * <p>Avoid passing message arguments that are expensive to compute; your code will always compute

    assertEquals(written, counter.getCount());

    counter.write(data, 2, 5);
    written += 5;
    assertEquals(written, out.size());
    assertEquals(written, counter.getCount());

    // Test that illegal arguments do not affect count
    assertThrows(IndexOutOfBoundsException.class, () -> counter.write(data, 0, data.length + 1));
    assertEquals(written, out.size());
    assertEquals(written, counter.getCount());
  }

    assertEquals(written, counter.getCount());

    counter.write(data, 2, 5);
    written += 5;
    assertEquals(written, out.size());
    assertEquals(written, counter.getCount());

    // Test that illegal arguments do not affect count
    assertThrows(IndexOutOfBoundsException.class, () -> counter.write(data, 0, data.length + 1));
    assertEquals(written, out.size());
    assertEquals(written, counter.getCount());
  }

    strings = new String[SAMPLES];
    for (int i = 0; i < SAMPLES; i++) {
      StringBuilder sb = new StringBuilder();
      for (int j = 0; j < charCount; j++) {
        int codePoint;
        // discard illegal surrogate "codepoints"
        do {
          codePoint = rnd.nextInt(maxCodePoint.value);
        } while (Character.isSurrogate((char) codePoint));
        sb.appendCodePoint(codePoint);
      }

 * request expiration in milliseconds, microseconds, or nanoseconds.)
 *
 * <p>Whitespace before and after commas and equal signs is ignored. Keys may not be repeated; it is
 * also illegal to use the following pairs of keys in a single value:
 *
 * <ul>
 *   <li>{@code maximumSize} and {@code maximumWeight}
 *   <li>{@code softValues} and {@code weakValues}
 * </ul>
 *

    if (string.length() == 0) {
      throw new NumberFormatException("empty string");
    }
    if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX) {
      throw new NumberFormatException("illegal radix: " + radix);
    }

    int maxSafePos = ParseOverflowDetection.maxSafeDigits[radix] - 1;
    long value = 0;
    for (int pos = 0; pos < string.length(); pos++) {

    }
  }

  /**
   * This verifies that putUnencodedChars(String) and hashUnencodedChars(String) are equivalent,
   * even for funny strings composed by (possibly unmatched, and mostly illegal) surrogate
   * characters. (But doesn't test that they do the right thing - just their consistency).
   */
  private static void assertHashStringWithSurrogatesEquivalence(
      HashFunction hashFunction, Random random) {

   *
   * @throws IllegalStateException if multiple charset values have been set for this media type
   * @throws IllegalCharsetNameException if a charset value is present, but illegal
   * @throws UnsupportedCharsetException if a charset value is present, but no support is available
   *     in this instance of the Java virtual machine
   */
  public Optional<Charset> charset() {