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.
   *

  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.
   *