code: private static int bitLength(final int bits) {
          int correct = bits;
          if (bits != SiHmac.HMAC256
              && bits != SiHmac.HMAC384
              && bits != SiHmac.HMAC512) {
              correct = SiHmac.HMAC256;
          }
          return correct;
      }
docs: Check for correct bit length.
  
  @param bits
  Given bit length
  @return Original bit length when appropriate, 256 bits otherwise.