docs: public void update ( byte[] input, int offset, int len ) {
          if ( log.isTraceEnabled() ) {
              log.trace("update: " + this.updates + " " + offset + ":" + len);
              log.trace(Hexdump.toHexString(input, offset, Math.min(len, 256)));
          }
          if ( len == 0 ) {
              return; /* CRITICAL */
          }
          this.digest.update(input, offset, len);
          this.updates++;
      }