docs: public String fileNameString() {
          BigInteger bigSiteId = BigInteger.valueOf(getSiteId());
          BigInteger bigBlockCounter = BigInteger.valueOf(getBlockId());
          final BigInteger BIT_64 = BigInteger.ONE.shiftLeft(64);
  
          if(bigSiteId.signum() < 0) {
              bigSiteId = bigSiteId.add(BIT_64);
          }
          if(bigBlockCounter.signum() < 0) {
              bigBlockCounter = bigBlockCounter.add(BIT_64);
          }
          return bigSiteId.toString() + "___" + bigBlockCounter.toString() + ".block";
      }