docs: public static BigInteger unsignedLongToBigInteger(int signum, long val)
      {
          byte[] magnitude = {
              (byte) ((val >> 56) & 0xFF),
              (byte) ((val >> 48) & 0xFF),
              (byte) ((val >> 40) & 0xFF),
              (byte) ((val >> 32) & 0xFF),
              (byte) ((val >> 24) & 0xFF),
              (byte) ((val >> 16) & 0xFF),
              (byte) ((val >>  8) & 0xFF),
              (byte) (val & 0xFF),
          };
          return new BigInteger(signum, magnitude);
      }