docs: public String toFString(int digits) {
          if (b.compareTo(BigInteger.ONE) != 0) {
              MathContext mc = new MathContext(digits, RoundingMode.DOWN);
              BigDecimal f = (new BigDecimal(a)).divide(new BigDecimal(b), mc);
              return (f.toString());
          } else {
              return a.toString();
          }
      }