return longBitsToDouble(significand | ONE_BITS);
  }

  static double bigToDouble(BigInteger x) {
    // This is an extremely fast implementation of BigInteger.doubleValue(). JDK patch pending.
    BigInteger absX = x.abs();
    int exponent = absX.bitLength() - 1;
    // exponent == floor(log2(abs(x)))
    if (exponent < Long.SIZE - 1) {
      return x.longValue();

    private BigDecimalToDoubleRounder() {}

    @Override
    double roundToDoubleArbitrarily(BigDecimal bigDecimal) {
      return bigDecimal.doubleValue();
    }

    @Override
    int sign(BigDecimal bigDecimal) {
      return bigDecimal.signum();
    }

    @Override
    BigDecimal toX(double d, RoundingMode mode) {
      return new BigDecimal(d);

        new EntryTransformer<Number, Number, Double>() {
          @Override
          public Double transformEntry(Number key, Number value) {
            return key.doubleValue() + value.doubleValue();
          }
        };

    Map<Object, Double> objectKeyed;
    Map<Number, Double> numberKeyed;
    Map<Integer, Double> integerKeyed;

  }

  private static class NumberOrdering extends Ordering<Number> {
    @Override
    public int compare(Number a, Number b) {
      return ((Double) a.doubleValue()).compareTo(b.doubleValue());
    }

    @Override
    public int hashCode() {
      return NumberOrdering.class.hashCode();
    }

    @Override
    public boolean equals(@Nullable Object other) {

  }

  private static class NumberOrdering extends Ordering<Number> {
    @Override
    public int compare(Number a, Number b) {
      return ((Double) a.doubleValue()).compareTo(b.doubleValue());
    }

    @Override
    public int hashCode() {
      return NumberOrdering.class.hashCode();
    }

    @Override
    public boolean equals(@Nullable Object other) {

                }
            } else if (doubleFieldSet.contains(key)) {
                if (value instanceof final Number num) {
                    value = num.doubleValue();
                } else {
                    value = DfTypeUtil.toDouble(value.toString());
                }
            }
            return new Pair<>(key, value);