LexiSortable.java

    public static String toLexiSortable(final double d) {
        long tmp = Double.doubleToRawLongBits(d);
        return toHexString('d', (tmp < 0) ? ~tmp : (tmp ^ SIGN_MASK));
    }

    public static double doubleFromLexiSortable(final String s) {
        if (!s.startsWith("d")) {
            throw new IllegalArgumentException(s
                    + " does not represent a double");
        }
        long tmp = fromHexString(s);
        tmp = (tmp < 0) ? (tmp ^ SIGN_MASK) : ~tmp;
        return Double.longBitsToDouble(tmp);
    }