This is a header(.h) which contains a new-designed class "large_float".
"a" is molecule.
"b" is denominator.
And when sign==0, it's equal to or greater than 0.
And when sign==1, it's negative number.
+
-
*
/
>
<
<=
>=
!=
==
% (only when it is an int type)
is_int() check wheather it is an int type.