Let say the target rate is:$$0.2312076819339227309219662514224185$$How to adjust this fraction $984398920/4257639330$ that gives this $\mbox{rate}\ ?$:$$0.23120768193392275902336706383252993860332457986759$$( matches the $16$th number after the floating point ) to match the $18$th number after the floating point ?.$$\mbox{The final fraction is:}\quad {939515904 \over 4063515088}$$Also the fraction parts should not exceed${\tt 0xffffffff} \left(4200000000\right)$.
The problem is I didn't know how to adjust it to know if I'm close to the exact rate ( $18$th number ) or not untill I get it, other says how will be the change ?.
