\frac{x - \sin x}{x - \tan x}\begin{array}{l}
\mathbf{if}\;x \le \frac{-7798915418074769}{288230376151711744} \lor \neg \left(x \le \frac{8668492433622581}{288230376151711744}\right):\\
\;\;\;\;\frac{x}{x - \tan x} - \frac{\sin x}{x - \tan x}\\
\mathbf{else}:\\
\;\;\;\;\frac{9}{40} \cdot {x}^{2} - \left(\frac{27}{2800} \cdot {x}^{4} + \frac{1}{2}\right)\\
\end{array}double f(double x) {
double r21659 = x;
double r21660 = sin(r21659);
double r21661 = r21659 - r21660;
double r21662 = tan(r21659);
double r21663 = r21659 - r21662;
double r21664 = r21661 / r21663;
return r21664;
}
double f(double x) {
double r21665 = x;
double r21666 = -7798915418074769.0;
double r21667 = 2.8823037615171174e+17;
double r21668 = r21666 / r21667;
bool r21669 = r21665 <= r21668;
double r21670 = 8668492433622581.0;
double r21671 = r21670 / r21667;
bool r21672 = r21665 <= r21671;
double r21673 = !r21672;
bool r21674 = r21669 || r21673;
double r21675 = tan(r21665);
double r21676 = r21665 - r21675;
double r21677 = r21665 / r21676;
double r21678 = sin(r21665);
double r21679 = r21678 / r21676;
double r21680 = r21677 - r21679;
double r21681 = 9.0;
double r21682 = 40.0;
double r21683 = r21681 / r21682;
double r21684 = 2.0;
double r21685 = pow(r21665, r21684);
double r21686 = r21683 * r21685;
double r21687 = 27.0;
double r21688 = 2800.0;
double r21689 = r21687 / r21688;
double r21690 = 4.0;
double r21691 = pow(r21665, r21690);
double r21692 = r21689 * r21691;
double r21693 = 1.0;
double r21694 = r21693 / r21684;
double r21695 = r21692 + r21694;
double r21696 = r21686 - r21695;
double r21697 = r21674 ? r21680 : r21696;
return r21697;
}



Bits error versus x
Results
if x < -0.027057923325783554 or 0.03007487465186483 < x Initial program 0.1
rmApplied div-sub0.1
if -0.027057923325783554 < x < 0.03007487465186483Initial program 63.2
Taylor expanded around 0 0.0
Simplified0.0
Final simplification0.0
herbie shell --seed 2019303
(FPCore (x)
:name "sintan (problem 3.4.5)"
:precision binary64
(/ (- x (sin x)) (- x (tan x))))