\cos^{-1} \left({\left(\left(\cosh a\right) \bmod \left(a \cdot a\right)\right)}^{\left(\mathsf{log1p}\left(a\right)\right)}\right)\begin{array}{l}
\mathbf{if}\;a \le 1.542338768776221979718923094404481642848 \cdot 10^{-162}:\\
\;\;\;\;\cos^{-1} \left({\left(\left(\cosh a\right) \bmod \left(a \cdot a\right)\right)}^{\left(\log \left(e^{\mathsf{fma}\left(a, a \cdot \mathsf{fma}\left(a, \frac{1}{3}, \frac{-1}{2}\right), a\right)}\right)\right)}\right)\\
\mathbf{else}:\\
\;\;\;\;\cos^{-1} \left({\left(\log \left(e^{\left(\left(\cosh a\right) \bmod \left(a \cdot a\right)\right)}\right)\right)}^{\left(\mathsf{log1p}\left(a\right)\right)}\right)\\
\end{array}double f(double a) {
double r18040 = a;
double r18041 = cosh(r18040);
double r18042 = r18040 * r18040;
double r18043 = fmod(r18041, r18042);
double r18044 = log1p(r18040);
double r18045 = pow(r18043, r18044);
double r18046 = acos(r18045);
return r18046;
}
double f(double a) {
double r18047 = a;
double r18048 = 1.542338768776222e-162;
bool r18049 = r18047 <= r18048;
double r18050 = cosh(r18047);
double r18051 = r18047 * r18047;
double r18052 = fmod(r18050, r18051);
double r18053 = 0.3333333333333333;
double r18054 = -0.5;
double r18055 = fma(r18047, r18053, r18054);
double r18056 = r18047 * r18055;
double r18057 = fma(r18047, r18056, r18047);
double r18058 = exp(r18057);
double r18059 = log(r18058);
double r18060 = pow(r18052, r18059);
double r18061 = acos(r18060);
double r18062 = exp(r18052);
double r18063 = log(r18062);
double r18064 = log1p(r18047);
double r18065 = pow(r18063, r18064);
double r18066 = acos(r18065);
double r18067 = r18049 ? r18061 : r18066;
return r18067;
}



Bits error versus a
if a < 1.542338768776222e-162Initial program 64.0
rmApplied add-log-exp61.3
Taylor expanded around 0 61.3
Simplified61.3
if 1.542338768776222e-162 < a Initial program 58.8
rmApplied add-log-exp56.9
Final simplification59.0
herbie shell --seed 2019325 +o rules:numerics
(FPCore (a)
:name "Random Jason Timeout Test 012"
:precision binary64
(acos (pow (fmod (cosh a) (* a a)) (log1p a))))