\lambda_1 + \tan^{-1}_* \frac{\cos \phi_2 \cdot \sin \left(\lambda_1 - \lambda_2\right)}{\cos \phi_1 + \cos \phi_2 \cdot \cos \left(\lambda_1 - \lambda_2\right)}\lambda_1 + \tan^{-1}_* \frac{\left(\cos \phi_2 \cdot \sin \lambda_1\right) \cdot \cos \lambda_2 + \cos \phi_2 \cdot \left(\cos \lambda_1 \cdot \sin \left(-\lambda_2\right)\right)}{\cos \phi_1 + \left(\sqrt[3]{{\left(\cos \lambda_1 \cdot \left(\cos \phi_2 \cdot \cos \lambda_2\right)\right)}^{3}} + \cos \phi_2 \cdot \left(\sin \lambda_1 \cdot \sin \lambda_2\right)\right)}double f(double lambda1, double lambda2, double phi1, double phi2) {
double r36911 = lambda1;
double r36912 = phi2;
double r36913 = cos(r36912);
double r36914 = lambda2;
double r36915 = r36911 - r36914;
double r36916 = sin(r36915);
double r36917 = r36913 * r36916;
double r36918 = phi1;
double r36919 = cos(r36918);
double r36920 = cos(r36915);
double r36921 = r36913 * r36920;
double r36922 = r36919 + r36921;
double r36923 = atan2(r36917, r36922);
double r36924 = r36911 + r36923;
return r36924;
}
double f(double lambda1, double lambda2, double phi1, double phi2) {
double r36925 = lambda1;
double r36926 = phi2;
double r36927 = cos(r36926);
double r36928 = sin(r36925);
double r36929 = r36927 * r36928;
double r36930 = lambda2;
double r36931 = cos(r36930);
double r36932 = r36929 * r36931;
double r36933 = cos(r36925);
double r36934 = -r36930;
double r36935 = sin(r36934);
double r36936 = r36933 * r36935;
double r36937 = r36927 * r36936;
double r36938 = r36932 + r36937;
double r36939 = phi1;
double r36940 = cos(r36939);
double r36941 = r36927 * r36931;
double r36942 = r36933 * r36941;
double r36943 = 3.0;
double r36944 = pow(r36942, r36943);
double r36945 = cbrt(r36944);
double r36946 = sin(r36930);
double r36947 = r36928 * r36946;
double r36948 = r36927 * r36947;
double r36949 = r36945 + r36948;
double r36950 = r36940 + r36949;
double r36951 = atan2(r36938, r36950);
double r36952 = r36925 + r36951;
return r36952;
}



Bits error versus lambda1



Bits error versus lambda2



Bits error versus phi1



Bits error versus phi2
Results
Initial program 0.9
rmApplied sub-neg0.9
Applied sin-sum0.9
Applied distribute-lft-in0.9
Simplified0.9
rmApplied cos-diff0.2
Applied distribute-lft-in0.2
rmApplied add-cbrt-cube0.2
Applied add-cbrt-cube0.2
Applied cbrt-unprod0.2
Applied add-cbrt-cube0.3
Applied cbrt-unprod0.3
Simplified0.3
Final simplification0.3
herbie shell --seed 2019294
(FPCore (lambda1 lambda2 phi1 phi2)
:name "Midpoint on a great circle"
:precision binary64
(+ lambda1 (atan2 (* (cos phi2) (sin (- lambda1 lambda2))) (+ (cos phi1) (* (cos phi2) (cos (- lambda1 lambda2)))))))