wj - \frac{wj \cdot e^{wj} - x}{e^{wj} + wj \cdot e^{wj}}\begin{array}{l}
\mathbf{if}\;wj \le 2.7403440668061758 \cdot 10^{-12}:\\
\;\;\;\;\left(wj \cdot wj + \left(\left(wj \cdot wj\right) \cdot \left(wj \cdot wj\right) - \left(wj \cdot wj\right) \cdot wj\right)\right) + \frac{x}{e^{wj} \cdot wj + e^{wj}}\\
\mathbf{else}:\\
\;\;\;\;\frac{\left(wj \cdot wj\right) \cdot wj - \left(\frac{wj}{1 + wj} \cdot \frac{wj}{1 + wj}\right) \cdot \frac{wj}{1 + wj}}{wj \cdot wj + \frac{wj}{1 + wj} \cdot \left(\frac{wj}{1 + wj} + wj\right)} + \frac{x}{e^{wj} \cdot wj + e^{wj}}\\
\end{array}double f(double wj, double x) {
double r8863416 = wj;
double r8863417 = exp(r8863416);
double r8863418 = r8863416 * r8863417;
double r8863419 = x;
double r8863420 = r8863418 - r8863419;
double r8863421 = r8863417 + r8863418;
double r8863422 = r8863420 / r8863421;
double r8863423 = r8863416 - r8863422;
return r8863423;
}
double f(double wj, double x) {
double r8863424 = wj;
double r8863425 = 2.7403440668061758e-12;
bool r8863426 = r8863424 <= r8863425;
double r8863427 = r8863424 * r8863424;
double r8863428 = r8863427 * r8863427;
double r8863429 = r8863427 * r8863424;
double r8863430 = r8863428 - r8863429;
double r8863431 = r8863427 + r8863430;
double r8863432 = x;
double r8863433 = exp(r8863424);
double r8863434 = r8863433 * r8863424;
double r8863435 = r8863434 + r8863433;
double r8863436 = r8863432 / r8863435;
double r8863437 = r8863431 + r8863436;
double r8863438 = 1.0;
double r8863439 = r8863438 + r8863424;
double r8863440 = r8863424 / r8863439;
double r8863441 = r8863440 * r8863440;
double r8863442 = r8863441 * r8863440;
double r8863443 = r8863429 - r8863442;
double r8863444 = r8863440 + r8863424;
double r8863445 = r8863440 * r8863444;
double r8863446 = r8863427 + r8863445;
double r8863447 = r8863443 / r8863446;
double r8863448 = r8863447 + r8863436;
double r8863449 = r8863426 ? r8863437 : r8863448;
return r8863449;
}




Bits error versus wj




Bits error versus x
Results
| Original | 13.5 |
|---|---|
| Target | 12.8 |
| Herbie | 0.4 |
if wj < 2.7403440668061758e-12Initial program 13.1
rmApplied div-sub13.1
Applied associate--r-6.9
Taylor expanded around 0 0.2
Simplified0.2
if 2.7403440668061758e-12 < wj Initial program 23.9
rmApplied div-sub23.9
Applied associate--r-23.9
rmApplied flip3--23.9
Simplified23.8
Simplified5.5
Final simplification0.4
herbie shell --seed 2019163
(FPCore (wj x)
:name "Jmat.Real.lambertw, newton loop step"
:herbie-target
(- wj (- (/ wj (+ wj 1)) (/ x (+ (exp wj) (* wj (exp wj))))))
(- wj (/ (- (* wj (exp wj)) x) (+ (exp wj) (* wj (exp wj))))))