Average Error: 29.5 → 0.4
Time: 16.9s
Precision: 64
\[e^{a \cdot x} - 1\]
↓
\[\begin{array}{l} \mathbf{if}\;a \cdot x \le -0.3967409376004402132842585615435382351279:\\ \;\;\;\;\frac{{\left(e^{a \cdot x}\right)}^{3} - {1}^{3}}{e^{2 \cdot \left(a \cdot x\right)} + 1 \cdot \left(e^{a \cdot x} + 1\right)}\\ \mathbf{else}:\\ \;\;\;\;x \cdot \left(a + \left(\left(x \cdot a\right) \cdot a\right) \cdot \left(\left(a \cdot x\right) \cdot \frac{1}{6} + \frac{1}{2}\right)\right)\\ \end{array}\]
e^{a \cdot x} - 1
↓
\begin{array}{l}
\mathbf{if}\;a \cdot x \le -0.3967409376004402132842585615435382351279:\\
\;\;\;\;\frac{{\left(e^{a \cdot x}\right)}^{3} - {1}^{3}}{e^{2 \cdot \left(a \cdot x\right)} + 1 \cdot \left(e^{a \cdot x} + 1\right)}\\

\mathbf{else}:\\
\;\;\;\;x \cdot \left(a + \left(\left(x \cdot a\right) \cdot a\right) \cdot \left(\left(a \cdot x\right) \cdot \frac{1}{6} + \frac{1}{2}\right)\right)\\

\end{array}
double f(double a, double x) {
        double r99533 = a;
        double r99534 = x;
        double r99535 = r99533 * r99534;
        double r99536 = exp(r99535);
        double r99537 = 1.0;
        double r99538 = r99536 - r99537;
        return r99538;
}
↓
double f(double a, double x) {
        double r99539 = a;
        double r99540 = x;
        double r99541 = r99539 * r99540;
        double r99542 = -0.3967409376004402;
        bool r99543 = r99541 <= r99542;
        double r99544 = exp(r99541);
        double r99545 = 3.0;
        double r99546 = pow(r99544, r99545);
        double r99547 = 1.0;
        double r99548 = pow(r99547, r99545);
        double r99549 = r99546 - r99548;
        double r99550 = 2.0;
        double r99551 = r99550 * r99541;
        double r99552 = exp(r99551);
        double r99553 = r99544 + r99547;
        double r99554 = r99547 * r99553;
        double r99555 = r99552 + r99554;
        double r99556 = r99549 / r99555;
        double r99557 = r99540 * r99539;
        double r99558 = r99557 * r99539;
        double r99559 = 0.16666666666666666;
        double r99560 = r99541 * r99559;
        double r99561 = 0.5;
        double r99562 = r99560 + r99561;
        double r99563 = r99558 * r99562;
        double r99564 = r99539 + r99563;
        double r99565 = r99540 * r99564;
        double r99566 = r99543 ? r99556 : r99565;
        return r99566;
}

Error

Bits error versus a

Bits error versus x

Try it out

Your Program's Arguments

Results

Enter valid numbers for all inputs

Target

Original29.5
Target0.2
Herbie0.4
\[\begin{array}{l} \mathbf{if}\;\left|a \cdot x\right| \lt 0.1000000000000000055511151231257827021182:\\ \;\;\;\;\left(a \cdot x\right) \cdot \left(1 + \left(\frac{a \cdot x}{2} + \frac{{\left(a \cdot x\right)}^{2}}{6}\right)\right)\\ \mathbf{else}:\\ \;\;\;\;e^{a \cdot x} - 1\\ \end{array}\]

Derivation

  1. Split input into 2 regimes

  2. if (* a x) < -0.3967409376004402

    1. Initial program 0.0

      \[e^{a \cdot x} - 1\]
    2. Using strategy rm

    3. Applied flip3--0.0

      \[\leadsto \color{blue}{\frac{{\left(e^{a \cdot x}\right)}^{3} - {1}^{3}}{e^{a \cdot x} \cdot e^{a \cdot x} + \left(1 \cdot 1 + e^{a \cdot x} \cdot 1\right)}}\]

    4. Simplified0.0

      \[\leadsto \frac{{\left(e^{a \cdot x}\right)}^{3} - {1}^{3}}{\color{blue}{e^{2 \cdot \left(a \cdot x\right)} + 1 \cdot \left(e^{a \cdot x} + 1\right)}}\]

    if -0.3967409376004402 < (* a x)

    1. Initial program 44.1

      \[e^{a \cdot x} - 1\]

    2. Taylor expanded around 0 14.4

      \[\leadsto \color{blue}{\frac{1}{2} \cdot \left({a}^{2} \cdot {x}^{2}\right) + \left(\frac{1}{6} \cdot \left({a}^{3} \cdot {x}^{3}\right) + a \cdot x\right)}\]

    3. Simplified4.7

      \[\leadsto \color{blue}{x \cdot \left(a + x \cdot \left({a}^{2} \cdot \left(\left(a \cdot x\right) \cdot \frac{1}{6} + \frac{1}{2}\right)\right)\right)}\]
    4. Using strategy rm

    5. Applied associate-*r*4.7

      \[\leadsto x \cdot \left(a + \color{blue}{\left(x \cdot {a}^{2}\right) \cdot \left(\left(a \cdot x\right) \cdot \frac{1}{6} + \frac{1}{2}\right)}\right)\]

    6. Simplified0.6

      \[\leadsto x \cdot \left(a + \color{blue}{\left(\left(x \cdot a\right) \cdot a\right)} \cdot \left(\left(a \cdot x\right) \cdot \frac{1}{6} + \frac{1}{2}\right)\right)\]
  3. Recombined 2 regimes into one program.

  4. Final simplification0.4

    \[\leadsto \begin{array}{l} \mathbf{if}\;a \cdot x \le -0.3967409376004402132842585615435382351279:\\ \;\;\;\;\frac{{\left(e^{a \cdot x}\right)}^{3} - {1}^{3}}{e^{2 \cdot \left(a \cdot x\right)} + 1 \cdot \left(e^{a \cdot x} + 1\right)}\\ \mathbf{else}:\\ \;\;\;\;x \cdot \left(a + \left(\left(x \cdot a\right) \cdot a\right) \cdot \left(\left(a \cdot x\right) \cdot \frac{1}{6} + \frac{1}{2}\right)\right)\\ \end{array}\]

Reproduce

herbie shell --seed 2019326 
(FPCore (a x)
  :name "expax (section 3.5)"
  :precision binary64
  :herbie-expected 14

  :herbie-target
  (if (< (fabs (* a x)) 0.1) (* (* a x) (+ 1 (+ (/ (* a x) 2) (/ (pow (* a x) 2) 6)))) (- (exp (* a x)) 1))

  (- (exp (* a x)) 1))