Average Error: 29.4 → 3.4
Time: 2.6s
Precision: binary64
\[e^{a \cdot x} - 1\]
↓
\[\begin{array}{l} \mathbf{if}\;a \cdot x \leq -5.561162085756807 \cdot 10^{-05}:\\ \;\;\;\;\frac{{\left(e^{a \cdot x}\right)}^{3} - 1}{1 + e^{a \cdot x} \cdot \left(e^{a \cdot x} + 1\right)}\\ \mathbf{elif}\;a \cdot x \leq -1.1504508473033879 \cdot 10^{-117} \lor \neg \left(a \cdot x \leq 2.3306237093067895 \cdot 10^{-55}\right):\\ \;\;\;\;x \cdot \left(a + \log \left({\left(e^{x}\right)}^{\left(\left(a \cdot a\right) \cdot \left(0.5 + a \cdot \left(x \cdot 0.16666666666666666\right)\right)\right)}\right)\right)\\ \mathbf{else}:\\ \;\;\;\;x \cdot \left(a + x \cdot \left(\left(a \cdot a\right) \cdot \left(0.5 + a \cdot \left(x \cdot 0.16666666666666666\right)\right)\right)\right)\\ \end{array}\]
e^{a \cdot x} - 1
↓
\begin{array}{l}
\mathbf{if}\;a \cdot x \leq -5.561162085756807 \cdot 10^{-05}:\\
\;\;\;\;\frac{{\left(e^{a \cdot x}\right)}^{3} - 1}{1 + e^{a \cdot x} \cdot \left(e^{a \cdot x} + 1\right)}\\

\mathbf{elif}\;a \cdot x \leq -1.1504508473033879 \cdot 10^{-117} \lor \neg \left(a \cdot x \leq 2.3306237093067895 \cdot 10^{-55}\right):\\
\;\;\;\;x \cdot \left(a + \log \left({\left(e^{x}\right)}^{\left(\left(a \cdot a\right) \cdot \left(0.5 + a \cdot \left(x \cdot 0.16666666666666666\right)\right)\right)}\right)\right)\\

\mathbf{else}:\\
\;\;\;\;x \cdot \left(a + x \cdot \left(\left(a \cdot a\right) \cdot \left(0.5 + a \cdot \left(x \cdot 0.16666666666666666\right)\right)\right)\right)\\

\end{array}
(FPCore (a x) :precision binary64 (- (exp (* a x)) 1.0))
↓
(FPCore (a x)
 :precision binary64
 (if (<= (* a x) -5.561162085756807e-05)
   (/
    (- (pow (exp (* a x)) 3.0) 1.0)
    (+ 1.0 (* (exp (* a x)) (+ (exp (* a x)) 1.0))))
   (if (or (<= (* a x) -1.1504508473033879e-117)
           (not (<= (* a x) 2.3306237093067895e-55)))
     (*
      x
      (+
       a
       (log
        (pow (exp x) (* (* a a) (+ 0.5 (* a (* x 0.16666666666666666))))))))
     (* x (+ a (* x (* (* a a) (+ 0.5 (* a (* x 0.16666666666666666))))))))))
double code(double a, double x) {
	return ((double) (((double) exp(((double) (a * x)))) - 1.0));
}
↓
double code(double a, double x) {
	double tmp;
	if ((((double) (a * x)) <= -5.561162085756807e-05)) {
		tmp = (((double) (((double) pow(((double) exp(((double) (a * x)))), 3.0)) - 1.0)) / ((double) (1.0 + ((double) (((double) exp(((double) (a * x)))) * ((double) (((double) exp(((double) (a * x)))) + 1.0)))))));
	} else {
		double tmp_1;
		if (((((double) (a * x)) <= -1.1504508473033879e-117) || !(((double) (a * x)) <= 2.3306237093067895e-55))) {
			tmp_1 = ((double) (x * ((double) (a + ((double) log(((double) pow(((double) exp(x)), ((double) (((double) (a * a)) * ((double) (0.5 + ((double) (a * ((double) (x * 0.16666666666666666))))))))))))))));
		} else {
			tmp_1 = ((double) (x * ((double) (a + ((double) (x * ((double) (((double) (a * a)) * ((double) (0.5 + ((double) (a * ((double) (x * 0.16666666666666666))))))))))))));
		}
		tmp = tmp_1;
	}
	return tmp;
}

Error

Bits error versus a

Bits error versus x

Try it out

Your Program's Arguments

Results

Enter valid numbers for all inputs

Target

Original29.4
Target0.1
Herbie3.4
\[\begin{array}{l} \mathbf{if}\;\left|a \cdot x\right| < 0.1:\\ \;\;\;\;\left(a \cdot x\right) \cdot \left(1 + \left(\frac{a \cdot x}{2} + \frac{{\left(a \cdot x\right)}^{2}}{6}\right)\right)\\ \mathbf{else}:\\ \;\;\;\;e^{a \cdot x} - 1\\ \end{array}\]

Derivation

  1. Split input into 3 regimes

  2. if (*.f64 a x) < -5.5611620857568068e-5

    1. Initial program 0.1

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

    3. Applied flip3--_binary640.1

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

    4. Simplified0.1

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

    5. Simplified0.1

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

    if -5.5611620857568068e-5 < (*.f64 a x) < -1.1504508473033879e-117 or 2.33062370930678952e-55 < (*.f64 a x)

    1. Initial program 54.5

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

    2. Taylor expanded around 0 37.1

      \[\leadsto \color{blue}{0.5 \cdot \left({a}^{2} \cdot {x}^{2}\right) + \left(0.16666666666666666 \cdot \left({a}^{3} \cdot {x}^{3}\right) + a \cdot x\right)}\]

    3. Simplified20.5

      \[\leadsto \color{blue}{x \cdot \left(a + x \cdot \left(0.5 \cdot \left(a \cdot a\right) + x \cdot \left(0.16666666666666666 \cdot {a}^{3}\right)\right)\right)}\]
    4. Using strategy rm

    5. Applied add-log-exp_binary6426.2

      \[\leadsto x \cdot \left(a + \color{blue}{\log \left(e^{x \cdot \left(0.5 \cdot \left(a \cdot a\right) + x \cdot \left(0.16666666666666666 \cdot {a}^{3}\right)\right)}\right)}\right)\]

    6. Simplified15.9

      \[\leadsto x \cdot \left(a + \log \color{blue}{\left({\left(e^{x}\right)}^{\left(\left(a \cdot a\right) \cdot \left(0.5 + \left(x \cdot 0.16666666666666666\right) \cdot a\right)\right)}\right)}\right)\]

    if -1.1504508473033879e-117 < (*.f64 a x) < 2.33062370930678952e-55

    1. Initial program 41.2

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

    2. Taylor expanded around 0 7.3

      \[\leadsto \color{blue}{0.5 \cdot \left({a}^{2} \cdot {x}^{2}\right) + \left(0.16666666666666666 \cdot \left({a}^{3} \cdot {x}^{3}\right) + a \cdot x\right)}\]

    3. Simplified3.9

      \[\leadsto \color{blue}{x \cdot \left(a + x \cdot \left(0.5 \cdot \left(a \cdot a\right) + x \cdot \left(0.16666666666666666 \cdot {a}^{3}\right)\right)\right)}\]

    4. Taylor expanded around 0 5.2

      \[\leadsto x \cdot \left(a + \color{blue}{\left(0.16666666666666666 \cdot \left({a}^{3} \cdot {x}^{2}\right) + 0.5 \cdot \left({a}^{2} \cdot x\right)\right)}\right)\]

    5. Simplified1.4

      \[\leadsto x \cdot \left(a + \color{blue}{x \cdot \left(\left(a \cdot a\right) \cdot \left(0.5 + \left(x \cdot 0.16666666666666666\right) \cdot a\right)\right)}\right)\]
  3. Recombined 3 regimes into one program.

  4. Final simplification3.4

    \[\leadsto \begin{array}{l} \mathbf{if}\;a \cdot x \leq -5.561162085756807 \cdot 10^{-05}:\\ \;\;\;\;\frac{{\left(e^{a \cdot x}\right)}^{3} - 1}{1 + e^{a \cdot x} \cdot \left(e^{a \cdot x} + 1\right)}\\ \mathbf{elif}\;a \cdot x \leq -1.1504508473033879 \cdot 10^{-117} \lor \neg \left(a \cdot x \leq 2.3306237093067895 \cdot 10^{-55}\right):\\ \;\;\;\;x \cdot \left(a + \log \left({\left(e^{x}\right)}^{\left(\left(a \cdot a\right) \cdot \left(0.5 + a \cdot \left(x \cdot 0.16666666666666666\right)\right)\right)}\right)\right)\\ \mathbf{else}:\\ \;\;\;\;x \cdot \left(a + x \cdot \left(\left(a \cdot a\right) \cdot \left(0.5 + a \cdot \left(x \cdot 0.16666666666666666\right)\right)\right)\right)\\ \end{array}\]

Reproduce

herbie shell --seed 2020219 
(FPCore (a x)
  :name "expax (section 3.5)"
  :precision binary64
  :herbie-expected 14

  :herbie-target
  (if (< (fabs (* a x)) 0.1) (* (* a x) (+ 1.0 (+ (/ (* a x) 2.0) (/ (pow (* a x) 2.0) 6.0)))) (- (exp (* a x)) 1.0))

  (- (exp (* a x)) 1.0))