Hyperbolic arcsine

Average Accuracy: 18.0% → 99.5%

Time: 9.4s

Precision: binary64

Cost: 20040

Math

\[\log \left(x + \sqrt{x \cdot x + 1}\right) \]

↓

\[\begin{array}{l} \mathbf{if}\;x \leq -1.05:\\ \;\;\;\;-\log \left(x \cdot -2 - \frac{0.5}{x}\right)\\ \mathbf{elif}\;x \leq 1.3:\\ \;\;\;\;x + \mathsf{fma}\left(0.075, {x}^{5}, -0.16666666666666666 \cdot {x}^{3}\right)\\ \mathbf{else}:\\ \;\;\;\;-\log \left(\frac{0.5}{x}\right)\\ \end{array} \]

FPCore

(FPCore (x) :precision binary64 (log (+ x (sqrt (+ (* x x) 1.0)))))

↓

(FPCore (x)
 :precision binary64
 (if (<= x -1.05)
   (- (log (- (* x -2.0) (/ 0.5 x))))
   (if (<= x 1.3)
     (+ x (fma 0.075 (pow x 5.0) (* -0.16666666666666666 (pow x 3.0))))
     (- (log (/ 0.5 x))))))

C

double code(double x) {
	return log((x + sqrt(((x * x) + 1.0))));
}

↓

double code(double x) {
	double tmp;
	if (x <= -1.05) {
		tmp = -log(((x * -2.0) - (0.5 / x)));
	} else if (x <= 1.3) {
		tmp = x + fma(0.075, pow(x, 5.0), (-0.16666666666666666 * pow(x, 3.0)));
	} else {
		tmp = -log((0.5 / x));
	}
	return tmp;
}

Julia

function code(x)
	return log(Float64(x + sqrt(Float64(Float64(x * x) + 1.0))))
end

↓

function code(x)
	tmp = 0.0
	if (x <= -1.05)
		tmp = Float64(-log(Float64(Float64(x * -2.0) - Float64(0.5 / x))));
	elseif (x <= 1.3)
		tmp = Float64(x + fma(0.075, (x ^ 5.0), Float64(-0.16666666666666666 * (x ^ 3.0))));
	else
		tmp = Float64(-log(Float64(0.5 / x)));
	end
	return tmp
end

Wolfram

code[x_] := N[Log[N[(x + N[Sqrt[N[(N[(x * x), $MachinePrecision] + 1.0), $MachinePrecision]], $MachinePrecision]), $MachinePrecision]], $MachinePrecision]

↓

code[x_] := If[LessEqual[x, -1.05], (-N[Log[N[(N[(x * -2.0), $MachinePrecision] - N[(0.5 / x), $MachinePrecision]), $MachinePrecision]], $MachinePrecision]), If[LessEqual[x, 1.3], N[(x + N[(0.075 * N[Power[x, 5.0], $MachinePrecision] + N[(-0.16666666666666666 * N[Power[x, 3.0], $MachinePrecision]), $MachinePrecision]), $MachinePrecision]), $MachinePrecision], (-N[Log[N[(0.5 / x), $MachinePrecision]], $MachinePrecision])]]

Target

Original	18.0%
Target	30.0%
Herbie	99.5%

\[\begin{array}{l} \mathbf{if}\;x < 0:\\ \;\;\;\;\log \left(\frac{-1}{x - \sqrt{x \cdot x + 1}}\right)\\ \mathbf{else}:\\ \;\;\;\;\log \left(x + \sqrt{x \cdot x + 1}\right)\\ \end{array} \]

Derivation

1. Split input into 3 regimes

2. if x < -1.05000000000000004

   1. Initial program 2.4%

      \[\log \left(x + \sqrt{x \cdot x + 1}\right) \]

   2. Simplified 3.8%

      \[\leadsto \color{blue}{\log \left(x + \mathsf{hypot}\left(1, x\right)\right)} \]
      Step-by-step derivation

      [Start] 2.4	\[ \log \left(x + \sqrt{x \cdot x + 1}\right) \]
      +-commutative [=>] 2.4	\[ \log \left(x + \sqrt{\color{blue}{1 + x \cdot x}}\right) \]
      hypot-1-def [=>] 3.8	\[ \log \left(x + \color{blue}{\mathsf{hypot}\left(1, x\right)}\right) \]

   3. Applied egg-rr 2.2%

      \[\leadsto \log \color{blue}{\left(\frac{x \cdot x}{x - \mathsf{hypot}\left(1, x\right)} - \frac{1 + x \cdot x}{x - \mathsf{hypot}\left(1, x\right)}\right)} \]
      Step-by-step derivation

      [Start] 3.8	\[ \log \left(x + \mathsf{hypot}\left(1, x\right)\right) \]
      flip-+ [=>] 3.3	\[ \log \color{blue}{\left(\frac{x \cdot x - \mathsf{hypot}\left(1, x\right) \cdot \mathsf{hypot}\left(1, x\right)}{x - \mathsf{hypot}\left(1, x\right)}\right)} \]
      div-sub [=>] 2.2	\[ \log \color{blue}{\left(\frac{x \cdot x}{x - \mathsf{hypot}\left(1, x\right)} - \frac{\mathsf{hypot}\left(1, x\right) \cdot \mathsf{hypot}\left(1, x\right)}{x - \mathsf{hypot}\left(1, x\right)}\right)} \]
      hypot-udef [=>] 2.2	\[ \log \left(\frac{x \cdot x}{x - \mathsf{hypot}\left(1, x\right)} - \frac{\color{blue}{\sqrt{1 \cdot 1 + x \cdot x}} \cdot \mathsf{hypot}\left(1, x\right)}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      hypot-udef [=>] 2.2	\[ \log \left(\frac{x \cdot x}{x - \mathsf{hypot}\left(1, x\right)} - \frac{\sqrt{1 \cdot 1 + x \cdot x} \cdot \color{blue}{\sqrt{1 \cdot 1 + x \cdot x}}}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      add-sqr-sqrt [<=] 2.2	\[ \log \left(\frac{x \cdot x}{x - \mathsf{hypot}\left(1, x\right)} - \frac{\color{blue}{1 \cdot 1 + x \cdot x}}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      metadata-eval [=>] 2.2	\[ \log \left(\frac{x \cdot x}{x - \mathsf{hypot}\left(1, x\right)} - \frac{\color{blue}{1} + x \cdot x}{x - \mathsf{hypot}\left(1, x\right)}\right) \]

   4. Simplified 100.0%

      \[\leadsto \log \color{blue}{\left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right)} \]
      Step-by-step derivation

      [Start] 2.2	\[ \log \left(\frac{x \cdot x}{x - \mathsf{hypot}\left(1, x\right)} - \frac{1 + x \cdot x}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      div-sub [<=] 3.3	\[ \log \color{blue}{\left(\frac{x \cdot x - \left(1 + x \cdot x\right)}{x - \mathsf{hypot}\left(1, x\right)}\right)} \]
      +-commutative [=>] 3.3	\[ \log \left(\frac{x \cdot x - \color{blue}{\left(x \cdot x + 1\right)}}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      associate--r+ [=>] 46.2	\[ \log \left(\frac{\color{blue}{\left(x \cdot x - x \cdot x\right) - 1}}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      +-inverses [=>] 100.0	\[ \log \left(\frac{\color{blue}{0} - 1}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      metadata-eval [=>] 100.0	\[ \log \left(\frac{\color{blue}{-1}}{x - \mathsf{hypot}\left(1, x\right)}\right) \]

   5. Applied egg-rr 100.0%

      \[\leadsto \color{blue}{\log \left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right) + 0} \]
      Step-by-step derivation

      [Start] 100.0	\[ \log \left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      *-un-lft-identity [=>] 100.0	\[ \log \color{blue}{\left(1 \cdot \frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right)} \]
      *-commutative [=>] 100.0	\[ \log \color{blue}{\left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)} \cdot 1\right)} \]
      log-prod [=>] 100.0	\[ \color{blue}{\log \left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right) + \log 1} \]
      metadata-eval [=>] 100.0	\[ \log \left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right) + \color{blue}{0} \]

   6. Simplified 100.0%

      \[\leadsto \color{blue}{-\log \left(\mathsf{hypot}\left(1, x\right) - x\right)} \]
      Step-by-step derivation

      [Start] 100.0	\[ \log \left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right) + 0 \]
      +-rgt-identity [=>] 100.0	\[ \color{blue}{\log \left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right)} \]
      metadata-eval [<=] 100.0	\[ \log \left(\frac{\color{blue}{\frac{1}{-1}}}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      associate-/r* [<=] 100.0	\[ \log \color{blue}{\left(\frac{1}{-1 \cdot \left(x - \mathsf{hypot}\left(1, x\right)\right)}\right)} \]
      neg-mul-1 [<=] 100.0	\[ \log \left(\frac{1}{\color{blue}{-\left(x - \mathsf{hypot}\left(1, x\right)\right)}}\right) \]
      log-rec [=>] 100.0	\[ \color{blue}{-\log \left(-\left(x - \mathsf{hypot}\left(1, x\right)\right)\right)} \]
      neg-sub0 [=>] 100.0	\[ -\log \color{blue}{\left(0 - \left(x - \mathsf{hypot}\left(1, x\right)\right)\right)} \]
      sub-neg [=>] 100.0	\[ -\log \left(0 - \color{blue}{\left(x + \left(-\mathsf{hypot}\left(1, x\right)\right)\right)}\right) \]
      +-commutative [<=] 100.0	\[ -\log \left(0 - \color{blue}{\left(\left(-\mathsf{hypot}\left(1, x\right)\right) + x\right)}\right) \]
      associate--r+ [=>] 100.0	\[ -\log \color{blue}{\left(\left(0 - \left(-\mathsf{hypot}\left(1, x\right)\right)\right) - x\right)} \]
      neg-sub0 [<=] 100.0	\[ -\log \left(\color{blue}{\left(-\left(-\mathsf{hypot}\left(1, x\right)\right)\right)} - x\right) \]
      remove-double-neg [=>] 100.0	\[ -\log \left(\color{blue}{\mathsf{hypot}\left(1, x\right)} - x\right) \]

   7. Taylor expanded in x around -inf 100.0%

      \[\leadsto -\log \color{blue}{\left(-2 \cdot x - 0.5 \cdot \frac{1}{x}\right)} \]

   8. Simplified 100.0%

      \[\leadsto -\log \color{blue}{\left(x \cdot -2 - \frac{0.5}{x}\right)} \]
      Step-by-step derivation

      [Start] 100.0	\[ -\log \left(-2 \cdot x - 0.5 \cdot \frac{1}{x}\right) \]
      *-commutative [=>] 100.0	\[ -\log \left(\color{blue}{x \cdot -2} - 0.5 \cdot \frac{1}{x}\right) \]
      associate-*r/ [=>] 100.0	\[ -\log \left(x \cdot -2 - \color{blue}{\frac{0.5 \cdot 1}{x}}\right) \]
      metadata-eval [=>] 100.0	\[ -\log \left(x \cdot -2 - \frac{\color{blue}{0.5}}{x}\right) \]

   if -1.05000000000000004 < x < 1.30000000000000004

   1. Initial program 7.5%

      \[\log \left(x + \sqrt{x \cdot x + 1}\right) \]

   2. Simplified 7.5%

      \[\leadsto \color{blue}{\log \left(x + \mathsf{hypot}\left(1, x\right)\right)} \]
      Step-by-step derivation

      [Start] 7.5	\[ \log \left(x + \sqrt{x \cdot x + 1}\right) \]
      +-commutative [=>] 7.5	\[ \log \left(x + \sqrt{\color{blue}{1 + x \cdot x}}\right) \]
      hypot-1-def [=>] 7.5	\[ \log \left(x + \color{blue}{\mathsf{hypot}\left(1, x\right)}\right) \]

   3. Taylor expanded in x around 0 100.0%

      \[\leadsto \color{blue}{-0.16666666666666666 \cdot {x}^{3} + \left(0.075 \cdot {x}^{5} + x\right)} \]

   4. Applied egg-rr 100.0%

      \[\leadsto \color{blue}{\mathsf{fma}\left(\mathsf{fma}\left(0.075, {x}^{5}, -0.16666666666666666 \cdot {x}^{3}\right), 1, x\right)} \]
      Step-by-step derivation

      [Start] 100.0	\[ -0.16666666666666666 \cdot {x}^{3} + \left(0.075 \cdot {x}^{5} + x\right) \]
      *-un-lft-identity [=>] 100.0	\[ \color{blue}{1 \cdot \left(-0.16666666666666666 \cdot {x}^{3} + \left(0.075 \cdot {x}^{5} + x\right)\right)} \]
      associate-+r+ [=>] 100.0	\[ 1 \cdot \color{blue}{\left(\left(-0.16666666666666666 \cdot {x}^{3} + 0.075 \cdot {x}^{5}\right) + x\right)} \]
      distribute-rgt-in [=>] 100.0	\[ \color{blue}{\left(-0.16666666666666666 \cdot {x}^{3} + 0.075 \cdot {x}^{5}\right) \cdot 1 + x \cdot 1} \]
      *-commutative [<=] 100.0	\[ \left(-0.16666666666666666 \cdot {x}^{3} + 0.075 \cdot {x}^{5}\right) \cdot 1 + \color{blue}{1 \cdot x} \]
      *-un-lft-identity [<=] 100.0	\[ \left(-0.16666666666666666 \cdot {x}^{3} + 0.075 \cdot {x}^{5}\right) \cdot 1 + \color{blue}{x} \]
      fma-def [=>] 100.0	\[ \color{blue}{\mathsf{fma}\left(-0.16666666666666666 \cdot {x}^{3} + 0.075 \cdot {x}^{5}, 1, x\right)} \]
      +-commutative [=>] 100.0	\[ \mathsf{fma}\left(\color{blue}{0.075 \cdot {x}^{5} + -0.16666666666666666 \cdot {x}^{3}}, 1, x\right) \]
      fma-def [=>] 100.0	\[ \mathsf{fma}\left(\color{blue}{\mathsf{fma}\left(0.075, {x}^{5}, -0.16666666666666666 \cdot {x}^{3}\right)}, 1, x\right) \]

   5. Applied egg-rr 100.0%

      \[\leadsto \color{blue}{\mathsf{fma}\left(0.075, {x}^{5}, -0.16666666666666666 \cdot {x}^{3}\right) + x} \]
      Step-by-step derivation

      [Start] 100.0	\[ \mathsf{fma}\left(\mathsf{fma}\left(0.075, {x}^{5}, -0.16666666666666666 \cdot {x}^{3}\right), 1, x\right) \]
      fma-udef [=>] 100.0	\[ \color{blue}{\mathsf{fma}\left(0.075, {x}^{5}, -0.16666666666666666 \cdot {x}^{3}\right) \cdot 1 + x} \]
      *-rgt-identity [=>] 100.0	\[ \color{blue}{\mathsf{fma}\left(0.075, {x}^{5}, -0.16666666666666666 \cdot {x}^{3}\right)} + x \]

   if 1.30000000000000004 < x

   1. Initial program 50.8%

      \[\log \left(x + \sqrt{x \cdot x + 1}\right) \]

   2. Simplified 96.8%

      \[\leadsto \color{blue}{\log \left(x + \mathsf{hypot}\left(1, x\right)\right)} \]
      Step-by-step derivation

      [Start] 50.8	\[ \log \left(x + \sqrt{x \cdot x + 1}\right) \]
      +-commutative [=>] 50.8	\[ \log \left(x + \sqrt{\color{blue}{1 + x \cdot x}}\right) \]
      hypot-1-def [=>] 96.8	\[ \log \left(x + \color{blue}{\mathsf{hypot}\left(1, x\right)}\right) \]

   3. Applied egg-rr 3.1%

      \[\leadsto \log \color{blue}{\left(\frac{x \cdot x}{x - \mathsf{hypot}\left(1, x\right)} - \frac{1 + x \cdot x}{x - \mathsf{hypot}\left(1, x\right)}\right)} \]
      Step-by-step derivation

      [Start] 96.8	\[ \log \left(x + \mathsf{hypot}\left(1, x\right)\right) \]
      flip-+ [=>] 3.1	\[ \log \color{blue}{\left(\frac{x \cdot x - \mathsf{hypot}\left(1, x\right) \cdot \mathsf{hypot}\left(1, x\right)}{x - \mathsf{hypot}\left(1, x\right)}\right)} \]
      div-sub [=>] 3.1	\[ \log \color{blue}{\left(\frac{x \cdot x}{x - \mathsf{hypot}\left(1, x\right)} - \frac{\mathsf{hypot}\left(1, x\right) \cdot \mathsf{hypot}\left(1, x\right)}{x - \mathsf{hypot}\left(1, x\right)}\right)} \]
      hypot-udef [=>] 3.1	\[ \log \left(\frac{x \cdot x}{x - \mathsf{hypot}\left(1, x\right)} - \frac{\color{blue}{\sqrt{1 \cdot 1 + x \cdot x}} \cdot \mathsf{hypot}\left(1, x\right)}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      hypot-udef [=>] 3.1	\[ \log \left(\frac{x \cdot x}{x - \mathsf{hypot}\left(1, x\right)} - \frac{\sqrt{1 \cdot 1 + x \cdot x} \cdot \color{blue}{\sqrt{1 \cdot 1 + x \cdot x}}}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      add-sqr-sqrt [<=] 3.1	\[ \log \left(\frac{x \cdot x}{x - \mathsf{hypot}\left(1, x\right)} - \frac{\color{blue}{1 \cdot 1 + x \cdot x}}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      metadata-eval [=>] 3.1	\[ \log \left(\frac{x \cdot x}{x - \mathsf{hypot}\left(1, x\right)} - \frac{\color{blue}{1} + x \cdot x}{x - \mathsf{hypot}\left(1, x\right)}\right) \]

   4. Simplified 3.1%

      \[\leadsto \log \color{blue}{\left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right)} \]
      Step-by-step derivation

      [Start] 3.1	\[ \log \left(\frac{x \cdot x}{x - \mathsf{hypot}\left(1, x\right)} - \frac{1 + x \cdot x}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      div-sub [<=] 3.1	\[ \log \color{blue}{\left(\frac{x \cdot x - \left(1 + x \cdot x\right)}{x - \mathsf{hypot}\left(1, x\right)}\right)} \]
      +-commutative [=>] 3.1	\[ \log \left(\frac{x \cdot x - \color{blue}{\left(x \cdot x + 1\right)}}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      associate--r+ [=>] 3.1	\[ \log \left(\frac{\color{blue}{\left(x \cdot x - x \cdot x\right) - 1}}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      +-inverses [=>] 3.1	\[ \log \left(\frac{\color{blue}{0} - 1}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      metadata-eval [=>] 3.1	\[ \log \left(\frac{\color{blue}{-1}}{x - \mathsf{hypot}\left(1, x\right)}\right) \]

   5. Applied egg-rr 3.1%

      \[\leadsto \color{blue}{\log \left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right) + 0} \]
      Step-by-step derivation

      [Start] 3.1	\[ \log \left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      *-un-lft-identity [=>] 3.1	\[ \log \color{blue}{\left(1 \cdot \frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right)} \]
      *-commutative [=>] 3.1	\[ \log \color{blue}{\left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)} \cdot 1\right)} \]
      log-prod [=>] 3.1	\[ \color{blue}{\log \left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right) + \log 1} \]
      metadata-eval [=>] 3.1	\[ \log \left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right) + \color{blue}{0} \]

   6. Simplified 6.2%

      \[\leadsto \color{blue}{-\log \left(\mathsf{hypot}\left(1, x\right) - x\right)} \]
      Step-by-step derivation

      [Start] 3.1	\[ \log \left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right) + 0 \]
      +-rgt-identity [=>] 3.1	\[ \color{blue}{\log \left(\frac{-1}{x - \mathsf{hypot}\left(1, x\right)}\right)} \]
      metadata-eval [<=] 3.1	\[ \log \left(\frac{\color{blue}{\frac{1}{-1}}}{x - \mathsf{hypot}\left(1, x\right)}\right) \]
      associate-/r* [<=] 3.1	\[ \log \color{blue}{\left(\frac{1}{-1 \cdot \left(x - \mathsf{hypot}\left(1, x\right)\right)}\right)} \]
      neg-mul-1 [<=] 3.1	\[ \log \left(\frac{1}{\color{blue}{-\left(x - \mathsf{hypot}\left(1, x\right)\right)}}\right) \]
      log-rec [=>] 6.2	\[ \color{blue}{-\log \left(-\left(x - \mathsf{hypot}\left(1, x\right)\right)\right)} \]
      neg-sub0 [=>] 6.2	\[ -\log \color{blue}{\left(0 - \left(x - \mathsf{hypot}\left(1, x\right)\right)\right)} \]
      sub-neg [=>] 6.2	\[ -\log \left(0 - \color{blue}{\left(x + \left(-\mathsf{hypot}\left(1, x\right)\right)\right)}\right) \]
      +-commutative [<=] 6.2	\[ -\log \left(0 - \color{blue}{\left(\left(-\mathsf{hypot}\left(1, x\right)\right) + x\right)}\right) \]
      associate--r+ [=>] 6.2	\[ -\log \color{blue}{\left(\left(0 - \left(-\mathsf{hypot}\left(1, x\right)\right)\right) - x\right)} \]
      neg-sub0 [<=] 6.2	\[ -\log \left(\color{blue}{\left(-\left(-\mathsf{hypot}\left(1, x\right)\right)\right)} - x\right) \]
      remove-double-neg [=>] 6.2	\[ -\log \left(\color{blue}{\mathsf{hypot}\left(1, x\right)} - x\right) \]

   7. Taylor expanded in x around inf 97.8%

      \[\leadsto -\log \color{blue}{\left(\frac{0.5}{x}\right)} \]
3. Recombined 3 regimes into one program.

4. Final simplification 99.5%

   \[\leadsto \begin{array}{l} \mathbf{if}\;x \leq -1.05:\\ \;\;\;\;-\log \left(x \cdot -2 - \frac{0.5}{x}\right)\\ \mathbf{elif}\;x \leq 1.3:\\ \;\;\;\;x + \mathsf{fma}\left(0.075, {x}^{5}, -0.16666666666666666 \cdot {x}^{3}\right)\\ \mathbf{else}:\\ \;\;\;\;-\log \left(\frac{0.5}{x}\right)\\ \end{array} \]

Alternatives

Alternative 1
Accuracy	99.5%
Cost	13768

\[\begin{array}{l} \mathbf{if}\;x \leq -1.05:\\ \;\;\;\;-\log \left(x \cdot -2 - \frac{0.5}{x}\right)\\ \mathbf{elif}\;x \leq 1.3:\\ \;\;\;\;-0.16666666666666666 \cdot {x}^{3} + \left(x + 0.075 \cdot {x}^{5}\right)\\ \mathbf{else}:\\ \;\;\;\;-\log \left(\frac{0.5}{x}\right)\\ \end{array} \]

Alternative 2
Accuracy	99.4%
Cost	7048

\[\begin{array}{l} \mathbf{if}\;x \leq -1.25:\\ \;\;\;\;\log \left(\frac{-0.5}{x}\right)\\ \mathbf{elif}\;x \leq 1.25:\\ \;\;\;\;x + -0.16666666666666666 \cdot {x}^{3}\\ \mathbf{else}:\\ \;\;\;\;-\log \left(\frac{0.5}{x}\right)\\ \end{array} \]

Alternative 3
Accuracy	99.5%
Cost	7048

\[\begin{array}{l} \mathbf{if}\;x \leq -0.96:\\ \;\;\;\;-\log \left(x \cdot -2 - \frac{0.5}{x}\right)\\ \mathbf{elif}\;x \leq 1.25:\\ \;\;\;\;x + -0.16666666666666666 \cdot {x}^{3}\\ \mathbf{else}:\\ \;\;\;\;-\log \left(\frac{0.5}{x}\right)\\ \end{array} \]

Alternative 4
Accuracy	99.1%
Cost	6920

\[\begin{array}{l} \mathbf{if}\;x \leq -1.25:\\ \;\;\;\;\log \left(\frac{-0.5}{x}\right)\\ \mathbf{elif}\;x \leq 1.25:\\ \;\;\;\;x\\ \mathbf{else}:\\ \;\;\;\;-\log \left(\frac{0.5}{x}\right)\\ \end{array} \]

Alternative 5
Accuracy	99.1%
Cost	6856

\[\begin{array}{l} \mathbf{if}\;x \leq -1.25:\\ \;\;\;\;\log \left(\frac{-0.5}{x}\right)\\ \mathbf{elif}\;x \leq 1.25:\\ \;\;\;\;x\\ \mathbf{else}:\\ \;\;\;\;\log \left(x + x\right)\\ \end{array} \]

Alternative 6
Accuracy	75.7%
Cost	6724

\[\begin{array}{l} \mathbf{if}\;x \leq 1.25:\\ \;\;\;\;x\\ \mathbf{else}:\\ \;\;\;\;\log \left(x + x\right)\\ \end{array} \]

Alternative 7
Accuracy	56.5%
Cost	6464

\[\mathsf{log1p}\left(x\right) \]

Alternative 8
Accuracy	51.7%
Cost	64

\[x \]

Reproduce

herbie shell --seed 2023158 
(FPCore (x)
  :name "Hyperbolic arcsine"
  :precision binary64

  :herbie-target
  (if (< x 0.0) (log (/ -1.0 (- x (sqrt (+ (* x x) 1.0))))) (log (+ x (sqrt (+ (* x x) 1.0)))))

  (log (+ x (sqrt (+ (* x x) 1.0)))))