Average Error: 4.6 → 0.9
Time: 12.0s
Precision: 64
\[\sqrt{\frac{e^{2 \cdot x} - 1}{e^{x} - 1}}\]
\[\begin{array}{l} \mathbf{if}\;x \le -1.31818012348102291 \cdot 10^{-5}:\\ \;\;\;\;\sqrt{\frac{e^{2 \cdot x} - 1}{e^{x + x} - 1 \cdot 1}} \cdot \sqrt{\mathsf{expm1}\left(\mathsf{log1p}\left(e^{x} + 1\right)\right)}\\ \mathbf{else}:\\ \;\;\;\;\sqrt{\mathsf{fma}\left(0.5, {x}^{2}, \mathsf{fma}\left(1, x, 2\right)\right)}\\ \end{array}\]
\sqrt{\frac{e^{2 \cdot x} - 1}{e^{x} - 1}}
\begin{array}{l}
\mathbf{if}\;x \le -1.31818012348102291 \cdot 10^{-5}:\\
\;\;\;\;\sqrt{\frac{e^{2 \cdot x} - 1}{e^{x + x} - 1 \cdot 1}} \cdot \sqrt{\mathsf{expm1}\left(\mathsf{log1p}\left(e^{x} + 1\right)\right)}\\

\mathbf{else}:\\
\;\;\;\;\sqrt{\mathsf{fma}\left(0.5, {x}^{2}, \mathsf{fma}\left(1, x, 2\right)\right)}\\

\end{array}
double f(double x) {
        double r14090 = 2.0;
        double r14091 = x;
        double r14092 = r14090 * r14091;
        double r14093 = exp(r14092);
        double r14094 = 1.0;
        double r14095 = r14093 - r14094;
        double r14096 = exp(r14091);
        double r14097 = r14096 - r14094;
        double r14098 = r14095 / r14097;
        double r14099 = sqrt(r14098);
        return r14099;
}

double f(double x) {
        double r14100 = x;
        double r14101 = -1.3181801234810229e-05;
        bool r14102 = r14100 <= r14101;
        double r14103 = 2.0;
        double r14104 = r14103 * r14100;
        double r14105 = exp(r14104);
        double r14106 = 1.0;
        double r14107 = r14105 - r14106;
        double r14108 = r14100 + r14100;
        double r14109 = exp(r14108);
        double r14110 = r14106 * r14106;
        double r14111 = r14109 - r14110;
        double r14112 = r14107 / r14111;
        double r14113 = sqrt(r14112);
        double r14114 = exp(r14100);
        double r14115 = r14114 + r14106;
        double r14116 = log1p(r14115);
        double r14117 = expm1(r14116);
        double r14118 = sqrt(r14117);
        double r14119 = r14113 * r14118;
        double r14120 = 0.5;
        double r14121 = 2.0;
        double r14122 = pow(r14100, r14121);
        double r14123 = fma(r14106, r14100, r14103);
        double r14124 = fma(r14120, r14122, r14123);
        double r14125 = sqrt(r14124);
        double r14126 = r14102 ? r14119 : r14125;
        return r14126;
}

Error

Bits error versus x

Derivation

  1. Split input into 2 regimes
  2. if x < -1.3181801234810229e-05

    1. Initial program 0.1

      \[\sqrt{\frac{e^{2 \cdot x} - 1}{e^{x} - 1}}\]
    2. Using strategy rm
    3. Applied flip--0.1

      \[\leadsto \sqrt{\frac{e^{2 \cdot x} - 1}{\color{blue}{\frac{e^{x} \cdot e^{x} - 1 \cdot 1}{e^{x} + 1}}}}\]
    4. Applied associate-/r/0.1

      \[\leadsto \sqrt{\color{blue}{\frac{e^{2 \cdot x} - 1}{e^{x} \cdot e^{x} - 1 \cdot 1} \cdot \left(e^{x} + 1\right)}}\]
    5. Applied sqrt-prod0.1

      \[\leadsto \color{blue}{\sqrt{\frac{e^{2 \cdot x} - 1}{e^{x} \cdot e^{x} - 1 \cdot 1}} \cdot \sqrt{e^{x} + 1}}\]
    6. Simplified0.0

      \[\leadsto \color{blue}{\sqrt{\frac{e^{2 \cdot x} - 1}{e^{x + x} - 1 \cdot 1}}} \cdot \sqrt{e^{x} + 1}\]
    7. Using strategy rm
    8. Applied expm1-log1p-u0.0

      \[\leadsto \sqrt{\frac{e^{2 \cdot x} - 1}{e^{x + x} - 1 \cdot 1}} \cdot \sqrt{\color{blue}{\mathsf{expm1}\left(\mathsf{log1p}\left(e^{x} + 1\right)\right)}}\]

    if -1.3181801234810229e-05 < x

    1. Initial program 34.5

      \[\sqrt{\frac{e^{2 \cdot x} - 1}{e^{x} - 1}}\]
    2. Taylor expanded around 0 6.7

      \[\leadsto \sqrt{\color{blue}{0.5 \cdot {x}^{2} + \left(1 \cdot x + 2\right)}}\]
    3. Simplified6.7

      \[\leadsto \sqrt{\color{blue}{\mathsf{fma}\left(0.5, {x}^{2}, \mathsf{fma}\left(1, x, 2\right)\right)}}\]
  3. Recombined 2 regimes into one program.
  4. Final simplification0.9

    \[\leadsto \begin{array}{l} \mathbf{if}\;x \le -1.31818012348102291 \cdot 10^{-5}:\\ \;\;\;\;\sqrt{\frac{e^{2 \cdot x} - 1}{e^{x + x} - 1 \cdot 1}} \cdot \sqrt{\mathsf{expm1}\left(\mathsf{log1p}\left(e^{x} + 1\right)\right)}\\ \mathbf{else}:\\ \;\;\;\;\sqrt{\mathsf{fma}\left(0.5, {x}^{2}, \mathsf{fma}\left(1, x, 2\right)\right)}\\ \end{array}\]

Reproduce

herbie shell --seed 2020047 +o rules:numerics
(FPCore (x)
  :name "sqrtexp (problem 3.4.4)"
  :precision binary64
  (sqrt (/ (- (exp (* 2 x)) 1) (- (exp x) 1))))