Average Error: 20.3 → 5.1
Time: 3.5s
Precision: 64
\[0.0 \lt x \lt 1 \land y \lt 1\]
\[\frac{\left(x - y\right) \cdot \left(x + y\right)}{x \cdot x + y \cdot y}\]
↓
\[\begin{array}{l} \mathbf{if}\;y \le -1.785532773814616831863731014933445423349 \cdot 10^{140}:\\ \;\;\;\;-1\\ \mathbf{elif}\;y \le -1.558923983411081976150022496277695268694 \cdot 10^{-162}:\\ \;\;\;\;\frac{1}{\frac{x \cdot x + y \cdot y}{\left(x - y\right) \cdot \left(x + y\right)}}\\ \mathbf{elif}\;y \le 3.047723682413627022763368644019132647617 \cdot 10^{-169}:\\ \;\;\;\;1\\ \mathbf{else}:\\ \;\;\;\;\frac{x - y}{\sqrt{x \cdot x + y \cdot y}} \cdot \frac{x + y}{\sqrt{x \cdot x + y \cdot y}}\\ \end{array}\]
\frac{\left(x - y\right) \cdot \left(x + y\right)}{x \cdot x + y \cdot y}
↓
\begin{array}{l}
\mathbf{if}\;y \le -1.785532773814616831863731014933445423349 \cdot 10^{140}:\\
\;\;\;\;-1\\

\mathbf{elif}\;y \le -1.558923983411081976150022496277695268694 \cdot 10^{-162}:\\
\;\;\;\;\frac{1}{\frac{x \cdot x + y \cdot y}{\left(x - y\right) \cdot \left(x + y\right)}}\\

\mathbf{elif}\;y \le 3.047723682413627022763368644019132647617 \cdot 10^{-169}:\\
\;\;\;\;1\\

\mathbf{else}:\\
\;\;\;\;\frac{x - y}{\sqrt{x \cdot x + y \cdot y}} \cdot \frac{x + y}{\sqrt{x \cdot x + y \cdot y}}\\

\end{array}
double f(double x, double y) {
        double r118773 = x;
        double r118774 = y;
        double r118775 = r118773 - r118774;
        double r118776 = r118773 + r118774;
        double r118777 = r118775 * r118776;
        double r118778 = r118773 * r118773;
        double r118779 = r118774 * r118774;
        double r118780 = r118778 + r118779;
        double r118781 = r118777 / r118780;
        return r118781;
}
↓
double f(double x, double y) {
        double r118782 = y;
        double r118783 = -1.7855327738146168e+140;
        bool r118784 = r118782 <= r118783;
        double r118785 = -1.0;
        double r118786 = -1.558923983411082e-162;
        bool r118787 = r118782 <= r118786;
        double r118788 = 1.0;
        double r118789 = x;
        double r118790 = r118789 * r118789;
        double r118791 = r118782 * r118782;
        double r118792 = r118790 + r118791;
        double r118793 = r118789 - r118782;
        double r118794 = r118789 + r118782;
        double r118795 = r118793 * r118794;
        double r118796 = r118792 / r118795;
        double r118797 = r118788 / r118796;
        double r118798 = 3.047723682413627e-169;
        bool r118799 = r118782 <= r118798;
        double r118800 = sqrt(r118792);
        double r118801 = r118793 / r118800;
        double r118802 = r118794 / r118800;
        double r118803 = r118801 * r118802;
        double r118804 = r118799 ? r118788 : r118803;
        double r118805 = r118787 ? r118797 : r118804;
        double r118806 = r118784 ? r118785 : r118805;
        return r118806;
}

Error

Bits error versus x

Bits error versus y

Try it out

Your Program's Arguments

Results

Enter valid numbers for all inputs

Target

Original20.3
Target0.0
Herbie5.1
\[\begin{array}{l} \mathbf{if}\;0.5 \lt \left|\frac{x}{y}\right| \lt 2:\\ \;\;\;\;\frac{\left(x - y\right) \cdot \left(x + y\right)}{x \cdot x + y \cdot y}\\ \mathbf{else}:\\ \;\;\;\;1 - \frac{2}{1 + \frac{x}{y} \cdot \frac{x}{y}}\\ \end{array}\]

Derivation

  1. Split input into 4 regimes

  2. if y < -1.7855327738146168e+140

    1. Initial program 58.1

      \[\frac{\left(x - y\right) \cdot \left(x + y\right)}{x \cdot x + y \cdot y}\]

    2. Taylor expanded around 0 0

      \[\leadsto \color{blue}{-1}\]

    if -1.7855327738146168e+140 < y < -1.558923983411082e-162

    1. Initial program 0.0

      \[\frac{\left(x - y\right) \cdot \left(x + y\right)}{x \cdot x + y \cdot y}\]
    2. Using strategy rm

    3. Applied clear-num0.0

      \[\leadsto \color{blue}{\frac{1}{\frac{x \cdot x + y \cdot y}{\left(x - y\right) \cdot \left(x + y\right)}}}\]

    if -1.558923983411082e-162 < y < 3.047723682413627e-169

    1. Initial program 30.6

      \[\frac{\left(x - y\right) \cdot \left(x + y\right)}{x \cdot x + y \cdot y}\]
    2. Using strategy rm

    3. Applied clear-num30.6

      \[\leadsto \color{blue}{\frac{1}{\frac{x \cdot x + y \cdot y}{\left(x - y\right) \cdot \left(x + y\right)}}}\]

    4. Taylor expanded around inf 15.9

      \[\leadsto \frac{1}{\color{blue}{1}}\]

    if 3.047723682413627e-169 < y

    1. Initial program 1.1

      \[\frac{\left(x - y\right) \cdot \left(x + y\right)}{x \cdot x + y \cdot y}\]
    2. Using strategy rm

    3. Applied add-sqr-sqrt1.1

      \[\leadsto \frac{\left(x - y\right) \cdot \left(x + y\right)}{\color{blue}{\sqrt{x \cdot x + y \cdot y} \cdot \sqrt{x \cdot x + y \cdot y}}}\]

    4. Applied times-frac1.6

      \[\leadsto \color{blue}{\frac{x - y}{\sqrt{x \cdot x + y \cdot y}} \cdot \frac{x + y}{\sqrt{x \cdot x + y \cdot y}}}\]
  3. Recombined 4 regimes into one program.

  4. Final simplification5.1

    \[\leadsto \begin{array}{l} \mathbf{if}\;y \le -1.785532773814616831863731014933445423349 \cdot 10^{140}:\\ \;\;\;\;-1\\ \mathbf{elif}\;y \le -1.558923983411081976150022496277695268694 \cdot 10^{-162}:\\ \;\;\;\;\frac{1}{\frac{x \cdot x + y \cdot y}{\left(x - y\right) \cdot \left(x + y\right)}}\\ \mathbf{elif}\;y \le 3.047723682413627022763368644019132647617 \cdot 10^{-169}:\\ \;\;\;\;1\\ \mathbf{else}:\\ \;\;\;\;\frac{x - y}{\sqrt{x \cdot x + y \cdot y}} \cdot \frac{x + y}{\sqrt{x \cdot x + y \cdot y}}\\ \end{array}\]

Reproduce

herbie shell --seed 2020001 
(FPCore (x y)
  :name "Kahan p9 Example"
  :precision binary64
  :pre (and (< 0.0 x 1) (< y 1))

  :herbie-target
  (if (< 0.5 (fabs (/ x y)) 2) (/ (* (- x y) (+ x y)) (+ (* x x) (* y y))) (- 1 (/ 2 (+ 1 (* (/ x y) (/ x y))))))

  (/ (* (- x y) (+ x y)) (+ (* x x) (* y y))))