Average Error: 20.2 → 0.0
Time: 1.3m
Precision: 64
Internal Precision: 128
\[\frac{\left(x - y\right) \cdot \left(x + y\right)}{x \cdot x + y \cdot y}\]
\[\frac{y + x}{\sqrt{y^2 + x^2}^*} \cdot \frac{x - y}{\sqrt{x^2 + y^2}^*}\]

Error

Bits error versus x

Bits error versus y

Target

Original20.2
Target0.0
Herbie0.0
\[\begin{array}{l} \mathbf{if}\;0.5 \lt \left|\frac{x}{y}\right| \lt 2:\\ \;\;\;\;\frac{\left(x - y\right) \cdot \left(x + y\right)}{x \cdot x + y \cdot y}\\ \mathbf{else}:\\ \;\;\;\;1 - \frac{2}{1 + \frac{x}{y} \cdot \frac{x}{y}}\\ \end{array}\]

Derivation

  1. Initial program 20.2

    \[\frac{\left(x - y\right) \cdot \left(x + y\right)}{x \cdot x + y \cdot y}\]
  2. Simplified20.2

    \[\leadsto \color{blue}{\frac{\left(x - y\right) \cdot \left(y + x\right)}{(x \cdot x + \left(y \cdot y\right))_*}}\]
  3. Using strategy rm
  4. Applied clear-num20.2

    \[\leadsto \color{blue}{\frac{1}{\frac{(x \cdot x + \left(y \cdot y\right))_*}{\left(x - y\right) \cdot \left(y + x\right)}}}\]
  5. Using strategy rm
  6. Applied add-sqr-sqrt20.2

    \[\leadsto \frac{1}{\frac{\color{blue}{\sqrt{(x \cdot x + \left(y \cdot y\right))_*} \cdot \sqrt{(x \cdot x + \left(y \cdot y\right))_*}}}{\left(x - y\right) \cdot \left(y + x\right)}}\]
  7. Applied times-frac20.2

    \[\leadsto \frac{1}{\color{blue}{\frac{\sqrt{(x \cdot x + \left(y \cdot y\right))_*}}{x - y} \cdot \frac{\sqrt{(x \cdot x + \left(y \cdot y\right))_*}}{y + x}}}\]
  8. Applied add-cube-cbrt20.2

    \[\leadsto \frac{\color{blue}{\left(\sqrt[3]{1} \cdot \sqrt[3]{1}\right) \cdot \sqrt[3]{1}}}{\frac{\sqrt{(x \cdot x + \left(y \cdot y\right))_*}}{x - y} \cdot \frac{\sqrt{(x \cdot x + \left(y \cdot y\right))_*}}{y + x}}\]
  9. Applied times-frac20.2

    \[\leadsto \color{blue}{\frac{\sqrt[3]{1} \cdot \sqrt[3]{1}}{\frac{\sqrt{(x \cdot x + \left(y \cdot y\right))_*}}{x - y}} \cdot \frac{\sqrt[3]{1}}{\frac{\sqrt{(x \cdot x + \left(y \cdot y\right))_*}}{y + x}}}\]
  10. Simplified20.2

    \[\leadsto \color{blue}{\frac{x - y}{\sqrt{x^2 + y^2}^*}} \cdot \frac{\sqrt[3]{1}}{\frac{\sqrt{(x \cdot x + \left(y \cdot y\right))_*}}{y + x}}\]
  11. Simplified0.0

    \[\leadsto \frac{x - y}{\sqrt{x^2 + y^2}^*} \cdot \color{blue}{\frac{y + x}{\sqrt{y^2 + x^2}^*}}\]
  12. Final simplification0.0

    \[\leadsto \frac{y + x}{\sqrt{y^2 + x^2}^*} \cdot \frac{x - y}{\sqrt{x^2 + y^2}^*}\]

Reproduce

herbie shell --seed 2019091 +o rules:numerics
(FPCore (x y)
  :name "Kahan p9 Example"
  :pre (and (< 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))))