Average Error: 33.4 → 10.6
Time: 56.8s
Precision: 64
\[\frac{\left(-b\right) + \sqrt{b \cdot b - 4 \cdot \left(a \cdot c\right)}}{2 \cdot a}\]
\[\begin{array}{l} \mathbf{if}\;b \le -8.78453392716348 \cdot 10^{+64}:\\ \;\;\;\;\frac{c}{b} - \frac{b}{a}\\ \mathbf{elif}\;b \le 7.643168247577731 \cdot 10^{-56}:\\ \;\;\;\;\frac{1}{\frac{a}{\left(\sqrt{(\left(c \cdot -4\right) \cdot a + \left(b \cdot b\right))_*} - b\right) \cdot \frac{1}{2}}}\\ \mathbf{else}:\\ \;\;\;\;-\frac{c}{b}\\ \end{array}\]
double f(double a, double b, double c) {
        double r5418340 = b;
        double r5418341 = -r5418340;
        double r5418342 = r5418340 * r5418340;
        double r5418343 = 4.0;
        double r5418344 = a;
        double r5418345 = c;
        double r5418346 = r5418344 * r5418345;
        double r5418347 = r5418343 * r5418346;
        double r5418348 = r5418342 - r5418347;
        double r5418349 = sqrt(r5418348);
        double r5418350 = r5418341 + r5418349;
        double r5418351 = 2.0;
        double r5418352 = r5418351 * r5418344;
        double r5418353 = r5418350 / r5418352;
        return r5418353;
}

double f(double a, double b, double c) {
        double r5418354 = b;
        double r5418355 = -8.78453392716348e+64;
        bool r5418356 = r5418354 <= r5418355;
        double r5418357 = c;
        double r5418358 = r5418357 / r5418354;
        double r5418359 = a;
        double r5418360 = r5418354 / r5418359;
        double r5418361 = r5418358 - r5418360;
        double r5418362 = 7.643168247577731e-56;
        bool r5418363 = r5418354 <= r5418362;
        double r5418364 = 1.0;
        double r5418365 = -4.0;
        double r5418366 = r5418357 * r5418365;
        double r5418367 = r5418354 * r5418354;
        double r5418368 = fma(r5418366, r5418359, r5418367);
        double r5418369 = sqrt(r5418368);
        double r5418370 = r5418369 - r5418354;
        double r5418371 = 0.5;
        double r5418372 = r5418370 * r5418371;
        double r5418373 = r5418359 / r5418372;
        double r5418374 = r5418364 / r5418373;
        double r5418375 = -r5418358;
        double r5418376 = r5418363 ? r5418374 : r5418375;
        double r5418377 = r5418356 ? r5418361 : r5418376;
        return r5418377;
}

\frac{\left(-b\right) + \sqrt{b \cdot b - 4 \cdot \left(a \cdot c\right)}}{2 \cdot a}
\begin{array}{l}
\mathbf{if}\;b \le -8.78453392716348 \cdot 10^{+64}:\\
\;\;\;\;\frac{c}{b} - \frac{b}{a}\\

\mathbf{elif}\;b \le 7.643168247577731 \cdot 10^{-56}:\\
\;\;\;\;\frac{1}{\frac{a}{\left(\sqrt{(\left(c \cdot -4\right) \cdot a + \left(b \cdot b\right))_*} - b\right) \cdot \frac{1}{2}}}\\

\mathbf{else}:\\
\;\;\;\;-\frac{c}{b}\\

\end{array}

Error

Bits error versus a

Bits error versus b

Bits error versus c

Target

Original33.4
Target20.6
Herbie10.6
\[\begin{array}{l} \mathbf{if}\;b \lt 0:\\ \;\;\;\;\frac{\left(-b\right) + \sqrt{b \cdot b - 4 \cdot \left(a \cdot c\right)}}{2 \cdot a}\\ \mathbf{else}:\\ \;\;\;\;\frac{c}{a \cdot \frac{\left(-b\right) - \sqrt{b \cdot b - 4 \cdot \left(a \cdot c\right)}}{2 \cdot a}}\\ \end{array}\]

Derivation

  1. Split input into 3 regimes
  2. if b < -8.78453392716348e+64

    1. Initial program 37.7

      \[\frac{\left(-b\right) + \sqrt{b \cdot b - 4 \cdot \left(a \cdot c\right)}}{2 \cdot a}\]
    2. Simplified37.7

      \[\leadsto \color{blue}{\frac{\frac{\sqrt{(b \cdot b + \left(\left(a \cdot c\right) \cdot -4\right))_*} - b}{2}}{a}}\]
    3. Taylor expanded around -inf 5.2

      \[\leadsto \color{blue}{\frac{c}{b} - \frac{b}{a}}\]

    if -8.78453392716348e+64 < b < 7.643168247577731e-56

    1. Initial program 14.7

      \[\frac{\left(-b\right) + \sqrt{b \cdot b - 4 \cdot \left(a \cdot c\right)}}{2 \cdot a}\]
    2. Simplified14.6

      \[\leadsto \color{blue}{\frac{\frac{\sqrt{(b \cdot b + \left(\left(a \cdot c\right) \cdot -4\right))_*} - b}{2}}{a}}\]
    3. Using strategy rm
    4. Applied *-un-lft-identity14.6

      \[\leadsto \frac{\frac{\sqrt{(b \cdot b + \left(\left(a \cdot c\right) \cdot -4\right))_*} - b}{2}}{\color{blue}{1 \cdot a}}\]
    5. Applied div-inv14.6

      \[\leadsto \frac{\color{blue}{\left(\sqrt{(b \cdot b + \left(\left(a \cdot c\right) \cdot -4\right))_*} - b\right) \cdot \frac{1}{2}}}{1 \cdot a}\]
    6. Applied times-frac14.7

      \[\leadsto \color{blue}{\frac{\sqrt{(b \cdot b + \left(\left(a \cdot c\right) \cdot -4\right))_*} - b}{1} \cdot \frac{\frac{1}{2}}{a}}\]
    7. Simplified14.7

      \[\leadsto \color{blue}{\left(\sqrt{(\left(-4 \cdot c\right) \cdot a + \left(b \cdot b\right))_*} - b\right)} \cdot \frac{\frac{1}{2}}{a}\]
    8. Simplified14.7

      \[\leadsto \left(\sqrt{(\left(-4 \cdot c\right) \cdot a + \left(b \cdot b\right))_*} - b\right) \cdot \color{blue}{\frac{\frac{1}{2}}{a}}\]
    9. Using strategy rm
    10. Applied associate-*r/14.6

      \[\leadsto \color{blue}{\frac{\left(\sqrt{(\left(-4 \cdot c\right) \cdot a + \left(b \cdot b\right))_*} - b\right) \cdot \frac{1}{2}}{a}}\]
    11. Using strategy rm
    12. Applied clear-num14.7

      \[\leadsto \color{blue}{\frac{1}{\frac{a}{\left(\sqrt{(\left(-4 \cdot c\right) \cdot a + \left(b \cdot b\right))_*} - b\right) \cdot \frac{1}{2}}}}\]

    if 7.643168247577731e-56 < b

    1. Initial program 53.4

      \[\frac{\left(-b\right) + \sqrt{b \cdot b - 4 \cdot \left(a \cdot c\right)}}{2 \cdot a}\]
    2. Simplified53.4

      \[\leadsto \color{blue}{\frac{\frac{\sqrt{(b \cdot b + \left(\left(a \cdot c\right) \cdot -4\right))_*} - b}{2}}{a}}\]
    3. Taylor expanded around inf 8.5

      \[\leadsto \color{blue}{-1 \cdot \frac{c}{b}}\]
    4. Simplified8.5

      \[\leadsto \color{blue}{-\frac{c}{b}}\]
  3. Recombined 3 regimes into one program.
  4. Final simplification10.6

    \[\leadsto \begin{array}{l} \mathbf{if}\;b \le -8.78453392716348 \cdot 10^{+64}:\\ \;\;\;\;\frac{c}{b} - \frac{b}{a}\\ \mathbf{elif}\;b \le 7.643168247577731 \cdot 10^{-56}:\\ \;\;\;\;\frac{1}{\frac{a}{\left(\sqrt{(\left(c \cdot -4\right) \cdot a + \left(b \cdot b\right))_*} - b\right) \cdot \frac{1}{2}}}\\ \mathbf{else}:\\ \;\;\;\;-\frac{c}{b}\\ \end{array}\]

Reproduce

herbie shell --seed 2019101 +o rules:numerics
(FPCore (a b c)
  :name "quadp (p42, positive)"

  :herbie-target
  (if (< b 0) (/ (+ (- b) (sqrt (- (* b b) (* 4 (* a c))))) (* 2 a)) (/ c (* a (/ (- (- b) (sqrt (- (* b b) (* 4 (* a c))))) (* 2 a)))))

  (/ (+ (- b) (sqrt (- (* b b) (* 4 (* a c))))) (* 2 a)))