Average Error: 33.3 → 13.8
Time: 17.6s
Precision: 64
\[\frac{\left(-b\right) + \sqrt{b \cdot b - \left(4 \cdot a\right) \cdot c}}{2 \cdot a}\]
\[\begin{array}{l} \mathbf{if}\;b \le -1.2957079292059776 \cdot 10^{+154}:\\ \;\;\;\;\frac{\frac{-2 \cdot b}{a}}{2}\\ \mathbf{elif}\;b \le 1.502588793204478 \cdot 10^{-55}:\\ \;\;\;\;\frac{\frac{\sqrt{\mathsf{fma}\left(b, b, c \cdot \left(-4 \cdot a\right)\right)} - b}{a}}{2}\\ \mathbf{else}:\\ \;\;\;\;\frac{\frac{\frac{a \cdot c}{b} \cdot -2}{a}}{2}\\ \end{array}\]
\frac{\left(-b\right) + \sqrt{b \cdot b - \left(4 \cdot a\right) \cdot c}}{2 \cdot a}
\begin{array}{l}
\mathbf{if}\;b \le -1.2957079292059776 \cdot 10^{+154}:\\
\;\;\;\;\frac{\frac{-2 \cdot b}{a}}{2}\\

\mathbf{elif}\;b \le 1.502588793204478 \cdot 10^{-55}:\\
\;\;\;\;\frac{\frac{\sqrt{\mathsf{fma}\left(b, b, c \cdot \left(-4 \cdot a\right)\right)} - b}{a}}{2}\\

\mathbf{else}:\\
\;\;\;\;\frac{\frac{\frac{a \cdot c}{b} \cdot -2}{a}}{2}\\

\end{array}
double f(double a, double b, double c) {
        double r1160995 = b;
        double r1160996 = -r1160995;
        double r1160997 = r1160995 * r1160995;
        double r1160998 = 4.0;
        double r1160999 = a;
        double r1161000 = r1160998 * r1160999;
        double r1161001 = c;
        double r1161002 = r1161000 * r1161001;
        double r1161003 = r1160997 - r1161002;
        double r1161004 = sqrt(r1161003);
        double r1161005 = r1160996 + r1161004;
        double r1161006 = 2.0;
        double r1161007 = r1161006 * r1160999;
        double r1161008 = r1161005 / r1161007;
        return r1161008;
}

double f(double a, double b, double c) {
        double r1161009 = b;
        double r1161010 = -1.2957079292059776e+154;
        bool r1161011 = r1161009 <= r1161010;
        double r1161012 = -2.0;
        double r1161013 = r1161012 * r1161009;
        double r1161014 = a;
        double r1161015 = r1161013 / r1161014;
        double r1161016 = 2.0;
        double r1161017 = r1161015 / r1161016;
        double r1161018 = 1.502588793204478e-55;
        bool r1161019 = r1161009 <= r1161018;
        double r1161020 = c;
        double r1161021 = -4.0;
        double r1161022 = r1161021 * r1161014;
        double r1161023 = r1161020 * r1161022;
        double r1161024 = fma(r1161009, r1161009, r1161023);
        double r1161025 = sqrt(r1161024);
        double r1161026 = r1161025 - r1161009;
        double r1161027 = r1161026 / r1161014;
        double r1161028 = r1161027 / r1161016;
        double r1161029 = r1161014 * r1161020;
        double r1161030 = r1161029 / r1161009;
        double r1161031 = r1161030 * r1161012;
        double r1161032 = r1161031 / r1161014;
        double r1161033 = r1161032 / r1161016;
        double r1161034 = r1161019 ? r1161028 : r1161033;
        double r1161035 = r1161011 ? r1161017 : r1161034;
        return r1161035;
}

Error

Bits error versus a

Bits error versus b

Bits error versus c

Target

Original33.3
Target20.5
Herbie13.8
\[\begin{array}{l} \mathbf{if}\;b \lt 0:\\ \;\;\;\;\frac{\left(-b\right) + \sqrt{b \cdot b - \left(4 \cdot a\right) \cdot c}}{2 \cdot a}\\ \mathbf{else}:\\ \;\;\;\;\frac{c}{a \cdot \frac{\left(-b\right) - \sqrt{b \cdot b - \left(4 \cdot a\right) \cdot c}}{2 \cdot a}}\\ \end{array}\]

Derivation

  1. Split input into 3 regimes
  2. if b < -1.2957079292059776e+154

    1. Initial program 60.9

      \[\frac{\left(-b\right) + \sqrt{b \cdot b - \left(4 \cdot a\right) \cdot c}}{2 \cdot a}\]
    2. Simplified60.9

      \[\leadsto \color{blue}{\frac{\frac{\sqrt{\mathsf{fma}\left(b, b, \left(a \cdot -4\right) \cdot c\right)} - b}{a}}{2}}\]
    3. Using strategy rm
    4. Applied add-sqr-sqrt60.9

      \[\leadsto \frac{\frac{\sqrt{\color{blue}{\sqrt{\mathsf{fma}\left(b, b, \left(a \cdot -4\right) \cdot c\right)} \cdot \sqrt{\mathsf{fma}\left(b, b, \left(a \cdot -4\right) \cdot c\right)}}} - b}{a}}{2}\]
    5. Applied sqrt-prod60.9

      \[\leadsto \frac{\frac{\color{blue}{\sqrt{\sqrt{\mathsf{fma}\left(b, b, \left(a \cdot -4\right) \cdot c\right)}} \cdot \sqrt{\sqrt{\mathsf{fma}\left(b, b, \left(a \cdot -4\right) \cdot c\right)}}} - b}{a}}{2}\]
    6. Applied fma-neg60.9

      \[\leadsto \frac{\frac{\color{blue}{\mathsf{fma}\left(\sqrt{\sqrt{\mathsf{fma}\left(b, b, \left(a \cdot -4\right) \cdot c\right)}}, \sqrt{\sqrt{\mathsf{fma}\left(b, b, \left(a \cdot -4\right) \cdot c\right)}}, -b\right)}}{a}}{2}\]
    7. Taylor expanded around -inf 2.0

      \[\leadsto \frac{\frac{\color{blue}{-2 \cdot b}}{a}}{2}\]
    8. Simplified2.0

      \[\leadsto \frac{\frac{\color{blue}{b \cdot -2}}{a}}{2}\]

    if -1.2957079292059776e+154 < b < 1.502588793204478e-55

    1. Initial program 12.7

      \[\frac{\left(-b\right) + \sqrt{b \cdot b - \left(4 \cdot a\right) \cdot c}}{2 \cdot a}\]
    2. Simplified12.7

      \[\leadsto \color{blue}{\frac{\frac{\sqrt{\mathsf{fma}\left(b, b, \left(a \cdot -4\right) \cdot c\right)} - b}{a}}{2}}\]
    3. Using strategy rm
    4. Applied *-commutative12.7

      \[\leadsto \frac{\frac{\sqrt{\mathsf{fma}\left(b, b, \color{blue}{c \cdot \left(a \cdot -4\right)}\right)} - b}{a}}{2}\]

    if 1.502588793204478e-55 < b

    1. Initial program 52.9

      \[\frac{\left(-b\right) + \sqrt{b \cdot b - \left(4 \cdot a\right) \cdot c}}{2 \cdot a}\]
    2. Simplified52.9

      \[\leadsto \color{blue}{\frac{\frac{\sqrt{\mathsf{fma}\left(b, b, \left(a \cdot -4\right) \cdot c\right)} - b}{a}}{2}}\]
    3. Taylor expanded around inf 18.8

      \[\leadsto \frac{\frac{\color{blue}{-2 \cdot \frac{a \cdot c}{b}}}{a}}{2}\]
  3. Recombined 3 regimes into one program.
  4. Final simplification13.8

    \[\leadsto \begin{array}{l} \mathbf{if}\;b \le -1.2957079292059776 \cdot 10^{+154}:\\ \;\;\;\;\frac{\frac{-2 \cdot b}{a}}{2}\\ \mathbf{elif}\;b \le 1.502588793204478 \cdot 10^{-55}:\\ \;\;\;\;\frac{\frac{\sqrt{\mathsf{fma}\left(b, b, c \cdot \left(-4 \cdot a\right)\right)} - b}{a}}{2}\\ \mathbf{else}:\\ \;\;\;\;\frac{\frac{\frac{a \cdot c}{b} \cdot -2}{a}}{2}\\ \end{array}\]

Reproduce

herbie shell --seed 2019155 +o rules:numerics
(FPCore (a b c)
  :name "The quadratic formula (r1)"

  :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)))