Average Error: 33.3 → 9.6
Time: 1.6m
Precision: 64
\[\frac{\left(-b\right) - \sqrt{b \cdot b - 4 \cdot \left(a \cdot c\right)}}{2 \cdot a}\]
\[\begin{array}{l} \mathbf{if}\;b \le -1.2303558036345968 \cdot 10^{-110}:\\ \;\;\;\;-\frac{c}{b}\\ \mathbf{elif}\;b \le 5.869467752933353 \cdot 10^{+121}:\\ \;\;\;\;\frac{\frac{\left(-b\right) - \sqrt{(\left(c \cdot a\right) \cdot -4 + \left(b \cdot b\right))_*}}{2}}{a}\\ \mathbf{else}:\\ \;\;\;\;\frac{c}{b} - \frac{b}{a}\\ \end{array}\]
\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 -1.2303558036345968 \cdot 10^{-110}:\\
\;\;\;\;-\frac{c}{b}\\

\mathbf{elif}\;b \le 5.869467752933353 \cdot 10^{+121}:\\
\;\;\;\;\frac{\frac{\left(-b\right) - \sqrt{(\left(c \cdot a\right) \cdot -4 + \left(b \cdot b\right))_*}}{2}}{a}\\

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

\end{array}
double f(double a, double b, double c) {
        double r4172127 = b;
        double r4172128 = -r4172127;
        double r4172129 = r4172127 * r4172127;
        double r4172130 = 4.0;
        double r4172131 = a;
        double r4172132 = c;
        double r4172133 = r4172131 * r4172132;
        double r4172134 = r4172130 * r4172133;
        double r4172135 = r4172129 - r4172134;
        double r4172136 = sqrt(r4172135);
        double r4172137 = r4172128 - r4172136;
        double r4172138 = 2.0;
        double r4172139 = r4172138 * r4172131;
        double r4172140 = r4172137 / r4172139;
        return r4172140;
}

double f(double a, double b, double c) {
        double r4172141 = b;
        double r4172142 = -1.2303558036345968e-110;
        bool r4172143 = r4172141 <= r4172142;
        double r4172144 = c;
        double r4172145 = r4172144 / r4172141;
        double r4172146 = -r4172145;
        double r4172147 = 5.869467752933353e+121;
        bool r4172148 = r4172141 <= r4172147;
        double r4172149 = -r4172141;
        double r4172150 = a;
        double r4172151 = r4172144 * r4172150;
        double r4172152 = -4.0;
        double r4172153 = r4172141 * r4172141;
        double r4172154 = fma(r4172151, r4172152, r4172153);
        double r4172155 = sqrt(r4172154);
        double r4172156 = r4172149 - r4172155;
        double r4172157 = 2.0;
        double r4172158 = r4172156 / r4172157;
        double r4172159 = r4172158 / r4172150;
        double r4172160 = r4172141 / r4172150;
        double r4172161 = r4172145 - r4172160;
        double r4172162 = r4172148 ? r4172159 : r4172161;
        double r4172163 = r4172143 ? r4172146 : r4172162;
        return r4172163;
}

Error

Bits error versus a

Bits error versus b

Bits error versus c

Target

Original33.3
Target20.2
Herbie9.6
\[\begin{array}{l} \mathbf{if}\;b \lt 0:\\ \;\;\;\;\frac{c}{a \cdot \frac{\left(-b\right) + \sqrt{b \cdot b - 4 \cdot \left(a \cdot c\right)}}{2 \cdot a}}\\ \mathbf{else}:\\ \;\;\;\;\frac{\left(-b\right) - \sqrt{b \cdot b - 4 \cdot \left(a \cdot c\right)}}{2 \cdot a}\\ \end{array}\]

Derivation

  1. Split input into 3 regimes
  2. if b < -1.2303558036345968e-110

    1. Initial program 50.8

      \[\frac{\left(-b\right) - \sqrt{b \cdot b - 4 \cdot \left(a \cdot c\right)}}{2 \cdot a}\]
    2. Simplified50.8

      \[\leadsto \color{blue}{\frac{\frac{\left(-b\right) - \sqrt{(\left(a \cdot c\right) \cdot -4 + \left(b \cdot b\right))_*}}{2}}{a}}\]
    3. Taylor expanded around 0 50.8

      \[\leadsto \frac{\frac{\left(-b\right) - \sqrt{\color{blue}{{b}^{2} - 4 \cdot \left(a \cdot c\right)}}}{2}}{a}\]
    4. Simplified50.8

      \[\leadsto \frac{\frac{\left(-b\right) - \sqrt{\color{blue}{(\left(a \cdot c\right) \cdot -4 + \left(b \cdot b\right))_*}}}{2}}{a}\]
    5. Using strategy rm
    6. Applied *-un-lft-identity50.8

      \[\leadsto \frac{\frac{\left(-b\right) - \sqrt{(\left(a \cdot c\right) \cdot -4 + \left(b \cdot b\right))_*}}{2}}{\color{blue}{1 \cdot a}}\]
    7. Applied div-inv50.8

      \[\leadsto \frac{\color{blue}{\left(\left(-b\right) - \sqrt{(\left(a \cdot c\right) \cdot -4 + \left(b \cdot b\right))_*}\right) \cdot \frac{1}{2}}}{1 \cdot a}\]
    8. Applied times-frac50.8

      \[\leadsto \color{blue}{\frac{\left(-b\right) - \sqrt{(\left(a \cdot c\right) \cdot -4 + \left(b \cdot b\right))_*}}{1} \cdot \frac{\frac{1}{2}}{a}}\]
    9. Simplified50.8

      \[\leadsto \color{blue}{\left(-\left(b + \sqrt{(a \cdot \left(c \cdot -4\right) + \left(b \cdot b\right))_*}\right)\right)} \cdot \frac{\frac{1}{2}}{a}\]
    10. Simplified50.8

      \[\leadsto \left(-\left(b + \sqrt{(a \cdot \left(c \cdot -4\right) + \left(b \cdot b\right))_*}\right)\right) \cdot \color{blue}{\frac{\frac{1}{2}}{a}}\]
    11. Taylor expanded around -inf 10.2

      \[\leadsto \color{blue}{-1 \cdot \frac{c}{b}}\]
    12. Simplified10.2

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

    if -1.2303558036345968e-110 < b < 5.869467752933353e+121

    1. Initial program 11.0

      \[\frac{\left(-b\right) - \sqrt{b \cdot b - 4 \cdot \left(a \cdot c\right)}}{2 \cdot a}\]
    2. Simplified11.0

      \[\leadsto \color{blue}{\frac{\frac{\left(-b\right) - \sqrt{(\left(a \cdot c\right) \cdot -4 + \left(b \cdot b\right))_*}}{2}}{a}}\]
    3. Taylor expanded around 0 11.0

      \[\leadsto \frac{\frac{\left(-b\right) - \sqrt{\color{blue}{{b}^{2} - 4 \cdot \left(a \cdot c\right)}}}{2}}{a}\]
    4. Simplified11.0

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

    if 5.869467752933353e+121 < b

    1. Initial program 51.7

      \[\frac{\left(-b\right) - \sqrt{b \cdot b - 4 \cdot \left(a \cdot c\right)}}{2 \cdot a}\]
    2. Simplified51.7

      \[\leadsto \color{blue}{\frac{\frac{\left(-b\right) - \sqrt{(\left(a \cdot c\right) \cdot -4 + \left(b \cdot b\right))_*}}{2}}{a}}\]
    3. Taylor expanded around inf 3.4

      \[\leadsto \color{blue}{\frac{c}{b} - \frac{b}{a}}\]
  3. Recombined 3 regimes into one program.
  4. Final simplification9.6

    \[\leadsto \begin{array}{l} \mathbf{if}\;b \le -1.2303558036345968 \cdot 10^{-110}:\\ \;\;\;\;-\frac{c}{b}\\ \mathbf{elif}\;b \le 5.869467752933353 \cdot 10^{+121}:\\ \;\;\;\;\frac{\frac{\left(-b\right) - \sqrt{(\left(c \cdot a\right) \cdot -4 + \left(b \cdot b\right))_*}}{2}}{a}\\ \mathbf{else}:\\ \;\;\;\;\frac{c}{b} - \frac{b}{a}\\ \end{array}\]

Reproduce

herbie shell --seed 2019119 +o rules:numerics
(FPCore (a b c)
  :name "quadm (p42, negative)"

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

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