\[\begin{array}{l} \mathbf{if}\;b \ge 0.0:\\ \;\;\;\;\frac{2 \cdot c}{\left(-b\right) - \sqrt{b \cdot b - \left(4 \cdot a\right) \cdot c}}\\ \mathbf{else}:\\ \;\;\;\;\frac{\left(-b\right) + \sqrt{b \cdot b - \left(4 \cdot a\right) \cdot c}}{2 \cdot a}\\ \end{array}\]

\begin{array}{l}
\mathbf{if}\;b \ge 0.0:\\
\;\;\;\;\frac{2 \cdot c}{\left(-b\right) - \sqrt{b \cdot b - \left(4 \cdot a\right) \cdot c}}\\

\mathbf{else}:\\
\;\;\;\;\frac{\left(-b\right) + \sqrt{b \cdot b - \left(4 \cdot a\right) \cdot c}}{2 \cdot a}\\

\end{array}

double f(double a, double b, double c) {
        double r8001 = b;
        double r8002 = 0.0;
        bool r8003 = r8001 >= r8002;
        double r8004 = 2.0;
        double r8005 = c;
        double r8006 = r8004 * r8005;
        double r8007 = -r8001;
        double r8008 = r8001 * r8001;
        double r8009 = 4.0;
        double r8010 = a;
        double r8011 = r8009 * r8010;
        double r8012 = r8011 * r8005;
        double r8013 = r8008 - r8012;
        double r8014 = sqrt(r8013);
        double r8015 = r8007 - r8014;
        double r8016 = r8006 / r8015;
        double r8017 = r8007 + r8014;
        double r8018 = r8004 * r8010;
        double r8019 = r8017 / r8018;
        double r8020 = r8003 ? r8016 : r8019;
        return r8020;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2019191 
(FPCore (a b c)
  :name "jeff quadratic root 2"
  (if (>= b 0.0) (/ (* 2.0 c) (- (- b) (sqrt (- (* b b) (* (* 4.0 a) c))))) (/ (+ (- b) (sqrt (- (* b b) (* (* 4.0 a) c)))) (* 2.0 a))))

Backtrace

get-representation: Unknown representation #f		L	C
loop	/data/pavpan/nightlies/herbie/interface2/src/points.rkt	122	4
prepare-points	/data/pavpan/nightlies/herbie/interface2/src/points.rkt	146	0
setup-prog!34	/data/pavpan/nightlies/herbie/interface2/src/mainloop.rkt	67	0
run-improve43	/data/pavpan/nightlies/herbie/interface2/src/mainloop.rkt	339	0
(unnamed)	/opt/racket-7.0/collects/racket/private/more-scheme.rkt	261	28
run	/opt/racket-7.0/share/pkgs/profile-lib/main.rkt	39	2
profile-thunk16	/opt/racket-7.0/share/pkgs/profile-lib/main.rkt	9	0
(unnamed)	/opt/racket-7.0/collects/racket/private/more-scheme.rkt	261	28