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

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

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

\end{array}

double f(double a, double b, double c) {
        double r8215 = b;
        double r8216 = 0.0;
        bool r8217 = r8215 >= r8216;
        double r8218 = -r8215;
        double r8219 = r8215 * r8215;
        double r8220 = 4.0;
        double r8221 = a;
        double r8222 = r8220 * r8221;
        double r8223 = c;
        double r8224 = r8222 * r8223;
        double r8225 = r8219 - r8224;
        double r8226 = sqrt(r8225);
        double r8227 = r8218 - r8226;
        double r8228 = 2.0;
        double r8229 = r8228 * r8221;
        double r8230 = r8227 / r8229;
        double r8231 = r8228 * r8223;
        double r8232 = r8218 + r8226;
        double r8233 = r8231 / r8232;
        double r8234 = r8217 ? r8230 : r8233;
        return r8234;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2019173 
(FPCore (a b c)
  :name "jeff quadratic root 1"
  (if (>= b 0.0) (/ (- (- b) (sqrt (- (* b b) (* (* 4.0 a) c)))) (* 2.0 a)) (/ (* 2.0 c) (+ (- b) (sqrt (- (* b b) (* (* 4.0 a) c)))))))

Backtrace

atab-pick-alt: contract violation expected: alt? given: '(#<alt (λ (a b c) (if (>= b 0.0) (/ (/ (- (- b) (sqrt (- (* b b) (* (* a c) 4.0)))) a) 2.0) (* (/ c (- (sqrt (- (* b b) (* (* a c) 4.0))) b)) 2.0)))>) in: the range of the #:picking-func argument of (-> alt-table? #:only-fresh boolean? #:picking-func (-> (listof alt?) alt?) (values alt? alt-table?)) contract from: /data/pavpan/nightlies/herbie/no-costs-2/src/core/alt-table.rkt blaming: /data/pavpan/nightlies/herbie/no-costs-2/src/mainloop.rkt (assuming the contract is correct) at: /data/pavpan/nightlies/herbie/no-costs-2/src/core/alt-table.rkt:13.3		L	C
raise-blame-error16	/opt/racket-7.0/collects/racket/contract/private/blame.rkt	347	0
(unnamed)	/data/pavpan/nightlies/herbie/no-costs-2/src/core/alt-table.rkt	59	0
(unnamed)	/opt/racket-7.0/collects/racket/contract/private/arrow-val-first.rkt	388	18
choose-best-alt!	/data/pavpan/nightlies/herbie/no-costs-2/src/mainloop.rkt	110	0
run-iter!	/data/pavpan/nightlies/herbie/no-costs-2/src/mainloop.rkt	319	0
for-loop	/data/pavpan/nightlies/herbie/no-costs-2/src/mainloop.rkt	353	4
run-improve43	/data/pavpan/nightlies/herbie/no-costs-2/src/mainloop.rkt	338	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