Exception for quad2m (problem 3.2.1, negative)

Math

\[\frac{\left(\left(-b_2\right) - \left(\sqrt{\left(\left(b_2 \cdot b_2\right) - \left(a \cdot c\right)\right)}\right)\right)}{a}\]

C

double f(double a, double b_2, double c) {
        double r2052874 = b_2;
        double r2052875 = -r2052874;
        double r2052876 = r2052874 * r2052874;
        double r2052877 = a;
        double r2052878 = c;
        double r2052879 = r2052877 * r2052878;
        double r2052880 = r2052876 - r2052879;
        double r2052881 = sqrt(r2052880);
        double r2052882 = r2052875 - r2052881;
        double r2052883 = r2052882 / r2052877;
        return r2052883;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 0 
(FPCore (a b_2 c)
  :name "quad2m (problem 3.2.1, negative)"
  (/.p16 (-.p16 (neg.p16 b_2) (sqrt.p16 (-.p16 (*.p16 b_2 b_2) (*.p16 a c)))) a))

Backtrace

hash-ref: no value found for key key: '(#<cpointer:posit16> #<cpointer:posit16> #<cpointer:posit16>)		L	C
for-loop	/home/p92/nightlies/herbie/optional-posits/src/core/alt-table.rkt	222	2
atab-min-errors	/home/p92/nightlies/herbie/optional-posits/src/core/alt-table.rkt	221	0
(unnamed)	/opt/racket-7.0/collects/racket/contract/private/arrow-val-first.rkt	388	18
finalize-iter!	/home/p92/nightlies/herbie/optional-posits/src/mainloop.rkt	272	0
run-improve43	/home/p92/nightlies/herbie/optional-posits/src/mainloop.rkt	340	0
(unnamed)	/opt/racket-7.0/collects/racket/private/more-scheme.rkt	261	28
(unnamed)	/opt/racket-7.0/collects/racket/private/more-scheme.rkt	261	28