Exception for quad2p (problem 3.2.1, positive)

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 r2052488 = b_2;
        double r2052489 = -r2052488;
        double r2052490 = r2052488 * r2052488;
        double r2052491 = a;
        double r2052492 = c;
        double r2052493 = r2052491 * r2052492;
        double r2052494 = r2052490 - r2052493;
        double r2052495 = sqrt(r2052494);
        double r2052496 = r2052489 + r2052495;
        double r2052497 = r2052496 / r2052491;
        return r2052497;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 0 
(FPCore (a b_2 c)
  :name "quad2p (problem 3.2.1, positive)"
  (/.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
best-and-tied-at-points	/home/p92/nightlies/herbie/optional-posits/src/core/alt-table.rkt	117	0
atab-add-altn	/home/p92/nightlies/herbie/optional-posits/src/core/alt-table.rkt	202	0
for-loop	/home/p92/nightlies/herbie/optional-posits/src/core/alt-table.rkt	56	2
(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