\[\frac{a \cdot c + b \cdot d}{c \cdot c + d \cdot d}\]

\frac{a \cdot c + b \cdot d}{c \cdot c + d \cdot d}

double f(double a, double b, double c, double d) {
        double r91655 = a;
        double r91656 = c;
        double r91657 = r91655 * r91656;
        double r91658 = b;
        double r91659 = d;
        double r91660 = r91658 * r91659;
        double r91661 = r91657 + r91660;
        double r91662 = r91656 * r91656;
        double r91663 = r91659 * r91659;
        double r91664 = r91662 + r91663;
        double r91665 = r91661 / r91664;
        return r91665;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2019323 
(FPCore (a b c d)
  :name "Complex division, real part"
  :precision binary64

  :herbie-target
  (if (< (fabs d) (fabs c)) (/ (+ a (* b (/ d c))) (+ c (* d (/ d c)))) (/ (+ b (* a (/ c d))) (+ d (* c (/ c d)))))

  (/ (+ (* a c) (* b d)) (+ (* c c) (* d d))))

Backtrace

get-representation: Unknown representation real		L	C
(unnamed)	/data/pavpan/nightlies/herbie/fix-interface-bugs/src/core/regimes.rkt	65	3
filter	/opt/racket-7.2/collects/racket/private/list.rkt	256	2
infer-splitpoints	/data/pavpan/nightlies/herbie/fix-interface-bugs/src/core/regimes.rkt	34	0
get-final-combination	/data/pavpan/nightlies/herbie/fix-interface-bugs/src/mainloop.rkt	369	0
(unnamed)	/opt/racket-7.2/collects/racket/private/more-scheme.rkt	261	28
run	/opt/racket-7.2/share/pkgs/profile-lib/main.rkt	39	2
profile-thunk16	/opt/racket-7.2/share/pkgs/profile-lib/main.rkt	9	0
(unnamed)	/opt/racket-7.2/collects/racket/private/more-scheme.rkt	261	28