\[\frac{b \cdot c - a \cdot d}{c \cdot c + d \cdot d} \]
(FPCore (a b c d)
 :precision binary64
 (/ (- (* b c) (* a d)) (+ (* c c) (* d d))))
double code(double a, double b, double c, double d) {
	return ((b * c) - (a * d)) / ((c * c) + (d * d));
}
real(8) function code(a, b, c, d)
    real(8), intent (in) :: a
    real(8), intent (in) :: b
    real(8), intent (in) :: c
    real(8), intent (in) :: d
    code = ((b * c) - (a * d)) / ((c * c) + (d * d))
end function
public static double code(double a, double b, double c, double d) {
	return ((b * c) - (a * d)) / ((c * c) + (d * d));
}
def code(a, b, c, d):
	return ((b * c) - (a * d)) / ((c * c) + (d * d))
function code(a, b, c, d)
	return Float64(Float64(Float64(b * c) - Float64(a * d)) / Float64(Float64(c * c) + Float64(d * d)))
end
function tmp = code(a, b, c, d)
	tmp = ((b * c) - (a * d)) / ((c * c) + (d * d));
end
code[a_, b_, c_, d_] := N[(N[(N[(b * c), $MachinePrecision] - N[(a * d), $MachinePrecision]), $MachinePrecision] / N[(N[(c * c), $MachinePrecision] + N[(d * d), $MachinePrecision]), $MachinePrecision]), $MachinePrecision]
\frac{b \cdot c - a \cdot d}{c \cdot c + d \cdot d}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2022150 
(FPCore (a b c d)
  :name "Complex division, imag part"
  :precision binary64

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

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

Backtrace

application: required keyword argument not supplied procedure: batch-egg-rewrite required keyword: #:rules arguments...: '(#<rule erfc-erf_binary64> #<rule erf-erfc_binary64> #<rule erf-odd_binary64> #<rule prod-diff_binary64> #<rule hypot-udef_binary64> #<rule expm1-log1p-u_binary64> #<rule log1p-expm1-u_binary64> #<rule log1p-udef_binary64> #<rule expm1-udef_binary64> #... #:depths '(1 1 1) #:roots '((2) (2) (2))LC
(unnamed)/opt/racket-8.1/collects/racket/private/kw.rkt155814
rewrite-expressions/data/pavpan/nightlies/herbie/timeline/src/core/matcher.rkt1710
gen-rewrites!/data/pavpan/nightlies/herbie/timeline/src/patch.rkt1440
patch-table-run/data/pavpan/nightlies/herbie/timeline/src/patch.rkt2910
(unnamed)/opt/racket-8.1/collects/racket/contract/private/arrow-val-first.rkt48618
run-iter!/data/pavpan/nightlies/herbie/timeline/src/mainloop.rkt2460
mutate!/data/pavpan/nightlies/herbie/timeline/src/mainloop.rkt3790
run-improve!/data/pavpan/nightlies/herbie/timeline/src/mainloop.rkt3260
(unnamed)/data/pavpan/nightlies/herbie/timeline/src/sandbox.rkt666
(unnamed)/opt/racket-8.1/share/pkgs/profile-lib/main.rkt4010
profile-thunk/opt/racket-8.1/share/pkgs/profile-lib/main.rkt90
(unnamed)/opt/racket-8.1/collects/racket/engine.rkt4224