\[\frac{\sqrt{\left(\left(\left(\left(a + b\right) + c\right) \cdot \left(\left(b + c\right) - a\right)\right) \cdot \left(\left(a + c\right) - b\right)\right) \cdot \left(\left(a + b\right) - c\right)}}{4}\]

\frac{\sqrt{\left(\left(\left(\left(a + b\right) + c\right) \cdot \left(\left(b + c\right) - a\right)\right) \cdot \left(\left(a + c\right) - b\right)\right) \cdot \left(\left(a + b\right) - c\right)}}{4}

double code(double a, double b, double c) {
	return ((double) (((double) sqrt(((double) (((double) (((double) (((double) (((double) (a + b)) + c)) * ((double) (((double) (b + c)) - a)))) * ((double) (((double) (a + c)) - b)))) * ((double) (((double) (a + b)) - c)))))) / 4.0));
}

Reproduce

herbie shell --seed 2020153 
(FPCore (a b c)
  :name "(/ (sqrt (* (* (* (+ (+ a b) c) (- (+ b c) a)) (- (+ a c) b)) (- (+ a b) c))) 4)"
  :precision binary64
  (/ (sqrt (* (* (* (+ (+ a b) c) (- (+ b c) a)) (- (+ a c) b)) (- (+ a b) c))) 4.0))

Cannot sample enough valid points. (more)

Reproduce