\[\sqrt{\frac{\left(\left(\left(\left(c + b\right) + a\right) \cdot \left(\frac{\left(c + b\right) + a}{2} - a\right)\right) \cdot \left(\frac{\left(c + b\right) + a}{2} - b\right)\right) \cdot \left(\frac{\left(c + b\right) + a}{2} - c\right)}{2}}\]

\sqrt{\frac{\left(\left(\left(\left(c + b\right) + a\right) \cdot \left(\frac{\left(c + b\right) + a}{2} - a\right)\right) \cdot \left(\frac{\left(c + b\right) + a}{2} - b\right)\right) \cdot \left(\frac{\left(c + b\right) + a}{2} - c\right)}{2}}

double code(double c, double b, double a) {
	return ((double) sqrt(((double) (((double) (((double) (((double) (((double) (((double) (c + b)) + a)) * ((double) (((double) (((double) (((double) (c + b)) + a)) / 2.0)) - a)))) * ((double) (((double) (((double) (((double) (c + b)) + a)) / 2.0)) - b)))) * ((double) (((double) (((double) (((double) (c + b)) + a)) / 2.0)) - c)))) / 2.0))));
}

Reproduce

herbie shell --seed 2020152 
(FPCore (c b a)
  :name "(sqrt (/ (* (* (* (+ (+ c b) a) (- (/ (+ (+ c b) a) 2) a)) (- (/ (+ (+ c b) a) 2) b)) (- (/ (+ (+ c b) a) 2) c)) 2))"
  :precision binary64
  (sqrt (/ (* (* (* (+ (+ c b) a) (- (/ (+ (+ c b) a) 2.0) a)) (- (/ (+ (+ c b) a) 2.0) b)) (- (/ (+ (+ c b) a) 2.0) c)) 2.0)))

Cannot sample enough valid points. (more)

Reproduce