Cubic equation solver in C

//---------------------------------------------------------------------------
// solve cubic equation x^3 + a*x^2 + b*x + c
// x - array of size 3
// In case 3 real roots: => x[0], x[1], x[2], return 3
//         2 real roots: x[0], x[1],          return 2
//         1 real root : x[0], x[1] ± i*x[2], return 1
unsigned int solveP3(double *x,double a,double b,double c) {
	double a2 = a*a;
    	double q  = (a2 - 3*b)/9;
	double r  = (a*(2*a2-9*b) + 27*c)/54;
    	double r2 = r*r;
	double q3 = q*q*q;
	double A,B;
    	if(r2<q3)
    	{
    		double t=r/sqrt(q3);
    		if( t<-1) t=-1;
    		if( t> 1) t= 1;
    		t=acos(t);
    		a/=3; q=-2*sqrt(q);
    		x[0]=q*cos(t/3)-a;
    		x[1]=q*cos((t+M_2PI)/3)-a;
    		x[2]=q*cos((t-M_2PI)/3)-a;
    		return 3;
    	}
    	else
    	{
    		A =-pow(fabs(r)+sqrt(r2-q3),1./3);
    		if( r<0 ) A=-A;
    		B = (0==A ? 0 : q/A);

		a/=3;
		x[0] =(A+B)-a;
		x[1] =-0.5*(A+B)-a;
		x[2] = 0.5*sqrt(3.)*(A-B);
		if(fabs(x[2])<eps) { x[2]=x[1]; return 2; }

		return 1;
        }
}