Recursion - Summing an 1-d array using binary sum

public class BinarySum {

public static void main (String args[]){

int array[] = {1,2,3,4,5,6,7,8};

int sum  =  binarySum(array , 0 , array.length);

System.out.println(sum);

}

//computing binary sum using recursion

public static  int binarySum(int[] array ,int startIndex , int length) {

if(length == 1 )

return array[startIndex];

else

return  binarySum(array,startIndex,(int)Math.ceil(length/2.0)) +                binarySum(array,startIndex+(int)Math.ceil(length/2.0),(int)Math.floor(length/2.0));

}

}

Recursion trace for binarySum(array , 0 ,  8)