merge sorting will work in c8051f120?

In c8051f120 controller, i use merge sorting technique of one of my application in a project. but problem is local variable acting as global variables within a function(auto keyword). following is a example of merge sorting.
divide(int left,int right)
{ int mid; if(left<right) { mid=(left+right)/2; divide(left,mid); divide(mid+1,right); }
}