hello i have following code

public class LSD{

public static int R=1<<8;
public static int bytesword=4;
public static void radixLSD(int a[],int l,int r){
  int  aux[]=new int[a.length];

 for (int d=bytesword-1;d>=0;d--){
   int i, j;
 int count[]=new int[R+1];
   for ( j=0;j<R;j++) count[j]=0;
   for (i=l;i<=r;i++)
  count[digit(a[i],d)+1]++;
   for (j=1;j<R;j++)
  count[j]+=count[j-1];
   for (i=l;i<=r;i++)
   aux[count[digit(a[i],d)]++]=a[i];
  for (i=l;i<=r;i++)
   a[i]=aux[i-1];
}

}


public static void main(String[]args){
int a[]=new int[]{3,6,5,7,4,8,9};
radixLSD(a,0,a.length-1);

 for (int i=0;i<a.length;i++){
  System.out.println(a[i]);
}











}


 public static int digit(int n,int d){
  return (n>>d)&1;



}
}

but it show me mistake

java.lang.ArrayIndexOutOfBoundsException: -1
 at LSD.radixLSD(LSD.java:19)
 at LSD.main(LSD.java:29)

please help me