Shell Sort in Java

public class ShellSort {

public static void sort(int[] arr) {
    
    int gap = 0;
    while ( gap < arr.length / 3 ) {
        gap = gap * 3 + 1;
    }
    
    while ( gap > 0 ) {
        // Perform insertion sort on the gap.
        for ( int i = gap; i < arr.length; i++ ) {
            int j = i;
            int tmp = arr[i];
            // While there exists an inversion on the sub array..
            while ( j >= gap && arr[j - gap] > tmp ) {
                // .. Shift the elements down..
                arr[j] = arr[j - gap];
                j = j - gap;
            }
            // .. And set the correct element.
            arr[j] = tmp;
            
        }
        gap = ( gap - 1 ) / 3;
    }
}
}