/**
     * Sorts the specified sub-array of longs into ascending order.
     */
    private static void sort1(long x[], int off, int len) {
    // Insertion sort on smallest arrays
    if (len < 7) {
        for (int i=off; i<len+off; i++)
        for (int j=i; j>off && x[j-1]>x[j]; j--)
            swap(x, j, j-1);
        return;
    }