|  |  |  |  |  |  |  |  | 
   
    | • | for chunks
    that contain a single cell value 
 |  | 
   
    |  | 
   
    |  | there is a single
    mapping in the HashMap 
 | 
   
    |  | 
   
    | • | for chunks
    with 64 different cell values 
 |  | 
   
    |  | 
   
    |  | there are 64
    mappings in the HashMap 
 |  | 
   
    |  | 
   
    | • | Iterating over
    (going through) the keys in 
 |  | 
   
    |  | 
   
    |  | the HashMap is
    necessary to get and set 
 |  | 
   
    |  | 
   
    |  | cell
    values, so generally this works faster 
 |  | 
   
    |  | 
   
    |  | for smaller
    numbers of mappings. 
 |  |