+--------+----------------------------------+
| bitmap | 00000000000000010000000000000000 |
+--------+----------------------------------+
|        | +-+                              |
| array  | | |                              |
|        | +++                              |
+--------+--+----+--------------------------+
            |
            |
            |
            v
       /---------\
       | foo → 1 |
       \---------/