|        a         |        b         | sel |       out        |
| 0000000000000000 | 0000000000000000 |  0  | 0000000000000000 |
| 0000000000000000 | 0000000000000000 |  1  | 0000000000000000 |
| 0000000000000000 | 0001001000110100 |  0  | 0000000000000000 |
| 0000000000000000 | 0001001000110100 |  1  | 0001001000110100 |
| 1001100001110110 | 0000000000000000 |  0  | 1001100001110110 |