The cdr-code is a 4-bit field of a 32-bit cons cell. It is treated as an on-page indicator bit and a 3-bit scaled offset.
Certain combinations are treated specially.
| on-page | offset | interpretation |
|---|---|---|
| 1 | 0 | CDR is NIL |
| 1 | 1 - 7 | CDR is at 2*offset (counted in 32-bit cells) on same page |
| 0 | 0 | CDR is indirect, CDR(car) |
| 0 | 1 - 7 | CDR is not a cons cell but is in the car of cell at 2*offset on same page |