# CDR CODING in cons cells

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 |