Function:

Rotates a BCD digit (4 bits) left out of the operand, through the low 4 bits
of AX.

                    AL                   reg/mem
             7 . . . . . . 0         7 . . . . . . 0
            ┌───────┬───────┐       ┌───────┬───────┐
            │       │       │<──────┤       │       │<───┐
            └───────┴───┬───┛       └───────┴───────┛    │
                        └──>─────────────────────────────┛

The first (smaller) clock count is for a register operand.
Note that 0F is treated as <POP CS> on the 88/86 and prefixes newer
instructions on 286+ CPUs.

(Supplied by Anthony Naggs)