The Hobbit (v1.0): Routine at 9B0C

9B0C: Get the address of a room record

Returns the address of the record for room number A (0-79) from the room pointer table at B8D0. Numbers of $50 (80) and above are not rooms; for those, A is set to 0 and the routine returns with the Z flag set.

Input
A	Room number

Output
IX	Room record

9B0C

CP $50

Is the room number 80 or higher (not a real room)?

9B0E

JR C,$9B12

No, it is a real room: go and find its record

9B10

XOR A

Not a real room: return 0, with Z set, so the caller knows there is no such room

9B11

RET

9B12

PUSH DE

Save DE for the caller

9B13

LD DE,$B8D0

HL will point into the room pointer table, which starts here

9B16

PUSH HL

Save HL for the caller

9B17

LD L,A

HL = the room number...

9B18

LD H,$00

9B1A

ADD HL,HL

...doubled, because each room has a 2-byte entry in the table

9B1B

ADD HL,DE

HL = the address of this room's entry in the pointer table

9B1C

LD E,(HL)

DE = the room's record address, read from the table (low byte)...

9B1D

INC HL

9B1E

LD D,(HL)

...then the high byte

9B1F

PUSH DE

Move that address onto the stack for a moment...

9B20

POP IX

...so it can be popped straight into IX, the register the rest of the game expects a room record in

9B22

POP HL

Restore the caller's HL

9B23

POP DE

Restore the caller's DE

9B24

RET