Through the Trap Door: Routine at 53317

53317: Set zero flag if room B has an entry in pathfinding data table, otherwise reset

Used by the routine at 53194.

Input
HL	Address of end of pathfinding data table
B	Index of room to check table for

Output
F	Zero flag set if room B is already stored in pathfinding data table, reset otherwise

53317

PUSH HL

Store HL (address of end of pathfinding data table)

53318

DEC HL

Move HL back to previous entry's room index...

53319

LD A,(HL)

...load into A...

53320

CP 255

...and if this is 255 (start marker, so room B not found)...

53322

JR Z,53330

...then skip ahead to 53330

53324

DEC HL

Move HL back to entry's direction index

53325

CP B

If room to search for not the same as current entry's room...

53326

JR NZ,53318

...then loop back to 53318 to test next entry

At this point, the room we're looking for (in B) is already stored in the pathfinding data table and the zero flag is set.

53328

POP HL

Restore HL (address of end of pathfinding data table)

53329

RET

Return

53330

POP HL

Restore HL (address of end of pathfinding data table)

53331

DEC A

Reset zero flag

53332

RET

Return