Martianoids: Routine at 42179

42179: Choose Direction

Used by the routine at MoveProgramPacket.

Finds a direction for a program packet to go in, which is the one that it is heading in if that is possible, and otherwise the one to the side, the opposite one, and the other side.

Input
A	Direction of the packet
DE	X position
HL	Y position

Output
A	The type of the cell, if the zero flag is set
C	The direction that has been chosen
F	The zero flag is set if the packet can go on

ChooseDirection

42179

CALL TestCellInDirection

Try the direction that the packet is heading in, and return if it can go there.

42182

RET Z

42183

LD A,C

Try the direction before it...

42184

DEC A

42185

AND 3

42187

CALL TestCellInDirection

...and return if the packet can go there.

42190

RET Z

42191

LD A,C

Try the opposite direction...

42192

XOR 2

42194

CALL TestCellInDirection

...and return if the packet can go there.

42197

RET Z

42198

LD A,C

Try the direction after the original one...

42199

INC A

42200

AND 3

42202

JR TestCellInDirection

Jump to TestCellInDirection.