module pick2
Title 'Pick a move using heuristics'
"PICK2 device 'P22V10'; 

" Inputs from PICK1 PLD
PICK3..PICK0               pin 1..4;  " Move, if any, from PICK1 PLD
" Inputs from Tic-Tac-Toe grid corners
X11, Y11, X13, Y13, X31, Y31, X33, Y33   pin 5..11, 13;
" Combined inputs from external NOR gates; 1 ==> corresponding cell is empty
E12, E21, E23, E32         pin 14..15, 22..23; 
" Move output
MOVE3..MOVE0               pin 17..20 istype 'com';

PICK = [PICK3..PICK0];  " Set definition
" Non-rotated move input and output encoding
MOVE = [MOVE3..MOVE0]; 
MOVE11 = [1,0,0,0]; MOVE12 = [0,1,0,0]; MOVE13 = [0,0,1,0];
MOVE21 = [0,0,0,1]; MOVE22 = [1,1,0,0]; MOVE23 = [0,1,1,1];
MOVE31 = [1,0,1,1]; MOVE32 = [1,1,0,1]; MOVE33 = [1,1,1,0];
NONE   = [0,0,0,0];

" Equations for empty corner cells
E11 = !X11 & !Y11; E13 = !X13 & !Y13; E31 = !X31 & !Y31; E33 = !X33 & !Y33;

equations

"Simplest approach -- pick corner if available, else side
WHEN PICK != NONE THEN MOVE = PICK;
ELSE WHEN E11 THEN MOVE = MOVE11;
ELSE WHEN E13 THEN MOVE = MOVE13;
ELSE WHEN E31 THEN MOVE = MOVE31;
ELSE WHEN E33 THEN MOVE = MOVE33;
ELSE WHEN E12 THEN MOVE = MOVE12;
ELSE WHEN E21 THEN MOVE = MOVE21;
ELSE WHEN E23 THEN MOVE = MOVE23;
ELSE WHEN E32 THEN MOVE = MOVE32;
ELSE MOVE = NONE;

end pick2