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        Arimaa >> Bot Development >> Evaluation of Goal Threats
        
(Message started by: jdb on Nov 26^th, 2011, 12:50pm)

Title: Evaluation of Goal Threats
Post by jdb on Nov 26^th, 2011, 12:50pm

There was some talk in the chatroom archives about evaluating goal threats.

Clueless analyzes each of the goal squares on the board. It estimates the number of steps required to goal on that square. It counts the number of steps required to clear the goal square (ie c8 ) and the gmt square (ie c7 ). It also counts the number of steps to the nearest rabbit.

Code:

/**
* Creates a lower bound estimate for the number of steps required to goal
* on a certain goal square. This lower bound is exact. It is impossible to goal
* in fewer steps, but of course it may require more steps.
* @param gs
* @param goal_index
* @return
*/

public int get_estimate(GameState gs, int goal_index) {

assert (goal_index >= 0 && goal_index <= 63);
assert (goal_index <= 7 || goal_index >= 56);

int player = (goal_index < 8) ? 1 : 0;
int enemy = player ^ 0x01;

long enemy_bb = gs.colour_bb[enemy]; // all enemy pieces
long player_bb = gs.colour_bb[player]; // all player pieces
long empty_bb = gs.empty_bb;

long goal_bb = TestForGoal.goal_pattern_bb[goal_index][0];
long touch_goal_bb = TestForGoal.goal_pattern_bb[goal_index][2];
long player_rabbit_bb = gs.piece_bb[player];
long gmt_bb = TestForGoal.goal_pattern_bb[goal_index][4];
long player_nr_bb = player_bb & ~player_rabbit_bb;
long touch_gmt_bb = TestForGoal.goal_pattern_bb[goal_index][5];
long three_step_bb = TestForGoal.goal_pattern_bb[goal_index][8];
long goal_and_gmt_bb = TestForGoal.goal_pattern_bb[goal_index][9];

int steps_required = 0; // Holds estimate of steps required to goal
long stronger_player_bb = player_bb; // Strong enough to clear goal and gmt square

// Analyze goal square
if ( goal_bb != 0 ) {
if ( (goal_bb & player_nr_bb) != 0 ) {
steps_required++;
}
if ( (goal_bb & enemy_bb) != 0 ) {
steps_required+=2;
// Only keep stronger player pieces
int pt = gs.getPieceType(goal_bb,enemy);
stronger_player_bb &= gs.stronger_enemy_bb[pt];
}
}

// Analyze gmt square
if ( gmt_bb != 0 ) {
if ( (gmt_bb & player_nr_bb) != 0 ) {
steps_required++;
}
if ( (gmt_bb & enemy_bb) != 0 ) {
steps_required+=2;
// Only keep stronger player pieces
int pt = gs.getPieceType(gmt_bb,enemy);
stronger_player_bb &= gs.stronger_enemy_bb[pt];
}
}

// Locate closest piece strong enough to clear goal and gmt square
if ( stronger_player_bb == 0 ) {
return 9999;
}
long reach_bb = stronger_player_bb;
long target_bb = goal_and_gmt_bb & enemy_bb;
int piece_steps = 0;

if ( target_bb != 0 ) {
while (piece_steps < 10) {
reach_bb |= touching_bb(reach_bb);
if ( (reach_bb & target_bb) != 0) {
break;
}
piece_steps++;
}
}
steps_required += piece_steps;

// Locate closest rabbit
reach_bb = player_rabbit_bb;
int rabbit_steps = 1;
while ( rabbit_steps<10 ) {
reach_bb |= touching_bb(reach_bb);
if ( (reach_bb & goal_bb) != 0 ) {
break;
}
rabbit_steps++;
}
steps_required+=rabbit_steps;

return steps_required;
}

Title: Re: Evaluation of Goal Threats
Post by Swynndla on Nov 26^th, 2011, 3:13pm

Nice - thank you for sharing! :D