feat: use board coverage in metrics

3 files changed, 31 insertions, 4 deletions

diff --git a/src/config.h b/src/config.h
index 5da6a21..1cadbc1 100644
--- a/src/config.h
+++ b/src/config.h
@@ -1,4 +1,4 @@
 #define BOARD_SIZE 8
 #define DEFAULT_FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
-#define MAX_DEPTH 5
+#define MAX_DEPTH 3
 #define INFINITY 1000000
diff --git a/src/main.c b/src/main.c
index b18c7ea..edb553b 100644
--- a/src/main.c
+++ b/src/main.c
@@ -261,6 +261,33 @@ int compute_material_advantage(int* board, int color) {
   return counter;
 }
 
+int compute_coverage(int* board, int color) {
+  int counter = 0;
+  for (int rank = 7; rank >= 0; rank--) {
+    for (int file = 0; file < 8; file++) {
+      int index = rank * 16 + file;
+      int piece = board[index];
+      if (piece != EMPTY && (piece % 2) == color) {
+        for (int rank_destination = 7; rank_destination >= 0; rank_destination--) {
+          for (int file_destination = 0; file_destination < 8; file_destination++) {
+            int index_destination = rank_destination * 16 + file_destination;
+            int move[2] = { index, index_destination };
+            if (validate_move(move, color, board) >= 0) {
+              counter++;
+            }
+          }
+        }
+      }
+    }
+  }
+  return counter;
+}
+
+int compute_score(int* board) {
+  int coverage_score = compute_coverage(board, WHITE) - compute_coverage(board, BLACK);
+  return compute_material_advantage(board, WHITE) + coverage_score;
+}
+
 // Alpha-beta pruning
 // Value here is white material advantage over black
 // Alpha is the best value for maximizer (white)
@@ -294,7 +321,7 @@ int find_best_move(int* board, int color, int depth, int alpha, int beta) {
 
               int value = depth < MAX_DEPTH
                 ? find_best_move(fake_board, 1 - color, depth + 1, alpha, beta)
-                : compute_material_advantage(fake_board, 0); // Always for maximizer (white)
+                : compute_score(fake_board);
 
               if (is_maximizer) {
                 if (value > best_value) {
@@ -341,7 +368,7 @@ int main() {
   int color = 0;
 
   while (1) {
-    printf("Current board advantage is %i\n", compute_material_advantage(board, 0));
+    printf("Current score is %i\n", compute_score(board));
     find_best_move(board, color, 0, -INFINITY, +INFINITY);
     printf("Enter a move for %s:\n", COLORS[color]);
     input_move(move);
diff --git a/src/pieces.h b/src/pieces.h
index a88626a..f975190 100644
--- a/src/pieces.h
+++ b/src/pieces.h
@@ -33,7 +33,7 @@ int knightMoves[] = { 33, 31, 18, 14, -33, -31, -18, -14, 0 };
 int kingMoves[] = { 17, 16, 15, 1, -1, -15, -16, -17, 0 };
 
 int pawnMoves[] = { 16, 0 };
-int blackPawnMoves[] = { 16, 0 };
+int blackPawnMoves[] = { -16, 0 };
 
 int newPawnMoves[] = { 32, 16, 0 };
 int newBlackPawnMoves[] = { -32, -16, 0 };