feat: compute positioning advantage

1 files changed, 65 insertions, 1 deletions

diff --git a/src/main.c b/src/main.c
index 100a80a..fe1836e 100644
--- a/src/main.c
+++ b/src/main.c
@@ -3,6 +3,7 @@
 #include <string.h>
 #include <time.h>
 #include <stdlib.h>
+#include <math.h>
 
 #include "config.h"
 #include "pieces.h"
@@ -304,6 +305,10 @@ int evaluate_pawn(int piece, int rank) {
   }
 }
 
+/*
+ * Compute material advantage of a player over an opponent
+ * Returns number in range (0, 30)
+ */
 int compute_material_advantage(int* board, int color) {
   int counter = 0;
   for (int rank = 7; rank >= 0; rank--) {
@@ -340,6 +345,10 @@ int compute_material_advantage(int* board, int color) {
   return counter;
 }
 
+/*
+ * Calculate amount of squares attack by players pieces
+ * Returns number in range (0, 64)
+ */
 int compute_coverage(int* board, int color) {
   int hit_map[128];
   for (int rank = 7; rank >= 0; rank--) {
@@ -402,9 +411,64 @@ int compute_coverage(int* board, int color) {
   return counter;
 }
 
+/*
+ * Compute player pieces score depending on how
+ * well they are positioned on the board
+ *
+ * Returns number in range(0, 112)
+ */
+int compute_positioning_score(int* board, int color) {
+  int total_score = 0;
+  double center = 3.5;
+
+  for (double rank = 7; rank >= 0; rank--) {
+    for (double file = 0; file < 8; file++) {
+      int index = rank * 16 + file;
+      int piece = board[index];
+      int score = 7 - (fabs(rank - center) + fabs(file - center));
+
+      int multiplier = 1;
+      switch (piece & NO_COLOR) {
+        case KNIGHT:
+          multiplier = 4;
+          break;
+        case BISHOP:
+          multiplier = 3;
+          break;
+        case PAWN:
+          multiplier = 2;
+          break;
+        case KING:
+          multiplier = -1; // Discourage king in center (encourage castle)
+          // TODO: encourage king in center after opponent has low material <= 6
+          break;
+        default:
+          multiplier = 1;
+          break;
+      }
+
+      total_score += score * multiplier;
+    }
+  }
+
+  return total_score;
+}
+
+/*
+ * Return a total board score symbolizing advantage
+ * for WHITE, meaining WHITE tries to maximize this
+ * value and BLACK tries to minimize it.
+ */
 int compute_score(int* board) {
+  int material_advantage = compute_material_advantage(board, WHITE);
+
   int coverage_score = compute_coverage(board, WHITE) - compute_coverage(board, BLACK);
-  return compute_material_advantage(board, WHITE)* 3 + coverage_score;
+  int normalized_coverage = coverage_score / 2;
+
+  int positioning_score = compute_positioning_score(board, WHITE) - compute_positioning_score(board, BLACK);
+  int normalized_positioning = positioning_score / 7;
+
+  return material_advantage + coverage_score + positioning_score;
 }
 
 int list_available_moves(Move moves[MAX_AVAILABLE_MOVES], int* board, int color) {