depth search

src/eval.c

@@ -1,5 +1,6 @@
 #include "types.h"
 #include "help.h"
+#include "moves.h"
 #include <stddef.h>
 #include <ctype.h>
 #include <stdio.h>
@@ -10,24 +11,29 @@
 #define ROOK_VALUE 500
 #define QUEEN_VALUE 900
 #define KING_VALUE 20000
+#define INF 9000000
+#define MAX_DEPTH 3  // Adjustable depth
 
 int evaluateBoard(game *game);
 void makeMove(game *g, move* m);
+int negamax(game *g, int depth, int alpha, int beta, int color);
 
 move *findBest(move* moves, size_t size, game* g){
-  int bestScore = -999999;
-  move *m = moves;
+  int bestScore = -INF;
+  move *bestMove = moves;
+  int color = g->whiteToMove ? 1 : -1;
+
   for (int i = 0; i < size; i++) {
     game gg = *g;
     makeMove(&gg, &moves[i]);
-    int score = evaluateBoard(&gg);
+    int score = -negamax(&gg, MAX_DEPTH, -INF, INF, -color);
     if (score > bestScore) {
       bestScore = score;
-      m = &moves[i];
+      bestMove = &moves[i];
       printf("info score cp %d\n", g->whiteToMove ? bestScore : -bestScore);
     }
   }
-  return m;
+  return bestMove;
 }
 
 int evaluateBoard(game *game) {
@@ -53,7 +59,6 @@ int evaluateBoard(game *game) {
     else if (game->black.king & bit) score -= KING_VALUE;
   }
 
-  score *= game->whiteToMove ? -1 : 1;
   return score;
 }
 
@@ -81,3 +86,32 @@ void makeMove(game *g, move* m) {
 
   g->whiteToMove = !g->whiteToMove;
 }
+
+int negamax(game *g, int depth, int alpha, int beta, int color) {
+  if (depth == 0)
+    return color * evaluateBoard(g);
+
+  move moves[1500];
+  int cnt = pawnMove(g, moves);
+  cnt += knightMove(g, moves + cnt);
+  cnt += rookMove(g, moves + cnt);
+  cnt += bishopMove(g, moves + cnt);
+  cnt += kingMove(g, moves + cnt);
+  cnt += queenMove(g, moves + cnt);
+
+  if (cnt == 0)
+    return 0;
+
+  int bestValue = -INF;
+  for (int i = 0; i < cnt; i++) {
+    game gg = *g;
+    makeMove(&gg, &moves[i]);
+
+    int value = -negamax(&gg, depth - 1, -beta, -alpha, -color);
+
+    if (value > bestValue) bestValue = value;
+    if (value > alpha) alpha = value;
+    if (alpha >= beta) break;
+  }
+  return bestValue;
+}