improving the bot

2 files changed, 44 insertions, 15 deletions

diff --git a/src/bot.cpp b/src/bot.cpp
index 5a4601e..ff7a771 100644
--- a/src/bot.cpp
+++ b/src/bot.cpp
@@ -10,7 +10,7 @@
 #include <iostream>
 #include <vector>
 
-const int SEARCH_DEPTH = 5;
+const int SEARCH_DEPTH = 4;
 
 const int PAWN_VALUE = 100;
 const int KNIGHT_VALUE = 320;
@@ -63,6 +63,29 @@ int ROOK_TABLE[64] = {
     5,  10, 10, 10, 10, 10, 10, 5,  //
     0,  0,  5,  10, 10, 5,  0,  0,  //
 };
+
+int QUEEN_TABLE[64] = {
+    -20, -10, -10, -5, -5, -10, -10, -20, //
+    -10, 0,   0,   0,  0,  0,   0,   -10, //
+    -10, 0,   5,   5,  5,  5,   0,   -10, //
+    -5,  0,   5,   5,  5,  5,   0,   -5,  //
+    0,   0,   5,   5,  5,  5,   0,   -5,  //
+    -10, 5,   5,   5,  5,  5,   0,   -10, //
+    -10, 0,   5,   0,  0,  0,   0,   -10, //
+    -20, -10, -10, -5, -5, -10, -10, -20, //
+};
+
+int KING_TABLE_EARLY[64] = {
+    -30, -40, -40, -50, -50, -40, -40, -30, //
+    -30, -40, -40, -50, -50, -40, -40, -30, //
+    -30, -40, -40, -50, -50, -40, -40, -30, //
+    -30, -40, -40, -50, -50, -40, -40, -30, //
+    -20, -30, -30, -40, -40, -30, -30, -20, //
+    -10, -20, -20, -20, -20, -20, -20, -10, //
+    20,  20,  0,   0,   0,   0,   20,  20,  //
+    20,  30,  10,  0,   0,   10,  30,  20,  //
+};
+
 int ScoreMove(const Game *board, const Move &move) {
   int score = 0;
 
@@ -94,18 +117,22 @@ int ScoreMove(const Game *board, const Move &move) {
   return score;
 }
 
+std::vector<Move> GetSortedLegalMoves(Game *g) {
+  auto moves = GetLegalMoves(g);
+  std::sort(moves.begin(), moves.end(), [&](const Move &a, const Move &c) {
+    return ScoreMove(g, a) > ScoreMove(g, c);
+  });
+  return moves;
+}
+
 Move EngineGetBestMove(Game *b) {
-  auto moves = GetLegalMoves(b);
+  auto moves = GetSortedLegalMoves(b);
   if (moves.size() == 0) {
     std::cout << "Expected a position with legal moves";
     assert(false && "Unhanled error zero legal moves for bot");
     exit(1);
   }
 
-  // sort legal moves
-  std::sort(moves.begin(), moves.end(), [&](const Move &a, const Move &c) {
-    return ScoreMove(b, a) > ScoreMove(b, c);
-  });
   Move bestMove = moves[0];
   float BestEval = (b->turn ? -INFINITY : INFINITY);
   for (Move move : moves) {
@@ -140,7 +167,7 @@ float minimax(int depth, Game *b, float alpha, float beta) {
     }
   }
 
-  auto moves = GetLegalMoves(b);
+  auto moves = GetSortedLegalMoves(b);
   if (depth == 0 || moves.size() == 0) {
     return EvaluateBoardForWhite(b, depth);
   }
@@ -185,8 +212,6 @@ int PSTIndex(int square, bool white) { return white ? square : (56 ^ square); }
 float EvaluateBoardForWhite(Game *b, int depth) {
   float score = 0;
 
-  bool isStaleMate = false;
-
   if (b->state == WHITE_WON) {
     return MATE + depth;
   }
@@ -194,7 +219,7 @@ float EvaluateBoardForWhite(Game *b, int depth) {
     return -MATE - depth;
   }
   if (b->state == STALEMATE || b->state == DRAW) {
-    isStaleMate = true;
+    return 0;
   }
 
   for (int i = 0; i < 64; i++) {
@@ -223,6 +248,10 @@ float EvaluateBoardForWhite(Game *b, int depth) {
       break;
     case QUEEN:
       value = QUEEN_VALUE;
+      value += QUEEN_TABLE[PSTIndex(i, piece.color)];
+      break;
+    case KING:
+      value = KING_TABLE_EARLY[PSTIndex(i, piece.color)];
       break;
     default:
       break;
@@ -233,13 +262,11 @@ float EvaluateBoardForWhite(Game *b, int depth) {
     else
       score -= value;
   }
-  if (IsPieceTypeAttacked(b, KING, true))
+  if (IsPieceTypeAttacked(b, KING, true)) {
     score -= CHECK; // white king attacked
-
-  if (IsPieceTypeAttacked(b, KING, false))
+  }
+  if (IsPieceTypeAttacked(b, KING, false)) {
     score += CHECK; // black king attacked
-  if (isStaleMate) {
-    return 0;
   }
   return score;
 }
diff --git a/src/bot.hpp b/src/bot.hpp
index b95822f..26ae9f2 100644
--- a/src/bot.hpp
+++ b/src/bot.hpp
@@ -2,8 +2,10 @@
 #define SRC_BOT_H_
 
 #include "board.hpp"
+#include <vector>
 Move EngineGetBestMove(Game *b);
 float EvaluateBoardForWhite(Game *b, int depth);
 float minimax(int depth, Game *b, float alpha, float beta);
 int ScoreMove(const Game *board, const Move &move);
+std::vector<Move> GetSortedLegalMoves(Game *g);
 #endif /* SRC_BOT_H_ */