two very minor move ordering improvement

ankan-ban · ankan-ban · commit c4511c70733d · 2015-02-09T20:01:33.000+05:30
- hardcode for only two killer slots per depth
- prioritize killer move slot
- generate promotions in order: queen, knight, root, bishop
diff --git a/chess.h b/chess.h
@@ -461,6 +461,8 @@ class Game
     // killer moves
     static CMove killers[MAX_GAME_LENGTH][MAX_KILLERS];
 
+    // the code assumes that there are only two killer moves
+    CT_ASSERT(MAX_KILLERS == 2);
 
     // perform alpha-beta search on the given position
     template<uint8 chance>
diff --git a/chess_cpu.exe b/chess_cpu.exe
diff --git a/move_gen.cpp b/move_gen.cpp
@@ -314,10 +314,10 @@ void BitBoardUtils::addCompactPawnMoves(int *nMoves, CMove **genMoves, uint8 fro
     // promotion
     if (dst & (RANK1 | RANK8))
     {
-        addCompactMove(nMoves, genMoves, from, to, flags | CM_FLAG_KNIGHT_PROMOTION);
-        addCompactMove(nMoves, genMoves, from, to, flags | CM_FLAG_BISHOP_PROMOTION);
         addCompactMove(nMoves, genMoves, from, to, flags | CM_FLAG_QUEEN_PROMOTION);
+        addCompactMove(nMoves, genMoves, from, to, flags | CM_FLAG_KNIGHT_PROMOTION);
         addCompactMove(nMoves, genMoves, from, to, flags | CM_FLAG_ROOK_PROMOTION);
+        addCompactMove(nMoves, genMoves, from, to, flags | CM_FLAG_BISHOP_PROMOTION);
     }
     else
     {
diff --git a/search.cpp b/search.cpp
@@ -290,24 +290,10 @@ int16 Game::alphabeta(HexaBitBoardPosition *pos, uint64 hash, int depth, int cur
             // update killer move table if this was a non-capture move
             if (!(ttMove.getFlags() & CM_FLAG_CAPTURE))
             {
-                // TODO: add to the first slot
-
-                bool foundKiller = false;
-                for (int j = 0; j < MAX_KILLERS; j++)
+                if (killers[depth][0] != ttMove)
                 {
-                    if (killers[depth][j] == ttMove)
-                    {
-                        foundKiller = true;
-                        break;
-                    }
-                }
-
-                if (!foundKiller)
-                {
-                    for (int j = 1; j < MAX_KILLERS; j++)
-                        killers[depth][j] = killers[depth][j - 1];
+                    killers[depth][1] = killers[depth][0];
                     killers[depth][0] = ttMove;
-
                 }
             }
 
@@ -390,7 +376,9 @@ int16 Game::alphabeta(HexaBitBoardPosition *pos, uint64 hash, int depth, int cur
     }
 
     // try killers first
-    // also filter out killers and TT move from the list
+    // also filter out killers and TT move from the list 
+    // TODO: no need to generate non captures if we get a cutoff on trying killer moves
+    //       need a move validity checker routine
     for (int i = searched; i < nMoves; i++)
     {
         // filter TT moves
@@ -399,16 +387,9 @@ int16 Game::alphabeta(HexaBitBoardPosition *pos, uint64 hash, int depth, int cur
             newMoves[i] = CMove();
             continue;
         }
-        bool isKiller = false;
 
-        for (int j = 0; j < MAX_KILLERS; j++)
-        {
-            if (killers[depth][j] == newMoves[i])
-            {
-                isKiller = true;
-                break;
-            }
-        }
+        bool isKiller = (killers[depth][0] == newMoves[i]) || 
+                        (killers[depth][1] == newMoves[i]);
 
         if (isKiller)
         {
@@ -419,7 +400,13 @@ int16 Game::alphabeta(HexaBitBoardPosition *pos, uint64 hash, int depth, int cur
             int16 curScore = -alphabeta<!chance>(&newPos, newHash, depth - 1, curPly + 1, -beta, -alpha, true);
             if (curScore >= beta)
             {
-                // TODO: increase priority of this killer
+                // increase priority of this killer
+                if (killers[depth][0] != newMoves[i])
+                {
+                    killers[depth][1] = killers[depth][0];
+                    killers[depth][0] = newMoves[i];
+                }
+
                 TranspositionTable::update(hash, curScore, SCORE_GE, newMoves[i], depth, curPly);
                 return curScore;
             }
@@ -454,8 +441,7 @@ int16 Game::alphabeta(HexaBitBoardPosition *pos, uint64 hash, int depth, int cur
             if (curScore >= beta)
             {
                 // update killer table
-                for (int j = 1; j < MAX_KILLERS; j++)
-                    killers[depth][j] = killers[depth][j - 1];
+                killers[depth][1] = killers[depth][0];
                 killers[depth][0] = newMoves[i];
 
                 TranspositionTable::update(hash, curScore, SCORE_GE, newMoves[i], depth, curPly);

Original file line number	Diff line number	Diff line change
`@@ -314,10 +314,10 @@ void BitBoardUtils::addCompactPawnMoves(int nMoves, CMove *genMoves, uint8 fro`
`314`	`314`	`// promotion`
`315`	`315`	`if (dst & (RANK1 \| RANK8))`
`316`	`316`	`{`
`317`		`- addCompactMove(nMoves, genMoves, from, to, flags \| CM_FLAG_KNIGHT_PROMOTION);`
`318`		`- addCompactMove(nMoves, genMoves, from, to, flags \| CM_FLAG_BISHOP_PROMOTION);`
`319`	`317`	`addCompactMove(nMoves, genMoves, from, to, flags \| CM_FLAG_QUEEN_PROMOTION);`
	`318`	`+ addCompactMove(nMoves, genMoves, from, to, flags \| CM_FLAG_KNIGHT_PROMOTION);`
`320`	`319`	`addCompactMove(nMoves, genMoves, from, to, flags \| CM_FLAG_ROOK_PROMOTION);`
	`320`	`+ addCompactMove(nMoves, genMoves, from, to, flags \| CM_FLAG_BISHOP_PROMOTION);`
`321`	`321`	`}`
`322`	`322`	`else`
`323`	`323`	`{`