Change how TT is handled in qSearch

Bench: 18354635

Author: Dannyj1

src/board.h

@@ -560,5 +560,36 @@ class Board {
             return blackPawns & ~combinedSpans;
         }
     }
+
+    template <PieceColor color>
+    [[nodiscard]] uint64_t promotionCandidates() const {
+        if (color == WHITE) {
+            const uint64_t whitePawns = getPieceBoard<WHITE_PAWN>();
+
+            return whitePawns & RANK_7;
+        } else {
+            const uint64_t blackPawns = getPieceBoard<BLACK_PAWN>();
+
+            return blackPawns & RANK_2;
+        }
+    }
+
+    template <PieceColor color>
+    [[nodiscard]] Piece getHighestValuePiece() const {
+        // Get the highest value piece on the board for color
+        constexpr Piece startingPiece = color == WHITE ? WHITE_QUEEN : BLACK_QUEEN;
+        constexpr Piece endingPiece = color == WHITE ? WHITE_PAWN : BLACK_PAWN;
+
+        for (int pieceIndex = startingPiece; pieceIndex >= endingPiece; pieceIndex -= 2) {
+            const Piece piece = static_cast<Piece>(pieceIndex);
+
+            if (getPieceBoard(piece)) {
+                return piece;
+            }
+        }
+
+        assert(false);
+        return EMPTY;
+    }
 };
 }  // namespace Zagreus

src/search.cpp

@@ -200,7 +200,7 @@ int pvSearch(Engine& engine, Board& board, int alpha, int beta, int depth, Searc
 #ifdef TRACE_SEARCH
     stats.ttProbes++;
 
-    if (ttScore != NO_TT_SCORE) {
+    if (ttEntry) {
         stats.ttHits++;
     }
 #endif
@@ -500,6 +500,7 @@ int qSearch(Engine& engine, Board& board, int alpha, int beta, int depth, Search
             const std::chrono::time_point<std::chrono::steady_clock>& endTime, SearchStack& searchStack) {
     assert(nodeType != ROOT);
     constexpr bool isPV = nodeType == PV;
+    constexpr PieceColor opponentColor = !color;
 
     if (board.isDraw()) {
         return DRAW_SCORE;
@@ -512,30 +513,29 @@ int qSearch(Engine& engine, Board& board, int alpha, int beta, int depth, Search
         }
     }
 
-    if (!isPV) {
-        TTEntry* ttEntry = nullptr;
-        const int16_t score = tt->probePosition(board.getZobristHash(), depth, alpha, beta, board.getPly(), ttEntry);
-
 #ifdef TRACE_SEARCH
-        stats.qTtProbes++;
-#endif
+    stats.qTtProbes++;
 
-        if (score != NO_TT_SCORE) {
-#ifdef TRACE_SEARCH
-            stats.qTtHits++;
+    if (tt->getEntry(board.getZobristHash()) != nullptr) {
+        stats.qTtHits++;
+    }
 #endif
-            return score;
+
+    TTEntry* ttEntry = nullptr;
+    const int16_t ttScore = tt->probePosition(board.getZobristHash(), depth, alpha, beta, board.getPly(), ttEntry);
+
+    if (!isPV) {
+        if (ttScore != NO_TT_SCORE) {
+            return ttScore;
         }
     }
 
     stats.qNodesSearched += 1;
 
     const bool isInCheck = board.isKingInCheck<color>();
-    int bestScore;
+    int bestScore = -MATE_SCORE;
 
-    if (isInCheck) {
-        bestScore = -MATE_SCORE;
-    } else {
+    if (!isInCheck) {
         bestScore = Evaluation(board).evaluate();
 
         // Stand pat
@@ -544,9 +544,16 @@ int qSearch(Engine& engine, Board& board, int alpha, int beta, int depth, Search
 #ifdef TRACE_SEARCH
                 stats.ttWrites++;
 #endif
-                tt->savePosition(board.getZobristHash(), depth, board.getPly(), bestScore, NO_MOVE, BETA);
+
+                if (!ttEntry) {
+                    tt->savePosition(board.getZobristHash(), depth, board.getPly(), bestScore, NO_MOVE, BETA);
+                }
             }
 
+# ifdef TRACE_SEARCH
+            stats.standpatPrunes++;
+# endif
+
             return bestScore;
         }
 
@@ -598,8 +605,7 @@ int qSearch(Engine& engine, Board& board, int alpha, int beta, int depth, Search
 
         legalMoves += 1;
 
-        const int score =
-            -qSearch<!color, nodeType>(engine, board, -beta, -alpha, depth - 1, stats, endTime, searchStack);
+        const int score = -qSearch<!color, nodeType>(engine, board, -beta, -alpha, depth - 1, stats, endTime, searchStack);
 
         board.unmakeMove();
 
@@ -611,14 +617,7 @@ int qSearch(Engine& engine, Board& board, int alpha, int beta, int depth, Search
                 alpha = score;
 
                 if (score >= beta) {
-                    if (!engine.isSearchStopped()) {
-#ifdef TRACE_SEARCH
-                        stats.ttWrites++;
-#endif
-                        tt->savePosition(board.getZobristHash(), depth, board.getPly(), score, move, BETA);
-                    }
-
-                    return score;
+                    break;
                 }
             }
         }
@@ -628,7 +627,7 @@ int qSearch(Engine& engine, Board& board, int alpha, int beta, int depth, Search
         bestScore = -MATE_SCORE + board.getPly();
     }
 
-    const TTNodeType ttNodeType = (isPV && bestMove != NO_MOVE) ? EXACT : ALPHA;
+    const TTNodeType ttNodeType = bestScore >= beta ? BETA : ALPHA;
 
     if (!engine.isSearchStopped()) {
 #ifdef TRACE_SEARCH
@@ -728,6 +727,7 @@ void SearchStats::printTrace(Engine& engine, int numPositions) const {
     printStatLine("Check Extensions", checkExtensions);
 
     ss << "\n--- Quiescence Search ---\n";
+    printStatLine("Standpat Prunes", standpatPrunes);
     printStatLine("SEE Prunes", seePrunes);
 
     ss << "-------------------------";
@@ -755,6 +755,7 @@ SearchStats& SearchStats::operator+=(const SearchStats& other) {
     checkExtensions += other.checkExtensions;
     singularExtensions += other.singularExtensions;
     singularAttempts += other.singularAttempts;
+    standpatPrunes += other.standpatPrunes;
     seePrunes += other.seePrunes;
 
     return *this;

src/search.h

@@ -79,6 +79,7 @@ struct SearchStats {
     uint64_t singularExtensions = 0;
     uint64_t singularAttempts = 0;
     uint64_t seePrunes = 0;
+    uint64_t standpatPrunes = 0;
 
     void clearTrace();
     void printTrace(Engine& engine, int numPositions = 1) const;