Merge pull request #12 from Dannyj1/late-move-reduction

Late move reduction ELO | 7.96 +- 4.98 (95%) SPRT | 10.0+0.10s Threads=1 Hash=64MB LLR | 2.96 (-2.94, 2.94) [0.00, 3.00] GAMES | N: 16448 W: 7443 L: 7066 D: 1939 Bench: 5504456
Dannyj1 · Jan 25, 2023 · 9dff520 · 9dff520
2 parents 530b135 + 4b8aa3d
commit 9dff520
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Showing 3 changed files with 38 additions and 1 deletion.
diff --git a/src/movepicker.cpp b/src/movepicker.cpp
@@ -53,4 +53,12 @@ namespace Zagreus {
     int MovePicker::size() {
         return moveList.size;
     }
+
+    int MovePicker::remaining() {
+        return moveList.size - searchStartIndex;
+    }
+
+    int MovePicker::movesSearched() {
+        return searchStartIndex;
+    }
 }
diff --git a/src/movepicker.h b/src/movepicker.h
@@ -39,5 +39,8 @@ namespace Zagreus {
 
         int size();
 
+        int remaining();
+
+        int movesSearched();
     };
 }
diff --git a/src/search.cpp b/src/search.cpp
@@ -157,6 +157,7 @@ namespace Zagreus {
         return bestMove;
     }
 
+    // TODO: use template
     int SearchManager::search(Bitboard &board, int depth, int alpha, int beta, Move &rootMove,
                                        Move &previousMove,
                                        std::chrono::time_point<std::chrono::high_resolution_clock> &endTime, Line &pvLine, ZagreusEngine &engine, bool isPv) {
@@ -241,6 +242,16 @@ namespace Zagreus {
             return ttScore;
         }
 
+        bool isOwnKingInCheck = false;
+
+        if (depth >= 3) {
+            if (board.getMovingColor() == PieceColor::WHITE) {
+                isOwnKingInCheck = board.isKingInCheck<PieceColor::WHITE>();
+            } else {
+                isOwnKingInCheck = board.isKingInCheck<PieceColor::BLACK>();
+            }
+        }
+
         while (moves.hasNext()) {
             if (searchStats.nodes % 2048 == 0 && (engine.stopRequested() || std::chrono::high_resolution_clock::now() > endTime)) {
                 return beta;
@@ -262,8 +273,23 @@ namespace Zagreus {
                 }
             }
 
+            int depthReduction = 0;
+            bool isOpponentKingInCheck = false;
+
+            if (depth >= 3) {
+                if (board.getMovingColor() == PieceColor::WHITE) {
+                    isOpponentKingInCheck = board.isKingInCheck<PieceColor::WHITE>();
+                } else {
+                    isOpponentKingInCheck = board.isKingInCheck<PieceColor::BLACK>();
+                }
+            }
+
+            if (depth >= 3 && move.captureScore != -1 && move.promotionPiece == PieceType::EMPTY && !isOwnKingInCheck && !isOpponentKingInCheck) {
+                depthReduction = depth / 2;
+            }
+
             int score;
-            score = search(board, depth - 1, -alpha - 1, -alpha, rootMove, previousMove, endTime, line, engine, false);
+            score = search(board, depth - 1 - depthReduction, -alpha - 1, -alpha, rootMove, previousMove, endTime, line, engine, false);
             score *= -1;
 
             if (score > alpha && score < beta) {