Reduce memory consumption of continuation history

No functional change for standard chess.

diff --git a/src/movepick.cpp b/src/movepick.cpp
index a70785e..663c9ac 100644 (file)
--- a/src/movepick.cpp
+++ b/src/movepick.cpp
@@ -22,6 +22,10 @@
 
 #include "movepick.h"
 
+int history_slot(Piece pc) {
+    return pc == NO_PIECE ? 0 : (type_of(pc) == KING ? PIECE_SLOTS - 1 : type_of(pc) % (PIECE_SLOTS - 1)) + color_of(pc) * PIECE_SLOTS;
+}
+
 namespace {
 
   enum Stages {
@@ -112,10 +116,10 @@ void MovePicker::score() {
 
       else if (Type == QUIETS)
           m.value =  (*mainHistory)[pos.side_to_move()][from_to(m)]
-                   + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
-                   + (*continuationHistory[1])[pos.moved_piece(m)][to_sq(m)]
-                   + (*continuationHistory[3])[pos.moved_piece(m)][to_sq(m)]
-                   + (*continuationHistory[5])[pos.moved_piece(m)][to_sq(m)] / 2;
+                   + (*continuationHistory[0])[history_slot(pos.moved_piece(m))][to_sq(m)]
+                   + (*continuationHistory[1])[history_slot(pos.moved_piece(m))][to_sq(m)]
+                   + (*continuationHistory[3])[history_slot(pos.moved_piece(m))][to_sq(m)]
+                   + (*continuationHistory[5])[history_slot(pos.moved_piece(m))][to_sq(m)] / 2;
 
       else // Type == EVASIONS
       {
@@ -124,7 +128,7 @@ void MovePicker::score() {
                        - Value(type_of(pos.moved_piece(m)));
           else
               m.value =  (*mainHistory)[pos.side_to_move()][from_to(m)]
-                       + (*continuationHistory[0])[pos.moved_piece(m)][to_sq(m)]
+                       + (*continuationHistory[0])[history_slot(pos.moved_piece(m))][to_sq(m)]
                        - (1 << 28);
       }
 }

diff --git a/src/movepick.h b/src/movepick.h
index 5513d22..b42b4c6 100644 (file)
--- a/src/movepick.h
+++ b/src/movepick.h
@@ -79,7 +79,7 @@ template <typename T, int D, int Size>
 struct Stats<T, D, Size> : public std::array<StatsEntry<T, D>, Size> {};
 
 /// In stats table, D=0 means that the template parameter is not used
-enum StatsParams { NOT_USED = 0 };
+enum StatsParams { NOT_USED = 0, PIECE_SLOTS = 8 };
 
 
 /// ButterflyHistory records how often quiet moves have been successful or
@@ -101,8 +101,9 @@ typedef Stats<int16_t, 29952, PIECE_NB, SQUARE_NB> PieceToHistory;
 /// ContinuationHistory is the combined history of a given pair of moves, usually
 /// the current one given a previous one. The nested history table is based on
 /// PieceToHistory instead of ButterflyBoards.
-typedef Stats<PieceToHistory, NOT_USED, PIECE_NB, SQUARE_NB> ContinuationHistory;
+typedef Stats<PieceToHistory, NOT_USED, 2 * PIECE_SLOTS, SQUARE_NB> ContinuationHistory;
 
+int history_slot(Piece pc);
 
 /// MovePicker class is used to pick one pseudo legal move at a time from the
 /// current position. The most important method is next_move(), which returns a

diff --git a/src/search.cpp b/src/search.cpp
index c34e380..8083a9e 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -826,7 +826,7 @@ namespace {
                 probCutCount++;
 
                 ss->currentMove = move;
-                ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)];
+                ss->continuationHistory = &thisThread->continuationHistory[history_slot(pos.moved_piece(move))][to_sq(move)];
 
                 assert(depth >= 5 * ONE_PLY);
 
@@ -998,8 +998,8 @@ moves_loop: // When in check, search starts from here
 
               // Countermoves based pruning (~20 Elo)
               if (   lmrDepth < 3 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1)
-                  && (*contHist[0])[movedPiece][to_sq(move)] < CounterMovePruneThreshold
-                  && (*contHist[1])[movedPiece][to_sq(move)] < CounterMovePruneThreshold)
+                  && (*contHist[0])[history_slot(movedPiece)][to_sq(move)] < CounterMovePruneThreshold
+                  && (*contHist[1])[history_slot(movedPiece)][to_sq(move)] < CounterMovePruneThreshold)
                   continue;
 
               // Futility pruning: parent node (~2 Elo)
@@ -1031,7 +1031,7 @@ moves_loop: // When in check, search starts from here
 
       // Update the current move (this must be done after singular extension search)
       ss->currentMove = move;
-      ss->continuationHistory = &thisThread->continuationHistory[movedPiece][to_sq(move)];
+      ss->continuationHistory = &thisThread->continuationHistory[history_slot(movedPiece)][to_sq(move)];
 
       // Step 15. Make the move
       pos.do_move(move, st, givesCheck);
@@ -1075,9 +1075,9 @@ moves_loop: // When in check, search starts from here
                   r -= 2 * ONE_PLY;
 
               ss->statScore =  thisThread->mainHistory[us][from_to(move)]
-                             + (*contHist[0])[movedPiece][to_sq(move)]
-                             + (*contHist[1])[movedPiece][to_sq(move)]
-                             + (*contHist[3])[movedPiece][to_sq(move)]
+                             + (*contHist[0])[history_slot(movedPiece)][to_sq(move)]
+                             + (*contHist[1])[history_slot(movedPiece)][to_sq(move)]
+                             + (*contHist[3])[history_slot(movedPiece)][to_sq(move)]
                              - 4000;
 
               // Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
@@ -1420,7 +1420,7 @@ moves_loop: // When in check, search starts from here
       }
 
       ss->currentMove = move;
-      ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)];
+      ss->continuationHistory = &thisThread->continuationHistory[history_slot(pos.moved_piece(move))][to_sq(move)];
 
       // Make and search the move
       pos.do_move(move, st, givesCheck);
@@ -1507,7 +1507,7 @@ moves_loop: // When in check, search starts from here
 
     for (int i : {1, 2, 4, 6})
         if (is_ok((ss-i)->currentMove))
-            (*(ss-i)->continuationHistory)[pc][to] << bonus;
+            (*(ss-i)->continuationHistory)[history_slot(pc)][to] << bonus;
   }