Introduce pawn structure based history

[stockfish] / src / position.cpp

diff --git a/src/position.cpp b/src/position.cpp
index 37c586abbaa537771fdef27a195ee2945707acf0..2bb47871555a3279c082b5432798d040569b508e 100644 (file)
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -49,7 +49,7 @@ namespace Zobrist {
 Key psq[PIECE_NB][SQUARE_NB];
 Key enpassant[FILE_NB];
 Key castling[CASTLING_RIGHT_NB];
-Key side;
+Key side, noPawns;
 }
 
 namespace {
@@ -128,7 +128,8 @@ void Position::init() {
     for (int cr = NO_CASTLING; cr <= ANY_CASTLING; ++cr)
         Zobrist::castling[cr] = rng.rand<Key>();
 
-    Zobrist::side = rng.rand<Key>();
+    Zobrist::side    = rng.rand<Key>();
+    Zobrist::noPawns = rng.rand<Key>();
 
     // Prepare the cuckoo tables
     std::memset(cuckoo, 0, sizeof(cuckoo));
@@ -337,6 +338,7 @@ void Position::set_check_info() const {
 void Position::set_state() const {
 
     st->key = st->materialKey  = 0;
+    st->pawnKey                = Zobrist::noPawns;
     st->nonPawnMaterial[WHITE] = st->nonPawnMaterial[BLACK] = VALUE_ZERO;
     st->checkersBB = attackers_to(square<KING>(sideToMove)) & pieces(~sideToMove);
 
@@ -348,7 +350,10 @@ void Position::set_state() const {
         Piece  pc = piece_on(s);
         st->key ^= Zobrist::psq[pc][s];
 
-        if (type_of(pc) != KING && type_of(pc) != PAWN)
+        if (type_of(pc) == PAWN)
+            st->pawnKey ^= Zobrist::psq[pc][s];
+
+        else if (type_of(pc) != KING)
             st->nonPawnMaterial[color_of(pc)] += PieceValue[pc];
     }
 
@@ -728,6 +733,8 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
                 assert(piece_on(to) == NO_PIECE);
                 assert(piece_on(capsq) == make_piece(them, PAWN));
             }
+
+            st->pawnKey ^= Zobrist::psq[captured][capsq];
         }
         else
             st->nonPawnMaterial[them] -= PieceValue[captured];
@@ -806,6 +813,7 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
 
             // Update hash keys
             k ^= Zobrist::psq[pc][to] ^ Zobrist::psq[promotion][to];
+            st->pawnKey ^= Zobrist::psq[pc][to];
             st->materialKey ^=
               Zobrist::psq[promotion][pieceCount[promotion] - 1] ^ Zobrist::psq[pc][pieceCount[pc]];
 
@@ -813,6 +821,9 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
             st->nonPawnMaterial[us] += PieceValue[promotion];
         }
 
+        // Update pawn hash key
+        st->pawnKey ^= Zobrist::psq[pc][from] ^ Zobrist::psq[pc][to];
+
         // Reset rule 50 draw counter
         st->rule50 = 0;
     }