Move PSQ score to Position

This patch simplifies Position::do_move() by moving the PSQ score from
StateInfo to Position and updating it inside the put/remove/move_piece
functions.

The downside is that there is now slightly more computation done in
Position::undo_move(), but the fishtest results are Elo neutral.

Passed STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 78820 W: 15775 L: 15760 D: 47285
http://tests.stockfishchess.org/tests/view/5b1cd1d00ebc5902ab9c64ab

Passed LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 32966 W: 5716 L: 5615 D: 21635
http://tests.stockfishchess.org/tests/view/5b31e1230ebc5902b2e5a833

Closes https://github.com/official-stockfish/Stockfish/pull/1647

No functional change.

src/position.cpp

@@ -36,10 +36,6 @@
 
 using std::string;
 
-namespace PSQT {
-  extern Score psq[PIECE_NB][SQUARE_NB];
-}
-
 namespace Zobrist {
 
   Key psq[PIECE_NB][SQUARE_NB];
@@ -381,7 +377,6 @@ void Position::set_state(StateInfo* si) const {
   si->key = si->materialKey = 0;
   si->pawnKey = Zobrist::noPawns;
   si->nonPawnMaterial[WHITE] = si->nonPawnMaterial[BLACK] = VALUE_ZERO;
-  si->psq = SCORE_ZERO;
   si->checkersBB = attackers_to(square<KING>(sideToMove)) & pieces(~sideToMove);
 
   set_check_info(si);
@@ -391,7 +386,6 @@ void Position::set_state(StateInfo* si) const {
       Square s = pop_lsb(&b);
       Piece pc = piece_on(s);
       si->key ^= Zobrist::psq[pc][s];
-      si->psq += PSQT::psq[pc][s];
   }
 
   if (si->epSquare != SQ_NONE)
@@ -752,7 +746,6 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
       Square rfrom, rto;
       do_castling<true>(us, from, to, rfrom, rto);
 
-      st->psq += PSQT::psq[captured][rto] - PSQT::psq[captured][rfrom];
       k ^= Zobrist::psq[captured][rfrom] ^ Zobrist::psq[captured][rto];
       captured = NO_PIECE;
   }
@@ -791,9 +784,6 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
       st->materialKey ^= Zobrist::psq[captured][pieceCount[captured]];
       prefetch(thisThread->materialTable[st->materialKey]);
 
-      // Update incremental scores
-      st->psq -= PSQT::psq[captured][capsq];
-
       // Reset rule 50 counter
       st->rule50 = 0;
   }
@@ -847,9 +837,6 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
           st->materialKey ^=  Zobrist::psq[promotion][pieceCount[promotion]-1]
                             ^ Zobrist::psq[pc][pieceCount[pc]];
 
-          // Update incremental score
-          st->psq += PSQT::psq[promotion][to] - PSQT::psq[pc][to];
-
           // Update material
           st->nonPawnMaterial[us] += PieceValue[MG][promotion];
       }
@@ -862,9 +849,6 @@ void Position::do_move(Move m, StateInfo& newSt, bool givesCheck) {
       st->rule50 = 0;
   }
 
-  // Update incremental scores
-  st->psq += PSQT::psq[pc][to] - PSQT::psq[pc][from];
-
   // Set capture piece
   st->capturedPiece = captured;
 

src/position.h

@@ -43,7 +43,6 @@ struct StateInfo {
   int    castlingRights;
   int    rule50;
   int    pliesFromNull;
-  Score  psq;
   Square epSquare;
 
   // Not copied when making a move (will be recomputed anyhow)
@@ -188,11 +187,16 @@ private:
   Bitboard castlingPath[CASTLING_RIGHT_NB];
   int gamePly;
   Color sideToMove;
+  Score psq;
   Thread* thisThread;
   StateInfo* st;
   bool chess960;
 };
 
+namespace PSQT {
+  extern Score psq[PIECE_NB][SQUARE_NB];
+}
+
 extern std::ostream& operator<<(std::ostream& os, const Position& pos);
 
 inline Color Position::side_to_move() const {
@@ -327,7 +331,7 @@ inline Key Position::material_key() const {
 }
 
 inline Score Position::psq_score() const {
-  return st->psq;
+  return psq;
 }
 
 inline Value Position::non_pawn_material(Color c) const {
@@ -384,6 +388,7 @@ inline void Position::put_piece(Piece pc, Square s) {
   index[s] = pieceCount[pc]++;
   pieceList[pc][index[s]] = s;
   pieceCount[make_piece(color_of(pc), ALL_PIECES)]++;
+  psq += PSQT::psq[pc][s];
 }
 
 inline void Position::remove_piece(Piece pc, Square s) {
@@ -401,6 +406,7 @@ inline void Position::remove_piece(Piece pc, Square s) {
   pieceList[pc][index[lastSquare]] = lastSquare;
   pieceList[pc][pieceCount[pc]] = SQ_NONE;
   pieceCount[make_piece(color_of(pc), ALL_PIECES)]--;
+  psq -= PSQT::psq[pc][s];
 }
 
 inline void Position::move_piece(Piece pc, Square from, Square to) {
@@ -415,6 +421,7 @@ inline void Position::move_piece(Piece pc, Square from, Square to) {
   board[to] = pc;
   index[to] = index[from];
   pieceList[pc][index[to]] = to;
+  psq += PSQT::psq[pc][to] - PSQT::psq[pc][from];
 }
 
 inline void Position::do_move(Move m, StateInfo& newSt) {