Explicitly use delta psqt values when possible

Instead of add and subtract pqst values corrisponding to
the move starting and destination squares, do it in one
go with the helper function pst_delta<>()

This simplifies the code and also better documents that what
we need is a delta value, not an absolute one.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/movepick.cpp

@@ -268,20 +268,23 @@ void MovePicker::score_noncaptures() {
   // First score by history, when no history is available then use
   // piece/square tables values. This seems to be better then a
   // random choice when we don't have an history for any move.
-  Move m;
+  Piece piece;
+  Square from, to;
   int hs;
 
   for (int i = 0; i < numOfMoves; i++)
   {
-      m = moves[i].move;
+      from = move_from(moves[i].move);
-      hs = H.move_ordering_score(pos.piece_on(move_from(m)), move_to(m));
+      to = move_to(moves[i].move);
+      piece = pos.piece_on(from);
+      hs = H.move_ordering_score(piece, to);
 
       // Ensure history is always preferred to pst
       if (hs > 0)
           hs += 1000;
 
       // pst based scoring
-      moves[i].score = hs + pos.mg_pst_delta(m);
+      moves[i].score = hs + pos.pst_delta<Position::MidGame>(piece, from, to);
   }
 }
 

src/position.cpp

@@ -735,7 +735,8 @@ void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
     assert(color_of_piece_on(from) == us);
     assert(color_of_piece_on(to) == them || piece_on(to) == EMPTY);
 
-    PieceType piece = type_of_piece_on(from);
+    Piece piece = piece_on(from);
+    PieceType pt = type_of_piece(piece);
 
     st->capture = type_of_piece_on(to);
 
@@ -745,23 +746,21 @@ void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
     // Move the piece
     Bitboard move_bb = make_move_bb(from, to);
     do_move_bb(&(byColorBB[us]), move_bb);
-    do_move_bb(&(byTypeBB[piece]), move_bb);
+    do_move_bb(&(byTypeBB[pt]), move_bb);
     do_move_bb(&(byTypeBB[0]), move_bb); // HACK: byTypeBB[0] == occupied squares
 
     board[to] = board[from];
     board[from] = EMPTY;
 
     // Update hash key
-    st->key ^= zobrist[us][piece][from] ^ zobrist[us][piece][to];
+    st->key ^= zobrist[us][pt][from] ^ zobrist[us][pt][to];
 
     // Update incremental scores
-    st->mgValue -= pst<MidGame>(us, piece, from);
+    st->mgValue += pst_delta<MidGame>(piece, from, to);
-    st->mgValue += pst<MidGame>(us, piece, to);
+    st->egValue += pst_delta<EndGame>(piece, from, to);
-    st->egValue -= pst<EndGame>(us, piece, from);
-    st->egValue += pst<EndGame>(us, piece, to);
 
     // If the moving piece was a king, update the king square
-    if (piece == KING)
+    if (pt == KING)
         kingSquare[us] = to;
 
     // Reset en passant square
@@ -772,7 +771,7 @@ void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
     }
 
     // If the moving piece was a pawn do some special extra work
-    if (piece == PAWN)
+    if (pt == PAWN)
     {
         // Reset rule 50 draw counter
         st->rule50 = 0;
@@ -793,7 +792,7 @@ void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
     }
 
     // Update piece lists
-    pieceList[us][piece][index[from]] = to;
+    pieceList[us][pt][index[from]] = to;
     index[to] = index[from];
 
     // Update castle rights, try to shortcut a common case
@@ -808,7 +807,7 @@ void Position::do_move(Move m, StateInfo& newSt, Bitboard dcCandidates) {
     // Update checkers bitboard, piece must be already moved
     st->checkersBB = EmptyBoardBB;
     Square ksq = king_square(them);
-    switch (piece)
+    switch (pt)
     {
     case PAWN:   update_checkers<PAWN>(&(st->checkersBB), ksq, from, to, dcCandidates);   break;
     case KNIGHT: update_checkers<KNIGHT>(&(st->checkersBB), ksq, from, to, dcCandidates); break;
@@ -923,9 +922,11 @@ void Position::do_castle_move(Move m) {
   set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
 
   // Update board array
+  Piece king = piece_of_color_and_type(us, KING);
+  Piece rook = piece_of_color_and_type(us, ROOK);
   board[kfrom] = board[rfrom] = EMPTY;
-  board[kto] = piece_of_color_and_type(us, KING);
+  board[kto] = king;
-  board[rto] = piece_of_color_and_type(us, ROOK);
+  board[rto] = rook;
 
   // Update king square
   kingSquare[us] = kto;
@@ -938,14 +939,10 @@ void Position::do_castle_move(Move m) {
   index[rto] = tmp;
 
   // Update incremental scores
-  st->mgValue -= pst<MidGame>(us, KING, kfrom);
+  st->mgValue += pst_delta<MidGame>(king, kfrom, kto);
-  st->mgValue += pst<MidGame>(us, KING, kto);
+  st->egValue += pst_delta<EndGame>(king, kfrom, kto);
-  st->egValue -= pst<EndGame>(us, KING, kfrom);
+  st->mgValue += pst_delta<MidGame>(rook, rfrom, rto);
-  st->egValue += pst<EndGame>(us, KING, kto);
+  st->egValue += pst_delta<EndGame>(rook, rfrom, rto);
-  st->mgValue -= pst<MidGame>(us, ROOK, rfrom);
-  st->mgValue += pst<MidGame>(us, ROOK, rto);
-  st->egValue -= pst<EndGame>(us, ROOK, rfrom);
-  st->egValue += pst<EndGame>(us, ROOK, rto);
 
   // Update hash key
   st->key ^= zobrist[us][KING][kfrom] ^ zobrist[us][KING][kto];
@@ -1121,12 +1118,11 @@ void Position::do_ep_move(Move m) {
   st->pawnKey ^= zobrist[them][PAWN][capsq];
 
   // Update incremental scores
+  Piece pawn = piece_of_color_and_type(us, PAWN);
+  st->mgValue += pst_delta<MidGame>(pawn, from, to);
+  st->egValue += pst_delta<EndGame>(pawn, from, to);
   st->mgValue -= pst<MidGame>(them, PAWN, capsq);
-  st->mgValue -= pst<MidGame>(us, PAWN, from);
-  st->mgValue += pst<MidGame>(us, PAWN, to);
   st->egValue -= pst<EndGame>(them, PAWN, capsq);
-  st->egValue -= pst<EndGame>(us, PAWN, from);
-  st->egValue += pst<EndGame>(us, PAWN, to);
 
   // Reset en passant square
   st->epSquare = SQ_NONE;

src/position.h

@@ -127,6 +127,11 @@ class Position {
   friend class EndgameFunctions;
 
 public:
+  enum GamePhase {
+      MidGame,
+      EndGame
+  };
+
   // Constructors
   Position() {};
   Position(const Position& pos);
@@ -272,7 +277,7 @@ public:
   Value eg_value() const;
   Value non_pawn_material(Color c) const;
   Phase game_phase() const;
-  Value mg_pst_delta(Move m) const;
+  template<GamePhase> Value pst_delta(Piece piece, Square from, Square to) const;
 
   // Game termination checks
   bool is_mate() const;
@@ -328,10 +333,6 @@ private:
   Key compute_material_key() const;
 
   // Computing incremental evaluation scores and material counts
-  enum GamePhase {
-      MidGame,
-      EndGame
-  };
   template<GamePhase> Value pst(Color c, PieceType pt, Square s) const;
   template<GamePhase> Value compute_value() const;
   Value compute_non_pawn_material(Color c) const;
@@ -622,15 +623,16 @@ inline Key Position::get_material_key() const {
   return st->materialKey;
 }
 
-template<Position::GamePhase Phase>
+template<Position::GamePhase Ph>
 inline Value Position::pst(Color c, PieceType pt, Square s) const {
-  return (Phase == MidGame ? MgPieceSquareTable[piece_of_color_and_type(c, pt)][s]
+  return (Ph == MidGame ? MgPieceSquareTable[piece_of_color_and_type(c, pt)][s]
                         : EgPieceSquareTable[piece_of_color_and_type(c, pt)][s]);
 }
 
-inline Value Position::mg_pst_delta(Move m) const {
+template<Position::GamePhase Ph>
-  return MgPieceSquareTable[piece_on(move_from(m))][move_to(m)]
+inline Value Position::pst_delta(Piece piece, Square from, Square to) const {
-        -MgPieceSquareTable[piece_on(move_from(m))][move_from(m)];
+  return (Ph == MidGame ? MgPieceSquareTable[piece][to] - MgPieceSquareTable[piece][from]
+                        : EgPieceSquareTable[piece][to] - EgPieceSquareTable[piece][from]);
 }
 
 inline Value Position::mg_value() const {