Remove SEE optimizations

Don't seem to help, perhaps because we
return an approximate SEE score instead of the
real negative score so that we have some bad capture
or evasion sub-optimal ordering that compensates
the speed up.

Anyhow after 999 games at 1+0
Mod vs Orig +240 =514 -245 -2 ELO

So almost no harm to remove and make the code simpler.

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

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 82edeec8ac0c43b666ea6df70d728da0989b62b9..fd0ef5b22cd558f9873560edc1e45b93b3e0eef1 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -1171,8 +1171,8 @@ namespace {
     Square b8 = relative_square(us, (square_file(s) == FILE_A) ? SQ_B8 : SQ_G8);
 
     if (   pos.piece_on(b6) == piece_of_color_and_type(opposite_color(us), PAWN)
-        && pos.see(s, b6, false) < 0
-        && pos.see(s, b8, false) < 0)
+        && pos.see(s, b6) < 0
+        && pos.see(s, b8) < 0)
     {
         ei.mgValue -= Sign[us] * TrappedBishopA7H7Penalty;
         ei.egValue -= Sign[us] * TrappedBishopA7H7Penalty;

diff --git a/src/position.cpp b/src/position.cpp
index 1fe723aec461e20a303582484349b9696ca9c552..4a0075cb841845bff231bd8a8091404b16ea7b5e 100644 (file)
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -1300,13 +1300,13 @@ void Position::undo_null_move() {
 int Position::see(Square to) const {
 
   assert(square_is_ok(to));
-  return see(SQ_NONE, to, false);
+  return see(SQ_NONE, to);
 }
 
 int Position::see(Move m) const {
 
   assert(move_is_ok(m));
-  return see(move_from(m), move_to(m), false);
+  return see(move_from(m), move_to(m));
 }
 
 int Position::see_sign(Move m) const {
@@ -1322,10 +1322,10 @@ int Position::see_sign(Move m) const {
       && type_of_piece_on(from) != KING)
          return 1;
 
-  return see(from, to, true);
+  return see(from, to);
 }
 
-int Position::see(Square from, Square to, bool shortcut) const {
+int Position::see(Square from, Square to) const {
 
   // Material values
   static const int seeValues[18] = {
@@ -1337,7 +1337,6 @@ int Position::see(Square from, Square to, bool shortcut) const {
   };
 
   Bitboard attackers, stmAttackers, b;
-  int pieceDiff = 0;
 
   assert(!shortcut || from != SQ_NONE);
   assert(square_is_ok(from) || from == SQ_NONE);
@@ -1356,22 +1355,6 @@ int Position::see(Square from, Square to, bool shortcut) const {
   if (type_of_piece(piece) == KING)
       return seeValues[capture];
 
-  // If captured piece is defended by enemy pawns or knights then SEE is negative
-  // when captured piece value does not compensate the lost of capturing one.
-  if (shortcut)
-  {
-      pieceDiff = seeValues[piece] - seeValues[capture];
-
-      if (   pieceDiff > seeValues[PAWN]
-          &&(attacks_from<PAWN>(to, us) & pieces(PAWN, them)))
-          return -(pieceDiff - seeValues[PAWN] / 2);
-
-      if (   pieceDiff > seeValues[KNIGHT]
-          && pieces(KNIGHT, them)
-          &&(pieces(KNIGHT, them) & attacks_from<KNIGHT>(to)))
-          return -(pieceDiff - seeValues[KNIGHT] / 2);
-  }
-
   // Handle en passant moves
   if (st->epSquare == to && type_of_piece_on(from) == PAWN)
   {
@@ -1442,15 +1425,6 @@ int Position::see(Square from, Square to, bool shortcut) const {
       for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
           assert(pt < KING);
 
-      // If captured piece is defended by an enemy piece then SEE is negative
-      // if captured piece value does not compensate the lost of capturing one.
-      if (pieceDiff > seeValues[pt])
-      {
-          assert(shortcut);
-          return -(pieceDiff - seeValues[pt] / 2);
-      } else
-          pieceDiff = 0; // Only first cycle
-
       // Remove the attacker we just found from the 'attackers' bitboard,
       // and scan for new X-ray attacks behind the attacker.
       b = stmAttackers & pieces(pt);

diff --git a/src/position.h b/src/position.h
index a55d1770fe59d225f550e97b11e75aaabd1c7ced..f2f517e219445a601f4d90690572cb1a40e1b288 100644 (file)
--- a/src/position.h
+++ b/src/position.h
@@ -229,7 +229,7 @@ public:
   void undo_null_move();
 
   // Static exchange evaluation
-  int see(Square from, Square to, bool shortcut) const;
+  int see(Square from, Square to) const;
   int see(Move m) const;
   int see(Square to) const;
   int see_sign(Move m) const;