Speedup see()

And rename next_attacker() SEE helper

This very simple patch is able to speed up
bench run of almost 2% !

No functional change.

diff --git a/src/position.cpp b/src/position.cpp
index ad7ed3d915b7913e76a0f7a7e51ecce342f59356..0c81763155d078275263430b17b4a044269daeab 100644 (file)
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -59,17 +59,18 @@ Key Position::exclusion_key() const { return st->key ^ Zobrist::exclusion;}
 
 namespace {
 
 
 namespace {
 

-// next_attacker() is an helper function used by see() to locate the least
+// min_attacker() is an helper function used by see() to locate the least

 // valuable attacker for the side to move, remove the attacker we just found
 // valuable attacker for the side to move, remove the attacker we just found

-// from the 'occupied' bitboard and scan for new X-ray attacks behind it.
+// from the bitboards and scan for new X-ray attacks behind it.

 
 template<int Pt> FORCE_INLINE
 
 template<int Pt> FORCE_INLINE

-PieceType next_attacker(const Bitboard* bb, const Square& to, const Bitboard& stmAttackers,
-                        Bitboard& occupied, Bitboard& attackers) {
+PieceType min_attacker(const Bitboard* bb, const Square& to, const Bitboard& stmAttackers,
+                       Bitboard& occupied, Bitboard& attackers) {

 
 

-  if (stmAttackers & bb[Pt])
+  Bitboard b = stmAttackers & bb[Pt];
+
+  if (b)

   {
   {

-      Bitboard b = stmAttackers & bb[Pt];

       occupied ^= b & ~(b - 1);
 
       if (Pt == PAWN || Pt == BISHOP || Pt == QUEEN)
       occupied ^= b & ~(b - 1);
 
       if (Pt == PAWN || Pt == BISHOP || Pt == QUEEN)


@@ -78,13 +79,15 @@ PieceType next_attacker(const Bitboard* bb, const Square& to, const Bitboard& st
       if (Pt == ROOK || Pt == QUEEN)
           attackers |= attacks_bb<ROOK>(to, occupied) & (bb[ROOK] | bb[QUEEN]);
 
       if (Pt == ROOK || Pt == QUEEN)
           attackers |= attacks_bb<ROOK>(to, occupied) & (bb[ROOK] | bb[QUEEN]);
 

+      attackers &= occupied; // Remove the just found attacker
+

       return (PieceType)Pt;
   }
       return (PieceType)Pt;
   }

-  return next_attacker<Pt+1>(bb, to, stmAttackers, occupied, attackers);
+  return min_attacker<Pt+1>(bb, to, stmAttackers, occupied, attackers);

 }
 
 template<> FORCE_INLINE
 }
 
 template<> FORCE_INLINE

-PieceType next_attacker<KING>(const Bitboard*, const Square&, const Bitboard&, Bitboard&, Bitboard&) {
+PieceType min_attacker<KING>(const Bitboard*, const Square&, const Bitboard&, Bitboard&, Bitboard&) {

   return KING; // No need to update bitboards, it is the last cycle
 }
 
   return KING; // No need to update bitboards, it is the last cycle
 }
 


@@ -1198,10 +1201,8 @@ int Position::see(Move m, int asymmThreshold) const {
       swapList[slIndex] = -swapList[slIndex - 1] + PieceValue[MG][captured];
       slIndex++;
 
       swapList[slIndex] = -swapList[slIndex - 1] + PieceValue[MG][captured];
       slIndex++;
 

-      // Locate and remove from 'occupied' the next least valuable attacker
-      captured = next_attacker<PAWN>(byTypeBB, to, stmAttackers, occupied, attackers);
-
-      attackers &= occupied; // Remove the just found attacker
+      // Locate and remove the next least valuable attacker
+      captured = min_attacker<PAWN>(byTypeBB, to, stmAttackers, occupied, attackers);

       stm = ~stm;
       stmAttackers = attackers & pieces(stm);
 
       stm = ~stm;
       stmAttackers = attackers & pieces(stm);