Simplify advanced pawn push pruning

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 959ccd8431cfba2e96cdf98ccfed8f1119c8cc62..2b7ab39678e7c461e224a0c0c7583af0812dfc41 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -126,6 +126,11 @@ namespace {
     S(0, 0), S(10, 28), S(17, 33), S(15, 41), S(62, 72), S(168, 177), S(276, 260)
   };
 
+  // OutpostRank[Rank] contains a bonus according to the rank of the outpost
+  constexpr Score OutpostRank[RANK_NB] = {
+    S(0, 0), S(0, 0), S(0, 0), S(28, 18), S(30, 24), S(32, 19)
+  };
+
   // Assorted bonuses and penalties
   constexpr Score BishopPawns        = S(  3,  7);
   constexpr Score CorneredBishop     = S( 50, 50);
@@ -237,7 +242,7 @@ namespace {
     // Init our king safety tables
     Square s = make_square(clamp(file_of(ksq), FILE_B, FILE_G),
                            clamp(rank_of(ksq), RANK_2, RANK_7));
-    kingRing[Us] = PseudoAttacks[KING][s] | s;
+    kingRing[Us] = s | PseudoAttacks[KING][s];
 
     kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
     kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
@@ -291,8 +296,8 @@ namespace {
         {
             // Bonus if piece is on an outpost square or can reach one
             bb = OutpostRanks & attackedBy[Us][PAWN] & ~pe->pawn_attacks_span(Them);
-            if (bb & s)
-                score += Outpost * (Pt == KNIGHT ? 2 : 1);
+            if (s & bb)
+                score += OutpostRank[relative_rank(Us, s)] * (Pt == KNIGHT ? 2 : 1);
 
             else if (Pt == KNIGHT && bb & b & ~pos.pieces(Us))
                 score += Outpost;
@@ -375,7 +380,7 @@ namespace {
     constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
                                            : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
 
-    Bitboard weak, b1, b2, safe, unsafeChecks = 0;
+    Bitboard weak, b1, b2, b3, safe, unsafeChecks = 0;
     Bitboard rookChecks, queenChecks, bishopChecks, knightChecks;
     int kingDanger = 0;
     const Square ksq = pos.square<KING>(Us);
@@ -434,19 +439,22 @@ namespace {
     else
         unsafeChecks |= knightChecks;
 
-    // Find the squares that opponent attacks in our king flank, and the squares
-    // which are attacked twice in that flank.
+    // Find the squares that opponent attacks in our king flank, the squares
+    // which they attack twice in that flank, and the squares that we defend.
     b1 = attackedBy[Them][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
     b2 = b1 & attackedBy2[Them];
+    b3 = attackedBy[Us][ALL_PIECES] & KingFlank[file_of(ksq)] & Camp;
 
-    int kingFlankAttacks = popcount(b1) + popcount(b2);
+    int kingFlankAttack = popcount(b1) + popcount(b2);
+    int kingFlankDefense = popcount(b3);
 
     kingDanger +=        kingAttackersCount[Them] * kingAttackersWeight[Them]
                  + 185 * popcount(kingRing[Us] & weak)
                  + 148 * popcount(unsafeChecks)
                  +  98 * popcount(pos.blockers_for_king(Us))
                  +  69 * kingAttacksCount[Them]
-                 +   3 * kingFlankAttacks * kingFlankAttacks / 8
+                 +   4 * (kingFlankAttack - kingFlankDefense)
+                 +   3 * kingFlankAttack * kingFlankAttack / 8
                  +       mg_value(mobility[Them] - mobility[Us])
                  - 873 * !pos.count<QUEEN>(Them)
                  - 100 * bool(attackedBy[Us][KNIGHT] & attackedBy[Us][KING])
@@ -463,7 +471,7 @@ namespace {
         score -= PawnlessFlank;
 
     // Penalty if king flank is under attack, potentially moving toward the king
-    score -= FlankAttacks * kingFlankAttacks;
+    score -= FlankAttacks * kingFlankAttack;
 
     if (T)
         Trace::add(KING, Us, score);
@@ -713,10 +721,10 @@ namespace {
     int complexity =   9 * pe->passed_count()
                     + 11 * pos.count<PAWN>()
                     +  9 * outflanking
-                    + 18 * pawnsOnBothFlanks
-                    + 49 * !pos.non_pawn_material()
-                    - 36 * almostUnwinnable
-                    -103 ;
+                    + 21 * pawnsOnBothFlanks
+                    + 51 * !pos.non_pawn_material()
+                    - 43 * almostUnwinnable
+                    - 95 ;
 
     // Now apply the bonus: note that we find the attacking side by extracting the
     // sign of the midgame or endgame values, and that we carefully cap the bonus