Tweak backward pawns definition

[stockfish] / src / pawns.cpp

diff --git a/src/pawns.cpp b/src/pawns.cpp
index c5f1b22c270e2bd40bb7fb2537720a12fa5dcad4..ee46279d8957a757f0877421c003c6df2b2020e5 100644 (file)
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -43,12 +43,8 @@ namespace {
   { S(25, 30), S(36, 35), S(40, 35), S(40, 35),
     S(40, 35), S(40, 35), S(36, 35), S(25, 30) } };
 
-  // Backward pawn penalty by opposed flag and file
-  const Score Backward[2][FILE_NB] = {
-  { S(30, 42), S(43, 46), S(49, 46), S(49, 46),
-    S(49, 46), S(49, 46), S(43, 46), S(30, 42) },
-  { S(20, 28), S(29, 31), S(33, 31), S(33, 31),
-    S(33, 31), S(33, 31), S(29, 31), S(20, 28) } };
+  // Backward pawn penalty by opposed flag
+  const Score Backward[2] = { S(67, 42), S(49, 24) };
 
   // Connected pawn bonus by opposed, phalanx, twice supported and rank
   Score Connected[2][2][2][RANK_NB];
@@ -110,9 +106,9 @@ namespace {
     const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
     const Square Left  = (Us == WHITE ? DELTA_NW : DELTA_SE);
 
-    Bitboard b, neighbours, doubled, connected, supported, phalanx;
+    Bitboard b, neighbours, doubled, supported, phalanx;
     Square s;
-    bool passed, isolated, opposed, backward, lever;
+    bool passed, isolated, opposed, backward, lever, connected;
     Score score = SCORE_ZERO;
     const Square* pl = pos.list<PAWN>(Us);
     const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)];
@@ -149,11 +145,12 @@ namespace {
         isolated    =  !neighbours;
 
         // Test for backward pawn.
-        // If the pawn is passed, isolated, connected or a lever it cannot be
+        // If the pawn is passed, isolated, lever or connected it cannot be
         // backward. If there are friendly pawns behind on adjacent files
-        // it cannot be backward either.
+        // or if it is sufficiently advanced, it cannot be backward either.
         if (   (passed | isolated | lever | connected)
-            || (ourPawns & pawn_attack_span(Them, s)))
+            || (ourPawns & pawn_attack_span(Them, s))
+            || (relative_rank(Us, s) >= RANK_5))
             backward = false;
         else
         {
@@ -181,18 +178,18 @@ namespace {
         if (isolated)
             score -= Isolated[opposed][f];
 
-        if (!supported && !isolated)
-            score -= UnsupportedPawnPenalty;
-
-        if (doubled)
-            score -= Doubled[f] / distance<Rank>(s, frontmost_sq(Us, doubled));
+        else if (backward)
+            score -= Backward[opposed];
 
-        if (backward)
-            score -= Backward[opposed][f];
+        else if (!supported)
+            score -= UnsupportedPawnPenalty;
 
         if (connected)
             score += Connected[opposed][!!phalanx][more_than_one(supported)][relative_rank(Us, s)];
 
+        if (doubled)
+            score -= Doubled[f] / distance<Rank>(s, frontmost_sq(Us, doubled));
+
         if (lever)
             score += Lever[relative_rank(Us, s)];
     }
@@ -294,14 +291,14 @@ Score Entry::do_king_safety(const Position& pos, Square ksq) {
 
   kingSquares[Us] = ksq;
   castlingRights[Us] = pos.can_castle(Us);
-  minKingPawnDistance[Us] = 0;
+  int minKingPawnDistance = 0;
 
   Bitboard pawns = pos.pieces(Us, PAWN);
   if (pawns)
-      while (!(DistanceRingBB[ksq][minKingPawnDistance[Us]++] & pawns)) {}
+      while (!(DistanceRingBB[ksq][minKingPawnDistance++] & pawns)) {}
 
   if (relative_rank(Us, ksq) > RANK_4)
-      return make_score(0, -16 * minKingPawnDistance[Us]);
+      return make_score(0, -16 * minKingPawnDistance);
 
   Value bonus = shelter_storm<Us>(pos, ksq);
 
@@ -312,7 +309,7 @@ Score Entry::do_king_safety(const Position& pos, Square ksq) {
   if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
       bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
 
-  return make_score(bonus, -16 * minKingPawnDistance[Us]);
+  return make_score(bonus, -16 * minKingPawnDistance);
 }
 
 // Explicit template instantiation