Refactor pawns shelter and storm

[stockfish] / src / pawns.cpp

diff --git a/src/pawns.cpp b/src/pawns.cpp
index 950994ef898b4843a869cd22898dbf933ada88e8..41d2e6f8148234d46d86a729c08a4468a737b597 100644 (file)
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -65,6 +65,22 @@ namespace {
 
   #undef S
 
+  typedef Value V;
+
+  // Weakness of our pawn shelter in front of the king indexed by [king pawn][rank]
+  const Value ShelterWeakness[2][8] =
+  { { V(141), V(0), V(38), V(102), V(128), V(141), V(141), V(141) },
+    { V( 61), V(0), V(16), V( 44), V( 56), V( 61), V( 61), V( 61) } };
+
+  // Danger of enemy pawns moving toward our king indexed by [pawn blocked][rank]
+  const Value StormDanger[2][8] =
+  { { V(26), V(0), V(128), V(51), V(26), V(0), V(0), V(0) },
+    { V(13), V(0), V( 64), V(25), V(13), V(0), V(0), V(0) } };
+
+  // Max bonus for king safety. Corresponds to start position with all the pawns
+  // in front of the king and no enemy pawns on the horizont.
+  const Value MaxSafetyBonus = V(263);
+
   inline Score apply_weight(Score v, Score w) {
     return make_score((int(mg_value(v)) * mg_value(w)) / 0x100,
                       (int(eg_value(v)) * eg_value(w)) / 0x100);
@@ -210,31 +226,66 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
 }
 
 
-/// PawnInfo::updateShelter() calculates and caches king shelter. It is called
-/// only when king square changes, about 20% of total king_shelter() calls.
 template<Color Us>
-Score PawnInfo::updateShelter(const Position& pos, Square ksq) {
+int PawnInfo::shelter_storm(const Position& pos, Square ksq) {
+
+  const Color Them = (Us == WHITE ? BLACK : WHITE);
+
+  int safety = 0;
+  Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, ksq) | RankBB[rank_of(ksq)]);
+  Bitboard ourPawns = b & pos.pieces(Us) & ~RankBB[rank_of(ksq)];
+  Bitboard theirPawns = b & pos.pieces(Them);
+  Rank rkUs, rkThem;
+  File kf = file_of(ksq);
+
+  // Compute shelter and storm values for the file the king is on, as well as
+  // the two adjacent files. Computation is done from the white point of view.
+  kf = (kf == FILE_A) ? kf++ : (kf == FILE_H) ? kf-- : kf;
+
+  for (int f = kf - 1; f <= kf + 1; f++)
+  {
+      // Shelter penalty is higher for the pawn in front of the king
+      b = ourPawns & FileBB[f];
+      rkUs = b ? rank_of(Us == WHITE ? first_1(b) : ~last_1(b)) : RANK_1;
+      safety -= ShelterWeakness[f != kf][rkUs];
+
+      // Storm danger is smaller if enemy pawn is blocked
+      b  = theirPawns & FileBB[f];
+      rkThem = b ? rank_of(Us == WHITE ? first_1(b) : ~last_1(b)) : RANK_1;
+      safety -= StormDanger[rkThem == rkUs + 1][rkThem];
+  }
 
-  const int Shift = (Us == WHITE ? 8 : -8);
+  return safety;
+}
+
+
+/// PawnInfo::update_safety() calculates and caches a bonus for king safety. It is
+/// called only when king square changes, about 20% of total king_safety() calls.
 
-  Bitboard pawns;
-  int r, shelter = 0;
+template<Color Us>
+Score PawnInfo::update_safety(const Position& pos, Square ksq) {
+
+  int bonus = 0;
 
   if (relative_rank(Us, ksq) <= RANK_4)
   {
-      pawns = pos.pieces(PAWN, Us) & this_and_adjacent_files_bb(file_of(ksq));
-      r = ksq & (7 << 3);
-      for (int i = 0; i < 3; i++)
-      {
-          r += Shift;
-          shelter += BitCount8Bit[(pawns >> r) & 0xFF] << (6 - i);
-      }
+      bonus = shelter_storm<Us>(pos, ksq);
+
+      // If we can castle use the bonus after the castle if is bigger
+      if (pos.can_castle(Us == WHITE ? WHITE_OO : BLACK_OO))
+          bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
+
+      if (pos.can_castle(Us == WHITE ? WHITE_OOO : BLACK_OOO))
+          bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
+
+      bonus += MaxSafetyBonus; // Offset to be sure bonus is always positive
   }
+
   kingSquares[Us] = ksq;
-  kingShelters[Us] = make_score(shelter, 0);
+  kingShelters[Us] = make_score(bonus, 0);
   return kingShelters[Us];
 }
 
 // Explicit template instantiation
-template Score PawnInfo::updateShelter<WHITE>(const Position& pos, Square ksq);
-template Score PawnInfo::updateShelter<BLACK>(const Position& pos, Square ksq);
+template Score PawnInfo::update_safety<WHITE>(const Position& pos, Square ksq);
+template Score PawnInfo::update_safety<BLACK>(const Position& pos, Square ksq);