Simplify WeakUnopposedPawn #2181

[stockfish] / src / pawns.cpp

diff --git a/src/pawns.cpp b/src/pawns.cpp
index e2b26344986ad51d129aafbf9fba91ba8d2857fc..47c89ed4c076c73d6be4647ba1cd16f960438cec 100644 (file)
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -18,6 +18,7 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <algorithm>
 #include <cassert>
 
 #include "bitboard.h"
@@ -34,9 +35,10 @@ namespace {
   constexpr Score Backward = S( 9, 24);
   constexpr Score Doubled  = S(11, 56);
   constexpr Score Isolated = S( 5, 15);
+  constexpr Score WeakUnopposed = S( 13, 27);
 
   // Connected pawn bonus
-  constexpr int Connected[RANK_NB] = { 0, 13, 17, 24, 59, 96, 171 };
+  constexpr int Connected[RANK_NB] = { 0, 7, 8, 12, 29, 48, 86 };
 
   // Strength of pawn shelter for our king by [distance from edge][rank].
   // RANK_1 = 0 is used for files where we have no pawn, or pawn is behind our king.
@@ -76,7 +78,7 @@ namespace {
     Bitboard ourPawns   = pos.pieces(  Us, PAWN);
     Bitboard theirPawns = pos.pieces(Them, PAWN);
 
-    e->passedPawns[Us] = e->pawnAttacksSpan[Us] = e->weakUnopposed[Us] = 0;
+    e->passedPawns[Us] = e->pawnAttacksSpan[Us] = 0;
     e->kingSquares[Us]   = SQ_NONE;
     e->pawnAttacks[Us]   = pawn_attacks_bb<Us>(ourPawns);
 
@@ -125,15 +127,16 @@ namespace {
         // Score this pawn
         if (support | phalanx)
         {
-            int v = (phalanx ? 3 : 2) * Connected[r];
-            v = 17 * popcount(support) + (v >> (opposed + 1));
+            int v =  Connected[r] * (phalanx ? 3 : 2) / (opposed ? 2 : 1)
+                   + 17 * popcount(support);
+
             score += make_score(v, v * (r - 2) / 4);
         }
         else if (!neighbours)
-            score -= Isolated, e->weakUnopposed[Us] += !opposed;
+            score -= Isolated + WeakUnopposed * int(!opposed);
 
         else if (backward)
-            score -= Backward, e->weakUnopposed[Us] += !opposed;
+            score -= Backward + WeakUnopposed * int(!opposed);
 
         if (doubled && !support)
             score -= Doubled;
@@ -171,18 +174,19 @@ Entry* probe(const Position& pos) {
 /// penalty for a king, looking at the king file and the two closest files.
 
 template<Color Us>
-Value Entry::evaluate_shelter(const Position& pos, Square ksq) {
+void Entry::evaluate_shelter(const Position& pos, Square ksq, Score& shelter) {
 
   constexpr Color     Them = (Us == WHITE ? BLACK : WHITE);
   constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH);
-  constexpr Bitboard  BlockRanks = (Us == WHITE ? Rank1BB | Rank2BB : Rank8BB | Rank7BB);
+  constexpr Bitboard BlockSquares =  (Rank1BB | Rank2BB | Rank7BB | Rank8BB)
+                                   & (FileABB | FileHBB);
 
   Bitboard b = pos.pieces(PAWN) & ~forward_ranks_bb(Them, ksq);
   Bitboard ourPawns = b & pos.pieces(Us);
   Bitboard theirPawns = b & pos.pieces(Them);
 
-  Value safety = (shift<Down>(theirPawns) & (FileABB | FileHBB) & BlockRanks & ksq) ?
-                 Value(374) : Value(5);
+  Value bonus[] = { (shift<Down>(theirPawns) & BlockSquares & ksq) ? Value(374) : Value(5),
+                    VALUE_ZERO };
 
   File center = clamp(file_of(ksq), FILE_B, FILE_G);
   for (File f = File(center - 1); f <= File(center + 1); ++f)
@@ -194,12 +198,16 @@ Value Entry::evaluate_shelter(const Position& pos, Square ksq) {
       Rank theirRank = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
 
       int d = std::min(f, ~f);
-      safety += ShelterStrength[d][ourRank];
-      safety -= (ourRank && (ourRank == theirRank - 1)) ? 66 * (theirRank == RANK_3)
-                                                        : UnblockedStorm[d][theirRank];
+      bonus[MG] += ShelterStrength[d][ourRank];
+
+      if (ourRank && (ourRank == theirRank - 1))
+          bonus[MG] -= 82 * (theirRank == RANK_3), bonus[EG] -= 82 * (theirRank == RANK_3);
+      else
+          bonus[MG] -= UnblockedStorm[d][theirRank];
   }
 
-  return safety;
+  if (bonus[MG] > mg_value(shelter))
+      shelter = make_score(bonus[MG], bonus[EG]);
 }
 
 
@@ -212,22 +220,27 @@ Score Entry::do_king_safety(const Position& pos) {
   Square ksq = pos.square<KING>(Us);
   kingSquares[Us] = ksq;
   castlingRights[Us] = pos.castling_rights(Us);
-  int minKingPawnDistance = 0;
 
   Bitboard pawns = pos.pieces(Us, PAWN);
-  if (pawns)
-      while (!(DistanceRingBB[ksq][++minKingPawnDistance] & pawns)) {}
+  int minPawnDist = pawns ? 8 : 0;
+
+  if (pawns & PseudoAttacks[KING][ksq])
+      minPawnDist = 1;
+
+  else while (pawns)
+      minPawnDist = std::min(minPawnDist, distance(ksq, pop_lsb(&pawns)));
 
-  Value bonus = evaluate_shelter<Us>(pos, ksq);
+  Score shelter = make_score(-VALUE_INFINITE, VALUE_ZERO);
+  evaluate_shelter<Us>(pos, ksq, shelter);
 
   // If we can castle use the bonus after the castling if it is bigger
   if (pos.can_castle(Us | KING_SIDE))
-      bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_G1)));
+      evaluate_shelter<Us>(pos, relative_square(Us, SQ_G1), shelter);
 
   if (pos.can_castle(Us | QUEEN_SIDE))
-      bonus = std::max(bonus, evaluate_shelter<Us>(pos, relative_square(Us, SQ_C1)));
+      evaluate_shelter<Us>(pos, relative_square(Us, SQ_C1), shelter);
 
-  return make_score(bonus, -16 * minKingPawnDistance);
+  return shelter - make_score(VALUE_ZERO, 16 * minPawnDist);
 }
 
 // Explicit template instantiation