X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fpawns.cpp;h=c89f2d0585891ec2ebe253b89de39eb305f56a8f;hp=1cdeb461d51e2a2e74a56860f3d3e3c65998d70d;hb=26a8b844177ad6abd4aca1bef2ebb7f644bd465c;hpb=1d4e7bbdf5a8b2e87daaa54eea52cbe01d699fdb

diff --git a/src/pawns.cpp b/src/pawns.cpp
index 1cdeb461..c89f2d05 100644
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -183,7 +183,7 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
   Square s;
   File f;
   Rank r;
-  int bonus;
+  int bonus, backwardWeight;
   bool passed, isolated, doubled, opposed, chain, backward, candidate;
   Score value = make_score(0, 0);
   const Square* ptr = pos.piece_list_begin(Us, PAWN);
@@ -214,7 +214,7 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
       pi->qsStormValue[Us] += QStormTable[relative_square(Us, s)] + bonus;
 
       // Our rank plus previous one. Used for chain detection.
-      b = rank_bb(r) | rank_bb(r + (Us == WHITE ? -1 : 1));
+      b = rank_bb(r) | rank_bb(Us == WHITE ? r - 1 : r + 1);
 
       // Passed, isolated, doubled or member of a pawn
       // chain (but not the backward one) ?
@@ -226,15 +226,16 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
 
       // Test for backward pawn
       //
+      backward = false;
+      backwardWeight = 6;
+
       // If the pawn is passed, isolated, or member of a pawn chain
       // it cannot be backward. If can capture an enemy pawn or if
       // there are friendly pawns behind on neighboring files it cannot
       // be backward either.
-      if (   (passed | isolated | chain)
-          || (ourPawns & attack_span_mask(opposite_color(Us), s))
-          || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
-          backward = false;
-      else
+      if (   !(passed | isolated | chain)
+          && !(ourPawns & attack_span_mask(opposite_color(Us), s))
+          && !(pos.attacks_from<PAWN>(s, Us) & theirPawns))
       {
           // We now know that there are no friendly pawns beside or behind this
           // pawn on neighboring files. We now check whether the pawn is
@@ -245,7 +246,12 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
           // Note that we are sure to find something because pawn is not passed
           // nor isolated, so loop is potentially infinite, but it isn't.
           while (!(b & (ourPawns | theirPawns)))
+          {
               Us == WHITE ? b <<= 8 : b >>= 8;
+              backwardWeight--;
+          }
+
+          assert(backwardWeight > 0);
 
           // The friendly pawn needs to be at least two ranks closer than the enemy
           // pawn in order to help the potentially backward pawn advance.
@@ -274,7 +280,7 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
       if (isolated)
       {
           value -= IsolatedPawnPenalty[f];
-          if (!(theirPawns & file_bb(f)))
+          if (!opposed)
               value -= IsolatedPawnPenalty[f] / 2;
       }
       if (doubled)
@@ -282,8 +288,8 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
 
       if (backward)
       {
-          value -= BackwardPawnPenalty[f];
-          if (!(theirPawns & file_bb(f)))
+          value -= backwardWeight * BackwardPawnPenalty[f] / 4;
+          if (!opposed)
               value -= BackwardPawnPenalty[f] / 2;
       }
       if (chain)