X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fpawns.cpp;h=45c404712a200b949dbc0e3b515ebc81f4475bae;hp=acc3d77096dd10f79742c4be15e69d2baa76fa9c;hb=4ae5a7b45a430aea5f4b21f9455b4db74ed1c44a;hpb=c83cbe42f3a6c9b145a4557ef874222fe685a9bc;ds=sidebyside

diff --git a/src/pawns.cpp b/src/pawns.cpp
index acc3d770..45c40471 100644
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -32,9 +32,9 @@ namespace {
   #define S(mg, eg) make_score(mg, eg)
 
   // Pawn penalties
-  constexpr Score Backward = S( 9, 24);
-  constexpr Score Doubled  = S(11, 56);
-  constexpr Score Isolated = S( 5, 15);
+  constexpr Score Backward      = S( 9, 24);
+  constexpr Score Doubled       = S(11, 56);
+  constexpr Score Isolated      = S( 5, 15);
   constexpr Score WeakUnopposed = S( 13, 27);
   constexpr Score Attacked2Unsupported = S( 0, 20);
 
@@ -108,17 +108,18 @@ namespace {
         phalanx    = neighbours & rank_bb(s);
         support    = neighbours & rank_bb(s - Up);
 
-        // A pawn is backward when it is behind all pawns of the same color
-        // on the adjacent files and cannot be safely advanced.
-        backward =  !(ourPawns & pawn_attack_span(Them, s + Up))
+        // A pawn is backward when it is behind all pawns of the same color on
+        // the adjacent files and cannot safely advance. Phalanx and isolated
+        // pawns will be excluded when the pawn is scored.
+        backward =  !(neighbours & forward_ranks_bb(Them, s))
                   && (stoppers & (leverPush | (s + Up)));
 
         // Passed pawns will be properly scored in evaluation because we need
         // full attack info to evaluate them. Include also not passed pawns
         // which could become passed after one or two pawn pushes when are
         // not attacked more times than defended.
-        if (   !(stoppers ^ lever) ||
-              (!(stoppers ^ leverPush) && popcount(phalanx) >= popcount(leverPush)))
+        if ( !(stoppers ^ lever) ||
+            (!(stoppers ^ leverPush) && popcount(phalanx) >= popcount(leverPush)))
             e->passedPawns[Us] |= s;
 
         else if (stoppers == square_bb(s + Up) && r >= RANK_5)
@@ -137,6 +138,7 @@ namespace {
 
             score += make_score(v, v * (r - 2) / 4);
         }
+
         else if (!neighbours)
             score -= Isolated + WeakUnopposed * int(!opposed);