Tweak backward pawns definition

[stockfish] / src / pawns.cpp

diff --git a/src/pawns.cpp b/src/pawns.cpp
index 5290efb2c70c2eb4fcd72cfe60ff774ced77000a..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) } };
 
   { 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(50, 52), S(63, 56), S(69, 56), S(69, 56),
-    S(69, 56), S(69, 56), S(63, 56), S(50, 52) },
-  { S(40, 38), S(49, 41), S(53, 41), S(53, 41),
-    S(53, 41), S(53, 41), S(49, 41), S(40, 38) } };
+  // 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];
 
   // Connected pawn bonus by opposed, phalanx, twice supported and rank
   Score Connected[2][2][2][RANK_NB];


@@ -151,9 +147,10 @@ namespace {
         // Test for backward pawn.
         // If the pawn is passed, isolated, lever or connected it cannot be
         // backward. If there are friendly pawns behind on adjacent files
         // Test for backward pawn.
         // 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)
         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
         {
             backward = false;
         else
         {


@@ -180,17 +177,19 @@ namespace {
         // Score this pawn
         if (isolated)
             score -= Isolated[opposed][f];
         // Score this pawn
         if (isolated)
             score -= Isolated[opposed][f];

+

         else if (backward)
         else if (backward)

-            score -= Backward[opposed][f];
+            score -= Backward[opposed];
+

         else if (!supported)
             score -= UnsupportedPawnPenalty;
 
         if (connected)
             score += Connected[opposed][!!phalanx][more_than_one(supported)][relative_rank(Us, s)];
         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 (doubled)
             score -= Doubled[f] / distance<Rank>(s, frontmost_sq(Us, doubled));

-                    
+

         if (lever)
             score += Lever[relative_rank(Us, s)];
     }
         if (lever)
             score += Lever[relative_rank(Us, s)];
     }