Bonus for file distance of the outermost pawns

[stockfish] / src / pawns.cpp

diff --git a/src/pawns.cpp b/src/pawns.cpp
index d9cfe409191a1b28dbf67b851fc8bdaf5cacb946..39bd689f2e30c921c60030a5287d5f6ec8b84489 100644 (file)
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -57,6 +57,9 @@ namespace {
     S( 0, 0), S( 6, 13), S(6,13), S(14,29),
     S(34,68), S(83,166), S(0, 0), S( 0, 0) };
 
+  // Bonus for file distance of the two outermost pawns
+  const Score PawnsFileSpan = S(0, 10);
+
   // Weakness of our pawn shelter in front of the king indexed by [rank]
   const Value ShelterWeakness[RANK_NB] =
   { V(100), V(0), V(27), V(73), V(92), V(101), V(101) };
@@ -124,7 +127,7 @@ namespace {
         // Test for backward pawn.
         // If the pawn is passed, isolated, or member of a pawn chain it cannot
         // be backward. If there are friendly pawns behind on adjacent files
-        // or if can capture an enemy pawn it cannot be backward either.
+        // or if it can capture an enemy pawn it cannot be backward either.
         if (   (passed | isolated | chain)
             || (ourPawns & pawn_attack_span(Them, s))
             || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
@@ -145,9 +148,9 @@ namespace {
 
         assert(opposed | passed | (pawn_attack_span(Us, s) & theirPawns));
 
-        // A not passed pawn is a candidate to become passed, if it is free to
+        // A not-passed pawn is a candidate to become passed, if it is free to
         // advance and if the number of friendly pawns beside or behind this
-        // pawn on adjacent files is higher or equal than the number of
+        // pawn on adjacent files is higher than or equal to the number of
         // enemy pawns in the forward direction on the adjacent files.
         candidate =   !(opposed | passed | backward | isolated)
                    && (b = pawn_attack_span(Them, s + pawn_push(Us)) & ourPawns) != 0
@@ -181,6 +184,14 @@ namespace {
         }
     }
 
+    // In endgame it's better to have pawns on both wings. So give a bonus according
+    // to file distance between left and right outermost pawns.
+    if (pos.count<PAWN>(Us) > 1)
+    {
+        b = ~e->semiopenFiles[Us] & 0xFF;
+        value += PawnsFileSpan * int(msb(b) - lsb(b));
+    }
+
     return value;
   }
 
@@ -188,7 +199,7 @@ namespace {
 
 namespace Pawns {
 
-/// init() initializes some tables by formula instead of hard-code their values
+/// init() initializes some tables by formula instead of hard-coding their values
 
 void init() {