Fine tuning of unsupported pawn penalty

[stockfish] / src / pawns.cpp

diff --git a/src/pawns.cpp b/src/pawns.cpp
index 626f2b57bd82958671cdbb6b2d1e9a845d255331..52f626f16b5c302c071d64d03f418c817230a0e8 100644 (file)
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -2,6 +2,7 @@
   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
   Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad
+  Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, Tord Romstad
 
   Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -41,8 +42,9 @@ namespace {
   // Backward pawn penalty by opposed flag
   const Score Backward[2] = { S(67, 42), S(49, 24) };
   
-  // Unsupported pawn penalty, for pawns which are neither isolated or backward
-  const Score Unsupported = S(20, 10);
+  // Unsupported pawn penalty for pawns which are neither isolated or backward,
+  // by number of pawns it supports [less than 2 / exactly 2].
+  const Score Unsupported[2] = { S(20, 10), S(25, 15) };
 
   // Connected pawn bonus by opposed, phalanx, twice supported and rank
   Score Connected[2][2][2][RANK_NB];
@@ -181,7 +183,7 @@ namespace {
             score -= Backward[opposed];
 
         else if (!supported)
-            score -= Unsupported;
+            score -= Unsupported[more_than_one(neighbours & rank_bb(s + Up))];
 
         if (connected)
             score += Connected[opposed][!!phalanx][more_than_one(supported)][relative_rank(Us, s)];