Fix reported DTZ for mate-in-1-ply positions

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 41c66812717e587dffeafbca3f8935cef8204861..69a36cf5ee4659a43b80050925054d2e71b3c223 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -171,6 +171,7 @@ namespace {
   constexpr Score KnightOnQueen      = S( 21, 11);
   constexpr Score LongDiagonalBishop = S( 22,  0);
   constexpr Score MinorBehindPawn    = S( 16,  0);
+  constexpr Score Overload           = S( 10,  5);
   constexpr Score PawnlessFlank      = S( 20, 80);
   constexpr Score RookOnPawn         = S(  8, 24);
   constexpr Score SliderOnQueen      = S( 42, 21);
@@ -520,7 +521,7 @@ namespace {
     Bitboard b, weak, defended, nonPawnEnemies, stronglyProtected, safeThreats;
     Score score = SCORE_ZERO;
 
-    // Non-pawn enemies attacked by a pawn
+    // Non-pawn enemies
     nonPawnEnemies = pos.pieces(Them) ^ pos.pieces(Them, PAWN);
 
     // Our safe or protected pawns
@@ -608,6 +609,12 @@ namespace {
     b = (pos.pieces(Us) ^ pos.pieces(Us, PAWN, KING)) & attackedBy[Us][ALL_PIECES];
     score += Connectivity * popcount(b);
 
+    // Bonus for overload (non-pawn enemies attacked and defended exactly once)
+    b =  nonPawnEnemies
+       & attackedBy[Us][ALL_PIECES]   & ~attackedBy2[Us]
+       & attackedBy[Them][ALL_PIECES] & ~attackedBy2[Them];
+    score += Overload * popcount(b);
+
     if (T)
         Trace::add(THREAT, Us, score);
 
@@ -731,8 +738,7 @@ namespace {
     // pawn, or if it is undefended and attacked by an enemy piece.
     Bitboard safe =   SpaceMask
                    & ~pos.pieces(Us, PAWN)
-                   & ~attackedBy[Them][PAWN]
-                   & (attackedBy[Us][ALL_PIECES] | ~attackedBy[Them][ALL_PIECES]);
+                   & ~attackedBy[Them][PAWN];
 
     // Find all squares which are at most three squares behind some friendly pawn
     Bitboard behind = pos.pieces(Us, PAWN);