Move draw by material check

[stockfish] / src / material.cpp

diff --git a/src/material.cpp b/src/material.cpp
index 88882959e9eec1befbd86a874f7dbb089e8f41f8..995a5b541e185e6a0e772e02fb879ba6c832e09a 100644 (file)
--- a/src/material.cpp
+++ b/src/material.cpp
@@ -173,10 +173,18 @@ Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
       return e;
   }
 
+  // Draw by insufficient material (trivial draws like KK, KBK and KNK)
+  if (   !pos.pieces(PAWN)
+      &&  pos.non_pawn_material(WHITE) + pos.non_pawn_material(BLACK) <= BishopValueMg)
+  {
+      e->evaluationFunction = &EvaluateKmmKm[pos.side_to_move()];
+      return e;
+  }
+
+  // Minor piece endgame with at least one minor piece per side and
+  // no pawns. Note that the case KmmK is already handled by KXK.
   if (!pos.pieces(PAWN) && !pos.pieces(ROOK) && !pos.pieces(QUEEN))
   {
-      // Minor piece endgame with at least one minor piece per side and
-      // no pawns. Note that the case KmmK is already handled by KXK.
       assert((pos.pieces(WHITE, KNIGHT) | pos.pieces(WHITE, BISHOP)));
       assert((pos.pieces(BLACK, KNIGHT) | pos.pieces(BLACK, BISHOP)));
 
@@ -240,8 +248,7 @@ Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
       }
   }
 
-  // No pawns makes it difficult to win, even with a material advantage. This
-  // catches some trivial draws like KK, KBK and KNK
+  // No pawns makes it difficult to win, even with a material advantage
   if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
   {
       e->factor[WHITE] = (uint8_t)
@@ -263,14 +270,14 @@ Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
       e->spaceWeight = make_score(minorPieceCount * minorPieceCount, 0);
   }
 
-  // Evaluate the material imbalance. We use NO_PIECE_TYPE as a place holder
+  // Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
   // for the bishop pair "extended piece", this allow us to be more flexible
   // in defining bishop pair bonuses.
   const int pieceCount[COLOR_NB][PIECE_TYPE_NB] = {
-  { pos.bishop_pair(WHITE)  , pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
-    pos.count<BISHOP>(WHITE), pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
-  { pos.bishop_pair(BLACK)  , pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
-    pos.count<BISHOP>(BLACK), pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
+  { pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
+    pos.count<BISHOP>(WHITE)    , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
+  { pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
+    pos.count<BISHOP>(BLACK)    , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
 
   e->value = (int16_t)((imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16);
   return e;