Move draw by material check

It is more natural to test this case among
others material distributions.

No functional change.

diff --git a/src/endgame.h b/src/endgame.h
index 49f39990ba513e6ca8584df55fa9ebadddfe6d9d..5ea40bbf91b995070a7bf804b52ecc8c0fec548e 100644 (file)
--- a/src/endgame.h
+++ b/src/endgame.h
@@ -43,7 +43,7 @@ enum EndgameType {
   KQKP,  // KQ vs KP
   KQKR,  // KQ vs KR
   KBBKN, // KBB vs KN
-  KmmKm, // K and two minors vs K and one or two minors
+  KmmKm, // K and one or two minors vs K and zero or one minor
 
 
   // Scaling functions

diff --git a/src/material.cpp b/src/material.cpp
index 0f1e19b9ee4a954f69bb84844e9227110f21709a..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)

diff --git a/src/position.cpp b/src/position.cpp
index 615763cdcf93007a3e09b42d8a2f8727e31f19c7..6885b135cafad835c691087a336ba9d66708228e 100644 (file)
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -1223,6 +1223,7 @@ Key Position::compute_material_key() const {
 /// game and the endgame. These functions are used to initialize the incremental
 /// scores when a new position is set up, and to verify that the scores are correctly
 /// updated by do_move and undo_move when the program is running in debug mode.
+
 Score Position::compute_psq_score() const {
 
   Score score = SCORE_ZERO;
@@ -1254,15 +1255,11 @@ Value Position::compute_non_pawn_material(Color c) const {
 }
 
 
-/// Position::is_draw() tests whether the position is drawn by material,
-/// repetition, or the 50 moves rule. It does not detect stalemates, this
-/// must be done by the search.
-bool Position::is_draw() const {
+/// Position::is_draw() tests whether the position is drawn by repetition
+/// or the 50 moves rule. It does not detect stalemates, this must be done
+/// by the search.
 
-  // Draw by material?
-  if (   !pieces(PAWN)
-      && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMg))
-      return true;
+bool Position::is_draw() const {
 
   // Draw by the 50 moves rule?
   if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))