Shrink Position::is_draw()

[stockfish] / src / position.cpp

diff --git a/src/position.cpp b/src/position.cpp
index d2aeb8221209ad391e54480e6442444d91d19749..3b59b24a19171190c1d7d62acd93e6faeaf11968 100644 (file)
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -415,20 +415,21 @@ const string Position::pretty(Move move) const {
 /// pieces, according to the call parameters. Pinned pieces protect our king and
 /// discovered check pieces attack the enemy king.
 
-Bitboard Position::hidden_checkers(Square ksq, Color c, Color toMove) const {
+Bitboard Position::hidden_checkers(Color c, Color kingColor) const {
 
   Bitboard b, pinners, result = 0;
+  Square ksq = king_square(kingColor);
 
   // Pinners are sliders that give check when a pinned piece is removed
   pinners = (  (pieces(  ROOK, QUEEN) & PseudoAttacks[ROOK  ][ksq])
-             | (pieces(BISHOP, QUEEN) & PseudoAttacks[BISHOP][ksq])) & pieces(c);
+             | (pieces(BISHOP, QUEEN) & PseudoAttacks[BISHOP][ksq])) & pieces(~kingColor);
 
   while (pinners)
   {
       b = between_bb(ksq, pop_lsb(&pinners)) & pieces();
 
       if (!more_than_one(b))
-          result |= b & pieces(toMove);
+          result |= b & pieces(c);
   }
   return result;
 }
@@ -1228,35 +1229,25 @@ 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.
+/// Position::is_draw() tests whether the position is drawn by material, 50 moves
+/// rule or repetition. It does not detect stalemates.
+
 bool Position::is_draw() const {
 
-  // Draw by material?
   if (   !pieces(PAWN)
       && (non_pawn_material(WHITE) + non_pawn_material(BLACK) <= BishopValueMg))
       return true;
 
-  // Draw by the 50 moves rule?
   if (st->rule50 > 99 && (!checkers() || MoveList<LEGAL>(*this).size()))
       return true;
 
-  int i = 4, e = std::min(st->rule50, st->pliesFromNull);
-
-  if (i <= e)
+  StateInfo* stp = st;
+  for (int i = 2, e = std::min(st->rule50, st->pliesFromNull); i <= e; i += 2)
   {
-      StateInfo* stp = st->previous->previous;
-
-      do {
-          stp = stp->previous->previous;
-
-          if (stp->key == st->key)
-              return true; // Draw after first repetition
-
-          i += 2;
+      stp = stp->previous->previous;
 
-      } while (i <= e);
+      if (stp->key == st->key)
+          return true; // Draw at first repetition
   }
 
   return false;