Fix move_is_capture() to detect capture promotions

We miss to account as a capture a promotion capture !

Incredible bug in this critical function that is here
since a long time (b50921fd5c of 21/10/2009 !!)

This patch fixes the bug and readds the faster
move_is_capture_or_promotion() that slightly increases
overall speed.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/movepick.cpp

@@ -103,7 +103,7 @@ MovePicker::MovePicker(const Position& p, Move ttm, Depth d, const History& h, S
       // Skip TT move if is not a capture or a promotion, this avoids
       // qsearch tree explosion due to a possible perpetual check or
       // similar rare cases when TT table is full.
-      if (ttm != MOVE_NONE && !pos.move_is_capture(ttm) && !move_is_promotion(ttm))
+      if (ttm != MOVE_NONE && !pos.move_is_capture_or_promotion(ttm))
           ttm = MOVE_NONE;
   }
   else

src/position.h

@@ -189,6 +189,7 @@ public:
   bool move_is_pl(const Move m) const;
   bool move_gives_check(Move m, const CheckInfo& ci) const;
   bool move_is_capture(Move m) const;
+  bool move_is_capture_or_promotion(Move m) const;
   bool move_is_passed_pawn_push(Move m) const;
   bool move_attacks_square(Move m, Square s) const;
 
@@ -534,10 +535,18 @@ inline bool Position::is_chess960() const {
   return chess960;
 }
 
+inline bool Position::move_is_capture_or_promotion(Move m) const {
+
+  assert(m != MOVE_NONE && m != MOVE_NULL);
+  return move_is_special(m) ? !move_is_castle(m) : !square_is_empty(move_to(m));
+}
+
 inline bool Position::move_is_capture(Move m) const {
 
-  assert (m != MOVE_NONE && m != MOVE_NULL);
+  assert(m != MOVE_NONE && m != MOVE_NULL);
-  return !move_is_special(m) ? !square_is_empty(move_to(m)) : move_is_ep(m);
+
+  // Note that castle is coded as "king captures the rook"
+  return (!square_is_empty(move_to(m)) && !move_is_castle(m)) || move_is_ep(m);
 }
 
 inline PieceType Position::captured_piece_type() const {

src/search.cpp

@@ -1013,7 +1013,7 @@ split_point_start: // At split points actual search starts from here
       // At Root and at first iteration do a PV search on all the moves to score root moves
       isPvMove = (PvNode && moveCount <= (RootNode ? depth <= ONE_PLY ? MAX_MOVES : MultiPV : 1));
       givesCheck = pos.move_gives_check(move, ci);
-      captureOrPromotion = pos.move_is_capture(move) || move_is_promotion(move);
+      captureOrPromotion = pos.move_is_capture_or_promotion(move);
 
       // Step 12. Decide the new search depth
       ext = extension<PvNode>(pos, move, captureOrPromotion, givesCheck, &dangerous);
@@ -1279,8 +1279,7 @@ split_point_start: // At split points actual search starts from here
 
         // Update killers and history only for non capture moves that fails high
         if (    bestValue >= beta
-            && !pos.move_is_capture(move)
+            && !pos.move_is_capture_or_promotion(move))
-            && !move_is_promotion(move))
         {
             if (move != ss->killers[0])
             {
@@ -1450,8 +1449,7 @@ split_point_start: // At split points actual search starts from here
           && !inCheck
           &&  givesCheck
           &&  move != ttMove
-          && !pos.move_is_capture(move)
+          && !pos.move_is_capture_or_promotion(move)
-          && !move_is_promotion(move)
           &&  ss->eval + PawnValueMidgame / 4 < beta
           && !check_is_dangerous(pos, move, futilityBase, beta, &bestValue))
       {
@@ -1650,7 +1648,7 @@ split_point_start: // At split points actual search starts from here
 
     assert(move_is_ok(m));
     assert(threat && move_is_ok(threat));
-    assert(!pos.move_is_capture(m) && !move_is_promotion(m));
+    assert(!pos.move_is_capture_or_promotion(m));
     assert(!pos.move_is_passed_pawn_push(m));
 
     Square mfrom, mto, tfrom, tto;