From: Stéphane Nicolet <cassio@free.fr>
Date: Sat, 21 May 2016 08:05:19 +0000 (+0200)
Subject: Teach check_blockers to check also non-king pieces
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=abac509ccb1f197da1159ce02daaf4fa737c32e5

Teach check_blockers to check also non-king pieces

This is a prerequisite for next patch

No functional change.
---

diff --git a/src/position.cpp b/src/position.cpp
index cd91b07f..6022518e 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -420,28 +420,27 @@ Phase Position::game_phase() const {
 }
 
 
-/// Position::check_blockers() returns a bitboard of all the pieces with color
-/// 'c' that are blocking check on the king with color 'kingColor'. A piece
-/// blocks a check if removing that piece from the board would result in a
-/// position where the king is in check. A check blocking piece can be either a
-/// pinned or a discovered check piece, according if its color 'c' is the same
-/// or the opposite of 'kingColor'.
+/// Position::slider_blockers() returns a bitboard of all the pieces in 'target' that
+/// are blocking attacks on the square 's' from 'sliders'. A piece blocks a slider
+/// if removing that piece from the board would result in a position where square 's'
+/// is attacked. For example, a king-attack blocking piece can be either a pinned or
+/// a discovered check piece, according if its color is the opposite or the same of
+/// the color of the slider.
 
-Bitboard Position::check_blockers(Color c, Color kingColor) const {
+Bitboard Position::slider_blockers(Bitboard target, Bitboard sliders, Square s) const {
 
   Bitboard b, pinners, result = 0;
-  Square ksq = square<KING>(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(~kingColor);
+  // Pinners are sliders that attack 's' when a pinned piece is removed
+  pinners = (  (PseudoAttacks[ROOK  ][s] & pieces(QUEEN, ROOK))
+             | (PseudoAttacks[BISHOP][s] & pieces(QUEEN, BISHOP))) & sliders;
 
   while (pinners)
   {
-      b = between_bb(ksq, pop_lsb(&pinners)) & pieces();
+      b = between_bb(s, pop_lsb(&pinners)) & pieces();
 
       if (!more_than_one(b))
-          result |= b & pieces(c);
+          result |= b & target;
   }
   return result;
 }
diff --git a/src/position.h b/src/position.h
index c3ba5ac8..b2538e96 100644
--- a/src/position.h
+++ b/src/position.h
@@ -131,6 +131,7 @@ public:
   Bitboard attacks_from(Piece pc, Square s) const;
   template<PieceType> Bitboard attacks_from(Square s) const;
   template<PieceType> Bitboard attacks_from(Square s, Color c) const;
+  Bitboard slider_blockers(Bitboard target, Bitboard sliders, Square s) const;
 
   // Properties of moves
   bool legal(Move m, Bitboard pinned) const;
@@ -186,7 +187,6 @@ private:
   void set_state(StateInfo* si) const;
 
   // Other helpers
-  Bitboard check_blockers(Color c, Color kingColor) const;
   void put_piece(Color c, PieceType pt, Square s);
   void remove_piece(Color c, PieceType pt, Square s);
   void move_piece(Color c, PieceType pt, Square from, Square to);
@@ -311,11 +311,11 @@ inline Bitboard Position::checkers() const {
 }
 
 inline Bitboard Position::discovered_check_candidates() const {
-  return check_blockers(sideToMove, ~sideToMove);
+  return slider_blockers(pieces(sideToMove), pieces(sideToMove), square<KING>(~sideToMove));
 }
 
 inline Bitboard Position::pinned_pieces(Color c) const {
-  return check_blockers(c, c);
+  return slider_blockers(pieces(c), pieces(~c), square<KING>(c));
 }
 
 inline bool Position::pawn_passed(Color c, Square s) const {