Connected / blocked pawns simplification

[stockfish] / src / bitboard.h

diff --git a/src/bitboard.h b/src/bitboard.h
index 93f838f8a6adce42ead12022368fce28959f34c9..1c5981080578fe4635cbcb7a5206267befceb302 100644 (file)
--- a/src/bitboard.h
+++ b/src/bitboard.h
@@ -110,6 +110,7 @@ inline Bitboard square_bb(Square s) {
   return SquareBB[s];
 }
 
+
 /// Overloads of bitwise operators between a Bitboard and a Square for testing
 /// whether a given bit is set in a bitboard, and for setting and clearing bits.
 
@@ -201,11 +202,25 @@ inline Bitboard adjacent_files_bb(Square s) {
 }
 
 
-/// between_bb() returns squares that are linearly between the given squares
-/// If the given squares are not on a same file/rank/diagonal, return 0.
+/// line_bb(Square, Square) returns a bitboard representing an entire line,
+/// from board edge to board edge, that intersects the given squares. If the
+/// given squares are not on a same file/rank/diagonal, returns 0. For instance,
+/// line_bb(SQ_C4, SQ_F7) will return a bitboard with the A2-G8 diagonal.
+
+inline Bitboard line_bb(Square s1, Square s2) {
+
+  assert(is_ok(s1) && is_ok(s2));
+  return LineBB[s1][s2];
+}
+
+
+/// between_bb() returns a bitboard representing squares that are linearly
+/// between the given squares (excluding the given squares). If the given
+/// squares are not on a same file/rank/diagonal, return 0. For instance,
+/// between_bb(SQ_C4, SQ_F7) will return a bitboard with squares D5 and E6.
 
 inline Bitboard between_bb(Square s1, Square s2) {
-  Bitboard b = LineBB[s1][s2] & ((AllSquares << s1) ^ (AllSquares << s2));
+  Bitboard b = line_bb(s1, s2) & ((AllSquares << s1) ^ (AllSquares << s2));
   return b & (b - 1); //exclude lsb
 }
 
@@ -229,8 +244,8 @@ inline Bitboard forward_file_bb(Color c, Square s) {
 
 
 /// pawn_attack_span() returns a bitboard representing all the squares that can
-/// be attacked by a pawn of the given color when it moves along its file,
-/// starting from the given square.
+/// be attacked by a pawn of the given color when it moves along its file, starting
+/// from the given square.
 
 inline Bitboard pawn_attack_span(Color c, Square s) {
   return forward_ranks_bb(c, s) & adjacent_files_bb(s);
@@ -241,7 +256,7 @@ inline Bitboard pawn_attack_span(Color c, Square s) {
 /// the given color and on the given square is a passed pawn.
 
 inline Bitboard passed_pawn_span(Color c, Square s) {
-  return forward_ranks_bb(c, s) & (adjacent_files_bb(s) | file_bb(s));
+  return pawn_attack_span(c, s) | forward_file_bb(c, s);
 }
 
 
@@ -249,7 +264,7 @@ inline Bitboard passed_pawn_span(Color c, Square s) {
 /// straight or on a diagonal line.
 
 inline bool aligned(Square s1, Square s2, Square s3) {
-  return LineBB[s1][s2] & s3;
+  return line_bb(s1, s2) & s3;
 }
 
 
@@ -264,7 +279,9 @@ template<> inline int distance<Square>(Square x, Square y) { return SquareDistan
 inline int edge_distance(File f) { return std::min(f, File(FILE_H - f)); }
 inline int edge_distance(Rank r) { return std::min(r, Rank(RANK_8 - r)); }
 
-/// Return the target square bitboard if we do not step off the board, empty otherwise
+
+/// safe_destination() returns the bitboard of target square for the given step
+/// from the given square. If the step is off the board, returns empty bitboard.
 
 inline Bitboard safe_destination(Square s, int step)
 {
@@ -272,6 +289,7 @@ inline Bitboard safe_destination(Square s, int step)
     return is_ok(to) && distance(s, to) <= 2 ? square_bb(to) : Bitboard(0);
 }
 
+
 /// attacks_bb(Square) returns the pseudo attacks of the give piece type
 /// assuming an empty board.
 
@@ -283,6 +301,7 @@ inline Bitboard attacks_bb(Square s) {
   return PseudoAttacks[Pt][s];
 }
 
+
 /// attacks_bb(Square, Bitboard) returns the attacks by the given piece
 /// assuming the board is occupied according to the passed Bitboard.
 /// Sliding piece attacks do not continue passed an occupied square.