Better document move_to_san()

[stockfish] / src / move.cpp

diff --git a/src/move.cpp b/src/move.cpp
index ff0adbe5b6d7cfce860b30b732d7dc17e7cccd0f..4a0a43b30fca539da6fb0d7db0e065904d8ab020 100644 (file)
--- a/src/move.cpp
+++ b/src/move.cpp
@@ -91,8 +91,9 @@ const string move_to_san(Position& pos, Move m) {
   assert(pos.is_ok());
   assert(move_is_ok(m));
 
-  MoveStack mlist[MAX_MOVES];
-  Square from = move_from(m);
+  Bitboard attackers;
+  bool ambiguousMove, ambiguousFile, ambiguousRank;
+  Square sq, from = move_from(m);
   Square to = move_to(m);
   PieceType pt = pos.type_of_piece_on(from);
   string san;
@@ -113,30 +114,34 @@ const string move_to_san(Position& pos, Move m) {
       {
           san = piece_type_to_char(pt);
 
-          // Collect all legal moves of piece type 'pt' with destination 'to'
-          MoveStack* last = generate<MV_LEGAL>(pos, mlist);
-          int f = 0, r = 0;
-
-          for (MoveStack* cur = mlist; cur != last; cur++)
-              if (   move_to(cur->move) == to
-                  && pos.type_of_piece_on(move_from(cur->move)) == pt)
-              {
-                  if (square_file(move_from(cur->move)) == square_file(from))
-                      f++;
-
-                  if (square_rank(move_from(cur->move)) == square_rank(from))
-                      r++;
-              }
-
-          assert(f > 0 && r > 0);
-
           // Disambiguation if we have more then one piece with destination 'to'
-          if (f == 1 && r > 1)
-              san += file_to_char(square_file(from));
-          else if (f > 1 && r == 1)
-              san += rank_to_char(square_rank(from));
-          else if (f > 1 && r > 1)
-              san += square_to_string(from);
+          // note that for pawns is not needed because starting file is explicit.
+          attackers = pos.attackers_to(to) & pos.pieces(pt, pos.side_to_move());
+          clear_bit(&attackers, from);
+          ambiguousMove = ambiguousFile = ambiguousRank = false;
+
+          while (attackers)
+          {
+              sq = pop_1st_bit(&attackers);
+
+              if (square_file(sq) == square_file(from))
+                  ambiguousFile = true;
+
+              if (square_rank(sq) == square_rank(from))
+                  ambiguousRank = true;
+
+              ambiguousMove = true;
+          }
+
+          if (ambiguousMove)
+          {
+              if (!ambiguousFile)
+                  san += file_to_char(square_file(from));
+              else if (!ambiguousRank)
+                  san += rank_to_char(square_rank(from));
+              else
+                  san += square_to_string(from);
+          }
       }
 
       if (pos.move_is_capture(m))
@@ -156,11 +161,11 @@ const string move_to_san(Position& pos, Move m) {
       }
   }
 
-  // The move gives check? We don't use pos.move_is_check() here
+  // The move gives check? We don't use pos.move_gives_check() here
   // because we need to test for a mate after the move is done.
   StateInfo st;
   pos.do_move(m, st);
-  if (pos.is_check())
+  if (pos.in_check())
       san += pos.is_mate() ? "#" : "+";
   pos.undo_move(m);