chess.js: Skip legality checking during disambiguation if not needed.

diff --git a/www/js/chess.js b/www/js/chess.js
index af275589f65e1924bf880d37ba480c1c6b763f49..91f6c1dda7af308f342e08e05095ca26238566c7 100644 (file)
--- a/www/js/chess.js
+++ b/www/js/chess.js
@@ -1120,7 +1120,14 @@ var Chess = function(fen) {
        return '';
     }
 
-    let moves = find_attacking_moves(move.to, piece, move.color, sloppy);
+    let moves = find_attacking_moves(move.to, piece, move.color);
+    if (moves.length <= 1) {
+       // There can be no ambiguity, so don't bother checking legality
+       // (we assume the move has already been found legal).
+       return '';
+    }
+
+    moves = possibly_filter_moves(moves, move.color, !sloppy);
 
     var ambiguities = 0;
     var same_rank = 0;
@@ -1169,11 +1176,12 @@ var Chess = function(fen) {
     return '';
   }
 
-  // Find all moves featuring the given piece attacking the given square
-  // (using symmetry of all non-pawn-or-castle moves, we simply generate
-  // moves backwards). Does not support kings or pawns. Assumes there's
-  // not already a piece of our own color on the destination square.
-  function find_attacking_moves(to, piece, us, sloppy) {
+  // Find all pseudolegal moves featuring the given piece attacking
+  // the given square (using symmetry of all non-pawn-or-castle moves,
+  // we simply generate // moves backwards). Does not support kings
+  // or pawns. Assumes there's // not already a piece of our own color
+  // on the destination square.
+  function find_attacking_moves(to, piece, us) {
     let moves = [];
 
     function add_move(board, moves, from, to, flags, rook_sq) {
@@ -1201,7 +1209,7 @@ var Chess = function(fen) {
       }
     }
 
-    return possibly_filter_moves(moves, us, !sloppy);
+    return moves;
   }
 
   function ascii() {