Add support for generating randomized starting position, ala Fischer

Random.

1 files changed, 62 insertions, 0 deletions

diff --git a/chess-random.el b/chess-random.el
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+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;
+;; Generate Fischer Random style positions
+;;
+;; Just call `chess-fischer-random-position' to generate such a
+;; position.
+;;
+;; $Revision$
+
+(require 'chess-pos)
+
+(defvar pieces-vector [?r ?n ?b ?q ?k ?b ?n ?r])
+
+(defun shuffle-vector (vector)
+  "Randomly permute the elements of VECTOR (all permutations equally likely)"
+  (let ((i 0)
+	j
+	temp
+	(len (length vector)))
+    (while (< i len)
+      (setq j (+ i (random (- len i))))
+      (setq temp (aref vector i))
+      (aset vector i (aref vector j))
+      (aset vector j temp)
+      (setq i (1+ i))))
+  vector)
+
+;;;###autoload
+(defun chess-fischer-random-position ()
+  (let (pieces position)
+    (while (null position)
+      (setq pieces (shuffle-vector pieces-vector))
+      (let (first-bishop first-rook king)
+	(catch 'retry
+	  (dotimes (i 8)
+	    (let ((piece (aref pieces i)))
+	      (cond
+	       ((= ?b piece)
+		(if first-bishop
+		    (if (= (mod i 2) first-bishop)
+			(throw 'retry t))
+		  (setq first-bishop (mod i 2))))
+	       ((= ?k piece)
+		(if (null first-rook)
+		    (throw 'retry t))
+		(setq king i))
+	       ((= ?r piece)
+		(if first-rook
+		    (if (null king)
+			(throw 'retry t))
+		  (setq first-rook i))))))
+	  (setq position (chess-pos-create)))))
+    (dotimes (i 8)
+      (chess-pos-set-piece position (chess-rf-to-index 0 i)
+			   (aref pieces i))
+      (chess-pos-set-piece position (chess-rf-to-index 7 i)
+			   (upcase (aref pieces i))))
+    position))
+
+(provide 'chess-random)
+
+;;; chess-random.el ends here