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diff --git a/chess-clock.el b/chess-clock.el
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+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;
+;; Implements a chess clock
+;;
+;; $Revision$
+
+(defvar chess-clock-last-time nil)
+(defvar chess-clock-timer nil)
+
+(make-variable-buffer-local 'chess-clock-last-time)
+(make-variable-buffer-local 'chess-clock-timer)
+
+(defsubst chess-clock-add-seconds (time seconds)
+  "To TIME, add SECONDS.  Return result as a time value."
+  (let* ((secint (truncate seconds))
+	 (hi (/ secint 65536))
+	 (lo (% secint 65536))
+	 (calc (+ (cadr time) lo)))
+    (if (< calc 65536)
+	(list (+ (car time) hi) calc)
+      (list (+ (car time) (1+ hi)) (% calc 65536)))))
+
+(defsubst chess-clock-time-to-seconds (time)
+  "Convert TIME to a floating point number."
+  (+ (* (car time) 65536.0)
+     (cadr time)
+     (/ (or (car (cdr (cdr time))) 0) 1000000.0)))
+
+(defsubst chess-clock-time-diff (t1 t2)
+  "Return the difference in seconds between T1 and T2."
+  (- (chess-clock-time-to-seconds t1)
+     (chess-clock-time-to-seconds t2)))
+
+(defun chess-clock-handler (game event &rest args)
+  (cond
+   ((eq event 'initialize)
+    (unless (chess-game-data game 'white-remaining)
+      (chess-game-set-data game 'white-remaining (float (car args))))
+    (unless (chess-game-data game 'black-remaining)
+      (chess-game-set-data game 'black-remaining (float (car args))))
+    (setq chess-clock-timer
+	  (run-with-timer 0 1 'chess-clock-tick-tock (current-buffer)))
+    t)
+
+   ((eq event 'post-undo)
+    (let ((last-ply (car (last (chess-game-plies game) 2))))
+      (chess-game-set-data game 'white-remaining
+			   (chess-ply-keyword last-ply :white))
+      (chess-game-set-data game 'black-remaining
+			   (chess-ply-keyword last-ply :black))))
+
+   ((eq event 'move)
+    (when (> (chess-game-index game) 0)
+      (let ((last-ply (car (last (chess-game-plies game) 2))))
+	(nconc last-ply
+	       (list :white (chess-game-data game 'white-remaining)
+		     :black (chess-game-data game 'black-remaining))))))
+
+   ((eq event 'destroy)
+    (cancel-timer chess-clock-timer))))
+
+(defvar chess-clock-tick-tocking nil)
+
+(defun chess-clock-tick-tock (module)
+  (unless chess-clock-tick-tocking
+    (let ((chess-clock-tick-tocking t))
+      (with-current-buffer module
+	(let ((last-time chess-clock-last-time) counter)
+	  (setq chess-clock-last-time (current-time))
+	  (when (> (chess-game-index chess-module-game) 0)
+	    (if (chess-pos-side-to-move (chess-game-pos chess-module-game))
+		(setq counter 'white-remaining)
+	      (setq counter 'black-remaining))
+	    (chess-game-set-data
+	     chess-module-game counter
+	     (- (chess-game-data chess-module-game counter)
+		(chess-clock-time-diff chess-clock-last-time last-time))))))
+      (force-mode-line-update))))
+
+(provide 'chess-clock)
+
+;;; chess-clock.el ends here