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|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; Convert a chess position to/from FEN notation
;;
;; FEN notation encodes a chess position using a simple string. The
;; format is:
;;
;; POSITION SIDE FLAGS
;;
;; The POSITION gives all eight ranks, by specifying a letter for each
;; piece on the position, and a number for any intervening spaces.
;; Trailing spaces need not be counted. Uppercase letters signify
;; white, and lowercase black. For example, if your position only had
;; a black king on d8, your POSITION string would be:
;;
;; 3k////////
;;
;; For the three spaces (a, b and c file), the black king, and then
;; all the remaining ranks (which are all empty, so their spaces can
;; be ignored).
;;
;; The SIDE is w or b, to indicate whose move it is.
;;
;; The FLAGS can contain K, Q, k or q, to signify whether the white or
;; black king can still castle on the king or queen side. You can
;; also have coordinates, such as e4, a5, to specify which pawns may
;; be captured by en passant.
;;
;; The starting chess position always looks like this:
;;
;; rnbqkbnr/pppppppp/////PPPPPPPP/RNBQKBNR/ w KQkq -
;;
;; And in "full" mode (where all spaces are accounted for):
;;
;; rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq -
;;
;; It may also have the current game sequence appended, but this
;; relate to the game, not the position.
;;
(defun chess-fen-to-pos (fen)
"Convert a FEN-like notation string to a chess position."
(let ((i 0) (l (length fen))
(rank 0) (file 0) (c ?0)
(position (chess-pos-create t))
error (space-count 0))
(setq c (aref fen i))
(while (and (null error)
(/= c ? ) (< i l))
(cond
((= c ?/)
(setq file 0 rank (1+ rank)))
((and (>= c ?1) (<= c ?9))
(setq file (+ file (- c ?0))))
((memq (upcase c) '(?K ?Q ?B ?N ?R ?P))
(chess-pos-set-piece position (chess-rf-to-index rank file) c)
(setq file (1+ file)))
(t
(setq error t)))
(setq i (1+ i) c (aref fen i)))
(if (= (aref fen i) ? )
(setq i (1+ i)))
(if (memq (aref fen i) '(?b ?w))
(progn
(chess-pos-set-side-to-move position (= (aref fen i) ?w))
(setq i (+ i 2)))
(setq error t))
(setq c (aref fen i))
(while (and (null error)
(< space-count 2) (< i l))
(cond
((= c ?-))
((= c ? ) (setq space-count (1+ space-count)))
((= c ?K) (chess-pos-set-can-castle position ?K t))
((= c ?Q) (chess-pos-set-can-castle position ?Q t))
((= c ?k) (chess-pos-set-can-castle position ?k t))
((= c ?q) (chess-pos-set-can-castle position ?q t))
((and (>= c ?a) (<= c ?h))
(chess-pos-set-en-passant position (chess-coord-to-index
(substring fen i (+ i 2))))
(setq i (1+ i)))
(t
(setq error t)))
(setq i (1+ i) c (and (< i l) (aref fen i))))
(unless error
position)))
(defun chess-pos-to-fen (position &optional full)
"Convert a chess POSITION to FEN-like notation.
If FULL is non-nil, represent trailing spaces as well."
(let ((blank 0) (str "") output)
(dotimes (rank 8)
(dotimes (file 8)
(let ((p (chess-pos-piece position (chess-rf-to-index rank file))))
(if (= p ? )
(setq blank (1+ blank))
(if (> blank 0)
(setq str (concat str (int-to-string blank)) blank 0))
(setq str (concat str (char-to-string p))))))
(if (and full (> blank 0))
(setq str (concat str (int-to-string blank))))
(setq blank 0 str (concat str "/")))
(setq str (if (chess-pos-side-to-move position)
(concat str " w ")
(concat str " b ")))
(if (chess-pos-can-castle position ?K)
(setq str (concat str "K") output t))
(if (chess-pos-can-castle position ?Q)
(setq str (concat str "Q") output t))
(if (chess-pos-can-castle position ?k)
(setq str (concat str "k") output t))
(if (chess-pos-can-castle position ?q)
(setq str (concat str "q") output t))
(if output
(setq str (concat str " "))
(setq str (concat str "- ")))
(let ((index (chess-pos-en-passant position)))
(if index
(concat str (chess-index-to-coord index))
(concat str "-")))))
(provide 'chess-fen)
;;; chess-fen.el ends here
|
