;;; Commentary:
;;; This code defines a ring data structure. A ring is a
-;;; (hd-index tl-index . vector)
+;;; (hd-index length . vector)
;;; list. You can insert to, remove from, and rotate a ring. When the ring
;;; fills up, insertions cause the oldest elts to be quietly dropped.
;;;
-;;; HEAD = index of the newest item on the ring.
-;;; TAIL = index of the oldest item on the ring.
+;;; In ring-ref, 0 is the index of the newest element. Higher indexes
+;;; correspond to older elements until they wrap.
+;;;
+;;; hd-index = index of the newest item on the ring.
+;;; length = number of ring items.
;;;
;;; These functions are used by the input history mechanism, but they can
;;; be used for other purposes as well.
;;; Code:
-(provide 'ring)
-
;;;###autoload
(defun ring-p (x)
- "T if X is a ring; NIL otherwise."
+ "Returns t if X is a ring; nil otherwise."
(and (consp x) (integerp (car x))
(consp (cdr x)) (integerp (car (cdr x)))
(vectorp (cdr (cdr x)))))
;;;###autoload
(defun make-ring (size)
- "Make a ring that can contain SIZE elts."
- (cons 1 (cons 0 (make-vector (+ size 1) nil))))
+ "Make a ring that can contain SIZE elements."
+ (cons 0 (cons 0 (make-vector size nil))))
+
+(defun ring-insert-at-beginning (ring item)
+ "Add to RING the item ITEM. Add it at the front (the early end)."
+ (let* ((vec (cdr (cdr ring)))
+ (veclen (length vec))
+ (hd (car ring))
+ (ln (car (cdr ring))))
+ (setq ln (min veclen (1+ ln))
+ hd (ring-minus1 hd veclen))
+ (aset vec hd item)
+ (setcar ring hd)
+ (setcar (cdr ring) ln)))
(defun ring-plus1 (index veclen)
"INDEX+1, with wraparound"
(- (if (= 0 index) veclen index) 1))
(defun ring-length (ring)
- "Number of elts in the ring."
- (let ((hd (car ring)) (tl (car (cdr ring))) (siz (length (cdr (cdr ring)))))
- (let ((len (if (<= hd tl) (+ 1 (- tl hd)) (+ 1 tl (- siz hd)))))
- (if (= len siz) 0 len))))
+ "Number of elements in the ring."
+ (car (cdr ring)))
(defun ring-empty-p (ring)
- (= 0 (ring-length ring)))
+ (= 0 (car (cdr ring))))
+
+(defun ring-index (index head ringlen veclen)
+ (setq index (mod index ringlen))
+ (mod (1- (+ head (- ringlen index))) veclen))
(defun ring-insert (ring item)
- "Insert a new item onto the ring. If the ring is full, dump the oldest
-item to make room."
- (let* ((vec (cdr (cdr ring))) (len (length vec))
- (new-hd (ring-minus1 (car ring) len)))
- (setcar ring new-hd)
- (aset vec new-hd item)
- (if (ring-empty-p ring) ;overflow -- dump one off the tail.
- (setcar (cdr ring) (ring-minus1 (car (cdr ring)) len)))))
-
-(defun ring-remove (ring)
- "Remove the oldest item retained on the ring."
- (if (ring-empty-p ring) (error "Ring empty")
- (let ((tl (car (cdr ring))) (vec (cdr (cdr ring))))
- (setcar (cdr ring) (ring-minus1 tl (length vec)))
- (aref vec tl))))
-
-;;; This isn't actually used in this package. I just threw it in in case
-;;; someone else wanted it. If you want rotating-ring behavior on your history
-;;; retrieval (analagous to kill ring behavior), this function is what you
-;;; need. I should write the yank-input and yank-pop-input-or-kill to go with
-;;; this, and not bind it to a key by default, so it would be available to
-;;; people who want to bind it to a key. But who would want it? Blech.
-(defun ring-rotate (ring n)
- (if (not (= n 0))
- (if (ring-empty-p ring) ;Is this the right error check?
- (error "ring empty")
- (let ((hd (car ring)) (tl (car (cdr ring))) (vec (cdr (cdr ring))))
- (let ((len (length vec)))
- (while (> n 0)
- (setq tl (ring-plus1 tl len))
- (aset ring tl (aref ring hd))
- (setq hd (ring-plus1 hd len))
- (setq n (- n 1)))
- (while (< n 0)
- (setq hd (ring-minus1 hd len))
- (aset vec hd (aref vec tl))
- (setq tl (ring-minus1 tl len))
- (setq n (- n 1))))
- (setcar ring hd)
- (setcar (cdr ring) tl)))))
-
-(defun ring-mod (n m)
- "Returns N mod M. M is positive.
-Answer is guaranteed to be non-negative, and less than m."
- (let ((n (% n m)))
- (if (>= n 0) n
- (+ n
- (if (>= m 0) m (- m)))))) ; (abs m)
+ "Insert onto ring RING the item ITEM, as the newest (last) item.
+If the ring is full, dump the oldest item to make room."
+ (let* ((vec (cdr (cdr ring)))
+ (veclen (length vec))
+ (hd (car ring))
+ (ln (car (cdr ring))))
+ (prog1
+ (aset vec (mod (+ hd ln) veclen) item)
+ (if (= ln veclen)
+ (setcar ring (ring-plus1 hd veclen))
+ (setcar (cdr ring) (1+ ln))))))
+
+(defun ring-remove (ring &optional index)
+ "Remove an item from the RING. Return the removed item.
+If optional INDEX is nil, remove the oldest item. If it's
+numeric, remove the element indexed."
+ (if (ring-empty-p ring)
+ (error "Ring empty")
+ (let* ((hd (car ring))
+ (ln (car (cdr ring)))
+ (vec (cdr (cdr ring)))
+ (veclen (length vec))
+ (tl (mod (1- (+ hd ln)) veclen))
+ oldelt)
+ (if (null index)
+ (setq index (1- ln)))
+ (setq index (ring-index index hd ln veclen))
+ (setq oldelt (aref vec index))
+ (while (/= index tl)
+ (aset vec index (aref vec (ring-plus1 index veclen)))
+ (setq index (ring-plus1 index veclen)))
+ (aset vec tl nil)
+ (setcar (cdr ring) (1- ln))
+ oldelt)))
(defun ring-ref (ring index)
- (let ((numelts (ring-length ring)))
- (if (= numelts 0) (error "indexed empty ring")
- (let* ((hd (car ring)) (tl (car (cdr ring))) (vec (cdr (cdr ring)))
- (index (ring-mod index numelts))
- (vec-index (ring-mod (+ index hd) (length vec))))
- (aref vec vec-index)))))
+ "Returns RING's INDEX element.
+INDEX need not be <= the ring length, the appropriate modulo operation
+will be performed. Element 0 is the most recently inserted; higher indices
+correspond to older elements until they wrap."
+ (if (ring-empty-p ring)
+ (error "indexed empty ring")
+ (let* ((hd (car ring)) (ln (car (cdr ring))) (vec (cdr (cdr ring))))
+ (aref vec (ring-index index hd ln (length vec))))))
+
+(provide 'ring)
;;; ring.el ends here
HCoop / bpt / emacs.git / blobdiff