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136 lines
4.2 KiB
EmacsLisp
136 lines
4.2 KiB
EmacsLisp
;;; ring.el --- handle rings of items
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;; Copyright (C) 1992 Free Software Foundation, Inc.
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;; Maintainer: FSF
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;; Keywords: extensions
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;; This file is part of GNU Emacs.
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;; GNU Emacs is free software; you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation; either version 2, or (at your option)
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;; any later version.
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;; GNU Emacs is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;; You should have received a copy of the GNU General Public License
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;; along with GNU Emacs; see the file COPYING. If not, write to the
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;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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;; Boston, MA 02111-1307, USA.
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;;; Commentary:
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;; This code defines a ring data structure. A ring is a
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;; (hd-index length . vector)
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;; list. You can insert to, remove from, and rotate a ring. When the ring
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;; fills up, insertions cause the oldest elts to be quietly dropped.
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;;
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;; In ring-ref, 0 is the index of the newest element. Higher indexes
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;; correspond to older elements until they wrap.
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;;
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;; hd-index = index of the newest item on the ring.
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;; length = number of ring items.
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;;
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;; These functions are used by the input history mechanism, but they can
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;; be used for other purposes as well.
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;;; Code:
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;;;###autoload
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(defun ring-p (x)
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"Returns t if X is a ring; nil otherwise."
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(and (consp x) (integerp (car x))
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(consp (cdr x)) (integerp (car (cdr x)))
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(vectorp (cdr (cdr x)))))
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;;;###autoload
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(defun make-ring (size)
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"Make a ring that can contain SIZE elements."
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(cons 0 (cons 0 (make-vector size nil))))
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(defun ring-insert-at-beginning (ring item)
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"Add to RING the item ITEM. Add it at the front (the early end)."
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(let* ((vec (cdr (cdr ring)))
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(veclen (length vec))
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(hd (car ring))
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(ln (car (cdr ring))))
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(setq ln (min veclen (1+ ln))
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hd (ring-minus1 hd veclen))
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(aset vec hd item)
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(setcar ring hd)
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(setcar (cdr ring) ln)))
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(defun ring-plus1 (index veclen)
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"INDEX+1, with wraparound"
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(let ((new-index (+ index 1)))
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(if (= new-index veclen) 0 new-index)))
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(defun ring-minus1 (index veclen)
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"INDEX-1, with wraparound"
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(- (if (= 0 index) veclen index) 1))
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(defun ring-length (ring)
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"Number of elements in the ring."
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(car (cdr ring)))
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(defun ring-empty-p (ring)
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(= 0 (car (cdr ring))))
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(defun ring-index (index head ringlen veclen)
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(setq index (mod index ringlen))
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(mod (1- (+ head (- ringlen index))) veclen))
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(defun ring-insert (ring item)
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"Insert onto ring RING the item ITEM, as the newest (last) item.
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If the ring is full, dump the oldest item to make room."
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(let* ((vec (cdr (cdr ring)))
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(veclen (length vec))
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(hd (car ring))
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(ln (car (cdr ring))))
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(prog1
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(aset vec (mod (+ hd ln) veclen) item)
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(if (= ln veclen)
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(setcar ring (ring-plus1 hd veclen))
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(setcar (cdr ring) (1+ ln))))))
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(defun ring-remove (ring &optional index)
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"Remove an item from the RING. Return the removed item.
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If optional INDEX is nil, remove the oldest item. If it's
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numeric, remove the element indexed."
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(if (ring-empty-p ring)
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(error "Ring empty")
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(let* ((hd (car ring))
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(ln (car (cdr ring)))
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(vec (cdr (cdr ring)))
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(veclen (length vec))
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(tl (mod (1- (+ hd ln)) veclen))
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oldelt)
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(if (null index)
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(setq index (1- ln)))
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(setq index (ring-index index hd ln veclen))
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(setq oldelt (aref vec index))
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(while (/= index tl)
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(aset vec index (aref vec (ring-plus1 index veclen)))
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(setq index (ring-plus1 index veclen)))
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(aset vec tl nil)
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(setcar (cdr ring) (1- ln))
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oldelt)))
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(defun ring-ref (ring index)
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"Returns RING's INDEX element.
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INDEX need not be <= the ring length, the appropriate modulo operation
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will be performed. Element 0 is the most recently inserted; higher indices
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correspond to older elements until they wrap."
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(if (ring-empty-p ring)
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(error "indexed empty ring")
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(let* ((hd (car ring)) (ln (car (cdr ring))) (vec (cdr (cdr ring))))
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(aref vec (ring-index index hd ln (length vec))))))
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(provide 'ring)
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;;; ring.el ends here
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