summaryrefslogtreecommitdiff
path: root/lisp/gnus/rtree.el
blob: 9bcf45ef655f5b5f1c5280ce7c3bda99cfa826ae (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
;;; rtree.el --- functions for manipulating range trees

;; Copyright (C) 2010, 2011 Free Software Foundation, Inc.

;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; A "range tree" is a binary tree that stores ranges.  They are
;; similar to interval trees, but do not allow overlapping intervals.

;; A range is an ordered list of number intervals, like this:

;; ((10 . 25) 56 78 (98 . 201))

;; Common operations, like lookup, deletion and insertion are O(n) in
;; a range, but an rtree is O(log n) in all these operations.
;; Transformation between a range and an rtree is O(n).

;; The rtrees are quite simple.  The structure of each node is

;; (cons (cons low high) (cons left right))

;; That is, they are three cons cells, where the car of the top cell
;; is the actual range, and the cdr has the left and right child.  The
;; rtrees aren't automatically balanced, but are balanced when
;; created, and can be rebalanced when deemed necessary.

;;; Code:

(eval-when-compile
  (require 'cl))

(defmacro rtree-make-node ()
  `(list (list nil) nil))

(defmacro rtree-set-left (node left)
  `(setcar (cdr ,node) ,left))

(defmacro rtree-set-right (node right)
  `(setcdr (cdr ,node) ,right))

(defmacro rtree-set-range (node range)
  `(setcar ,node ,range))

(defmacro rtree-low (node)
  `(caar ,node))

(defmacro rtree-high (node)
  `(cdar ,node))

(defmacro rtree-set-low (node number)
  `(setcar (car ,node) ,number))

(defmacro rtree-set-high (node number)
  `(setcdr (car ,node) ,number))

(defmacro rtree-left (node)
  `(cadr ,node))

(defmacro rtree-right (node)
  `(cddr ,node))

(defmacro rtree-range (node)
  `(car ,node))

(defsubst rtree-normalise-range (range)
  (when (numberp range)
    (setq range (cons range range)))
  range)

(defun rtree-make (range)
  "Make an rtree from RANGE."
  ;; Normalize the range.
  (unless (listp (cdr-safe range))
    (setq range (list range)))
  (rtree-make-1 (cons nil range) (length range)))

(defun rtree-make-1 (range length)
  (let ((mid (/ length 2))
	(node (rtree-make-node)))
    (when (> mid 0)
      (rtree-set-left node (rtree-make-1 range mid)))
    (rtree-set-range node (rtree-normalise-range (cadr range)))
    (setcdr range (cddr range))
    (when (> (- length mid 1) 0)
      (rtree-set-right node (rtree-make-1 range (- length mid 1))))
    node))

(defun rtree-memq (tree number)
  "Return non-nil if NUMBER is present in TREE."
  (while (and tree
	      (not (and (>= number (rtree-low tree))
			(<= number (rtree-high tree)))))
    (setq tree
	  (if (< number (rtree-low tree))
	      (rtree-left tree)
	    (rtree-right tree))))
  tree)

(defun rtree-add (tree number)
  "Add NUMBER to TREE."
  (while tree
    (cond
     ;; It's already present, so we don't have to do anything.
     ((and (>= number (rtree-low tree))
	   (<= number (rtree-high tree)))
      (setq tree nil))
     ((< number (rtree-low tree))
      (cond
       ;; Extend the low range.
       ((= number (1- (rtree-low tree)))
	(rtree-set-low tree number)
	;; Check whether we need to merge this node with the child.
	(when (and (rtree-left tree)
		   (= (rtree-high (rtree-left tree)) (1- number)))
	  ;; Extend the range to the low from the child.
	  (rtree-set-low tree (rtree-low (rtree-left tree)))
	  ;; The child can't have a right child, so just transplant the
	  ;; child's left tree to our left tree.
	  (rtree-set-left tree (rtree-left (rtree-left tree))))
	(setq tree nil))
       ;; Descend further to the left.
       ((rtree-left tree)
	(setq tree (rtree-left tree)))
       ;; Add a new node.
       (t
	(let ((new-node (rtree-make-node)))
	  (rtree-set-low new-node number)
	  (rtree-set-high new-node number)
	  (rtree-set-left tree new-node)
	  (setq tree nil)))))
     (t
      (cond
       ;; Extend the high range.
       ((= number (1+ (rtree-high tree)))
	(rtree-set-high tree number)
	;; Check whether we need to merge this node with the child.
	(when (and (rtree-right tree)
		   (= (rtree-low (rtree-right tree)) (1+ number)))
	  ;; Extend the range to the high from the child.
	  (rtree-set-high tree (rtree-high (rtree-right tree)))
	  ;; The child can't have a left child, so just transplant the
	  ;; child's left right to our right tree.
	  (rtree-set-right tree (rtree-right (rtree-right tree))))
	(setq tree nil))
       ;; Descend further to the right.
       ((rtree-right tree)
	(setq tree (rtree-right tree)))
       ;; Add a new node.
       (t
	(let ((new-node (rtree-make-node)))
	  (rtree-set-low new-node number)
	  (rtree-set-high new-node number)
	  (rtree-set-right tree new-node)
	  (setq tree nil))))))))

(defun rtree-delq (tree number)
  "Remove NUMBER from TREE destructively.  Returns the new tree."
  (let ((result tree)
	prev)
    (while tree
      (cond
       ((< number (rtree-low tree))
	(setq prev tree
	      tree (rtree-left tree)))
       ((> number (rtree-high tree))
	(setq prev tree
	      tree (rtree-right tree)))
       ;; The number is in this node.
       (t
	(cond
	 ;; The only entry; delete the node.
	 ((= (rtree-low tree) (rtree-high tree))
	  (cond
	   ;; Two children.  Replace with successor value.
	   ((and (rtree-left tree) (rtree-right tree))
	    (let ((parent tree)
		  (successor (rtree-right tree)))
	      (while (rtree-left successor)
		(setq parent successor
		      successor (rtree-left successor)))
	      ;; We now have the leftmost child of our right child.
	      (rtree-set-range tree (rtree-range successor))
	      ;; Transplant the child (if any) to the parent.
	      (rtree-set-left parent (rtree-right successor))))
	   (t
	    (let ((rest (or (rtree-left tree)
			    (rtree-right tree))))
	      ;; One or zero children.  Remove the node.
	      (cond
	       ((null prev)
		(setq result rest))
	       ((eq (rtree-left prev) tree)
		(rtree-set-left prev rest))
	       (t
		(rtree-set-right prev rest)))))))
	 ;; The lowest in the range; just adjust.
	 ((= number (rtree-low tree))
	  (rtree-set-low tree (1+ number)))
	 ;; The highest in the range; just adjust.
	 ((= number (rtree-high tree))
	  (rtree-set-high tree (1- number)))
	 ;; We have to split this range.
	 (t
	  (let ((new-node (rtree-make-node)))
	    (rtree-set-low new-node (rtree-low tree))
	    (rtree-set-high new-node (1- number))
	    (rtree-set-low tree (1+ number))
	    (cond
	     ;; Two children; insert the new node as the predecessor
	     ;; node.
	     ((and (rtree-left tree) (rtree-right tree))
	      (let ((predecessor (rtree-left tree)))
		(while (rtree-right predecessor)
		  (setq predecessor (rtree-right predecessor)))
		(rtree-set-right predecessor new-node)))
	     ((rtree-left tree)
	      (rtree-set-right new-node tree)
	      (rtree-set-left new-node (rtree-left tree))
	      (rtree-set-left tree nil)
	      (cond
	       ((null prev)
		(setq result new-node))
	       ((eq (rtree-left prev) tree)
		(rtree-set-left prev new-node))
	       (t
		(rtree-set-right prev new-node))))
	     (t
	      (rtree-set-left tree new-node))))))
	(setq tree nil))))
    result))

(defun rtree-extract (tree)
  "Convert TREE to range form."
  (let (stack result)
    (while (or stack
	       tree)
      (if tree
	  (progn
	    (push tree stack)
	    (setq tree (rtree-right tree)))
	(setq tree (pop stack))
	(push (if (= (rtree-low tree)
		     (rtree-high tree))
		  (rtree-low tree)
		(rtree-range tree))
	      result)
	(setq tree (rtree-left tree))))
    result))

(defun rtree-length (tree)
  "Return the number of numbers stored in TREE."
  (if (null tree)
      0
    (+ (rtree-length (rtree-left tree))
       (1+ (- (rtree-high tree)
	      (rtree-low tree)))
       (rtree-length (rtree-right tree)))))

(provide 'rtree)

;;; rtree.el ends here