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source: branches/f4grobner/priority-queue.lisp@ 448

Last change on this file since 448 was 448, checked in by Marek Rychlik, 9 years ago

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1;;; -*- Mode: Lisp; Package: Maxima; Syntax: Common-Lisp; Base: 10 -*-
2;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
3;;;
4;;; Copyright (C) 1999, 2002, 2009, 2015 Marek Rychlik <rychlik@u.arizona.edu>
5;;;
6;;; This program is free software; you can redistribute it and/or modify
7;;; it under the terms of the GNU General Public License as published by
8;;; the Free Software Foundation; either version 2 of the License, or
9;;; (at your option) any later version.
10;;;
11;;; This program is distributed in the hope that it will be useful,
12;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
13;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14;;; GNU General Public License for more details.
15;;;
16;;; You should have received a copy of the GNU General Public License
17;;; along with this program; if not, write to the Free Software
18;;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
19;;;
20;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
21
22;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
23;;
24;; A conventional implementation of priority queues based on heaps
25;;
26;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
27
28(defpackage "PRIORITY-QUEUE"
29 (:use :cl)
30 (:export "*PRIORITY-QUEUE-ALLOCATION-SIZE*"
31 "MAKE-PRIORITY-QUEUE"
32 "PRIORITY-QUEUE-INSERT"
33 "PRIORITY-QUEUE-REMOVE"
34 "PRIORITY-QUEUE-EMPTY-P"
35 "PRIORITY-QUEUE-SIZE"
36 ))
37
38(in-package :priority-queue)
39(defparameter *priority-queue-allocation-size* 16)
40
41(defun priority-queue-make-heap (&key (element-type 'fixnum))
42 (make-array *priority-queue-allocation-size* :element-type element-type :fill-pointer 1
43 :adjustable t))
44
45(defstruct (priority-queue (:constructor priority-queue-construct))
46 (heap (priority-queue-make-heap))
47 test)
48
49(defun make-priority-queue (&key (element-type 'fixnum)
50 (test #'<=)
51 (element-key #'identity))
52 (priority-queue-construct
53 :heap (priority-queue-make-heap :element-type element-type)
54 :test #'(lambda (x y) (funcall test (funcall element-key y) (funcall element-key x)))))
55
56(defun priority-queue-insert (pq item)
57 (priority-queue-heap-insert (priority-queue-heap pq) item (priority-queue-test pq)))
58
59(defun priority-queue-remove (pq)
60 (priority-queue-heap-remove (priority-queue-heap pq) (priority-queue-test pq)))
61
62(defun priority-queue-empty-p (pq)
63 (priority-queue-heap-empty-p (priority-queue-heap pq)))
64
65(defun priority-queue-size (pq)
66 (fill-pointer (priority-queue-heap pq)))
67
68(defun priority-queue-upheap (a k
69 &optional
70 (test #'<=)
71 &aux (v (aref a k)))
72 (declare (fixnum k))
73 (assert (< 0 k (fill-pointer a)))
74 (loop
75 (let ((parent (ash k -1)))
76 (when (zerop parent) (return))
77 (unless (funcall test (aref a parent) v)
78 (return))
79 (setf (aref a k) (aref a parent)
80 k parent)))
81 (setf (aref a k) v)
82 a)
83
84
85(defun priority-queue-heap-insert (a item &optional (test #'<=))
86 (vector-push-extend item a)
87 (priority-queue-upheap a (1- (fill-pointer a)) test))
88
89(defun priority-queue-downheap (a k
90 &optional
91 (test #'<=)
92 &aux (v (aref a k)) (j 0) (n (fill-pointer a)))
93 (declare (fixnum k n j))
94 (loop
95 (unless (<= k (ash n -1))
96 (return))
97 (setf j (ash k 1))
98 (if (and (< j n) (not (funcall test (aref a (1+ j)) (aref a j))))
99 (incf j))
100 (when (funcall test (aref a j) v)
101 (return))
102 (setf (aref a k) (aref a j)
103 k j))
104 (setf (aref a k) v)
105 a)
106
107(defun priority-queue-heap-remove (a &optional (test #'<=) &aux (v (aref a 1)))
108 (when (<= (fill-pointer a) 1) (error "Empty queue."))
109 (setf (aref a 1) (vector-pop a))
110 (priority-queue-downheap a 1 test)
111 (values v a))
112
113(defun priority-queue-heap-empty-p (a)
114 (<= (fill-pointer a) 1))
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