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1// Copyright 2009 the V8 project authors. All rights reserved.
2// Redistribution and use in source and binary forms, with or without
3// modification, are permitted provided that the following conditions are
4// met:
5//
6//     * Redistributions of source code must retain the above copyright
7//       notice, this list of conditions and the following disclaimer.
8//     * Redistributions in binary form must reproduce the above
9//       copyright notice, this list of conditions and the following
10//       disclaimer in the documentation and/or other materials provided
11//       with the distribution.
12//     * Neither the name of Google Inc. nor the names of its
13//       contributors may be used to endorse or promote products derived
14//       from this software without specific prior written permission.
15//
16// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27
28
29/**
30 * Constructs a ConsArray object. It is used mainly for tree traversal.
31 * In this use case we have lots of arrays that we need to iterate
32 * sequentally. The internal Array implementation is horribly slow
33 * when concatenating on large (10K items) arrays due to memory copying.
34 * That's why we avoid copying memory and insead build a linked list
35 * of arrays to iterate through.
36 *
37 * @constructor
38 */
39function ConsArray() {
40  this.tail_ = new ConsArray.Cell(null, null);
41  this.currCell_ = this.tail_;
42  this.currCellPos_ = 0;
43};
44
45
46/**
47 * Concatenates another array for iterating. Empty arrays are ignored.
48 * This operation can be safely performed during ongoing ConsArray
49 * iteration.
50 *
51 * @param {Array} arr Array to concatenate.
52 */
53ConsArray.prototype.concat = function(arr) {
54  if (arr.length > 0) {
55    this.tail_.data = arr;
56    this.tail_ = this.tail_.next = new ConsArray.Cell(null, null);
57  }
58};
59
60
61/**
62 * Whether the end of iteration is reached.
63 */
64ConsArray.prototype.atEnd = function() {
65  return this.currCell_ === null ||
66      this.currCell_.data === null ||
67      this.currCellPos_ >= this.currCell_.data.length;
68};
69
70
71/**
72 * Returns the current item, moves to the next one.
73 */
74ConsArray.prototype.next = function() {
75  var result = this.currCell_.data[this.currCellPos_++];
76  if (this.currCellPos_ >= this.currCell_.data.length) {
77    this.currCell_ = this.currCell_.next;
78    this.currCellPos_ = 0;
79  }
80  return result;
81};
82
83
84/**
85 * A cell object used for constructing a list in ConsArray.
86 *
87 * @constructor
88 */
89ConsArray.Cell = function(data, next) {
90  this.data = data;
91  this.next = next;
92};
93