consarray.mjs 3.2 KB

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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. * Constructs a ConsArray object. It is used mainly for tree traversal.
  29. * In this use case we have lots of arrays that we need to iterate
  30. * sequentally. The internal Array implementation is horribly slow
  31. * when concatenating on large (10K items) arrays due to memory copying.
  32. * That's why we avoid copying memory and insead build a linked list
  33. * of arrays to iterate through.
  34. *
  35. * @constructor
  36. */
  37. export class ConsArray {
  38. constructor() {
  39. this.tail_ = new ConsArrayCell(null, null);
  40. this.currCell_ = this.tail_;
  41. this.currCellPos_ = 0;
  42. }
  43. /**
  44. * Concatenates another array for iterating. Empty arrays are ignored.
  45. * This operation can be safely performed during ongoing ConsArray
  46. * iteration.
  47. *
  48. * @param {Array} arr Array to concatenate.
  49. */
  50. concat(arr) {
  51. if (arr.length > 0) {
  52. this.tail_.data = arr;
  53. this.tail_ = this.tail_.next = new ConsArrayCell(null, null);
  54. }
  55. }
  56. /**
  57. * Whether the end of iteration is reached.
  58. */
  59. atEnd() {
  60. return this.currCell_ === null ||
  61. this.currCell_.data === null ||
  62. this.currCellPos_ >= this.currCell_.data.length;
  63. }
  64. /**
  65. * Returns the current item, moves to the next one.
  66. */
  67. next() {
  68. const result = this.currCell_.data[this.currCellPos_++];
  69. if (this.currCellPos_ >= this.currCell_.data.length) {
  70. this.currCell_ = this.currCell_.next;
  71. this.currCellPos_ = 0;
  72. }
  73. return result;
  74. }
  75. }
  76. /**
  77. * A cell object used for constructing a list in ConsArray.
  78. *
  79. * @constructor
  80. */
  81. class ConsArrayCell {
  82. constructor(data, next) {
  83. this.data = data;
  84. this.next = next;
  85. }
  86. }