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+/* eslint-disable */
+
+'use strict'
+
+// Extracted from node/lib/internal/fixed_queue.js
+
+// Currently optimal queue size, tested on V8 6.0 - 6.6. Must be power of two.
+const kSize = 2048;
+const kMask = kSize - 1;
+
+// The FixedQueue is implemented as a singly-linked list of fixed-size
+// circular buffers. It looks something like this:
+//
+// head tail
+// | |
+// v v
+// +-----------+ <-----\ +-----------+ <------\ +-----------+
+// | [null] | \----- | next | \------- | next |
+// +-----------+ +-----------+ +-----------+
+// | item | <-- bottom | item | <-- bottom | [empty] |
+// | item | | item | | [empty] |
+// | item | | item | | [empty] |
+// | item | | item | | [empty] |
+// | item | | item | bottom --> | item |
+// | item | | item | | item |
+// | ... | | ... | | ... |
+// | item | | item | | item |
+// | item | | item | | item |
+// | [empty] | <-- top | item | | item |
+// | [empty] | | item | | item |
+// | [empty] | | [empty] | <-- top top --> | [empty] |
+// +-----------+ +-----------+ +-----------+
+//
+// Or, if there is only one circular buffer, it looks something
+// like either of these:
+//
+// head tail head tail
+// | | | |
+// v v v v
+// +-----------+ +-----------+
+// | [null] | | [null] |
+// +-----------+ +-----------+
+// | [empty] | | item |
+// | [empty] | | item |
+// | item | <-- bottom top --> | [empty] |
+// | item | | [empty] |
+// | [empty] | <-- top bottom --> | item |
+// | [empty] | | item |
+// +-----------+ +-----------+
+//
+// Adding a value means moving `top` forward by one, removing means
+// moving `bottom` forward by one. After reaching the end, the queue
+// wraps around.
+//
+// When `top === bottom` the current queue is empty and when
+// `top + 1 === bottom` it's full. This wastes a single space of storage
+// but allows much quicker checks.
+
+class FixedCircularBuffer {
+ constructor() {
+ this.bottom = 0;
+ this.top = 0;
+ this.list = new Array(kSize);
+ this.next = null;
+ }
+
+ isEmpty() {
+ return this.top === this.bottom;
+ }
+
+ isFull() {
+ return ((this.top + 1) & kMask) === this.bottom;
+ }
+
+ push(data) {
+ this.list[this.top] = data;
+ this.top = (this.top + 1) & kMask;
+ }
+
+ shift() {
+ const nextItem = this.list[this.bottom];
+ if (nextItem === undefined)
+ return null;
+ this.list[this.bottom] = undefined;
+ this.bottom = (this.bottom + 1) & kMask;
+ return nextItem;
+ }
+}
+
+module.exports = class FixedQueue {
+ constructor() {
+ this.head = this.tail = new FixedCircularBuffer();
+ }
+
+ isEmpty() {
+ return this.head.isEmpty();
+ }
+
+ push(data) {
+ if (this.head.isFull()) {
+ // Head is full: Creates a new queue, sets the old queue's `.next` to it,
+ // and sets it as the new main queue.
+ this.head = this.head.next = new FixedCircularBuffer();
+ }
+ this.head.push(data);
+ }
+
+ shift() {
+ const tail = this.tail;
+ const next = tail.shift();
+ if (tail.isEmpty() && tail.next !== null) {
+ // If there is another queue, it forms the new tail.
+ this.tail = tail.next;
+ }
+ return next;
+ }
+};