add hw2

node_modules/fast-fifo/index.js

@@ -0,0 +1,48 @@
+const FixedFIFO = require('./fixed-size')
+
+module.exports = class FastFIFO {
+  constructor (hwm) {
+    this.hwm = hwm || 16
+    this.head = new FixedFIFO(this.hwm)
+    this.tail = this.head
+    this.length = 0
+  }
+
+  clear () {
+    this.head = this.tail
+    this.head.clear()
+    this.length = 0
+  }
+
+  push (val) {
+    this.length++
+    if (!this.head.push(val)) {
+      const prev = this.head
+      this.head = prev.next = new FixedFIFO(2 * this.head.buffer.length)
+      this.head.push(val)
+    }
+  }
+
+  shift () {
+    if (this.length !== 0) this.length--
+    const val = this.tail.shift()
+    if (val === undefined && this.tail.next) {
+      const next = this.tail.next
+      this.tail.next = null
+      this.tail = next
+      return this.tail.shift()
+    }
+
+    return val
+  }
+
+  peek () {
+    const val = this.tail.peek()
+    if (val === undefined && this.tail.next) return this.tail.next.peek()
+    return val
+  }
+
+  isEmpty () {
+    return this.length === 0
+  }
+}