add hw2

node_modules/fast-fifo/fixed-size.js

@@ -0,0 +1,39 @@
+module.exports = class FixedFIFO {
+  constructor (hwm) {
+    if (!(hwm > 0) || ((hwm - 1) & hwm) !== 0) throw new Error('Max size for a FixedFIFO should be a power of two')
+    this.buffer = new Array(hwm)
+    this.mask = hwm - 1
+    this.top = 0
+    this.btm = 0
+    this.next = null
+  }
+
+  clear () {
+    this.top = this.btm = 0
+    this.next = null
+    this.buffer.fill(undefined)
+  }
+
+  push (data) {
+    if (this.buffer[this.top] !== undefined) return false
+    this.buffer[this.top] = data
+    this.top = (this.top + 1) & this.mask
+    return true
+  }
+
+  shift () {
+    const last = this.buffer[this.btm]
+    if (last === undefined) return undefined
+    this.buffer[this.btm] = undefined
+    this.btm = (this.btm + 1) & this.mask
+    return last
+  }
+
+  peek () {
+    return this.buffer[this.btm]
+  }
+
+  isEmpty () {
+    return this.buffer[this.btm] === undefined
+  }
+}