buffer: iterator optimization

Author: vkurchatkin

benchmark/buffers/buffer-iterate.js

@@ -0,0 +1,43 @@
+var SlowBuffer = require('buffer').SlowBuffer;
+var common = require('../common.js');
+var assert = require('assert');
+
+var bench = common.createBenchmark(main, {
+  size: [16, 512, 1024, 4096, 16386],
+  type: ['fast', 'slow'],
+  method: ['for', 'forOf'],
+  n: [1e3]
+});
+
+function main(conf) {
+  var len = +conf.size;
+  var clazz = conf.type === 'fast' ? Buffer : SlowBuffer;
+  var buffer = new clazz(len);
+  buffer.fill(0);
+
+  if (conf.method === 'for')
+    benchFor(buffer, conf.n);
+  else
+    benchForOf(buffer, conf.n);
+}
+
+
+function benchFor(buffer, n) {
+  bench.start();
+
+  for (var k = 0; k < n; k++)
+    for (var i = 0; i < buffer.length; i++)
+      assert(buffer[i] === 0);
+
+  bench.end(n);
+}
+
+function benchForOf(buffer, n) {
+  bench.start();
+
+  for (var k = 0; k < n; k++)
+    for (var b of buffer)
+      assert(b === 0);
+
+  bench.end(n);
+}

lib/buffer.js

@@ -934,43 +934,66 @@ Buffer.prototype.writeDoubleBE = function writeDoubleBE(val, offset, noAssert) {
 // ES6 iterator
 
 var ITERATOR_KIND_KEYS = 1;
-var ITERATOR_KIND_VALUES = 2;
 var ITERATOR_KIND_ENTRIES = 3;
 
+function BufferIteratorResult(value, done) {
+  this.value = value;
+  this.done = done;
+}
+
+var resultCache = new Array(256);
+
+for (var i = 0; i < 256; i++)
+  resultCache[i] = Object.freeze(new BufferIteratorResult(i, false));
+
+var finalResult = Object.freeze(new BufferIteratorResult(undefined, true));
+
 function BufferIterator(buffer, kind) {
   this._buffer = buffer;
   this._kind = kind;
   this._index = 0;
 }
 
-function BufferIteratorResult(value, done) {
-  this.value = value;
-  this.done = done;
-}
-
 BufferIterator.prototype.next = function() {
   var buffer = this._buffer;
   var kind = this._kind;
   var index = this._index;
 
   if (index >= buffer.length)
-    return new BufferIteratorResult(undefined, true);
+    return finalResult;
 
   this._index++;
 
-  if (kind === ITERATOR_KIND_VALUES)
-    return new BufferIteratorResult(buffer[index], false);
-
   if (kind === ITERATOR_KIND_ENTRIES)
     return new BufferIteratorResult([index, buffer[index]], false);
 
   return new BufferIteratorResult(index, false);
 };
 
+function BufferValueIterator(buffer) {
+  BufferIterator.call(this, buffer, null);
+}
+
+BufferValueIterator.prototype.next = function() {
+  var buffer = this._buffer;
+  var index = this._index;
+
+  if (index >= buffer.length)
+    return finalResult;
+
+  this._index++;
+
+  return resultCache[buffer[index]];
+};
+
+
 BufferIterator.prototype[Symbol.iterator] = function() {
   return this;
 };
 
+BufferValueIterator.prototype[Symbol.iterator] =
+    BufferIterator.prototype[Symbol.iterator];
+
 Buffer.prototype.keys = function() {
   return new BufferIterator(this, ITERATOR_KIND_KEYS);
 };
@@ -980,7 +1003,7 @@ Buffer.prototype.entries = function() {
 };
 
 Buffer.prototype.values = function() {
-  return new BufferIterator(this, ITERATOR_KIND_VALUES);
+  return new BufferValueIterator(this);
 };
 
 Buffer.prototype[Symbol.iterator] = Buffer.prototype.values;

test/parallel/test-buffer-iterator.js

@@ -31,7 +31,7 @@ var b;
 arr = [];
 
 for (b of buffer)
-    arr.push(b);
+  arr.push(b);
 
 assert.deepEqual(arr, [1, 2, 3, 4, 5]);