buffer: optimize Buffer.byteLength

Buffer.byteLength is important for speed because it is called whenever a
new Buffer is created from a string.

This commit optimizes Buffer.byteLength execution by:
- moving base64 length calculation into JS-land, which is now much
  faster
- remove redundant code and streamline the UTF8 length calculation

It also adds a benchmark and better tests.

PR-URL: https://github.com/nodejs/io.js/pull/1713
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

1 files changed, 55 insertions, 0 deletions

diff --git a/benchmark/buffers/buffer-bytelength.js b/benchmark/buffers/buffer-bytelength.js
new file mode 100644
index 0000000000..6a7afe6921
--- /dev/null
+++ b/benchmark/buffers/buffer-bytelength.js
@@ -0,0 +1,55 @@
+var common = require('../common');
+
+var bench = common.createBenchmark(main, {
+  encoding: ['utf8', 'base64'],
+  len: [1, 2, 4, 16, 64, 256], // x16
+  n: [5e6]
+});
+
+// 16 chars each
+var chars = [
+  'hello brendan!!!', // 1 byte
+  'ΰαβγδεζηθικλμνξο', // 2 bytes
+  '挰挱挲挳挴挵挶挷挸挹挺挻挼挽挾挿', // 3 bytes
+  '𠜎𠜱𠝹𠱓𠱸𠲖𠳏𠳕𠴕𠵼𠵿𠸎𠸏𠹷𠺝𠺢' // 4 bytes
+];
+
+function main(conf) {
+  var n = conf.n | 0;
+  var len = conf.len | 0;
+  var encoding = conf.encoding;
+
+  var strings = [];
+  for (var string of chars) {
+    // Strings must be built differently, depending on encoding
+    var data = buildString(string, len);
+    if (encoding === 'utf8') {
+      strings.push(data);
+    } else if (encoding === 'base64') {
+      // Base64 strings will be much longer than their UTF8 counterparts
+      strings.push(new Buffer(data, 'utf8').toString('base64'));
+    }
+  }
+
+  // Check the result to ensure it is *properly* optimized
+  var results = strings.map(function(val) {
+    return Buffer.byteLength(val, encoding);
+  });
+
+  bench.start();
+  for (var i = 0; i < n; i++) {
+    var index = n % strings.length;
+    // Go!
+    var r = Buffer.byteLength(strings[index], encoding);
+
+    if (r !== results[index])
+      throw Error('incorrect return value');
+  }
+  bench.end(n);
+}
+
+function buildString(str, times) {
+  if (times == 1) return str;
+
+  return str + buildString(str, times - 1);
+}