Recently V8's optimizing pipeline (Crankshaft) got full support for external arrays (aka WebGL typed arrays). One of core NodeJS types - Buffer - is exposed to JavaScript code as an external unsigned byte array so I decided to do a small unscientific benchmark to see the improvement with my own eyes:

var LONG_STRING = "qwertyuiop";

for (var i = 0; i < 13; i++) LONG_STRING += LONG_STRING;

// force cons-string flattening outside of timed loop.
LONG_STRING.charCodeAt();

console.log("LONG_STRING is %s chars long", LONG_STRING.length);

function Str2BufferJS(s) {
  var length = s.length;
  var b = new Buffer(length);
  for (var i = 0; i < length; i++) b[i] = s.charCodeAt(i);
  return b;
}

function Str2BufferNative(s) {
  var length = s.length;
  var b = new Buffer(length);
  b.asciiWrite(s, 0);
  return b;
}

var N = 1000;

function LoopAndTime(name, f) {
 var start = Date.now();
 for (var i = 0; i < N; i++) f();
 var end = Date.now();
 console.log("%s took %s ms per %s calls", name, end - start, N);
}

LoopAndTime("Str2BufferNative", function() { Str2BufferNative(LONG_STRING); });
LoopAndTime("Str2BufferJS", function() { Str2BufferJS(LONG_STRING); });

Results were fascinating:

# node 0.4.4 with V8 3.1.8.5
LONG_STRING is 81920 chars long
Str2BufferNative took 224 ms per 1000 calls
Str2BufferJS took 1180 ms per 1000 calls
# node 0.4.4. with V8 3.2.7 (current bleeding_edge)
LONG_STRING is 81920 chars long
Str2BufferNative took 254 ms per 1000 calls
Str2BufferJS took 231 ms per 1000 calls

As you can see JS function optimized by Crankshaft is now on par with native implementation of Buffer.writeAscii.

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