src: use subarray() in Buffer#slice() for speedup

Use the built-in Typed Array method subarray() to improve performance of
Buffer#slice().

Benchmark improvements:

    benchmark/buffer-slice: 40%
    benchmark/buffer-creation (pool): 25%

Additional tests also added.

PR-URL: nodejs#2777
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>

lib/buffer.js

@@ -73,7 +73,7 @@ function allocate(size) {
   if (size < (Buffer.poolSize >>> 1)) {
     if (size > (poolSize - poolOffset))
       createPool();
-    var b = binding.slice(allocPool, poolOffset, poolOffset + size);
+    var b = allocPool.slice(poolOffset, poolOffset + size);
     poolOffset += size;
     alignPool();
     return b;
@@ -94,7 +94,7 @@ function fromString(string, encoding) {
   if (length > (poolSize - poolOffset))
     createPool();
   var actual = allocPool.write(string, poolOffset, encoding);
-  var b = binding.slice(allocPool, poolOffset, poolOffset + actual);
+  var b = allocPool.slice(poolOffset, poolOffset + actual);
   poolOffset += actual;
   alignPool();
   return b;
@@ -552,30 +552,9 @@ Buffer.prototype.toJSON = function() {
 // TODO(trevnorris): currently works like Array.prototype.slice(), which
 // doesn't follow the new standard for throwing on out of range indexes.
 Buffer.prototype.slice = function slice(start, end) {
-  var len = this.length;
-  start = ~~start;
-  end = end === undefined ? len : ~~end;
-
-  if (start < 0) {
-    start += len;
-    if (start < 0)
-      start = 0;
-  } else if (start > len) {
-    start = len;
-  }
-
-  if (end < 0) {
-    end += len;
-    if (end < 0)
-      end = 0;
-  } else if (end > len) {
-    end = len;
-  }
-
-  if (end < start)
-    end = start;
-
-  return binding.slice(this, start, end);
+  const buffer = this.subarray(start, end);
+  Object.setPrototypeOf(buffer, Buffer.prototype);
+  return buffer;
 };
 
 

src/node_buffer.cc

@@ -456,29 +456,6 @@ void CreateFromArrayBuffer(const FunctionCallbackInfo<Value>& args) {
 }
 
 
-void Slice(const FunctionCallbackInfo<Value>& args) {
-  CHECK(args[0]->IsUint8Array());
-  CHECK(args[1]->IsNumber());
-  CHECK(args[2]->IsNumber());
-  Environment* env = Environment::GetCurrent(args);
-  Local<Uint8Array> ab_ui = args[0].As<Uint8Array>();
-  Local<ArrayBuffer> ab = ab_ui->Buffer();
-  ArrayBuffer::Contents ab_c = ab->GetContents();
-  size_t offset = ab_ui->ByteOffset();
-  size_t start = args[1]->NumberValue() + offset;
-  size_t end = args[2]->NumberValue() + offset;
-  CHECK_GE(end, start);
-  size_t size = end - start;
-  CHECK_GE(ab_c.ByteLength(), start + size);
-  Local<Uint8Array> ui = Uint8Array::New(ab, start, size);
-  Maybe<bool> mb =
-      ui->SetPrototype(env->context(), env->buffer_prototype_object());
-  if (!mb.FromMaybe(false))
-    return env->ThrowError("Unable to set Object prototype");
-  args.GetReturnValue().Set(ui);
-}
-
-
 template <encoding encoding>
 void StringSlice(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
@@ -1002,7 +979,6 @@ void Initialize(Local<Object> target,
   env->SetMethod(target, "createFromString", CreateFromString);
   env->SetMethod(target, "createFromArrayBuffer", CreateFromArrayBuffer);
 
-  env->SetMethod(target, "slice", Slice);
   env->SetMethod(target, "byteLengthUtf8", ByteLengthUtf8);
   env->SetMethod(target, "compare", Compare);
   env->SetMethod(target, "fill", Fill);

test/parallel/test-buffer.js

@@ -1061,14 +1061,46 @@ assert.equal(buf.readInt8(0), -1);
   assert.equal(buf.slice(-10, 10), '0123456789');
   assert.equal(buf.slice(-20, 10), '0123456789');
   assert.equal(buf.slice(-20, -10), '');
+  assert.equal(buf.slice(), '0123456789');
+  assert.equal(buf.slice(0), '0123456789');
+  assert.equal(buf.slice(0, 0), '');
+  assert.equal(buf.slice(undefined), '0123456789');
+  assert.equal(buf.slice('foobar'), '0123456789');
+  assert.equal(buf.slice(undefined, undefined), '0123456789');
+
+  assert.equal(buf.slice(2), '23456789');
+  assert.equal(buf.slice(5), '56789');
+  assert.equal(buf.slice(10), '');
+  assert.equal(buf.slice(5, 8), '567');
+  assert.equal(buf.slice(8, -1), '8');
+  assert.equal(buf.slice(-10), '0123456789');
+  assert.equal(buf.slice(0, -9), '0');
+  assert.equal(buf.slice(0, -10), '');
   assert.equal(buf.slice(0, -1), '012345678');
   assert.equal(buf.slice(2, -2), '234567');
   assert.equal(buf.slice(0, 65536), '0123456789');
   assert.equal(buf.slice(65536, 0), '');
+  assert.equal(buf.slice(-5, -8), '');
+  assert.equal(buf.slice(-5, -3), '56');
+  assert.equal(buf.slice(-10, 10), '0123456789');
   for (var i = 0, s = buf.toString(); i < buf.length; ++i) {
+    assert.equal(buf.slice(i), s.slice(i));
+    assert.equal(buf.slice(0, i), s.slice(0, i));
     assert.equal(buf.slice(-i), s.slice(-i));
     assert.equal(buf.slice(0, -i), s.slice(0, -i));
   }
+
+  var utf16Buf = new Buffer('0123456789', 'utf16le');
+  assert.deepEqual(utf16Buf.slice(0, 6), Buffer('012', 'utf16le'));
+
+  assert.equal(buf.slice('0', '1'), '0');
+  assert.equal(buf.slice('-5', '10'), '56789');
+  assert.equal(buf.slice('-10', '10'), '0123456789');
+  assert.equal(buf.slice('-10', '-5'), '01234');
+  assert.equal(buf.slice('-10', '-0'), '');
+  assert.equal(buf.slice('111'), '');
+  assert.equal(buf.slice('0', '-111'), '');
+
   // try to slice a zero length Buffer
   // see https://github.com/joyent/node/issues/5881
   SlowBuffer(0).slice(0, 1);