faster with negative start args

aheckmann · Sep 29, 2012 · 06c735a · 06c735a
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Showing 4 changed files with 103 additions and 7 deletions.
diff --git a/README.md b/README.md
@@ -7,12 +7,36 @@ A faster alternative to `[].slice.call(arguments)`.
 
 Example output from [benchmark.js](https://github.com/bestiejs/benchmark.js)
 
-    Array.prototype.slice.call x 1,289,592 ops/sec ±2.88% (87 runs sampled)
-    [].slice.call x 1,345,451 ops/sec ±1.68% (97 runs sampled)
-    cached slice.call x 10,719,886 ops/sec ±1.04% (99 runs sampled)
-    sliced x 15,809,545 ops/sec ±1.46% (93 runs sampled)
+    Array.prototype.slice.call x 1,320,205 ops/sec ±2.35% (92 runs sampled)
+    [].slice.call x 1,314,605 ops/sec ±1.60% (95 runs sampled)
+    cached slice.call x 10,468,380 ops/sec ±1.45% (95 runs sampled)
+    sliced x 16,608,237 ops/sec ±1.40% (92 runs sampled)
     fastest is sliced
 
+    Array.prototype.slice.call(arguments, 1) x 1,383,584 ops/sec ±1.73% (97 runs sampled)
+    [].slice.call(arguments, 1) x 1,494,735 ops/sec ±1.33% (95 runs sampled)
+    cached slice.call(arguments, 1) x 10,085,270 ops/sec ±1.51% (97 runs sampled)
+    sliced(arguments, 1) x 16,620,480 ops/sec ±1.29% (95 runs sampled)
+    fastest is sliced(arguments, 1)
+
+    Array.prototype.slice.call(arguments, -1) x 1,303,262 ops/sec ±1.62% (94 runs sampled)
+    [].slice.call(arguments, -1) x 1,325,615 ops/sec ±1.36% (97 runs sampled)
+    cached slice.call(arguments, -1) x 9,673,603 ops/sec ±1.70% (96 runs sampled)
+    sliced(arguments, -1) x 16,384,575 ops/sec ±1.06% (91 runs sampled)
+    fastest is sliced(arguments, -1)
+
+    Array.prototype.slice.call(arguments, -2, -10) x 1,404,390 ops/sec ±1.61% (95 runs sampled)
+    [].slice.call(arguments, -2, -10) x 1,514,367 ops/sec ±1.21% (96 runs sampled)
+    cached slice.call(arguments, -2, -10) x 9,836,017 ops/sec ±1.21% (95 runs sampled)
+    sliced(arguments, -2, -10) x 18,544,882 ops/sec ±1.30% (91 runs sampled)
+    fastest is sliced(arguments, -2, -10)
+
+    Array.prototype.slice.call(arguments, -2, -1) x 1,458,604 ops/sec ±1.41% (97 runs sampled)
+    [].slice.call(arguments, -2, -1) x 1,536,547 ops/sec ±1.63% (99 runs sampled)
+    cached slice.call(arguments, -2, -1) x 10,060,633 ops/sec ±1.37% (96 runs sampled)
+    sliced(arguments, -2, -1) x 18,608,712 ops/sec ±1.08% (93 runs sampled)
+    fastest is sliced(arguments, -2, -1)
+
 _Benchmark  [source](https://github.com/aheckmann/sliced/blob/master/bench.js)._
 
 ##Usage

diff --git a/bench.js b/bench.js
@@ -19,6 +19,70 @@ s.add('Array.prototype.slice.call', function () {
 })
 .run();
 
+var s = new Bench.Suite;
+s.add('Array.prototype.slice.call(arguments, 1)', function () {
+  Array.prototype.slice.call(arguments, 1);
+}).add('[].slice.call(arguments, 1)', function () {
+  [].slice.call(arguments, 1);
+}).add('cached slice.call(arguments, 1)', function () {
+  slice.call(arguments, 1)
+}).add('sliced(arguments, 1)', function () {
+  sliced(arguments, 1)
+}).on('cycle', function (evt) {
+  console.log(String(evt.target));
+}).on('complete', function () {
+  console.log('fastest is %s', this.filter('fastest').pluck('name'));
+})
+.run();
+
+var s = new Bench.Suite;
+s.add('Array.prototype.slice.call(arguments, -1)', function () {
+  Array.prototype.slice.call(arguments, -1);
+}).add('[].slice.call(arguments, -1)', function () {
+  [].slice.call(arguments, -1);
+}).add('cached slice.call(arguments, -1)', function () {
+  slice.call(arguments, -1)
+}).add('sliced(arguments, -1)', function () {
+  sliced(arguments, -1)
+}).on('cycle', function (evt) {
+  console.log(String(evt.target));
+}).on('complete', function () {
+  console.log('fastest is %s', this.filter('fastest').pluck('name'));
+})
+.run();
+
+var s = new Bench.Suite;
+s.add('Array.prototype.slice.call(arguments, -2, -10)', function () {
+  Array.prototype.slice.call(arguments, -2, -10);
+}).add('[].slice.call(arguments, -2, -10)', function () {
+  [].slice.call(arguments, -2, -10);
+}).add('cached slice.call(arguments, -2, -10)', function () {
+  slice.call(arguments, -2, -10)
+}).add('sliced(arguments, -2, -10)', function () {
+  sliced(arguments, -2, -10)
+}).on('cycle', function (evt) {
+  console.log(String(evt.target));
+}).on('complete', function () {
+  console.log('fastest is %s', this.filter('fastest').pluck('name'));
+})
+.run();
+
+var s = new Bench.Suite;
+s.add('Array.prototype.slice.call(arguments, -2, -1)', function () {
+  Array.prototype.slice.call(arguments, -2, -1);
+}).add('[].slice.call(arguments, -2, -1)', function () {
+  [].slice.call(arguments, -2, -1);
+}).add('cached slice.call(arguments, -2, -1)', function () {
+  slice.call(arguments, -2, -1)
+}).add('sliced(arguments, -2, -1)', function () {
+  sliced(arguments, -2, -1)
+}).on('cycle', function (evt) {
+  console.log(String(evt.target));
+}).on('complete', function () {
+  console.log('fastest is %s', this.filter('fastest').pluck('name'));
+})
+.run();
+
 /**
  * Output:
  *

diff --git a/lib/sliced.js b/lib/sliced.js
@@ -10,16 +10,19 @@
 
 module.exports = function (args, slice, sliceEnd) {
   var ret = [];
+  var len = args.length;
+
+  if (0 === len) return ret;
 
   var start = slice < 0
-    ? slice + args.length
+    ? Math.max(0, slice + len)
     : slice || 0;
 
   var end = 3 === arguments.length
     ? sliceEnd < 0
-      ? sliceEnd + args.length
+      ? sliceEnd + len
       : sliceEnd
-    : args.length;
+    : len;
 
   for (var i = start; i < end; ++i) {
     ret[i - start] = args[i];

diff --git a/test/index.js b/test/index.js
@@ -40,6 +40,11 @@ describe('sliced', function(){
       assert.equal(2, r.length);
       assert.equal(o[2], r[0]);
       assert.equal(o[3], r[1]);
+
+      var r = sliced(o, -12);
+      assert.equal(4, r.length);
+      assert.equal(o[0], r[0]);
+      assert.equal(o[1], r[1]);
     })
   })
   describe('with negative start and positive end', function(){