Fast Loop Analysis

JS Loop Testing

Preparation code

<script>
  Benchmark.prototype.setup = function() {
    var sum = 0;
    var values = [1, 1, 1, 1, 1];
    var i = values.length;
  };
</script>


Testing in Chrome 21.0.1180.82 on Mac OS X 10.8.1
Test	Ops/sec
While reverse cached and guarded
  while (--i >= 0) {
   sum += values[i];
  }
306,249,873
±17.11%
23% slower

While reversed pre dec
  while (i) {
   sum += values[--i];
  }
310,934,905
±12.54%
19% slower

[Raw] While reverse cached and guarded
  while (--i >= 0) {}
311,447,273
±16.99%
22% slower

[Raw] While reversed pre dec
  while (i) {
    --i;
  }
398,675,661
±17.29%
fastest

Basic For loop
  for (var i2 = 0, i = values.length; i2 < i; i2++) {
    sum += values[i2];
  }
61,732,131
±13.28%
84% slower

For loop cached
  for (i2 = 0; i2 < i; i2++) {
    sum += values[i2];
  }
31,511,582
±17.60%
92% slower

[Raw] Basic For Loop
  for (var i2 = 0, i = values.length; i2 < i; i2++) {}
101,568,535
±12.75%
73% slower

[Raw] For loop cached
  for (i2 = 0; i2 < i; i2++) {}
44,769,742
±16.22%
89% slower