Unrolled loops

JavaScript performance comparison

Revision 11 of this test case created

Info

It seems the latest and greatest JavaScript engines have catched up and loop unrolling is not as great a speedup as it once was. Still, both unrolled loop variants are 10% to 25% faster than the for loop on both Safari 5 and Chrome 5.

Preparation code

<script>
  var a = 0;
</script>

Test runner

Warning! For accurate results, please disable Firebug before running the tests. (Why?)

Java applet disabled.

Testing in unknown unknown
Test Ops/sec
For loop
 
for (var i = 0; i < 100; i++) a++;
 pending…
Unrolled loop
 
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
a++;
 pending…
Unrolled loop (1 statement)
 
a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++;
 pending…
Partial Unrolling
 
for (var i = 0; i < 10; i++) {
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
}
 pending…
Larger Partial Unrolling
 
for (var i = 0; i < 2; i++) {
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
 a++;
}
 pending…
Larger Partial Unrolling (single statement)
 
for (var i = 0; i < 2; i++) {
 a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++, a++;
}
 pending…

Compare results of other browsers

Revisions

You can edit these tests or add even more tests to this page by appending /edit to the URL. Here’s a list of current revisions for this page:

0 comments

Add a comment