Unrolled loops

JavaScript performance comparison

Revision 8 of this test case created by TW

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

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Java applet disabled.

Testing in unknown unknown
Test Ops/sec
For loop
 
for (var i = 0; i < 100; i++) a++;
 pending…
Unrolled loop
 
a++;
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 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++;
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 a++;
 a++;
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 a++;
 a++;
 a++;
 a++;
 a++;
}
 pending…

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Revisions

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