Math.round vs hack (v19)

Revision 19 of this benchmark created by BrianMB on

Description

Math.round() has a function call overhead, so using the ~~ hack (truncate towards 0) and adding 0.5 works quicker, but if you want to handle negative numbers too then you have to check whether to add or subtract 0.5 .... and this wipes out the speed advantage. So ~~(0.5+num) is only worth it if you know your numbers always have the same sign...

Preparation HTML

<script>
  var somenum = -500 + (Math.random() * 1000);
  var rounded;
  
  function customRound(numbah) {
    return (0.5 + numbah) | 0;
  }
</script>

Test runner

Ready to run.

Testing in
TestOps/sec
"proper" rounding
rounded = Math.round(somenum);
ready
Custom rounding function
rounded = customRound(somenum);
ready

Revisions

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