Math.round vs hack

Benchmark created by Tim 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;
</script>

Test runner

Ready to run.

Testing in
TestOps/sec
"proper" rounding
rounded = Math.round(somenum);
ready
Hack rounding
rounded = ~~ (0.5 + somenum);
ready
Proper hack rounding
rounded = ~~ (somenum + (somenum > 0 ? .5 : -.5));
ready

Revisions

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