Math.round vs hack (v60)

Revision 60 of this benchmark created 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
Hack with bitwise OR
rounded = (0.5 + somenum) | 0;
ready
Hack with bitwise shift
rounded = (0.5 + somenum) << 0;
ready
Floor
rounded = Math.floor(somenum);
ready
Ceil
rounded = Math.ceil(somenum);
ready
Hack with bitwise OR without add 0.5
rounded = somenum | 0;
ready
Hack with bitwise XOR
rounded = somenum ^ 0;
ready
Hack with bitwise XOR rounded
rounded = (somenum - (somenum > 0 ? -0.5 : 0.5)) ^ 0;
ready
parseInt()
rounded = parseInt(somenum);
ready

Revisions

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