Math.round vs hack (v13)

Revision 13 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>
  function hack_round(n) {
   return~~ (0.5 + n);
  }
  
  var somenum = -500 + (Math.random() * 1000);
  var rounded;
</script>

Test runner

Ready to run.

Testing in
TestOps/sec
"proper" floor
rounded = Math.floor(somenum);
ready
Hack floor
rounded = ~~somenum;
ready
Proper hack floor
rounded = ~~ (somenum + (somenum > 0 ? .5 : -.5));
ready
Hack with bitwise OR
rounded = (somenum) | 0;
ready
Hack with bitwise shift
rounded = (somenum) << 0;
ready
Hack rounding with call overhead
rounded = hack_round(somenum);
ready
corrected bitwise or
rounded = (somenum > 0) ? ((somenum + 0.5) | 0) : ((somenum - 0.5) | 0);
ready

Revisions

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