Math.round vs hack (v46)

Revision 46 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 = (Math.random());
var rounded;
var hackInFunction = function(num){
      return (num) | 0;
};
</script>

Setup

var othernum = (Math.random());
    var otherrounded;
    var hackInFunctionInProto = function(num){
          return (num) | 0;
    };

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
Hack with bitwise OR large num first
rounded = (somenum + 0.5) | 0;
ready
rounded = hackInFunction(somenum + 0.5);
ready
in setup?
otherrounded = Math.round(othernum);
ready
in setup again?
otherrounded = (othernum + 0.5) | 0;
ready
once again.
otherrounded = hackInFunctionInProto(othernum + 0.5)
ready
outside inside
otherrounded = Math.round(somenum);
ready
once agian inside my proto thingy magic sauce
otherrounded= ~~ (0.5 + othernum);
ready

Revisions

You can edit these tests or add more tests to this page by appending /edit to the URL.