Math.round vs hack (v32)

Revision 32 of this benchmark created by Andreas Wagner 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;
var MyMath = {
        round: function( a ) {
                return (a + (a > 0 ? .5 : -.5)) << 0;
        }
};
round = MyMath.round;
</script>

Test runner

Ready to run.

Testing in
TestOps/sec
"proper" rounding in function call
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
proper in function call
rounded = round(somenum);
ready
Proper hack wrapped in function call
rounded = MyMath.round(somenum);
ready
Proprer hack with bitwise
rounded = (somenum + (somenum > 0 ? .5 : -.5)) | 0;
ready
Proprer hack with bitwise <<
rounded = (somenum + (somenum > 0 ? .5 : -.5)) << 0;
ready

Revisions

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