# Math.round vs hack (v31)

## 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(n) {
return ~~ (n + (n > 0 ? .5 : -.5));
}
}
round=Math.round;
</script>``````

## Test runner

Testing in
TestOps/sec
"proper" rounding in function call
``rounded = Math.round(somenum);``
Hack rounding
``rounded = ~~ (0.5 + somenum);``
Proper hack rounding
``rounded = ~~ (somenum + (somenum > 0 ? .5 : -.5));``
Hack with bitwise OR
``rounded = (0.5 + somenum) | 0;``
Hack with bitwise shift
``rounded = (0.5 + somenum) << 0;``
proper in function call
``rounded = round(somenum);``
``rounded = MyMath.round(somenum);``
``rounded = (somenum + (somenum > 0 ? .5 : -.5)) | 0;``
``rounded = (somenum + (somenum > 0 ? .5 : -.5)) << 0;``