Math.round vs hack

JavaScript performance comparison

Revision 41 of this test case created

Info

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 code

<canvas id="canvas1" width="500" height="500"></canvas>
<script>
  var can = document.getElementById('canvas1');
  var ctx = can.getContext('2d');
 
 
 
</script>

Preparation code output

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Testing in unknown unknown
Test Ops/sec
"proper" rounding
ctx.save();
ctx.restore();
pending…
Hack rounding
ctx.setTransform(1, 0 , 0 , 1, 0 , 0 );
 
pending…

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