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I was trying to benchmark the gain/loss of "caching" math.floor, in hopes that I could make calls faster.
Here was the test:
<html>
<head>
<script>
window.onload = function()
{
var startTime = new Date().getTime();
var k = 0;
for(var i = 0; i < 1000000; i++) k += Math.floor(9.99);
var mathFloorTime = new Date().getTime() - startTime;
startTime = new Date().getTime();
window.mfloor = Math.floor;
k = 0;
for(var i = 0; i < 1000000; i++) k += window.mfloor(9.99);
var globalFloorTime = new Date().getTime() - startTime;
startTime = new Date().getTime();
var mfloor = Math.floor;
k = 0;
for(var i = 0; i < 1000000; i++) k += mfloor(9.99);
var localFloorTime = new Date().getTime() - startTime;
document.getElementById("MathResult").innerHTML = mathFloorTime;
document.getElementById("globalResult").innerHTML = globalFloorTime;
document.getElementById("localResult").innerHTML = localFloorTime;
};
</script>
</head>
<body>
Math.floor: <span id="MathResult"></span>ms <br />
var mathfloor: <span id="globalResult"></span>ms <br />
window.mathfloor: <span id="localResult"></span>ms <br />
</body>
</html>
My results from the test:
[Chromium 5.0.308.0]:
Math.floor: 49ms
var mathfloor: 271ms
window.mathfloor: 40ms
[IE 8.0.6001.18702]
Math.floor: 703ms
var mathfloor: 9890ms [LOL!]
window.mathfloor: 375ms
[Firefox [Minefield] 3.7a4pre]
Math.floor: 42ms
var mathfloor: 2257ms
window.mathfloor: 60ms
[Safari 4.0.4[531.21.10] ]
Math.floor: 92ms
var mathfloor: 289ms
window.mathfloor: 90ms
[Opera 10.10 build 1893]
Math.floor: 500ms
var mathfloor: 843ms
window.mathfloor: 360ms
[Konqueror 4.3.90 [KDE 4.3.90 [KDE 4.4 RC1]]]
Math.floor: 453ms
var mathfloor: 563ms
window.mathfloor: 312ms
The variance is random, of course, but for the most part
In all cases [this shows time taken]:
[takes longer] mathfloor > Math.floor > window.mathfloor [is faster]
Why is this? In my projects i've been using var mfloor = Math.floor, and according to my not-so-amazing benchmarks, my efforts to "optimize" actually slowed down the script by ALOT...
Is there any other way to make my code more "efficient"...? I'm at the stage where i basically need to optimize, so no, this isn't "premature optimization"...
262
Conclusion: In most cases, local variables will be faster than global variables.
Moreover, the access to local variables is faster than to global ones.
It all depends on the scope of the variable. If you feel that a certain variable will take multiple values by passing through various functions then use local variables and pass them in function calls. If you feel that a certain variable you need to use will have constant value, then declare it as a global variable.
Global variables are really slow, in addition to all the other reasons not to use them.
You have these two variables labelled incorrectly:
var mathfloor: <span id="globalResult"></span>ms <br />
window.mathfloor: <span id="localResult"></span>ms <br />
@David's alternatives are worth looking into, as would some kind of memoisation.
88
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