Post Topic » Tag: Duff's Device

Post Topic » Tag: Duff's Device - Recent Posts http://posttopic.com/tags/duff039s-device Open For Discussion en-US Thu, 09 Sep 2010 16:27:32 +0000 http://bbpress.org/?v=1.1-alpha-2475 Chad Smith on "jQuery Duff's Device" http://posttopic.com/topic/jquery-duffs-device#post-146 Fri, 28 Aug 2009 05:28:01 +0000 Chad Smith 146@http://posttopic.com/ Duff's device explained
Duff's device makes loops faster by using a method called unrolling. When you have a typical loop, the time it takes to execute that loop equals the time to execute function each time plus the time to see if it should continue each time. So the formula for a standard loop would be:

Number of iterations (N)
Time to execute (E)
Time to check to continue (C)

T=NE+NC

Duff says if we iterate our loop and only do test every 8 times (plus a few remainders) it would go faster, and it does. Duff's device "unrolls" the loop, or essentially executes more and checks less to see if it should continue. The function it uses is along the lines of:

Number of iterations (N)
Time to execute (E)
Time to check to continue (C)

T=NE+C(N%8+floor(N/8))(plus trivial operation time for Floor, % and / one time)

This means Duff's device is faster than a standard loop when

N%8+floor(N/8)<N]]> Chad Smith on "jQuery Duff's Device" http://posttopic.com/topic/jquery-duffs-device#post-145 Fri, 28 Aug 2009 05:54:50 +0000 Chad Smith 145@http://posttopic.com/ .code{color:#3a6ff8}.code span{color:#0ec925}h3 a{color:#333;cursor:pointer;text-decoration:none}.small{font-size:.8em}

jQuery Duff's Device

Summary

Use Duff's device for faster^* loops.

Author

Chad Smith (email)

Requires

jQuery

Download

jquery-duff.js (842 bytes)

License

Dual licensed under the MIT and GPL licenses.

Usage

Use: $(element).duff(function(){...}); or $.duff(element,function(){...});
In place of: $(element).each(function(){...}); and $.each(element,function(){...});

^*Duff's device is faster in many cases, but not every case. Loop speed depends on the browser and number of iterations, and can differ on each run.