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List:       kde-devel
Subject:    Re: c++ question: code duplication across classes
From:       Guillaume Laurent <glaurent () telegraph-road ! org>
Date:       2006-09-20 8:23:45
Message-ID: 4510FA91.9080304 () telegraph-road ! org
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Thiago Macieira wrote:
> Benoît Jacob wrote:
>   
>> is the overhead for virtual methods a speed overhead ? 
>>     
>
> The overhead of a virtual method is an indirect jump (instead of a direct 
> one). This used to be a problem because it would throw off all prediction 
> done in modern CPUs, because they didn't predict indirect branches. I 
> don't know if that's still true.
>
> So, if you can, avoid virtuals if speed is an issue.
>   
Last time I tried to measure the speed overhead of a virtual method, 
that was about 3 years ago on a Pentium 3, and it would take millions of 
calls for the overhead to be noticeable. Which is quite possible when 
doing computations in a large matrix.

-- 
Guillaume
http://telegraph-road.org

 
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